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pdf2018 Revision to:
Technical Guidance for Assessing the
Effects of Anthropogenic Sound on
Marine Mammal Hearing (Version 2.0)
Underwater Thresholds for Onset of Permanent
and Temporary Threshold Shifts
Office of Protected Resources
National Marine Fisheries Service
Silver Spring, MD 20910
U.S. Department of Commerce
National Oceanic and Atmospheric Administration
National Marine Fisheries Service
NOAA Technical Memorandum NMFS-OPR-59
April 2018
2018 Revisions to:
Technical Guidance for Assessing the Effects of
Anthropogenic Sound on Marine Mammal Hearing
(Version 2.0)
Underwater Thresholds for Onset of Permanent and Temporary
Threshold Shifts
NOAA Technical Memorandum NMFS-OPR-59
April 2018
U.S. Department of Commerce
Wilbur Ross, Secretary
National Oceanic and Atmospheric Administration
Tim Gallaudet, Ph.D., USN Ret., Acting Administrator
National Marine Fisheries Service
Chris Oliver, Assistant Administrator for Fisheries
Recommended citation:
National Marine Fisheries Service. 2018. 2018 Revisions to: Technical Guidance for Assessing
the Effects of Anthropogenic Sound on Marine Mammal Hearing (Version 2.0): Underwater
Thresholds for Onset of Permanent and Temporary Threshold Shifts. U.S. Dept. of Commer.,
NOAA. NOAA Technical Memorandum NMFS-OPR-59, 167 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:
NOAA Fisheries Publication web site
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)
2018 REVISION TO: 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
I.
INTRODUCTION................................................................................................................. 6
1.1.
THRESHOLDS WITHIN THE CONTEXT OF AN EFFECTS ANALYSIS ........................................... 7
1.2
ADDRESSING UNCERTAINTY AND DATA LIMITATIONS ........................................................... 7
1.2.1 Assessment Framework ............................................................................................. 7
1.2.2 Data Standards ........................................................................................................... 8
II.
NMFS’ THRESHOLDS FOR ONSET OF PERMANENT THRESHOLD SHIFTS IN MARINE
MAMMALS ......................................................................................................................... 8
2.1
MARINE MAMMAL HEARING GROUPS.................................................................................. 8
2.1.1 Application of Marine Mammal Hearing Groups ....................................................... 10
2.2
MARINE MAMMAL AUDITORY W EIGHTING FUNCTIONS ....................................................... 11
2.2.1 Use of Auditory Weighting Functions in Assessing Susceptibility to Noise-Induced Hearing
Loss........................................................................................................................... 11
2.2.2 Marine Mammal Auditory Weighting Functions ........................................................ 12
2.2.3 Derivation of Function Parameters ........................................................................... 15
2.2.4 Application of Marine Mammal Auditory Weighting Functions for PTS Onset Thresholds
.................................................................................................................................. 18
2.3
PTS ONSET THRESHOLDS............................................................................................... 19
2.3.1 Impulsive and Non-Impulsive Source Thresholds .................................................... 20
2.3.2 Metrics....................................................................................................................... 22
2.3.3 Development of PTS Onset Thresholds ................................................................... 24
III.
UPDATING OF ACOUSTIC TECHNICAL GUIDANCE AND THRESHOLDS ................ 29
3.1
PROCEDURE AND TIMELINE FOR UPDATING THE TECHNICAL GUIDANCE ............................. 29
3.1.1 Consideration for New Scientific Publication ............................................................ 29
APPENDIX A:
FINNERAN TECHNICAL REPORT ............................................................ 32
ADMINISTRATIVEINFORMATION ............................................................................................... 34
EXECUTIVE SUMMARY ............................................................................................................... 35
I.
1.1
1.2
1.3
1.4
1.5
INTRODUCTION............................................................................................................... 39
OVERVIEW ...................................................................................................................... 39
IMPULSE VS. NON-IMPULSIVE NOISE .................................................................................. 39
NOISE-INDUCED THRESHOLD SHIFTS ................................................................................ 39
AUDITORY WEIGHTING FUNCTIONS ................................................................................... 40
TAP PHASE 3 WEIGHTING FUNCTIONS AND TTS/PTS THRESHOLDS................................... 40
II.
WEIGHTING FUNCTIONS AND EXPOSURE FUNCTIONS ........................................... 42
III.
METHODOLOGY TO DERIVE FUNCTION PARAMETERS ........................................... 47
IV.
4.1
4.2
4.3
4.4
4.5
4.6
MARINE MAMMAL SPECIES GROUPS ......................................................................... 49
LOW-FREQUENCY (LF) CETACEANS.................................................................................. 49
MID-FREQUENCY (MF) CETACEANS .................................................................................. 49
HIGH-FREQUENCY (HF) CETACEANS ................................................................................ 49
SIRENIANS ...................................................................................................................... 49
PHOCIDS ........................................................................................................................ 50
OTARIIDS AND OTHER NON-PHOCID MARINE CARNIVORES .................................................. 50
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V.
COMPOSITE AUDIOGRAMS .......................................................................................... 52
VI.
EQUAL LOUDNESS DATA.............................................................................................. 60
VII.
EQUAL LATENCY DATA................................................................................................. 61
VIII.
8.1
8.2
8.3
TTS DATA ........................................................................................................................ 62
NON-IMPULSIVE (STEADY-STATE) EXPOSURES – TTS........................................................ 62
NON-IMPULSIVE (STEADY-STATE) EXPOSURES – PTS........................................................ 64
IMPULSIVE EXPOSURES.................................................................................................... 65
IX.
9.1
9.2
9.3
TTS EXPOSURE FUNCTIONS FOR SONARS ............................................................... 74
LOW- AND HIGH-FREQUENCY EXPONENTS (a, b)................................................................ 74
FREQUENCY CUTOFFS (ʄ1, ʄ2) ........................................................................................... 74
GAIN PARAMETERS K AND C ............................................................................................ 76
X.
PTS EXPOSURE FUNCTIONS FOR SONARS ............................................................... 83
XI.
TTS/PTS EXPOSURE FUNCTIONS FOR EXPLOSIVES................................................ 84
XII.
SUMMARY........................................................................................................................ 87
APPENDIX A1.
ESTIMATING A LOW-FREQUENCY CETACEAN AUDIOGRAM ............ 92
A1.1. BACKGROUND..................................................................................................................... 92
A1.2. AUDIOGRAM FUNCTIONAL FORM AND REQUIRED PARAMETERS ............................................... 93
A1.3. ESTIMATING AUDIOGRAM PARAMETERS ................................................................................ 95
XIII.
REFERENCES.................................................................................................................. 98
APPENDIX B:
I.
RESEARCH RECOMMENDATIONS FOR IMPROVED THRESHOLDS ..... 108
SUMMARY OF RESEARCH RECOMMENDATIONS ................................................... 108
1.1
LOW-FREQUENCY CETACEAN HEARING.......................................................................... 108
1.2
HEARING DIVERSITY AMONG SPECIES AND AUDITORY PATHWAYS ................................... 109
1.3
REPRESENTATIVENESS OF CAPTIVE INDIVIDUALS ............................................................ 109
1.3.1 Impacts of Age on Hearing ..................................................................................... 109
1.4
ADDITIONAL TTS MEASUREMENTS WITH MORE SPECIES AND/OR INDIVIDUALS ................. 110
1.5
SOUND EXPOSURE TO MORE REALISTIC SCENARIOS ...................................................... 111
1.5.1 Frequency and Duration of Exposure ..................................................................... 111
1.5.2 Multiple Sources ..................................................................................................... 111
* Frequency-dependent hearing loss and overall hearing ability within a hearing group is taken into
account, quantitatively, with auditory weighting functions. ..................................... 112
1.5.3 Possible Protective Mechanisms ............................................................................ 112
1.5.4 Long-Term Consequences of Exposure ................................................................. 113
1.6
IMPACTS OF NOISE-INDUCED THRESHOLD SHIFTS ON FITNESS ........................................ 113
1.7
BEHAVIOR OF MARINE MAMMALS UNDER EXPOSURE CONDITIONS WITH THE POTENTIAL TO CAUSE
HEARING IMPACTS ........................................................................................................ 114
1.8
CHARACTERISTICS OF SOUND ASSOCIATED WITH NIHL AND IMPACTS OF PROPAGATION .. 115
1.9
NOISE-INDUCED THRESHOLD SHIFT GROWTH RATES AND RECOVERY ............................. 115
1.10
METRICS AND TERMINOLOGY ......................................................................................... 115
1.11
EFFECTIVE QUIET ......................................................................................................... 116
1.12
TRANSLATING BIOLOGICAL COMPLEXITY INTO PRACTICAL APPLICATION ........................... 117
APPENDIX C:
TECHNICAL GUIDANCE REVIEW PROCESSES: PEER REVIEW, PUBLIC
COMMENT, AND REVIEW UNDER EXECUTIVE ORDER 13795 ................................ 118
I.
PEER REVIEW PROCESS ............................................................................................ 118
1.1
2013 INITIAL PEER REVIEW (ASSOCIATED WITH 2013 DRAFT GUIDANCE) ........................ 119
1.2
2015 SECOND PEER REVIEW (REVIEW OF THE FINNERAN TECHNICAL REPORT)............... 119
1.2.1 2016 Follow-Up to Second Peer Review ................................................................ 120
1.3
2015 THIRD PEER REVIEW (REVIEW OF TRANSITION RANGE METHODOLOGY) ................. 120
1.4
CONFLICT OF INTEREST DISCLOSURE ............................................................................. 121
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II.
PUBLIC COMMENT PERIODS...................................................................................... 121
2013/2014 INITIAL PUBLIC COMMENT PERIOD (ASSOCIATED WITH 2013 DRAFT TECHNICAL
GUIDANCE) .................................................................................................................. 122
2.1.1 Summary of Public Comments Received ............................................................... 122
2.2
2015 SECOND PUBLIC COMMENT PERIOD (ASSOCIATED WITH 2015 DRAFT TECHNICAL GUIDANCE)
................................................................................................................................... 123
2.2.1 Summary of Public Comments Received ............................................................... 123
2016 THIRD PUBLIC COMMENT PERIOD (ASSOCIATED WITH 2016 PROPOSED CHANGES FROM DRAFT
2.3
TECHNICAL GUIDANCE)................................................................................................. 123
2.3.1 Summary of Public Comments Received ............................................................... 124
2.1
III.
REVIEW UNDER EXECUTIVE ORDER 13795.............................................................. 125
3.1
REVIEW OF 2016 TECHNICAL GUIDANCE UNDER EO 13795 ........................................... 125
3.1.1 2017 Public Comment Period ................................................................................. 125
3.1.2 2017 Federal Interagency Consultation.................................................................. 126
3.2
REVISIONS TO THE 2016 TECHNICAL GUIDANCE AS A RESULT OF REVIEW UNDER EO 13795127
APPENDIX D:
ALTERNATIVE METHODOLOGY ........................................................... 129
I.
INTRODUCTION............................................................................................................. 129
II.
WEIGHTING FACTOR ADJUSTMENT ASSOCIATED WITH SELCUM THRESHOLDS129
APPLICATION FOR NARROWBAND SOUNDS ..................................................................... 129
132
2.2
APPLICATION FOR BROADBAND SOUNDS ........................................................................ 132
2.2.1 Special Considerations for Broadband Source....................................................... 133
2.3
OVERRIDING THE W EIGHTING FACTOR ADJUSTMENT ...................................................... 134
2.1
III.
MODELING CUMULATIVE SOUND EXPOSURE LEVELS.......................................... 135
3.1
MORE SOPHISTICATED MODELS .................................................................................... 135
3.2
LESS SOPHISTICATED MODELS ...................................................................................... 136
3.2.1 Mobile Sources ....................................................................................................... 136
3.2.2 Stationary Sources.................................................................................................. 140
APPENDIX E:
GLOSSARY .............................................................................................. 141
LITERATURE CITED................................................................................................................... 149
LIST OF TABLES
Table ES1:
Marine mammal hearing groups. ........................................................................................ 3
Table ES2:
Summary of auditory weighting and exposure function parameters................................... 3
Table ES3:
Summary of PTS onset thresholds. .................................................................................... 4
Table 1: Marine mammal hearing groups. .............................................................................................. 10
Table 2:
Summary of data available for deriving composite audiograms ............................................ 16
Table 3: Summary of auditory weighting and exposure function parameters......................................... 18
Table 4: Summary of PTS onset thresholds. .......................................................................................... 21
Table 5:
Available underwater marine mammal threshold shift studies. ............................................. 26
Table 6:
TTS onset thresholds for non-impulsive sounds. .................................................................. 27
Table AE-1.
Summary of weighting function parameters and TTS/PTS thresholds............................. 36
Table A1.
Species group designations for Navy Phase 3 auditory weighting functions. ....................... 51
References, species, and individual subjects used to derive the composite audiograms..... 54
Table A2.
Composite audiogram parameters values for use in Eq. (A9)............................................... 55
Table A3.
Table A4.
Normalized composite audiogram parameters values for use in Eq. (A9). ........................... 55
Table A5.
Frequency of best hearing and the magnitude of the low-frequency slope derived from
composite audiograms and equal latency contours. .......................................................................... 59
Table A6.
Summary of marine mammal TTS growth data and onset exposure levels.......................... 71
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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. ......................................................... 77
Table A8.
Weighting function and TTS exposure function parameters for steady-state exposures...... 78
TTS and PTS thresholds for explosives and other impulsive sources .................................. 86
Table A9.
Table A10. Summary of weighting function parameters and TTS/PTS thresholds. ................................ 88
Table B1:
Summary of currently available marine mammal data. ....................................................... 108
Table B2:
Additional factors for consideration (frequency and duration of exposure) in association with
PTS onset thresholds. ...................................................................................................................... 112
Initial peer review panel. ...................................................................................................... 119
Table C1:
Table C2:
Second peer review panel. .................................................................................................. 120
Table C3:
Third peer review panel. ...................................................................................................... 121
Table C4:
Summary of commenters..................................................................................................... 126
Ten Federal agency attendees ............................................................................................ 127
Table C5:
Applicability of weighting factor adjustments for frequencies associated with broadband
Table D1:
sounds ............................................................................................................................................. 134
Table D2:
Comparison of adjustment associated with incorporating entire broadband spectrum vs.
default, single frequency WFA for a seismic array........................................................................... 135
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
Auditory weighting functions for low-frequency, mid-frequency, and high-frequency
Figure 1:
cetaceans. .......................................................................................................................................... 12
Figure 2:
Underwater auditory weighting functions for otariid and phocid pinnipeds. ......................... 13
Illustration of function parameter in both auditory weighting functions and exposure
Figure 3:
functions ............................................................................................................................................. 14
Resulting normalized composite audiograms for low-frequency, mid-frequency, and highFigure 4:
frequency cetaceans and phocid (PW) and otariid (OW) pinnipeds .................................................. 15
Navy Phase 3 weighting functions for all species groups................................................. 36
Figure AE-1.
Figure AE-2.
TTS and PTS exposure functions for sonars and other (non-impulsive) active acoustic
sources . ......................................................................................................................................... 37
TTS and PTS exposure functions for explosives, impact pile driving, air guns, and other
Figure AE-3.
impulsive sources ............................................................................................................................... 38
Figure A1.
Examples of weighting function and exposure function........................................................ 43
Influence of parameter values on the resulting shapes of the weighting functions and
Figure A2.
exposure functions ............................................................................................................................. 44
Figure A3.
Navy Phase 2 weighting function for the mid-frequency cetacean group. ........................... 45
Figure A4. Comparison of Otariid, Mustelid, and Odobenid psychophysical hearing thresholds
measured underwater.. ...................................................................................................................... 50
Figure A5.
Thresholds and composite audiograms for the six species groups...................................... 56
Normalized thresholds and composite audiograms for the six species groups.................... 57
Figure A6.
Composite audiograms for the various species groups, derived with the original data and
Figure A7.
normalized data .................................................................................................................................. 58
Figure A8. Underwater marine mammal equal latency contours are available for Phocoena phocoena
and Tursiops truncatus ....................................................................................................................... 61
Figure A9. TTS measured using behavioral and AEP methods do not necessarily agree, with marine
mammal studies reporting larger TTS obtained using AEP methods. ............................................... 63
TTS growth data for mid-frequency cetaceans obtained using behavioral methods........ 67
Figure A10.
Figure A11.
TTS growth data for mid-frequency cetaceans obtained using AEP methods. ................ 68
Figure A12.
TTS growth data for high-frequency cetaceans obtained using behavioral and AEP
methods. .......................................................................................................................................... 69
TTS growth data for pinnipeds obtained using behavioral methods................................. 70
Figure A13.
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Figure A14.
The cutoff frequencies ...................................................................................................... 75
Figure A15.
Effect of ΔT adjustment on the TTS exposure functions for the mid-frequency cetaceans
and high-frequency cetaceans ........................................................................................................... 75
Figure A16.
Relationship between ΔT and the resulting mean-squared error between the exposure
functions and onset TTS data. ........................................................................................................... 76
Figure A17.
Exposure functions with the parameters specified in Table A7. ....................................... 79
Figure A18.
Mid-frequency cetacean exposure function, composite audiogram, and Phase 2 exposure
functions compared to mid-frequency cetacean TTS data................................................................. 80
Figure A19.
High-frequency cetacean TTS exposure function, composite audiogram, and Phase 2
exposure functions compared to high-frequency cetacean TTS data................................................ 81
Figure A20. Phocid (underwater) exposure function, composite audiogram, and Phase 2 exposure
functions compared to phocid TTS data. ........................................................................................... 82
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. ....... 87
Figure A22.
TTS and PTS exposure functions for sonars and other (non-impulsive) active acoustic
sources. . ......................................................................................................................................... 90
Figure A23.
TTS and PTS exposure functions for explosives, impact pile driving, air guns, and other
impulsive sources.. ............................................................................................................................. 91
FIGURE A1.1.
Relationship between estimated threshold, T(f), low-frequency term, L(f), and highfrequency term.................................................................................................................................... 95
FIGURE A1.2.
Comparison of proposed LF cetacean thresholds to those predicted by anatomical and
finite-element models. ........................................................................................................................ 97
Figure D1: Example illustrating concept of weighting factor adjustment at 1 kHz (red line) with cetacean
(top) and pinniped (bottom) auditory weighting functions. ............................................................... 131
Figure D2:
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).. ............................................... 132
Figure D3: Example auditory weighting function illustrating where the use of weighting factor
adjustments are and are not appropriate for broadband sources. ................................................... 133
Figure D4: Maximum one-third octave band source level in the horizontal plane for a generic 8000 in3
seismic array .................................................................................................................................... 134
Figure D5: Illustration of the concept for mobile sources, with each red dot representing the source
traveling over time. ........................................................................................................................... 137
Figure E1. Example audiogram. ........................................................................................................... 141
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ABBREVIATIONS, ACRONYMS, AND SYMBOLS
SY BOLS
a
ABR
AEP
AM
ANSI
b
BOEM
C
CT
D
dB
PK
DPOAE
Eaud(ƒ)
E0
EEH
EO
EQL
ES
ESA
ƒ0
ƒ1
ƒ2
G&G
h
HF
HISA
Hz
in3
ISI
ISO
IQG
K
kHz
LDEO
LF
L0-pk
L0-pk,flat
LE,24h
MF
min
Low-frequency exponent
Auditory Brainstem
Response
Auditory Evoked Potentials
Amplitude Modulated
American National Standards
Institute
High-frequency exponent
Bureau of Ocean Energy
Management
Weighting function gain (dB)
Computerized Tomography
Duty Cycle
Decibel
Peak sound level
Distortion product
otoacoustic emission
Auditory exposure function
Exposure Threshold
Equal Energy Hypothesis
Executive Order
Equal Loudness
Executive Summary
Endangered Species Act
Best hearing (kHz)
Low-frequency cutoff (kHz)
High-frequency cutoff (kHz)
Geological and Geophysical
hour
High-frequency
Highly Influential Scientific
Assessment
Hertz
Cubic inches
Influential Scientific
Information
International Organization for
Standardization
Information Quality
Guidelines
Exposure function gain (dB)
Kilohertz
Lamont-Doherty Earth
Observatory
Low-frequency
Peak sound pressure level
Peak sound pressure level
(unweighted)
Sound exposure level,
cumulative 24h
Mid-frequency
Minutes
MMC
MMPA
MSA
MSE
m
msec
NAZ
NIHL
NMFS
NMSA
NOAA
NOS
NRC
NS2
NSF
OMB
ONMS
OPR
OSHA
OW
p0
Pa
π
PK
PTS
PW
R
R0
R2
RMS
S
SE
s
s
s0
SEL
SELcum
SIO
SL
Marine Mammal Commission
Marine Mammal Protection
Act
Magnuson-Stevens Fishery
Conservation and
Management Act
Mean-squared error
meter
Milliseconds
Narrow Azimuth
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
National Science Foundation
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
pi
peak sound pressure level
Permanent Threshold Shift
Phocids in water
Range
“Safe Distance”
Goodness of fit
Root-Mean-Square sound
pressure level
Source Factor
Energy Source Factor
Seconds
Distance from source
Slope
Sound exposure level
Cumulative sound exposure
level
Scripps Institution of
Oceanography
Source Level
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SLE
s0
SPL
SSC-PAC
τ
TAP
TS
TTS
µPa
µPa2-s
USFWS
𝑣𝑣
Waud(ƒ)
WAZ
WFA
Energy Source Level
Slope (dB/decade)
Sound Pressure Level
SPAWAR Systems Center
Pacific
1/repetition rate
U.S. Navy’s Tactical Training
Theater Assessment and
Planning Program
Threshold Shift
Temporary Threshold Shift
Micropascal
Micropascal squared second
U.S. Fish and Wildlife
Service
Velocity (transit speed)
Auditory weighting function
Wide Azimuth
Weighting factor adjustments
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EXECUTIVE SUMMARY
SU
ARY
This document provides voluntary 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 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 Technical Guidance may
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 potential impacts to marine mammal hearing via acoustic exposure. Please
note that action proponents have discretion as to whether to use the Technical Guidance; other
scientifically rigorous methods are acceptable. This document outlines the development of NMFS’
thresholds and describes how they will be updated in the future.
NMFS has compiled, interpreted, and synthesized the scientific literature, including a Technical
Report by Dr. James Finneran (U.S. Navy-SPAWAR Systems Center Pacific (SSC-PAC))
(Finneran 2016; Appendix A of this Technical Guidance), to produce thresholds for onset of
temporary (TTS) and permanent threshold shifts (PTS) (Table ES2). This document includes a
protocol for estimating PTS onset 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 onset thresholds. These
thresholds are presented using dual metrics of weighted cumulative sound exposure level
(SELcum) and peak sound level (PK) for impulsive sounds and weighted SELcum for non-impulsive
sounds.
While the Technical Guidance’s 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. NMFS recognizes
that the implementation of marine mammal weighting functions and the weighted 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, Technical Guidance’s companion User Spreadsheet tool 1, and
recently developed User Spreadsheet Manual (NMFS 2018)1).
These 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., 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. The Technical Guidance may inform decisions related to mitigation and monitoring
requirements, but it does not mandate any specific mitigation be required. The Technical
Guidance does not address or change NMFS’ application of these thresholds in the regulatory
context, under applicable statutes and does not create or confer any rights for or on any person,
or operate to bind the public. It only updates NMFS’ thresholds based on the most recent science.
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).
1
Link to Technical Guidance web page.
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REVISIONS TO 2016 TECHNICAL GUIDANCE
Presidential Executive Order (EO) 13795, Implementing an America-First Offshore Energy
Strategy (82 FR 20815; April 28, 2017), states in section 2 that “It shall be the policy of the United
States to encourage energy exploration and production, including on the Outer Continental Shelf,
in order to maintain the Nation’s position as a global energy leader and foster energy security and
resilience for the benefit of the American people, while ensuring that any such activity is safe and
environmentally responsible.” Section 10 of the E.O. called for a review of the 2016 Technical
Guidance for Assessing the Effects of Anthropogenic Sound on Marine Mammal Hearing
(Technical Guidance; NMFS 2016a) as follows: “The Secretary of Commerce shall review
[Technical Guidance] for consistency with the policy set forth in Section 2 of this order and, after
consultation with the appropriate Federal agencies, take all steps permitted by law to rescind or
revise that guidance, if appropriate.”
To assist the Secretary in carrying out the directive under EO 13795, NMFS held a 45-day public
comment period (82 FR 24950; May 31, 2017) and a Federal Interagency Consultation
(September 25, 2017) to solicit comments on the Technical Guidance for consistency with the
EO’s policy.
Many of the comments NMFS received, including those from Federal agencies, were supportive
of the Technical Guidance, including the science used in its derivation and the robust process
that NMFS followed, including four independent peer reviews. The majority of commenters
recommended that the Technical Guidance remain unchanged. The Federal agencies, Members
of Congress, and subject matter experts expressed support for the Technical Guidance as
reflecting the best available science. NMFS received no recommendations to rescind the 2016
Technical Guidance. The majority of comments pertained to recommendations to improve
implementation of the Technical Guidance, rather than the Technical Guidance itself, or were
beyond the scope of the Technical Guidance and/or its review under section 10 of EO 13795.
NMFS’ evaluation of comments received during this process affirmed that the Technical
Guidance is based on upon the best available science. However, to facilitate its use and
implementation, NMFS revised the 2016 Technical Guidance (NMFS 2016a), per approval of the
Secretary of Commerce, to provide improvements and clarification on implementation of the
document (i.e., 2018 Revised Technical Guidance, Version 2.0).
SUMMARY OF TECHNICAL ASPECTS
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’ thresholds for onset of PTS for marine mammals exposed to underwater sound are
presented in Section II. NMFS’ plan for periodically updating thresholds is presented in Section
III. More details on the development of 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 thresholds (Table ES3).
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Table ES1:
Marine mammal hearing groups.
Generalized Hearing
Range*
Hearing Group
Low-frequency (LF) cetaceans
7 Hz to 35 kHz
(baleen whales)
Mid-frequency (MF) cetaceans
150 Hz to 160 kHz
(dolphins, toothed whales, beaked whales, bottlenose whales)
High-frequency (HF) cetaceans
(true porpoises, Kogia, river dolphins, cephalorhynchid,
275 Hz to 160 kHz
Lagenorhynchus cruciger & L. australis)
Phocid pinnipeds (PW) (underwater)
50 Hz to 86 kHz
(true seals)
Otariid pinnipeds (OW) (underwater)
60 Hz to 39 kHz
(sea lions and fur seals)
* 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 auditory 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)
a
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
C
(dB)
0.13
1.20
1.36
0.75
0.64
K
(dB)
179
177
152
180
198
* Equations associated with Technical Guidance’s auditory weighting (Waud(f)) and exposure functions (Eaud(f)):
(J I t,Y"
}
2 '
dB
dB
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Table ES3:
Summary of PTS onset thresholds.
PTS Onset Thresholds*
(Received Level)
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
Lp,0-pk,flat: 219 dB
LE,p, LF,24h: 183 dB
Cell 3
Lp,0-pk,flat: 230 dB
LE,p, MF,24h: 185 dB
Cell 5
Lp,0-pk,flat: 202 dB
LE,p,HF,24h: 155 dB
Cell 7
Lp,0-pk.flat: 218 dB
LE,p,PW,24h: 185 dB
Cell 9
Lp,0-pk,flat: 232 dB
LE,p,OW,24h: 203 dB
Non-impulsive
Cell 2
LE,p, LF,24h: 199 dB
Cell 4
LE,p, MF,24h: 198 dB
Cell 6
LE,p, HF,24h: 173 dB
Cell 8
LE,p,PW,24h: 201 dB
Cell 10
LE,p,OW,24h: 219 dB
* Dual metric 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 are recommended for consideration.
Note: Peak sound pressure level (Lp,0-pk) has a reference value of 1 µPa, and weighted cumulative sound exposure level
(LE,p) has a reference value of 1µPa2s. In this Table, thresholds are abbreviated to be more reflective of International
Organization for Standardization standards (ISO 2017). The subscript “flat” is being included to indicate peak sound
pressure are flat weighted or unweighted within the generalized hearing range of marine mammals (i.e., 7 Hz to 160 kHz).
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 weighted 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 thresholds will be exceeded.
2018 REVISION TO: TECHNICAL GUIDANCE FOR ASSESSING THE EFFECTS OF ANTHROPOGENIC SOUND ON MARINE MAMMAL
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--
0
"
,-..
i:Q
"O
'-'
✓
-10
11,)
::::l
.<:::
-
.8
\
✓
-20
E
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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(a)
AEP
(b)
AEP
Cl) 30
II- 20
behavioral
10
0
~~~-~~-~~~~~-
1
10
100
1000
~~~-~~~~~~~~~
10000
10
100
1000
10000
time post-exposure (min)
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 overestimate 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.
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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
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
2018 REVISION TO: TECHNICAL GUIDANCE FOR ASSESSING THE EFFECTS OF ANTHROPOGENIC SOUND ON MARINE MAMMAL
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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) 37 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
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
37
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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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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40
(a)
(c)
(b)
30
20
10
3 kHz
•
0
---
40
(d)
CO 30
..,,
~
Cl) 20
3 kHz •
II- 10
•
•
(e )
(f)
(h)
(i)
•
0
40
I
(g)
I
I
30
I
14.1kHz,
20
I
I
0
56 .6 kHz ,
9'
I
I
I
10
,e 10 kHz
0
120 140 160 180 200 220
140 160 180 200 220
SEL (dB re 1
Figure A10.
140 160 180 200 220
µPa 2 s)
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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(b)
(c)
o'
I
22 .5 kHz '
50
I
40
.,
I
I.)
30
,.._20
en
~
;
10
Cl) 0
II- 60
;
;
(d)
;
22.5 kHz ., ,,
.,
(M)
50
;
40
.,
;
30
0
20
10
o,,
§"" •
;
.,
.,
., ;
., .,
0
160 170 180 190 200 210
170 180 190 200 210
.,
.,
~.,~.
_§- "o
j
22.5 kHz
(F)
I I •
170 180 190 200 210
SEL (dB re 1 µPa2 s)
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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40
(a)
(c)
(b)
I
I
I
30
I
6.5 kHz
4 kHz
20
1-2 kHz
10
0
I
---co
""O
(d)
40
(e)
I
0
(f)
30
( /)
I- 20
I10
I
~
0
140
(g)
40
160
180
200
140
160
180
200
SEL (dB re 1 µPa2 s)
30
20
10
0
.)
140
•
160
im pu lsive
180
200
SEL (dB re 1 µPa 2s)
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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20
~
(a)
(b)
(c)
02
4 kHz
2.5 kHz
10
T
~
2~
--yf
Pv
0
~
160
180
200
160
180
Ma
200
160
180
200
2
SEL (dB re 1 µPa s)
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)
MF
Tursiops
truncatus
BEN
3
0
7
211*
0.21
—
—
MF
Tursiops
truncatus
NAY
3
0
5
—
0.13
—
—
MF
Tursiops
truncatus
BLU
3
4
11
207*
1.5
—
—
intermittent
(Finneran et al., 2010a)
10(c)
MF
Tursiops
truncatus
BLU
3
0
23
206*
1.0
240
34
TTS onset higher
than subsequent
tests
(Finneran et al., 2010b)
10(d)
MF
Tursiops
truncatus
TYH
3
0
9
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)
MF
Tursiops
truncatus
BLU
3
7.1
10
14.1
20
28.3
MF
Tursiops
truncatus
TYH
40
56.6
0
0
11
12
182
181
0.46
1.1
—
—
—
—
MF
Delphinapterus
leucas
N/a
32
20
40
—
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
MF
Delphinapterus
leucas
MF
Delphinapterus
leucas
male
11.2
22.5
45
90
MF
Delphinapterus
leucas
female
22.5
0
40
184*
1.7
206
MF
Delphinapterus
leucas
male
22.5
12
40
—
1.2
HF
Phocoena
phocoena
02
4
2
15
165
HF
Phocoena
phocoena
02
~1.5
~1.5
0
0
32
7
HF
Phocoena
phocoena
02
6.5
6.5
1
0
HF
Phocoena
phocoena
02
~6.5
~6.5
HF
Neophocaena
phocaenoides
male
HF
Neophocaena
phocaenoides
HF
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)
22
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
0
20
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)
OW
Zalophus
californianus
Rio
2.5
5
9
199
0.17
—
PW
Phoca vitulina
Sprouts
2.5
3
12
183
6.4
PW
Mirounga
angustirostris
Burnyce
2.5
3
5
—
PW
Phoca vitulina
01
4
0
10
PW
Phoca vitulina
02
4
0
11
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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--100
co
"'O
"'O
0
..c
80
(/)
~
..c
.....
frequency
Figure A14.
-
N
The cutoff frequencies f1 and f2 were defined as the frequencies below and above f0
at which the composite audiogram values were ΔT-dB above the threshold at f0 (the
lowest threshold).
0
en
cu
MF
a..::1.
200
..-
180
-
160
0> 200
,._
en
"'O
.._,,,
Q)
~ 180
••
0
en
II-
1
10
140
100
120
1
10
100
frequency (kHz)
Figure A15.
Effect of ΔT adjustment on the TTS exposure functions for the mid-frequency
cetaceans (left) and high-frequency cetaceans (right). To calculate the exposure
functions, a and b were defined as a = s0/20 and b = 2. ΔT was then varied from 0 to
20. At each value of ΔT, K was adjusted to minimize the squared error between the
exposure function and the onset TTS data (symbols). As ΔT increases, f1 decreases
and f2 increases, causing the pass-band of the function to increase and the function
to “flatten”.
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
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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.
•
I
e 22
I...
I...
Q)
20
0
-c
~ 18
cu
·\ \
~ rigin al
\• \ 'o,
5-16
<{' 14
C
\
ffi
12
E 10
normalized
/
I/ l
0
I I
Nj.(o,//
o"O·J' o
✓
.,
•'•-•·•/
t
8
0
5
10
15
20
~ T (dB)
Figure A16.
9.3
Relationship between ΔT 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 ΔT values from 0 to 20. The lowest MSE value was obtained
using the audiograms based on normalized thresholds with ΔT = 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
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
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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.
TTS onset
at f0
(dB re 1 μPa2s)
Group
f0
(kHz)
Threshold
at f0
(dB re 1 μPa)
LF
5.6
54
MF
55
54
179
125
HF
105
48
156
108
SI
16
61
OW
12
67
199
132
PW
8.6
53
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
a
b
f1
(kHz)
f2
(kHz)
K
(dB)
C
(dB)
Weighted TTS
threshold
(dB SEL)
R2
LF
1
2
0.20
19
179
0.13
179
—
MF
1.6
2
8.8
110
177
1.20
178
0.825
HF
1.8
2
12
140
152
1.36
153
0.864
SI
1.8
2
4.3
25
183
2.62
186
—
OW
2
2
0.94
25
198
0.64
199
—
PW
1
2
1.9
30
180
0.75
181
0.557
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---
'
''
200
''
···' "·-···._
(/)
N (U
180
a_
::i.
T"""
160
LF
Q)
~
HF
MF
a:l 140 ......__._................................_........................................................__..................._...................._..................................__..................._..................._.........
10
100
0.1
~
0.01
1
10
10
100
+-'
Q)
(/)
C 220
0
Cf)
II- 200
' ••
180
SI
0.1
. ..... .... .. . ······ ··
1
10
ow
100
0 .1
PW
10
100
frequency (kHz)
Figure A17.
0.1
10
100
- - Exposure fun ction [Eq. (2)1
- - Composite audiogram
· · ·· · · Phase 2 exposure function
• TTS onset data
0 Estimated TTS onset
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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7
--
210
'
(/)
N
ro
0..
::i
'1 T 11
~
I
I
I
I
~4.311
200
I
T"""
[>o,3,
Q)
L.
I
m 190
--.....
Q)
180
~
I>
0
Cf)
II-
()
•
(/)
c::
T
!I<1"
'"O
0
.
*0
170
Schlund! 2000
Nachtigall 2003
Nachtigall 2004
Finneran 2005
Finneran 2007 (behav)
Finneran 2007 (AEP)
Mooney 2009a
Mooney 2009b
Finneran 201 Oa
Finneran 201 Ob
Popov 2011a
Finnera n 2013
Popov 2013
Popov 2014 (F)
Popov 2014 (M)
Popov 2015
Exposure function
• • • • Phase 2 function
- - Composite audiogram
160
1
Figure A18.
10
frequen cy (kHz)
100
Mid-frequency cetacean exposure function, (normalized) composite audiogram, and
Phase 2 exposure functions compared to mid-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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()
-
190
Cl')
N
C'Cl
a..
::i
.....
i
180
Q)
'--
en 170
"O
--......
........... .....................
ci35
"
C:
0
Cf)
cJ8
~
... ...
160
*
i
cJ5 cJ3
T
030037<:Js <:JO
Q)
Cl')
0
d sd o cJ5
cJ3
cJ5
0 18
()
I
[I
<>
Popov (2011)
Kastele in (2012a)
Kastele in (2013b)
Kastele in (2014a)
Kastele in (2014a)
Kastele in (2014b)
Kastele in (2014b)
Kastele in (2015a)
Kastele in (2015a)
.
-
6.5 kHz
9.2 kHz
100%
10%
100%
10%
- E xposure function
• • • • Phase 2 function
- - Composite aud iogram
150
140
0.5
Figure A19.
1
10
frequency (kHz)
100
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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N
''
en 210
ro
a..
:::i..
T"""
ID
200
I...
ID
en
I
I
'
''
''
'
''
T SO+
'
190
C
0
...
I
.A 44
''
•?
I
I
I
- Exposure function
• • • • Phase 2 func tion
- - Composite audiogram
I
''
'
,,
•.
Kasta k 2005
Kaslele in 20 12 (sea l 01 )
Kastele in 20 12 (sea l 02 )
Kastele in 2013
Kasta k 2008
,,
Cl)
II- 180
170
0.1
1
10
frequency (kHz)
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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X.
PTS EXPOSURE FUNCTIONS
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.
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
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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, C 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
are 170 and 140 dB re 1 μPa2s, respectively, making
= 11 dB. Therefore, for each
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
chinchillas. The appropriate frequency weighting function for each functional hearing
group is applied only when using the SEL-based thresholds to predict PTS.
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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)
LF
54
168
213
183
219
MF
54
170
224
185
230
HF
48
140
196
155
202
SI
61
175
220
190
226
OW
67
188
226
203
232
PW
53
170
212
185
218
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XII.
SUMMARY
SUM ARY
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).
0
.,, ,,
...--..
co
LF
"O
..__
Q)
I.
-20
"O
:::J
-+-'
Q.
E
-40
co
-60
0.01
0.1
1
10
100
0.1
1
10
100
frequency (kHz)
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.
(/! J.)'°
{
W(/) = C+IOlog,o [1+(/! 1.)'J[1+(/
Non-impulsive
TTS
threshold
PTS
threshold
Impulse
TTS
threshold
PTS
threshold
b
SEL
peak SPL
peak SPL
f2
C
SEL
SEL
SEL
f1
(unweight (weighted (unweight
(kHz) (kHz) (dB) (weighted) (weighted) (weighted)
)
ed)
ed)
2
0.20
19
0.13
179
199
168
213
183
219
MF 1.6 2
8.8
110 1.20
178
198
170
224
185
230
HF
1.8 2
12
140 1.36
153
173
140
196
155
202
SI
1.8 2
4.3
25
2.62
186
206
175
220
190
226
Grou
a
p
LF
1
OW
2
2
0.94
25
0.64
199
219
188
226
203
232
PW
1
2
1.9
30
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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·· ·· ·· ·~
\
--
180
'3_
160
.
.:
~
(/)
N
co
LF
Q)
,._
CD
,:,
--w
140
0.01
MF
0.1
1
10
10
100
1
10
100
_J
en 220
200
'
180
-- - - - - - - - -
'
,
ow
SI
0.1
10
100
0.1
PW
1
10
100
0 .1
10
100
frequency (kHz)
- ·· · · ··
-
Figure A22.
Phase 2 Phase 2 Phase 3 Phase 3 -
TTS
PTS
TTS
PTS
Exposure function
Exposure function
Exposure function
Exposure function
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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.//, '
·· ·•······........
...
180
en
N
~
'
'
,'/
--
I
I
,
160
ro
a..:::t
140
LF
MF
~
Q}
,_
co
--w
-0
0.01
220
1
10
10
100
·····\ ·······•······· · ·1
_J
en
0.1
',
200
·:·~ ,,/
10
100
I
180
SI
ow
160,__...............uL.-..................-""L......................___..~~.................................__.............c..............................................................................................................._....
0.1
1
10
100
0. 1
1
10
100
0.1
1
10
100
frequency (kHz)
Figure A23.
- · ·· ···
-
Phase
Phase
Phase
Phase
2
2
3
3
- TTS
- PTS
- TTS
- PTS
Exposu re function
Exposu re func tion
Exposu re function
Exposu re func tion
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
AUDIOGRA
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:
(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
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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
(
T(f)=To +Alog rn
F
1 (f1
8
,
ll+__1_j
+l-J
f
F2
(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:
T(f) = T0 + L(f)+ H(f),
(A1.2)
where
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(
l Fl
j) ,
(A1.3)
.
(A1.4)
L(f)=Alog10 1+
and
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
(Fl
L(f)=Alog 10
l j) ,
(A1.5)
which can also be written as
L(f) = Alog10 f; - Alog 10 f .
(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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70
60
in
50
"C
40
--
H(f)
"C
0
..c 30
en
I
(1)
I
I
L..
..c
20
+-'
I
10
0
-10
0.01
-----------0.1
1
,,
I
10
frequency (kHz)
FIGURE A1.1.
Relationship between estimated threshold, T(f), (thick, gray line), lowfrequency 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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~=
r(10T'/A_1) .
(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). Highfrequency 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).
proposed LF cetacea n
- - - - Cranford (20 15)- fin
- - Houser (2001 ) - humpback
70
60
---~ 50
--- ....
i:::::,
0
..c
40
Cl)
Q.)
~
..c
.......
30
,·,
...
, ,.
'
--, ,
'
20
'
10
0
0.01
0.1
...
.'
I
I
I
I
'
,'
'
'
'
'
I
I
,
I
,''
-. , , '
''
'
'
'
I
.-
I
I
'
1
I
I
10
frequency (kHz)
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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9
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APPENDIX B:
RESEARCH RECOMMENDATIONS
RECOM ENDATIONS FOR
FOR IMPROVED
I PROVED
THRESHOLDS
In compiling, interpreting, and synthesizing the scientific literature to produce 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:
Summary of currently available marine mammal data.
Hearing Group
LF Cetaceans
MF Cetaceans
HF Cetaceans
PW Pinnipeds
OW Pinnipeds
Audiogram
Data/Number of
Species
Predictive
modeling/2
species
TTS
Data/Number of
Species
Behavioral/8
species
Behavioral/2
species
Behavioral/2
species
Behavioral/5
species
Behavioral/3
species
Behavioral/1
species
Behavioral/2
species
Behavioral/1
species
None/0 species
Sound Sources for TTS Studies
None
Octave-band noise; Tones; Midfrequency 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; 38 Houser and Moore 2014; Lucke et al. 2014; Popper et al. 2014; 39 Williams
et al. 2014; Erbe et al. 2016; Lucke et al. 2016). Note: Just because there may not be enough
information to allow for quantifiable modifications to thresholds associated with many of these
recommendations, does not mean these recommendations cannot be incorporated as qualitative
considerations within the comprehensive effects analysis.
I.
1.1
SUMMARY OF RESEARCH
RESEARCH RECOMMENDATIONS
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
38
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.
39
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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data 40 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).
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.” Similarly, data from Ruser et al.
(2017) reported that harbor porpoise live-stranded (15 individuals both males and females;
subadults and adults) and wild individuals incidentally caught in pound nets (12 both males and
females; subadult and adults) had “the shape of the hearing curve is generally similar to
previously published results from behavioral trials.” Thus, from these studies, it appears that for
baseline hearing measurements, captive individuals may be appropriate surrogates for freeranging 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 highfrequency hearing limits were consistent with previously tested captive individuals. However,
these are currently the only studies of their kind, 41 and more research is needed to examine if this
trend is applicable to other species (Lucke et al. 2016).
1.3.1
40
Impacts of Age on Hearing
Data should be collected under appropriate permits or authorizations.
41
NMFS is aware that additional baseline hearing measurements have been recorded for additional free-ranging 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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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 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.”
•
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 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 thresholds or if harbor porpoises are the exception.
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.
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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?).
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 42) 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 thresholds (Table B2).
However, there are not enough data to establish numerical thresholds based on these added
factors (beyond what has already been included in this document, in terms of marine mammal
auditory 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).
42
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; Kastelein et al. 2017b; Kastelein
et al. 2017c) 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 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; NRC 2016)
* Frequency-dependent hearing loss and overall hearing ability within a hearing group is taken into account,
quantitatively, with auditory weighting functions.
1.5.3
Possible Protective Mechanisms
Nachtigall and Supin (2013) 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 by a
warning signal. Nachtigall and Supin (2014) reported a similar finding in a bottlenose dolphin, a
beluga (Nachtigall et al. 2016a), and in harbor porpoises (Nacthigall et al. 2016b). 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. 2016c).
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. Popov et
al. (2016) investigated the impact of prolonged sound stimuli (i.e., 1500 s continuous pip
successions vs. 500-msec 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
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during prolonged stimulation. The authors also caution that adaptation will vary with sound
parameters. Finneran (2018) confirmed that bottlenose dolphins can “self mitigate” when warned
of an upcoming exposure and that mechanism for this mitigation occurs in the cochlea or auditory
nerve.
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 noise-induced 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 low-level 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 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 lifetime 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
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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 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 M ARINE M AMMALS 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.
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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 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 thresholds that are more complex 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.
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
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metrics for establishing thresholds and predicting impacts to hearing would be useful in
confirming the value of providing dual metric thresholds using the PK and weighted 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 thresholds are based on the EEH, which is known to be
inaccurate in some situations. 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) or more appropriately the more recent International
Organization for Standardization (ISO) 43. 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 44 (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 thresholds expressed by the weighted SELcum metric
because if not taken into consideration unrealistically low levels of exposure with long enough
exposure durations could accumulate to exceed current weighted SELcum 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).
Currently, defining effective quiet for marine mammals is not possible due to lack of data.
However, a 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) 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 weighted 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 noise-induced hearing
loss.
43
This version (2.0) of Technical Guidance is more reflective of ISO 18405 (ISO 2017). ISO 18405 is the preferred
standard because it was developed specifically for underwater acoustics, compared with standards developed for airborne
acoustics that use different conventions.
44
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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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 thresholds are likely to become. For example, before the 2016 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 thresholds better represent the current state of knowledge, they have created
additional challenges for implementation. Practical application always needs to be weighed
against making thresholds overly complicated (cost vs. benefit considerations). The creation of
tools to help ensure action proponents, as well as managers apply complex thresholds correctly,
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:
TECHNICAL GUIDANCE REVIEW PROCESSES: PEER
REVIEW, PUBLIC
U DER
PUBLIC COMMENT,
CO ME T, AND REVIEW UNDER
EXECUTIVE ORDER 13795
The Technical Guidance (NMFS 2016a) before its finalization in 2016 went through several
stages of peer review and public comment. Additionally, this document underwent further review
under E0 13795.
I.
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 45 (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 peerreviewed 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), 46 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 (NMFS 2016a) 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 onset thresholds based on physical
characteristics at the source and how those characteristics change with range. 47 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.
45
NOAA's Information Quality Guidelines.
46
“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 Technical Guidance is not a regulatory action subject to a cost-benefit analysis under Executive
Orders12866 and 13563. The Technical Guidance was classified as a HISA because it was novel and precedent setting,
not due to the potential financial implications.
47
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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1.1
2013 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 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, 48 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
Dr. Paul Nachtigall
Dr. Doug Nowacek
Dr. Klaus Lucke*
Dr. Aaron Thode
Affiliation
University of Hawaii
Duke University
Wageningen University and Research (The Netherlands)
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: Link to Technical Guidance's Peer Review Plan.
1.2
2015 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.
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 49 specifically in marine mammal hearing
(i.e., behavior and/or AEP) and/or noise-induced hearing loss. Of the twelve nominated
48
Reviewer credentials are posted at: Link to Technical Guidance's Peer Review Plan.
49
Reviewer credentials are posted at: Link to Technical Guidance's Peer Review Plan.
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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
Dr. Whitlow Au
Dr. Colleen Le Prell
Dr. Klaus Lucke
Dr. Jack Terhune
Affiliation
University of Hawaii
University of Florida*
Curtin University (Australia)
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: Link to Technical Guidance's Peer Review Plan.
1.2.1
2016 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 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: Link to Technical Guidance's Peer Review Plan.
1.3
2015 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 onset 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
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volunteered, were available, had no conflicts of interest, and had the appropriate area of
expertise 50 to complete an individual review of the technical section (Table C3).
Additionally, NMFS wanted peer reviewers with expertise in marine and terrestrial mammal noiseinduced 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).
Table C3:
Third peer review panel.
Name
Dr. Robert Burkard
Dr. Peter Dahl*
Dr. Colleen Reichmuth+
Dr. Kevin Williams*
Affiliation
University at Buffalo
University of Washington
University of California Santa Cruz
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: Link to Technical Guidance's Peer Review Plan.
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.
II.
PUBLIC COMMENT
CO MENT 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 statutes. The first two public
50
Reviewer Credentials.
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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
2013/2014 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.
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 51 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 nongovernmental organizations; an environmental consulting firm; and a regulatory watchdog group.
Each provided substantive comments addressing technical aspects or issues relating to the
implementation of thresholds, which were addressed in the Final Technical Guidance or related
Federal Register Notice. 52
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 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.
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.
51
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.
52
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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2.2
2015 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 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.
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: Link to Technical Guidance web page.
2016 THIRD PUBLIC COMMENT PERIOD (ASSOCIATED WITH 2016 PROPOSED CHANGES FROM
DRAFT TECHNICAL GUIDANCE) 53
2.3
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 thresholds for LF cetaceans
•
Movement of the white-beaked dolphin (Lagenorhynchus albirostris) from MF to HF
cetaceans 54
53
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).
54
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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•
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
auditory weighting function
•
Removal of PK thresholds for non-impulsive sounds
•
Use of dynamic range to predict PK 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 2016b).
2.3.1
Summary of Public Comments Received
A total of 20 55 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 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 56 of the 14-day public comment period. Specific comments can be viewed on
Regulations.gov.
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.
CHANGES TO TECHNICAL GUIDANCE AS A RESULT OF PUBLIC COMMENTS
2.4
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 auditory weighting function and thresholds
throughout the public comment process
55
One group of commenters had trouble 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.
56
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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•
Updated methodology (dynamic range) for approximating PK thresholds for species
where TTS data from impulsive sources were not available
•
Removal of PK thresholds for non-impulsive sources
•
Addition of an appendix providing research recommendations
•
Adoption of a consistent accumulation period (24-h)
•
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
Research Recommendations (Appendix B).
•
Replacement of alternative 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).
III.
Ill.
REVIEW UNDER
UNDER EXECUTIVE
EXECUTIVE ORDER 13795
Presidential Executive Order (EO) 13795, Implementing an America-First Offshore Energy
Strategy (82 FR 20815; April 28, 2017), stated in section 2 that “It shall be the policy of the United
States to encourage energy exploration and production, including on the Outer Continental Shelf,
in order to maintain the Nation’s position as a global energy leader and foster energy security and
resilience for the benefit of the American people, while ensuring that any such activity is safe and
environmentally responsible.” Section 10 of the EO called for a review of the 2016 Technical
Guidance for Assessing the Effects of Anthropogenic Sound on Marine Mammal Hearing
(Technical Guidance; NMFS 2016a) as follows: “The Secretary of Commerce shall review
[Technical Guidance] for consistency with the policy set forth in Section 2 of this order and, after
consultation with the appropriate Federal agencies, take all steps permitted by law to rescind or
revise that guidance, if appropriate.”
3.1
REVIEW OF 2016 TECHNICAL GUIDANCE UNDER EO 13795
3.1.1
2017 Public Comment Period
To assist the Secretary in carrying out that directive under EO 13795, NMFS held a 45-day public
comment period (82 FR 24950; May 31, 2017) to solicit comments on the Technical Guidance
(NMFS 2016a) for consistency with the EO’s policy.
3.1.1.1 Summary of Comments Received
NMFS received 62 comments directly related to the 2016 Technical Guidance. 57 Comments were
submitted by Federal agencies (Bureau of Ocean Energy Management (BOEM), U.S. Navy,
57
NMFS received an additional 137 comments during the Technical Guidance’s public comment period relating to an
overlapping public comment period for “Takes of Marine Mammals Incidental to Specified Activities; Taking Marine
Mammals Incidental to Geophysical Surveys in the Atlantic Ocean” (82 FR 26244). Thus, the majority (approximately
70%) of public comments NMFS received during the Technical Guidance’s public comment period related to the proposed
action of oil and gas activity in the Atlantic.
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MMC), oil and gas industry representatives, Members of Congress, subject matter experts, nongovernmental organizations, a foreign statutory advisory group, a regulatory advocacy group, and
members of the public (Table C4).
Table C4:
Summary of commenters
Commenter
Category
U.S. Federal
agencies
Members of
Congress*
Oil & gas industry
representatives
Non-Governmental
Organization
Regulatory advocacy
group
Foreign statutory
advisor Group
Subject matter
experts (SME)
General public
Specific Commenter
Bureau of Ocean Energy Management; Marine Mammal Commission;
U.S. Navy
22 members
American Petroleum Institute/International Association of Geophysical
Contractors/Alaska Oil and Gas Association/National Ocean Industries
Association
Natural Resources Defense Council/The Human Society of the
US/Whale and Dolphin Conservation; Ocean Conservation Research
Center for Regulatory Effectiveness
Joint Nature Conservation Committee
Marine scientist/mammologist; Geophysicist/Geochemist; Acoustician
47 members
; indicates separate comments, while / indicates comments submitted together.
* Letter sent directly to Secretary Ross (i.e., not submitted to Regulations.gov).
Most of the comments (85%) recommended no changes to the Technical Guidance, and no
public commenter suggested rescinding the Technical Guidance. The U.S. Navy, Marine Mammal
Commission, Members of Congress, and subject matter experts expressed support for the
Technical Guidance’s thresholds and weighting functions as reflecting the best available science.
The remaining comments (15%) focused on additional scientific publications for consideration or
recommended revisions to improve implementation of the Technical Guidance. All public
comments received during this review can be found at: Regulations.gov.
3.1.2
2017 Federal Interagency Consultation
Further, to assist the Secretary in carrying out the directive under EO 13795, NMFS invited, via
letter, 15 Federal agencies to participate in an in-person meeting (i.e., Interagency Consultation)
on September 25, 2017, at NMFS Headquarters in Silver Spring, Maryland, to serve as a formal
forum to discuss this document and provide additional comments. Ten of the eleven 58 expected
Federal agencies participated in this meeting (Table C5).
58
The U.S Fish & Wildlife Service, U.S. Coast Guard, and The U.S. Environmental Protection Agency declined NMFS’
invitation to participate. U.S. Department of Energy did not reply.
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Table C5:
Ten Federal agency attendees*
Bureau of Ocean Energy Management
Department of State
Federal Highway Administration
Marine Mammal Commission
National Park Service
National Science Foundation
U.S. Air Force
U.S. Army Corps of Engineers
U.S. Geological Survey+
U.S. Navy
*Bureau of Safety and Environmental Enforcement did not attend.
+USGS
participated via webinar/teleconference.
3.1.2.1 Summary of Interagency Comments
At the Federal Interagency Consultation, none of the Federal agencies recommended rescinding
the Technical Guidance. Federal agencies were supportive of the Technical Guidance’s
thresholds and auditory weighting functions and the science behind their derivation and were
appreciative of the opportunity to provide input. Comments received at the meeting focused on
improvements to implementation of the Technical Guidance and recommendations for future
working group discussions to address implementation of the Technical Guidance based on any
new scientific information as it becomes available.
3.2
REVISIONS TO THE 2016 TECHNICAL GUIDANCE AS A RESULT OF REVIEW UNDER EO 13795
NMFS acknowledges the importance of supporting sustainable ocean use, such as energy
exploration and production on the Outer Continental Shelf, provided activities are conducted in a
safe and environmentally responsible manner. Our development and implementation of the
Technical Guidance are consistent with allowing activities vital to our nation’s security and
economy to proceed, including those mentioned in EO 13795, and allows for decisions to be
made based upon the best available information.
The EO 13795 review process provided NMFS the opportunity to acquire valuable feedback from
the public/stakeholders and Federal agencies on the 2016 Technical Guidance and its
implementation, since its finalization. During both NMFS’ public comment period and Federal
Interagency Consultation, neither the public/stakeholders nor Federal agencies recommended the
2016 Technical Guidance (NMFS 2016a) be rescinded. Most comments were supportive of the
thresholds and auditory weighting functions within 2016 Technical Guidance. Of those providing
comments, most offered recommendations for improving the clarity of the document and
facilitating implementation.
During both the public comment period and the Federal Interagency Consultation, three key topic
areas were raised: (1) the limited scientific data on the impacts of sound on LF cetacean hearing;
(2) the need to determine the accumulation period for all species of marine mammals; and (3) the
need to improve the 2016 Technical Guidance’s optional User Spreadsheet tool. Commenters
also encouraged the agency to establish working groups to address these data gaps and future
needs.
NMFS’ evaluation of comments received during this process affirms that the Technical Guidance
is based on the best available science. Nevertheless, based on consideration of comments
received and per the approval of the Secretary of Commerce, NMFS made the following revisions
to the 2016 Technical Guidance and/or companion User Spreadsheet tool to improve
implementation and facilitate its use by action proponents, thereby further advancing the policy in
section 2 of EO. 13795 (as reflected in this 2018 Technical Guidance, Version 2.0):
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•
To promote a more realistic assessment of the potential impacts of sound on marine
mammal hearing, using the Technical Guidance, NMFS will re-evaluate implementation
of the default 24-h accumulation period and plans to convene a working group later in
2018 to investigate means for deriving more realistic accumulation periods.
•
To understand further the impacts of sound on hearing of LF cetaceans, a marine
mammal group where no direct data on hearing exists, NMFS plans to convene a
working group later in 2018 to explore this topic. NMFS will incorporate any changes that
may result from the working group’s efforts in future updates to the Technical Guidance.
•
NMFS created a new User Manual for NMFS’ User Spreadsheet tool that provides
detailed instructions and examples on how to use this optional tool. This new User
Manual (NMFS 2018) is available at: Link to Technical Guidance web page. NMFS plans
to submit the User Manual for public comment later in 2018 to gain input from
stakeholders and inform future versions of the User Manual.
•
NMFS issued an updated optional User Spreadsheet tool to provide PTS onset isopleths
associated with the Technical Guidance’s PK thresholds associated with impulsive
sources, so action proponents will not have to perform this calculation separately. The
modified version (Version 2.0) of the optional User Spreadsheet tool is available at: Link
to Technical Guidance web page.
•
NMFS issued an updated optional User Spreadsheet tool to include a custom sheet for
vibratory pile driving activities to facilitate the ease of assessing PTS onset for this
commonly used sound source. Custom tabs for multiple and single
explosives/detonations were also added to the updated optional User Spreadsheet tool.
These custom tabs, within the optional User Spreadsheet tool (Version 2.0), are available
at: Link to Technical Guidance web page.
•
NMFS summarized and conducted a preliminary analysis of the relevant scientific
literature published since the 2016 Technical Guidance’s finalization (Section 3.1.1).
•
NMFS modified the Technical Guidance threshold’s symbols and glossary to be more
reflective of the International Organization for Standardization (ISO) 2017 Underwater
Acoustics – Terminology standard (ISO 18405), which was specifically developed for
underwater acoustics.
•
Appendix A has been updated to include the Navy’s finalized version (Technical Report
3026, December 2016) of their Technical Report that NMFS used to derive the Technical
Guidance’s thresholds and auditory weighting functions.
•
To increase understanding of how regulatory programs use and recommend the use of
the Technical Guidance, which would facilitate implementation and thereby further
advance the Policy in section 2 of EO 13795, NMFS is developing a separate document
describing how the Technical Guidance is used in the MMPA incidental take authorization
process to estimate “take” and inform mitigation decisions.. This document, once
available, will be found at: Link to Incidental Take Authorization web page.
Note: Several comments received during both the public comment period and Federal
Interagency Consultation were beyond the scope of the Technical Guidance and/or its review
under section 10 of EO 13795. However, NMFS is evaluating these recommendations and
determining the best way to address them via other means outside this review.
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APPENDIX D:
I.
ALTERNATIVE METHODOLOGY
ETHODOLOGY
INTRODUCTION
This Appendix is provided to assist action proponents in the application of thresholds presented in
this Technical Guidance. Since the adoption of NMFS’ original thresholds for assessing auditory
impacts (i.e., RMS SPL: 180 dB for cetaceans; 190 dB for pinnipeds), 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 thresholds. However, NMFS recognizes in updating our 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 apply NMFS’ thresholds for the onset of PTS for all sound sources. These tools are
incorporated in NMFS’ optional User Spreadsheet tool, with examples provided in the recently
developed User Spreadsheet Manual (NMFS 2018) 59.
There is no obligation to use the optional User Spreadsheet tool, and the use of more
sophisticated exposure modeling or consideration of additional action- or location-specific factors,
if possible, is encouraged.
II.
WEIGHTING
WEIGHTI G FACTOR
FACTOR ADJUSTMENT ASSOCIATED WITH SEL
SELcu
CUM 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 auditory 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
auditory weighting functions.
WFAs use the same thresholds contained in the Technical Guidance and allow adjustments to be
made for each hearing group based on source-specific information.
NMFS has provided a companion User Spreadsheet tool and User Manual for the User
Spreadsheet tool to help action proponents incorporate WFAs to determine isopleths for PTS
onset associated with their activity: Link to Technical Guidance web page.
2.1
APPLICATION FOR NARROWBAND SOUNDS
For narrowband sources, the selection of the appropriate frequency for consideration associated
with WFAs is straightforward. WFAs for a narrowband sound would take the auditory weighting
59
The most recent version of the optional User Spreadsheet tool and companion User Manual (NMFS 2018) is available
at: Link to Technical Guidance web page.
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function amplitude, for each hearing group, associated with the particular frequency of interest
and use it to make an adjustment to 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 weighted 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: NMFS reminds action proponents to 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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WiFA
0
,__
i:i:l
"C
.._.,
-10
/
II)
/
"C
-~
t<
-20
.!=
-30
C
/
-
/
-
ti
LF
MF
• • • HF
C
;:)
i:...
0/J
-40
.5
:c0/J
~
-SO
WFA
.
.
.. ...
-10
..
.
.
.
...
-20
-30
-40
.....
...
.
.
..
-
o ta riid
• • •
Ph ocid
-50
-60
0.01
0.1
10
100
Frequency (kHz)
Figure D1:
Example illustrating concept of weighting factor adjustment at 1 kHz (solid
red line) with cetacean (top) and pinniped (bottom) auditory weighting
functions.
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'\
I
I\ -
'
- ...
/
}
MF cetacean isopleth : 1.2 m
LF cetacean isopleth: 30 m
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 non-impulsive source, the PTS
onset weighted 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).
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 tool and User Manual for User Spreadsheet tool).
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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 auditory
weighting function be used to make adjustments (i.e., frequencies below those where the auditory
weighting function amplitude is zero 60 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 auditory
weighting function (i.e., frequencies above those where the auditory weighting function amplitude
is zero). For a frequency on the “right side” of the auditory weighting function (Table D1), any
adjustment is inappropriate and WFAs cannot be used (i.e., an action proponent would be
advised to not use auditory weighting functions and evaluate its source as essentially
unweighted; see “Use” frequencies in Table D1, which will result in a auditory weighting function
amplitude of 0 dB).
,_
~
~
- 10
~
"O
...:I
~ -20
~C:
·.§0..
~
-30
r--:---~~---+
~-----------;---1-1
Appropriate frequencies
Inappropriat
to use WFA
-40
fr quencies
OJ)
C
]
OJ)
·•
~
-
-:>O
-60
0.01
0.1
1
10
100
Frequency (kHz)
Figure D3:
Example auditory weighting function illustrating where the use of
weighting factor adjustments are (Green: “left side”) and are not (Red:
“right side”) appropriate for broadband sources.
60
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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Table D1:
Applicability of weighting factor adjustments for frequencies associated
with broadband sounds
Hearing Group
Low-Frequency Cetaceans (LF)
Mid-Frequency Cetaceans (MF)
High-Frequency Cetaceans (HF)
Phocid Pinnipeds (PW)
Otariid Pinnipeds (OW)
Applicable Frequencies
4.8 kHz and lower
43 kHz and lower
59 kHz and lower
11 kHz and lower
8.5 kHz and lower
Non-Applicable Frequencies*
Above 4.8 kHz (Use: 1.7 kHz)
Above 43 kHz (Use: 28 kHz)
Above 59 kHz (Use: 42 kHz)
Above 11 kHz (Use: 6.2 kHz)
Above 8.5 kHz (Use: 4.9 kHz)
* With non-applicable frequencies, users input the “use” frequency in the User Spreadsheet tool, which will result in an
auditory weighting function amplitude of 0 dB (i.e., unweighted).
2.3
OVERRIDING THE WEIGHTING FACTOR ADJUSTMENT
An action proponent is not obligated to use WFAs. If an action proponent has data or
measurements depicting the spectrum of their sound source, they may use these data to override
the User Spreadsheet WFA output. By including a source’s entire spectrum, this will allow an
action proponent to incorporate the Technical Guidance’s marine mammal auditory weighting
functions over the entire broadband frequency range of the source, rather than just for one
frequency via the WFA. As a result, overriding the optional User Spreadsheet’s WFA with a
sound sources’ spectrum will result in more realistic (i.e., likely smaller) isopleths. NMFS is
currently evaluating whether surrogate spectrum are available and applicable for particular sound
sources, if an applicant does not have data of their own to use.
As an example, Figure 118 in Appendix D of the Final Environmental Impact Statement for Gulf of
Mexico OCS Proposed Geological and Geophysical Activities (BOEM 2017) provides a generic
spectrum for an 8000 in3 airgun array (Figure D4).
.....E
@)
220
NI
:r:.
So
~ i
D..
200
::::II.
,....
@'
fC1
1180
'1CII
...JI
LUI
VJ,
1160
~:
:;:II
~:
10
Figure D4:
_ _J
140
100
1000
Frequency (Hz),
Maximum one-third octave band source level in the horizontal plane for a
generic 8000 in3 seismic array (BOEM 2017)
Table D2 provides a comparison of the dB adjustment between using the BOEM 2017 spectrum
used to override the optional User Spreadsheet tool’s default WFA and the direct use of the
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default WFA. As NMFS has stated previously, the more factors an action proponent can
incorporate in their modeling, the more realistic results expected.
Table D2:
Comparison of adjustment (dB) associated with incorporating entire
broadband spectrum vs. default, single frequency WFA for a seismic array.
Weighting
Default WFA
(1 kHz)
Seismic array spectrum
(BOEM 2017)*
LF
cetacean
MF
cetacean
HF
cetacean
PW
pinniped
OW
pinniped
-0.06 dB
-29.11 dB
-37.55 dB
-5.90 dB
-4.87 dB
-12.7 dB
-57.4 dB
-65.7 dB
-28.7 dB
-33.6 dB
* BOEM 2017 spectrum digitized using WebPlotDigitizer: Link to WebPlotDigitizer web page.
III.
Ill.
MODELING CUMULATIVE SOUND EXPOSURE LEVELS
To apply the PTS onset thresholds expressed as the weighted SELcum metric, a specified
accumulation period is necessary. 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 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 61).
Previous NMFS thresholds only accounted for the proximity of the sound source to the receiver,
but thresholds in the Technical Guidance (i.e., expressed as weighted 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 weighted 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 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.
61
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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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
needs to 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 above previous
NMFS thresholds. NMFS proposes two alternative methods: one for mobile sources and one for
stationary sources.
3.2.1
Mobile Sources 62
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 63 (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
SL/(10
dB)
• Source factor (S) = 10
μPa2m2
64
• Energy source factor (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.
62
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 thresholds
presented in the Technical Guidance.
63
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 2017, entry 3.3.2.1 “source level.”
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 2017, entry 3.3.2.2 “energy
source level.”
64
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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 65 (Equation D1.;
e.g., Urick 1983; ANSI 1986; Madsen 2005):
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 66 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 D5.
I
/
I
I
I
I
~
-=- - -..
/
I
I
I
/
I
Source-Receive
//
Separation ~
I
.
;'
/
/
I
I
I
/
I
I
D :.stance source
travels °'rer time
based on source
velocity
I
I
I
l
"--",
Safe Distance (Ro)
Source
[Sowce-Receive: Separ:ltior. :..tClo:::est
Pomtof Approach]
Figure D5:
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 67,b).
65
Equation D1 assumes a constant source-receiver separation distance.
66
The threshold considered by Sivle et al. 2014 was associated with behavioral reactions.
This equation matches Equation 3 from Sivle et al. (2014), but is written in a simpler manner.
67
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a
𝑅𝑅0 =
For impulsive sources, SD is replaced with SE/τ:
b
where:
𝑅𝑅0 =
π
𝑆𝑆𝑆𝑆
𝐸𝐸0 𝑣𝑣
Equations D2a,b
π 𝑆𝑆𝐸𝐸
𝐸𝐸0 𝑣𝑣 𝜏𝜏
S = source factor (10SL/(10 dB) µPa2m2)
D =duty cycle (pulse duration x repetition rate)
𝑣𝑣= transit speed
E0 =exposure threshold (10SEL0 /(10 dB) ) µPa2s)
SE = energy source factor (10SL𝐸𝐸 /(10 dB) µPa2m2s)
τ = 1/repetition rate
R0 represents the exposure isopleth calculated using NMFS’ thresholds. Thus, area calculations
and exposure calculations would be performed in the same manner 68 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).
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 PTS onset acoustic threshold (expressed as weighted SELcum metric)
provided within the Technical Guidance.
For this approach to be applicable to a broad range of activities, the following assumptions 69 are
made:
68
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.
69
If any of these assumptions are violated and there is concern that the isopleth produced is potentially underestimated, it
is recommended action proponents 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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•
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. Note: Action
proponents can override the WFA if spectral data for their sound source is available (See
Section 2.3 of this Appendix).
•
The movement of the source is simple (i.e., source moves at a constant speed and in a
constant direction). Caution is recommended 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 thresholds compared to those receivers that
would avoid or naturally change positions in the water column over time. Caution
is recommended 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 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 70: 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) 71. Thus, modifications to theR0 predicted may be necessary in
these situations.
Despite these assumptions, this approach offers a better approximation of the source-receiver
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.
70
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).
71
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, are recommended for
consideration when evaluating whether spherical spreading is potentially resulting in an underestimation of exposure.
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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 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 tool and User Manual for the User
Spreadsheet tool to help action proponents use this methodology to determine isopleths for PTS
onset associated with their activity (Link to Technical Guidance web page).
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 are advised to contact NMFS for possible applicable alternative methods.
NMFS has provided a companion User Spreadsheet tool and User Manual (NMFS 2018) for the
User Spreadsheet tool to help action proponents wanting to use this methodology to determine
isopleths for PTS onset associated with their activity (Link to Technical Guidance web page).
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APPENDIX
APPE DX 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).
cc
"C
-a;
.c
C)
:f
>
•
••
••
Cl
...J
...::::,
Cl
•··•
••
' - - - - - - - - - - A u dible - - - - - - - - • ••
•••••••
(above line)
•• • • • • •
•~
11'1
11'1
Cl
...
a.
"C
C:
::::,
•••
..
.•
•
••
•
~
••• ••
0
en
3:
_g
••
Inaudible (below line)
Low
Figure E1.
I
:
.
•••
••
•••••••••••••••••••••••
Inaudible (below line)
------------ --- -- --- ---------------- --------------- ----------------• High
Frequency (kHz)
Example audiogram.
Auditory adaptation: Temporary decrease in hearing sensitivity occurring during the
presentation of an acoustic stimulus (opposed to auditory fatigue which occurs post-stimulation)
(ANSI 1995).
Auditory bulla: The ear bone in odontocetes that houses the middle ear structure (Perrin et al.
2009).
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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).
Specifically, this function represents a specified frequency-dependent characteristic of hearing
sensitivity in a particular animal, by which an acoustic quantity is adjusted to reflect the
importance of that frequency dependence to that animal (ISO 2017). 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).
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). Within the Technical Guidance, this metric is weighted based on the document’s marine
mammal auditory weighting functions.
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).
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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).
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).
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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 nonacoustic 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 72).
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).
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. Link to NOAA's
Information Quality Guidelines
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).
72
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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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 (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.
Mean-square sound pressure: Integral over a specified time interval of squared sound
pressure, divided by the duration of the time interval for a specified frequency range (ISO 2017).
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
“(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).
One-third octave (base 10): The frequency ratio corresponding to a decidecade or one tenth of
a decade (ISO 2017).
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 magnitude of the sound pressure,
which can arise from a positive or negative sound pressure, during a specified time, for a specific
frequency range (ISO 2017).
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): Ten times the logarithm to the
base 10 of the ratio of the mean-square sound pressure to the specified reference value in
decibels (ISO 2017).
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: An alteration in pressure propagated by the action of elastic stresses in an elastic
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medium and that involves local compression and expansion of the medium (ISO 2017).
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-mean-square
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 (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).
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).
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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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| File Type | application/pdf |
| File Title | 2018 Revisions to: Technical Guidance for Assessing the Effects of Anthropogenic Sound on Marine Mammal Hearing (Version 2.0) |
| Author | NOAA Fisheries |
| File Modified | 2018-06-18 |
| File Created | 2018-05-02 |