Acoustic Technical Guidance

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Acoustic Technical Guidance

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Technical Guidance for Assessing the
Effects of Anthropogenic Sound on
Marine Mammal Hearing
Underwater Acoustic Thresholds for Onset of
Permanent and Temporary Threshold Shifts

U.S. Department of Commerce
National Oceanic and Atmospheric Administration
National Marine Fisheries Service
NOAA Technical Memorandum NMFS-OPR-55
July 2016

Technical Guidance for Assessing the Effects of
Anthropogenic Sound on Marine Mammal Hearing
Underwater Acoustic Thresholds for Onset of Permanent and
Temporary Threshold Shifts
Office of Protected Resources
National Marine Fisheries Service
Silver Spring, MD 20910

NOAA Technical Memorandum NMFS-OPR-55
July 2016

U.S. Department of Commerce
Penny S. Pritzker, Secretary
National Oceanic and Atmospheric Administration
Kathryn D. Sullivan, Administrator
National Marine Fisheries Service
Eileen Sobeck, Assistant Administrator for Fisheries

Recommended citation:
National Marine Fisheries Service. 2016. Technical Guidance for Assessing the Effects of
Anthropogenic Sound on Marine Mammal Hearing: Underwater Acoustic Thresholds for Onset
of Permanent and Temporary Threshold Shifts. U.S. Dept. of Commer., NOAA. NOAA
Technical Memorandum NMFS-OPR-55, 178 p.

Copies of this report may be obtained from:
Office of Protected Resources
National Oceanic and Atmospheric Administration
1315 East-West Highway, F/PR2
Silver Spring, MD 20910

Or online at:
http://www.nmfs.noaa.gov/pr/publications/techmemos.htm

Photo Credits:
Bearded seal (Erignathus barbatus), Phocid pinniped Photo: John Jansen (NOAA)
North Atlantic right whales (Eubalaena glacialis), Low-frequency cetacean Photo: NOAA
Bottlenose dolphin (Tursiops truncatus), Mid-frequency cetacean Photo: Allison Henry (NOAA)
Dall’s porpoise (Phocoenoides dalli), High-frequency cetacean Photo: Kate Stafford (NOAA)
California sea lion (Zalophus californianus), Otariid pinniped Photo: Sharon Melin (NOAA)

TECHNICAL GUIDANCE FOR ASSESSING THE EFFECTS OF ANTHROPOGENIC SOUND ON MARINE MAMMAL HEARING
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TABLE OF CONTENTS
LIST OF TABLES .....................................................................................................................v
LIST OF FIGURES ................................................................................................................ VI
ABBREVIATIONS, ACRONYMS, AND SYMBOLS ........................................................ VIII
EXECUTIVE SUMMARY ........................................................................................................ 1
TECHNICAL GUIDANCE FOR ASSESSING THE EFFECTS OF ANTHROPOGENIC
SOUND ON MARINE MAMMAL HEARING ..........................................................6
I.

II.

INTRODUCTION .......................................................................................................6
NEED FOR TECHNICAL GUIDANCE AND UPDATED UNDERWATER
ACOUSTIC THRESHOLDS ................................................................................................. 7
1.1.1 Acoustic thresholds within the Context of an Effects Analysis ................................................... 8
1.2
ADDRESSING UNCERTAINTY AND DATA LIMITATIONS .................................................. 8
1.2.1 Assessment Framework .................................................................................................... 8
1.2.2 Data Standards............................................................................................................... 9

1.1

NMFS’ ACOUSTIC THRESHOLDS FOR ONSET OF PERMANENT
THRESHOLD SHIFTS IN MARINE MAMMALS .................................................. 10
2.1
MARINE MAMMAL HEARING GROUPS .......................................................................... 10
2.1.1 Application of Marine Mammal Hearing Groups ................................................................ 12
2.2
MARINE MAMMAL AUDITORY WEIGHTING FUNCTIONS .............................................. 13
2.2.1 Use of Auditory Weighting Functions in Assessing Susceptibility to Noise-Induced Hearing Loss .. 14
2.2.2 Marine Mammal Auditory Weighting Functions ................................................................. 14
2.2.3 Derivation of Function Parameters .................................................................................... 18
2.2.4 Application of Marine Mammal Auditory Weighting Functions for PTS Onset Acoustic
thresholds ..................................................................................................................... 23
2.3
PTS ONSET ACOUSTIC THRESHOLDS............................................................................ 24
2.3.1 Impulsive and Non-Impulsive Acoustic Thresholds ............................................................... 26
2.3.2 Metrics ........................................................................................................................ 27
2.3.3 Development of PTS Onset Acoustic Thresholds .................................................................. 31

III.
3.1

UPDATING OF ACOUSTIC TECHNICAL GUIDANCE AND ACOUSTIC
THRESHOLDS .......................................................................................................... 36
PROCEDURE AND TIMELINE FOR UPDATING THE TECHNICAL GUIDANCE ................. 36

APPENDIX A: FINNERAN TECHNICAL REPORT ......................................................... 37
EXECUTIVE SUMMARY ...................................................................................................... 39
I.

1.1
1.2
1.3
1.4
1.5

INTRODUCTION ..................................................................................................... 43
OVERVIEW ...................................................................................................................................... 43
IMPULSE VS. NON-IMPULSIVE NOISE ......................................................................................... 43
NOISE-INDUCED THRESHOLD SHIFTS ....................................................................................... 43
AUDITORY WEIGHTING FUNCTIONS ......................................................................................... 44
TAP PHASE 3 WEIGHTING FUNCTIONS AND TTS/PTS THRESHOLDS ............................... 44

II.

WEIGHTING FUNCTIONS AND EXPOSURE FUNCTIONS ............................. 46

III.

METHODOLOGY TO DERIVE FUNCTION PARAMETERS ............................. 51

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IV.
4.1
4.2
4.3
4.4
4.5
4.6

MARINE MAMMAL SPECIES GROUPS ................................................................. 53
LOW-FREQUENCY (LF) CETACEANS .......................................................................................... 53
MID-FREQUENCY (MF) CETACEANS.......................................................................................... 53
HIGH-FREQUENCY (HF) CETACEANS........................................................................................ 53
SIRENIANS ....................................................................................................................................... 53
PHOCIDS .......................................................................................................................................... 54
OTARIIDS AND OTHER NON-PHOCID MARINE CARNIVORES................................................ 54

COMPOSITE AUDIOGRAMS .................................................................................. 56

VI.

EQUAL LOUDNESS DATA ...................................................................................... 64

VII.

EQUAL LATENCY DATA ........................................................................................ 65

VIII.
8.1
8.2
8.3

TTS DATA .................................................................................................................. 66
NON-IMPULSIVE (STEADY-STATE) EXPOSURES – TTS ........................................................... 66
NON-IMPULSIVE (STEADY-STATE) EXPOSURES – PTS ........................................................... 68
IMPULSIVE EXPOSURES................................................................................................................. 69

IX.
9.1
9.2
9.3

TTS EXPOSURE FUNCTIONS FOR SONARS ...................................................... 78
LOW- AND HIGH-FREQUENCY EXPONENTS............................................................................. 78
FREQUENCY CUTOFFS .................................................................................................................. 78
GAIN PARAMETERS ....................................................................................................................... 80

PTS EXPOSURE FUNCTIONS FOR SONARS....................................................... 87

XI.

TTS/PTS EXPOSURE FUNCTIONS FOR EXPLOSIVES ..................................... 88

XII.

SUMMARY ................................................................................................................. 91

APPENDIX A1. ESTIMATING A LOW-FREQUENCY CETACEAN AUDIOGRAM ...... 96
A1.1. BACKGROUND .................................................................................................................................... 96
A1.2. AUDIOGRAM FUNCTIONAL FORM AND REQUIRED PARAMETERS ............................................ 97
A1.3. ESTIMATING AUDIOGRAM PARAMETERS ........................................................................... 99
XIII.

REFERENCES ......................................................................................................... 102

APPENDIX B: RESEARCH RECOMMENDATIONS FOR IMPROVED ACOUSTIC
THRESHOLDS ......................................................................................................... 111
I.

SUMMARY OF RESEARCH RECOMMENDATIONS .........................................112
1.1
LOW-FREQUENCY CETACEAN HEARING .................................................................... 112
1.2
HEARING DIVERSITY AMONG SPECIES AND AUDITORY PATHWAYS .......................... 112
1.3
REPRESENTATIVENESS OF CAPTIVE INDIVIDUALS ..................................................... 113
1.3.1 Impacts of Age on Hearing ............................................................................................ 113
1.4
ADDITIONAL TTS MEASUREMENTS WITH MORE SPECIES AND/OR INDIVIDUALS ..... 114
1.5
SOUND EXPOSURE TO MORE REALISTIC SCENARIOS ................................................. 115
1.5.1 Frequency and Duration of Exposure .............................................................................. 115
1.5.2 Multiple Sources .......................................................................................................... 115
1.5.3 Possible Protective Mechanisms ....................................................................................... 116
1.5.4 Long-Term Consequences of Exposure ............................................................................. 117
1.6
IMPACTS OF NOISE-INDUCED THRESHOLD SHIFTS ON FITNESS................................. 118
1.7
BEHAVIOR OF MARINE MAMMALS UNDER EXPOSURE CONDITIONS WITH THE
POTENTIAL TO CAUSE HEARING IMPACTS ................................................................. 119
1.8
CHARACTERISTICS OF SOUND ASSOCIATED WITH NIHL AND IMPACTS OF
PROPAGATION............................................................................................................ 120

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1.9
1.10
1.11
1.12

NOISE-INDUCED THRESHOLD SHIFT GROWTH RATES AND RECOVERY .................... 120
METRICS AND TERMINOLOGY .................................................................................... 121
EFFECTIVE QUIET....................................................................................................... 121
TRANSLATING BIOLOGICAL COMPLEXITY INTO PRACTICAL APPLICATION ............... 122

APPENDIX C: PEER REVIEW PROCESS AND PUBLIC COMMENT PERIOD ......... 123
I.

II.

PEER REVIEW PROCESS ...................................................................................... 123
1.1
INITIAL PEER REVIEW (ASSOCIATED WITH 2013 DRAFT TECHNICAL GUIDANCE) ..... 124
1.2
SECOND PEER REVIEW (REVIEW OF THE FINNERAN TECHNICAL REPORT)............... 124
1.2.1 Follow-Up to Second Peer Review ................................................................................... 125
1.3
THIRD PEER REVIEW (REVIEW OF TRANSITION RANGE METHODOLOGY) ................ 126
1.4
CONFLICT OF INTEREST DISCLOSURE......................................................................... 127
PUBLIC COMMENT PERIODS ............................................................................ 127
INITIAL PUBLIC COMMENT PERIOD (ASSOCIATED WITH 2013 DRAFT
TECHNICAL GUIDANCE)............................................................................................. 128
2.1.1 Summary of Public Comments Received ............................................................................ 128
2.2
SECOND PUBLIC COMMENT PERIOD (ASSOCIATED WITH 2015 DRAFT
TECHNICAL GUIDANCE)............................................................................................. 129
2.2.1 Summary of Public Comments Received ............................................................................ 129
2.3
THIRD PUBLIC COMMENT PERIOD (ASSOCIATED WITH 2016 PROPOSED
CHANGES FROM DRAFT TECHNICAL GUIDANCE) ..................................................... 130
2.3.1 Summary of Public Comments Received ............................................................................ 131

2.1

APPENDIX D: ALTERNATIVE METHODOLOGY ........................................................ 133
I.
II.

INTRODUCTION ................................................................................................... 133
WEIGHTING FACTOR ADJUSTMENT ASSOCIATED WITH SELCUM
ACOUSTIC THRESHOLDS ................................................................................... 133
2.1
APPLICATION FOR NARROWBAND SOUNDS ................................................................ 134
2.2
APPLICATION FOR BROADBAND SOUNDS ................................................................... 136
2.2.1 Special Considerations for Broadband Source ..................................................................... 137

III.
MODELING CUMULATIVE SOUND EXPOSURE LEVELS ............................. 138
3.1
MORE SOPHISTICATED MODELS ................................................................................. 139
3.2
LESS SOPHISTICATED MODELS ................................................................................... 139
3.2.1 Mobile Sources ............................................................................................................ 140
3.2.2 Stationary Sources ........................................................................................................ 146
APPENDIX E: GLOSSARY .................................................................................................. 147
LITERATURE CITED ......................................................................................................... 156

LIST OF TABLES
Table ES1: Marine mammal hearing groups. ............................................................................................... 3
Table ES2: Summary of weighting and exposure function parameters. .................................................. 3
Table ES3: Summary of PTS onset acoustic thresholds. ........................................................................... 4
Table 1: Marine mammal hearing groups. ................................................................................................12
Table 2: Summary of data available for deriving composite audiograms. ............................................20
TECHNICAL GUIDANCE FOR ASSESSING THE EFFECTS OF ANTHROPOGENIC SOUND ON MARINE MAMMAL HEARING
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Table 3: Summary of weighting and exposure function parameters.....................................................22
Table 4: Summary of PTS onset acoustic thresholds. .............................................................................26
Table 5: Available underwater marine mammal threshold shift studies. ..............................................32
Table 6: TTS onset auditory acoustic thresholds for non-impulsive sounds. .....................................33
Table AE-1. Summary of weighting function parameters and TTS/PTS thresholds.. .....................40
Table A1. Species group designations auditory weighting functions. ......................................................55
Table A2. References, species, and individual subjects used to derive the composite audiograms. 58
Table A3. Composite audiogram parameters values…………………..……………………….. 59
Table A4. Normalized composite audiogram parameters values..........................................................59
Table A5. Frequency of best hearing and the magnitude of the low-frequency slope derived from
composite audiograms and equal latency contours. ..........................................................................63
Table A6. Summary of marine mammal TTS growth data and onset exposure levels. .....................75
Table A7. Differences between composite threshold values and TTS onset values at the frequency
of best hearing for the in-water marine mammal species groups. ...................................................81
Table A8. Weighting function and TTS exposure function parameters. .............................................82
Table A9. TTS and PTS thresholds for explosives and other impulsive sources...............................90
Table A10. Summary of weighting function parameters and TTS/PTS thresholds.............................92
Table B1: Summary of currently available marine mammal data. ......................................................... 111
Table B2: Additional factors for consideration in association with PTS onset acoustic
thresholds…………………………………………………………………………………..116
Table C1: Initial peer review panel (Associated with 2013 Draft Guidance). ..................................... 124
Table C2: Second peer review panel (Review of the Finneran Technical Report) ............................. 125
Table C3: Third peer review panel (Review of Transition Range Methodology) ............................... 127
Table D1: Applicability of weighting factor adjustments for frequencies associated with broadband
sounds……………………………………………………………………………………...137

LIST OF FIGURES
Figure ES1: Auditory weighting functions for low-frequency, mid-frequency, and high-frequency
cetaceans… ................................................................................................................................................ 5
Figure ES2: Underwater auditory weighting functions for otariid and phocid pinnipeds...................
………………………………………………………………………………………………..5
Figure 1:
Auditory weighting functions for low-frequency, mid-frequency, and high-frequency
cetaceans...................................................................................................................................................15
Figure 2:
Underwater auditory weighting functions for otariid and phocid pinnipeds...................16
Figure 3:
Illustration of function parameter in both auditory weighting functions and exposure
functions...................................................................................................................................................18
Figure 4:
Resulting normalized composite audiograms for low-frequency, mid-frequency, and
high-frequency cetaceans and phocid and otariid pinnipeds...........................................................19
Figure AE-1. Navy Phase 3 weighting functions for all species groups. ..............................................40
Figure AE-2. TTS and PTS exposure functions for sonars and other (non-impulsive) active
acoustic sources. ......................................................................................................................................41
Figure AE-3. TTS and PTS exposure functions for explosives, impact pile driving, air guns, and
other impulsive sources..........................................................................................................................42
Figure A1. Examples of weighting function and exposure function…………………………… 47
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Figure A2. Influence of parameter values on the resulting shapes of the weighting functions and
exposure functions..................................................................................................................................48
Figure A3. Navy Phase 2 weighting function for the mid-frequency cetacean group. .......................49
Figure A4.
Comparison of Otariid, Mustelid, and Odobenid psychophysical hearing thresholds
measured underwater. ............................................................................................................................54
Figure A5. Thresholds and composite audiograms for the six species groups....................................60
Figure A6. Normalized thresholds and composite audiograms for the six species groups. ..............61
Figure A7. Composite audiograms for the various species groups, derived with the original data
and normalized data ...............................................................................................................................62
Figure A8. Underwater marine mammal equal latency contours are available for Phocoena phocoena
and Tursiops truncatus ...............................................................................................................................65
Figure A9. TTS measured using behavioral and AEP methods do not necessarily agree, with
marine mammal studies reporting larger TTS obtained using AEP methods. ..............................67
Figure A10. TTS growth data for mid-frequency cetaceans obtained using behavioral methods..71
Figure A11. TTS growth data for mid-frequency cetaceans obtained using AEP methods. ..........72
Figure A12. TTS growth data for high-frequency cetaceans obtained using behavioral and AEP
methods. .............................................................................................................................................73
Figure A13. TTS growth data for pinnipeds obtained using behavioral methods............................74
Figure A14. The cutoff frequencies .........................................................................................................79
Figure A15. Effect of ΔT adjustment on the TTS exposure functions for the mid-frequency
cetaceans and high-frequency cetaceans ..............................................................................................79
Figure A16. Relationship between ΔT and the resulting mean-squared error between the
exposure functions and onset TTS data. .............................................................................................80
Figure A17. Exposure functions……………………………………………………………….83
Figure A18. Mid-frequency cetacean exposure function, composite audiogram, and Phase 2
exposure functions compared to mid-frequency cetacean TTS data.. ............................................84
Figure A19. High-frequency cetacean TTS exposure function, composite audiogram, and Phase 2
exposure functions compared to high-frequency cetacean TTS data. ............................................85
Figure A20.
Phocid (underwater) exposure function, composite audiogram, and Phase 2
exposure functions compared to phocid TTS data. ..........................................................................86
Figure A21. Navy Phase 3 weighting functions for marine mammal species groups exposed to
underwater sound ...................................................................................................................................91
Figure A22. TTS and PTS exposure functions for sonars and other (non-impulsive) active
acoustic sources. ......................................................................................................................................94
Figure A23. TTS and PTS exposure functions for explosives, impact pile driving, air guns, and
other impulsive sources. ........................................................................................................................95
Figure A1.1. Relationship between estimated threshold, low-frequency term, and high-frequency
term. ..........................................................................................................................................................99
Figure A1.2. Comparison of proposed LF cetacean thresholds to those predicted by anatomical and
finite-element models. ......................................................................................................................... 101
Figure D1: Example illustrating concept of weighting factor adjustment.......................................... 135
Figure D2:
Simple example illustrating concept of weighting factor adjustment on isopleths .. 136
Figure D3: Example weighting function illustrating where the use of weighting function
adjustments are and are not appropriate for broadband sources. ................................................ 138
Figure D4: Illustration of concept for mobile sources .......................................................................... 142
Figure E1. Example audiogram. .............................................................................................................. 147
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ABBREVIATIONS, ACRONYMS, AND SYMBOLS
a

ABR
AEP
AM
ANSI

b
C

dB
PK
DPOAE

E(ƒ)
E0

EEH
EQL
ES
ESA

ƒ0
ƒ1
ƒ2

h
HF
HISA
Hz
ISI
IQG
ITA

kHz

Low-frequency exponent
Auditory Brainstem
Response
Auditory Evoked Potentials
Amplitude Modulated
American National
Standards Institute
High-frequency exponent
Weighting function gain
(dB)
Computerized Tomography
Duty Cycle
Decibel
Peak sound level
Distortion product
otoacoustic emission
Exposure function
Exposure Threshold
Equal Energy Hypothesis
Equal Loudness
Executive Summary
Endangered Species Act
Best hearing (kHz)
Low-frequency cutoff
(kHz)
High-frequency cutoff
(kHz)
hour
High-frequency
Highly Influential Scientific
Assessment
Hertz
Influential Scientific
Information
Information Quality
Guidelines
Incidental Take
Authorizations
Exposure function gain
(dB)
Kilohertz

Lpk
Lpk,flat
LE,24h
MF
min
MMC

MMPA
MSA
MSE
m
ms
NIHL
NMFS
NMSA
NOAA
NOS
NRC
NS2
OMB
ONMS
OPR
OSHA
OW

Low-frequency
Peak sound pressure level
Peak sound pressure level
(unweighted)
Sound exposure level,
cumulative 24h
Mid-frequency
Minutes
Marine Mammal
Commission
Marine Mammal Protection
Act
Magnuson-Stevens Fishery
Conservation and
Management Act
Mean-squared error
meter
Milliseconds
Noise-induced Hearing
Loss
National Marine Fisheries
Service
National Marine
Sanctuaries Act
National Oceanic and
Atmospheric
Administration
National Ocean Service
National Research Council
National Standard 2
Office of Management and
Budget
Office of National Marine
Sanctuaries
Office of Protected
Resources
Occupational Safety and
Health Administration
Otariids in water
Sound Pressure Level
Pascals

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pi
Permanent Threshold Shift
Phocids in water
R
Range
R0
“Safe Distance”
2
R
Goodness of fit
RMS
Root Mean Square
S
Source Factor
SE
Energy Source Factor
s
Seconds
s
Distance from source
s0
Slope
SEL
Sound exposure level
SELcum
Cumulative sound exposure
level
SL
Source Level
Energy Source Level
SLE
s0
Slope (dB/decade)
SPL
Sound Pressure Level
SSC-PAC SPAWAR Systems Center
Pacific
τ
1/repetition rate
TAP
U.S. Navy’s Tactical
Training Theater
Assessment and Planning
Program
TS
Threshold Shift
TTS
Temporary Threshold Shift
µPa
Micropascal
µPa2-s
Micropascal squared second
USFWS U.S. Fish and Wildlife
Service
𝑣𝑣
Velocity (transit speed)
W(ƒ)
Weighting function
WFA
Weighting factor
adjustments
π
PTS
PW

TECHNICAL GUIDANCE FOR ASSESSING THE EFFECTS OF ANTHROPOGENIC SOUND ON MARINE MAMMAL
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TECHNICAL GUIDANCE FOR ASSESSING THE EFFECTS OF ANTHROPOGENIC SOUND ON MARINE MAMMAL
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EXECUTIVE SUMMARY
This document provides technical guidance for assessing the effects of underwater
anthropogenic (human-made) sound on the hearing of marine mammal species under the
jurisdiction of the National Marine Fisheries Service (NMFS) and was completed in
collaboration with the National Ocean Service (NOS), Office of National Marine
Sanctuaries. Specifically, it identifies the received levels, or acoustic thresholds, at which
individual marine mammals are predicted to experience changes in their hearing sensitivity
(either temporary or permanent) for acute, incidental exposure to underwater anthropogenic
sound sources. This is the first time NMFS has presented this information in a single,
comprehensive document. This Technical Guidance is intended for use by NMFS
analysts/managers and other relevant action proponents/stakeholders, including other
federal agencies, when seeking to determine whether and how their activities are expected to
result in potential impacts to marine mammal hearing via acoustic exposure. This document
outlines the development of NMFS’ acoustic thresholds and describes how they will be
updated in the future.
NMFS has compiled, interpreted, and synthesized the scientific literature, including a recent
Technical Report by Dr. James Finneran (U.S. Navy-SPAWAR Systems Center Pacific (SSCPAC)) (Finneran 2016; Appendix A of this Technical Guidance), to produce acoustic
thresholds for onset of temporary (TTS) and permanent threshold shifts (PTS) (Table ES2)
that update those currently in use by NMFS. Updates include a protocol for estimating PTS
onset acoustic thresholds for impulsive (e.g., airguns, impact pile drivers) and non-impulsive
(e.g., tactical sonar, vibratory pile drivers) sound sources, the formation of marine mammal
hearing groups (low- (LF), mid- (MF), and high- (HF) frequency cetaceans, and otariid (OW)
and phocid (PW) pinnipeds; Table ES1), and the incorporation of marine mammal auditory
weighting functions (Figures ES1 and ES2) into the derivation of PTS acoustic thresholds.
These acoustic thresholds are presented using dual metrics of cumulative sound exposure
level (SELcum) and peak sound level (PK) for impulsive sounds and SELcum for non-impulsive
sounds.
While the Technical Guidance’s acoustic thresholds are more complex than those used to
date in most cases by NMFS, they reflect the current state of scientific knowledge regarding
the characteristics of sound that have the potential to impact marine mammal hearing
sensitivity. Given the specific nature of these updates, it is not possible to generally or
directly compare the updated acoustic thresholds presented in this document with the
thresholds they will replace because outcomes will depend on project-specific specifications.
NMFS recognizes that the implementation of marine mammal weighting functions and the
SELcum metric represent new factors for consideration, which may extend beyond the
capabilities of some action proponents. Thus, NMFS has developed alternative tools for
those who cannot fully incorporate these factors (See Appendix D and Technical Guidance’s
companion User Spreadsheet 1).
These updated PTS acoustic thresholds do not represent the entirety of a comprehensive
analysis of the effects of a proposed action, but rather serve as one tool (along with, e.g.,
1

Located at: http://www.nmfs.noaa.gov/pr/acoustics/guidelines.htm.

TECHNICAL GUIDANCE FOR ASSESSING THE EFFECTS OF ANTHROPOGENIC SOUND ON MARINE MAMMAL
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behavioral impact thresholds, auditory masking assessments, evaluations to help understand
the ultimate effects of any particular type of impact on an individual’s fitness, population
assessments, etc.) to help evaluate the effects of a proposed action and make the relevant
findings required by NOAA’s various statutes.
This Technical Guidance is classified as a Highly Influential Scientific Assessment (HISA) by
the President’s Office of Management and Budget (OMB). As such, independent peer
review was required prior to broad public dissemination by the Federal Government. Details
of the three peer reviews, associated with the Technical Guidance, are within this document
(Appendix C).
This document is organized so that the most pertinent information can be found easily in
the main body. Additional details are provided in the appendices. Section I introduces the
document. NMFS’ updated acoustic thresholds for onset of PTS for marine mammals
exposed to underwater sound are presented in Section II. NMFS’ plan for periodically
updating acoustic thresholds is presented in Section III. More details on the development of
acoustic thresholds, the peer review and public comment process, research
recommendations, alternative methodology, and a glossary of acoustic terms are found in the
appendices.
The following Tables and Figures summarize the three main aspects of the Technical
Guidance: 1) Marine mammal hearing groups (Table ES1), 2) Marine mammal auditory
weighting functions (Figures ES1 and ES2; Table ES2), and PTS onset acoustic thresholds
(Table ES3).

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Table ES1:

Marine mammal hearing groups.
Generalized
Hearing Range*

Hearing Group
Low-frequency (LF) cetaceans
(baleen whales)
Mid-frequency (MF) cetaceans
(dolphins, toothed whales, beaked whales, bottlenose whales)
High-frequency (HF) cetaceans
(true porpoises, Kogia, river dolphins, cephalorhynchid,
Lagenorhynchus cruciger & L. australis)
Phocid pinnipeds (PW) (underwater)
(true seals)
Otariid pinnipeds (OW) (underwater)
(sea lions and fur seals)

7 Hz to 35 kHz
150 Hz to 160 kHz
275 Hz to 160 kHz
50 Hz to 86 kHz
60 Hz to 39 kHz

* Represents the generalized hearing range for the entire group as a composite (i.e., all species within the
group), where individual species’ hearing ranges are typically not as broad. Generalized hearing range chosen
based on ~65 dB threshold from normalized composite audiogram, with the exception for lower limits for
LF cetaceans (Southall et al. 2007) and PW pinniped (approximation).

Table ES2:

Summary of weighting and exposure function parameters.*
Hearing Group

Low-frequency (LF) cetaceans
Mid-frequency (MF) cetaceans
High-frequency (HF) cetaceans
Phocid pinnipeds (PW) (underwater)
Otariid pinnipeds (OW) (underwater)

1.0
1.6
1.8
1.0
2.0

b
2
2
2
2
2

ƒ1

(kHz)

0.2
8.8
12
1.9
0.94

ƒ2

(kHz)

19
110
140
30
25

(dB)

0.13
1.20
1.36
0.75
0.64

(dB)

179
177
152
180
198

* Equations associated with Technical Guidance’s weighting (W(f)) and exposure functions (E(f)):



( f / f1 ) 2 a
W ( f ) = C + 10 log10 
2 a
2 b 
[1 + ( f / f1 ) ] [1 + ( f / f 2 ) ] 

TECHNICAL GUIDANCE FOR ASSESSING THE EFFECTS OF ANTHROPOGENIC SOUND ON MARINE MAMMAL
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Table ES3:

Summary of PTS onset acoustic thresholds.
PTS Onset Acoustic Thresholds*

Hearing Group
Low-Frequency (LF)
Cetaceans
Mid-Frequency (MF)
Cetaceans
High-Frequency (HF)
Cetaceans
Phocid Pinnipeds (PW)
(Underwater)
Otariid Pinnipeds (OW)
(Underwater)

Impulsive
Cell 1

Lpk,flat: 219 dB
LE,LF,24h: 183 dB
Cell 3

(Received Level)

Non-impulsive
Cell 2

LE,LF,24h: 199 dB
Cell 4

Lpk,flat: 230 dB
LE,MF,24h: 185 dB

LE,MF,24h: 198 dB

Cell 7

Cell 8

Cell 5

Lpk,flat: 202 dB
LE,HF,24h: 155 dB
Lpk,flat: 218 dB

LE,PW,24h: 185 dB
Cell 9

Lpk,flat: 232 dB

LE,OW,24h: 203 dB

Cell 6

LE,HF,24h: 173 dB

LE,PW,24h: 201 dB
Cell 10

LE,OW,24h: 219 dB

* Dual metric acoustic thresholds for impulsive sounds: Use whichever results in the largest isopleth for
calculating PTS onset. If a non-impulsive sound has the potential of exceeding the peak sound pressure level
thresholds associated with impulsive sounds, these thresholds should also be considered.
Note: Peak sound pressure (Lpk) has a reference value of 1 µPa, and cumulative sound exposure level (LE)
has a reference value of 1µPa2s. In this Table, thresholds are abbreviated to reflect American National
Standards Institute standards (ANSI 2013). However, peak sound pressure is defined by ANSI as
incorporating frequency weighting, which is not the intent for this Technical Guidance. Hence, the subscript
“flat” is being included to indicate peak sound pressure should be flat weighted or unweighted within the
generalized hearing range. The subscript associated with cumulative sound exposure level thresholds indicates
the designated marine mammal auditory weighting function (LF, MF, and HF cetaceans, and PW and OW
pinnipeds) and that the recommended accumulation period is 24 hours. The cumulative sound exposure level
thresholds could be exceeded in a multitude of ways (i.e., varying exposure levels and durations, duty cycle).
When possible, it is valuable for action proponents to indicate the conditions under which these acoustic
thresholds will be exceeded.

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Figure ES1:

Auditory weighting functions for low-frequency (LF), mid-frequency
(MF), and high-frequency (HF) cetaceans.

Figure ES2:

Underwater auditory weighting functions for otariid (OW) and phocid
(PW) pinnipeds.

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TECHNICAL GUIDANCE FOR ASSESSING THE EFFECTS OF
ANTHROPOGENIC SOUND ON MARINE MAMMAL HEARING
UNDERWATER ACOUSTIC THRESHOLDS FOR ONSET OF PERMANENT
AND TEMPORARY THRESHOLD SHIFTS
I.

INTRODUCTION

This document provides technical guidance 2 for assessing the effects of anthropogenic
(human-made) sound on the hearing of marine mammal species under the jurisdiction 3 of
the National Marine Fisheries Service (NMFS) and was completed in collaboration 4 with the
National Ocean Service (NOS), Office of National Marine Sanctuaries. Specifically, it
identifies the received levels, or acoustic thresholds, at which individual marine mammals are
predicted to experience changes in their hearing sensitivity for acute, incidental exposure to
all underwater anthropogenic sound sources. This Technical Guidance is intended for use by
NMFS analysts/ managers and other relevant action proponents/stakeholders, including
other federal agencies, when seeking to determine whether and how their activities are
expected to result in impacts to marine mammal hearing via acoustic exposure. This
document outlines NMFS’ updated acoustic thresholds, describing in detail threshold
development (via Appendix A), and how they will be revised and updated in the future.
The acoustic thresholds presented in this document do not represent the entirety of an
effects analysis, but rather serve as one tool among others (e.g., behavioral impact
thresholds, auditory masking assessments, evaluations to help understand the effects of any
particular type of impact on an individual’s fitness, population assessments, etc.), to help
evaluate the effects of a proposed action and make findings required by NOAA’s various
statutes.
2

This Technical Guidance does not create or confer any rights for or on any person, or operate to bind the
public. An alternative approach that has undergone independent peer review may be proposed (by federal
agencies or prospective action proponents) and used if case-specific information/data indicate that the
alternative approach is likely to produce a more accurate estimate of auditory impact for the project being
evaluated; and if NMFS determines the approach satisfies the requirements of the applicable statutes and
regulations.
3

http://www.nmfs.noaa.gov/pr/species/mammals/. This document does not pertain to marine mammal
species under the U.S. Fish and Wildlife Service’s (USFWS) jurisdiction (e.g., walrus, polar bears, West Indian
manatees, sea otters). However, since marine mammal audiogram data are limited, a decision was made to
include all available datasets from in-water groups, including sirenian datasets (Gerstein et al. 1999; Mann et al.
2009), to derive composite audiogram parameters and threshold of best hearing for LF cetaceans (see
Appendix A1). Additionally, audiogram data from a single Pacific walrus (Kastelein et al. 2002) and a single sea
otter (Ghoul and Reichmuth 2014) were included in the derivation of the composite audiogram for OW
pinnipeds.
4

Draft versions of this document referred to it as a joint document by NOS and NMFS. However, this final
version more accurately identifies it as a NMFS-directed effort/document that was completed in association
with NOS.
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Note: This document does not directly address mitigation and monitoring measures 5 that
may be associated with particular activities, nor does it set forth requirements to conduct
sound source verification studies.
This Technical Guidance is classified as a Highly Influential Scientific Assessment (HISA) 6
by the President’s Office of Management and Budget (OMB); as such, independent peer
review was required before it could be disseminated more broadly by the Federal
Government. As such, the Technical Guidance underwent three independent peer reviews
(details provided in Appendix C). NMFS also sought informal input from key federal
agencies regarding various aspects of this document in early stages of its development.
1.1

NEED FOR TECHNICAL GUIDANCE AND UPDATED UNDERWATER ACOUSTIC
THRESHOLDS

Prior to this Technical Guidance, NMFS has primarily relied on two generic acoustic
thresholds for assessing auditory impacts (i.e., permanent threshold shift [PTS] onset) for
most underwater sound sources: one for cetaceans (RMS SPL 180 dB), and one for
pinnipeds (RMS SPL 190 dB). These generic thresholds were developed in the late 1990s
using the best information available (e.g., NOAA 1998; HESS 1999). Other sound sources,
like tactical sonar and underwater explosives, have relied on more recently developed
acoustic thresholds (e.g., Finneran and Jenkins 2012; NOAA 2014). Since the adoption of
these original generic thresholds, the understanding of the effects of noise on marine
mammal hearing has greatly advanced (e.g., Southall et al. 2007; Finneran 2015; Erbe et al.
2016) making it necessary to more comprehensively examine the current state of science and
the acoustic thresholds.
For this document, NMFS has compiled, interpreted, and synthesized the scientific literature
on the impacts of sound on marine mammal hearing, including the recent Finneran
Technical Report (Finneran 2016; Appendix A of this Technical Guidance), to produce
updated underwater acoustic thresholds for the onset of TTS and PTS. These acoustic
thresholds update those currently in use by NMFS estimating PTS onset from all sources, as
well as those currently in use for estimating TTS 7 onset from underwater detonations. The
5

Mitigation and monitoring requirements associated with an MMPA authorization or ESA consultation or
permit are independent management decisions made in the context of the proposed activity and
comprehensive effects analysis, and are beyond the scope of the Technical Guidance. NMFS acknowledges
exclusion zones and monitoring zones often correspond to acoustic thresholds but that is not a legal
requirement, and the updated thresholds may make such a simple correlation more challenging. The Technical
Guidance can be used to inform the development of mitigation or monitoring.

Its dissemination could have a potential impact of more than $500 million in any one year on either the
public or private sector; or that the dissemination is novel, controversial, or precedent-setting; or that it has
significant interagency interest (OMB 2005). The decision to designate the Technical Guidance as a HISA was
based on the latter part of OMB’s definition (i.e., precedent-setting).
7

TTS onset thresholds are found in Appendix A, Table A10.

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Technical Guidance’s acoustic thresholds are more complex reflecting the current state of
scientific knowledge regarding marine mammal hearing and the characteristics of sound that
have the potential to impact marine mammal hearing sensitivity.
This is the first time NMFS has presented this information in a single, comprehensive
document, which can be used by NMFS analysts/managers and other relevant action
proponents/stakeholders, including other federal agencies, when seeking to determine
whether and how their activities are expected to result in auditory impacts to marine
mammals via acoustic exposure.
1.1.1

Acoustic thresholds within the Context of an Effects Analysis

The Technical Guidance’s acoustic thresholds do not represent the entirety of an effects
analysis, but rather serve as one tool to help evaluate the effects of sound produced during a
proposed action on marine mammals and make findings required by NOAA’s various
statutes. In a regulatory context, NMFS uses acoustic thresholds to help assess and quantify
“take” and to conduct more comprehensive effects analyses under several statutes.
Specifically, the Technical Guidance will be used in conjunction with sound source
characteristics, environmental factors that influence sound propagation, anticipated marine
mammal occurrence and behavior near the activity, as well as other available activity-specific
factors, to estimate the number and types of takes of marine mammals. This document only
addresses acoustic thresholds for auditory impact (i.e., does not address or make
recommendations associated with sound propagation or marine mammal occurrence or
density).
1.2

ADDRESSING UNCERTAINTY AND DATA LIMITATIONS

Inherent data limitations occur in many instances when assessing acoustic effects on marine
mammal hearing. Data limitations, which make it difficult to account for uncertainty and
variability, are not unique to assessing the effects of anthropogenic sound on marine
mammals and are commonly encountered by resource managers (Ludwig et al. 1993; Francis
and Shotton 1997; Harwood and Stokes 2003; Punt and Donovan 2007). Southall et al.
(2007) and Finneran (2016) acknowledged the inherent data limitations when making
recommendations for criteria to assess the effects of noise on marine mammals, including
data available from a limited number of species, a limited number of individuals within a
species, and/or limited number of sound sources. Both Finneran (2016) and Southall et al.
(2007) applied certain extrapolation procedures to estimate effects that had not been directly
measured but that could be reasonably approximated using existing information and
reasoned logic. The Technical Guidance articulates where NMFS has faced such uncertainty
and variability in the development of its acoustic thresholds.
1.2.1

Assessment Framework

NMFS’ approach applies a set of assumptions to address uncertainty in predicting potential
auditory effects of sound on individual marine mammals. One of these assumptions includes
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the use of “representative” or surrogate individuals/species for establishing PTS onset
acoustic thresholds for species where little to no data exists. The use of representative
individuals/species is done as a matter of practicality (i.e., it is unlikely that adequate data will
exist for the all marine mammal species found worldwide or that we will be able to account
for all sources of variability at an individual level) but is also scientifically based (i.e.,
taxonomy, hearing group). As new data become available for more species, this approach
can be reevaluated. NMFS recognizes that additional applicable data may become available
to better address many of these issues (e.g., uncertainty, surrogate species, etc.). 8 As these
new data become available, NMFS has an approach for updating this document (see Section
III).
1.2.2

Data Standards

In assessing potential acoustic effects on marine mammals, as with any such issue facing the
agency, standards for determining applicable data need to be articulated. Specifically, NOAA
has Information Quality Guidelines 9 (IQG) for “ensuring and maximizing the quality,
objectivity, utility, and integrity of information disseminated by the agency” (with each of
these terms defined within the IQG). Further, the IQG stipulate that “To the degree that the
agency action is based on science, NMFS will use (a) the best available science and
supporting studies (including peer-reviewed science and supporting studies when available),
conducted in accordance with sound and objective scientific practices, and (b) data collected
by accepted methods or best available methods.”
The National Research Council (NRC 2004) provided basic guidelines for National Standard
2 (NS2) in section 301 of the Magnuson-Stevens Fishery Conservation and Management
Act, which states that “Conservation and management measures shall be based upon the
best scientific information available” (NOAA 2013). They recommended that data
underlying the decision-making and/or policy-setting process be: 1) relevant, 2) inclusive, 3)
objective, 4) transparent and open, 5) timely, 6) verified and validated, and 7) peer
reviewed. 10 Although NRC’s guidelines (NRC 2004) were not written specifically for marine
mammals and this particular issue, they do provide a means of articulating minimum data
standards. NMFS considered this in assessing acoustic effects on marine mammals. Use of
the NRC Guidelines does not preclude development of acoustic-specific data standards in
the future.

NMFS is aware that the authors of Southall et al. (2007) are in the process of updating their original
publication and recognizes that when this updated publication becomes available, it may suggest alternative
means for predicting an auditory weighting function and acoustic thresholds for LF cetaceans. Accordingly,
NMFS may re-evaluate our methodology for LF cetaceans when this updated Southall et al. publication
becomes available.
9

http://www.st.nmfs.noaa.gov/science-quality-assurance/national-standards/ns2_revisions.

NMFS also requires Peer Review Plans for Highly Influential Scientific Assessments (HISA) and Influential
Scientific Information (ISI).

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II.

NMFS’ ACOUSTIC THRESHOLDS FOR ONSET OF PERMANENT
THRESHOLD SHIFTS IN MARINE MAMMALS

The Technical Guidance advances NMFS’ assessment ability based upon the compilation,
interpretation, and synthesis of the scientific literature. This document provides thresholds
for the onset of PTS based on characteristics defined at the acoustic source. No direct
measurements of marine mammal PTS have been published; PTS onset acoustic thresholds
have been extrapolated from marine mammal TTS measurements (i.e., using growth rates
from terrestrial and marine mammal data). PTS onset acoustic thresholds, for all sound
sources are divided into two broad categories: 1) impulsive and 2) non-impulsive. Acoustic
thresholds are also presented as dual metric acoustic thresholds using cumulative sound
exposure level (SELcum,) and peak sound pressure (PK) metrics for impulsive sounds. As dual
metrics, NMFS considers onset of PTS to have occurred when either one of the two metrics
is exceeded. For non-impulsive sounds, thresholds are provided using the SELcum metric.
Additionally, to account for the fact that different species groups use and hear sound
differently, marine mammals are sub-divided into five broad hearing groups (i.e., LF, MF,
HF, PW, and OW) and acoustic thresholds in the SELcum metric incorporate auditory
weighting functions.
2.1

MARINE MAMMAL HEARING GROUPS

Current data (via direct behavioral and electrophysiological measurements) and predictions
(based on inner ear morphology, modeling, behavior, vocalizations, or taxonomy) indicate
that not all marine mammal species have equal hearing capabilities, in terms of absolute
hearing sensitivity and the frequency band of hearing (Richardson et al. 1995; Wartzok and
Ketten 1999; Southall et al. 2007; Au and Hastings 2008). Hearing has been directly
measured in some odontocete and pinniped species11 (see reviews in Southall et al. 2007;
Erbe et al. 2016; Finneran 2016). Direct measurements of mysticete hearing are lacking. 12
Thus, hearing predictions for mysticetes are based on other methods including: anatomical
studies and modeling (Houser et al. 2001; Parks et al. 2007; Tubelli et al. 2012; Cranford and
Krysl 2015 13); vocalizations14 (see reviews in Richardson et al. 1995; Wartzok and Ketten
1999; Au and Hastings 2008); taxonomy; and behavioral responses to sound (Dahlheim and
Ljungblad 1990; see review in Reichmuth 2007).
11

Hearing measurements both in air and underwater have been collected for pinniped species.

There was an unsuccessful attempt to directly measure hearing in a stranded gray whale calf by Ridgway and
Carder 2001.
13

Note: The modeling of Cranford and Krsyl (2015) predicts that the primary mechanism for hearing in LF
cetaceans is bone conduction. Additionally, this predictive model was based on the skull geometry of a
newborn fin whale.
14

Studies in other species indicate that perception of frequencies may be broader than frequencies produced
(e.g., Luther and Wiley 2009).

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To better reflect marine mammal hearing capabilities, Southall et al. (2007) recommended
that marine mammals be divided into hearing groups (Table 1). NMFS made the following
modifications to the hearing groups proposed in Southall et al. (2007) 15:
•

Division of pinnipeds into PW and OW hearing groups: NMFS subdivided
pinnipeds into their two families: Phocidae and Otariidae. Based on a review of the
literature, phocid species have consistently demonstrated an extended frequency
range of hearing compared to otariids, especially in the higher frequency range
(Hemilä et al. 2006; Kastelein et al. 2009a; Reichmuth et al. 2013). Phocid ears are
anatomically distinct from otariid ears in that phocids have larger, more dense middle
ear ossicles, inflated auditory bulla, and larger sections of the inner ear (i.e., tympanic
membrane, oval window, and round window), which make them more adapted for
underwater hearing (Terhune and Ronald 1975; Schusterman and Moore 1978;
Kastak and Schusterman 1998; Hemilä et al. 2006; Mulsow et al. 2011; Reichmuth et
al. 2013).

•

Recategorizatin of hourglass (Lagenorhynchus cruciger) and Peale’s (L. australis) dolphins
from MF cetacean to HF cetacean hearing group: 16 Echolocation data (Kyhn et al.
2009; Kyhn et al. 2010; Tougaard and Kyhn. 2010) indicate that the hourglass and
Peale’s dolphin produce sounds (i.e., higher mean peak frequency) similar to other
narrow band high-frequency cetaceans, such as porpoises, Kogia, and Cephalorhynchus,
and are distinctly different from other Lagenorhynchus species. Genetic data also
suggest these two species are more closely related to Cephalorhynchus species (MayCollado and Agnarsson 2006). Thus, based on this information, NMFS has decided
to move these two species from MF cetaceans to HF cetaceans.

NMFS considered dividing LF cetaceans into two separate groups (i.e., some species may have better low
frequency hearing than others, like blue and fin whales; Clark and Ellison 2004), but decided there was not
enough data to support such a division at this time. NMFS also considered separating sperm whales from
other MF cetaceans, but there are not enough data are available to stipulate exactly how this should be done.
Sperm whale placement within MF cetaceans is considered appropriate based on Ketten (2000), which
classified sperm whales as having Type I cochlea, similar to other MF cetaceans.

In March 2016, NMFS also proposed moving the white-beaked dolphin (L. albirostris) to the HF cetacean
hearing group. However, upon re-evaluation, it was decided this move was not fully supported (i.e., move not
supported to the level of that of the other two species in this family).

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Table 1:

Marine mammal hearing groups.
Hearing Group

Low-frequency (LF) cetaceans
(baleen whales)
Mid-frequency (MF) cetaceans
(dolphins, toothed whales, beaked whales, bottlenose whales)
High-frequency (HF) cetaceans
(true porpoises, Kogia, river dolphins, cephalorhynchid,
Lagenorhynchus cruciger & L. australis)
Phocid pinnipeds (PW) (underwater)
(true seals)
Otariid pinnipeds (OW) (underwater)
(sea lions and fur seals)

Generalized
Hearing Range*
7 Hz to 35 kHz
150 Hz to 160 kHz
275 Hz to 160 kHz
50 Hz to 86 kHz
60 Hz to 39 kHz

NMFS’ modification results in marine mammal hearing groups being defined in this
Technical Guidance as depicted in Table 1. Table 1 defines a generalized hearing range each
hearing group. This generalized hearing range was determined based on the ~65 dB 17
threshold from the normalized composite audiograms (Figure 4). For LF cetaceans and PW
pinnipeds, the ~65 dB threshold resulted in a lower bound that was considered too low to
be biologically plausible for these two groups. Instead, for LF cetaceans the lower frequency
limit from Southall et al. 2007 was used, while for PW pinnipeds 50 Hz was chosen as a
reasonable approximation for the lower frequency limit (relative to otariid pinnipeds) 18.
2.1.1

Application of Marine Mammal Hearing Groups

The application of marine mammal hearing groups occurs throughout the Technical
Guidance in two ways. First, acoustic thresholds are divided by hearing group to
acknowledge that not all marine mammal species have identical hearing or susceptibility to
noise-induced hearing loss (NIHL). Outside the generalized hearing range, the risk of
auditory impacts from sounds is considered highly unlikely or very low 19 (the exception
17

In humans, functional hearing range is typically defined as 60 dB above the hearing threshold at greatest
hearing sensitivity. To account for uncertainty associated with marine mammal hearing, NMFS based the
Technical Guidance’s generalized hearing range on 65 dB.

Understanding of low-frequency pinniped hearing is limited (i.e., few studies have direct measurements of
hearing below 100 Hz).

Animals are able to detect sounds beyond their generalized hearing range by non-auditory mechanisms.
However, typically, these sounds have to be extremely loud and would be considered uncomfortable (Wartzok
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would be if a sound above/below this range has the potential to cause physical injury, i.e.,
lung or gastrointestinal tract injury from underwater explosives).
Second, marine mammal hearing groups are used in the establishment of marine mammal
auditory weighting functions discussed next.
2.2

MARINE MAMMAL AUDITORY WEIGHTING FUNCTIONS

The ability to hear sounds varies across a species’ hearing range. Most mammal audiograms
have a typical “U-shape,” with frequencies at the bottom of the “U” being those to which
the animal is more sensitive, in terms of hearing (i.e. the animal’s best hearing range; for
example audiogram, see Glossary, Figure F1). Auditory weighting functions best reflect an
animal’s ability to hear a sound (and do not necessarily reflect how an animal will perceive
and behaviorally react to that sound). To reflect higher hearing sensitivity at particular
frequencies, sounds are often weighted. For example, A-weighting for humans deemphasize
frequencies below 1 kHz and above 6 kHz based on the inverse of the idealized (smoothed)
40-phon equal loudness hearing function across frequencies, standardized to 0 dB at 1 kHz
(e.g., Harris 1998). Other types of weighting functions for humans (e.g., B, C, D)
deemphasize different frequencies to different extremes (e.g., flattens equal-loudness
perception across wider frequencies with increasing received level; for example, C-weighting
is uniform from 50 Hz to 5 kHz; ANSI 2011).
Auditory weighting functions have been proposed for marine mammals, specifically
associated with PTS acoustic thresholds expressed in the SELcum 20 metric, which take into
account what is known about marine mammal hearing (Southall et al. 2007; Erbe et al. 2016).
The Finneran Technical Report (Finneran 2016), recently developed updated marine
mammal auditory weighting functions that reflect new data on:
•

Marine mammal hearing (e.g., Sills et al. 2014; Sills et al. 2015; Cranford and Krysl,
2015; Kastelein et al. 2015c)

•

Marine mammal equal latency contours (e.g., Reichmuth 2013; Wensveen et al. 2014;
Mulsow et al. 2015

•

Effects of noise on marine mammal hearing (e.g., Kastelein et al. 2012a; Kastelein et
al. 2012b; Finneran and Schlundt 2013; Kastelein et al. 2013a; Kastelein et al.
2013b; Popov et al. 2013; Kastelein et al. 2014a; Kastelein et al. 2014b; Popov et al.

and Ketten 1999). If a sound is on the edge of a hearing group’s generalized hearing range and there is the
potential for exposure to high sound pressure levels, then one should consider the potential for detection
beyond normal auditory pathways.
20

Auditory weighting functions are not to be applied to PTS or TTS onset acoustic thresholds expressed as
the PK metric (i.e., PK thresholds are flat or unweighted within the generalized hearing range). For more
information, please see Section 2.3.2.2.

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2014; Finneran et al. 2015; Kastelein et al., 2015a; Kastelein et al. 2015b; Popov et
al. 2015).
This recent update reflects a transition from auditory weighting functions that have
previously been more similar to human dB(C) functions (i.e., M-weighting from Southall et
al. 2007) to that more similar to human dB(A) functions. Updated marine mammal auditory
weighting functions also provide a more consistent approach/methodology for all hearing
groups.
Upon evaluation, NMFS determined that the proposed methodology in Finneran 2016
reflects the scientific literature and incorporated it directly into this Technical Guidance
(Appendix A) following an independent peer review (see Appendix C for details on peer
review and link to Peer Review Report).
2.2.1

Use of Auditory Weighting Functions in Assessing Susceptibility to NoiseInduced Hearing Loss

Auditory weighting functions are used for human noise standards to assess the overall
hazard of noise on hearing. Specifically, human auditory weighting functions provide a
“rating that indicates the injurious effects of noise on human hearing” (OSHA 2013). Thus,
while these functions are based on regions of equal loudness and best hearing, in the context
of human risk assessments, as well as their use in the Technical Guidance, they are meant to
reflect the susceptibility of the ear to noise-induced threshold shifts (TSs). Regions of
enhanced susceptibility to noise may not perfectly mirror a species’ region of best hearing
(e.g., TTS measurements from bottlenose dolphin, belugas, and Yangtze finless porpoise
support this). Thus, within the Technical Guidance, auditory weighting functions are meant
to assess risk of NIHL and do not necessarily encompass the entire range of best hearing for
every species within the hearing group.
2.2.2

Marine Mammal Auditory Weighting Functions

Updated frequency-dependent marine mammal auditory weighting functions were derived
using data on hearing ability (composite audiograms), effects of noise on hearing, and data
on equal latency (Finneran 2016 21). Separate functions were derived for each marine
mammal hearing group (Figures 1 and 2).

Wright 2015 provides a critique of this methodology. For NMFS’ response associated with this critique, see
the Federal Register notice associated with the finalized Technical Guidance, specifically the section responding
to public comments.
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Figure 1:

Auditory weighting functions for low-frequency (LF), mid-frequency
(MF), and high-frequency (HF) cetaceans.

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Figure 2:

Underwater auditory weighting functions for otariid (OW) and phocid
(PW) pinnipeds.

The overall shape of the auditory weighting functions is based on a generic band-pass filter
described by Equation 1:



( f / f1 ) 2 a
W ( f ) = C + 10 log10 
2 a
2 b  dB
[1 + ( f / f1 ) ] [1 + ( f / f 2 ) ] 

Equation 1

where W(ƒ) is the weighting function amplitude in decibels (dB) at a particular frequency (ƒ)
in kilohertz (kHz). The function shape is determined by the following weighting function
parameters:
•

Low-frequency exponent (a): This parameter determines the rate at which the
weighting function amplitude declines with frequency at the lower frequencies. As
the frequency decreases, the change in amplitude becomes linear with the logarithm
of frequency with a slope of 20a dB/decade.

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•

High-frequency exponent (b): Rate at which the weighting function amplitude
declines with frequency at the upper frequencies. As the frequency increases, the
change in amplitude becomes linear with the logarithm of frequency with a slope of
20b dB/decade.

Low-frequency cutoff (ƒ1 ): This parameter defines the lower limit of the band-pass
filter (i.e., the lower frequency where weighting function amplitude begins to roll off
or decline from the flat, central portion of the function). This parameter is directly
dependent on the value of the low-frequency exponent (a).

High-frequency cutoff (ƒ2): This parameter defines the upper limit the band-pass
filter (i.e., the upper frequency where weighting function amplitude begins to roll off
or decline from the flat, central portion of the function). This parameter is directly
dependent on the value of the high-frequency exponent (b).
Weighting function gain(C): This parameter determines the vertical position of the
function and is adjusted to set the maximum amplitude of the weighting function to
0 dB.

Finneran (2016) illustrates the influence of each parameter value on the shape of the
weighting function (Appendix A, Figure A2).
In association with auditory weighting functions are exposure functions that illustrate how
auditory weighting functions relate to auditory acoustic thresholds. Exposure functions
(Equation 2) are the inversion of Equation 1:

dB
Equation 2

where E(ƒ) is the acoustic exposure as a function of frequency (ƒ) and the gain parameter
constant (K), which is adjusted to set the minimum value of the curve to the weighted
PTS/TTS onset auditory threshold. All other parameters are the same as those in Equation
1. Figure 3 illustrates how the various weighting parameters relate to one another in both the
auditory weighting and exposure functions.

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Figure 3:

Illustration of function parameter in both auditory weighting functions
and exposure functions (from Finneran 2016). Reference to Equations
1 and 2 match those in the Technical Guidance.

Finneran (2016) (Appendix A, Figures A-22 and A-23) provides a comparison of these
updated auditory weighting functions with previously derived weighting functions (Finneran
and Jenkins 2012 used in Navy Phase 2 Analysis).
2.2.3

Derivation of Function Parameters

Numeric values associated with weighting function parameters were derived from available
data from audiograms (measured and predicted), equal latency contours, and marine
mammal TTS data using the following steps from Finneran (2016):
1. Derivation of marine mammal composite audiograms (original and normalized) for
each hearing group (Resulting normalized composite audiogram: Figure 4; Data
sources: Table 2).

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Figure 4:

Resulting normalized composite audiograms for low-frequency (LF),
mid-frequency (MF), and high-frequency (HF) cetaceans and phocid
(PW) and otariid (OW) pinnipeds (from Finneran 2016). For resulting
original composite audiogram, see Appendix A, Figure A5.

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Table 2:

Summary of data available for deriving composite audiograms.†

Hearing Group

Species (number of
individuals)

Beluga (9)

Mid-Frequency (MF)
cetaceans

High-frequency (HF)
cetaceans

Bottlenose dolphin
(6)
False killer whale (1)
Killer whale (2)
Risso’s dolphin (1)
Pacific white-sided
dolphin (1)
Striped dolphin (1)
Tucuxi (1)
Amazon River
dolphin (1)
Harbor porpoise (3)
Harbor seal (4)

Phocid pinnipeds
(underwater)

Otariid pinnipeds*
(underwater)
†

Northern elephant
seal (1)
Ringed seal (1)
Spotted seal (2)
California sea lion
(4)
Northern fur seal
(3)
Steller sea lion (2)

References
White et al. 1978; Awbrey et al. 1988; Johnson et al.
1989; Ridgway et al. 2001; Finneran et al. 2005b
Johnson 1967; Ljungblad et al. 1982; Lemonds 1999;
Brill et al. 2001;Schlundt et al. 2008; Finneran et al.
2010a
Thomas et al. 1988
Szymanski et al. 1999
Nachtigall et al. 1995
Tremel et al. 1996
Kastelein et al. 2003
Sauerland and Dehnhardt 1998
Jacobs and Hall 1972
Kastelein et al. 2010; Kastelein et al. 2015c
Terhune 1988; Kastelein et al. 2009b; Reichmuth et
al. 2013
Kastak and Schusterman 1999
Sills et al. 2015
Sills et al. 2014
Mulsow et al. 2012; Reichmuth and Southall 2012;
Reichmuth et al. 2013
Moore and Schusterman 1987; Babushina et al. 1991
Kastelein et al. 2005a

More details on individual subjects are available in Appendix A (Table A2). Some datasets were excluded due
to subjects having high-frequency hearing loss or aberrant audiograms. These included subjects from: Møhl
1968; Andersen 1970; Hall and Johnson 1972; Terhune and Ronald 1972; Terhune and Ronald 1975; Thomas
et al. 1990; Wang et al. 1992; Babushina 1997; Kastak et al. 2002; Finneran et al. 2005 (Turner); Yuen et al.
2005; Finneran et al. 2007a; Sills et al. 2015 (Natchek). Decisions to exclude data were based on comparison of
the individual published audiograms and ambient noise characteristics to those for other individuals of the
same or closely related species. The most common reasons for excluding an individual’s data were abnormal
audiograms featuring high-frequency hearing loss (typically seen in older animals) or “notches” in the
audiogram, or data collected in the presence of relatively high ambient noise that resulted in elevated
thresholds. Excluding these data ensured that the composite audiograms were not artificially elevated, which
could result in unrealistically high acoustic thresholds.

* The otariid pinniped (underwater)hearing group’s composite audiogram contains data from a single Pacific

walrus (Odobenus rosmarus) from Kastelein et al. 2002 and a single sea otter (Enhydra lutris nereis) from Ghoul and
Reichmuth 2014, which are species under the jurisdiction of the USFWS. However, since marine mammal
audiogram data are limited, a decision was made to include all available datasets from in-water groups to derive
composite audiograms for this hearing group. For frequencies below 30 kHz, the difference in the composite
audiogram with and without these data are < 2 dB. For comparison, see Appendix A, Figure A4.

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In deriving marine mammal composite audiograms, NMFS established an informal
data hierarchy in terms of assessing these types of data. Specifically, audiograms
obtained via behavioral methodologies were determined to provide the most
representative (sensitive) presentation of hearing ability (Finneran et al. 2007a),
followed by auditory evoked potential (AEP) data, 22 and lastly by
mathematical/anatomical models for species where no data are available (i.e., LF
cetaceans). Thus, the highest quality data available for a specific hearing group were
used. 23
For LF cetaceans, only two studies were available for consideration (i.e., predicted
audiogram for a humpback whale from Houser et al. 2001 and fin whale from
Cranford and Krysl 2015), which alone was not enough to derive a predicted
audiogram for this entire hearing group. Thus, an alternative approach was used to
derive a composite audiogram 24 and associated weighting function for LF cetaceans
(i.e., composite audiogram parameters had to be predicted; For specifics, on this
process, see Appendix A1).
2. The low-frequency exponent (a) was defined using the smaller of the low-frequency
slope from either the composite audiogram or the lower-frequency slope of the equal
latency contours (if available) and then divided by twenty (s0/20 ). This results in the
slope matching the shallower slope of the audiogram.
3. The high-frequency exponent (b) was set equal to two to match the previously
derived marine mammal auditory weighting functions from Finneran and Jenkins
(2012), since no new TTS measurements were available at higher frequencies and
equal latency data at these frequencies are considered highly variable.

4. Low- (ƒ1) and high-frequency cutoffs (ƒ2) were defined as the frequencies below and
above the frequency of best hearing (ƒ0) from original data, where the threshold
22

Despite not directly including AEP audiograms in the development of a hearing groups’ composite
audiogram, these date were evaluated to ensure species were placed within the appropriate hearing group and
to ensure a species where only AEP data are available were within the bounds of the composite audiogram for
that hearing group. Furthermore, AEP TTS data are presented within the Technical Guidance for comparative
purposes alongside TTS data collected by behavioral methods illustrating that the AEP TTS data are within the
bounds (the majority of the time above) of those collected by behavioral methods.
23

Behavioral techniques for obtaining audiograms measure perception of sound by a receiver, while AEP
methods measure only neural activity (Jewett and Williston 1971) (i.e., two methodologies are not necessarily
equivalent). As a result, behavioral techniques consistently produce lower thresholds than those obtained by
AEPs (e.g., Szymanski et al. 1999; Yuen et al. 2005; Houser and Finneran 2006). Currently, there are no means
established for “correcting” AEP data so that it may be more comparable to those obtained via behavioral
methods (Heffner and Heffner 2003; Finneran 2015; Sisneros et al. 2016; Erbe et al. 2016).
24

During the third public comment period on the Technical Guidance in March 2016, ambient noise levels
from Clark and Ellison 2004 were offered by a group of subject matter experts as additional scientific support
to NMFS’ LF cetacean weighting function (for direct comparison to NOAA’s 2016 LF cetacean weighting
function see: https://www.regulations.gov/#!documentDetail;D=NOAA-NMFS-2013-0177-0155).
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values were ΔT above the threshold at ƒ0 . These two parameters reflect the hearing
group’s most susceptible frequency range.

5. To determine ΔT, the exposure function amplitude was calculated for MF and HF
cetaceans examining ΔT values ranging from zero to 20 dB. Then, the K gain
parameter was adjusted to minimize the mean-squared error (MSE) between the
function amplitude (original and normalized composite audiograms) and MF and HF
cetacean TTS data. The value of ΔT resulting the lowest MSE was eleven for both
the normalized and original data. This value was used for other hearing groups.

6. Hearing groups where TTS data are available (i.e., MF and HF cetaceans and PW
and OW pinniped) were used to define K (Step 4 above). For LF cetaceans, where
data were not available, TTS onset was estimated by assuming the numeric difference
between auditory threshold (Figure 4, original data) and TTS onset at the frequency
of best hearing (ƒ0) would be similar across hearing groups. For LF cetaceans
auditory threshold had to be predicted, since no data exist (For specifics on
methodology, see Appendix A, Table A7).

7. The weighting function parameter (C) was determined by substituting parameters a,
b, ƒ1, and ƒ2 in Equation 1 and setting the peak amplitude of the function to zero.

For each hearing group, the resulting numeric values associated with these parameters and
resulting weighted TTS onset threshold for non-impulsive sources (SELcum metric) are listed
in Table 3 and resulting weighting functions are depicted in Figures 1 and 2.
Table 3:

Summary of weighting and exposure function parameters.

Hearing Group
Low-frequency (LF)
cetaceans
Mid-frequency (MF)
cetaceans
High-frequency (HF)
cetaceans
Phocid pinnipeds (PW)
(underwater)
Otariid pinnipeds (OW)
(underwater)

Weighted TTS onset
threshold* (SELcum)

(kHz)

1.0 2

ƒ1

0.2

ƒ2

0.13 179

179 dB

1.6 2

8.8

110

1.20 177

178 dB

1.8 2

140

1.36 152

153 dB

1.0 2

1.9

0.75 180

181 dB

2.0 2

0.94

0.64 198

199 dB

(kHz)

(dB)

* Determined from minimum value of exposure function and the weighting function at its peak (i.e.,
mathematically equivalent to K + C).

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Note: Appendix A, Figure A17 illustrates that the resulting exposure functions (and
subsequent weighting functions) are broader than the composite audiograms or audiogram
from an individual species. This is important to note because the weighting/exposure
functions are derived not just from data associated with the composite audiogram but also
account for available TTS onset data.
2.2.4

Application of Marine Mammal Auditory Weighting Functions for PTS Onset
Acoustic Thresholds

The application of marine mammal auditory weighting functions emphasizes the importance
of making measurements and characterizing sound sources in terms of their overlap with
biologically-important frequencies (e.g., frequencies used for environmental awareness,
communication or the detection of predators or prey), and not only the frequencies of
interest or concern for the completion of the sound-producing activity (i.e., context of sound
source).
If the frequencies produced by a sound source are outside a hearing group’s most susceptible
hearing range (where the weighting function amplitude is 0), sounds at those frequencies
must have a higher sound pressure level to produce a similar threshold shift (i.e., PTS onset)
as sounds with frequencies in the hearing group’s most susceptible hearing range. Because
auditory weighting functions take into account a hearing group’s differing susceptibility to
frequencies, the implementation of these functions typically results in smaller isopleths 25 for
frequencies where the group is less susceptible. Additionally, if the sound source produces
frequencies completely outside the generalized hearing range of a given hearing group (i.e.,
has no harmonics/subharmonics that are capable of producing sound within the hearing
range of a hearing group), then the likelihood of the sound causing hearing loss is considered
low. 26
Marine mammal auditory weighting functions should be used in conjunction with
corresponding SELcum PTS onset acoustic thresholds. If the use of the full auditory
weighting function is not possible by an action proponent (i.e., consider weighting function
over multiple frequencies for broadband source), NMFS has provided an alternative tool
based on a simpler weighting function (See Appendix D).

Note: Acoustic thresholds associated with a hearing group do not change depending on how much a sound
may overlap a group’s most susceptible frequency range. Instead, weighting functions affect exposure
modeling/analysis via the resulting size of the isopleth (area) associated with the threshold based on how
susceptible that particular hearing group is to the sound being modeled. For example, a hearing group could
have different size isopleths associated with the same threshold, if one sound was within its most susceptible
frequency range and the other was not (i.e., sound in most susceptible hearing range will result in larger isopleth
compared to sound outside the most susceptible hearing range).
26

The potential for sound to damage beyond the level the ear can perceive exists (Akay 1978), which is why
the acoustic thresholds also include the PK metric, which are flat or unweighted within the generalized hearing
range of a hearing group.
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Tougaard et al. (2015) reviewed the impacts of using auditory weighting functions and
various considerations when applying them during the data evaluation and implementation
stages (e.g., consequences of using too broad or too narrow of a filter) and suggested some
modifications (correction factors) to account for these considerations. However, there are no
data to support doing so (i.e., selection would be arbitrary). Moreover, various conservative
factors have been accounted for in the development of weighting functions and acoustic
thresholds: A 6 dB threshold shift was used to represent TTS onset; the methodology does
not incorporate exposures where TTS did not occur; and the potential for recovery is not
accounted for. Additionally, the means by which NMFS is applying auditory weighting
functions is supported and consistent with what has been done for humans (i.e., A-weighted
thresholds used in conjunction with A-weighting during implementation).
2.2.4.1 Measuring and Maintaining Full Spectrum for Future Analysis
Marine mammal auditory weighting functions should be applied after sound field
measurements 27 have been obtained (i.e., post-processing; auditory weighting functions
should not be applied beforehand), with the total spectrum of sound preserved for later
analysis (i.e., if weighting functions are updated or if there is interest in additional species,
then data can still be used). Additionally, it is important to consider measurements that
encompass the entire frequency band that a sound source may be capable of producing (i.e.,
sources often produce sounds, like harmonics/subharmonics, beyond the frequency/band
of interest; e.g., Deng et al. 2014; Hastie et al. 2014).
2.3

PTS ONSET ACOUSTIC THRESHOLDS

Available data from humans and other terrestrial mammals indicate that a 40 dB threshold
shift approximates PTS onset (see Ward et al. 1958; Ward et al. 1959; Ward 1960; Kryter et
al. 1966; Miller 1974; Ahroon et al. 1996; Henderson et al. 2008). Southall et al. (2007) also
recommended this definition of PTS onset.
PTS onset acoustic thresholds for marine mammals have not been directly measured and
must be extrapolated from available TTS onset measurements. Thus, based on cetacean
measurements from TTS studies (see Southall et al. 2007; Finneran 2015; Finneran 2016
found in Appendix A of this Technical Guidance) a threshold shift of 6 dB is considered the
minimum threshold shift clearly larger than any day-to-day or session-to-session variation 28
in a subject’s normal hearing ability and is typically the minimum amount of threshold shift
that can be differentiated in most experimental conditions (Finneran et al. 2000; Schlundt et
27

Note: Sound field measurements refers to actual field measurements, which are not a requirement of this
Technical Guidance, and not to exposure modeling analyses, where it may be impractical due to data storage
and cataloging restraints.
28

Similarly, for humans, NIOSH (1998) regards the range of audiometric testing variability to be
approximately 5 dB.

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al. 2000; Finneran et al. 2002). Thus, NMFS has set the onset of TTS at the lowest level that
exceeds recorded variation (i.e., 6 dB).
There are different mechanisms (e.g., anatomical, neurophysiological) associated with TTS
vs. PTS onset, making the relationship between these types of TSs not completely direct.
Nevertheless, the only data available for marine mammals, currently and likely in the future,
will be from TTS studies (i.e., unlike for terrestrial mammals where direct measurements of
PTS exist). Thus, TTS represents the best information available from which PTS onset can
be estimated.
The acoustic thresholds presented in Table 4 update all NMFS acoustic thresholds for PTS
onset. The acoustic thresholds consist of both an acoustic threshold and weighting function
for the SELcum metric (weighting functions are considered not appropriate for PK metric).

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Table 4:

Summary of PTS onset acoustic thresholds.
PTS Onset Thresholds*

Hearing Group
Low-Frequency (LF)
Cetaceans
Mid-Frequency (MF)
Cetaceans
High-Frequency (HF)
Cetaceans
Phocid Pinnipeds (PW)
(Underwater)
Otariid Pinnipeds (OW)
(Underwater)

Impulsive

(Received Level)

Cell 1

Lpk,flat: 219 dB
LE,LF,24h: 183 dB
Cell 3

Non-impulsive
Cell 2

LE,LF,24h: 199 dB
Cell 4

Lpk,flat: 230 dB
LE,MF,24h: 185 dB

LE,MF,24h: 198 dB

Cell 7

Cell 8

Cell 5

Lpk,flat: 202 dB
LE,HF,24h: 155 dB
Lpk,flat: 218 dB

LE,PW,24h: 185 dB
Cell 9

Lpk,flat: 232 dB

LE,OW,24h: 203 dB

Cell 6

LE,HF,24h: 173 dB

LE,PW,24h: 201 dB
Cell 10

LE,OW,24h: 219 dB

* Dual metric acoustic thresholds for impulsive sounds: Use whichever results in the largest isopleth for
calculating PTS onset. If a non-impulsive sound has the potential of exceeding the peak sound pressure level
thresholds associated with impulsive sounds, these thresholds should also be considered.
Note: Peak sound pressure (Lpk) has a reference value of 1 µPa, and cumulative sound exposure level (LE) has
a reference value of 1µPa2s. In this Table, thresholds are abbreviated to reflect American National Standards
Institute standards (ANSI 2013). However, peak sound pressure is defined by ANSI as incorporating
frequency weighting, which is not the intent for this Technical Guidance. Hence, the subscript “flat” is being
included to indicate peak sound pressure should be flat weighted or unweighted within the generalized
hearing range. The subscript associated with cumulative sound exposure level thresholds indicates the
designated marine mammal auditory weighting function (LF, MF, and HF cetaceans, and PW and OW
pinnipeds) and that the recommended accumulation period is 24 hours. The cumulative sound exposure level
thresholds could be exceeded in a multitude of ways (i.e., varying exposure levels and durations, duty cycle).
When possible, it is valuable for action proponents to indicate the conditions under which these acoustic
thresholds will be exceeded.

NMFS recognizes that the implementation of marine mammal weighting functions
represents a new factor for consideration that may exceed the capabilities of some action
proponents. Thus, NMFS has developed alternative tools for those who cannot fully apply
weighting functions associated with the SELcum metric (See Appendix D).
2.3.1

Impulsive and Non-Impulsive Acoustic Thresholds

This Technical Guidance divides sources into impulsive and non-impulsive based on
physical characteristics at the source, with impulsive sound having physical characteristics
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making them more injurious 29 (e.g., high peak sound pressures and rapid rise times) than
non-impulsive sound sources (terrestrial mammal data: Buck et al. 1984; Dunn et al. 1991;
Hamernik et al. 1993; Clifford and Rogers 2009; marine mammal data: reviewed in Southall
et al. 2007 and Finneran 2016 that appears as Appendix A of this Technical Guidance).
The characteristics of the sound at a receiver, rather than at the source, are the relevant
consideration for determining potential impacts. However, understanding these physical
characteristics in a dynamic system with receivers moving over space and time is difficult.
Nevertheless, it is known that as sound propagates from the source the characteristics of
impulsive sounds that make them more injurious start to dissipate due to effects of
propagation (e.g., time dispersion/time spreading; Urick 1983; Sertlek et al. 2014).
For the purposes of this Technical Guidance, 30 sources are divided and defined as the
following:
•

Impulsive: produce sounds that are typically transient, brief (less than 1 second),
broadband, and consist of high peak sound pressure with rapid rise time and rapid
decay (ANSI 1986; NIOSH 1998; ANSI 2005).

•

Non-impulsive: produce sounds that can be broadband, narrowband or tonal, brief
or prolonged, continuous or intermittent) and typically do not have a high peak
sound pressure with rapid rise/decay time that impulsive sounds do (ANSI 1995;
NIOSH 1998).

Note: The term “impulsive” in this document relates specifically to NIHL and specifies the
physical characteristics of an impulsive sound source, which likely gives them a higher
potential to cause auditory TTS/PTS. This definition captures how these sound types may
be more likely to affect auditory physiology and is not meant to reflect categorizations
associated with behavioral disturbance.
2.3.2

Metrics

2.3.2.1 Cumulative Sound Exposure Level (SELcum) Metric
The SELcum metric takes into account both received level and duration of exposure (ANSI
2013), both factors that contribute to NIHL. Often this metric is normalized to a single
sound exposure of one second. NMFS intends for the SELcum metric to account for the
accumulated exposure (i.e., SELcum cumulative exposure over the duration of the activity within
a 24-h period).
29

Exposure to impulsive sounds more often lead to mechanical damage of the inner ear, as well as more
complex patterns of hearing recovery (e.g., Henderson and Hamernik 1986; Hamernik and Hsueh 1991).

If there is a source where it is unclear how it should be defined, consider the most applicable definition and
consult with NMFS.
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The recommended application of the SELcum metric is for individual activities/sources. It is
not intended for accumulating sound exposure from multiple activities occurring within the
same area or over the same time or to estimate the impacts of those exposures to an animal
occurring over various spatial or temporal scales. Current data available for deriving acoustic
thresholds using this metric are based on exposure to only a single source and may not be
appropriate for situations where exposure to multiple sources is occurring. As more data
become available, the use of this metric can be re-evaluated, in terms of appropriateness, for
application of exposure from multiple activities occurring in space and time.

Equal Energy Hypothesis
One assumption made when applying the SELcum metric is the equal energy hypothesis
(EEH), where it is assumed that sounds of equal SELcum produce an equal risk for hearing
loss (i.e., if the SELcum of two sources are similar, a sound from a lower level source with a
longer exposure duration may have similar risks to a shorter duration exposure from a higher
level source). As has been shown to be the case with humans and terrestrial mammals
(Henderson et al. 1991), the EEH does not always accurately describe all exposure situations
for marine mammals due the inherent complexity of predicting TSs (e.g., Kastak et al. 2007;
Mooney et al. 2009a; Mooney et al. 2009b; Finneran et al. 2010a; Finneran et al. 2010b;
Finneran and Schlundt 2010; Kastelein et al. 2012b; Kastelein et al. 2013b; Kastelein et al.
2014a; Popov et al. 2014).
Factors like sound level (e.g., overall level, sensation level, or level above background),
duration, duty cycle (intermittent versus continuous exposure; potential recovery between
intermittent periods), number of transient components (short duration and high amplitude),
and/or frequency (especially in relation to hearing sensitivity) often are also important
factors associated with TSs (e.g., Buck et al. 1984; Clark et al. 1987; Ward 1991; Lataye and
Campo 1996). This is especially the case for exposure to impulsive sound sources (Danielson
et al. 1991; Henderson et al. 1991; Hamernik et al. 2003), which is why acoustic thresholds in
this Technical Guidance are also expressed as a PK metric (see next section). However, in
many cases the EEH approach functions reasonably well as a first-order approximation,
especially for higher-level, short-duration sound exposures such as those that are most likely
to result in TTS in marine mammals 31 (Finneran 2015). Additionally, no currently supported
alternative method to accumulate exposure is available. If alternative methods become
available, they can be evaluated and considered when the Technical Guidance is updated.

Recommended Accumulation Period
To apply the SELcum metric, accumulation time must be specified. Generally, it is predicted
that most receivers will minimize the amount of time they remain in the closest ranges to a
sound source/activity. Exposures at the closest point of approach are the primary exposures
31

When possible, it is valuable for action proponents to indicate the exposure conditions under which these
acoustic thresholds are likely to be exceeded.

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contributing to a receiver’s accumulated level (Gedamke et al. 2011). Additionally, several
important factors determine the likelihood and duration a receiver is expected to be in close
proximity to a sound source (i.e., overlap in space and time between the source and receiver).
For example, accumulation time for fast moving (relative to the receiver) mobile sources is
driven primarily by the characteristics of source (i.e., speed, duty cycle). Conversely, for
stationary sources, accumulation time is driven primarily by the characteristics of the receiver
(i.e., swim speed and whether transient or resident to the area where the activity is
occurring). NMFS recommends a baseline accumulation period of 24 hours, but
acknowledges that there may be specific exposure situations where this accumulation period
requires adjustment (e.g., if activity lasts less than 24 hours or for situations where receivers
are predicted to experience unusually long exposure durations 32).
After sound exposure ceases or between successive sound exposures, the potential for
recovery from hearing loss exists, with PTS resulting in incomplete recovery and TTS
resulting in complete recovery. Predicting recovery from sound exposure can be quite
complicated. Currently, recovery in wild marine mammals cannot be accurately quantified.
However, Finneran et al. (2010a) and Finneran and Schlundt (2013) proposed a model that
approximates recovery in bottlenose dolphins and whose applicability to other species and
other exposure conditions has yet to be determined. In the development of the Technical
Guidance’s acoustic thresholds, NMFS assumes for intermittent, repeated exposure that
there is no recovery between subsequent exposures, although it has been demonstrated in
terrestrial mammals (Clark et al. 1987; Ward 1991) and more recently in a marine mammal
studies (Finneran et al. 2010b; Kastelein et al. 2014a; Kastelein et al. 2015b), that there is a
reduction in damage and hearing loss with intermittent exposures.
Existing NMFS acoustic thresholds have only accounted for proximity of the sound source
to the receiver, but acoustic thresholds in this Technical Guidance (i.e., expressed as SELcum)
now take into account the duration, as well as level of exposure. NMFS recognizes that
accounting for duration of exposure, although supported by the scientific literature, adds a
new factor, as far as application of this metric to real-world activities and that not all action
proponents may have the ability to easily apply this additional component.
NMFS does not provide specifications necessary to perform exposure modeling and relies
on the action proponent to determine the model that best represents their activity. However,
NMFS acknowledges that different action proponents may have different capabilities and
levels of modeling sophistication. NMFS has provided a simple means of approximating
exposure for applicants that are unable to apply various factors into their model (See
Appendix D).

For example, where a resident population could be found in a small and/or confined area (Ferguson et al.
2015) and/or exposed to a long-duration activity with a large sound source, or where a continuous stationery
activity is nearby an area where marine mammals congregate, like a pinniped pupping beach.
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2.3.2.2 Peak Sound Pressure Level (PK) Metric 33
Sound exposure containing transient components (e.g., short duration and high amplitude;
impulsive sounds) can create a greater risk of causing direct mechanical fatigue to the inner
ear (as opposed to strictly metabolic) compared to sounds that are strictly non-impulsive
(Henderson and Hamernik 1986; Levine et al. 1998; Henderson et al. 2008). Often the risk
of damage from these transients does not depend on the duration of exposure. This is the
concept of “critical level,” where damage switches from being primarily metabolic to more
mechanical and short duration of impulse can be less than the ear’s integration time, leading
to the potential to damage beyond the level the ear can perceive (Akay 1978).
Human noise standards recognize and provide separate acoustic thresholds for impulsive
sound sources using the PK metric (Occupational Safety and Health Administration
(OSHA) 29 CFR 1910.95; Starck et al. 2003). Thus, SELcum is not an appropriate metric to
capture all the effects of impulsive sounds (i.e., often violates EEH; NIOSH 1998), which is
why instantaneous PK level has also been chosen as part of NMFS’ dual metric acoustic
thresholds for impulsive sounds. 34 Auditory weighting is not considered appropriate with the
PK metric, as direct mechanical damage associated with sounds having high peak sound
pressures typically does not strictly reflect the frequencies an individual species hears best
(Ward 1962; Saunders et al. 1985; ANSI 1986; DOD 2004; OSHA 29 CFR 1910.95). Thus,
this Technical Guidance is recommends that the PK thresholds be considered
unweighted/flat-weighted within the entire frequency band of a hearing group.
2.3.2.3 Comparison Among Metrics
NMFS’ existing acoustic thresholds were expressed as root-mean-square sound pressure
level (RMS SPL), which is a different metric from the PK and SELcum that are being
recommended for the PTS onset acoustic thresholds in this Technical Guidance. Thus,
NMFS recommends caution when comparing prior acoustic thresholds to those presented in
this document (i.e., metrics are not directly comparable). For example, a RMS SPL threshold
of 180 dB is not equal to a PK threshold of 180 dB. Further, the SELcum metric incorporates
exposure duration and is an energy level with a different reference value (re: 1μPa2-s). Thus,
it is not directly comparable to other metrics that describe sound pressure levels (re: 1 μPa) 35.
33

Note: Peak sound pressure level should not be confused with maximum root mean square sound pressure
level.
34

For non-impulsive sounds, the SELcum threshold will likely to result in the largest isopleth, compared to the
PK threshold. Thus, for the majority of non-impulsive sounds, the consideration of the PK threshold is
unnecessary. However, if a non-impulsive sound has the potential of exceeding the PK threshold associated
with impulsive sounds, these thresholds should be considered (i.e., dual metrics).
Recently, publications on how to estimate PK from SEL for seismic airguns and offshore impact pile drivers
may be useful to applicants (Galindo-Romero et al. 2015; Lippert et al. 2015).
35

For more information and illustrations on metrics, see Discovery of Sound in the Sea:
http://www.dosits.org/science/advancedtopics/signallevels/.

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2.3.3

Development of PTS Onset Acoustic Thresholds

The development of the PTS onset acoustic thresholds consisted of the following procedure
described in Finneran 2016 (Appendix A 36):
1. Identification of available data on marine mammal hearing and noise-induced
hearing loss (e.g., Southall et al. 2007; Finneran 2015; Finneran 2016 references listed
in available reports/publications).
2. Methodology to derive marine mammal auditory weighting functions (described in
more detail in Section 2.2.3 and Appendix A).
3. Evaluation and summary of currently available published data (32 studies found in
Table 5) on hearing loss associated with sound exposure in marine mammals.
• Because no published measurements exist on PTS in marine mammals, TTS
onset measurements and associated acoustic thresholds were evaluated and
summarized to extrapolate to PTS onset acoustic thresholds.
•

Studies divided into the following categories:
o Temporal Characteristics: Impulsive and Non-impulsive
o Marine Mammal Hearing Groups: LF Cetaceans, MF Cetaceans, HF
Cetaceans, PW Pinnipeds, and OW Pinniped

Wright 2015 provides a critique of this methodology. For NMFS’ response to this critique, see the Federal
Register notice associated with the finalized Technical Guidance, specifically the section responding to public
comments.
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Table 5:

Available underwater marine mammal threshold shift studies.

References in
Chronologic Order+

Sound Source

(Sound Source Category)

Sound-Exposed
Species (number of
individuals^)

Kastak et al. 1999

Octave-band noise (non-impulsive)

Finneran et al. 2000
Schlundt et al. 2000
Finneran et al. 2002
Finneran et al. 2003
Nachtigall et al. 2003
Nachtigall et al. 2004
Finneran et al. 2005a

Explosion simulator (impulsive)*
Tones (non-impulsive)
Seismic watergun (impulsive)
Arc-gap transducer (impulsive)*
Octave-band noise (non-impulsive)
Octave-band noise (non-impulsive)
Tones (non-impulsive)

Kastak et al. 2005

Octave-band noise (non-impulsive)

Finneran et al. 2007a
Lucke et al. 2009
Mooney et al. 2009a
Mooney et al. 2009b
Finneran et al. 2010a
Finneran et al. 2010b
Finneran and Schlundt
2010

Tones (non-impulsive)
Single airgun (impulsive)
Octave-band noise (non-impulsive)
Mid-frequency sonar (non-impulsive)
Tones (non-impulsive)
Tones (non-impulsive)

California sea lion (1), northern
elephant seal (1), & harbor seal (1)
Bottlenose dolphin (2) & beluga (1)
Bottlenose dolphin (5) & beluga (2)
Bottlenose dolphin (1) & beluga (1)
California sea lion (2)
Bottlenose dolphin (1)
Bottlenose dolphin (1)
Bottlenose dolphin (2)
California sea lion (1), northern
elephant seal (1), & harbor seal (1)
Bottlenose dolphin (1)
Harbor porpoise (1)
Bottlenose dolphin (1)
Bottlenose dolphin (1)
Bottlenose dolphin (2)
Bottlenose dolphin (1)

Tones (non-impulsive)

Bottlenose dolphin (1)

Popov et al. 2011a
Popov et al. 2011b
Kastelein et al. 2012a
Kastelein et al. 2012b
Finneran and Schlundt
2013
Popov et al. 2013
Kastelein et al. 2013a
Kastelein et al. 2013b
Popov et al. 2014
Kastelein et al. 2014a
Kastelein et al. 2014b
Kastelein et al. 2015a
Kastelein et al. 2015b
Finneran et al. 2015*
Popov et al. 2015
Kastelein et al. 2016*

Half-octave band noise (nonimpulsive)
Half-octave band noise (nonimpulsive)
Octave-band noise (non-impulsive)
Octave-band noise (non-impulsive)
Tones (non-impulsive)
Half-octave band noise (nonimpulsive)
Octave-band noise (non-impulsive)
Tone (non-impulsive)
Half-octave band noise (nonimpulsive)
1-2 kHz sonar (non-impulsive)
6.5 kHz tone (non-impulsive)
Impact pile driving (impulsive)
6-7 kHz sweeps (non-impulsive)
Single airgun producing shots
(impulsive)*
Half-octave band noise (nonimpulsive)
Impact pile driving (impulsive)

+Peer reviewed studies available and evaluated as of 31 May 2016.
^Note: Some individuals have been used in multiple studies.
*No incidents of temporary threshold shift were recorded in study.

Yangtze finless porpoise (2)
Beluga (1)
Harbor seal (2)
Harbor porpoise (1)
Bottlenose dolphin (2)
Beluga (2)
Harbor seal (1)
Harbor porpoise (1)
Beluga (2)
Harbor porpoise (1)
Harbor porpoise (1)
Harbor porpoise (1)
Harbor porpoise (1)
Bottlenose dolphin (3)
Beluga (1)
Harbor porpoise (2)

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4. Determination of TTS onset threshold by individual (RLs, in both PK and SELcum
metrics) based on methodology from Finneran 2016 for impulsive and nonimpulsive sounds (Full detail in Appendix A).
•

Non-impulsive sounds:
o Only TTS data from behavioral studies were used, since studies using
AEP methodology typically result in larger thresholds shifts (e.g., up
to 10 dB difference, Finneran et al. 2007a) and are considered to be
non-representative (as illustrated in Appendix A, Figure A9)
o TTS onset derived on a per individual basis by combining available
data to create single TTS growth curve (e.g., dB TTS/dB noise) by
frequency as a function of SELcum.
o TTS onset was defined as the SEL cum value from the growth curve
interpolated at a value of TTS = 6 dB. Only datasets where data were
available with a threshold shift (TS) above and below 6 dB were used
to define TTS onset (i.e., extrapolation was not performed on
datasets not meeting this criterion).
o Interpolation was used to estimate SEL cum necessary to induce 6 dB
of TTS by hearing group (Appendix A, Figures A10-A13). Note:
Appendix A, Figures A18-A20 illustrate available marine mammal
TTS data in relation to the composite audiogram and exposure
function.

Table 6:

o Finally, weighted thresholds for TTS onset were determined by the
minimum value of the exposure function (Equation 2), which is
mathematically equivalent to K + C (Table 6).

TTS onset auditory acoustic thresholds for non-impulsive sounds.

Hearing Group
Low-frequency (LF) cetaceans
Mid-frequency (MF) cetaceans
High-frequency (HF) cetaceans
Phocid pinnipeds (underwater)
Otariid pinnipeds (underwater)

(dB)

Weighted TTS
onset acoustic
threshold

179
177
152
180
198

0.13
1.20
1.36
0.75
0.64

179 dB
178 dB
153 dB
181 dB
199 dB

(SEL cum)

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•

Impulsive sounds:
o Available TTS data for impulsive sources were weighted based on
weighting functions for the appropriate hearing group (MF and HF
cetaceans only from two studies: Finneran et al. 2002; Lucke et al.
2009).
o For hearing groups, where impulsive TTS onset data did not exist
(LF cetaceans and PW and OW pinnipeds), Finneran (2015) derived
impulsive TTS onset acoustic thresholds using the relationship
between non-impulsive TTS onset thresholds and impulsive TTS
onset thresholds for MF and HF cetaceans (i.e., similar to what was
presented in Southall et al. 2007). Using the mean/median of these
data resulted in an 11 dB relationship, which was used as a surrogate
for the other hearing groups (i.e., non-impulsive TTS threshold was
11 dB higher than impulsive TTS threshold).
o A similar approach was investigated for the PK threshold, resulting in
a 45 dB relationship, which was considered unrealistic (approaching
cavitation level of water; Southall et al. 2007). Upon further
consideration, the auditory system’s dynamic range was determined a
more appropriate methodology for estimating PK sound pressure
acoustic thresholds. 37
The dynamic range methodology assumes that the PK TTS onset
acoustic threshold for MF and HF cetaceans defines the upper end of
those hearing groups’ dynamic range (i.e., PK threshold: 224 dB for
MF cetaceans and PK threshold: 196 dB for HF cetaceans), with the
threshold of audibility derived from the frequency of best hearing (ƒ0)
from the composite audiogram (i.e., 54 dB for MF cetaceans and 48
dB for HF cetaceans) defining the lower end of the groups’ dynamic
range.
This results in a dynamic range of 170 dB for MF cetaceans and 148
dB for HF cetaceans. The median/mean dynamic range from these
two hearing groups (i.e., 159 dB) is used as the surrogate dynamic
range for LF cetaceans (best hearing at ƒ0= 54 dB; Resulting in a PK
TTS threshold of 213 dB); PW pinnipeds (best hearing at ƒ0=53 dB;
Resulting in a PK TTS threshold of 212 dB); and OW pinnipeds
(best hearing at ƒ0 =67 dB; Resulting in a PK TTS threshold of 226
dB).

Dynamic range is used in human noise standards to define the PK acoustic threshold for impulsive sounds
(e.g., 140 dB from OSHA 29 CFR 1910.95). For the purposes of this Technical Guidance, the intent is to relate
the threshold of audibility and TTS onset level, not the threshold of pain, as dynamic range is typically defined
(Yost 2007).
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5. Extrapolation for PTS onset threshold (in both PK and SEL metrics) based on data
from humans and terrestrial mammals, with the assumption that the mechanisms
associated with noise-induced TS in marine mammals is similar, if not identical, to
that recorded in terrestrial mammals.
•

Non-impulsive sounds:
o PTS onset acoustic thresholds were estimated using TTS growth rates
based on those marine mammal studies where 20 dB or more of a TS
was induced. This was done to estimate more accurately PTS onset,
since using growth rates based on smaller TSs are often shallower
than compared to those inducing greater TSs (See Appendix A,
Figures A10-A13).
o PTS onset was derived using the same methodology as TTS onset,
with PTS onset defined as the SELcum value from the fitted curve at a
TTS of 40 dB.
o Offset between TTS and PTS onset acoustic thresholds were
examined and ranged from 13 to 37 dB (mean/median: 25/25 dB for
cetacean data). Thus, based on these data, a conservative 20 dB offset
was chosen to estimate PTS onset thresholds from TTS onset
thresholds for non-impulsive sources (i.e., 20 dB was added to K to
determine PTS onset, assuming the shape of the PTS exposure
function is identical to the TTS exposure function for that hearing
group).

•

Impulsive sounds: Based on limited available marine mammal impulsive data,
the relationships previously derived in Southall et al. (2007), which relied
upon terrestrial mammal growth rates (Henderson and Hamernik 1982;
Henderson and Hamernik 1986; Price and Wansack 1989; Levine et al. 1998;
Henderson et al. 2008), was used to predict PTS onset:
o Resulting in an approximate 15 dB difference between TTS and PTS
onset acoustic thresholds in the SELcum metric.
o Southall et al. (2007) recommended a 6 dB of TTS/dB of noise
growth rate for PK acoustic thresholds. This recommendation was
based on several factors, including ensuring that the PK acoustic
threshold did not unrealistically exceed the cavitation threshold of
water. Resulting in an approximate 6 dB difference between TTS and
PTS onset thresholds in the PK metric.

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III.

UPDATING OF ACOUSTIC TECHNICAL GUIDANCE AND ACOUSTIC
THRESHOLDS

Research on the effects of anthropogenic sound on marine mammals has increased
dramatically in the last decade and will likely continue to increase in the future. As such, the
Technical Guidance will be reviewed periodically and updated as appropriate to reflect the
compilation, interpretation, and synthesis of the scientific literature.
NMFS’ initial approach for updating current acoustic thresholds for protected marine
species consisted of providing acoustic thresholds for underwater PTS onset for marine
mammals via this document. As more data become available, acoustic thresholds may be
established for additional protected marine species, such as sea turtles and marine fishes. As
with this document, public review and outside peer review will be integral to the process.
3.1

PROCEDURE AND TIMELINE FOR UPDATING THE TECHNICAL GUIDANCE

NMFS will continue to monitor and evaluate new data as they become available and
periodically convene staff from our various offices, regions, and science centers to update
the Technical Guidance as appropriate (anticipating updates to occur on a three to five year
cycle). In addition to evaluating new, relevant scientific studies, NMFS will also periodically
re-examine basic concepts and definitions (e.g., hearing groups, PTS, TTS, weighting
functions), appropriate metrics, temporal and spatial considerations, and other relevant
topics. Updates will be posted at http://www.nmfs.noaa.gov/pr/acoustics/guidelines.htm
Since the methodology for deriving composite audiograms and associated marine mammal
auditory weighting functions, as well as TTS thresholds is data driven, any new information
that becomes available has the potential to cause some amount of change for that specific
hearing group but also other hearing groups, if they rely on surrogate data. It may not be
feasible to make changes every time a new data point becomes available. Instead, NMFS will
periodically examine new data to date and consider the impacts of those studies on the
Technical Guidance to determine what revisions/updates may be appropriate. At the same
time, there may be special circumstances that merit evaluation of data on a more accelerated
timeline (e.g., LF cetacean data that could result in significant changes to the current
Technical Guidance).

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APPENDIX A:

FINNERAN TECHNICAL REPORT

The entire Finneran Technical Report (Finneran 2016), regarding methodology for deriving
auditory weighting functions and acoustic thresholds for marine mammal species under
NMFS’ jurisdiction, is included for reference in Appendix A. Its contents have not been
modified by NMFS, other than adding “A” before figures and tables to denote Appendix A
and be consistent with the other appendices in the Technical Guidance.
Note: Literature cited in this section are included at the end of this Appendix (i.e., not all
references found in this Appendix are included in the Literature Cited for the Technical
Guidance). Additionally, terminology, symbols, and abbreviations used in this appendix may
not match those used elsewhere in the Technical Guidance.
Since the final Finneran Technical Report was received an additional TTS study became
available (Kastelein et al. 2016). Information regarding this study is added as a footnote by
NMFS.

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TECHNICAL REPORT XXXX
May 2016

Auditory weighting functions and
TTS/PTS exposure functions for
marine mammals exposed
to underwater noise

J. J. Finneran
SSC Pacific

Approved for public release;
distribution is unlimited.

SSC Pacific

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EXECUTIVE SUMMARY

The US Navy’s Tactical Training Theater Assessment and Planning (TAP) Program
addresses environmental challenges that affect Navy training ranges and operating areas.
As part of the TAP process, acoustic effects analyses are conducted to estimate the
potential effects of Navy activities that introduce high-levels of sound or explosive
energy into the marine environment. Acoustic effects analyses begin with mathematical
modeling to predict the sound transmission patterns from Navy sources. These data are
then coupled with marine species distribution and abundance data to determine the sound
levels likely to be received by various marine species. Finally, criteria and thresholds are
applied to estimate the specific effects that animals exposed to Navy-generated sound
may experience.
This document describes the rationale and steps used to define proposed numeric
thresholds for predicting auditory effects on marine mammals exposed to active sonars,
other (non-impulsive) active acoustic sources, explosives, pile driving, and air guns for
Phase 3 of the TAP Program. Since the derivation of TAP Phase 2 acoustic criteria and
thresholds, important new data have been obtained related to the effects of noise on
marine mammal hearing. Therefore, for Phase 3, new criteria and thresholds for the onset
of temporary and permanent hearing loss have been developed, following a consistent
approach for all species of interest and utilizing all relevant, available data. The effects of
noise frequency on hearing loss are incorporated by using auditory weighting functions to
emphasize noise at frequencies where a species is more sensitive to noise and deemphasize noise at frequencies where susceptibility is low.
Marine mammals were divided into six groups for analysis: low-frequency cetaceans
(group LF: mysticetes), mid-frequency cetaceans (group MF: delphinids, beaked whales,
sperm whales), high-frequency cetaceans (group HF: porpoises, river dolphins), sirenians
(group SI: manatees), phocids in water (group PW: true seals), and otariids and other
non-phocid marine carnivores in water (group OW: sea lions, walruses, otters, polar
bears).
For each group, a frequency-dependent weighting function and numeric thresholds for the
onset of temporary threshold shift (TTS) and permanent threshold shift (PTS) were
derived from available data describing hearing abilities of and effects of noise on marine
mammals. The resulting weighting function amplitudes are illustrated in Figure AE-1;
Table AE-1 summarizes the parameters necessary to calculate the weighting function
amplitudes. For Navy Phase 3 analyses, the onset of TTS is defined as a TTS of 6 dB
measured approximately 4 min after exposure. PTS is assumed to occur from exposures
resulting in 40 dB or more of TTS measured approximately 4 min after exposure.
Exposures just sufficient to cause TTS or PTS are denoted as “TTS onset” or “PTS
onset” exposures.

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Figure AE-1. Navy Phase 3 weighting functions for all species groups. Parameters
required to generate the functions are provided in Table AE-1.
Table AE-1.

Summary of weighting function parameters and TTS/PTS thresholds. SEL
thresholds are in dB re 1 μPa2s and peak SPL thresholds are in dB re 1 μPa.
Non-impulsive

Impulse

TTS
PTS
threshold threshold

TTS
threshold

PTS
threshold

Group

f1
(kHz)

f2
(kHz)

C
(dB)

0.20

0.13

179

199

168

213

183

219

1.6

8.8

110

1.20

178

198

170

224

185

230

1.8

140

1.36

153

173

140

196

155

202

1.8

4.3

2.62

186

206

175

220

190

226

0.94

0.64

199

219

188

226

203

232

1.9

0.75

181

201

170

212

185

218

SEL
SEL
SEL
peak SPL
SEL
peak SPL
(weighted) (weighted) (weighted) (unweighted) (weighted) (unweighted)

To compare the Phase 3 weighting functions and TTS/PTS thresholds to those used in
TAP Phase 2 analyses, both the weighting function shape and the weighted threshold
values must be taken into account; the weighted thresholds by themselves only indicate
the TTS/PTS threshold at the most susceptible frequency (based on the relevant
weighting function). In contrast, the TTS/PTS exposure functions incorporate both the
shape of the weighting function and the weighted threshold value, they provide the best
means of comparing the frequency-dependent TTS/PTS thresholds for Phase 2 and 3.
Figures AE-2 and AE-3 compare the TTS/PTS exposure functions for non-impulsive
sounds (e.g., sonars) and impulsive sounds (e.g., explosions), respectively, used in TAP
Phase 2 and Phase 3.

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Figure AE-2. TTS and PTS exposure functions for sonars and other (non-impulsive)
active acoustic sources. Heavy solid lines — Navy Phase 3 TTS
exposure functions (Table AE-1). Thin solid lines — Navy Phase 3
PTS exposure functions (Table AE-1). Dashed lines — Navy Phase 2
TTS exposure functions. Short dashed lines — Navy Phase 2 PTS
exposure functions.

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Figure AE-3. TTS and PTS exposure functions for explosives, impact pile driving,
air guns, and other impulsive sources. Heavy solid lines — Navy
Phase 3 TTS exposure functions (Table AE-1). Thin solid lines —
Navy Phase 3 PTS exposure functions (Table AE-1). Dashed lines —
Navy Phase 2 TTS exposure functions. Short dashed lines — Navy
Phase 2 PTS exposure functions.
The most significant differences between the Phase 2 and Phase 3 functions include: (1)
Thresholds at low frequencies are generally higher for Phase 3 compared to Phase 2. This
is because the Phase 2 weighting functions utilized the “M-weighting” functions at lower
frequencies, where no TTS existed at that time. Since derivation of the Phase 2 weighting
functions, additional data have been collected to support the use of new functions more
similar to human auditory weighting functions. (2) Impulsive TTS/PTS thresholds near
the region of best hearing sensitivity are lower for Phase 3 compared to Phase 2.

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INTRODUCTION

1.1

OVERVIEW

IMPULSE VS. NON-IMPULSIVE NOISE

When analyzing the auditory effects of noise exposure, it is often helpful to broadly
categorize noise as either impulse noise — noise with high peak sound pressure, short
duration, fast rise-time, and broad frequency content — or non-impulsive (i.e., steadystate) noise. When considering auditory effects, sonars, other coherent active sources, and
vibratory pile driving are considered to be non-impulsive sources, while explosives,
impact pile driving, and air guns are treated as impulsive sources. Note that the terms
non-impulsive or steady-state do not necessarily imply long duration signals, only that
the acoustic signal has sufficient duration to overcome starting transients and reach a
steady-state condition. For harmonic signals, sounds with duration greater than
approximately 5 to 10 cycles are generally considered to be steady-state.
1.3

NOISE-INDUCED THRESHOLD SHIFTS

Exposure to sound with sufficient duration and sound pressure level (SPL) may result in
an elevated hearing threshold (i.e., a loss of hearing sensitivity), called a noise-induced
threshold shift (NITS). If the hearing threshold eventually returns to normal, the NITS is
called a temporary threshold shift (TTS); otherwise, if thresholds remain elevated after
some extended period of time, the remaining NITS is called a permanent threshold shift
(PTS). TTS and PTS data have been used to guide the development of safe exposure
guidelines for people working in noisy environments. Similarly, TTS and PTS criteria
and thresholds form the cornerstone of Navy analyses to predict auditory effects in
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marine mammals incidentally exposed to intense underwater sound during naval
activities.
1.4

AUDITORY WEIGHTING FUNCTIONS

Animals are not equally sensitive to noise at all frequencies. To capture the frequencydependent nature of the effects of noise, auditory weighting functions are used. Auditory
weighting functions are mathematical functions used to emphasize frequencies where
animals are more susceptible to noise exposure and de-emphasize frequencies where
animals are less susceptible. The functions may be thought of as frequency-dependent
filters that are applied to a noise exposure before a single, weighted SPL or sound
exposure level (SEL) is calculated. The filter shapes are normally “band-pass” in nature;
i.e., the function amplitude resembles an inverted “U” when plotted versus frequency.
The weighting function amplitude is approximately flat within a limited range of
frequencies, called the “pass-band,” and declines at frequencies below and above the
pass-band.
Auditory weighting functions for humans were based on equal loudness contours —
curves that show the combinations of SPL and frequency that result in a sensation of
equal loudness in a human listener. Equal loudness contours are in turn created from data
collected during loudness comparison tasks. Analogous tasks are difficult to perform with
non-verbal animals; as a result, equal loudness contours are available for only a single
marine mammal (a dolphin) across a limited range of frequencies (2.5 to 113 kHz)
(Finneran and Schlundt, 2011). In lieu of performing loudness comparison tests, reaction
times to tones can be measured, under the assumption that reaction time is correlated with
subjective loudness (Stebbins, 1966; Pfingst et al., 1975). From the reaction time vs. SPL
data, curves of equal response latency can be created and used as proxies for equal
loudness contours.
Just as human damage risk criteria use auditory weighting functions to capture the
frequency-dependent aspects of noise, US Navy acoustic impact analyses use weighting
functions to capture the frequency-dependency of TTS and PTS in marine mammals.
1.5

TAP PHASE 3 WEIGHTING FUNCTIONS AND TTS/PTS THRESHOLDS

Navy weighting functions for TAP Phase 2 (Finneran and Jenkins, 2012) were based on
the “M-weighting” curves defined by Southall et al. (2007), with additional highfrequency emphasis for cetaceans based on equal loudness contours for a bottlenose
dolphin (Finneran and Schlundt, 2011). Phase 2 TTS/PTS thresholds also relied heavily
on the recommendations of Southall et al. (2007), with modifications based on
preliminary data for the effects of exposure frequency on dolphin TTS (Finneran, 2010;
Finneran and Schlundt, 2010) and limited TTS data for harbor porpoises (Lucke et al.,
2009; Kastelein et al., 2011).

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Since the derivation of TAP Phase 2 acoustic criteria and thresholds, new data have been
obtained regarding marine mammal hearing (e.g., Dow Piniak et al., 2012; Martin et al.,
2012; Ghoul and Reichmuth, 2014; Sills et al., 2014; Sills et al., 2015), marine mammal
equal latency contours (e.g., Reichmuth, 2013; Wensveen et al., 2014; Mulsow et al.,
2015), and the effects of noise on marine mammal hearing (e.g., Kastelein et al., 2012b;
Kastelein et al., 2012a; Finneran and Schlundt, 2013; Kastelein et al., 2013a; Kastelein et
al., 2013b; Popov et al., 2013; Kastelein et al., 2014b; Kastelein et al., 2014a; Popov et
al., 2014; Finneran et al., 2015; Kastelein et al., 2015c; Kastelein et al., 2015b; Popov et
al., 2015). As a result, new weighting functions and TTS/PTS thresholds have been
developed for Phase 3. The new criteria and thresholds are based on all relevant data and
feature a consistent approach for all species of interest.
Marine mammals were divided into six groups for analysis. For each group, a frequencydependent weighting function and numeric thresholds for the onset of TTS and PTS were
derived from available data describing hearing abilities and effects of noise on marine
mammals. Measured or predicted auditory threshold data, as well as measured equal
latency contours, were used to influence the weighting function shape for each group. For
species groups for which TTS data are available, the weighting function parameters were
adjusted to provide the best fit to the experimental data. The same methods were then
applied to other groups for which TTS data did not exist.

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II.

WEIGHTING FUNCTIONS AND EXPOSURE FUNCTIONS

The shapes of the Phase 3 auditory weighting functions are based on a generic band-pass
filter described by

(A1)

where W( f ) is the weighting function amplitude (in dB) at the frequency f (in kHz). The
shape of the filter is defined by the parameters C, f1, f2, a, and b (Figs. A1 and A2, left
panels):
C weighting function gain (dB). The value of C defines the vertical position of
the curve. Changing the value of C shifts the function up/down. The value of
C is often chosen to set the maximum amplitude of W to 0 dB (i.e., the value
of C does not necessarily equal the peak amplitude of the curve).
f1 low-frequency cutoff (kHz). The value of f1 defines the lower limit of the filter
pass-band; i.e., the lower frequency at which the weighting function amplitude
begins to decline or “roll-off” from the flat, central portion of the curve. The
specific amplitude at f1 depends on the value of a. Decreasing f1 will enlarge
the pass-band of the function (the flat, central portion of the curve).
f2 high-frequency cutoff (kHz). The value of f2 defines the upper limit of the
filter pass-band; i.e., the upper frequency at which the weighting function
amplitude begins to roll-off from the flat, central portion of the curve. The
amplitude at f2 depends on the value of b. Increasing f2 will enlarge the passband of the function.
a

low-frequency exponent (dimensionless). The value of a defines the rate at
which the weighting function amplitude declines with frequency at the lower
frequencies. As frequency decreases, the change in weighting function
amplitude becomes linear with the logarithm of frequency, with a slope of 20a
dB/decade. Larger values of a result in lower amplitudes at f1 and steeper
rolloffs at frequencies below f1.

high-frequency exponent (dimensionless). The value of b defines the rate at
which the weighting function amplitude declines with frequency at the upper
frequencies. As frequency increases, the change in weighting function
amplitude becomes linear with the logarithm of frequency, with a slope of 20b dB/decade. Larger values of b result in lower amplitudes at f2 and steeper
rolloffs at frequencies above f2.

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If a = 2 and b = 2, Eq. (A1) is equivalent to the functions used to define Navy Phase 2
Type I and EQL weighting functions, M-weighting functions, and the human Cweighting function (American National Standards Institute (ANSI), 2001; Southall et al.,
2007; Finneran and Jenkins, 2012). The change from fixed to variable exponents for
Phase 3 was done to allow the low- and high-frequency rolloffs to match available
experimental data. During implementation, the weighting function defined by Eq. (A1) is
used in conjunction with a weighted threshold for TTS or PTS expressed in units of SEL.

Figure A1.

Examples of (left) weighting function amplitude described by Eq. (A1)
and (right) exposure function described by Eq. (A2). The parameters f1
and f2 specify the extent of the filter pass-band, while the exponents a
and b control the rate of amplitude change below f1 and above f2,
respectively. As the frequency decreases below f1 or above f2, the
amplitude approaches linear-log behavior with a slope magnitude of
20a or 20b dB/decade, respectively. The constants C and K determine
the vertical positions of the curves.

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Figure A2.

Influence of parameter values on the resulting shapes of the weighting
functions (left) and exposure functions (right). The arrows indicate the
direction of change when the designated parameter is increased.

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For developing and visualizing the effects of the various weighting functions, it is helpful
to invert Eq. (A1), yielding

(A2)

where E( f ) is the acoustic exposure as a function of frequency f, the parameters f1, f2, a,
and b are identical to those in Eq. (A1), and K is a constant. The function described by
Eq. (A2) has a “U-shape” similar to an audiogram or equal loudness/latency contour
(Figs. A1 and A2, right panels). If K is adjusted to set the minimum value of E( f ) to
match the weighted threshold for the onset of TTS or PTS, Eq. (A2) reveals the manner
in which the exposure necessary to cause TTS or PTS varies with frequency. Equation
(A2) therefore allows the frequency-weighted threshold values to be directly compared to
TTS data. The function defined by Eq. (A2) is referred to as an exposure function, since
the curve defines the acoustic exposure that equates to TTS or PTS as a function of
frequency. To illustrate the relationship between weighting and exposure functions, Fig.
A3 shows the Navy Phase 2 weighting function [Eq. (A1), left panel] and TTS exposure
function [Eq. (A2), right panel] for mid-frequency cetaceans exposed to sonars.

Figure A3.

(left panel) Navy Phase 2 weighting function for the mid-frequency cetacean
group. This function was used in conjunction with a weighted TTS threshold
of 178 dB re 1 μPa2s. For narrowband signals, the effective, weighted TTS
threshold at a particular frequency is calculated by adding the weighting
function amplitude at that frequency to the weighted TTS threshold (178 dB
re 1 μPa2s). To visualize the frequency-dependent nature of the TTS
threshold, the weighting function is inverted and the minimum value set
equal to the weighted TTS threshold. This is illustrated in the right panel,
which shows the SEL required for TTS onset as a function of frequency. The
advantage of this representation is that it may be directly compared to TTS
onset data at different exposure frequencies.

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The relationships between Eqs. (A1) and (A2) may be highlighted by defining the
function X( f ) as

(A3)

The peak value of X( f ) depends on the specific values of f1, f2, a, and b and will not
necessarily equal zero. Substituting Eq. (A3) into Eqs. (A1) and (A2) results in
(A4)
and
,

(A5)

respectively. The maximum of the weighting function and the minimum of the exposure
function occur at the same frequency, denoted fp. The constant C is defined so the
weighting function maximum value is 0 dB; i.e., W( fp ) = 0, so
.

(A6)

The constant K is defined so that the minimum of the exposure function [i.e., the value of
E( f ) when f = fp ] equals the weighted TTS or PTS threshold, Twgt, so
.

(A7)

Adding Eqs. (A6) and (A7) results in
.

(A8)

The constants C, K, and the weighted threshold are therefore not independent and any one
of these parameters can be calculated if the other two are known.

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III.

METHODOLOGY TO DERIVE FUNCTION PARAMETERS

Weighting and exposure functions are defined by selecting appropriate values for the
parameters C, K, f1, f2, a, and b in Eqs. (A1) and (A2). Ideally, these parameters would be
based on experimental data describing the manner in which the onset of TTS or PTS
varied as a function of exposure frequency. In other words, a weighting function for TTS
should ideally be based on TTS data obtained using a range of exposure frequencies,
species, and individual subjects within each species group. However, at present, there are
only limited data for the frequency-dependency of TTS in marine mammals. Therefore,
weighting and exposure function derivations relied upon auditory threshold
measurements (audiograms), equal latency contours, anatomical data, and TTS data when
available.
Although the weighting function shapes are heavily influenced by the shape of the
auditory sensitivity curve, the two are not identical. Essentially, the auditory sensitivity
curves are adjusted to match the existing TTS data in the frequency region near best
sensitivity (step 4 below). This results in “compression” of the auditory sensitivity curve
in the region near best sensitivity to allow the weighting function shape to match the TTS
data, which show less change with frequency compared to hearing sensitivity curves in
the frequency region near best sensitivity.

Weighting and exposure function derivation consisted of the following steps:
1. Marine mammals were divided into six groups based on auditory,
ecological, and phylogenetic relationships among species.
2. For each species group, a representative, composite audiogram (a graph
of hearing threshold vs. frequency) was estimated.
3. The exponent a was defined using the smaller of the low-frequency
slope from the composite audiogram or the low-frequency slope of equal
latency contours. The exponent b was set equal to two.
4. The frequencies f1 and f2 were defined as the frequencies at which the
composite threshold values are ∆T-dB above the lowest threshold value.
The value of ∆T was chosen to minimize the mean-squared error between
Eq. (2) and the non-impulsive TTS data for the mid- and high-frequency
cetacean groups.
5. For species groups for which TTS onset data exist, K was adjusted to
minimize the squared error between Eq. (A2) and the steady-state (nonimpulsive) TTS onset data. For other species, K was defined to provide the
best estimate for TTS onset at a representative frequency. The minimum
value of the TTS exposure function (which is not necessarily equal to K)
was then defined as the weighted TTS threshold.
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6. The constant C was defined to set the peak amplitude of the function
defined by Eq. (A1) to zero. This is mathematically equivalent to setting C
equal to the difference between the weighted threshold and K [see Eq.
(A8)].
7. The weighted threshold for PTS was derived for each group by adding a
constant value (20 dB) to the weighted TTS thresholds. The constant was
based on estimates of the difference in exposure levels between TTS onset
and PTS onset (i.e., 40 dB of TTS) obtained from the marine mammal
TTS growth curves.
8. For the mid- and high-frequency cetaceans, weighted TTS and PTS
thresholds for explosives and other impulsive sources were obtained from
the available impulse TTS data. For other groups, the weighted SEL
thresholds were estimated using the relationship between the steady-state
TTS weighted threshold and the impulse TTS weighted threshold for the
mid- and high-frequency cetaceans. Peak SPL thresholds were estimated
using the relationship between hearing thresholds and the impulse TTS
peak SPL thresholds for the mid- and high-frequency cetaceans.

The remainder of this document addresses these steps in detail.

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IV.

MARINE MAMMAL SPECIES GROUPS

Marine mammals were divided into six groups (Table A1), with the same weighting
function and TTS/PTS thresholds used for all species within a group. Species were
grouped by considering their known or suspected audible frequency range, auditory
sensitivity, ear anatomy, and acoustic ecology (i.e., how they use sound), as has been
done previously (e.g., Ketten, 2000; Southall et al., 2007; Finneran and Jenkins, 2012).
4.1

LOW-FREQUENCY (LF) CETACEANS

The LF cetacean group contains all of the mysticetes (baleen whales). Although there
have been no direct measurements of hearing sensitivity in any mysticete, an audible
frequency range of approximately 10 Hz to 30 kHz has been estimated from observed
vocalization frequencies, observed reactions to playback of sounds, and anatomical
analyses of the auditory system. A natural division may exist within the mysticetes, with
some species (e.g., blue, fin) having better low-frequency sensitivity and others (e.g.,
humpback, minke) having better sensitivity to higher frequencies; however, at present
there is insufficient knowledge to justify separating species into multiple groups.
Therefore, a single species group is used for all mysticetes.
4.2

MID-FREQUENCY (MF) CETACEANS

The MF cetacean group contains most delphinid species (e.g., bottlenose dolphin,
common dolphin, killer whale, pilot whale), beaked whales, and sperm whales (but not
pygmy and dwarf sperm whales of the genus Kogia, which are treated as high-frequency
species). Hearing sensitivity has been directly measured for a number of species within
this group using psychophysical (behavioral) or auditory evoked potential (AEP)
measurements.
4.3

HIGH-FREQUENCY (HF) CETACEANS

The HF cetacean group contains the porpoises, river dolphins, pygmy/dwarf sperm
whales, Cephalorhynchus species, and some Lagenorhynchus species. Hearing sensitivity
has been measured for several species within this group using behavioral or AEP
measurements. High-frequency cetaceans generally possess a higher upper-frequency
limit and better sensitivity at high frequencies compared to the mid-frequency cetacean
species.

4.4

SIRENIANS

The sirenian group contains manatees and dugongs. Behavioral and AEP threshold
measurements for manatees have revealed lower upper cutoff frequencies and
sensitivities compared to the mid-frequency cetaceans.
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4.5

PHOCIDS

This group contains all earless seals or “true seals,” including all Arctic and Antarctic ice
seals, harbor or common seals, gray seals and inland seals, elephant seals, and monk
seals. Underwater hearing thresholds exist for some Northern Hemisphere species in this
group.
4.6

OTARIIDS AND OTHER NON-PHOCID MARINE CARNIVORES

This group contains all eared seals (fur seals and sea lions), walruses, sea otters, and polar
bears. The division of marine carnivores by placing phocids in one group and all others
into a second group was made after considering auditory anatomy and measured
audiograms for the various species and noting the similarities between the non-phocid
audiograms (Fig. A4). Underwater hearing thresholds exist for some Northern
Hemisphere species in this group.

Figure A4.

Comparison of Otariid, Mustelid, and Odobenid psychophysical
hearing thresholds measured underwater. The thick, solid line is the
composite audiogram based on data for all species. The thick, dashed
line is the composite audiogram based on the otariids only.

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Table A1. Species group designations for Navy Phase 3 auditory weighting functions.
Code
LF

Name
Low-frequency
cetaceans

Members
Family Balaenidae (right and bowhead whales)
Family Balaenopteridae (rorquals)
Family Eschrichtiidae (gray whale)
Family Neobalaenidae (pygmy right whale)

Mid-frequency
cetaceans

Family Ziphiidae (beaked whales)
Family Physeteridae (Sperm whale)
Family Monodontidae (Irrawaddy dolphin, beluga, narwhal)
Subfamily Delphininae (white-beaked/white-sided/
Risso’s/bottlenose/spotted/spinner/striped/common dolphins)
Subfamily Orcininae (melon-headed whales, false/pygmy killer whale, killer whale,
pilot whales)
Subfamily Stenoninae (rough-toothed/humpback dolphins)
Genus Lissodelphis (right whale dolphins)
Lagenorhynchus albirostris (white-beaked dolphin)
Lagenorhynchus acutus (Atlantic white-sided dolphin)
Lagenorhynchus obliquidens (Pacific white-sided dolphin)
Lagenorhynchus obscurus (dusky dolphin)

High-frequency
cetaceans

Family Phocoenidae (porpoises)
Family Platanistidae (Indus/Ganges river dolphins)
Family Iniidae (Amazon river dolphins)
Family Pontoporiidae (Baiji/ La Plata river dolphins)
Family Kogiidae (Pygmy/dwarf sperm whales)
Genus Cephalorhynchus (Commersen’s, Chilean, Heaviside’s, Hector’s dolphins)
Lagenorhynchus australis (Peale’s or black-chinned dolphin)
Lagenorhynchus cruciger (hourglass dolphin)

Sirenians

Family Trichechidae (manatees)
Family Dugongidae (dugongs)

Otariids and other
non-phocid marine
carnivores (water)

Family Otariidae (eared seals and sea lions)
Family Odobenidae (walrus)
Enhydra lutris (sea otter)
Ursus maritimus (polar bear)

Phocids (water)

Family Phocidae (true seals)

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COMPOSITE AUDIOGRAMS

Composite audiograms for each species group were determined by first searching the
available literature for threshold data for the species of interest. For each group, all
available AEP and psychophysical (behavioral) threshold data were initially examined.
To derive the composite audiograms, the following rules were applied:
1. For species groups with three or more behavioral audiograms (all
groups except LF cetaceans), only behavioral (no AEP) data were used.
Mammalian AEP thresholds are typically elevated from behavioral
thresholds in a frequency-dependent manner, with increasing discrepancy
between AEP and behavioral thresholds at the lower frequencies where
there is a loss of phase synchrony in the neurological responses and a
concomitant increase in measured AEP thresholds. The frequencydependent relationship between the AEP and behavioral data is
problematic for defining the audiogram slope at low frequencies, since the
AEP data will systematically over-estimate thresholds and therefore overestimate the low-frequency slope of the audiogram. As a result of this rule,
behavioral data were used for all marine mammal groups.
For the low-frequency cetaceans, for which no behavioral or AEP
threshold data exist, hearing thresholds were estimated by synthesizing
information from anatomical measurements, mathematical models of
hearing, and animal vocalization frequencies (see Appendix A1).
2. Data from an individual animal were included only once at a particular
frequency. If data from the same individual were available from multiple
studies, data at overlapping frequencies were averaged.
3. Individuals with obvious high-frequency hearing loss for their species
or aberrant audiograms (e.g., obvious notches or thresholds known to be
elevated for that species due to masking or hearing loss) were excluded.
4. Linear interpolation was performed within the threshold data for each
individual to estimate a threshold value at each unique frequency present
in any of the data for that species group. This was necessary to calculate
descriptive statistics at each frequency without excluding data from any
individual subject.
5. Composite audiograms were determined using both the original
threshold values from each individual (in dB re 1 μPa) and normalized
thresholds obtained by subtracting the lowest threshold value for that
subject.
Table A2 lists the individual references for the data ultimately used to construct the
composite audiograms (for all species groups except the LF cetaceans). From these data,
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the median (50th percentile) threshold value was calculated at each frequency and fit by
the function
,

(A9)

where T( f ) is the threshold at frequency f, and T0, F1, F2, A, and B are fitting parameters.
The median value was used to reduce the influence of outliers. The particular form of Eq.
(A9) was chosen to provide linear-log rolloff with variable slope at low frequencies and a
steep rise at high frequencies. The form is similar to that used by Popov et al. (2007) to
describe dolphin audiograms; the primary difference between the two is the inclusion of
two frequency parameters in Eq. (A9), which allows a more shallow slope in the region
of best sensitivity. Equation (A9) was fit to the median threshold data using nonlinear
regression (National Instruments LabVIEW 2015). The resulting fitting parameters and
goodness of fit values (R2) are provided in Tables 3 and 4 for the original and normalized
data, respectively. Equation (A9) was also used to describe the shape of the estimated
audiogram for the LF cetaceans, with the parameter values chosen to provide reasonable
thresholds based on the limited available data regarding mysticete hearing (see Appendix
A1 for details).
Figures A5 and A6 show the original and normalized threshold data, respectively, as well
as the composite audiograms based on the fitted curve. The composite audiograms for
each species group are compared in Fig. A6. To allow comparison with other audiograms
based on the original threshold data, the lowest threshold for the low-frequency cetaceans
was estimated to be 54 dB re 1 μPa, based on the median of the thresholds for the other
in-water species groups (MF, HF, SI, OW, PW). From the composite audiograms, the
frequency of lowest threshold, f0, and the slope at the lower frequencies, s0, were
calculated (Table A5). For the species with composite audiograms based on experimental
data (i.e., all except LF cetaceans), audiogram slopes were calculated across a frequency
range of one decade beginning with the lowest frequency present for each group. The
low-frequency slope for LF cetaceans was not based on a curve-fit but explicitly defined
during audiogram derivation (see Appendix A1).

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Table A2.
Group
MF

SI
OW

References, species, and individual subjects used to derive the composite
audiograms.
Reference

Species

Subjects

(Finneran et al., 2005b)

Delphinapterus leucas

Beethoven

(Szymanski et al., 1999)

Orcinus orca

Yaka, Vigga

(Nachtigall et al., 1995)

Grampus griseus

N/a

(Kastelein et al., 2003)

Stenella coeruleoalba

Meyen

(Lemonds, 1999)

Tursiops truncatus

Itsi Bitsy

(Brill et al., 2001)

Tursiops truncatus

CAS

(Ljungblad et al., 1982)

Tursiops truncatus

12-y male

(Johnson, 1967)

Tursiops truncatus

Salty

(Sauerland and Dehnhardt, 1998)

Sotalia fluviatilis

Paco

(Johnson et al., 1989)

Delphinapterus leucas

2-y female

(White et al., 1978)

Delphinapterus leucas

Edwina, Kojak

(Awbrey et al., 1988)

Delphinapterus leucas

Kojak, female, male

(Thomas et al., 1988)

Pseudorca crassidens

I'a nui hahai

(Finneran et al., 2010b)

Tursiops truncatus

TYH

(Schlundt et al., 2008)

Tursiops truncatus

WEN

(Ridgway et al., 2001)

Delphinapterus leucas

MUK, NOC

(Tremel et al., 1998)

Lagenorhynchus obliquidens

female

(Jacobs and Hall, 1972)

Inia geoffrensis

male

(Kastelein et al., 2002a)**

Phocoena phocoena

PpSH047

(Kastelein et al., 2010)

Phocoena phocoena

Jerry

(Kastelein et al., 2015a)

Phocoena phocoena

ID No. 04

(Gaspard et al., 2012)

Trichechus manatus

Buffet, Hugh

(Gerstein et al., 1999)

Trichechus manatus

Stormy, Dundee

(Moore and Schusterman, 1987)

Callorhinus ursinus

Lori, Tobe

(Babushina et al., 1991)

Callorhinus ursinus

N/a

(Kastelein et al., 2002b)

Odobenus rosmarus

Igor

(Mulsow et al., 2012)

Zalophus californianus

JFN

(Reichmuth and Southall, 2012)

Zalophus californianus

Rio, Sam

(Reichmuth et al., 2013)

Zalophus californianus

Ronan

(Kastelein et al., 2005)

Eumetopias jubatus

EjZH021, EjZH022

(Ghoul and Reichmuth, 2014)

Enhydra lutris nereis

Charlie

(Kastak and Schusterman, 1999)

Mirounga angustirostris

Burnyce

(Terhune, 1988)

Phoca vitulina

N/a

(Reichmuth et al., 2013)

Phoca vitulina

Sprouts

(Kastelein et al., 2009)

Phoca vitulina

01, 02

(Sills et al., 2014)

Phoca largha

Amak, Tunu

(Sills et al., 2015)

Pusa hispida

Nayak

** Corrected thresholds from Kastelein et al. (2010) were used.

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Table A3.

Composite audiogram parameters values for use in Eq. (A9). For all groups
except LF cetaceans, values represent the best-fit parameters from fitting
Eq. (A9) to experimental threshold data. For the low-frequency cetaceans,
parameter values for Eq. (A9) were estimated as described in Appendix A1.

Group

T0 (dB)

F1 (kHz)

F2 (kHz)

53.19

0.412

9.4

3.2

–

46.2

25.9

47.8

35.5

3.56

0.977

46.4

7.57

126

42.3

17.1

0.968

-40.4

3990

3.8

37.3

1.7

0.982

63.1

3.06

11.8

30.1

3.23

0.939

43.7

10.2

3.97

20.1

1.41

0.907

Table A4.

Normalized composite audiogram parameters values for use in Eq. (A9).
For all groups except LF cetaceans, values represent the best-fit
parameters after fitting Eq. (A9) to normalized threshold data. For the lowfrequency cetaceans, parameter values for Eq. (A9) were estimated as
described in Appendix A1.
Group

T0 (dB)

F1 (kHz)

F2 (kHz)

-0.81

0.412

9.4

3.2

–

3.61

12.7

64.4

31.8

4.5

0.960

2.48

9.68

126

40.1

0.969

-109

5590

2.62

38.1

1.53

0.963

2.36

0.366

12.8

73.5

3.4

0.958

-39.6

368

2.21

20.5

1.23

0.907

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Figure A5.

Thresholds and composite audiograms for the six species groups.
Thin lines represent the threshold data from individual animals. Thick
lines represent either the predicted threshold curve (LF cetaceans) or
the best fit of Eq. (A9) to experimental data (all other groups).
Derivation of the LF cetacean curve is described in Appendix A1. The
minimum threshold for the LF cetaceans was estimated to be 54 dB re
1 μPa, based on the median of the lowest thresholds for the other
groups.

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Figure A6.

Normalized thresholds and composite audiograms for the six species
groups. Thin lines represent the threshold data from individual
animals. Thick lines represent either the predicted threshold curve (LF
cetaceans) or the best fit of Eq. (A9) to experimental data (all other
groups). Thresholds were normalized by subtracting the lowest value
for each individual data set (i.e., within-subject). Composite
audiograms were then derived from the individually normalized
thresholds (i.e., the composite audiograms were not normalized and
may have a minimum value ≠ 0). Derivation of the LF cetacean curve
is described in Appendix A1.

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Figure A7.

Composite audiograms for the various species groups, derived with the
original data (upper) and normalized data (lower). The gray lines in
the upper left panel represent ambient noise spectral density levels
(referenced to the left ordinate, in dB re 1 μPa2/Hz) corresponding to
the limits of prevailing noise and various sea-state conditions, from 0.5
to 6 (National Research Council (NRC), 2003).

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Table A5.

Frequency of best hearing (f0) and the magnitude of the low-frequency
slope (s0) derived from composite audiograms and equal latency contours.
For the species with composite audiograms based on experimental data
(i.e., all except LF cetaceans), audiogram slopes were calculated across a
frequency range of one decade beginning with the lowest frequency
present for each group. The low-frequency slope for LF cetaceans was not
based on a curve-fit but explicitly defined during audiogram derivation (see
Appendix A1). Equal latency slopes were calculated from the available
equal latency contours (Fig. A8).

Group

Original data
composite audiogram

Normalized data
composite audiogram

Equal latency
curves

(kHz)

(dB/decade)

(kHz)

(dB/decade)

5.6

—

105

—

8.6

—

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VI.

EQUAL LOUDNESS DATA

Finneran and Schlundt (2011) conducted a subjective loudness comparison task with a
bottlenose dolphin and used the resulting data to derive equal loudness contours and
auditory weighting functions. The weighting functions agreed closely with dolphin TTS
data over the frequency range 3 to 56 kHz (Finneran and Schlundt, 2013); however, the
loudness data only exist for frequencies between 2.5 kHz and 113 kHz and cannot be
used to estimate the shapes of loudness contours and weighting functions at lower
frequencies.

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VII.

EQUAL LATENCY DATA

Reaction times to acoustic tones have been measured in several marine mammal species
and used to derive equal latency contours and weighting functions (Fig. A8, Wensveen et
al., 2014; Mulsow et al., 2015). Unlike the dolphin equal loudness data, the latency data
extend to frequencies below 1 kHz and may be used to estimate the slopes of auditory
weighting functions at lower frequencies.

Figure A8.

Underwater marine mammal equal latency contours are available for
Phocoena phocoena (Wensveen et al., 2014) and Tursiops truncatus
(Mulsow et al., 2015). The slopes for the contours at low frequencies
were obtained from the literature (Phocoena phocoena ) or calculated
from the best linear-log fits to the lower frequency data. The slope of
the contour passing through an SPL approximately 40 dB above the
threshold at f0 was selected as the most appropriate based on: (1)
human A-weighting, (2) observations that the relationship between
equal latency and loudness can break down at higher sensation levels,
and (3) for many data sets the slopes increase at higher SPLs rather
than decrease as expected. The resulting slopes are listed in Table A5.

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VIII.

TTS DATA

8.1

NON-IMPULSIVE (STEADY-STATE) EXPOSURES – TTS

For weighting function derivation, the most critical data required are TTS onset exposure
levels as a function of exposure frequency. These values can be estimated from published
literature by examining TTS as a function of SEL for various frequencies.
To estimate TTS onset values, only TTS data from psychophysical (behavioral) hearing
tests were used. Studies have shown differences between the amount of TTS from
behavioral threshold measurements and that determined using AEP thresholds (Fig. A9).
TTS determined from AEP thresholds is typically larger than that determined behaviorally,
and AEP-measured TTS of up to ~ 10 dB has been observed with no corresponding change
in behavioral thresholds (e.g., Finneran et al., 2007). Although these data suggest that AEP
amplitudes and thresholds provide more sensitive indicators (than behavioral thresholds) of
the auditory effects of noise, Navy acoustic impact analyses use TTS both as an indicator of
the disruption of behavioral patterns that are mediated by the sense of hearing and to predict
when the onset of PTS is likely to occur. Navy analyses assume that exposures resulting in a
NITS > 40 dB measured a few minutes after exposure will result in some amount of residual
PTS. This is based on relationships observed in early human TTS studies utilizing
psychophysical threshold measurements. To date, there have been no reports of PTS in a
marine mammal whose initial behavioral threshold shift was 40 dB or less; however,
behavioral shifts of 35 to 40 dB have required multiple days to recover, suggesting that these
exposures are near those capable of resulting in PTS. In contrast, studies utilizing AEP
measurements in marine mammals have reported TTSs of 45 dB that recovered in 40 min
and 60 dB that recovered in < 24 h, suggesting that these exposures were not near those
capable of resulting in PTS (Popov et al., 2013).

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Figure A9.

TTS measured using behavioral and AEP methods do not necessarily
agree, with marine mammal studies reporting larger TTS obtained
using AEP methods. For the data above, thresholds were determined
using both techniques before and after the same noise exposure.
Hearing thresholds were measured at 30 kHz. Behavioral thresholds
utilized FM tones with 10% bandwidth. AEP thresholds were based on
AM tones with a modulation frequency of 1.05 kHz. Noise exposures
consisted of (a) a single, 20-kHz tone with duration of 64 s and SPL of
185 dB re 1 μPa (SEL = 203 dB re 1 μPa2s) and (b) three 16-s tones at 20
kHz, with mean SPL = 193 dB re 1 μPa (cumulative SEL = 210 dB re 1
μPa2s). Data from Finneran et al. (2007).

To determine TTS onset for each subject, the amount of TTS observed after exposures
with different SPLs and durations were combined to create a single TTS growth curve as
a function of SEL. The use of (cumulative) SEL is a simplifying assumption to
accommodate sounds of various SPLs, durations, and duty cycles. This is referred to as
an “equal energy” approach, since SEL is related to the energy of the sound and this
approach assumes exposures with equal SEL result in equal effects, regardless of the
duration or duty cycle of the sound. It is well-known that the equal energy rule will overestimate the effects of intermittent noise, since the quiet periods between noise exposures
will allow some recovery of hearing compared to noise that is continuously present with
the same total SEL (Ward, 1997). For continuous exposures with the same SEL but
different durations, the exposure with the longer duration will also tend to produce more
TTS (e.g., Kastak et al., 2007; Mooney et al., 2009; Finneran et al., 2010b). Despite these
limitations, however, the equal energy rule is still a useful concept, since it includes the
effects of both noise amplitude and duration when predicting auditory effects. SEL is a
simple metric, allows the effects of multiple noise sources to be combined in a
meaningful way, has physical significance, and is correlated with most TTS growth data
reasonably well — in some cases even across relatively large ranges of exposure duration
(see Finneran, 2015). The use of cumulative SEL for Navy sources will always overTECHNICAL GUIDANCE FOR ASSESSING THE EFFECTS OF ANTHROPOGENIC SOUND ON MARINE MAMMAL
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estimate the effects of intermittent or interrupted sources, and the majority of Navy
sources feature durations shorter than the exposure durations typically utilized in marine
mammal TTS studies, therefore the use of (cumulative) SEL will tend to over-estimate
the effects of many Navy sound sources.
Marine mammal studies have shown that the amount of TTS increases with SEL in an
accelerating fashion: At low exposure SELs, the amount of TTS is small and the growth
curves have shallow slopes. At higher SELs, the growth curves become steeper and
approach linear relationships with the noise SEL. Accordingly, TTS growth data were fit
with the function
,

(A10)

where t is the amount of TTS, L is the SEL, and m1 and m2 are fitting parameters. This
particular function has an increasing slope when L < m2 and approaches a linear
relationship for L > m2 (Maslen, 1981). The linear portion of the curve has a slope of
m1/10 and an x-intercept of m2. After fitting Eq. (10) to the TTS growth data,
interpolation was used to estimate the SEL necessary to induce 6 dB of TTS — defined
as the “onset of TTS” for Navy acoustic impact analyses. The value of 6 dB has been
historically used to distinguish non-trivial amounts of TTS from fluctuations in threshold
measurements that typically occur across test sessions. Extrapolation was not performed
when estimating TTS onset; this means only data sets with exposures producing TTS both
above and below 6 dB were used.
Figures A10 to A13 show all behavioral and AEP TTS data to which growth curves
defined by Eq. (A10) could be fit. The TTS onset exposure values, growth rates, and
references to these data are provided in Table A6.
8.2

NON-IMPULSIVE (STEADY-STATE) EXPOSURES – PTS

Since no studies have been designed to intentionally induce PTS in marine mammals (but
see Kastak et al., 2008), onset-PTS levels for marine mammals must be estimated.
Differences in auditory structures and sound propagation and interaction with tissues
prevent direct application of numerical thresholds for PTS in terrestrial mammals to
marine mammals; however, the inner ears of marine and terrestrial mammals are
analogous and certain relationships are expected to hold for both groups. Experiments
with marine mammals have revealed similarities between marine and terrestrial mammals
with respect to features such as TTS, age-related hearing loss, ototoxic drug-induced
hearing loss, masking, and frequency selectivity (e.g., Nachtigall et al., 2000; Finneran et
al., 2005b). For this reason, relationships between TTS and PTS from marine and
terrestrial mammals can be used, along with TTS onset values for marine mammals, to
estimate exposures likely to produce PTS in marine mammals (Southall et al., 2007).
A variety of terrestrial and marine mammal data sources (e.g., Ward et al., 1958; Ward et
al., 1959; Ward, 1960; Miller et al., 1963; Kryter et al., 1966) indicate that threshold
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shifts up to 40 to 50 dB may be induced without PTS, and that 40 dB is a conservative
upper limit for threshold shift to prevent PTS; i.e., for impact analysis, 40 dB of NITS is
an upper limit for reversibility and that any additional exposure will result in some PTS.
This means that 40 dB of TTS, measured a few minutes after exposure, can be used as a
conservative estimate for the onset of PTS. An exposure causing 40 dB of TTS is
therefore considered equivalent to PTS onset.
To estimate PTS onset, TTS growth curves based on more than 20 dB of measured TTS
were extrapolated to determine the SEL required for a TTS of 40 dB. The SEL difference
between TTS onset and PTS onset was then calculated. The requirement that the
maximum amount of TTS must be at least 20 dB was made to avoid over-estimating PTS
onset by using growth curves based on small amounts of TTS, where the growth rates are
shallower than at higher amounts of TTS.
8.3

IMPULSIVE EXPOSURES

Marine mammal TTS data from impulsive sources are limited to two studies with
measured TTS of 6 dB or more: Finneran et al. (2002) reported behaviorally-measured
TTSs of 6 and 7 dB in a beluga exposed to single impulses from a seismic water gun
(unweighted SEL = 186 dB re 1 μPa2s, peak SPL = 224 dB re 1 μPa) and Lucke et al.
(2009) reported AEP-measured TTS of 7 to 20 dB in a harbor porpoise exposed to single
impulses from a seismic air gun [Fig. A12(f), TTS onset = unweighted SEL of 162 dB re
1 μPa2s or peak SPL of 195 dB re 1 μPa]. The small reported amounts of TTS and/or the
limited distribution of exposures prevent these data from being used to estimate PTS
onset.
In addition to these data, Kastelein et al. (2015c) 38 reported behaviorally-measured mean
TTS of 4 dB at 8 kHz and 2 dB at 4 kHz after a harbor porpoise was exposed to a series
of impulsive sounds produced by broadcasting underwater recordings of impact pile
driving strikes through underwater sound projectors. The exposure contained 2760
individual impulses presented at an interval of 1.3 s (total exposure time was 1 h). The
average single-strike, unweighted SEL was approximately 146 dB re 1 μPa2s and the
cumulative (unweighted) SEL was approximately 180 dB re 1 μPa2s. The pressure
waveforms for the simulated pile strikes exhibited significant “ringing” not present in the
original recordings and most of the energy in the broadcasts was between 500 and 800
Hz, near the resonance of the underwater sound projector used to broadcast the signal. As
a result, some questions exist regarding whether the fatiguing signals were representative
of underwater pressure signatures from impact pile driving.
Several impulsive noise exposure studies have also been conducted without measurable
(behavioral) TTS. Finneran et al. (2000) exposed dolphins and belugas to single impulses
38

Footnote added by NMFS: Since the NMFS received this version of the Finneran Technical Report, another
TTS study became available (Kastelein et al. 2016). In this study, two harbor porpoises were exposed to
playbacks of impact pile driving strikes. Neither individual had a TTS of 6 dB after exposure. Kastelein et al.
2016 estimated TTS onset to occur at SELcum 175 dB (unweighted).

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from an “explosion simulator” (maximum unweighted SEL = 179 dB re 1 μPa2s, peak
SPL = 217 dB re 1 μPa) and Finneran et al. (2015) exposed three dolphins to sequences
of 10 impulses from a seismic air gun (maximum unweighted cumulative SEL = 193 to
195 dB re 1 μPa2s, peak SPL =196 to 210 dB re 1 μPa) without measurable TTS.
Finneran et al. (2003) exposed two sea lions to single impulses from an arc-gap
transducer with no measurable TTS (maximum unweighted SEL = 163 dB re 1 μPa2s,
peak SPL = 203 dB re 1 μPa). Reichmuth et al. (2016) exposed two spotted seals (Phoca
largha) and two ringed seals (Pusa hispida) to single impulses from a 10 in3 sleeve air
gun with no measurable TTS (maximum unweighted SEL = 181 dB re 1 μPa2s, peak SPL
~ 203 dB re 1 μPa).

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Figure A10.

TTS growth data for mid-frequency cetaceans obtained using
behavioral methods. Growth curves were obtained by fitting Eq. (A10)
to the TTS data as a function of SEL. Onset TTS was defined as the
SEL value from the fitted curve at a TTS = 6 dB, for only those
datasets that bracketed 6 dB of TTS. Onset PTS was defined as the
SEL value from the fitted curve at a TTS = 40 dB, for only those
datasets with maximum TTS > 20 dB. Frequency values within the
panels indicate the exposure frequencies. Solid lines are fit to the filled
symbols; dashed lines are fit to the open symbols. See Table A6 for
explanation of the datasets in each panel. Frequencies listed in each
panel denote the exposure frequency.

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Figure A11.

TTS growth data for mid-frequency cetaceans obtained using AEP
methods. Growth curves were obtained by fitting Eq. (A10) to the TTS
data as a function of SEL. Onset TTS was defined as the SEL value
from the fitted curve at a TTS = 6 dB, for only those datasets that
bracketed 6 dB of TTS. Onset PTS was defined as the SEL value from
the fitted curve at a TTS = 40 dB, for only those datasets with
maximum TTS > 20 dB. Frequency values within the panels indicate
the exposure frequencies. Solid lines are fit to the filled symbols;
dashed lines are fit to the open symbols. See Table A6 for explanation
of the datasets in each panel.

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Figure A12.

TTS growth data for high-frequency cetaceans obtained using
behavioral and AEP methods. Growth curves were obtained by fitting
Eq. (A10) to the TTS data as a function of SEL. Onset TTS was
defined as the SEL value from the fitted curve at a TTS = 6 dB, for
only those datasets that bracketed 6 dB of TTS. Onset PTS was
defined as the SEL value from the fitted curve at a TTS = 40 dB, for
only those datasets with maximum TTS > 20 dB. The exposure
frequency is specified in normal font; italics indicate the hearing test
frequency. Percentages in panels (b), (d) indicate exposure duty cycle
(duty cycle was 100% for all others). Solid lines are fit to the filled
symbols; dashed lines are fit to the open symbols. See Table A6 for
explanation of the datasets in each panel.

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Figure A13.

TTS growth data for pinnipeds obtained using behavioral methods.
Growth curves were obtained by fitting Eq. (A10) to the TTS data as a
function of SEL. Onset TTS was defined as the SEL value from the
fitted curve at a TTS = 6 dB, for only those datasets that bracketed 6
dB of TTS. Frequency values within the panels indicate the exposure
frequencies. Numeric values in panel (c) indicate subjects 01 and 02.
Solid lines are fit to the filled symbols; dashed lines are fit to the open
symbols. See Table A6 for explanation of the datasets in each panel.

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Table A6.

Summary of marine mammal TTS growth data and onset exposure levels. Only those data from which growth curves
could be generated are included. TTS onset values are expressed in SEL, in dB re 1 μPa2s. Tests featured continuous
exposure to steady-state noise and behavioral threshold measurements unless otherwise indicated.

Min
TTS
(dB)

Max
TTS
(dB)

TTS
Onset
(dB
SEL)

TTS
growth
rate
(dB/dB)

PTS
Onset
(dB
SEL)

TTSPTS
offset
(dB)

Notes

Reference

Figure

TTS onset higher
than subsequent
test

(Finneran et al., 2005a)

10(a)

(Finneran et al., 2005a)

10(b)

Group

Species

Subject

Freq.
(kHz)

Tursiops
truncatus

BEN

211*

0.21

—

Tursiops
truncatus

NAY

—

0.13

—

Tursiops
truncatus

BLU

207*

1.5

—

intermittent

(Finneran et al., 2010a)

10(c)

Tursiops
truncatus

BLU

206*

1.0

240

TTS onset higher
than subsequent
tests

(Finneran et al., 2010b)

10(d)

Tursiops
truncatus

TYH

194

0.35

—

(Finneran et al., 2010b)

10(e)

0
0
1
0
0
0

13
7
13
22
25
30

190
184
179
176
181
177

0.28
0.21
0.48
0.95
1.2
4.5

—
—
—
213
212
190

—
—
—
37
31
13

(Finneran and Schlundt,
2013)

10(f)
10(f)
10(g)
10(g)
10(h)
10(h)

(Finneran and Schlundt,
2013)

10(i)
10(i)

(Popov et al., 2011b)

11(a)

Tursiops
truncatus

BLU

3
7.1
10
14.1
20
28.3

Tursiops
truncatus

TYH

40
56.6

0
0

11
12

182
181

0.46
1.1

—
—

Delphinapterus
leucas

N/a

—

1.4

195

—

AEP

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Subject

Freq.
(kHz)

Min
TTS
(dB)

Max
TTS
(dB)

TTS
Onset
(dB
SEL)

TTS
growth
rate
(dB/dB)

PTS
Onset
(dB
SEL)

TTSPTS
offset
(dB)

female

11.2
22.5
45
90

25
38
9
21

50
63
51
31

—
—
—
—

2.8
2.5
3.0
0.8

190
183
193
208

—
—
—
—

15
28
13
8

48
55
42
24

—
—
—
—

2.5
1.7
2.7
1.5

195
188
198
210

—
—
—
—

Group

Species

Delphinapterus
leucas

male

11.2
22.5
45
90

Delphinapterus
leucas

female

22.5

184*

1.7

206

Delphinapterus
leucas

male

22.5

—

1.2

Phocoena
phocoena

165

Phocoena
phocoena

~1.5
~1.5

0
0

32
7

Phocoena
phocoena

6.5
6.5

1
0

Phocoena
phocoena

~6.5
~6.5

Neophocaena
phocaenoides

male

Neophocaena
phocaenoides

Phocoena
phocoena

Notes

Reference

Figure

(Popov et al., 2013)

11(b)
11(b)
11(c)
11(c)

AEP

(Popov et al., 2013)

11(d)
11(d)
11(e)
11(e)

AEP

(Popov et al., 2014)

11(f)

197

—

AEP

(Popov et al., 2014)

11(f)

0.3

—

(Kastelein et al., 2012a)

12(a)

191
197*

2.8
0.4

207
—

16
—

100% duty cycle
10% duty cycle

(Kastelein et al., 2014b)

12(b)
12(b)

13
22

161
176*

0.3
1.3

—
204

—
28

6.5 kHz test freq.
9.2 kHz test freq.

(Kastelein et al., 2014a)

12(c)
12(c)

2
2

21
13

180*
182*

2.7
1.3

197
—

17
—

100% duty cycle
10% duty cycle

(Kastelein et al., 2015b)

12(d)
12(d)

22
32

28
25

35
45

—
—

0.7
1.0

186
177

—
—

AEP

(Popov et al., 2011a)

12(e)

female

45
90

23
18

30
25

—
—

0.36
0.48

213
213

—
—

AEP

(Popov et al., 2011a)

12(f)

Eigil

impulse

162

—

AEP

(Lucke et al., 2009)

12(g)

AEP

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Min
TTS
(dB)

Max
TTS
(dB)

TTS
Onset
(dB
SEL)

TTS
growth
rate
(dB/dB)

PTS
Onset
(dB
SEL)

TTSPTS
offset
(dB)

Group

Species

Subject

Freq.
(kHz)

Zalophus
californianus

Rio

2.5

199

0.17

—

Phoca vitulina

Sprouts

2.5

183

6.4

Mirounga
angustirostris

Burnyce

2.5

—

Phoca vitulina

Notes

Reference

Figure

—

(Kastak et al., 2005)

13(a)

—

(Kastak et al., 2005)

13(b)

—

(Kastak et al., 2005)

13(b)

180

0.33

—

(Kastelein et al., 2012b)

13(c)

183*

0.68

—

(Kastelein et al., 2012b)

13(c)

TTS16

* SELs not used in subsequent analyses to optimize ∆T or define K for TTS or PTS exposure functions. Reasons for exclusion include: (i) another data set resulted in a lower
onset TTS at the same frequency, (ii) the data set featured a duty cycle less than 100%, (iii) TTS values were measured at times significantly larger than 4 min, (iv) data
were obtained from AEP testing, or (v) a lower TTS onset was found at a different hearing test frequency (also see Notes).
** Distribution of data did not support an accurate estimate for growth rate (the standard error was four orders of magnitude larger than the slope estimate)

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IX.

TTS EXPOSURE FUNCTIONS FOR SONARS

Derivation of the weighting function parameters utilized the exposure function form
described by Eq. (A2), so that the shapes of the functions could be directly compared to
the TTS onset data (Table A6) when available. The function shapes were first determined
via the parameters a, b, f1, and f2, then the gain constant K was determined for each group
to provide the best fit to the TTS data or estimated TTS onset value at a particular
frequency.
9.1

LOW- AND HIGH-FREQUENCY EXPONENTS (a, b)

The high-frequency exponent, b, was fixed at b = 2. This was done to match the previous
value used in the Phase 2 functions, since no new TTS data are available at the higher
frequencies and the equal latency data are highly variable at the higher frequencies.
The low-frequency exponent, a, was defined as a = s0/20, where s0 is the lower of the
slope of the audiogram or equal latency curves (in dB/decade) at low frequencies (Table
A5). This causes the weighting function slope to match the shallower slope of the
audiogram or equal latency contours at low frequencies. In practice, the audiogram slopes
were lower than the equal latency slopes for all groups except the mid-frequency
cetaceans (group MF).
9.2

FREQUENCY CUTOFFS (ʄ1, ʄ2)

The frequency cutoffs f1 and f2 were defined as the frequencies below and above the
frequency of best hearing (f0, Table A5) where the composite audiogram thresholds
values were ∆T-dB above the threshold at f0 (Fig. A14). If ∆T = 0, the weighting function
shape would match the shape of the inverse audiogram. Values of ∆T > 0 progressively
“compress” the weighting function, compared to the audiogram, near the frequency
region of best sensitivity. This compression process is included to match the marine
mammal TTS data, which show less change in TTS onset with frequency than would be
predicted by the audiogram in the region near best sensitivity.
To determine ∆T, the exposure function amplitude defined by Eq. (A2) was calculated for
the mid- and high-frequency cetaceans using ∆T values that varied from 0 to 20 dB. For
each ∆T value, the constant K was adjusted to minimize the mean-squared error between
the function amplitude and the TTS data (Fig. A15). This process was performed using
composite audiograms based on both the original and normalized threshold data. Fits
were performed using only TTS data resulting from continuous exposures (100% duty
cycle). If hearing was tested at multiple frequencies after exposure, the lowest TTS onset
value was used.

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Figure A14.

The cutoff frequencies f1 and f2 were defined as the frequencies below
and above f0 at which the composite audiogram values were ∆T -dB
above the threshold at f0 (the lowest threshold).

Figure A15.

Effect of ∆T adjustment on the TTS exposure functions for the midfrequency cetaceans (left) and high-frequency cetaceans (right). To
calculate the exposure functions, a and b were defined as a = s 0/20 and
b = 2. ∆T was then varied from 0 to 20. At each value of ∆T , K was
adjusted to minimize the squared error between the exposure function
and the onset TTS data (symbols). As ∆T increases, f1 decreases and f2
increases, causing the pass-band of the function to increase and the
function to “flatten”.

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For the original and normalized data, the errors between the best-fit exposure functions and
the TTS data for the MF and HF cetaceans were squared, summed, and divided by the total
number of TTS data points (12). This provided an overall mean-squared error (MSE) for the
original and normalized data as a function of ∆T (Fig. A16). The conditions (∆T value and
original/normalized threshold audiograms) resulting in the lowest MSE indicated the best
fit of the exposure functions to the TTS data. For the MF and HF cetacean data, the
lowest MSE occurred with the normalized threshold data with ∆T = 9 dB. Therefore, f1
and f2 for the remaining species groups were defined using composite audiograms
based on normalized thresholds with ∆T = 9 dB.

Figure A16.

9.3

Relationship between ∆T and the resulting mean-squared error (MSE)
between the exposure functions and onset TTS data. The MSE was
calculated by adding the squared errors between the exposure
functions and TTS data for the MF and HF cetacean groups, then
dividing by the total number of TTS data points. This process was
performed using the composite audiograms based on original and
normalized threshold data and ∆T values from 0 to 20. The lowest
MSE value was obtained using the audiograms based on normalized
thresholds with ∆T = 9 dB (arrow).

GAIN PARAMETERS K AND C

The gain parameter K was defined to minimize the squared error between the exposure
function and the TTS data for each species group. Note that K is not necessarily equal to
the minimum value of the exposure function.
For the low-frequency cetaceans and sirenians, for which no TTS data exist, TTS onset at
the frequency of best hearing (f0) was estimated by assuming that, at the frequency of best
hearing, the numeric difference between the auditory threshold (in dB SPL) and the onset
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of TTS (in dB SEL) would be similar to that observed in the other species groups. Table
A7 summarizes the onset TTS and composite threshold data for the MF, HF, OW, and
PW groups. For these groups, the median difference between the TTS onset and
composite audiogram threshold at f0 was 126 dB. In the absence of data, the hearing
threshold at f0 for the LF group was set equal to the median threshold at f0 for the other
groups (MF, HF, SI, OW, PW, median = 54 dB re 1 μPa). The TTS onset value at f0 is
therefore 180 dB re 1 μPa2s for the low-frequency cetaceans (Table A7). For the
sirenians, the lowest threshold was 61 dB re 1 μPa, making the onset TTS estimate 187
dB re 1 μPa2s (Table A7).

Table A7.

Differences between composite threshold values (Fig. A5) and TTS onset
values at the frequency of best hearing (f0) for the in-water marine mammal
species groups. The values for the low-frequency cetaceans and sirenians
were estimated using the median difference (126) from the MF, HF, OW, and
PW groups.

Group

f0
(kHz)

Threshold
at f0
(dB re 1 μPa)

TTS onset
at f0
(dB re 1 μPa2s)

5.6

179

125

105

156

108

199

132

8.6

181

128

Difference

Estimated
difference

Estimated
TTS onset at f0
(dB re 1 μPa2s)

126

180

126

187

Once K was determined, the weighted threshold for onset TTS was determined from the
minimum value of the exposure function. Finally, the constant C was determined by
substituting parameters a, b, f1, and f2 into Eq. (A1), then adjusting C so the maximum
amplitude of the weighting function was 0 dB; this is equivalent to the difference
between the weighted TTS threshold and K [see Eqs. (A3)–(A8)].
Table A8 summarizes the various function parameters, the weighted TTS thresholds, and
the goodness of fit values between the TTS exposure functions and the onset TTS data.
The various TTS exposure functions are presented in Figs. A17–A20.

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Table A8.

Weighting function and TTS exposure function parameters for use in Eqs.
(A1) and (A2) for steady-state exposures. R2 values represent goodness of
fit between exposure function and TTS onset data (Table A6).

Group

f1
(kHz)

f2
(kHz)

K
(dB)

C
(dB)

Weighted TTS
threshold
(dB SEL)

0.20

179

0.13

179

—

1.6

8.8

110

177

1.20

178

0.825

1.8

140

152

1.36

153

0.864

1.8

4.3

183

2.62

186

—

0.94

198

0.64

199

—

1.9

180

0.75

181

0.557

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Figure A17.

Exposure functions (solid lines) generated from Eq. (A2) with the
parameters specified in Table A7. Dashed lines — (normalized)
composite audiograms used for definition of parameters a , f1, and f2. A
constant value was added to each audiogram to equate the minimum
audiogram value with the exposure function minimum. Short dashed
line — Navy Phase 2 exposure functions for TTS onset for each group.
Filled symbols — onset TTS exposure data (in dB SEL) used to define
exposure function shape and vertical position. Open symbols —
estimated TTS onset for species for which no TTS data exist.

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Figure A18.

Mid-frequency cetacean exposure function, (normalized) composite
audiogram, and Phase 2 exposure functions compared to midfrequency cetacean TTS data. Large symbols with no numeric values
indicate onset TTS exposures. Smaller symbols represent specific
amounts of TTS observed, with numeric values giving the amount (or
range) or measured TTS. Filled and half-filled symbols — behavioral
data. Open symbols — AEP data.

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Figure A19.

High-frequency cetacean TTS exposure function, (normalized)
composite audiogram, and Phase 2 exposure functions compared to
high-frequency cetacean TTS data. Large symbols with no numeric
values indicate onset TTS exposures. Smaller symbols represent
specific amounts of TTS observed, with numeric values giving the
amount (or range) or measured TTS. Filled and half-filled symbols —
behavioral data. Open symbols — AEP data.

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Figure A20.

Phocid (underwater) exposure function, (normalized) composite
audiogram, and Phase 2 exposure functions compared to phocid TTS
data. Large symbols with no numeric values indicate onset TTS
exposures. Smaller symbols represent specific amounts of TTS
observed, with numeric values giving the amount (or range) or
measured TTS.

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PTS EXPOSURE FUNCTIONS FOR SONARS

As in previous acoustic effects analyses (Southall et al., 2007; Finneran and Jenkins,
2012), the shape of the PTS exposure function for each species group is assumed to be
identical to the TTS exposure function for that group. Thus, definition of the PTS
function only requires the value for the constant K to be determined. This equates to
identifying the increase in noise exposure between the onset of TTS and the onset of PTS.
For Phase 2, Navy used a 20-dB difference between TTS onset and PTS onset for
cetaceans and a 14-dB difference for phocids, otariids, odobenids, mustelids, ursids, and
sirenians (Finneran and Jenkins, 2012). The 20-dB value was based on human data (Ward
et al., 1958) and the available marine mammal data, essentially following the
extrapolation process proposed by Southall et al. (2007). The 14-dB value was based on a
2.5 dB/dB growth rate reported by Kastak et al. (2007) for a California sea lion tested in
air.
For Phase 3, a difference of 20 dB between TTS onset and PTS onset is used for all
species groups. This is based on estimates of exposure levels actually required for PTS
(i.e., 40 dB of TTS) from the marine mammal TTS growth curves (Table 6), which show
differences of 13 to 37 dB (mean = 24, median = 22, n = 9) between TTS onset and PTS
onset in marine mammals. These data show most differences between TTS onset and PTS
onset are larger than 20 dB and all but one value are larger than 14 dB.
The value of K for each PTS exposure function and the weighted PTS threshold are
therefore determined by adding 20 dB to the K-value for the TTS exposure function or
the TTS weighted threshold, respectively (see Table A10).

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XI.

TTS/PTS EXPOSURE FUNCTIONS FOR EXPLOSIVES

The shapes of the TTS and PTS exposure functions for explosives and other impulsive
sources are identical to those used for sonars and other active acoustic sources (i.e.,
steady-state or non-impulsive noise sources). Thus, defining the TTS and PTS functions
only requires the values for the constant K to be determined.
Phase 3 analyses for TTS and PTS from underwater detonations and other impulsive
sources follow the approach proposed by Southall et al. (2007) and used in Phase 2
analyses (Finneran and Jenkins, 2012), where a weighted SEL threshold is used in
conjunction with an unweighted peak SPL threshold. The threshold producing the greater
range for effect is used for estimating the effects of the noise exposure.
Peak SPL and SEL thresholds for TTS were based on TTS data from impulsive sound
exposures that produced 6 dB or more TTS for the mid- and high-frequency cetaceans
(the only groups for which data are available). The peak SPL thresholds were taken
directly from the literature: 224 and 196 dB re 1 μPa, for the mid- and high-frequency
cetaceans, respectively (Table A9). The SEL-based thresholds were determined by
applying the Phase 3 weighting functions for the appropriate species groups to the
exposure waveforms that produced TTS, then calculating the resulting weighted SELs.
When this method is applied to the exposure data from Finneran et al. (2002) and Lucke
et al. (2009), the SEL-based weighted TTS thresholds are 170 and 140 dB re 1 μPa2s for
the mid- and high-frequency cetaceans, respectively (Table A9). Note that the data from
Lucke et al. (2009) are based on AEP measurements and may thus under-estimate TTS
onset; however, they are used here because of the very limited nature of the impulse TTS
data for marine mammals and the likelihood that the high-frequency cetaceans are more
susceptible than the mid-frequency cetaceans (i.e., use of the mid-frequency cetacean
value is not appropriate). Based on the limited available data, it is reasonable to assume
that the exposures described by Lucke et al. (2009), which produced AEP-measured TTS
of up to 20 dB, would have resulted in a behavioral TTS of at least 6 dB.
The harbor porpoise data from Kastelein et al. (2015c) were not used to derive the highfrequency cetacean TTS threshold, since the largest observed TTS was only 4 dB.
However, these data provide an opportunity to check the TTS onset proposed for the
high-frequency cetacean group. Kastelein et al. (2015c) provide a representative
frequency spectrum for a single, simulated pile driving strike at a specific measurement
location. When the high-frequency cetacean weighting function is applied to this
spectrum and the 1/3-octave SELs combined across frequency, the total weighted SEL
for a single strike is found to be 114 dB re 1 μPa2s. For 2760 impulses, the cumulative,
weighted SEL would then be 148 dB re 1 μPa2s. The average SEL in the pool was
reported to be 9 dB lower than the SEL at the measurement position, thus the average,
cumulative weighted SEL would be approximately 139 dB re 1 μPa2s, which compares
favorably to the high-frequency cetacean TTS threshold of 140 dB re 1 μPa2s derived
from the Lucke et al. (2009) air gun data.

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For species groups for which no impulse TTS data exist, the weighted SEL thresholds
were estimated using the relationship between the steady-state TTS weighted threshold
and the impulse TTS weighted threshold for the groups for which data exist (the mid- and
high-frequency cetaceans):
,

(A11)

where G indicates thresholds for a species group for which impulse TTS data are not
available,
indicates the median threshold for the groups for which data exist, the
subscript s indicates a steady-state threshold, and the subscript i indicates an impulse
threshold (note that since data are only available for the mid- and high-frequency
cetaceans the median and mean are identical). Equation (A11) is equivalent to the
relationship used by Southall et al. (2007), who expressed the relationship as
. For the mid- and high-frequency cetaceans, the steady-state TTS
thresholds are 178 and 153 dB re 1 μPa2s, respectively, and the impulse TTS thresholds
= 11 dB. Therefore, for each
are 170 and 140 dB re 1 μPa2s, respectively, making
of the remaining groups the SEL-based impulse TTS threshold is 11 dB below the steadystate TTS threshold (Table A9).
To estimate peak SPL-based thresholds, Southall et al. (2007) used Eq. (A11) with peakSPL values for the impulse thresholds and SEL-based values for the steady-state
thresholds. For the mid- and high-frequency cetaceans, the steady-state (SEL) TTS
thresholds are 178 and 153 dB re 1 μPa2s, respectively, and the peak SPL, impulse TTS
thresholds are 224 and 196 dB re 1 μPa, respectively, making
= -44 dB. Based on
this relationship, the peak SPL-based impulse TTS threshold (in dB re 1 μPa) would be
44 dB above the steady-state TTS threshold (in dB re 1 μPa2s), making the peak SPL
thresholds vary from 222 to 243 dB re 1 μPa. Given the limited nature of the underlying
data, and the relatively high values for some of these predictions, for Phase 3 analyses
impulsive peak SPL thresholds are estimated using a “dynamic range” estimate based on
the difference (in dB) between the impulsive noise, peak SPL TTS onset (in dB re 1 μPa)
and the hearing threshold at f0 (in dB re 1 μPa) for the groups for which data are available
(the mid- and high-frequency cetaceans). For the mid-frequency cetaceans, the hearing
threshold at f0 is 54 dB re 1 μPa and the peak SPL TTS threshold is 224 dB re 1 μPa,
resulting in a dynamic range of 170 dB. For the high-frequency cetaceans, the hearing
threshold at f0 is 48 dB re 1 μPa and the peak SPL-based TTS threshold is 196 dB re 1
μPa, resulting in a dynamic range of 148 dB. The median dynamic range for the mid- and
high-frequency cetaceans is therefore 159 dB (since there are only two values, the mean
and median are equal). For the remaining species groups, the impulsive peak SPL-based
TTS thresholds are estimated by adding 159 dB to the hearing threshold at f0 (Table A9).
Since marine mammal PTS data from impulsive noise exposures do not exist, onset-PTS
levels for impulsive exposures were estimated by adding 15 dB to the SEL-based TTS
threshold and adding 6 dB to the peak pressure based thresholds. These relationships
were derived by Southall et al. (2007) from impulse noise TTS growth rates in
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chinchillas. The appropriate frequency weighting function for each functional hearing
group is applied only when using the SEL-based thresholds to predict PTS.

Table A9.

TTS and PTS thresholds for explosives and other impulsive sources. SEL
thresholds are in dB re 1 μPa2s and peak SPL thresholds are in dB re 1
μPa.

Group

Hearing
threshold at f0

TTS
threshold

PTS
threshold

SPL
(dB SPL)

SEL (weighted)
(dB SEL)

peak SPL
(dB SPL)

SEL (weighted)
(dB SEL)

peak SPL
(dB SPL)

168

213

183

219

170

224

185

230

140

196

155

202

175

220

190

226

188

226

203

232

170

212

185

218

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XII.

SUMMARY

Figure A21 illustrates the shapes of the various Phase 3 auditory weighting functions.
Table A10 summarizes the parameters necessary to calculate the weighting function
amplitudes using Eq. (A1).

Figure A21.

Navy Phase 3 weighting functions for marine mammal species groups
exposed to underwater sound. Parameters required to generate the
functions are provided in Table A10.

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Table A10.

Summary of weighting function parameters and TTS/PTS thresholds. SEL
thresholds are in dB re 1 μPa2s and peak SPL thresholds are in dB re 1 μPa.
Non-impulsive
TTS
threshold

PTS
threshold

Impulse
TTS
threshold

PTS
threshold

peak SPL
SEL
peak SPL
f1
f2
C
SEL
SEL
SEL
(unweight (weighted (unweight
(kHz) (kHz) (dB) (weighted) (weighted) (weighted)
ed)
)
ed)

0.20

0.13

179

199

168

213

183

219

MF 1.6 2

8.8

110 1.20

178

198

170

224

185

230

1.8 2

140 1.36

153

173

140

196

155

202

1.8 2

4.3

2.62

186

206

175

220

190

226

Grou
a
p
LF

0.94

0.64

199

219

188

226

203

232

1.9

0.75

181

201

170

212

185

218

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To properly compare the TTS/PTS criteria and thresholds used by Navy for Phase 2 and
Phase 3, both the weighting function shape and weighted threshold values must be taken
into account; the weighted thresholds by themselves only indicate the TTS/PTS threshold
at the most susceptible frequency (based on the relevant weighting function). Since the
exposure functions incorporate both the shape of the weighting function and the weighted
threshold value, they provide the best means of comparing the frequency-dependent
TTS/PTS thresholds for Phase 2 and 3 (Figs A22 and A23).
The most significant differences between the Phase 2 and Phase 3 functions include the
following:
(1) Thresholds at low frequencies are generally higher for Phase 3 compared to Phase 2.
This is because the Phase 2 weighting functions utilized the “M-weighting” functions
(Southall et al., 2007) at lower frequencies, where no TTS existed at that time. Since
derivation of the Phase 2 thresholds, additional data have been collected (e.g., Kastelein
et al., 2012a; Kastelein et al., 2013b; Kastelein et al., 2014b) to support the use of
exposure functions that continue to increase at frequencies below the region of best
sensitivity, similar to the behavior of mammalian audiograms and human auditory
weighting functions.
(2) In the frequency region near best hearing sensitivity, the Phase 3 underwater
thresholds for otariids and other marine carnivores (group OW) are lower than those used
in Phase 2. In Phase 2, the TTS onset for the otariids was taken directly from the
published literature (Kastak et al., 2005); for Phase 3, the actual TTS data from Kastak et
al. (2005) were fit by a TTS growth curve using identical methods as those used with the
other species groups.
(3) Impulsive TTS/PTS thresholds near the region of best hearing sensitivity are lower
for Phase 3 compared to Phase 2.

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Figure A22.

TTS and PTS exposure functions for sonars and other (non-impulsive)
active acoustic sources. Heavy solid lines — Navy Phase 3 TTS
exposure functions (Table A10). Thin solid lines — Navy Phase 3 PTS
exposure functions for TTS (Table A10). Dashed lines — Navy Phase
2 TTS exposure functions. Short dashed lines — Navy Phase 2 PTS
exposure functions.

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Figure A23.

TTS and PTS exposure functions for explosives, impact pile driving,
air guns, and other impulsive sources. Heavy solid lines — Navy
Phase 3 TTS exposure functions (Table A10). Thin solid lines — Navy
Phase 3 PTS exposure functions for TTS (Table A10). Dashed lines —
Navy Phase 2 TTS exposure functions. Short dashed lines — Navy
Phase 2 PTS exposure functions.

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APPENDIX A1.

ESTIMATING A LOW-FREQUENCY CETACEAN
AUDIOGRAM

A1.1. BACKGROUND

Psychophysical and/or electrophysiological auditory threshold data exist for at least one
species within each hearing group, except for the low-frequency (LF) cetacean (i.e.,
mysticete) group, for which no direct measures of auditory threshold have been made.
For this reason, an alternative approach was necessary to estimate the composite
audiogram for the LF cetacean group.
The published data sources available for use in estimating mysticete hearing thresholds
consist of: cochlear frequency-place maps created from anatomical measurements of
basilar membrane dimensions (e.g., Ketten, 1994; Parks et al., 2007); scaling
relationships between inter-aural time differences and upper-frequency limits of hearing
(see Ketten, 2000); finite element models of head-related and middle-ear transfer
functions (Tubelli et al., 2012; Cranford and Krysl, 2015); a relative hearing sensitivity
curve derived by integrating cat and human threshold data with a frequency-place map
for the humpback whale (Houser et al., 2001); and measurements of the source levels and
frequency content of mysticete vocalizations (see review by Tyack and Clark, 2000).
These available data sources are applied here to estimate a mysticete composite
audiogram. Given that these data are limited in several regards and are quite different
from the type of data supporting composite audiograms in other species, additional
sources of information, such as audiograms from other marine mammals, are also
considered and applied to make conservative extrapolations at certain decision points.
Mathematical models based on anatomical data have been used to predict hearing curves
for several mysticete species (e.g., Ketten and Mountain, 2009; Cranford and Krysl,
2015). However, these predictions are not directly used to derive the composite
audiogram for LF cetaceans for two primary reasons:
(1) There are no peer-reviewed publications that provide a complete description
of the mathematical process by which frequency-place maps based on anatomical
measurements were integrated with models of middle-ear transfer functions
and/or other information to derive the predicted audiograms presented in several
settings by Ketten/Mountain (e.g., Ketten and Mountain, 2009). As a result, the
validity of the resulting predicted audiograms cannot be independently evaluated,
and these data cannot be used in the present effort.
(2) Exclusion of the Ketten/Mountain predicted audiograms leaves only the
Cranford/Krysl predicted fin whale hearing curve (Cranford and Krysl, 2015).
However, this curve cannot be used by itself to predict hearing thresholds for all
mysticetes because:

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(a) The Cranford/Krysl model is based on sound transmission through the head
to the ear of the fin whale, but does not include the sensory receptors of the
cochlea. There is therefore no way to properly predict the upper cutoff of
hearing and the shape of the audiogram at frequencies above the region of best
predicted sensitivity.
(b) The audiogram does not possess the typical shape one would expect for an
individual with normal hearing based on measurements from other mammals.
Specifically, the “hump” in the low-frequency region and the shallow roll-off
at high frequencies do not match patterns typically seen in audiometric data
from other mammals with normal hearing. Given these considerations, the
proposed audiogram cannot be considered representative of all mysticetes
without other supporting evidence. Although the specific numeric thresholds
from Cranford and Krysl (2015) are not directly used in the revised approach
explained here, the predicted thresholds are still used to inform the LF
cetacean composite audiogram derivation.
Vocalization data also cannot be used to directly estimate auditory sensitivity and audible
range, since there are many examples of mammals that vocalize below the frequency
range where they have best hearing sensitivity, and well below their upper hearing limit.
However, it is generally expected that animals have at least some degree of overlap
between the auditory sensitivity curve and the predominant frequencies present in
conspecific communication signals. Therefore vocalization data can be used to evaluate,
at least at a general level, whether the composite audiogram is reasonable; i.e., to ensure
that the predicted thresholds make sense given what we know about animal vocalization
frequencies, source levels, and communication range.
The realities of the currently available data leave only a limited amount of anatomical
data and finite element modeling results to guide the derivation of the LF cetacean
composite audiogram, supplemented with extrapolations from the other marine mammal
species groups where necessary and a broad evaluation of the resulting audiogram in the
context of whale bioacoustics.
A1.2. AUDIOGRAM FUNCTIONAL FORM AND REQUIRED PARAMETERS

Navy Phase 3 composite audiograms are defined by the equation

(A1.1)

where T( f ) is the threshold at frequency f, and T0, F1, F2, A, and B are constants. To
understand the physical significance and influence of the parameters T0, F1, F2, A, and B,
Eq. (A1.1) may be viewed as the sum of three individual terms:

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(A1.2)

where
,

(A1.3)

and

(A1.4)

The first term, T0, controls the vertical position of the curve; i.e., T0 shifts the audiogram
up and down.
The second term, L(f ), controls the low-frequency behavior of the audiogram. At low
frequencies, when f < F1, Eq. (A1.3) approaches
,

(A1.5)

which can also be written as
.

(A1.6)

Equation (A.6) has the form of y(x) = b - Ax, where x = log10f; i.e., Eq. (A.6) describes a
linear function of the logarithm of frequency. This means that, as frequency gets smaller
and smaller, Eq. (A.3) — the low-frequency portion of the audiogram function —
approaches a linear function with the logarithm of frequency, and has a slope of ‑A
dB/decade. As frequency increases towards F1, L(f ) asymptotically approaches zero.
The third term, H(f ), controls the high-frequency behavior of the audiogram. At low
frequencies, when f << F2, Eq. (A1.4) has a value of zero. As f increases, H(f )
exponentially grows. The parameter F2 defines the frequency at which the thresholds
begin to exponentially increase, while the factor B controls the rate at which thresholds
increase. Increasing F2 will move the upper cutoff frequency to the right (to higher
frequencies). Increasing B will increase the “sharpness” of the high-frequency increase.

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FIGURE A1.1. Relationship between estimated threshold, T(f), (thick, gray line),
low-frequency term, L(f), (solid line), and high-frequency term, H(f),
(dashed line).
A1.3. ESTIMATING AUDIOGRAM PARAMETERS

To derive a composite mysticete audiogram using Eq. (A1.1), the values of T0, F1, F2, A,
and B must be defined. The value for T0 is determined by either adjusting T0 to place the
lowest threshold value to zero (to obtain a normalized audiogram), or to place the lowest
expected threshold at a specific SPL (in dB re 1 μPa). For Navy Phase 3 analyses, the
lowest LF cetacean threshold is defined to match the median threshold of the in-water
marine mammal species groups (MF cetaceans, HF cetaceans, sirenians, otariids and
other marine carnivores in water, and phocids in water; median = 54 dB re 1 μPa). The
choices for the other parameters are informed by the published information regarding
mysticete hearing.
The constant A is defined by assuming a value for the low-frequency slope of the
audiogram, in dB/decade. Most mammals for which thresholds have been measured have
low-frequency slopes ~30 to 40 dB/decade. However, finite element models of middle
ear function in fin whales (Cranford and Krysl, 2015) and minke whales (Tubelli et al.,
2012) suggest lower slopes, of ~25 or 20 dB/decade, respectively. We therefore
conservatively assume that A = 20 dB/decade.
To define F1, we first define the variable T′ as the maximum threshold tolerance within
the frequency region of best sensitivity (i.e., within the frequency range of best
sensitivity, thresholds are within T′ dB of the lowest threshold). Further, let f ′ be the
lower frequency bound of the region of best sensitivity. When f = f ′, L(f ) = T′, and Eq.
(A1.3) can then be solved for F1 as a function of f ′, T′, and A:
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(A1.7)

Anatomically-based models of mysticete hearing have resulted in various estimates for
audible frequency ranges and frequencies of best sensitivity. Houser et al. (2001)
estimated best sensitivity in humpback whales to occur in the range of 2 to 6 kHz, with
thresholds within 3 dB of best sensitivity from ~1.4 to 7.8 kHz. For right whales, Parks et
al. (2007) estimated the audible frequency range to be 10 Hz to 22 kHz. For minke
whales, Tubelli et al. (2012) estimated the most sensitive hearing range, defined as the
region with thresholds within 40 dB of best sensitivity, to extend from 30 to 100 Hz up to
7.5 to 25 kHz, depending on the specific model used. Cranford and Krysl (2015)
predicted best sensitivity in fin whales to occur at 1.2 kHz, with thresholds within 3-dB
of best sensitivity from ~1 to 1.5 kHz. Together, these model results broadly suggest best
sensitivity (thresholds within ~3 dB of the lowest threshold) from ~1 to 8 kHz, and
thresholds within ~40 dB of best sensitivity as low as ~30 Hz and up to ~25 kHz.
Based on this information, we assume LF cetacean thresholds are within 3 dB of the
lowest threshold over a frequency range of 1 to 8 kHz, therefore T′ = 3 dB and f ′= 1
kHz, resulting in F1 = 0.41 kHz [Eq. (A1.7)]. In other words, we define F1 so that
thresholds are ≤ 3 dB relative to the lowest threshold when the frequency is within the
region of best sensitivity (1 to 8 kHz).
To define the high-frequency portion of the audiogram, the values of B and F2 must be
estimated. To estimate B for LF cetaceans, we take the median of the B values from the
composite audiograms for the other in-water marine mammal species groups (MF
cetaceans, HF cetaceans, sirenians, otariids and other marine carnivores in water, and
phocids in water). This results in B = 3.2 for the LF cetaceans. Once B is defined, F2 is
adjusted to achieve a threshold value at 30 kHz of 40 dB relative to the lowest threshold.
This results in F2 = 9.4 kHz. Finally, T0 is adjusted to set the lowest threshold value
to 0 dB for the normalized curve, or 54 dB re 1 μPa for the non-normalized curve;
this results in T0 = -0.81 and 53.19 for the normalized and non-normalized curves,
respectively.
The resulting composite audiogram is shown in Fig. A1.2. For comparison, predicted
audiograms for the fin whale (Cranford and Krysl, 2015), and humpback whale (Houser
et al., 2001) are included. The LF cetacean composite audiogram has lowest threshold at
5.6 kHz, but the audiogram is fairly shallow in the region of best sensitivity, and
thresholds are within 1 dB of the lowest threshold from ~1.8 to 11 kHz, and within 3 dB
of the lowest threshold from ~0.75 to 14 kHz. Low-frequency (< ~500 Hz) thresholds are
considerably lower than those predicted by Cranford and Krysl (2015). High-frequency
thresholds are also substantially lower than those predicted for the fin whale, with
thresholds at 30 kHz only 40 dB above best hearing thresholds, and those at 40 kHz
approximately 90 dB above best threshold. The resulting LF composite audiogram
appears reasonable in a general sense relative the predominant frequencies present in
mysticete conspecific vocal communication signals. While some species (e.g., blue
whales) produce some extremely low (e.g., 10 Hz) frequency call components, the
majority of mysticete social calls occur in the few tens of Hz to few kHz range,
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overlapping reasonably well with the predicted auditory sensitivity shown in the
composite audiogram (within ~0 to 30 dB of predicted best sensitivity). A general pattern
of some social calls containing energy shifted below the region of best hearing sensitivity
is well-documented in other low-frequency species including many phocid seals (see
Wartzok and Ketten, 1999) and some terrestrial mammals, notably the Indian elephant
(Heffner and Heffner, 1982).

FIGURE A1.2. Comparison of proposed LF cetacean thresholds to those predicted
by anatomical and finite-element models.

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XIII.

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APPENDIX B: RESEARCH RECOMMENDATIONS FOR
IMPROVED ACOUSTIC THRESHOLDS
In compiling, interpreting, and synthesizing the scientific literature to produce updated
acoustic thresholds for this Technical Guidance, it is evident that additional data would be
useful for future iterations of this document, since many data gaps still exist (Table B1). The
need for the Technical Guidance to identify critical data gaps was also recommended during
the initial peer review and public comment period.
Table B1:
Hearing
Group
LF Cetaceans

Summary of currently available marine mammal data.
Audiogram
Data/Number of
Species
Predictive modeling/2
species

TTS Data/Number
of Species
None/0 species

MF Cetaceans

Behavioral/8 species

Behavioral/2 species

HF Cetaceans

Behavioral/2 species

Behavioral/1 species

PW Pinnipeds

Behavioral/5 species

Behavioral/2 species

OW Pinnipeds

Behavioral/3 species

Behavioral/1 species

Sound Sources for
TTS Studies
None
Octave-band noise;
Tones; Mid-frequency
sonar; Explosion
simulator; Watergun;
Airgun
Tones, Mid-frequency
sonar; Impact pile
driver; Airgun*
Octave-band noise;
Impact pile driver
Octave-band noise;
Arc-gap transducer

* Data collected using AEP methodology (directly incorporated in Technical Guidance, since only data set
available).

Below is a list of research recommendations that NMFS believes would help address current
data gaps. Some of these areas of recommended research have been previously identified in
other publications/reports (e.g., NRC 1994; NRC 2000; Southall et al. 2007; Southall et al.
2009; Hawkins et al. 2014; 39 Houser and Moore 2014; Lucke et al. 2014; Popper et al. 2014; 40
Williams et al. 2014; Erbe et al. 2016; Lucke et al. 2016). Note: Just because there may not be
39

Although, Hawkins et al. 2014 identifies research gaps for fishes and invertebrates, many of the research
recommendations can also be considered for other species, like marine mammals.
40

Although, Popper et al. 2014 identifies research gaps for fishes and sea turtles, many of the research
recommendations can also be considered for other species, like marine mammals.
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enough information to allow for quantifiable modifications to acoustic thresholds associated
with many of these recommendations, does not mean these recommendations cannot be
incorporated as qualitative considerations within the comprehensive effects analysis.
I.

SUMMARY OF RESEARCH RECOMMENDATIONS

1.1

LOW-FREQUENCY CETACEAN HEARING

As previously stated, direct measurements of LF cetacean hearing are lacking. Therefore,
hearing predictions for these species are based on other methods (e.g., anatomical studies,
predictive models, vocalizations, taxonomy, and behavioral responses to sound). Thus,
additional data 41 collected would be extremely valuable to furthering the understanding of
hearing ability within this hearing group and validating other methods for approximating
hearing ability. For example, data collected on either stranded or animals associated with
subsistence hunts would be extremely useful in confirming current predictions of LF
cetacean hearing ability and would allow for the development of more accurate auditory
weighting functions (e.g., Do species that vocalize at ultra-low frequencies, like blue and fin
whales, have dramatically different hearing abilities than other mysticete species?). Until
direct measurements can be made, predictive models based on anatomical data will be the
primary means of approximating hearing abilities, with validation remaining a critical
component of any modeling exercise (e.g., Cranford and Krysl 2014).
1.2

HEARING DIVERSITY AMONG SPECIES AND AUDITORY PATHWAYS

A better understanding of hearing diversity among species within a hearing group is also
needed (e.g., Mooney et al. 2014) to comprehend how representative certain species (e.g.,
bottlenose dolphins, harbor porpoise, harbor seals) are of their hearing group as a whole.
For example, are there certain species more susceptible to hearing loss from sound (i.e., all
members of HF cetaceans), or are there additional delineations needed among the current
hearing groups (e.g., deep diving species, etc.)? Having more data from species within a
hearing group would also help identify if additional hearing groups are needed. This is
especially the case for HF cetaceans where data are only available from four individuals of
two species and those individuals have a lower hearing threshold compared to all other
hearing groups.
Additionally, having a more complete understanding of how sound enters the heads/bodies
of marine mammals and its implication on hearing and impacts of noise among various
species is another area of importance (e.g., bone conduction mechanism in mysticetes:
Cranford and Krysl 2015; previously undescribed acoustic pathways in odontocetes:
Cranford et al. 2008; Cranford et al. 2010; filtering/amplification of transmission pathway:
Cranford and Krysl 2012; directional hearing: Renaud and Popper 1975; Au and Moore
1984; Kastelein et al. 2005b).

Data should be collected under appropriate permits or authorizations.

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1.3

REPRESENTATIVENESS OF CAPTIVE INDIVIDUALS

Data from Castellote et al. (2014), from free-ranging belugas in Alaska, indicate that of the
seven healthy individuals tested (3 females/4 males; 1 subadult/6 adults), all had hearing
abilities “similar to those of belugas measured in zoological settings.” Thus, from this one
study, it appears that for baseline hearing measurements, captive individuals may be
appropriate surrogates for free-ranging animals. Additionally, Mulsow et al. (2011) measured
aerial hearing abilities of seven stranded California sea lions and found a high degree of
intersubject variability but that high-frequency hearing limits were consistent with previously
tested captive individuals. However, these are currently the only studies of their kind, 42 and
more research is needed to examine if this trend is applicable to other species (Lucke et al.
2016).
1.3.1

Impacts of Age on Hearing

Hearing loss can result from a variety of factors beyond anthropogenic noise, including
exposure to ototoxic compounds (chemicals poisonous to auditory structures), disease and
infection, and heredity, as well as a natural part of aging (Corso 1959; Kearns 1977; WGSUA
1988; Yost 2007). High-frequency hearing loss, presumably a normal process of aging that
occurs in humans and other terrestrial mammals, has also been demonstrated in captive
cetaceans (Ridgway and Carder 1997; Yuen et al. 2005; Finneran et al. 2005b; Houser and
Finneran 2006; Finneran et al. 2007b; Schlundt et al. 2011) and in stranded individuals
(Mann et al. 2010). Thus, the potential impacts of age on hearing can be a concern when
extrapolating from older to younger individuals.
Few studies have examined this phenomenon in marine mammals, particularly in terms of
the potential impact of aging on hearing ability and TSs:
•

Houser and Finneran (2006) conducted a comprehensive study of the hearing
sensitivity of the U.S. Navy bottlenose dolphin population (i.e., tested 42 individuals
from age four to 47 years; 28 males/14 females). They found that high-frequency
hearing loss typically began between the ages of 20 and 30 years. However, the
frequencies where this species is most susceptible to noise-induced hearing loss (i.e.,
10 to 30 kHz) are the frequencies where the lowest variability exists in mean acoustic
thresholds between individuals of different ages.

•

Houser et al. (2008) measured hearing abilities of 13 Pacific bottlenose dolphins,
ranging in age from 1.5 to 18 years. The authors’ reported that “Variability in the
range of hearing and age-related reductions in hearing sensitivity and range of
hearing were consistent with those observed in Atlantic bottlenose dolphins.”

NMFS is aware that additional baseline hearing measurements have been recorded for additional freeranging belugas by Castellote et al. with the analysis still in process. Furthermore, NMFS is aware that
audiogram (AEP) data are often obtained during marine mammal stranding events exists, but these have yet to
be published.
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•

Mulsow et al. (2014) examined aerial hearing thresholds for 16 captive sea lions,
from age one to 26 years, and found that only the two 26-year old individuals had
hearing classified as “aberrant” compared to other individuals (i.e., high-frequency
hearing loss), which were deemed to have similar hearing abilities to previously
measured individuals.

•

Additionally, for harbor seals, similar exposure levels associated with TTS onset were
found in Kastelein et al. 2012a for individuals of four to five years of age compared
to that used in Kastak et al. 2005, which was 14 years old and for belugas in Popov et
al. 2014 for an individual of 2 years of age compared to those used in Schlundt et al.
2000, which were 20 to 22 years old or 29 to 31 years old.

From these limited data, it appears that age may not be a significant complicating factor, in
terms of assessing TSs for animals of different ages. Nevertheless, additional data are needed
to confirm if these data are representative for all species (Lucke et al. 2016).
1.4

ADDITIONAL TTS MEASUREMENTS WITH MORE SPECIES AND/OR INDIVIDUALS

Currently, TTS measurements only exist for four species of cetaceans (bottlenose dolphins,
belugas, harbor porpoises, and Yangtze finless porpoise) and three species of pinnipeds
(Northern elephant seal, harbor seal, and California sea lion). Additionally, the existing
marine mammal TTS measurements are from a limited number of individuals within these
species. Having more data from a broader range of species and individuals would be useful
to confirm how representative current individuals are of their species and/or entire hearing
groups (Lucke et al. 2016). For example, TTS onset acoustic thresholds for harbor porpoise
(HF cetacean) are much lower compared to other odontocetes (MF cetaceans), and it would
be useful to know if all HF cetaceans share these lower TTS onset acoustic thresholds or if
harbor porpoises are the exception.
Recently measured underwater hearing of two captive spotted seals (Sills et al. 2014) and
two captive ringed seals (Sills et al. 2015) found these species’ hearing abilities are
comparable to harbor seals. Thus, harbor seals, where TTS data are available, are an
appropriate surrogate for ice seal species. As more data become available, this assumption
will be re-evaluated.
Finally, cetaceans are often used as surrogates for pinnipeds when no direct data exist.
Having more information on the appropriateness of using cetaceans as surrogates for
pinnipeds would be useful (i.e., Is there another mammalian group more appropriate?).

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1.5

SOUND EXPOSURE TO MORE REALISTIC SCENARIOS

Most marine mammal TTS measurements are for individuals exposed to a limited number of
sound sources (i.e., mostly tones and octave-band noise 43) in laboratory settings.
Measurements from exposure to actual sound sources (opposed to tones or octave-band
noise) under more realistic exposure conditions (e.g., more realistic exposure durations
and/or scenarios, including multiple pulses/pile strikes and at frequencies below 1 kHz
where most anthropogenic noise occurs) are needed.
1.5.1

Frequency and Duration of Exposure

In addition to received level, NMFS recognizes that other factors, such as frequency and
duration of exposure, are also important to consider within the context of PTS onset
acoustic thresholds (Table B2). However, there are not enough data to establish numerical
acoustic thresholds based on these added factors (beyond what has already been included in
this document, in terms of marine mammal weighting functions and SELcum thresholds).
When more data become available, it may be possible to incorporate these factors into
quantitative assessments.
Further, it has been demonstrated that exposure to lower-frequency broadband sounds has
the potential to cause TSs at higher frequencies (e.g., Lucke et al. 2009; Kastelein et al.
2015a; Kastelein et al. 2016). The consideration of duty cycle (i.e., energy per unit time) is
another important consideration in the context of exposure duration (e.g., Kastelein et al.
2015b). Having a better understanding of these phenomena would be helpful.
1.5.2

Multiple Sources

Further, a better understanding of the effects of multiple sources and multiple activities on
TS, as well as impacts from long-term exposure is needed. Studies on terrestrial mammals
indicate that exposure scenarios from complex exposures (i.e., those involving multiple types
of sound sources) result in more complicated patterns of NIHL (e.g., Ahroon et al. 1993).

More recent studies (e.g., Lucke et al. 2009; Mooney et al. 2009b; Kastelein et al. 2014a; Kastelein et al.
2014b; Kastelein et al. 2015a; Kastelein et al. 2015b; Finneran et al. 2015; Kastelein et al. 2016) have used
exposures from more realistic sources, like airguns, impact pile drivers, or tactical sonar.
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Table B2:

Additional factors for consideration (frequency and duration of
exposure) in association with PTS onset acoustic thresholds.

I. Frequency*:
General Trend Identified:
1) Growth of TS: Growth rates of TS (dB of TTS/dB noise) are higher for frequencies
where hearing is more sensitive (e.g., Finneran and Schlundt 2010; Finneran and
Schlundt 2013; Kastelein et al. 2014a; Kastelein et al. 2015b)
II. Duration:
General Trends Identified:
1) Violation of EEH: Non-impulsive, intermittent exposures require higher SELcum to
induce a TS compared to continuous exposures of the same duration (e.g., Mooney
et al. 2009a; Finneran et al. 2010b; Kastelein et al. 2014a)
2) Violation of EEH: Exposures of longer duration and lower levels induce a TTS at a
lower level than those exposures of higher level (below the critical level) and shorter
duration with the same SELcum (e.g., Kastak et al. 2005; Kastak et al. 2007; Mooney et
al. 2009b; Finneran et al. 2010a; Kastelein et al. 2012a; Kastelein et al. 2012b)
3) Recovery from a TS: With the same SELcum, longer exposures require longer
durations to recover (e.g., Mooney et al. 2009b; Finneran et al. 2010a)
4) Recovery from a TS: Intermittent exposures recover faster compared to continuous
exposures of the same duration (e.g., Finneran et al. 2010b; Kastelein et al. 2014a;
Kastelein et al. 2015b)
III. Cumulative Exposure+:
General Trend Identified:
1) Animals may be exposed to multiple sound sources and stressors, beyond acoustics,
during an activity, with the possibility of the possibility of additive or synergistic
effects (e.g., Sih et al. 2004; Rohr et al. 2006; Chen et al. 2007; Lucke et al. 2016)
* Frequency-dependent hearing loss and overall hearing ability within a hearing group is taken into account,
quantitatively, with auditory weighting functions.

Note: NMFS is currently supporting a National Academies project entitled “Assessment of the Cumulative
Effects of Anthropogenic Stressors on Marine Mammals” to better address this issue
(https://www8.nationalacademies.org/cp/projectview.aspx?key=49715).
+

NOAA is also in the process of developing an agency Ocean Noise Strategy Roadmap, which includes
examining the acute, chronic, and cumulative effects of noise. (http://cetsound.noaa.gov/ons).

1.5.3

Possible Protective Mechanisms

Nachtigall and Supin (2013) recently reported that a false killer whale was able to reduce its
hearing sensitivity (i.e., conditioned dampening of hearing) when a loud sound was preceded
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by a warning signal. Nachtigall and Supin (2014) reported a similar finding in a bottlenose
dolphin and a beluga (Nachtigall et al. 2016a). Further studies showed that conditioning is
associated with the frequency of the warning signal (Nachtigall and Supin 2015), as well as if
an animal is able to anticipate when a loud sound is expected to occur after a warning signal
(Nachtigall et al. 2016b).
Additionally, Finneran et al. (2015) observed two of the three dolphins in their study
displayed “anticipatory” behavior (e.g., head movement) during an exposure sequence to
multiple airgun shots. It is unknown if this behavior resulted in some mitigating effects of
the exposure. Recently, Popov et al. (2016) investigated the impact of prolonged sound
stimuli (i.e., 1500 s continuous pip successions vs. 500-ms pip trains) on the beluga auditory
system and found that auditory adaptation occurred during exposure (i.e., decrease in
amplitude of rate following response associated with evoked potentials) at levels below
which TTS onset would likely be induced. The amount of amplitude reduction depended on
stimulus duration, with higher reductions occurring during prolonged stimulation. The
authors also caution that adaptation will vary with sound parameters.
In the wild, potential protective mechanisms have been observed, with synchronous
surfacing associated with exposure to playbacks of tactical sonar recorded in long-finned
pilot whales(Miller et al. 2012). However, it is unclear how effective this behavior is in
reducing received levels (Wensveen et al. 2015).
Thus, marine mammals may have multiple means of reducing or ameliorating the effects
noise exposure. However, at this point, directly incorporating them into a comprehensive
effects analysis that anticipates the likelihood of exposure ahead of an activity is difficult.
More information on these mechanisms, especially associated with real-world exposure
scenarios, would be useful.
1.5.4

Long-Term Consequences of Exposure

Kujawa and Liberman (2009) found that with large, but recoverable noise-induced
thresholds shifts (maximum 40 dB TS measured by auditory brainstem response (ABR)),
sound could cause delayed cochlear nerve degeneration in mice. Further, Lin et al. (2011)
reported a similar pattern of neural degeneration in mice after large but recoverable noiseinduced TSs (maximum ~50 dB TS measured by ABR), which suggests a common
phenomenon in all mammals. The long-term consequences of this degeneration remain
unclear.
Another study reported impaired auditory cortex function (i.e., behavioral and neural
discrimination of sound in the temporal domain (discriminate between pulse trains of
various repetition rates)) after sound exposure in rats that displayed no impairment in
hearing (Zhou and Merzenich 2012). Zheng (2012) found reorganization of the neural
networks in the primary auditory cortex (i.e., tonotopic map) of adult rats exposed to lowlevel noise, which suggests an adaptation to living in a noisy environment (e.g., noise
exposed rats performed tasks better in noisy environment compared to control rats).
Heeringa and van Dijk (2014) reported firing rates in the inferior colliculus of guinea pigs
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had a different recovery pattern compared to ABR thresholds. Thus, it is recommended that
there be additional studies to look at these potential effects in marine mammals (Tougaard et
al. 2015).
Finally, it is also important to understand how repeated exposures resulting in TTS could
potentially lead to PTS (e.g., Kastak et al. 2008; Reichmuth 2009). For example, occupational
noise standards, such as those from the Occupational Safety & Health Administration
(OSHA), consider the impact of noise exposure over a life-time of exposure (e.g., 29 CFR
Part 1926 over 40 years). Similar, longer-term considerations are needed for marine
mammals.
1.6

IMPACTS OF NOISE-INDUCED THRESHOLD SHIFTS ON FITNESS

When considering noise-induced thresholds shifts, it is important to understand that hearing
is more than merely the mechanical process of the ear and neural coding of sound
(detection). It also involves higher processing and integration with other stimuli (perception)
(Yost 2007; Alain and Berstein 2008). Currently, more is known about the aspects of neural
coding of sounds compared to the higher-level processing that occurs on an individual level.
Typically, effects of noise exposure resulting in energetic (Williams et al. 2006; Barber et al.
2010) and fitness consequences (increased mortality or decreased reproductive success) are
deemed to have the potential to affect a population/stock (NRC 2005; Southall et al. 2007;
SMRU Marine 2014) or as put by Gill et al. 2001 “From a conservation perspective, human
disturbance of wildlife is important only if it affects survival or fecundity and hence causes a
population to decline.” The number of individuals exposed and the location and duration of
exposure are important factors, as well. To determine whether a TS will result in a fitness
consequence requires one to consider several factors.
First, one has to consider the likelihood an individual would be exposed for a long enough
duration or to a high enough level to induce a TS (e.g., realistic exposure scenarios).
Richardson et al. (1995) hypothesized that “Disturbance effects are likely to cause most
marine mammals to avoid any ‘zone of discomfort or nonauditory effects’ that may exist”
and that “The greatest risk of immediate hearing damage might be if a powerful source were
turned on suddenly at full power while a mammal was nearby.” It is uncertain how
frequently individuals in the wild are experiencing situations where TSs are likely from
individual sources (Richardson et al.1995; Erbe and Farmer 2000; Erbe 2002; Holt 2008;
Mooney et al. 2009b).
In determining the severity of a TS, it is important to consider the magnitude of the TS, time
to recovery (seconds to minutes or hours to days), the frequency range of the exposure, the
frequency range of hearing and vocalization for the particular species (i.e., how animal uses
sound in the frequency range of anthropogenic noise exposure; e.g., Kastelein et al. 2014b),
and their overlap (e.g., spatial, temporal, and spectral). Richardson et al. (1995) noted, “To
evaluate the importance of this temporary impairment, it would be necessary to consider the
ways in which marine mammals use sound, and the consequences if access to this
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information were impaired.” Thus, exposure to an anthropogenic sound source, may affect
individuals and species differently (Sutherland 1996).
Finally, different degrees of hearing loss exist: ranging from slight/mild to moderate and
from severe to profound (Clark 1981), with profound loss being synonymous with deafness
(CDC 2004; WHO 2015). For hearing loss in humans, Miller (1974) summarized “any injury
to the ear or any change in hearing threshold level that places it outside the normal range
constitutes a hearing impairment. Whether a particular impairment constitutes a hearing
handicap or a hearing disability can only be judged in relation to an individual’s life pattern
or occupation.” This statement can translate to considering effects of hearing loss in marine
mammals, as well (i.e., substituting “occupation” for “fitness”).
Simply because a hearing impairment may be possible does not necessarily mean an
individual will experience a disability in terms of overall fitness consequence. However, there
needs to be a better understanding of the impacts of repeated exposures. As Kight and
Swaddle (2011) indicate “Perhaps the most important unanswered question in anthropogenic
noise research – and in anthropogenic disturbance research, in general – is how repeated
exposure over a lifetime cumulatively impacts an individual, both over the short- (e.g.
condition, survival) and long- (e.g., reproductive success) term.” Thus, more research is
needed to understand the true consequences of noise-induced TSs (acute and chronic) to
overall fitness.
1.7

BEHAVIOR OF MARINE MAMMALS UNDER EXPOSURE CONDITIONS WITH THE
POTENTIAL TO CAUSE HEARING IMPACTS

Although assessing the behavioral response of marine mammals to sound is outside the
scope of this document, understanding these reactions, especially in terms of exposure
conditions having the potential to cause NIHL is critical to be able to predict exposure
better. Understanding marine mammal responses to anthropogenic sound exposure presents
a set of unique challenges, which arise from the inherent complexity of behavioral reactions.
Responses can depend on numerous factors, including intrinsic, natural extrinsic (e.g., ice
cover, prey distribution), or anthropogenic , as well as the interplay among factors (Archer et
al. 2010). Behavioral reactions can vary not only among individuals but also within an
individual, depending on previous experience with a sound source, hearing sensitivity, sex,
age, reproductive status, geographic location, season, health, social behavior, or context.
Severity of behavioral responses can also vary depending on characteristics associated with
the sound source (e.g., whether it is moving or stationary, number of sound sources, distance
from the source) or the potential for the source and individuals to co-occur temporally and
spatially (e.g., persistence or recurrence of the sound in specific areas; how close to shore,
region where animals may be unable to avoid exposure, propagation characteristics that are
either enhancing or reducing exposure) (Richardson et al. 1995; NRC 2003; Wartzok et al.
2004; NRC 2005; Southall et al. 2007; Bejder et al. 2009).
Further, not all species or individuals react identically to anthropogenic sound exposure.
There may be certain species-specific behaviors (e.g., fight or flight responses; particularly
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behaviorally sensitive species) that make a species or individuals of that species more or less
likely to react to anthropogenic sound. Having this information would be useful in
improving the recommended accumulations period (i.e., 24 h) and understanding situations
where individuals are more likely to be exposed to noise over longer durations and are more
at risk for NIHL, either temporary or permanent.
1.8

CHARACTERISTICS OF SOUND ASSOCIATED WITH NIHL AND IMPACTS OF
PROPAGATION

It is known as sound propagates through the environment various physical characteristics
change (e.g., frequency content with lower frequencies typically propagating further than
higher frequencies; pulse length due to reverberation or multipath propagation in shallow
and deep water). Having a better understanding of the characteristics of a sound that makes
it injurious (e.g., peak pressure amplitude, rise time, pulse duration, etc.; Henderson and
Hamernik 1986; NIOSH 1998) and how those characteristics change under various
propagation conditions would be extremely helpful in the application of appropriate
thresholds and be useful in supporting a better understanding as to how sounds could
possess less injurious characteristics further from the source (e.g., transition range).
Further, validation and/or comparison of various propagation and exposure models for a
variety of sources would be useful to regulators, who with more complex acoustic thresholds
will be faced with evaluating the results from a multitude of models. This would also allow
for a more complete comparison to the methodologies provided in this Technical Guidance.
This would allow for a determination of how precautionary these methodologies are under
various scenarios and allow for potential refinement.
1.9

NOISE-INDUCED THRESHOLD SHIFT GROWTH RATES AND RECOVERY

TS growth rate data for marine mammals are limited, with higher growth rates for
frequencies where hearing is more sensitive (Finneran and Schlundt 2010; Finneran and
Schlundt 2013; Kastelein et al. 2015b). Understanding how these trends vary with exposure
to more complex sound sources (e.g., broadband impulsive sources) and among various
species would be valuable.
Understanding recovery after sound exposure is also an important consideration. Currently,
there is a lack of recovery data for marine mammals, especially for exposure to durations and
levels expected under real-world scenarios. Thus, additional marine mammal noise-induced
recovery data would be useful. A better understanding of likely exposure scenarios, including
the potential for recovery, including how long after noise exposure recovery is likely to
occur, could also improve the recommended baseline accumulation period.

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1.10

METRICS AND TERMINOLOGY

Sound can be described using a variety of metrics, with some being more appropriate for
certain sound types or effects compared with others (e.g., Coles et al. 1968; Hamernik et al.
2003; Madsen 2005; Davis et al. 2009; Zhu et al. 2009). A better understanding of the most
appropriate metrics for establishing acoustic thresholds and predicting impacts to hearing
would be useful in confirming the value of providing dual metric thresholds using the PK
and SELcum metrics for impulsive sources. As science advances, additional or more
appropriate metrics may be identified and further incorporated by NMFS. However, caution
is recommended when comparing sound descriptions in different metrics (i.e., they are not
directly comparable). Additionally, the practicality of measuring and applying metrics is
another important consideration.
Further, the Technical Guidance’s acoustic thresholds are based on the EEH, which is
known to be inaccurate in some situations. Recently, Popov et al. 2014 suggested that RMS
SPL multiplied by log duration better described their data than the EEH. Thus, better means
of describing the interaction between SPL and duration of exposure would be valuable.
Finally, in trying to define metrics and certain terms (e.g., impulsive and non-impulsive)
within the context of the Technical Guidance, NMFS often found difficulties due to lack of
universally accepted standards and common terminology. Within the Technical Guidance,
NMFS has tried to adopt terminology, definitions, symbols, and abbreviations that reflect
those of the American National Standards Institute (ANSI). However, none of these
standards are specific for underwater sound. 44 Thus, NMFS encourages the further
development of appropriate standards for marine application.
1.11

EFFECTIVE QUIET

“Effective quiet” is defined as the maximum sound pressure level that will fail to produce
any significant TS in hearing despite duration of exposure and amount of accumulation
(Ward et al. 1976; Ward 1991). Effective quiet can essentially be thought of as a “safe
exposure level” (i.e., risks for TS are extremely low or nonexistent) in terms of hearing loss 45
(Mills 1982; NRC 1993) and is frequency dependent (Ward et al. 1976; Mills 1982). Effective
quiet is an important consideration for the onset TTS and PTS acoustic thresholds expressed
by the SELcum metric because if not taken into consideration unrealistically low levels of
exposure with long enough exposure durations could accumulate to exceed current SELcum
acoustic thresholds, when the likelihood of an actual TS is extremely low (e.g., humans
exposed to continuous levels of normal speech levels throughout the day are not typically
subjected to TTS from this type of exposure).
44

NMFS is aware of a draft international standard addressing underwater acoustic terminology (ISO/DIS
18405) and will further examine this standard, once it becomes final.

Note: “Effective quiet” only applies to hearing loss and not to behavioral response (i.e., levels below
“effective quiet” could result in behavioral responses). It also is separate consideration from defining “quiet”
areas (NMFS 2009).
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Currently, defining effective quiet for marine mammals is not possible due to lack of data.
However, a recent study by Popov et al. 2014 on belugas exposed to half-octave noise
centered at 22.5 kHz indicates that effective quiet for this exposure scenario and species
might be around 154 dB. In Finneran’s (2015) recent review of NIHL in marine mammals,
effective quiet is predicted to vary by species (e.g., below 150 to 160 dB for bottlenose
dolphins and belugas; below 140 dB for Yangtze finless porpoise; 124 dB for harbor
porpoise; and 174 dB for California sea lions).
As more data become available, they would be useful in contributing to the better
understanding of appropriate accumulations periods for the SELcum metric and NIHL, as
well as the potential of low-level (e.g., Coping et al. 2014; Schuster et al. 2015), continuously
operating sources (e.g., alternative energy tidal, wave, or wind turbines) to induce noiseinduced hearing loss.
1.12

TRANSLATING BIOLOGICAL COMPLEXITY INTO PRACTICAL APPLICATION

Although, not a specific research recommendation, practical application of science is an
important consideration. As more is learned about the potential effects of sound on marine
mammals, the more complex future acoustic thresholds are likely to become. For example,
before this Technical Guidance, NMFS primarily relied on two generic thresholds for
assessing auditory impacts, with one for cetaceans (SPL RMS 180 dB) and one for pinnipeds
(SPL RMS 190 dB). In this document, these two simple thresholds have now been replaced
by ten PTS onset thresholds (with dual metrics for impulsive sounds), including the addition
of auditory weighting functions. Although, these updated acoustic thresholds better
represent the current state of knowledge, they have created additional challenges for
implementation. Practical application always needs to be weighed against making acoustic
thresholds overly complicated (cost vs. benefit considerations). The creation of tools to help
ensure complex thresholds are applied correctly by action proponents, as well as managers, is
a critical need.
Additionally, there is always a need for basic, practical acoustic training opportunities for
action proponents and managers (most acoustic classes available are for students within an
academic setting and not necessarily those who deal with acoustics in a more applied
manner). Having the background tools and knowledge to be able to implement the
Technical Guidance is critical to this document being a useful and effective tool in assessing
the effects of noise on marine mammal hearing.

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APPENDIX C:

PEER REVIEW PROCESS AND PUBLIC
COMMENT PERIOD

PEER REVIEW PROCESS

The President’s Office Management and Budget (OMB 2005) states, “Peer review is one of
the important procedures used to ensure that the quality of published information meets the
standards of the scientific and technical community. It is a form of deliberation involving an
exchange of judgments about the appropriateness of methods and the strength of the
author’s inferences. Peer review involves the review of a draft product for quality by
specialists in the field who were not involved in producing the draft.”
The peer review of this document was conducted in accordance with NOAA’s Information
Quality Guidelines 46 (IQG), which were designed for “ensuring and maximizing the quality,
objectivity, utility, and integrity of information disseminated by the agency” (with each of
these terms defined within the IQG). Further, the IQG stipulate that “To the degree that the
agency action is based on science, NOAA will use (a) the best available science and
supporting studies (including peer-reviewed science and supporting studies when available),
conducted in accordance with sound and objective scientific practices, and (b) data collected
by accepted methods or best available methods.” Under the IQG and in consistent with
OMB’s Final Information Quality Bulletin for Peer Review (OMB Peer Review Bulletin
(OMB 2005), the Technical Guidance was considered a Highly Influential Scientific
Assessments (HISA), 47 and peer review was required before it could be disseminated by the
Federal Government. OMB (2005) notes “Peer review should not be confused with public
comment and other stakeholder processes. The selection of participants in a peer review is
based on expertise, with due consideration of independence and conflict of interest.”
The peer review of the Technical Guidance consisted of three independent reviews covering
various aspects of the document: 1) There was an initial peer review of the entire draft
Guidance in 2013, 2) a second peer review in March/April 2015 that focused on newly
available science from the Finneran Technical Report (Finneran 2016; See Appendix A), and
3) a third peer review in April 2015 in response to public comments received during the
initial public comment period, which focused on a particular technical section relating to the
proposed application of impulsive and non-impulsive PTS acoustic thresholds based on
physical characteristics at the source and how those characteristics change with range. 48
46

http://www.cio.noaa.gov/services_programs/IQ_Guidelines_011812.html

“its dissemination could have a potential impact of more than $500 million in any one year on either the
public or private sector; or that the dissemination is novel, controversial, or precedent-setting; or that it has
significant interagency interest” (OMB 2005).

Note: Upon evaluation of public comment received during the Technical Guidance’s second public
comment period (July 2015), NMFS decided to postpone implementing this methodology until more data were
available to support its use.
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Upon completion of the three peer reviews, NMFS was required to post and respond to all
peer reviewer comments received via three separate Peer Review Reports.
1.1

INITIAL PEER REVIEW (ASSOCIATED WITH 2013 DRAFT GUIDANCE)

For the initial peer review of this document (July to September 2013), potential qualified
peer reviewers were nominated by a steering committee put together by the Marine Mammal
Commission (MMC). The steering committee consisted of MMC Commissioners and
members of the Committee of Scientific Advisors (Dr. Daryl Boness, Dr. Douglas Wartzok,
and Dr. Sue Moore).
Nominated peer reviewers were those with expertise marine mammalogy,
acoustics/bioacoustics, and/or acoustics in the marine environment. Of the ten nominated
reviewers, four volunteered, had no conflicts of interest, had the appropriate area of
expertise, 49 and were available to complete an individual review (Table C1). The focus of the
peer review was on the scientific/technical studies that have been applied and the manner
that they have been applied in this document.
Table C1:

Initial peer review panel.

Name
Affiliation
Dr. Paul Nachtigall University of Hawaii
Dr. Doug Nowacek Duke University
Dr. Klaus Lucke*
Wageningen University and Research (The Netherlands)
Dr. Aaron Thode
Scripps Institution of Oceanography
* Present affiliation: Curtin University (Australia)
Peer reviewers’ comments and NMFS’ responses to the comments, from this initial peer
review, can be found at: http://www.cio.noaa.gov/services_programs/prplans/ID43.html.
1.2

SECOND PEER REVIEW (REVIEW OF THE FINNERAN TECHNICAL REPORT)

For their Phase 3 Acoustic Effects Analysis, the U.S. Navy provided NMFS with a technical
report, by Dr. James Finneran, describing their proposed methodology for updating auditory
weighting functions and subsequent numeric thresholds for predicting auditory effects
(TTS/PTS thresholds) on marine animals exposed to active sonars, other (non-impulsive)
active acoustic sources, explosives, pile driving, and air guns utilized during Navy training
and testing activities.

Reviewer credentials are posted at: http://www.cio.noaa.gov/services_programs/prplans/ID43.html.

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Upon evaluation, NMFS preliminarily determined that the proposed methodology, within
the Finneran Technical Report (Finneran 2016), reflected the scientific literature and decided
to incorporate it into the Technical Guidance. Before doing so, we commissioned an
independent peer review of the Finneran Technical Report (i.e. second peer review). Note:
Reviewers were not asked to review the entire Technical Guidance document.
For the second peer review (March to April 2015), NMFS again requested the assistance of
the MMC to nominate peer reviewers. As with the initial peer review, potential qualified peer
reviewers were nominated by a steering committee put together by the MMC, which
consisted of MMC Commissioners and members of the Committee of Scientific Advisors
(Dr. Daryl Boness, Dr. Douglas Wartzok, and Dr. Sue Moore).
Nominated peer reviewers were those with expertise 50 specifically in marine mammal hearing
(i.e., behavior and/or AEP) and/or noise-induced hearing loss. Of the twelve nominated
reviewers, four volunteered, had not conflicts of interest, had the appropriate area of
expertise, and were available to complete an individual review of the Finneran Technical
Report (Table C2).
Table C2:

Second peer review panel.

Name
Affiliation
Dr. Whitlow Au
University of Hawaii
Dr. Colleen Le Prell
University of Florida*
Dr. Klaus Lucke
Curtin University (Australia)
Dr. Jack Terhune
University of New Brunswick (Canada)
* Affiliation during initial review (Affiliation during follow-up peer review: The University of Texas at Dallas)
Peer reviewers’ comments and NMFS’ responses to the comments, from the second peer
review, can be found at: http://www.cio.noaa.gov/services_programs/prplans/ID43.html.
1.2.1

Follow-Up to Second Peer Review

Concurrent with the Technical Guidance’s third public comment period (see Section 2.3 of
this appendix), a follow-up peer review was conducted. The focus of this peer review was
whether the 2016 Proposed Changes to the Technical Guidance, associated with the third
public comment period, would substantially change any of the peer reviewers’ comments
provided during their original review (i.e., peer reviewers were not asked to re-review the
Finneran Technical Report). Additionally, peer reviewers were not asked to comment on any
potential policy or legal implications of the application of the Technical Guidance, or on the

Reviewer credentials are posted at: http://www.cio.noaa.gov/services_programs/prplans/ID43.html.

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amount of uncertainty that is acceptable or the amount of precaution that should be
embedded in any regulatory analysis of impacts.
All four previous peer reviewers were available to perform the follow-up peer review. Peer
reviewers’ comments and NMFS’ responses to the comments, from this follow-up peer
review, can be found at: http://www.cio.noaa.gov/services_programs/prplans/ID43.html.
1.3

THIRD PEER REVIEW (REVIEW OF TRANSITION RANGE METHODOLOGY)

During the Technical Guidance’s initial public comment period, NMFS received numerous
comments relating to how the Technical Guidance classifies acoustic sources based on
characteristics at the source (i.e., non-impulsive vs. impulsive). Many expressed concern that
as sound propagates through the environment and eventually reaches a receiver (i.e., marine
mammal) that physical characteristics of the sound may change and that NMFS’
categorization may not be fully reflective of real-world scenarios. Thus, NMFS re-evaluated
its methodology for categorizing sound sources to reflect these concerns. Thus, a third peer
review focused on particular technical section relating to the Technical Guidance's proposed
application of impulsive and non-impulsive PTS acoustic thresholds based on physical
characteristics at the source and how those characteristics change with range (i.e., transition
range). Note: Reviewers were not asked to review the entire Technical Guidance document.
Since the focus of the third peer review was focused on the physical changes a sound
experiences as it propagates through the environment, the Acoustical Society of America’s
Underwater Technical Council was asked to nominate peer reviewers with expertise in
underwater sound propagation and physical characteristics of impulsive sources, especially
high explosives, seismic airguns, and/or impact pile drivers. Of the six nominated reviewers,
two volunteered, were available, had no conflicts of interest, and had the appropriate area of
expertise 51 to complete an individual review of the technical section (Table C3).
Additionally, NMFS wanted peer reviewers with expertise in marine and terrestrial mammal
noise-induced hearing loss to review this technical section and ensure the proposed
methodology was ground-truthed in current biological knowledge. Thus, NMFS re-evaluated
peer reviewer nominees previously made by the MMC for the first and second peer reviews.
From this list, two reviewers volunteered, were available, had no conflicts of interest, and
had the appropriate area of expertise to serve as peer reviewers (Table C3).

Reviewer credentials are posted at: http://www.cio.noaa.gov/services_programs/prplans/ID43.html.

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Table C3:

Third peer review panel.
Name
Affiliation
Dr. Robert Burkard
University at Buffalo
Dr. Peter Dahl*
University of Washington
+
Dr. Colleen Reichmuth
University of California Santa Cruz
Dr. Kevin Williams*
University of Washington
* Peer reviewers with expertise in underwater acoustic propagation
+ Dr. Reichmuth was an alternate on the MMC original peer reviewer nomination list

Peer reviewers’ comments and NMFS’ responses to the comments, from the third peer
review, can be found at: http://www.cio.noaa.gov/services_programs/prplans/ID43.html.
Note: In response to public comments made during the second public comment period,
NMFS decided to withdraw its proposed transition range methodology until more data can
be collected to better support this concept (i.e., see Appendix B: Research
Recommendations).
1.4

CONFLICT OF INTEREST DISCLOSURE

Each peer reviewer (i.e., initial, second, and third peer review) completed a conflict of
interest disclosure form. It is essential that peer reviewers of NMFS influential scientific
information (ISI) or HISA not be compromised by any significant conflict of interest. For
this purpose, the term “conflict of interest” means any financial or other interest which
conflicts with the service of the individual because it (1) could significantly impair the
individual's objectivity or (2) could create an unfair competitive advantage for any person or
organization. No individual can be appointed to review information subject to the OMB
Peer Review Bulletin if the individual has a conflict of interest that is relevant to the
functions to be performed.
The following website contains information on the peer review process including: the charge
to peer reviewers, peer reviewers’ names, peer reviewers’ individual reports, and NMFS’
response to peer reviewer reports:
http://www.cio.noaa.gov/services_programs/prplans/ID43.html.
II.

PUBLIC COMMENT PERIODS

In addition to the peer review process, NMFS recognizes the importance of feedback from
action proponents/stakeholders and other members of the public. The focus of the public
comment process was on both the technical aspects of the document, as well as the
implementation of the science in NMFS’ policy decisions under the various applicable
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statutes. The first two public comment periods were held after the peer review to ensure the
public received the most scientifically sound product for review and comment. A third
public focused comment period was held after incorporation of recommendations made by
NMFS and Navy scientists (SSC-PAC) during further evaluation of the Finneran Technical
Report after the second public comment period. During this third public comment period,
there was a concurrent follow-up peer review. See section 1.2.1 above.
2.1

INITIAL PUBLIC COMMENT PERIOD (ASSOCIATED WITH 2013 DRAFT
TECHNICAL GUIDANCE)

A public meeting/webinar was held to inform interested parties and solicit comments on the
first publicly available version of the Draft Technical Guidance. The meeting/webinar was
held on January 14, 2014, in the NOAA Science Center in Silver Spring, Maryland. The
presentation and transcript from this meeting is available electronically
(http://www.nmfs.noaa.gov/pr/acoustics/publicmeeting_transcript.pdf).
This public comment period was advertised via the Federal Register and originally lasted 30
days, opening on December 27, 2013 (NMFS 2013). During this 30-day period, multiple
groups requested that the public comment period be extended beyond 30 days. Thus, the
public comment period was extended an additional 45 days and closed on March 13, 2014
(NMFS 2014).
2.1.1

Summary of Public Comments Received

A total of 129 52 comments were received from individuals, groups, organizations, and
affiliations. Twenty-eight of these were in the form of a letter, spreadsheet, or individual
comment submitted by representatives of a group/organization/affiliation (some submitted
on behalf of an organization and/or as an individual). Those commenting included: 11
members of Congress; eight state/federal/international government agencies; two Alaskan
native groups; seven industry groups; five individual subject matter experts; a scientific
professional organization; 12 non-governmental organizations; an environmental consulting
firm; and a regulatory watchdog group. Each provided substantive comments addressing
technical aspects or issues relating to the implementation of updated acoustic thresholds,
which were addressed in the Final Technical Guidance or related Federal Register Notice. 53
Of those not mentioned above, an additional 101 comments were submitted in the form of a
letter or individual comment. Twelve of these comments specifically requested an extension
of the original 30-day public comment period (a 45-day extension to original public
52

Of this number, one comment was directed to the Federal Communications Commission (i.e., not meant for
the Technical Guidance) and one commenter submitted their comments twice. In addition, one comment was
not included in this total, nor posted because it contained threatening language.

With the updates made to the Technical Guidance as a result of the second and third peer reviews, some of
the comments made during the initial public comment period were no longer relevant and as such were not
addressed.

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comment period was granted). The remaining 89 comments were not directly applicable to
the Technical Guidance (e.g., general concern over impacts of noise on marine mammals
from various industry or military activities) and were not further addressed. Specific
comments can be viewed on Regulations.gov:
http://www.regulations.gov/#!docketDetail;D=NOAA-NMFS-2013-0177.
NMFS’ responses to substantive comments made during the initial public comment period
were published in the Federal Register located on the following web site in conjunction with
the Final Technical Guidance: http://www.nmfs.noaa.gov/pr/acoustics/guidelines.htm.
2.2

SECOND PUBLIC COMMENT PERIOD (ASSOCIATED WITH 2015 DRAFT
TECHNICAL GUIDANCE)

Because of the significant changes made to the Draft Technical Guidance from the two
additional peer reviews, NMFS proposed a second 45-day public comment, which occurred
in the summer of 2015. Notice of this public comment period was published in the Federal
Register on July 31, 2015, and closed September 14, 2015 (NMFS 2015).
2.2.1

Summary of Public Comments Received

A total of 20 comments were received from individuals, groups, organizations, and
affiliations in the form of a letter or individual comment submitted by representatives of a
group/organization/affiliation (some submitted on behalf of an organization and/or as an
individual). Those commenting included: two federal agencies; four industry groups; seven
subject matter experts; a scientific professional organization; seven non-governmental
organizations; two Alaskan native groups; an environmental consulting firm; and a regulatory
watchdog group. Each provided substantive comments addressing technical aspects and/or
issues relating to the implementation of updated acoustic thresholds, which were addressed
in the Final Technical Guidance or related Federal Register Notice.
Of those not mentioned above, an additional four comments were submitted in the form of
a letter or individual comment. One of these comments specifically requested an extension
of the 45-day public comment period, while the remaining three comments were not directly
applicable to the Technical Guidance (e.g., general concern over impacts of noise on marine
mammals from various industry or military activities) and were not further addressed.
Specific comments can be viewed on Regulations.gov:
http://www.regulations.gov/#!docketDetail;D=NOAA-NMFS-2013-0177.
NMFS responses to substantive comments made during the second public comment period
were published in the Federal Register located on the following web site in conjunction with
the Final Technical Guidance: http://www.nmfs.noaa.gov/pr/acoustics/guidelines.htm.

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2.3

THIRD PUBLIC COMMENT PERIOD (ASSOCIATED WITH 2016 PROPOSED
CHANGES FROM DRAFT TECHNICAL GUIDANCE) 54

While NMFS was working to address public comments and finalize the Technical Guidance,
after the second public comment period, the Finneran Technical Report was further
evaluated internally by NMFS, as well as externally by Navy scientists (SSC-PAC). As a
result, several recommendations/modifications were suggested.
The recommendations included:
• Modification of methodology to establish predicted the composite audiogram and
weighting/exposure functions for LF cetaceans
•

Modification of the methodology used to establish auditory acoustic thresholds for
LF cetaceans

•

Movement of the white-beaked dolphin (Lagenorhynchus albirostris) from MF to HF
cetaceans 55

•

Inclusion of a newly published harbor porpoise audiogram (HF cetacean) from
Kastelein et al. 2015c

•

The exclusion of multiple data sets, based on expert evaluation, from the phocid
pinniped weighting function

•

Removal of PK acoustic thresholds for non-impulsive sounds

•

Use of dynamic range to predict PK acoustic thresholds for hearing groups where
impulsive data did not exist.

After consideration of these recommendations, NMFS proposed to update the Draft
Technical Guidance to reflect these suggested changes and solicited public comment on the
revised sections of the document via a focused 14-day public comment period. This public
comment period was advertised via the Federal Register and opened on March 16, 2016, and
closed March 30, 2016 (NMFS 2016).

Concurrent with this third public comment period, NMFS requested that the peer reviewers of the Finneran
Technical Report review the Draft Technical Guidance’s proposed changes and indicate if the revisions would
significantly alter any of the comments made during their original review (i.e., follow-up to second peer review).
55

Upon re-evaluation and considering comments made during the third public comment period, it was
decided this move was not fully supported (i.e., move not supported to the level of that of the other two
species in this family). Thus, this species remains a MF cetacean.
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2.3.1

Summary of Public Comments Received

A total of 20 56 comments were received from individuals, groups, organizations, and
affiliations in the form of a letter or individual comment submitted by representatives of a
group/organization/affiliation (some submitted on behalf of an organization and/or as an
individual). Those commenting included: two federal agencies; seven industry groups; three
subject matter experts; a scientific professional organization; and nine non-governmental
organizations. Each provided substantive comments addressing technical aspects and/or
issues relating to the implementation of updated acoustic thresholds, which were addressed
in the Final Technical Guidance or related Federal Register Notice.
Of those not mentioned above, an additional comment was submitted from a member of
the public in the form of an individual comment. Three of these comments specifically
requested an extension 57 of the 14-day public comment period. Specific comments can be
viewed on Regulations.gov: http://www.regulations.gov/#!docketDetail;D=NOAA-NMFS2013-0177.
NMFS responses to substantive comments made during the third public comment period
were published in the Federal Register located on the following web site in conjunction with
the Final Technical Guidance: http://www.nmfs.noaa.gov/pr/acoustics/guidelines.htm.
2.4

CHANGES TO TECHNICAL GUIDANCE AS A RESULT OF PUBLIC COMMENTS

Public comment provided NMFS with valuable input during the development of the
Technical Guidance. As a result of public comments, numerous changes were incorporated
in the Final Technical Guidance, with the most significant being:
•

Re-examination and consideration of LF weighting function and thresholds
throughout the public comment process

•

Updated methodology (dynamic range) for approximating PK acoustic thresholds
for species where TTS data from impulsive sources were not available

•

Removal of PK acoustic thresholds for non-impulsive sources

•

Addition of an appendix providing research recommendations

•

Adoption of a consistent accumulation period (24-h)

One group of commenters experienced difficulty in submitting their public comments via regulations.gov.
As a result, their duplicate comments were submitted three times and were counted toward this total of 20
public comments.
57

The majority of the 20 comments received requested an extension of the public comment period. Three
comments were from industry groups that only requested an extension and never provided additional
comments (i.e., others in additional to requesting an extension provided substantive comments).
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•

More consistent means of defining generalized hearing range for each marine
mammal hearing group based on ~65 dB threshold from the normalized composite
audiogram.

•

Modification to reflect ANSI standard symbols and abbreviations.

•

Withdraw of the proposed transition range methodology (July 2015 Draft) until
more data can be collected to better support this concept. Instead, this concept has
been moved to the Research Recommendations (Appendix B).

•

Replacement of alternative acoustic thresholds with weighting factor adjustments
(WFAs) that more accurately allow those incapable of fully implementing the
auditory weighting functions to implement this concept (Technical Guidance;
Appendix D).

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APPENDIX D:
I.

ALTERNATIVE METHODOLOGY

INTRODUCTION

This Appendix is provided to assist action proponents in the application of the updated
acoustic thresholds presented in this Technical Guidance. Since the adoption of NMFS’
original thresholds for assessing auditory impacts, the understanding of the effects of noise
on marine mammal hearing has greatly advanced (e.g., Southall et al. 2007; Finneran 2015;
Finneran 2016) making it necessary to re-examine the current state of science and our
acoustic thresholds. However, NMFS recognizes in updating our acoustic thresholds to
reflect the scientific literature, they have become more complex.
This Appendix provides a set of alternative tools, examples, and weighting factor
adjustments (WFAs) to allow action proponents with different levels of exposure modeling
capabilities to be able to accurately apply NMFS’ updated acoustic thresholds for the onset
of PTS for all sound sources.
Note: The alternative methods, within this Appendix, include multiple conservative
assumptions and therefore would be expected to typically result in higher estimates of
instances of hearing impairment. The larger the scale of the activity, the more these
conservative overestimates would be compounded if the alternative methodologies were
used.
II.

WEIGHTING FACTOR ADJUSTMENT ASSOCIATED WITH SELCUM
ACOUSTIC THRESHOLDS

Numerical criteria presented in the Technical Guidance consist of both an acoustic threshold
and auditory weighting function associated with the SELcum metric. NMFS recognizes that
the implementation of marine mammal weighting functions represents a new factor for
consideration, which may extend beyond the capabilities of some action proponents. Thus,
NMFS has developed simple weighting factor adjustments (WFA) for those who cannot
fully apply auditory weighting functions associated with the SELcum metric.
WFAs consider marine mammal auditory weighting functions by focusing on a single
frequency. This will typically result in similar, if not identical, predicted exposures for
narrowband sounds or higher predicted exposures for broadband sounds, since only one
frequency is being considered, compared to exposures associated with the ability to fully
incorporate the Technical Guidance’s weighting functions.
WFAs use the same acoustic thresholds contained in the Technical Guidance and allow for
adjustments to be made for each hearing group based on source-specific information.

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NMFS has provided a companion User Spreadsheet to help action proponents incorporate
WFAs to determine isopleths for PTS onset associated with their activity:
http://www.nmfs.noaa.gov/pr/acoustics/guidelines.htm.
2.1

APPLICATION FOR NARROWBAND SOUNDS

For narrowband sources, the selection of the appropriate frequency for consideration
associated with WFAs is fairly straightforward. WFAs for a narrowband sound would take
the weighting function amplitude, for each hearing group, associated with the particular
frequency of interest and use it to make an adjustment to better reflect the hearing’s group
susceptibility to that narrowband sound.
As an example, a 1 kHz narrowband sound would result in the following WFAs:
•
•
•
•
•

LF cetaceans: -0.06 dB
MF cetaceans: -29.11 dB
HF cetaceans: -37.55 dB
Phocid pinnipeds: -5.90 dB
Otariid pinnipeds: -4.87 dB

As this example illustrates, WFAs always result in zero or a negative dB amplitude.
Additionally, the more a sound’s frequency is outside a hearing group’s most susceptible
range (most susceptible range is where the weighting function amplitude equal zero), the
more negative WFA that results (i.e., in example above 1 kHz is outside the most susceptible
range for MF and HF cetaceans but in the most susceptible range for LF cetaceans; Figure
D1). Further, the more negative WFA that results will lead to a smaller effect distance
(isopleth) compared to a less negative or zero WFA. In other words, considering an identical
SELcum acoustic threshold, a more negative WFA (i.e., source outside most susceptible
frequency range) will result in a smaller effect distance (isopleth) compared to one that is less
negative or closer to zero (i.e., source inside most susceptible frequency range; Figure D2).
Note: Action proponents should be aware and consider that sources may not always adhere
to manufacturer specifications and only produce sound within the specified frequency (i.e.,
often sources are capable of producing sounds, like harmonics and subharmonics, outside
their specified bands; Deng et al. 2014; Hastie et al. 2014). If it is unclear whether a source is
narrowband or not, please consult with NMFS.

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Figure D1:

Example illustrating concept of weighting factor adjustment at 1 kHz
(red line) with cetacean (top) and pinniped (bottom) auditory
weighting functions.

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Figure D2:

2.2

Simple example illustrating concept of weighting factor adjustment on
isopleths for LF and MF cetaceans using hypothetical 1 kHz
narrowband, intermittent source represented by the red dot (RMS
source level of 200 dB; 1-second ping every 2 minutes). For a nonimpulsive source, the PTS onset SELcum threshold for LF cetaceans is
199 dB, while for MF cetaceans is 198 dB. Despite LF cetaceans having
a higher PTS onset threshold than MF cetaceans, the isopleth
associated with LF cetaceans (30 m solid purple circle) is larger than
that for MF cetaceans (1.2 m dashed green circle) based on 1 kHz
being within LF cetacean’s most susceptible frequency range vs.
outside the most susceptible frequency range for MF cetaceans
(isopleths not to scale).

APPLICATION FOR BROADBAND SOUNDS

For broadband sources, the selection of the appropriate frequency for consideration
associated with WFAs is more complicated. The selection of WFAs associated with
broadband sources is similar to the concept used for to determine the 90% total cumulative
energy window (5 to 95%) for consideration of duration associated with the RMS metric and
impulsive sounds (Madsen 2005) but considered in the frequency domain, rather than the
time domain. This is typically referred to as the 95% frequency contour percentile (Upper
frequency below which 95% of total cumulative energy is contained; Charif et al. 2010).
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NMFS recognizes the consideration of WFAs may be new for action proponents and have
provided representative “default” values for various broadband sources (see associated User
Spreadsheet).
2.2.1

Special Considerations for Broadband Source

Since the intent of WFAs is to broadly account for auditory weighting functions below the
95% frequency contour percentile, it is important that only frequencies on the “left side” of
the weighting function be used to make adjustments (i.e., frequencies below those where the
weighting function amplitude is zero 58 or below where the function is essentially flat;
resulting in every frequency below the WFA always having a more negative amplitude than
the chosen WFA) (Figure D3). It is inappropriate to use WFAs for frequencies on the “right
side” of the weighting function (i.e., frequencies above those where the weighting function
amplitude is zero). For a frequency on the “right side” of the weighting function (Table D1),
any adjustment is inappropriate and WFAs cannot be used (i.e., an action proponent would
be advised to not use weighting functions and evaluate its source as essentially unweighted;
see “Use” frequencies in Table D1, which will result in a weighting function amplitude of 0
dB).
Table D1:

Applicability of weighting factor adjustments for frequencies
associated with broadband sounds

Hearing Group

Applicable Frequencies

Non-Applicable
Frequencies*
Above 4.8 kHz (Use: 1.7 kHz)

Low-Frequency Cetaceans
4.8 kHz and lower
(LF)
Mid-Frequency Cetaceans
43 kHz and lower
Above 43 kHz (Use: 28 kHz)
(MF)
High-Frequency Cetaceans
59 kHz and lower
Above 59 kHz (Use: 42 kHz)
(HF)
Phocid Pinnipeds (PW)
11 kHz and lower
Above 11 kHz (Use: 6.2 kHz)
Otariid Pinnipeds (OW)
8.5 kHz and lower
Above 8.5 kHz (Use: 4.9 kHz)
* With non-applicable frequencies, user should input the “use” frequency in the User Spreadsheet, which will
result in a weighting function amplitude of 0 dB (i.e., unweighted).

A criteria of a -0.4 dB weighting function amplitude from the Technical Guidance’s auditory weighting
function was used to determine the demarcation between appropriate and inappropriate frequencies to use the
WFAs.
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Figure D3:

III.

Example weighting function illustrating where the use of weighting
function adjustments are (Green: “left side”) and are not (Red: “right
side”) appropriate for broadband sources.

MODELING CUMULATIVE SOUND EXPOSURE LEVELS

To apply the PTS onset auditory acoustic thresholds expressed as the SELcum metric,
accumulation time must be specified. Generally, it is predicted that most receivers will
minimize their time in the closest ranges to a sound source/activity and that exposures at
the closest point of approach are the primary exposures contributing to a receiver’s
accumulated level (Gedamke et al. 2011). Additionally, several important factors determine
the likelihood and duration of time a receiver is expected to be in close proximity to a sound
source (i.e., overlap in space and time between the source and receiver). For example,
accumulation time for fast moving (relative to the receiver), mobile source, is driven
primarily by the characteristics of source (i.e., transit speed, duty cycle). Conversely, for
stationary sources, accumulation time is driven primarily by the characteristics of the receiver
(i.e., swim speed and whether species is transient or resident to the area where the activity is
occurring). For all sources, NMFS recommends a baseline accumulation period of 24-h, but
acknowledges that there may be specific exposure situations where this accumulation period

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requires an adjustment (e.g., if activity lasts less than 24 hours or for situations where
receivers are predicted to experience unusually long exposure durations 59).
Previous NMFS acoustic thresholds only accounted for the proximity of the sound source to
the receiver, but acoustic thresholds in the Technical Guidance (i.e., expressed as SELcum)
now take into account the duration of exposure. NMFS recognizes that accounting for
duration of exposure, although supported by the science literature, adds a new factor, as far
as the application of this metric to real-world activities and that all action proponents may
not have the ability to easily incorporate this additional component. NMFS does not provide
specifications necessary to perform exposure modeling and relies on the action proponent to
determine the model that best represents their activity.
3.1

MORE SOPHISTICATED MODELS

Because of the time component associated with the SELcum metric, the use of different types
of models to predict sound exposure may necessitate different approaches in evaluating
likely effects in the context of the PTS onset acoustic thresholds. All marine mammals and
some sources move in space and time, however, not all models are able to simulate relative
source and receiver movement. Additionally, some models are able to predict the received
level of sound at each modeled animal (often called animats) and accumulate sound at these
receivers while incorporating the changing model environment.
Models that are more sophisticated may allow for the inclusion of added details to achieve
more realistic results based on the accumulation of sound (e.g. information on residence
time of individuals, swim speeds for transient species, or specific times when activity
temporarily ceases). Alternatively, there may be case-specific circumstances where the
accumulation time should be modified to account for situations where animals are expected
to be in closer proximity to the source over a significantly longer amount of time, based on
activity, site, and species-specific information (e.g., where a resident population could be
found in a small and/or confined area (Ferguson et al. 2015) and a long-duration activity
with a large sound source, or a continuous stationery activity nearby a pinniped pupping
beach).
3.2

LESS SOPHISTICATED MODELS

For action proponents unable to incorporate animal and/or source movement, it may not be
realistic to assume that animals will remain at a constant distance from the source
accumulating acoustic energy for 24 hours. Thus, alternative methods are needed, which can
provide a distance from the source where exposure exceeding a threshold is expected to
occur and can be used in the same manner as distance has been used to calculate exposures

For example, where a resident population could be found in a small and/or confined area (Ferguson et al.
2015) and/or exposed to a long-duration activity with a large sound source, or there could be a continuous
stationery activity nearby an area where marine mammals congregate, like a pinniped pupping beach.
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above previous NMFS thresholds. NMFS proposes two alternative methods: one for mobile
sources and one for stationary sources.
3.2.1

Mobile Sources 60

3.2.1.1 Linear Equivalents Used in Appendix
In underwater acoustics, equations/derivations are typically expressed in terms of
logarithmic terms (i.e., levels). These equations can be further simplified by introducing
linear equivalents of the levels (i.e., factors) related by multiplication instead of by addition.
For example, source level 61 (SL) is replaced by the “source factor” 10SL/(10 dB) (Ainslie 2010).
In this appendix, the following linear equivalents are used:
•
•
•
•

Sound exposure (E) = 10SEL/(10 dB) μPa2s
���2 ) = 10SPL/(10 dB) μPa2
Mean-square sound pressure (𝑝𝑝
Source factor (S) = 10SL/(10 dB) μPa2m2
Energy source factor 62 (SE) = 10SL𝐸𝐸 /(10 dB) μPa2 m2s

Both source level and energy source level (and their corresponding factors) are evaluated and
reported in the direction producing the maximum SL.
3.2.1.2 “Safe Distance” Methodology
Cumulative sound exposure can be computed using a simple equation, assuming a constant
received sound pressure level (SPL) that does not change over space and time 63 (Equation
E1.; e.g., Urick 1983; ANSI 1986; Madsen 2005):
60

The methodology for mobile sources presented in this Appendix underwent peer review via the publication
process (Sivle et al. 2014) but did not undergo a separate peer review. It is an optional tool for the application
of the acoustic thresholds presented in the Technical Guidance.
61

For definition of SL, see Ainslie 2010. SL ≡ 10log10 [p(s)2s2 /(1 μPa2 m2)] dB (Ainslie writes this as SL ≡
10log10 p2s2 dB re 1 μPa2s m2.) For a point source, s is a small distance from the source, where distortions due
to absorption, refraction, reflection, or diffraction are negligible and p(s) is the RMS sound pressure at that
distance. For a large (i.e., finite) source, p is the hypothetical sound pressure that would exist at distance s from a
point source with the same far-field radiant intensity as the true source. For further clarification see ISO 18405
Underwater Acoustics - Terminology, entry 2.3.2.1 “source level.”
62

For definition of SLE, see Ainslie 2010. SLE ≡ 10log10 [E(s)s2 /(1 µPa2 m2 s)] dB (Ainslie writes this as SLE
≡10 log10 E (s)s2 dB 1 μPa2 m2s). For a point source, s is a small distance from the source, where distortions
due to absorption, refraction, reflection, or diffraction are negligible and E(s) is the unweighted sound exposure
at that distance. For a large (i.e., finite) source, E is the hypothetical sound exposure that would exist at distance
s from a point source with the same duration and far-field radiant intensity as the true source. For further
clarification see ISO 18405 Underwater Acoustics - Terminology, entry 2.3.2.2 “energy source level.”
63

Equation D1 assumes a constant source-receiver separation distance.

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SELcum = SPL + 10 log10 (duration of exposure, expressed in seconds) dB
Equation D1

However, if one assumes a stationary receiver and a source moving at a constant speed in a
constant direction, then exposure changes over space and time (i.e., greatest rate of
accumulation at closest point of approach).
An alternative approach for modeling moving sources is the concept of a “safe distance”
(R0), which is defined by Sivle et al. (2014) as “the distance from the source beyond which a
threshold 64 for that metric (SPL0 or SEL0) is not exceeded.” This concept allows one to
determine at what distance from a source a receiver would have to remain in order not to
exceed a predetermined exposure threshold (i.e., 𝐸𝐸0 which equals the weighted SELcum PTS
onset threshold in this Technical Guidance) and is further illustrated in Figure D4.

The threshold considered by Sivle et al. 2014 was associated with behavioral reactions.

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Figure D4:

Illustration of the concept for mobile sources, with each red dot
representing the source traveling over time. As the source travels
further from the receiver, the source-receiver separation increases (i.e.,
hypotenuse gets longer).

This methodology accounts for several factors, including source level, duty cycle, and transit
speed of the source and is independent of exposure duration (Equations D2a 65,b).

This equation matches Equation 3 from Sivle et al. (2014), but is written in a simpler manner.

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𝑅𝑅0 =

π
𝑆𝑆𝑆𝑆
𝐸𝐸0 𝑣𝑣
OR

Equations D2a,b

For impulsive sources, SD is replaced with SE/τ:
b
π 𝑆𝑆𝐸𝐸
𝑅𝑅0 =
𝐸𝐸0 𝑣𝑣 𝜏𝜏
where:

S = source factor (10SL/(10 dB) µPa2 m2)
D =duty cycle (pulse duration x repetition rate)
𝑣𝑣= transit speed
E0 =exposure threshold (10SEL0 /(10 dB) ) µPa2 s)
SE = energy source factor (10SL𝐸𝐸 /(10 dB) µPa2 m2 s)
τ = 1/repetition rate

R0 represents the exposure isopleth calculated using NMFS’ acoustic thresholds. Thus, area
calculations and exposure calculations would be performed in the same manner 66 action
proponents have previously used (e.g., determine area covered over a 24-h period multiplied
by the density of a marine mammal species).
This approach considers four factors:
1. Source level (direct relationship: as source level increases, so does R0; higher source
level results is a greater accumulation of energy).

2. Duty cycle (direct relationship: as duty cycle increases, so does R0; higher duty cycle
results in more energy within a unit of time and leads a greater accumulation of
energy).
3. Source transit speed (inverse relationship: as transit speed decreases, R0 increases or
vice versa; a faster transit speed results in less energy within a unit of time and leads
to a lower accumulation of energy, while a slower transit speed will result in a greater
accumulation of energy).
66

Note: “Take” calculations are typically based on speed expressed in kilometers per hour, duration of an
exposure expressed in hours (i.e., 24 hours), isopleths expressed in kilometers, and animal density expresses as
animals per square kilometers. Thus, units would need to be converted to use Equations D2a,b.
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4. Exposure threshold (inverse relationship: as the exposure threshold decreases, R0
increases or vice versa; a higher exposure threshold result in needing more energy to
exceed it compared to a lower threshold).
The action proponent is responsible for providing information on factors one through three
above, while factor four is the updated PTS onset acoustic threshold (expressed as SELcum
metric) provided within the Technical Guidance.
For this approach to be applicable to a broad range of activities, the following assumptions 67
must be made:
•

Action proponents that are unable to apply full auditory weighting functions will rely
on WFAs. This will create larger isopleths, for broadband sources, compared to
action proponents capable of fully applying auditory weighting functions.

•

The movement of the source is simple (i.e., source moves at a constant speed and in
a constant direction). Caution should be applied if the source has the potential to
move in a manner where the same group of receivers could be exposed to multiple
passes from the source.

•

Minimal assumptions are made about the receivers. They are considered stationary
and assumed to not move up or down within the water column. There is no
avoidance and the receiver accumulates sound via one pass of the source (i.e.,
receiver is not exposed to multiple passes from the source). Because this
methodology only examines one pass of the source relative to receiver, this method
is essentially time-independent (i.e., action proponent does not need to specify how
long an activity occurs within a 24-h period).
o These assumptions are appropriate for sources that are expected to move
much faster than the receiver does. Further, assuming receivers do not avoid
the source or change position vertically or horizontally in the water column
will result in more exposures exceeding the acoustic thresholds compared to
those receivers that would avoid or naturally change positions in the water
column over time. Caution should be applied if the receiver has the potential
to follow or move with the sound source.

•

Distance (i.e., velocity x change over time) between “pulses” for intermittent sources
is small compared with R0, and the distance between “pulses” for intermittent
sources is consistent. This assumption is appropriate for intermittent sources with a

If any of these assumptions are violated and there is concern that the isopleth produced is potentially
underestimated, action proponents should contact NMFS to see if any there are any appropriate adjustments
that can be made (e.g., addition of a buffer, etc.). If not, the action proponent is advised to pursue other
methodology capable of more accurately modeling exposure.
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predictable duty cycle. If the duty cycle decreases,R0 will become larger, while if the
duty cycle increases, it will become smaller. Further, for intermittent sources, it is
assumed there is no recovery in hearing threshold between pulses.
•

Sound propagation is simple (i.e., approach uses spherical spreading 68: 20 log R, with
no absorption). NMFS recognizes that this might not be appropriate for all activities,
especially those occurring in shallow water (i.e., sound could propagate further than
predicted by this model) 69. Thus, modifications to theR0 predicted may be necessary
in these situations.

Despite these assumptions, this approach offers a better approximation of the sourcereceiver distance over space and time for various mobile sources than choosing a set
accumulation period for all sources, which assumes a fixed source-receiver distance over that
time.
Ainslie and Von Benda-Beckmann (2013) investigated the effect various factors had on the
derivation of R0 and found exposures were highest for stationary receivers in the path of a
source, compared to mobile receivers swimming away from the source. However, the
authors did acknowledge, if the receivers actively swam toward the source, cumulative
exposure would increase. Uncertainty associated with R0 was found to be primarily driven
by the exposure threshold (i.e., Technical Guidance’s acoustic thresholds). Increasing duty
cycle of the source or reducing speed (either source or receiver) will result in an increased R0
(Sivle et al. 2014)
NMFS has provided a companion User Spreadsheet to help action proponents use this
methodology to determine isopleths for PTS onset associated with their activity
(http://www.nmfs.noaa.gov/pr/acoustics/guidelines.htm).

Note: NMFS’ alternative methods apply only to acoustic thresholds in the SELcum metric.
NMFS assumes action proponents will be able to perform exposure modeling using acoustic
thresholds expressed using the PK metric (i.e., methodology is similar to that used with
NMFS previous thresholds but with a different metric), and reminds action proponents
since the Technical Guidance presents dual thresholds for impulsive sounds, they must
evaluate thresholds using both metrics.

Assuming spherical spreading allows for Equations D2a,b to remain simplified (i.e., assuming another
spreading model results in more complicated equations that are no longer user-friendly nor as easy to
implement).
69

Note: Many moving sources, like seismic airguns or sonar, can be highly-directional (i.e., most of time sound
source is directed to the ocean floor, with less sound propagating horizontally, compared to the vertical
direction), which is not accounted for with this methodology. Additionally, many higher-frequency sounds, like
sonar, are also attenuated by absorption, which is also taken into account in this model. These, among other
factors, should be considered when evaluating whether spherical spreading is potentially resulting in an
underestimation of exposure.
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3.2.2

Stationary Sources

If there is enough information to accurately predict the travel speed of a receiver past a
stationary sound source (including the assumption that the receiver swims on a straight
trajectory past the source), then the mobile source approach can be modified for stationary
sources (i.e., transit speed of the source is replaced by speed of the receiver). However,
NMFS acknowledges that characteristics of the receiver are less predictable compared to
those of the source (i.e., velocity and travel path), which is why the mobile source approach
may not be appropriate for stationary sources and an alternate method is provided below.
An alternative approach is to calculate the accumulated isopleth associated with a stationary
sound source within a 24-h period. For example, if vibratory pile driving was expected to
occur over ten hours within a 24-h period, then the isopleth would be calculated by adding
area with each second the source is producing sound. This is a highly conservative means of
calculating an isopleth because it assumes that animals on the edge of the isopleth (in order
to exceed a threshold) will remain there for the entire time of the activity.
For stationary, impulsive sources with high source levels (i.e., impulsive pile driving
associated with large piles, stationary airguns associated with vertical seismic profiling
(VSPs), and large explosives) accumulating over a 24-h period, depending on how many
strikes or shots occur, could lead to unrealistically large isopleths associated with PTS onset.
For these situations, action proponents should contact NMFS for possible applicable
alternative methods.
NMFS has provided a companion User Spreadsheet to help action proponents wanting to
use this methodology to determine isopleths for PTS onset associated with their activity
(http://www.nmfs.noaa.gov/pr/acoustics/guidelines.htm).
Note: NMFS’ alternative methods apply only to acoustic thresholds in the SELcum metric.
NMFS assumes action proponents will be able to perform exposure modeling using acoustic
thresholds expressed using the PK metric (i.e., methodology is similar to that used with
NMFS previous thresholds but with a different metric) and reminds action proponents since
the Technical Guidance presents dual thresholds for impulsive sounds, they must evaluate
thresholds using both metrics.

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APPENDIX E:

GLOSSARY

95% Frequency contour percentile: Upper frequency below which 95% of total
cumulative energy is contained (Charif et al. 2010).
Accumulation period: The amount of time a sound accumulates for the SELcum metric.
Acoustic threshold: An acoustic threshold in this document identifies the level of sound,
after which exceeded, NMFS anticipates a change in auditory sensitivity (temporary or
permanent threshold shift).
Ambient noise: All-encompassing sound at a given place, usually a composite of sound
from many sources near and far (ANSI 1994).
Animat: A simulated marine mammal.
Anthropogenic: Originating (caused or produced by) from human activity.
Audible: Heard or capable of being heard. Audibility of sounds depends on level, frequency
content, and can be reduced in the presence of other sounds (Morfey 2001)
Audiogram: A graph depicting hearing threshold as a function of frequency (ANSI 1995;
Yost 2007) (Figure E1).

Figure E1.

Example audiogram.

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Auditory adaptation: Temporary decrease in hearing sensitivity occurring during the
presentation of an acoustic stimulus (opposed to auditory fatigue which occurs poststimulation) (ANSI 1995).
Auditory bulla: The ear bone in odontocetes that houses the middle ear structure (Perrin et
al. 2009).
Auditory weighting function: Auditory weighting functions take into account what is
known about marine mammal hearing sensitivity and susceptibility to noise-induced hearing
loss and can be applied to a sound-level measurement to account for frequency-dependent
hearing (i.e.,. an expression of relative loudness as perceived by the ear)(Southall et al. 2007;
Finneran 2016). Similar to OSHA (2013), marine mammal auditory weighting functions in
this document are used to reflect the risk of noise exposure on hearing and not necessarily
capture the most sensitive hearing range of every member of the hearing group.
Background noise: Total of all sources of interference in a system used for the production,
detection, measurement, or recording of a signal, independent of the presence of the signal
(ANSI 2013).
Band-pass filter: A filter that passes frequencies within a defined range without reducing
amplitude and attenuates frequencies outside that defined range (Yost 2007).
Bandwidth: Bandwidth (Hz or kHz) is the range of frequencies over which a sound occurs
or upper and lower limits of frequency band(ANSI 2005). Broadband refers to a source that
produces sound over a broad range of frequencies (for example, seismic airguns), while
narrowband or tonal sources produce sounds over a more narrow frequency range, typically
with a spectrum having a localized a peak in amplitude (for example, sonar) (ANSI 1986;
ANSI 2005).
Bone conduction: Transmission of sound to the inner ear primarily by means of
mechanical vibration of the cranial bones (ANSI 1995).
Broadband: See “bandwidth”.
Cetacean: Any number of the order Cetacea of aquatic, mostly marine mammals that
includes whales, dolphins, porpoises, and related forms; among other attributes they have a
long tail that ends in two transverse flukes (Perrin et al. 2009).
Cochlea: Spirally coiled, tapered cavity within the temporal bone, which contains the
receptor organs essential to hearing (ANSI 1995). For cetaceans, based on cochlear
measurements two cochlea types have been described for echolocating odontocetes (type I
and II) and one cochlea type for mysticetes (type M). Cochlea type I is found in species like
the harbor porpoise and Amazon river dolphin, which produce high-frequency echolocation
signals. Cochlea type II is found in species producing lower frequency echolocation signals
(Ketten 1992).

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Continuous sound: A sound whose sound pressure level remains above ambient sound
during the observation period (ANSI 2005).
Critical level: The level at which damage switches from being primarily metabolic to more
mechanical; e.g., short duration of impulse can be less than the ear’s integration time, leading
for the potential to damage beyond level the ear can perceive (Akay 1978).
Cumulative sound exposure level (SELcum; re: 1µPa2s): Level of acoustic energy
accumulated over a given period of time or event (EPA 1982) or specifically, ten times the
logarithm to the base ten of the ratio of a given time integral of squared instantaneous
frequency-weighted sound pressure over a stated time interval or event to the reference
sound exposure (ANSI 1995; ANSI 2013).
Deafness: A condition caused by a hearing loss that results in the inability to use auditory
information effectively for communication or other daily activities (ANSI 1995).
Decibel (dB): One-tenth of a bel. Unit of level when the base of the logarithm is the tenth
root of ten, and the quantities concerned are proportional to power (ANSI 2013).
dB/decade: This unit is typically used to describe roll-off, where a decade is a 10-times
increase in frequency (roll-off can also be described as decibels per octave, where an octave
is 2-times increase in frequency)
Duty cycle: On/off cycle time or proportion of time signal is active (calculated by: pulse
length x repetition rate). A continuous sound has a duty cycle of 1 or 100%.
Dynamic range of auditory system: Reflects the range of the auditory system from the
ability to detect a sound to the amount of sound tolerated before damage occurs (i.e., the
threshold of pain minus the threshold of audibility) (Yost 2007). For the purposes of this
document, the intent is relating the threshold of audibility and TTS onset levels, not the
threshold of pain.
Effective quiet: The maximum sound pressure level that will fail to produce any significant
threshold shift in hearing despite duration of exposure and amount of accumulation (Ward
et al. 1976; Ward 1991).
Endangered Species Act (ESA): The Endangered Species Act of 1973 (16. U.S.C 1531 et.
seq.) provides for the conservation of species that are endangered or threatened throughout
all or a significant portion of their range, and the conservation of the ecosystems on which
they depend.
NOAA’s National Marine Fisheries Service and the U.S. Fish and Wildlife Service (USFWS)
share responsibility for implementing the ESA.
Energy Source Level (SLE): The time-integrated squared signal sound pressure level
measured in a given radian direction, corrected for absorption, and scaled to a reference
distance (1 m) (adapted from Morfey 2001).
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Equal Energy Hypothesis (EEH): Assumption that sounds of equal energy produce the
equal risk for hearing loss (i.e., if the cumulative energy of two sources are similar, a sound
from a lower level source with a longer exposure duration may have similar risks to a shorter
duration exposure from a higher level source) (Henderson et al. 1991).
Equal latency: A curve that describe the frequency-dependent relationships between sound
pressure level and reaction time and are similar in shape to equal loudness contours in
humans (loudness perception can be studied under the assumption that sounds of equal
loudness elicit equal reaction times; e.g., Liebold and Werner 2002).
Equal-loudness contour: A curve or curves that show, as a function of frequency, the
sound pressure level required to cause a given loudness for a listener having normal hearing,
listening to a specified kind of sound in a specified manner (ANSI 2013).
Far-field: The acoustic field sufficiently distant from a distributed source that the sound
pressure decreases linearly with increasing distance (neglecting reflections, refraction, and
absorption) (ANSI 2013).
Fitness: Survival and lifetime reproductive success of an individual.
Frequency: The number of periods occurring over a unit of time (unless otherwise stated,
cycles per second or hertz) (Yost 2007).
Functional hearing range: There is no standard definition of functional hearing arrange
currently available. “Functional” refers to the range of frequencies a group hears without
incorporating non-acoustic mechanisms (Wartzok and Ketten 1999). Southall et al. 2007
defined upper and lower limits of the functional hearing range as ~60-70 dB above the
hearing threshold at greatest hearing sensitivity (based on human and mammalian definition
of 60 dB 70).
Fundamental frequency: Frequency of the sinusoid that has the same period as the
periodic quantity (Yost 2007; ANSI 2013). First harmonic of a periodic signal (Morfey 2001).
Harmonic: A sinusoidal quantity that has a frequency which is an integral multiple of the
fundamental frequency of the periodic quantity to which it is related (Yost 2007; ANSI
2013).
Hearing loss growth rates: The rate of threshold shift increase (or growth) as decibel level
or exposure duration increase (expressed in dB of temporary threshold shift/dB of
noise).Growth rates of threshold shifts are higher for frequencies where hearing is more
sensitive (Finneran and Schlundt 2010). Typically in terrestrial mammals, the magnitude of a
threshold shift increases with increasing duration or level of exposure, until it becomes
asymptotic (growth rate begins to level or the upper limit of TTS; Mills et al. 1979; Clark et
al. 1987; Laroche et al. 1989; Yost 2007).
In humans, functional hearing is typically defined as frequencies at a threshold of 60 to 70 dB and below
(Masterson et al. 1969; Wartzok and Ketten 1999), with normal hearing in the most sensitive hearing range
considered 0 dB (i.e., 60 to 70 dB above best hearing sensitivity).

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Hertz (Hz): Unit of frequency corresponding to the number of cycles per second. One
hertz corresponds to one cycle per second.
Impulsive sound: Sound sources that produce sounds that are typically transient, brief (less
than 1 second), broadband, and consist of high peak sound pressure with rapid rise time and
rapid decay (ANSI 1986; NIOSH 1998; ANSI 2005). They can occur in repetition or as a
single event. Examples of impulsive sound sources include: explosives, seismic airguns, and
impact pile drivers.
Information Quality Guidelines (IQG): Section 515 of the Treasury and General
Government Appropriations Act for Fiscal Year 2001 (Public Law 106-554), directs the
Office of Management and Budget (OMB) to issue government-wide guidelines that
“provide policy and procedural guidance to federal agencies for ensuring and maximizing the
quality, objectivity, utility, and integrity of information (including statistical information)
disseminated by federal agencies.” OMB issued guidelines directing each federal agency to
issue its own guidelines.
NOAA’s Information Quality Guidelines can be viewed at:
http://www.cio.noaa.gov/services_programs/IQ_Guidelines_011812.html
Integration time (of the ear): For a signal to be detected by the ear, it must have some
critical amount of energy. The process of summing the power to generate the required
energy is completed over a particular integration time. If the duration of a signal is less than
the integration time required for detection, the power of the signal must be increased for it
to be detected by the ear (Yost 2007).
Intermittent sound: Interrupted levels of low or no sound (NIOSH 1998) or bursts of
sounds separated by silent periods (Richardson and Malme 1993). Typically, intermittent
sounds have a more regular (predictable) pattern of bursts of sounds and silent periods (i.e.,
duty cycle).
Isopleth: A line drawn through all points having the same numerical value. In the case of
sound, the line has equal sound pressure or exposure levels.
Kurtosis: Statistical quantity that represents the impulsiveness (“peakedness”) of the event;
specifically the ratio of fourth- order central moment to the squared second-order central
moment (Hamernik et al. 2003; Davis et al. 2009).
Linear interpolation: A method of constructing new data points within the range of
a discrete set of known data points, with linear interpolation being a straight line between
two points.
Marine Mammal Protection Act (MMPA): The Marine Mammal Protection Act (16.
U.S.C. 1361 et. seq.)was enacted on October 21, 1972 and MMPA prohibits, with certain
exceptions, the “take” of marine mammals in U.S. waters and by U.S. citizens on the high
seas, and the importation of marine mammals and marine mammal products into the United
States. NOAA’s National Marine Fisheries Service and the U.S. Fish and Wildlife Service
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(USFWS) share responsibility for implementing the MMPA.
Masking: Obscuring of sounds of interest by interfering sounds, generally of the similar
frequencies (Richardson et al. 1995).
Mean-squared error (MSE): In statistics, this measures the average of the squares of the
“errors,” that is, the difference between the estimator and what is estimated.
Multipath propagation: This phenomenon occurs whenever there is more than one
propagation path between the source and receiver (i.e., direct path and paths from
reflections off the surface and bottom or reflections within a surface or deep-ocean duct;
Urick 1983).
Mysticete: The toothless or baleen (whalebone) whales, including the rorquals, gray whale,
and right whale; the suborder of whales that includes those that bulk feed and cannot
echolocate (Perrin et al. 2009).
Narrowband: See “bandwidth”.
National Marine Sanctuaries Act (NMSA): The National Marine Sanctuaries Act (16
U.S.C. 1431 et. seq.) authorizes the Secretary of Commerce to designate and protect areas of
the marine environment with special national significance due to their conservation,
recreational, ecological, historical, scientific, cultural, archeological, educational, or esthetic
qualities as national marine sanctuaries. Day-to-day management of national marine
sanctuaries has been delegated by the Secretary of Commerce to NOAA’s Office of National
Marine Sanctuaries.
National Standard 2 (NS2): The Magnuson-Stevens Fishery Conservation and
Management Act (MSA) (16 U.S.C. 1801 et. seq.) is the principal law governing marine
fisheries in the U.S. and includes ten National Standards to guide fishery conservation and
management. One of these standards, referred to as National Standard 2 (NS2), guides
scientific integrity and states that “(fishery) conservation and management measures shall be
based upon the best scientific information available.
Non-impulsive sound: Sound sources that produce sounds that can be broadband,
narrowband or tonal, brief or prolonged, continuous or intermittent) and typically do not
have a high peak sound pressure with rapid rise time that impulsive sounds do. Examples of
non-impulsive sound sources include: marine vessels, machinery operations/construction
(e.g., drilling), certain active sonar (e.g. tactical), and vibratory pile drivers.
Octave: The interval between two sounds having a basic frequency ratio of two (Yost 2007).
For example, one octave above 400 Hz is 800 Hz. One octave below 400 Hz is 200 Hz.
Odontocete: The toothed whales, including sperm and killer whales, belugas, narwhals,
dolphins and porpoises; the suborder of whales including those able to echolocate (Perrin et
al. 2009).
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Omnidirectional: Receiving or transmitting signals in all directions (i.e., variation with
direction is designed to be as small as possible).
Otariid: The eared seals (sea lions and fur seals), which use their foreflippers for propulsion
(Perrin et al. 2009).
Peak sound pressure level (PK; re: 1 µPa): The greatest absolute instantaneous sound
pressure within a specified time interval and frequency band (ANSI 1986; ANSI 2013).
Perception: Perception is the translation of environmental signals to neuronal
representations (Dukas 2004).
Permanent threshold shift (PTS): A permanent, irreversible increase in the threshold of
audibility at a specified frequency or portion of an individual’s hearing range above a
previously established reference level. The amount of permanent threshold shift is
customarily expressed in decibels (ANSI 1995; Yost 2007). Available data from humans and
other terrestrial mammals indicate that a 40 dB threshold shift approximates PTS onset (see
Ward et al. 1958, 1959; Ward 1960; Kryter et al. 1966; Miller 1974; Ahroon et al. 1996;
Henderson et al. 2008).
Phocid: A family group within the pinnipeds that includes all of the “true” seals (i.e. the
“earless” species). Generally used to refer to all recent pinnipeds that are more closely related
to Phoca than to otariids or the walrus (Perrin et al. 2009).
Pinniped: Seals, sea lions and fur seals (Perrin et al. 2009).
Pulse duration: For impulsive sources, window that makes up 90% of total cumulative
energy (5%-95%) (Madsen 2005)
Propagation loss: Reduction in magnitude of some characteristic of a signal between two
stated points in a transmission system (for example the reduction in the magnitude of a
signal between a source and a receiver) (ANSI 2013).
Received level: The level of sound measured at the receiver.
Reference pressure: See sound pressure level.
Repetition rate: Number of pulses of a repeating signal in a specific time unit, normally
measured in pulses per second.
Rise time: The time interval a signal takes to rise from 10% to 90% of its highest peak
(ANSI 1986; ANSI 2013).
Roll-off: Change in weighting function amplitude (-dB) with changing frequency.
Root-mean-square sound pressure level (RMS SPL; re: 1 µPa): The square root of the
average of the square of the pressure of the sound signal over a given duration (ANSI 2005).
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Sensation level (dB): The pressure level of a sound above the hearing threshold for an
individual or group of individuals (ANSI 1995; Yost 2007).
Sound Exposure Level (SELcum; re: 1µPa2s): A measure of sound level that takes into
account the duration of the signal. Ten times the logarithm to the base 10 of the ration of a
given time integral of squared instantaneous frequency-weighted sound pressure over a
stated time interval or event to the product of the squared reference sound pressure and
reference duration of one second (ANSI 2013).
Sound Pressure Level (SPL): A measure of sound level that represents only the pressure
component of sound. Ten times the logarithm to the base 10 of the ratio of time-meansquare pressure of a sound in a stated frequency band to the square of the reference pressure
(1 µPa in water)(ANSI 2013).
Source Level (SL): Sound pressure level measured in a given radian direction, corrected for
absorption, and scaled to a reference distance (Morfey 2001). For underwater sources, the
sound pressure level of is measured in the far-field and scaled to a standard reference
distance 71 (1 meter) away from the source (Richardson et al. 1995; ANSI 2013).
Spatial: Of or relating to space or area.
Spectral/spectrum: Of or relating to frequency component(s) of sound. The spectrum of a
function of time is a description of its resolution into components (frequency, amplitude,
etc.). The spectrum level of a signal at a particular frequency is the level of that part of the
signal contained within a band of unit width and centered at a particular frequency (Yost
2007).
Spectral density levels: Level of the limit, as the width of the frequency band approaches
zero, of the quotient of a specified power-like quantity distributed within a frequency band,
by the width of the band (ANSI 2013).
Subharmonic: Sinusoidal quantity having a frequency that is an integral submultiple of the
fundamental frequency of a periodic quantity to which it is related (ANSI 2013).
Temporal: Of or relating to time.
Temporary threshold shift (TTS): A temporary, reversible increase in the threshold of
audibility at a specified frequency or portion of an individual’s hearing range above a
previously established reference level. The amount of temporary threshold shift is
customarily expressed in decibels (ANSI 1995, Yost 2007). Based on data from cetacean
TTS measurements (see Southall et al. 2007 for a review), a TTS of 6 dB is considered the
minimum threshold shift clearly larger than any day-to-day or session-to-session variation in
a subject’s normal hearing ability (Schlundt et al. 2000; Finneran et al. 2000; Finneran et al.
2002).
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Threshold (of audibility): The threshold of audibility (auditory threshold) for a specified
signal is the minimum effective sound pressure level of the signal that is capable of evoking
an auditory sensation in a specified fraction of trials (either physiological or behavioral) (Yost
2007). It recommended that this threshold be defined as the lowest sound pressure level at
which responses occur in at least 50% of ascending trials. (ANSI 2009).
Threshold shift: A change, usually an increase, in the threshold of audibility at a specified
frequency or portion of an individual’s hearing range above a previously established
reference level. The amount of threshold shift is customarily expressed in decibels (ANSI
1995, Yost 2007).
Tone: A sound wave capable of exciting an auditory sensation having pitch. A pure tone is a
sound sensation characterized by a single pitch (one frequency). A complex tone is a sound
sensation characterized by more than one pitch (more than one frequency) (ANSI 2013).
Uncertainty: Lack of knowledge about a parameter’s true value (Bogen and Spears 1987;
Cohen et al. 1996).
Variability: Differences between members of the populations that affects the magnitude of
risk to an individual (Bogen and Spears 1987; Cohen et al. 1996; Gedamke et al. 2011).

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TECHNICAL GUIDANCE FOR ASSESSING THE EFFECTS OF ANTHROPOGENIC SOUND ON MARINE MAMMAL
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File Type	application/pdf
File Title	National Oceanic and Atmospheric Administration Final Guidance for Assessing the Effects of Anthropogenic Sound on Marine Mammal
Author	Amy_Scholik
File Modified	2016-07-26
File Created	2016-07-26