2018 Revision to:Technical Guidance for Assessing theEffects 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 TemporaryThreshold 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)

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TABLE OF CONTENTS
LIST OF TABLES ............................................................................................................................V
LIST OF FIGURES .........................................................................................................................VIABBREVIATIONS, ACRONYMS, AND SYMBOLS ....................................................................VIIIEXECUTIVE 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 ........................................................ 122.2.3 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 CAUSEHEARING 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, PUBLICCOMMENT, 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 TECHNICALGUIDANCE) .................................................................................................................. 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 THRESHOLDS129APPLICATION 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 fromcomposite 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 ofbest 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 withPTS 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 otherFigure 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 andFigure 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 andFigure 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 tounderwater 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 otherimpulsive 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 andfinite-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 reddot (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 SYMBOLSSY 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,24hMFmin

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
DecibelPeak sound level
Distortion productotoacoustic 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 Geophysicalhour
High-frequency
Highly Influential Scientific
Assessment
Hertz
Cubic inches
Influential Scientific
Information
International Organization forStandardization
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
SELcumSIO
SL

Marine Mammal Commission
Marine Mammal Protection
Act
Magnuson-Stevens FisheryConservation andManagement Act
Mean-squared error
meterMilliseconds
Narrow Azimuth
Noise-induced Hearing Loss
National Marine FisheriesServiceNational Marine Sanctuaries
Act
National Oceanic andAtmospheric Administration
National Ocean Service
National Research Council
National Standard 2
National Science Foundation
Office of Management andBudgetOffice of National Marine
Sanctuaries
Office of Protected
Resources
Occupational Safety and
Health Administration
Otariids in waterSound Pressure Level
Pascalspi
peak sound pressure level
Permanent Threshold Shift
Phocids in water
Range“Safe Distance”
Goodness of fit
Root-Mean-Square soundpressure level
Source Factor
Energy Source Factor
Seconds
Distance from source
SlopeSound 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 LevelSPAWAR Systems Center
Pacific
1/repetition rate
U.S. Navy’s Tactical Training
Theater Assessment andPlanning 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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2018 REVISION TO: TECHNICAL GUIDANCE FOR ASSESSING THE EFFECTS OF ANTHROPOGENIC SOUND ON MARINE MAMMALHEARING (VERSION 2.0)
Page xEXECUTIVE SUMMARYSU
ARYThis document provides voluntary technical guidance for assessing the effects of underwater
anthropogenic (human-made) sound on the hearing of marine mammal species under thejurisdiction 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 toexperience 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; otherscientifically 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) andnon-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 mostcases 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 metricrepresent 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, andrecently 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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Page 1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 UnitedStates 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 andresilience for the benefit of the American people, while ensuring that any such activity is safe andenvironmentally 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 orrevise that guidance, if appropriate.”
To assist the Secretary in carrying out the directive under EO 13795, NMFS held a 45-day publiccomment 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 supportiveof the Technical Guidance, including the science used in its derivation and the robust processthat NMFS followed, including four independent peer reviews. The majority of commenters
recommended that the Technical Guidance remain unchanged. The Federal agencies, Membersof Congress, and subject matter experts expressed support for the Technical Guidance asreflecting 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 werebeyond 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 andimplementation, NMFS revised the 2016 Technical Guidance (NMFS 2016a), per approval of theSecretary 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 arepresented 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 foundin 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 3Lp,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 9Lp,0-pk,flat: 232 dB
LE,p,OW,24h: 203 dB

Non-impulsive
Cell 2LE,p, LF,24h: 199 dB
Cell 4LE,p, MF,24h: 198 dB
Cell 6

LE,p, HF,24h: 173 dB
Cell 8LE,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 soundpressure 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.

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" --

0

,-..
i:Q

"O

'-'

✓

-10

11,)

::::l

.<:::

E

-

\

✓

-a -20
.8

\

✓

"O

<C

\

✓

\

-30

\

u

C

::::l
~
bl)

-

..•.•

-40

.5

.c
bl)

~

-

LF

-

MF

• • • HF

\

....

•

-50

.•

_.•

- 60

1

0.1

0.01

10

100

Frequency (kHz)
Figure ES1:

,-...
i:Q
"C

Auditory weighting functions for low-frequency (LF; dashed line), midfrequency (MF; solid line), and high-frequency (HF; dotted line) cetaceans.

0

'-'
11,)

"C
::l

..
.
.
..
.
.
.•

-10

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I<

-20

-

-30

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otariid• • • Phocid

.•
.
.
..

-40

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bl)

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-50

-60
0.01

0.1

1

10

100

Frequency (kHz)
Figure ES2:

Underwater auditory weighting functions for otariid (OW; solid line) andphocid (PW; dotted line) pinnipeds.

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Page 5REVISION TO: TECHNICAL GUIDANCE FOR ASSESSING THE EFFECTS OF
ANTHROPOGENIC SOUND ON MARINEARI E MAMMALAMMAL HEARINGHEARING (VERSION 2.0)
UNDERWATERUNDERWATER THRESHOLDS FOR ONSET OF PERMANENT AND
TEMPORARY THRESHOLD SHIFTSI.

INTRODUCTION

This document provides technical guidance 2 for assessing the effects of anthropogenic (humanmade) sound on the hearing of marine mammal species under the jurisdiction 3 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 intheir hearing sensitivity for acute, incidental exposure to all underwater anthropogenic soundsources. This Technical Guidance is intended for use by NMFS analysts/ managers and otherrelevant action proponents/stakeholders, including other federal agencies, when seeking todetermine whether and how their activities are expected to result in impacts to marine mammal
hearing via acoustic exposure. This document outlines NMFS’ thresholds, describing in detailthreshold development (via Appendix A), and how they will be revised and updated in the future.
The thresholds presented in this document do not represent the entirety of an effects analysis,
but rather serve as one tool among others (e.g., behavioral impact thresholds, auditory masking
assessments, evaluations to help understand the effects of any particular type of impact on an
individual’s fitness, population assessments, etc.), to help evaluate the effects of a proposed
action and make findings required by NOAA’s various statutes. The Technical Guidance may
inform decisions related to mitigation and monitoring requirements, but it does not mandate any
specific mitigation be required 4. The Technical Guidance does not address or change NMFS’application of these thresholds in the regulatory context, under applicable statutes and does notcreate 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.

2

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

3

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

Mitigation and monitoring requirements associated with a Marine Mammal Protection Act (MMPA) authorization or an
Endangered Species Act (ESA) consultation or permit are independent management decisions made in the context of the
proposed activity and comprehensive effects analysis, and are beyond the scope of the Technical Guidance. NMFS
acknowledges exclusion zones and monitoring zones often correspond to thresholds but that is not a legal requirement,
and the thresholds may make such a simple correlation more challenging. The Technical Guidance can be used to informthe development of mitigation or monitoring. NMFS is currently developing a separate document further describing how
the Technical Guidance is used in the MMPA authorization process to inform mitigation decisions. This document, whenavailable, can be found at: NMFS Incidental Take Authorization web page.

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Note: This document does not set forth requirements to conduct sound source verification
studies.

1.1.

THRESHOLDS WITHIN THE CONTEXT OF AN EFFECTS ANALYSISThe Technical Guidance’s thresholds do not represent the entirety of an effects analysis, butrather serve as one tool to help evaluate the effects of sound produced during a proposed action
on marine mammals and make findings required by NOAA’s various statutes. In a regulatory
context, NMFS uses thresholds to help assess and quantify “take” and to conduct morecomprehensive effects analyses under several statutes. NMFS is currently developing a separate
document 5 further describing how the Technical Guidance is used in the MMPA authorization
process to estimate “take.”Specifically, the Technical Guidance will be used in conjunction with sound source
characteristics, environmental factors that influence sound propagation, anticipated marine
mammal occurrence and behavior near the activity, as well as other available activity-specificfactors, to estimate the number and types of takes of marine mammals. This document only
addresses thresholds for auditory impact (i.e., does not address or make recommendations
associated with sound propagation or marine mammal occurrence or density).

1.2

ADDRESSING UNCERTAINTY AND DATA LIMITATIONS

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

1.2.1

Assessment Framework

NMFS’ approach applies a set of assumptions to address uncertainty in predicting potential
auditory effects of sound on individual marine mammals. One of these assumptions includes theuse of “representative” or surrogate individuals/species for establishing PTS onset thresholds for
species where little to no data exists. The use of representative individuals/species is done as amatter of practicality (i.e., it is unlikely that adequate data will exist for the all marine mammal
species found worldwide or that we will be able to account for all sources of variability at anindividual level) but is also scientifically based (i.e., taxonomy, hearing group). As new data
become available for more species, this approach can be reevaluated. NMFS recognizes that
additional applicable data may become available to better address many of these issues (e.g.,
uncertainty, surrogate species, etc.). 6 As these new data become available, NMFS has an
approach for updating this document (see Section III).

5

Document, when available, can be found at: NMFS Incidental Take Authorization web page.

6

NMFS is aware that the authors of Southall et al. (2007) are in the process of updating their original publication andrecognizes that when this updated publication becomes available, it may suggest alternative means for predicting an

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1.2.2

Data Standards

In assessing potential acoustic effects on marine mammals, as with any such issue facing theagency, standards for determining applicable data need to be articulated. Specifically, NOAA has
Information Quality Guidelines 7 (IQG) for “ensuring and maximizing the quality, objectivity, utility,
and integrity of information disseminated by the agency” (with each of these terms defined within
the IQG). Further, the IQG stipulate that “To the degree that the agency action is based on
science, NMFS will use (a) the best available science and supporting studies (including peerreviewed science and supporting studies when available), conducted in accordance with soundand objective scientific practices, and (b) data collected by accepted methods or best available
methods.”
The National Research Council (NRC 2004) provided basic guidelines for National Standard 2(NS2) in section 301 of the Magnuson-Stevens Fishery Conservation and Management Act,
which states that “Conservation and management measures shall be based upon the best
scientific information available” (NOAA 2013). They recommended that data underlying thedecision-making and/or policy-setting process be: 1) relevant, 2) inclusive, 3) objective, 4)transparent and open, 5) timely, 6) verified and validated, and 7) peer reviewed. 8 Although NRC’sguidelines (NRC 2004) were not written specifically for marine mammals and this particular issue,
they do provide a means of articulating minimum data standards. NMFS considered this inassessing acoustic effects on marine mammals. Use of the NRC Guidelines does not preclude
development of acoustic-specific data standards in the future.

II.

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

2.1

M ARINE M AMMAL HEARING GROUPS

Current data (via direct behavioral and electrophysiological measurements) and predictions(based on inner ear morphology, modeling, behavior, vocalizations, or taxonomy) indicate that not
auditory weighting function and thresholds for LF cetaceans. Accordingly, NMFS may re-evaluate our methodology for LF
cetaceans when this updated Southall et al. publication becomes available.
7

NMFS National Standards 2 web page.

8

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

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all marine mammal species have equal hearing capabilities, in terms of absolute hearing
sensitivity and the frequency band of hearing (Richardson et al. 1995; Wartzok and Ketten 1999;
Southall et al. 2007; Au and Hastings 2008). Hearing has been directly measured in someodontocete and pinniped species 9 (see reviews in Southall et al. 2007; Erbe et al. 2016; Finneran2016). Direct measurements of mysticete hearing are lacking. 10 Thus, hearing predictions formysticetes are based on other methods including: anatomical studies and modeling (Houser et al.
2001; Parks et al. 2007; Tubelli et al. 2012; Cranford and Krysl 2015 11); vocalizations 12 (seereviews in Richardson et al. 1995; Wartzok and Ketten 1999; Au and Hastings 2008); taxonomy;
and behavioral responses to sound (Dahlheim and Ljungblad 1990; see review in Reichmuth2007).
To better reflect marine mammal hearing capabilities, Southall et al. (2007) recommended thatmarine mammals be divided into hearing groups (Table 1). NMFS made the following
modifications to the hearing groups proposed in Southall et al. (2007) 13:

9•

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

•

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

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

10

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

11
Note: The modeling of Cranford and Krsyl (2015) predicts that the primary mechanism for hearing in LF cetaceans isbone conduction. Additionally, this predictive model was based on the skull geometry of a newborn fin whale.
12

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

13

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

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Table 1:

Marine mammal hearing groups.
Hearing Group

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

Generalized Hearing
Range*
7 Hz to 35 kHz
150 Hz to 160 kHz
275 Hz to 160 kHz
50 Hz to 86 kHz
60 Hz to 39 kHz* Represents the generalized hearing range for the entire group as a composite (i.e., all species within the group), whereindividual 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).

NMFS’ modification results in marine mammal hearing groups being defined in this Technical
Guidance as depicted in Table 1. Table 1 defines a generalized hearing range each hearing
group. This generalized hearing range was determined based on the ~65 dB 14 threshold from thenormalized composite audiograms (Figure 4). For LF cetaceans and PW pinnipeds, the ~65 dB
threshold resulted in a lower bound that was considered too low to be biologically plausible forthese two groups. Instead, for LF cetaceans the lower frequency limit from Southall et al. 2007
was used, while for PW pinnipeds 50 Hz was chosen as a reasonable approximation for the lower
frequency limit (relative to otariid pinnipeds) 15.

2.1.1

Application of Marine Mammal Hearing Groups

The application of marine mammal hearing groups occurs throughout the Technical Guidance in
two ways. First, thresholds are divided by hearing group to acknowledge that not all marine
mammal species have identical hearing or susceptibility to noise-induced hearing loss (NIHL).
Outside the generalized hearing range, the risk of auditory impacts from sounds is consideredhighly unlikely or very low 16 (the exception would be if a sound above/below this range has thepotential to cause physical injury, i.e., lung or gastrointestinal tract injury from underwater
explosives).
Second, marine mammal hearing groups are used in the establishment of marine mammal
auditory weighting functions discussed next.

14

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

15
Understanding of low-frequency pinniped hearing is limited (i.e., few studies have direct measurements of hearing
below 100 Hz).
16

Animals are able to detect sounds beyond their generalized hearing range by non-auditory mechanisms. However,typically, these sounds have to be extremely loud and would be considered uncomfortable (Wartzok and Ketten 1999). If asound is on the edge of a hearing group’s generalized hearing range and there is the potential for exposure to high soundpressure levels, then consider the potential for detection beyond normal auditory pathways.

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2.2

M ARINE M AMMAL AUDITORY WEIGHTING FUNCTIONS

The ability to hear sounds varies across a species’ hearing range. Most mammal audiograms
have a typical “U-shape,” with frequencies at the bottom of the “U” being those to which theanimal is more sensitive, in terms of hearing (i.e. the animal’s best hearing range; for example
audiogram, see Glossary, Figure F1). Auditory weighting functions best reflect an animal’s ability
to hear a sound (and do not necessarily reflect how an animal will perceive and behaviorally react
to that sound). To reflect higher hearing sensitivity at particular frequencies, sounds are often
weighted. For example, A-weighting for humans deemphasize frequencies below 1 kHz andabove 6 kHz based on the inverse of the idealized (smoothed) 40-phon equal loudness hearing
function across frequencies, standardized to 0 dB at 1 kHz (e.g., Harris 1998). Other types ofweighting functions for humans (e.g., B, C, D) deemphasize different frequencies to different
extremes (e.g., flattens equal-loudness perception across wider frequencies with increasingreceived level; for example, C-weighting is uniform from 50 Hz to 5 kHz; ANSI 2011).
Auditory weighting functions have been proposed for marine mammals, specifically associatedwith PTS onset thresholds expressed in the weighted SELcum 17 metric, which take into accountwhat is known about marine mammal hearing (Southall et al. 2007; Erbe et al. 2016). The
Finneran Technical Report (Finneran 2016) developed marine mammal auditory weighting
functions that reflect new data on:•

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

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

Effects of noise on marine mammal hearing (e.g., Kastelein et al. 2012a; Kastelein et al.
2012b; Finneran and Schlundt 2013; Kastelein et al. 2013a; Kastelein et al. 2013b;
Popov et al. 2013; Kastelein et al. 2014a; Kastelein et al. 2014b; Popov et al. 2014;
Finneran et al. 2015; Kastelein et al., 2015a; Kastelein et al. 2015b; Popov et al. 2015).

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

2.2.1

Use of Auditory Weighting Functions in Assessing Susceptibility to Noise-Induced
Hearing Loss

Auditory weighting functions are used for human noise standards to assess the overall hazard ofnoise on hearing. Specifically, human auditory weighting functions provide a “rating that indicatesthe injurious effects of noise on human hearing” (OSHA 2013). Thus, while these functions are
based on regions of equal loudness and best hearing, in the context of human risk assessments,
as well as their use in the Technical Guidance, they are meant to reflect the susceptibility of theear to noise-induced threshold shifts (TSs). Regions of enhanced susceptibility to noise may not
17

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

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Page 11perfectly mirror a species’ region of best hearing (e.g., TTS measurements from bottlenose
dolphin, belugas, and Yangtze finless porpoise support this). Thus, within the Technical
Guidance, auditory weighting functions are meant to assess risk of NIHL and do not necessarily
encompass the entire range of best hearing for every species within the hearing group.

2.2.2

Marine Mammal Auditory Weighting Functions

Frequency-dependent marine mammal auditory weighting functions were derived using data on
hearing ability (composite audiograms), effects of noise on hearing, and data on equal latency(Finneran 2016 18). Separate functions were derived for each marine mammal hearing group(Figures 1 and 2).

, --,,.-...

~

"'C

-10

/

cu

/

"'C

::

:::

-a. -20
E

<C:

·-...
0

\

/
/

\

-30

'

u

C:

::

~

0/J

-40

....5

•
.•.•

..c:

0/J -50

~

.•.•

-

LF

-

MF

• • • HF

\

.• •

-60
0.01

0.1

---

1

10

100

Frequency (kHz)
Figure 1:

Auditory weighting functions for low-frequency (LF; dashed line), midfrequency (MF; solid line), and high-frequency (HF; dotted line) cetaceans.

18

Wright 2015 provides a critique of this methodology. For NMFS’ response associated with this critique, see the Federal
Register Notice associated with 2016 Technical Guidance (81 FR 51694; August 4, 2016), specifically the section
responding to public comments.

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Page 12

---

0

i:o

"O
(I)

"O

-1 0

I

i-

r

:l

--=
Q..

s

-20

...u

-30

<C

.8

-.
•
.
.
...

.•.•

•
.
•
.
.•.

C
:l

~
Of)

....5

-40

'

-50

ti

-

otariid• • • Phocid

.•

-60
0.01

0.1

1

10

100

Frequency (kHz)

Figure 2:

Underwater auditory weighting functions for otariid (OW; solid line) andphocid (PW; dotted line) pinnipeds.

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

Equation 1

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

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

High-frequency exponent (b): Rate at which the weighting function amplitude declines
with frequency at the upper frequencies. As the frequency increases, the change in
amplitude becomes linear with the logarithm of frequency with a slope of 20b dB/decade.
Low-frequency cutoff (ƒ1): This parameter defines the lower limit of the band-pass filter(i.e., the lower frequency where weighting function amplitude begins to roll off or decline
from the flat, central portion of the function). This parameter is directly dependent on thevalue of the low-frequency exponent (a).

2018 REVISION TO: TECHNICAL GUIDANCE FOR ASSESSING THE EFFECTS OF ANTHROPOGENIC SOUND ON MARINE MAMMALHEARING (VERSION 2.0)
Page 13••High-frequency cutoff (ƒ2): This parameter defines the upper limit the band-pass filter (i.e.,
the upper frequency where weighting function amplitude begins to roll off or decline fromthe flat, central portion of the function). This parameter is directly dependent on the valueof the high-frequency exponent (b).
Weighting function gain (C): This parameter determines the vertical position of thefunction and is adjusted to set the maximum amplitude of the auditory weighting function
to 0 dB.

Finneran (2016) illustrates the influence of each parameter value on the shape of the auditory
weighting function (Appendix A, Figure A2).
In association with auditory weighting functions are exposure functions that illustrate how auditory
weighting functions relate to auditory thresholds. Auditory exposure functions (Equation 2) are theinversion of Equation 1:(J) = K -10 102 {

E
~ ud

-10

dB

(J I J;)l"[l+(J I 1,/ [l+(J I f:f1

Equation 2
where Eaud(ƒ) is the acoustic exposure as a function of frequency (ƒ) and the gain parameter
constant (K), which is adjusted to set the minimum value of the curve to the weighted PTS/TTS
onset auditory threshold. All other parameters are the same as those in Equation 1. Figure 3
illustrates how the various weighting parameters relate to one another in both the auditory
weighting and exposure functions.

Eq . (1) - weighting function

Eq. (2) - exposure function

cf
20b
Q.)

"C

::::I
:t::::

a.

-20b

E

ro

frequency
Figure 3:

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

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

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2.2.3

Derivation of Function Parameters

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

80
60
- . 40co"O..__,,

20

"O

0

..c

0

Cl)

~ -20

-

..c

"O
Q)

LF

0.01

HF
0.1

10

100

0.1

10

100

0.1

10

100

0.1

10

100

80

N

ro 60

E
.....
0

40

C

20
0
-20

ow
0.1

10

100

freq uency (kHz)
Figure 4:

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

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Table 2:

Summary of data available for deriving composite audiograms.†

Hearing GroupSpecies (number ofindividuals)
Beluga (9)Bottlenose dolphin(6)Mid-Frequency (MF)
Cetaceans

High-Frequency (HF)
Cetaceans

False killer whale (1)Killer whale (8)Risso’s dolphin (1)Pacific white-sided
dolphin (1)Striped dolphin (1)Tucuxi (1)Amazon Riverdolphin (1)Harbor porpoise (5)Harbor seal (4)Phocid Pinnipeds(PW) Underwater

Otariid Pinnipeds*(OW) UnderwaterNorthern elephantseal (1)Ringed seal (1)Spotted seal (2)California sea lion
(4)
Northern fur seal (3)Steller sea lion (2)References
White et al. 1978; Awbrey et al. 1988; Johnson et al.
1989; Ridgway et al. 2001; Finneran et al. 2005b
Johnson 1967; Ljungblad et al. 1982; Lemonds 1999;
Brill et al. 2001;Schlundt et al. 2008; Finneran et al.
2010aThomas et al. 1988
Szymanski et al. 1999; Branstetter et al. 2017+
Nachtigall et al. 1995
Tremel et al. 1996
Kastelein et al. 2003
Sauerland and Dehnhardt 1998
Jacobs and Hall 1972
Kastelein et al. 2010; Kastelein et al. 2015c; Kastelein
et al. 2017a+
Terhune 1988; Kastelein et al. 2009b; Reichmuth et al.
2013
Kastak and Schusterman 1999
Sills et al. 2015
Sills et al. 2014
Mulsow et al. 2012; Reichmuth and Southall 2012;
Reichmuth et al. 2013
Moore and Schusterman 1987; Babushina et al. 1991
Kastelein et al. 2005a† More details on individual subjects are available in Appendix A (Table A2). Some datasets were excluded due tosubjects having high-frequency hearing loss or aberrant audiograms. These included subjects from: Møhl 1968; Andersen
1970; Hall and Johnson 1972; Terhune and Ronald 1972; Terhune and Ronald 1975; Thomas et al. 1990; Wang et al.
1992; Babushina 1997; Kastak et al. 2002; Finneran et al. 2005 (Turner); Yuen et al. 2005; Finneran et al. 2007a; Sills et
al. 2015 (Natchek). Decisions to exclude data were based on comparison of the individual published audiograms andambient noise characteristics to those for other individuals of the same or closely related species. The most common
reasons for excluding an individual’s data were abnormal audiograms featuring high-frequency hearing loss (typicallyseen in older animals) or “notches” in the audiogram, or data collected in the presence of relatively high ambient noisethat resulted in elevated thresholds. Excluding these data ensured that the composite audiograms were not artificiallyelevated, which could result in unrealistically high thresholds.

+Two publications with behavioral audiograms became available after the Technical Guidance’s finalization in 2016.
However, upon consideration of these two studies during EO 13795 review of the Technical Guidance, including
recommendations from other Federal agencies, NMFS determined it is not practical from an implementation standpoint to
add these studies at this time. NMFS will include these studies in the next revision of this document (i.e., Version 3.0). For
more detail on these studies, see Section III.

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

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In deriving marine mammal composite audiograms, NMFS established an informal data
hierarchy in terms of assessing these types of data. Specifically, audiograms obtained via
behavioral methodologies were determined to provide the most representative (sensitive)
presentation of hearing ability (Finneran et al. 2007a), followed by auditory evoked
potential (AEP) data, 19 and lastly by mathematical/anatomical models for species where
no data are available (i.e., LF cetaceans). Thus, the highest quality data available for a
specific hearing group were used. 20
For LF cetaceans, only two studies were available for consideration (i.e., predictedaudiogram for a humpback whale from Houser et al. 2001 and fin whale from Cranford
and Krysl 2015), which alone was not enough to derive a predicted audiogram for thisentire hearing group. Thus, an alternative approach was used to derive a composite
audiogram 21 and associated auditory weighting function for LF cetaceans (i.e., composite
audiogram parameters had to be predicted; For specifics, on this process, see Appendix
A1).
2. The low-frequency exponent (a) was defined using the smaller of the low-frequency slope
from either the composite audiogram or the lower-frequency slope of the equal latency
contours (if available) and then divided by twenty (s0/20 ). This results in the slope
matching the shallower slope of the audiogram.

3. The high-frequency exponent (b) was set equal to two to match the previously derived
marine mammal auditory weighting functions from Finneran and Jenkins (2012), since no
new TTS measurements were available at higher frequencies and equal latency data atthese frequencies are considered highly variable.
4. Low- (ƒ1) and high-frequency cutoffs (ƒ2) were defined as the frequencies below andabove the frequency of best hearing (ƒ0) from original data, where the threshold values
were ΔT above the threshold at ƒ0 . These two parameters reflect the hearing group’s
most susceptible frequency range.

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

19

6. Hearing groups where TTS data are available (i.e., MF and HF cetaceans and PW andOW pinniped) were used to define K (Step 4 above). For LF cetaceans, where data were

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

20

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

21

During the third public comment period on the Technical Guidance in March 2016, ambient noise levels from Clark andEllison 2004 were offered by a group of subject matter experts as additional scientific support to NMFS’ LF cetacean
weighting function (for direct comparison to NOAA’s 2016 LF cetacean weighting function see: Public comment made via
Regulations.gov).
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not available, TTS onset was estimated by assuming the numeric difference between
auditory threshold (Figure 4, original data) and TTS onset at the frequency of best
hearing (ƒ0) would be similar across hearing groups. For LF cetaceans auditory threshold
had to be predicted, since no data exist (For specifics on methodology, see Appendix A,
Table A7).
7. The weighting function parameter (C) was determined by substituting parameters a, b, ƒ1,and ƒ2 in Equation 1 and setting the peak amplitude of the function to zero.

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

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

(kHz)

0.13

K

Weighted TTS onset
threshold* (SELcum)

19

C

(dB)

0.2

ƒ2

(dB)

2

ƒ1

(kHz)

1.0

b

179

179 dB

1.6

2

8.8

110

1.20

177

178 dB

1.8

2

12

140

1.36

152

153 dB

1.0

2

1.9

30

0.75

180

181 dB

2.0

2

0.94

25

0.64

198

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

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

2.2.4

Application of Marine Mammal Auditory Weighting Functions for PTS Onset
Thresholds

The application of marine mammal auditory weighting functions emphasizes the importance ofmaking measurements and characterizing sound sources in terms of their overlap withbiologically-important frequencies (e.g., frequencies used for environmental awareness,
communication or the detection of predators or prey), and not only the frequencies of interest orconcern for the completion of the sound-producing activity (i.e., context of sound source).
If the frequencies produced by a sound source are outside a hearing group’s most susceptible
hearing range (where the auditory weighting function amplitude is 0), sounds at those frequencies
are required to have a higher sound pressure level to produce a similar threshold shift (i.e., PTS
onset) as sounds with frequencies in the hearing group’s most susceptible hearing range.
Because auditory weighting functions take into account a hearing group’s differing susceptibility
to frequencies, the implementation of these functions typically results in smaller isopleths 22 for
22
Note: Thresholds associated with a hearing group do not change depending on how much a sound may overlap agroup’s most susceptible frequency range. Instead, weighting functions affect exposure modeling/analysis via theresulting size of the isopleth (area) associated with the threshold based on how susceptible that particular hearing group2018 REVISION TO: TECHNICAL GUIDANCE FOR ASSESSING THE EFFECTS OF ANTHROPOGENIC SOUND ON MARINE MAMMALHEARING (VERSION 2.0)
Page 18

frequencies where the group is less susceptible. Additionally, if the sound source produces
frequencies completely outside the generalized hearing range of a given hearing group (i.e., has
no harmonics/subharmonics that are capable of producing sound within the hearing range of ahearing group), then the likelihood of the sound causing hearing loss is considered low. 23
Marine mammal auditory weighting functions are used in conjunction with corresponding
weighted SELcum PTS onset thresholds. If the use of the full auditory weighting function is notpossible by an action proponent (i.e., consider auditory weighting function over multiple
frequencies for broadband source), NMFS has provided an alternative tool based on a simpler
auditory weighting function (See Appendix D).
Tougaard et al. (2015) reviewed the impacts of using auditory weighting functions and various
considerations when applying them during the data evaluation and implementation stages (e.g.,consequences of using too broad or too narrow of a filter) and suggested some modifications(correction factors) to account for these considerations. However, there are no data to support
doing so (i.e., selection would be arbitrary). Moreover, various conservative factors have beenaccounted for in the development of auditory weighting functions and thresholds: A 6 dB
threshold shift was used to represent TTS onset; the methodology does not incorporate
exposures where TTS did not occur; and the potential for recovery is not accounted for.
Additionally, the means by which NMFS is applying auditory weighting functions is supported andconsistent with what has been done for humans (i.e., A-weighted thresholds used in conjunction
with A-weighting during implementation).

2.2.4.1 Measuring and Maintaining Full Spectrum for Future Analysis
It is recommended marine mammal auditory weighting functions be applied after sound fieldmeasurements 24 have been obtained (i.e., post-processing; it is recommended that auditory
weighting functions not be applied beforehand), with the total spectrum of sound preserved forlater analysis (i.e., if auditory weighting functions are updated or if there is interest in additional
species, then data can still be used). Additionally, it is important to consider measurements thatencompass the entire frequency band that a sound source may be capable of producing (i.e.,sources often produce sounds, like harmonics/subharmonics, beyond the frequency/band ofinterest; e.g., Deng et al. 2014; Hastie et al. 2014).

2.3

PTS ONSET THRESHOLDS

Available data from humans and other terrestrial mammals indicate that a 40 dB threshold shift
approximates PTS onset (see Ward et al. 1958; Ward et al. 1959; Ward 1960; Kryter et al. 1966;
Miller 1974; Ahroon et al. 1996; Henderson et al. 2008). Southall et al. (2007) also recommended
this definition of PTS onset.
PTS onset thresholds for marine mammals have not been directly measured and are extrapolated
from available TTS onset measurements. Thus, based on cetacean measurements from TTS
is to the sound being modeled. For example, a hearing group could have different size isopleths associated with the same
threshold, if one sound was within its most susceptible frequency range and the other was not (i.e., sound in mostsusceptible hearing range will result in larger isopleth compared to sound outside the most susceptible hearing range).
23

The potential for sound to damage beyond the level the ear can perceive exists (Akay 1978), which is why thethresholds also include the PK metric, which are flat or unweighted within the generalized hearing range of a hearing
group.

24
Note: Sound field measurements refers to actual field measurements, which are not a requirement of this Technical
Guidance, and not to exposure modeling analyses, where it may be impractical due to data storage and cataloging
restraints.

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studies (see Southall et al. 2007; Finneran 2015; Finneran 2016 found in Appendix A of thisTechnical Guidance) a threshold shift of 6 dB is considered the minimum threshold shift clearlylarger than any day-to-day or session-to-session variation 25 in a subject’s normal hearing ability
and is typically the minimum amount of threshold shift that can be differentiated in mostexperimental conditions (Finneran et al. 2000; Schlundt et al. 2000; Finneran et al. 2002). Thus,
NMFS has set the onset of TTS at the lowest level that exceeds recorded variation (i.e., 6 dB).
There are different mechanisms (e.g., anatomical, neurophysiological) associated with TTS vs.
PTS onset, making the relationship between these types of TSs not completely direct.
Nevertheless, the only data available for marine mammals, currently and likely in the future, will
be from TTS studies (i.e., unlike for terrestrial mammals where direct measurements of PTS
exist). Thus, TTS represents the best information available from which PTS onset can be
estimated.
The thresholds presented in Table 4 consist of both an acoustic threshold and auditory weighting
function for the SELcum metric (auditory weighting functions are considered not appropriate for PK
metric).
NMFS recognizes that the implementation of marine mammal auditory weighting functions
represents a new factor for consideration that may exceed the capabilities of some action
proponents. Thus, NMFS has developed alternative tools for those who cannot fully apply
auditory weighting functions associated with the weighted SELcum metric (See Appendix D).

2.3.1

Impulsive and Non-Impulsive Source Thresholds

This Technical Guidance divides sources into impulsive and non-impulsive based on physicalcharacteristics at the source, with impulsive sound having physical characteristics making themmore injurious 26 (e.g., high peak sound pressures and rapid rise times) than non-impulsive soundsources (terrestrial mammal data: Buck et al. 1984; Dunn et al. 1991; Hamernik et al. 1993;
Clifford and Rogers 2009; marine mammal data: reviewed in Southall et al. 2007 and Finneran
2016 that appears as Appendix A of this Technical Guidance).
The characteristics of the sound at a receiver, rather than at the source, are the relevant
consideration for determining potential impacts. However, understanding these physicalcharacteristics in a dynamic system with receivers moving over space and time is difficult.
Nevertheless, it is known that as sound propagates from the source the characteristics ofimpulsive sounds that make them more injurious start to dissipate due to effects of propagation(e.g., time dispersion/time spreading; Urick 1983; Sertlek et al. 2014).

25

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

26

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

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Table 4:

Summary of PTS onset thresholds.

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

PTS Onset Thresholds*(Received Level)
Impulsive
Non-impulsive
Cell 1
Cell 2
Lpk,flat: 219 dB
LE,LF,24h: 199 dB
LE,LF,24h: 183 dB
Cell 3Cell 4
Lpk,flat: 230 dB
LE,MF,24h: 198 dB
LE,MF,24h: 185 dB
Cell 5Cell 6
Lpk,flat: 202 dB
LE,HF,24h: 173 dB
LE,HF,24h: 155 dB
Cell 7
Cell 8
Lpk,flat: 218 dB
LE,PW,24h: 201 dB
LE,PW,24h: 185 dB
Cell 9Cell 10
Lpk,flat: 232 dB
LE,OW,24h: 219 dB
LE,OW,24h: 203 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 soundpressure are flat weighted or unweighted within the generalized hearing range of marine mammals (i.e., 7 Hz to 160 kHz).
The subscript associated with weighted cumulative sound exposure level thresholds indicates the designated marine
mammal auditory weighting function (LF, MF, and HF cetaceans, and PW and OW pinnipeds) and that the recommended
accumulation period is 24 hours. The cumulative sound exposure level thresholds could be exceeded in a multitude ofways (i.e., varying exposure levels and durations, duty cycle). When possible, it is valuable for action proponents toindicate the conditions under which these thresholds will be exceeded.

For the purposes of this Technical Guidance, 27 sources are divided and defined as the following:•

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

•

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

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

27

If there is unclear, consider the most applicable definition and consult with NMFS.

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2.3.2

Metrics

2.3.2.1 Weighted Cumulative Sound Exposure Level (SELcum) Metric
The weighted SELcum metric takes into account both received level and duration of exposure(ANSI 2013), both factors that contribute to NIHL. Often this metric is normalized to a single
sound exposure of one second. NMFS intends for the weighted SELcum metric to account for theaccumulated exposure (i.e., weighted SELcum cumulative exposure over the duration of theactivity within a 24-h period).
The recommended application of the weighted SELcum metric is for individual activities/sources. It
is not intended for accumulating sound exposure from multiple activities occurring within thesame area or over the same time or to estimate the impacts of those exposures to an animal
occurring over various spatial or temporal scales. Current data available for deriving thresholds
using this metric are based on exposure to only a single source and may not be appropriate forsituations where exposure to multiple sources is occurring. As more data become available, theuse of this metric can be re-evaluated, in terms of appropriateness, for application of exposure
from multiple activities occurring in space and time.
Equal Energy Hypothesis
One assumption made when applying the weighted SELcum metric is the equal energy hypothesis(EEH), where it is assumed that sounds of equal SELcum produce an equal risk for hearing loss
(i.e., if the weighted SELcum of two sources are similar, a sound from a lower level source with alonger exposure duration may have similar risks to a shorter duration exposure from a higher
level source). As has been shown to be the case with humans and terrestrial mammals(Henderson et al. 1991), the EEH does not always accurately describe all exposure situations formarine mammals due the inherent complexity of predicting TSs (e.g., Kastak et al. 2007; Mooneyet al. 2009a; Mooney et al. 2009b; Finneran et al. 2010a; Finneran et al. 2010b; Finneran and
Schlundt 2010; Kastelein et al. 2012b; Kastelein et al. 2013b; Kastelein et al. 2014a; Popov et al.
2014).
Factors like sound level (e.g., overall level, sensation level, or level above background), duration,
duty cycle (intermittent versus continuous exposure; potential recovery between intermittent
periods), number of transient components (short duration and high amplitude), and/or frequency(especially in relation to hearing sensitivity) often are also important factors associated with TSs(e.g., Buck et al. 1984; Clark et al. 1987; Ward 1991; Lataye and Campo 1996). This is especiallythe case for exposure to impulsive sound sources (Danielson et al. 1991; Henderson et al. 1991;
Hamernik et al. 2003), which is why thresholds in this Technical Guidance are also expressed asa PK metric (see next section). However, in many cases the EEH approach functions reasonably
well as a first-order approximation, especially for higher-level, short-duration sound exposures
such as those that are most likely to result in TTS in marine mammals 28 (Finneran 2015).
Additionally, no currently supported alternative method to accumulate exposure is available. If
alternative methods become available, they can be evaluated and considered when the Technical
Guidance is updated.
Recommended Accumulation Period
To apply the weighted SELcum metric, a specified accumulation period is needed. Generally, it ispredicted that most receivers will minimize the amount of time they remain in the closest ranges
to a sound source/activity. Exposures at the closest point of approach are the primary exposurescontributing to a receiver’s accumulated level (Gedamke et al. 2011). Additionally, several
28

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

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important factors determine the likelihood and duration a receiver is expected to be in close
proximity to a sound source (i.e., overlap in space and time between the source and receiver).
For example, accumulation time for fast moving (relative to the receiver) mobile sources is driven
primarily by the characteristics of source (i.e., speed, duty cycle). Conversely, for stationary
sources, accumulation time is driven primarily by the characteristics of the receiver (i.e., swim
speed and whether transient or resident to the area where the activity is occurring). NMFS
recommends a maximum baseline accumulation period of 24 hours, but acknowledges that there
may be specific exposure situations where this accumulation period requires adjustment (e.g., if
activity lasts less than 24 hours or for situations where receivers are predicted to experience
unusually long exposure durations 29).
After sound exposure ceases or between successive sound exposures, the potential for recovery
from hearing loss exists, with PTS resulting in incomplete recovery and TTS resulting in complete
recovery. Predicting recovery from sound exposure can be quite complicated. Currently, recovery
in wild marine mammals cannot be accurately quantified. However, Finneran et al. (2010a) and
Finneran and Schlundt (2013) proposed a model that approximates recovery in bottlenose
dolphins and whose applicability to other species and other exposure conditions has yet to be
determined. In the development of the Technical Guidance’s thresholds, NMFS assumes forintermittent, repeated exposure that there is no recovery between subsequent exposures,
although it has been demonstrated in terrestrial mammals (Clark et al. 1987; Ward 1991) andmore recently in a marine mammal studies (Finneran et al. 2010b; Kastelein et al. 2014a;
Kastelein et al. 2015b), that there is a reduction in damage and hearing loss with intermittent
exposures.
Existing NMFS thresholds have only accounted for proximity of the sound source to the receiver,
but thresholds in this Technical Guidance (i.e., expressed as weighted SELcum) now take into
account the duration, as well as level of exposure. NMFS recognizes that accounting for durationof exposure, although supported by the scientific literature, adds a new factor, as far as
application of this metric to real-world activities and that not all action proponents may have theability to easily apply this additional component.
NMFS does not provide specifications necessary to perform exposure modeling and relies on theaction proponent to determine the model that best represents their activity. However, NMFS
acknowledges that different action proponents may have different capabilities and levels ofmodeling sophistication. NMFS has provided a simple means of approximating exposure foraction proponents that are unable to apply various factors into their model (See Appendix D).
NMFS will convene a working group to investigate means for deriving more realistic accumulation
periods, especially for stationary sources (anticipated in 2018).
2.3.2.2 Peak Sound Pressure Level (PK) Metric 30
Sound exposure containing transient components (e.g., short duration and high amplitude;
impulsive sounds) can create a greater risk of causing direct mechanical fatigue to the inner ear(as opposed to strictly metabolic) compared to sounds that are strictly non-impulsive (Henderson
and Hamernik 1986; Levine et al. 1998; Henderson et al. 2008). Often the risk of damage fromthese transients does not depend on the duration of exposure. This is the concept of “criticallevel,” where damage switches from being primarily metabolic to more mechanical and short

29

For example, where a resident population could be found in a small and/or confined area (Ferguson et al. 2015) and/or
exposed to a long-duration activity with a large sound source, or where a continuous stationery activity is nearby an area
where marine mammals congregate, like a pinniped pupping beach.

30

Note: Do not confuse peak sound pressure level with maximum root mean square sound pressure level.

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duration of impulse can be less than the ear’s integration time, leading to the potential to damage
beyond the level the ear can perceive (Akay 1978).
Human noise standards recognize and provide separate thresholds for impulsive sound sources
using the PK metric (Occupational Safety and Health Administration (OSHA) 29 CFR 1910.95;
Starck et al. 2003). Thus, weighted SELcum is not an appropriate metric to capture all the effects
of impulsive sounds (i.e., often violates EEH; NIOSH 1998), which is why instantaneous PK levelhas also been chosen as part of NMFS’ dual metric thresholds for impulsive sounds. 31 Auditory
weighting is not considered appropriate with the PK metric, as direct mechanical damage
associated with sounds having high peak sound pressures typically does not strictly reflect thefrequencies an individual species hears best (Ward 1962; Saunders et al. 1985; ANSI 1986; DOD
2004; OSHA 29 CFR 1910.95). Thus, this Technical Guidance recommends that the PK
thresholds be considered unweighted/flat-weighted within the generalized hearing range ofmarine mammals (i.e., 7 Hz to 160 kHz).

2.3.2.3 Comparison Among Metrics
NMFS’ existing thresholds were expressed as root-mean-square sound pressure level (RMS
SPL), which is a different metric from the PK and weighted SELcum that are being recommended
for the PTS onset thresholds in this Technical Guidance. Thus, NMFS recommends caution whencomparing prior thresholds to those presented in this document (i.e., metrics are not directlycomparable). For example, a RMS SPL threshold of 180 dB is not equal to a PK threshold of 180
dB. Further, the weighted SELcum metric incorporates exposure duration and is an energy levelwith a different reference value (re: 1μPa2-s). Thus, it is not directly comparable to other metrics
that describe sound pressure levels (re: 1 μPa) 32.
2.3.3

Development of PTS Onset Thresholds

The development of the PTS onset thresholds consisted of the following procedure described in
Finneran 2016 (Appendix A 33):
1. Identification of available data on marine mammal hearing and noise-induced hearing
loss (e.g., Southall et al. 2007; Finneran 2015; Finneran 2016 references listed inavailable reports/publications).
2. Methodology to derive marine mammal auditory weighting functions (described in moredetail in Section 2.2.3 and Appendix A).
3. Evaluation and summary of currently available published data (32 studies found in Table5) on hearing loss associated with sound exposure in marine mammals.
• Because no published measurements exist on PTS in marine mammals, TTS
onset measurements and associated thresholds were evaluated and summarized
to extrapolate to PTS onset thresholds.
31

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

32

For more information and illustrations on metrics, see: Discovery of Sound in the Sea.

33

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

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

4. Determination of TTS onset threshold by individual (RLs, in both PK and SELcum metrics)
based on methodology from Finneran 2016 for impulsive and non-impulsive sounds (Fulldetail in Appendix A).
• Non-impulsive sounds:o Only TTS data from behavioral studies were used, since studies using
AEP methodology typically result in larger thresholds shifts (e.g., up to
10 dB difference, Finneran et al. 2007a) and are considered to be nonrepresentative (as illustrated in Appendix A, Figure A9)2018 REVISION TO: TECHNICAL GUIDANCE FOR ASSESSING THE EFFECTS OF ANTHROPOGENIC SOUND ON MARINE MAMMALHEARING (VERSION 2.0)
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Table 5:

Available underwater marine mammal threshold shift studies.

References in
Chronologic Order+

Sound Source(Sound Source Category)Species (number ofindividuals^)

Kastak et al. 1999

Octave-band noise (non-impulsive)

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

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

Kastak et al. 2005

Octave-band noise (non-impulsive)

Finneran et al. 2007a
Lucke et al. 2009
Mooney et al. 2009aMooney et al. 2009b
Finneran et al. 2010aFinneran et al. 2010b
Finneran and Schlundt
2010
Popov et al. 2011aPopov et al. 2011b
Kastelein et al. 2012aKastelein et al. 2012b
Finneran and Schlundt
2013
Popov et al. 2013
Kastelein et al. 2013aKastelein et al. 2013b
Popov et al. 2014
Kastelein et al. 2014aKastelein et al. 2014b
Kastelein et al. 2015aKastelein et al. 2015bTones (non-impulsive)
Single airgun (impulsive)
Octave-band noise (non-impulsive)Mid-frequency sonar (non-impulsive)
Tones (non-impulsive)
Tones (non-impulsive)

California sea lion (1); northernelephant seal (1); harbor seal (1)Bottlenose dolphin (2); beluga (1)Bottlenose dolphin (5); beluga (2)Bottlenose dolphin (1); beluga (1)California sea lion (2)Bottlenose dolphin (1)Bottlenose dolphin (1)Bottlenose dolphin (2)California sea lion (1); northernelephant seal (1); harbor seal (1)Bottlenose dolphin (1)Harbor porpoise (1)Bottlenose dolphin (1)Bottlenose dolphin (1)Bottlenose dolphin (2)Bottlenose dolphin (1)Tones (non-impulsive)

Bottlenose dolphin (1)½ octave band noise (non-impulsive)½ octave band noise (non-impulsive)
Octave-band noise (non-impulsive)
Octave-band noise (non-impulsive)

Yangtze finless porpoise (2)Beluga (1)Harbor seal (2)Harbor porpoise (1)Tones (non-impulsive)

Bottlenose dolphin (2)½ -octave band noise (non-impulsive)
Octave-band noise (non-impulsive)
Tone (non-impulsive)½ octave band noise (non-impulsive)
1-2 kHz sonar (non-impulsive)
6.5 kHz tone (non-impulsive)
Impact pile driving (impulsive)
6-7 kHz sweeps (non-impulsive)
Single airgun producing multiple shots(impulsive)*½ octave band noise (non-impulsive)
Impact pile driving (impulsive)*
Single airgun (impulsive) *½ octave band noise (non-impulsive)
Simultaneous airguns producing
multiple shots (impulsive)
3.5-4.1 kHz sonar (non-impulsive)

Beluga (2)Harbor seal (1)Harbor porpoise (1)Beluga (2)Harbor porpoise (1)Harbor porpoise (1)Harbor porpoise (1)Harbor porpoise (1)Finneran et al. 2015
Popov et al. 2015
Kastelein et al. 2016
Reichmuth et al. 2016
Popov et al. 2017
Kastelein et al. 2017b
Kastelein et al. 2017c

Bottlenose dolphin (3)Beluga (1)Harbor porpoise (2)Ringed seals (2); Spotted seals (2)Beluga (1)Harbor porpoise (1)Harbor porpoise (2)^Note: Some individuals have been used in multiple studies.
*No incidents of temporary threshold shift were recorded in study.

o TTS onset derived on a per individual basis by combining available data
to create single TTS growth curve (e.g., dB TTS/dB noise) by frequency
as a function of SELcum.
o TTS onset was defined as the SEL cum value from the growth curveinterpolated at a value of TTS = 6 dB. Only datasets where data wereavailable with a threshold shift (TS) above and below 6 dB were used to2018 REVISION TO: TECHNICAL GUIDANCE FOR ASSESSING THE EFFECTS OF ANTHROPOGENIC SOUND ON MARINE MAMMALHEARING (VERSION 2.0)
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define TTS onset (i.e., extrapolation was not performed on datasets notmeeting this criterion).
o Interpolation was used to estimate SEL cum necessary to induce 6 dB of
TTS by hearing group (Appendix A, Figures A10-A13). Note: Appendix
A, Figures A18-A20 illustrate available marine mammal TTS data in
relation to the composite audiogram and auditory exposure function.
o Finally, weighted thresholds for TTS onset were determined by theminimum value of the auditory exposure function (Equation 2), which ismathematically equivalent to K + C (Table 6).
Table 6:

TTS onset thresholds for non-impulsive sounds.

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

K

C

(dB)

(dB)

179
177
152
180
198

0.13
1.20
1.36
0.75
0.64

Weighted TTS
onset acoustic
threshold(SEL cum)
179 dB178 dB
153 dB
181 dB
199 dB

Impulsive sounds:o Available TTS data for impulsive sources were weighted based on
auditory weighting functions for the appropriate hearing group (MF and
HF cetaceans only from two studies: Finneran et al. 2002; Lucke et al.
2009).
o For hearing groups, where impulsive TTS onset data did not exist (LF
cetaceans and PW and OW pinnipeds), Finneran (2015) derived
impulsive TTS onset thresholds using the relationship between nonimpulsive TTS onset thresholds and impulsive TTS onset thresholds for
MF and HF cetaceans (i.e., similar to what was presented in Southall et
al. 2007). Using the mean/median of these data resulted in an 11 dB
relationship, which was used as a surrogate for the other hearing groups(i.e., non-impulsive TTS threshold was 11 dB higher than impulsive TTS
threshold).
o A similar approach was investigated for the PK threshold, resulting in a
45 dB relationship, which was considered unrealistic (approachingcavitation level of water; Southall et al. 2007). Upon further
consideration, the auditory system’s dynamic range was determined amore appropriate methodology for estimating PK sound pressure
thresholds. 34
The dynamic range methodology assumes that the PK TTS onset
acoustic threshold for MF and HF cetaceans defines the upper end of34

Dynamic range is used in human noise standards to define the PK acoustic threshold for impulsive sounds (e.g., 140dB from OSHA 29 CFR 1910.95). For the purposes of this Technical Guidance, the intent is to relate the threshold ofaudibility and TTS onset level, not the threshold of pain, as dynamic range is typically defined (Yost 2007).

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Page 27those hearing groups’ dynamic range (i.e., PK threshold: 224 dB for MF
cetaceans and PK threshold: 196 dB for HF cetaceans), with thethreshold of audibility derived from the frequency of best hearing (ƒ0) fromthe composite audiogram (i.e., 54 dB for MF cetaceans and 48 dB for HF
cetaceans) defining the lower end of the groups’ dynamic range.
This results in a dynamic range of 170 dB for MF cetaceans and 148 dB
for HF cetaceans. The median/mean dynamic range from these twohearing groups (i.e., 159 dB) is used as the surrogate dynamic range for
LF cetaceans (best hearing at ƒ0= 54 dB; Resulting in a PK TTS
threshold of 213 dB); PW pinnipeds (best hearing at ƒ0=53 dB; Resulting
in a PK TTS threshold of 212 dB); and OW pinnipeds (best hearing at ƒ0=67 dB; Resulting in a PK TTS threshold of 226 dB).
5. Extrapolation for PTS onset threshold (in both PK and SEL metrics) based on data fromhumans and terrestrial mammals, with the assumption that the mechanisms associatedwith noise-induced TS in marine mammals is similar, if not identical, to that recorded interrestrial mammals.
•

Non-impulsive sounds:
o PTS onset thresholds were estimated using TTS growth rates based on
those marine mammal studies where 20 dB or more of a TS was
induced. This was done to estimate more accurately PTS onset, sinceusing growth rates based on smaller TSs are often shallower thancompared to those inducing greater TSs (See Appendix A, Figures A10A13).
o PTS onset was derived using the same methodology as TTS onset, withPTS onset defined as the SELcum value from the fitted curve at a TTS of
40 dB.
o Offset between TTS and PTS onset thresholds were examined andranged from 13 to 37 dB (mean/median: 25/25 dB for cetacean data).
Thus, based on these data, a conservative 20 dB offset was chosen to
estimate PTS onset thresholds from TTS onset thresholds for nonimpulsive sources (i.e., 20 dB was added to K to determine PTS onset,
assuming the shape of the PTS auditory exposure function is identical to
the TTS auditory exposure function for that hearing group).

•

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

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III.
Ill.

UPDATING OF ACOUSTIC TECHNICAL GUIDANCE AND
THRESHOLDS

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

3.1

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

3.1.1

Consideration for New Scientific Publication

During the Technical Guidance’s recent review under EO 13795 (i.e., public comment period; 82
FR 24950; May 31, 2017), several commenters provided information on newly published scientific
literature (i.e., 12 publications) for consideration and inclusion in a revised version of theTechnical Guidance. NMFS reviewed all literature suggested by commenters. The majority ofsuggested papers were either already considered within the 2016 Technical Guidance or were
not applicable for incorporation (i.e., many newly available marine mammal audiograms werecollected via auditory evoked potential (AEP), which cannot be directly incorporated in the current
methodology). Of the studies suggested, only the Branstetter et al. 2017 publication, which
provides behavioral audiograms for six individual killer whales, was appropriate for consideration
within the Technical Guidance. Since the close of the public comment period, a paper providing
two new additional behavioral audiograms for harbor porpoise (Kastelein et al. 2017a), a paper
examining TTS in harbor porpoise exposed to multiple airgun shots (Kastelein et al. 2017b), anda paper examining TTS in harbor porpoise exposed to mid-frequency sonar playbacks (Kastelein
et al. 2017c) were published. These three additional papers are also appropriate for consideration
within the Technical Guidance.

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The Technical Guidance’s methodology (Appendix A) is data driven, meaning every new
publication has the potential to result in some change to either the thresholds and/or auditory
weighting functions for a single or multiple hearing groups (i.e., those groups whose data areused as surrogates for other hearing groups), and with every change comes a necessarytransition period to allow action proponents to adapt to these changes. Thus, there are scientific,
as well as practical implications that need consideration before making even a minor a change to
the Technical Guidance. One commenter said it best by “The value of a revision of any sciencebased advice hinges on the balance between the availability of new scientific evidence and theneed for a period of stability. The greater the complexity of the advice the greater the need for along stable period to assimilate that advice before it is updated 35.” The Marine Mammal
Commission (MMC) and U.S. Navy offered similar cautions about the practicality of revising theTechnical Guidance every time a new study becomes available.
Upon consideration of these most recent studies during our review under EO 13795 andconsidering recommendations from other Federal agencies and public commenters, NMFS
determined it is not practical from an implementation standpoint to add these studies at this time.
NMFS will include these studies in the next revision of this document (i.e., Version 3.0) andadhere to our stipulated 3 to 5 year update schedule, where we can evaluate all new relevantpublications and make changes in a more predictable manner.

3.1.1.1 Preliminary Analysis of Branstetter et al. 2017, Kastelein et al. 2017a, Kastelein etal. 2017b, and Kastelein et al. 2017c
NMFS conducted a preliminary analysis examining the new data provided in Branstetter et al.
2017, Kastelein et al. 2017a, Kastelein et al. 2017b, and Kastelein et al. 2017c in the context of
the Technical Guidance’s current MF and HF cetacean composite audiograms (Branstetter et al.
2017; Kastelein et al. 2017a) and HF cetacean TTS/PTS onset thresholds (Kastelein et al. 2017b;
Kastelein et al. 2017c).
Branstetter et al. 2017
The Technical Guidance’s composite audiogram for MF cetaceans does incorporate behavioral
audiograms from two individual killer whales (i.e., Vigga and Yakka from Szymanski et al. 1999).
In Figure 3 from the Branstetter et al. 2017 publication, they plot Vigga and Yakka’s audiogram
data as a comparison to the audiograms obtained to in their study. From this figure andcorresponding threshold table (Table 1 in Branstetter et al. 2017), in the killer whale’s mostsensitive hearing range, the data already included in the Technical Guidance align with
Branstetter et al.’s new audiograms, and for most frequencies, Vigga and Yakka have lower
thresholds.
Kastelein et al. 2017a
The Technical Guidance’s composite audiogram for HF cetaceans does incorporate behavioral
audiograms for three harbor porpoises (i.e., PpSH047 and Jerry from Kastelein et al. 2010; ID
No. 04 from Kastelein et al. 2015c). In Figure 1 from Kastelein et al. 2017a, they plot theirpreviously published audiograms from these three individuals as a comparison to the two newindividual audiograms obtained in this study. Kastelein et al. (2017) concluded from this mostrecent study “The basic audiograms of the young female and male harbor porpoises in thepresent study were similar to those of the three previously tested young male harbor porpoises(Fig 1).”35

Link to public comment made on Regulations.gov.

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Kastelein et al. 2017b
In this study, a harbor porpoise was exposed to either 10 or 20 consecutive shots from two
airings simultaneously. A mean threshold shift of 4.4 dB occurred after exposure to a weighted
cumulative level of 140.3 dB. The Technical Guidance’s TTS onset threshold (weighted SELcum)for HF cetaceans and impulsive sources is 140 dB, which is consistent with the results from thismost recent study. This paper also concludes, “the initial results indicate that the frequencyweighting function proposed by NOAA (NMFS, 2016) provides a reasonably robust measure of
low levels of TTS occurring over a range of spectra of impulsive sound sources.”

Kastelein et al. 2017c
This study exposed two harbor porpoises to mid-frequency sonar (3.5 to 4.1 kHz) and reported
that to induce a 6 dB threshold shift in harbor porpoises an unweighted cumulative level between
175 and 180 dB would be needed. If these data were weighted using the Technical Guidance’s
auditory weighting function, the values would be ~157.7 and ~162.7 dB SELcum 36. The Technical
Guidance’s TTS onset threshold (weighted SELcum) for HF cetaceans and non-impulsive sources
is 153 dB, which is consistent with the results from this most recent study (i.e., the thresholds
from Kastelein et al. 2017c are likely slightly higher than the Technical Guidance because it was
an intermittent source allowing for a greater potential for recovery between pauses of the various
signal components).

Preliminary Conclusions
Thus, from this preliminary analysis, NMFS concludes that the Branstetter el. 2017 and Kastelein
et al. 2017a audiograms are consistent with data already included in the Technical Guidance forthese two species (i.e., the data from these two recent studies align with previous data collected
and incorporated within the current version of the Technical Guidance). Additionally, the HF
cetacean TTS data presented in Kastelein et al. 2017b and Kastelein et al. 2017c are consistent
with the HF cetacean thresholds presented in the Technical Guidance.

36

NMFS contacted the authors of this paper to confirm weighted levels.

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Page 31APPENDIX A:FINNERANFl NERA TECHNICAL REPORTThe entire Finneran Technical Report (Finneran 2016), regarding methodology for deriving
auditory weighting functions and thresholds for marine mammal species under NMFS’ jurisdiction,is included for reference in Appendix A. Its contents have not been modified by NMFS, other thanadding “A” before figures and tables to denote Appendix A and be consistent with the otherappendices in the Technical Guidance.
Notes:
a. Literature cited in this section are included at the end of this Appendix (i.e., not allreferences found in this Appendix are included in the Literature Cited for the Technical
Guidance). Additionally, terminology, symbols, and abbreviations used in this appendix
may not match those used elsewhere in the Technical Guidance.
b. The derivation of the Technical Guidance's thresholds and auditory weighting functions
are from two primary sets of data: 1) Audiogram data (used to derive composite
audiograms for each hearing group) and 2) TTS onset data (used to derive auditory
weighting functions and TTS onset thresholds by hearing group). For each of these two
primary data sets, either data points were derived directly from the published study or if
data were originally reported in terms of sound pressure level and duration, they
converted to sound exposure level via standard relationships.
c.

Since the final Finneran Technical Report was received, an additional TTS study became
available (Kastelein et al. 2016). Information regarding this study is added as a footnote
by NMFS.

d. After the Technical Guidance’s finalization, an additional two TTS studies became
available (Kastelein et al. 2017b; Kastelein et al. 2017c). In the Kastelein et al. 2017b
study, a harbor porpoise was exposed to either 10 or 20 consecutive shots from two
airguns simultaneously. Kastelein et al. 2017c exposed two harbor porpoises to midfrequency sonar (3.5 to 4.1 kHz). The HF cetacean TTS data (i.e., TTS onset levels)presented in these two most recent studies are consistent with the HF cetacean
thresholds presented in the Technical Guidance.
e. Additionally, two behavioral audiogram publications became available after the Technical
Guidance’s finalization in 2016 (Branstetter et al. 2017; Kastelein et al. 2017a). However,upon consideration of these two studies during EO 13795 review of the Technical
Guidance, including recommendations from other Federal agencies (e.g. Navy), NMFS
determined it is not practical from an implementation standpoint to add these studies atthis time (i.e., Version 2.0). NMFS will include these studies in the next revision of thisdocument (i.e., Version 3.0). From this preliminary analysis, NMFS concludes that theBranstetter el. 2017 and Kastelein et al. 2017a audiograms are consistent with data
already included in the Technical Guidance for these two species (i.e., the data fromthese two recent studies align with previous data collected and incorporated within thecurrent version of the Technical Guidance).

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Page 32TECHNICAL REPORT 3026
December 2016

Auditory Weighting Functions and
TTS/PTS Exposure Functions for Marine
Mammals Exposed to Underwater NoiseJ. J. Finneran
Approved for public release.

SSC Pacific
San Diego, CA 92152-5001

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Page 33

SSC SAN DIEGOSan Diego, Califo rn ia 92152~5001. V .. Fllynn CAPT, US I
Oomrnanding Officer

C. .A. Keeney
IE:xeoutive Direct,or

ADMINISTRATIVE INFORMATIONThis work described in this report was prepared for Commander, U.S. Fleet Forces
Command, Norfolk, VA, by the Marine Mammal Scientific & Vet Support Branch (Code71510) of the Biosciences Division (Code 71500), Space and Naval Warfare Systems
Center Pacific (SSC Pacific), San Diego, CA.

Released under authority of
M. J. Xitco, Head
Biosciences DivisionThis is a work of the United States Government and therefore is not copyrighted. This
work may be copied and disseminated without restriction. Many SSC San Diego public
release documents are available in electronic format at SPAWAR publication web site.

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Page 34

EXECUTIVE SUMMARY
SU MARY

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

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Page 35

-ca

LF

"O
Q)

,,

-20

"O
:J

,,

PW

~

,

0.. -40

E

ow

C1l

-60
0.01

0.1

10

100

0.1

100

10

freq uency (kHz)

Figure AE-1.

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

Table AE-1.

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

W(J) ~ C + IOk,g
ID

l

l

(/if,)"[1+(11 .1;)'J[1+(f/ .1SJ

Non-impulsive

ImpulseTTS
PTS
threshold threshold

TTS
thresholdPTS
threshold

Group

a

b

f1
(kHz)

f2
(kHz)

C
(dB)

LF

1

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

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

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

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

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Page 36·•, ..'.',,_ .. . .... ......... .
~-"'

200 '

VJ

180

"'ctl

'3_ 160

LF

Q)

MF

L.

co 140 0 .01
~

LU
Cl)

0.1

10

V,/

_J

220

10

100

\

'

200

.

\

'

- ------- --

180

ow

SI

0.1

10

100

0.1

100

,~/2

\

'

10

-

_.·

\

PW
10

100

0.1

10

100

freq uency (kHz)- -Phase 2 - TTS faposure function· · · · · · Phase 2 - PTS Exposure function-

Figure AE-2.

- Phase 3 - TTS faposure function
Phase 3 - PTS 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 (TableAE-1). Thin solid lines — Navy Phase 3 PTS exposure functions (Table AE-1).
Dashed lines — Navy Phase 2 TTS exposure functions. Short dashed lines — Navy
Phase 2 PTS exposure functions.

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Page 37

:·"'~ .............

/ /,' ' -~ ·-. ... y ,1,
180

....

'

- - ...

en" 160Nroa..

....:i. 140 LF
Q)L..

en 220

0.01

0.1

10

10

100

10

100

~
....J

llJ
(f)

200

180

'

ow

SI
160
0.1

10

100

0.1

1

10

100

frequency (kHz)

Figure AE-3.

0.1

10

100

- - Phase 2 - TTS E,posure function· · · · · · Phase 2 - PTS Exposure function
Phase 3 - TTS E,posure function
Phase 3 - PTS Exposure function

TTS and PTS exposure functions for explosives, impact pile driving, air guns, andother impulsive sources. Heavy solid lines — Navy Phase 3 TTS exposure functions(Table AE-1). Thin solid lines — Navy Phase 3 PTS exposure functions (Table AE1). Dashed lines — Navy Phase 2 TTS exposure functions. Short dashed lines —Navy Phase 2 PTS exposure functions.

The most significant differences between the Phase 2 and Phase 3 functions include: (1)Thresholds at low frequencies are generally higher for Phase 3 compared to Phase 2. Thisis because the Phase 2 weighting functions utilized the “M-weighting” functions at lower
frequencies, where no TTS existed at that time. Since derivation of the Phase 2 weighting
functions, additional data have been collected to support the use of new functions moresimilar to human auditory weighting functions. (2) Impulsive TTS/PTS thresholds near
the region of best hearing sensitivity are lower for Phase 3 compared to Phase 2.

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Page 38

I.I.

INTRODUCTION

1.1

OVERVIEWThe US Navy’s Tactical Training Theater Assessment and Planning (TAP) Program
addresses environmental challenges that affect Navy training ranges and operating areas.
As part of the TAP process, acoustic effects analyses are conducted to estimate thepotential effects of Navy training and testing activities that introduce high-levels of soundor explosive energy into the marine environment. Acoustic effects analyses begin withmathematical modeling to predict the sound transmission patterns from Navy sources.
These data are then coupled with marine species distribution and abundance data to
determine sound levels likely to be received by various marine species. Finally, criteria
and thresholds are applied to estimate the specific effects that animals exposed to Navygenerated sound may experience.
This document describes the rationale and steps used to define proposed numericthresholds for predicting auditory effects on marine mammals exposed to underwatersound from active sonars, other (non-impulsive) active acoustic sources, explosives, piledriving, and air guns for Phase 3 of the TAP Program. The weighted threshold values andauditory weighting function shapes are summarized in Section 12.
1.2

IMPULSE VS. NON-IMPULSIVE NOISE

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

NOISE-INDUCED THRESHOLD SHIFTS

Exposure to sound with sufficient duration and sound pressure level (SPL) may result inan elevated hearing threshold (i.e., a loss of hearing sensitivity), called a noise-induced
threshold shift (NITS). If the hearing threshold eventually returns to normal, the NITS iscalled a temporary threshold shift (TTS); otherwise, if thresholds remain elevated aftersome extended period of time, the remaining NITS is called a permanent threshold shift(PTS). TTS and PTS data have been used to guide the development of safe exposure
guidelines for people working in noisy environments. Similarly, TTS and PTS criteria
and thresholds form the cornerstone of Navy analyses to predict auditory effects in2018 REVISION TO: TECHNICAL GUIDANCE FOR ASSESSING THE EFFECTS OF ANTHROPOGENIC SOUND ON MARINE MAMMALHEARING (VERSION 2.0)
Page 39

marine mammals incidentally exposed to intense underwater sound during naval
activities.
1.4

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

TAP PHASE 3 WEIGHTING FUNCTIONS AND TTS/PTS THRESHOLDS

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

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

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II.I.

WEIGHTING FUNCTIONSFUNCTIONS AND EXPOSURE FUNCTIONSFU CTIO S

The shapes of the Phase 3 auditory weighting functions are based on a generic band-passfilter described by(I! 1irrf / J.)2a1

W(f) = C + IO log
10

,

(A1)

[1+(! / 1irJ[1+(f !

where W( f ) is the weighting function amplitude (in dB) at the frequency f (in kHz). The
shape of the filter is defined by the parameters C, f1, f2, a, and b (Figs. A1 and A2, left
panels):C weighting function gain (dB). The value of C defines the vertical position of
the curve. Changing the value of C shifts the function up/down. The value of
C is often chosen to set the maximum amplitude of W to 0 dB (i.e., the valueof C does not necessarily equal the peak amplitude of the curve).
f1 low-frequency cutoff (kHz). The value of f1 defines the lower limit of the filter
pass-band; i.e., the lower frequency at which the weighting function amplitude
begins to decline or “roll-off” from the flat, central portion of the curve. The
specific amplitude at f1 depends on the value of a. Decreasing f1 will enlarge
the pass-band of the function (the flat, central portion of the curve).
f2 high-frequency cutoff (kHz). The value of f2 defines the upper limit of thefilter pass-band; i.e., the upper frequency at which the weighting function
amplitude begins to roll-off from the flat, central portion of the curve. The
amplitude at f2 depends on the value of b. Increasing f2 will enlarge the passband of the function.
alow-frequency exponent (dimensionless). The value of a defines the rate at
which the weighting function amplitude declines with frequency at the lower
frequencies. As frequency decreases, the change in weighting function
amplitude becomes linear with the logarithm of frequency, with a slope of 20adB/decade. Larger values of a result in lower amplitudes at f1 and steeper
rolloffs at frequencies below f1.

b

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

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Page 42If a = 2 and b = 2, Eq. (A1) is equivalent to the functions used to define Navy Phase 2
Type I and EQL weighting functions, M-weighting functions, and the human Cweighting function (American National Standards Institute (ANSI), 2001; Southall et al.,2007; Finneran and Jenkins, 2012). The change from fixed to variable exponents for
Phase 3 was done to allow the low- and high-frequency rolloffs to match available
experimental data. During implementation, the weighting function defined by Eq. (A1) isused in conjunction with a weighted threshold for TTS or PTS expressed in units of SEL.

(1) - weighting function

Eq. (2) - exposure function

cf
20b

-20b
K

frequency
Figure A1.

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

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(1) - weighting function

Eq . (2) - exposure function

frequency
Figure A2.

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

2018 REVISION TO: TECHNICAL GUIDANCE FOR ASSESSING THE EFFECTS OF ANTHROPOGENIC SOUND ON MARINE MAMMALHEARING (VERSION 2.0)
Page 44For developing and visualizing the effects of the various weighting functions, it is helpful
to invert Eq. (A1), yieldingl (f I J°J2a

E(j) = K -10 lo~
0[1+(111.rJ[1+(1 /1irJ

),

(A2)

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

-

weighting function

exposure function

C l)

N

0

ro 220

a..

:::t

.....

~

i -20

co 200

::l

~

:3,

~ -40

Q)

a.

.....
Cl)

§ 180
CJ)

-60 L.L..a.......................................................................__._...........wL......o

0.01

0.1

10

100

~
0.01

0.1

10

100

frequency (kHz)
Figure A3.

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

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

X(f) = IO log
iol[I+(//(f I J;)2a1;)2J[I+(// _t;)2r

).

(A3)

The peak value of X( f ) depends on the specific values of f1, f2, a, and b and will notnecessarily equal zero. Substituting Eq. (A3) into Eqs. (A1) and (A2) results inW(f) = C + X(f)(A4)

E(f)=K-X(f) ,

(A5)

and

respectively. The maximum of the weighting function and the minimum of the exposure
function occur at the same frequency, denoted fp. The constant C is defined so theweighting function maximum value is 0 dB; i.e., W( fp ) = 0, so.
W(fp )=O=C+X(f)p(A6)

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

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

Twgt =C+K.

(A8)

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

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III.
Ill.

METHODOLOGY TO DERIVEDERIVE FUNCTION PARAMETERSPARA ETERS

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

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

The remainder of this document addresses these steps in detail.

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IV.

MARINE MAMMALAM AL SPECIES GROUPS

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

LOW-FREQUENCY (LF) CETACEANS

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

MID-FREQUENCY (MF) CETACEANS

The MF cetacean group contains most delphinid species (e.g., bottlenose dolphin,common dolphin, killer whale, pilot whale), beaked whales, and sperm whales (but notpygmy and dwarf sperm whales of the genus Kogia, which are treated as high-frequency
species). Hearing sensitivity has been directly measured for a number of species within
this group using psychophysical (behavioral) or auditory evoked potential (AEP)
measurements.
4.3

HIGH-FREQUENCY (HF) CETACEANS

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

4.4

SIRENIANS

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

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

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

0..

140

::i.

..- 120~!g 100

--0
O

.c.
(/)

80

Q)

..c 60 ········ Odobenid-- - Otariid

0.1

1

10

100

frequency (kHz)
Figure A4.

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

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Table A1.

Species group designations for Navy Phase 3 auditory weighting functions.

Code

Name

Members

LF

Low-frequency
cetaceans

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

Mid-frequency
cetaceans

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

HF

High-frequency
cetaceans

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

SI

Sirenians

Family Trichechidae (manatees)
Family Dugongidae (dugongs)

OW

Otariids and othernon-phocid marinecarnivores (water)

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

PW

Phocids (water)

Family Phocidae (true seals)

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V.

COMPOSITE
CO POSITE AUDIOGRAMS

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

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the median (50th percentile) threshold value was calculated at each frequency and fit by
the function,(A9)

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

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Table A2.

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

Group

ReferenceMF(Finneran et al., 2005b)

Delphinapterus leucas

Beethoven(Szymanski et al., 1999)

Orcinus orca

Yaka, Vigga(Nachtigall et al., 1995)

Grampus griseus

N/a(Kastelein et al., 2003)

Stenella coeruleoalba

Meyen(Lemonds, 1999)

Tursiops truncatus

Itsi Bitsy(Brill et al., 2001)

Tursiops truncatus

CAS(Ljungblad et al., 1982)

Tursiops truncatus

12-y male(Johnson, 1967)

Tursiops truncatus

Salty(Sauerland and Dehnhardt, 1998)

Sotalia fluviatilis

Paco(Johnson et al., 1989)

Delphinapterus leucas

2-y female(White et al., 1978)

Delphinapterus leucas

Edwina, Kojak(Awbrey et al., 1988)

Delphinapterus leucas

Kojak, female, male(Thomas et al., 1988)

Pseudorca crassidens

I'a nui hahai(Finneran et al., 2010b)

Tursiops truncatus

TYH(Schlundt et al., 2008)

Tursiops truncatus

WEN(Ridgway et al., 2001)

Delphinapterus leucas

MUK, NOC(Tremel et al., 1998)

Lagenorhynchus obliquidens

female

HF

SI
OW

PW

Species

Subjects(Jacobs and Hall, 1972)

Inia geoffrensis

male(Kastelein et al., 2002a)**

Phocoena

PpSH047(Kastelein et al., 2010)

Phocoena

Jerry(Kastelein et al., 2015a)

Phocoena

ID No. 04(Gaspard et al., 2012)

Trichechus manatus

Buffet, Hugh(Gerstein et al., 1999)

Trichechus manatus

Stormy, Dundee(Moore and Schusterman, 1987)

Callorhinus ursinus

Lori, Tobe

(Babushina et al., 1991)

Callorhinus ursinus

N/a(Kastelein et al., 2002b)

Odobenus rosmarus

Igor(Mulsow et al., 2012)

Zalophus californianus

JFN(Reichmuth and Southall, 2012)

Zalophus californianus

Rio, Sam(Reichmuth et al., 2013)

Zalophus californianus

Ronan(Kastelein et al., 2005)

Eumetopias jubatus

EjZH021, EjZH022(Ghoul and Reichmuth, 2014)

Enhydra lutris nereisCharlie(Kastak and Schusterman, 1999)

Mirounga angustirostris

Burnyce(Terhune, 1988)

Phoca vitulina

N/a(Reichmuth et al., 2013)

Phoca vitulina

Sprouts(Kastelein et al., 2009)

Phoca vitulina

01, 02(Sills et al., 2014)

Phoca largha

Amak, Tunu

(Sills et al., 2015)

Pusa hispida

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

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Table A3.

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

Group

T0 (dB)F1 (kHz)F2 (kHz)

A

B

R2

LF

53.19

0.412

9.4

20

3.2

–

MF

46.2

25.9

47.8

35.5

3.56

0.977

HF

46.4

7.57

126

42.3

17.1

0.968

SI

-40.4

3990

3.8

37.3

1.7

0.982

OW

63.1

3.06

11.8

30.1

3.23

0.939

PW

43.7

10.2

3.97

20.1

1.41

0.907

Table A4.

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

T0 (dB)F1 (kHz)F2 (kHz)

A

B

R2

LF

-0.81

0.412

9.4

20

3.2

–

MF

3.61

12.7

64.4

31.8

4.5

0.960

HF

2.48

9.68

126

40.1

17

0.969

SI

-109

5590

2.62

38.1

1.53

0.963

OW

2.36

0.366

12.8

73.5

3.4

0.958

PW

-39.6

368

2.21

20.5

1.23

0.907

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Page 55120,....._ 100coa.. 80
::1.
T"""

60

Q)
I....

co

40

"'O 20..._...
"'O

LF
0.1

HF
1

10

100

0.1

1

10

100

0.1

1

10

100

0.1

10

100

10

100

_g 140en~ 120...c::
+-'

100
80
60
40

ow

SI
0.1

1

10

100

0.1

1

frequency (kHz)
Figure A5.

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

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-

60

c:c

---

,:, 40
,:,
0 20

..c:
(/)

Q)

0

L..

..c:
_, -20
,:,

LF

0.01

HF
0.1

1

10

100

0.1

1

10

100

0.1

1

10

100

1

10

100

Q)

N

80

cu
E 60
L..

0

C

40
20
0
-20

ow

SI
0.1

1

10

100

0.1

PW
1

10

100

0.1

frequency (kHz)
Figure A6.

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

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original

PW...-....

coI

a..~ 120

;

T"""

Q)

'(l'.)

"C

100
80
LF

"C

0

..c

en
Q)

'-

..c
....,

60
HF

40
20
0.1
80

1

10

100

normalized

PW...-....

(l'.)

"C
"C

0

I

60

I

40

..c

en
Q)

'-

..c
....,

;

I

20

. .·'·~

·,.

LF

~-, .

0
-20

0.1

1

10

100

freq uency (kHz)
Figure A7.

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

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Table A5.

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

Group

Original data
composite audiogram

Normalized data
composite audiogram

Equal latency
curves

f0

s0

f0

s0

s0

(kHz)

(dB/decade)(kHz)(dB/decade)(dB/decade)

LF

5.6

20

5.6

20

—

MF

55

35

58

31

31

HF

105

37

105

36

50

SI

16

36

12

37

—

OW

12

27

10

39

—

PW

8.6

19

13

20

—

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VI.

EQUAL LOUDNESS DATA

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

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VII.

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

200
Tursiops truncatus

180

.
"
'

,'

"

,......,
cu 160

:,,"

a..

'"
"'

::i

,..... 140....Q)

co 120

-0

...J

a..
Cl)

100
80

'•.,.'

60
40

thresholdthreshold

0.1

10

100

0.1

1

10

100

frequency (kHz)
Figure A8. Underwater marine mammal equal latency contours are available for Phocoena phocoena(Wensveen et al., 2014) and Tursiops truncatus (Mulsow et al., 2015). The slopes forthe contours at low frequencies were obtained from the literature (Phocoena
phocoena) or calculated from the best linear-log fits to the lower frequency data.
The slope of the contour passing through an SPL approximately 40 dB above thethreshold at f0 was selected as the most appropriate based on: (1) human Aweighting, (2) observations that the relationship between equal latency and loudness
can break down at higher sensation levels, and (3) for many data sets the slopes
increase at higher SPLs rather than decrease as expected. The resulting slopes arelisted in Table A5.

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VIII.

TTS DATA

8.1

NON-IMPULSIVE (STEADY-STATE) EXPOSURES – TTS

For weighting function derivation, the most critical data required are TTS onset exposurelevels as a function of exposure frequency. These values can be estimated from publishedliterature by examining TTS as a function of SEL for various frequencies.
To estimate TTS onset values, only TTS data from psychophysical (behavioral) hearing
tests were used. Studies have shown differences between the amount of TTS frombehavioral threshold measurements and that determined using AEP thresholds (Fig. A9).
TTS determined from AEP thresholds is typically larger than that determined behaviorally,
and AEP-measured TTS of up to ~ 10 dB has been observed with no corresponding change
in behavioral thresholds (e.g., Finneran et al., 2007). Although these data suggest that AEP
amplitudes and thresholds provide more sensitive indicators (than behavioral thresholds) of
the auditory effects of noise, Navy acoustic impact analyses use TTS both as an indicator ofthe disruption of behavioral patterns that are mediated by the sense of hearing and to predict
when the onset of PTS is likely to occur. Navy analyses assume that exposures resulting in a
NITS > 40 dB measured a few minutes after exposure will result in some amount of residual
PTS. This is based on relationships observed in early human TTS studies utilizing
psychophysical threshold measurements. To date, there have been no reports of PTS in amarine 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 thosecapable of resulting in PTS (Popov et al., 2013).

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(a)

AEP

(b)

AEP

Cl) 30II- 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 exposureswith different SPLs and durations were combined to create a single TTS growth curve asa function of SEL. The use of (cumulative) SEL is a simplifying assumption toaccommodate 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 thisapproach assumes exposures with equal SEL result in equal effects, regardless of theduration 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 withthe 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 theselimitations, however, the equal energy rule is still a useful concept, since it includes theeffects 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 ameaningful way, has physical significance, and is correlated with most TTS growth datareasonably 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 Navysources 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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Page 63

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 andapproach 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. Thisparticular 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 — definedas 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 thresholdmeasurements that typically occur across test sessions. Extrapolation was not performed
when estimating TTS onset; this means only data sets with exposures producing TTS bothabove 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, andreferences 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 (butsee 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 tomarine mammals; however, the inner ears of marine and terrestrial mammals areanalogous and certain relationships are expected to hold for both groups. Experimentswith 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 etal., 2005b). For this reason, relationships between TTS and PTS from marine andterrestrial mammals can be used, along with TTS onset values for marine mammals, toestimate 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 etal., 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 a2018 REVISION TO: TECHNICAL GUIDANCE FOR ASSESSING THE EFFECTS OF ANTHROPOGENIC SOUND ON MARINE MAMMALHEARING (VERSION 2.0)
Page 64conservative estimate for the onset of PTS. An exposure causing 40 dB of TTS istherefore 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 areshallower than at higher amounts of TTS.
8.3

IMPULSIVE EXPOSURESMarine mammal TTS data from impulsive sources are limited to two studies withmeasured 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 thelimited 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 seriesof impulsive sounds produced by broadcasting underwater recordings of impact piledriving 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 thecumulative (unweighted) SEL was approximately 180 dB re 1 μPa2s. The pressure
waveforms for the simulated pile strikes exhibited significant “ringing” not present in theoriginal 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 representativeof 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 sequencesof 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 piledriving 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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Page 65

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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Page 66

40

(a)

(c)

(b)

30
20
10

3 kHz

•

0

---

40

(d)

CO 30

..,,

~

Cl) 203 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 kHz0
120 140 160 180 200 220

140 160 180 200 220

SEL (dB re
Figure A10.

140 160 180 200 220

1 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 withmaximum 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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Page 67

(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 withmaximum 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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Page 68

40

(a)

(c)

(b)

I
I
I

30

I

6.5 kHz4 kHz

20
1-2 kHz

10
0
I

(d)

40

---co 30

(e)

I

0

(f)

""O

( /)

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 afunction 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 thosedatasets 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 forexplanation of the datasets in each panel.

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Page 69

20

~

(a)

(b)

(c)
02
4 kHz

2.5 kHz

T

10 ~
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 thosedatasets 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-statenoise and behavioral threshold measurements unless otherwise indicated.

Min
TTS
(dB)

Max
TTS
(dB)

TTS
Onset
(dB
SEL)

TTS
growthrate(dB/dB)

PTS
Onset
(dB
SEL)

TTSPTS
offset(dB)

Notes

Reference

FigureTTS 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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Page 71Subject

Freq.
(kHz)

Min
TTS
(dB)

Max
TTS
(dB)

TTS
Onset
(dB
SEL)

TTS
growthrate(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

SpeciesMF

Delphinapterus
leucasMF

Delphinapterus
leucas

male

11.2
22.5
45
90

MF

Delphinapterus
leucasfemale

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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Page 72

Min
TTS
(dB)

Max
TTS
(dB)

TTS
Onset
(dB
SEL)

TTS
growthrate(dB/dB)

PTS
Onset
(dB
SEL)

TTSPTS
offset(dB)

GroupSpecies

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)2018 REVISION TO: TECHNICAL GUIDANCE FOR ASSESSING THE EFFECTS OF ANTHROPOGENIC SOUND ON MARINE MAMMAL HEARING (VERSION 2.0)

Page 73

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 groupto provide the best fit to the TTS data or estimated TTS onset value at a particularfrequency.
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 theslope 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 theaudiogram 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 thefrequency 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 forthe 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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Page 74

--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 (thelowest 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 andthe 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 theoriginal and normalized data as a function of ∆T (Fig. A16). The conditions (∆T value and2018 REVISION TO: TECHNICAL GUIDANCE FOR ASSESSING THE EFFECTS OF ANTHROPOGENIC SOUND ON MARINE MAMMALHEARING (VERSION 2.0)
Page 75

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, thelowest 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<{' 14C

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 thesquared 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 obtainedusing 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 tothe minimum value of the exposure function.
For the low-frequency cetaceans and sirenians, for which no TTS data exist, TTS onset atthe 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 onsetof 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, andPW groups. For these groups, the median difference between the TTS onset andcomposite 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 othergroups (MF, HF, SI, OW, PW, median = 54 dB re 1 μPa). The TTS onset value at f0 istherefore 180 dB re 1 μPa2s for the low-frequency cetaceans (Table A7). For the2018 REVISION TO: TECHNICAL GUIDANCE FOR ASSESSING THE EFFECTS OF ANTHROPOGENIC SOUND ON MARINE MAMMALHEARING (VERSION 2.0)
Page 76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 themedian 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

Estimateddifference

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 theminimum value of the exposure function. Finally, the constant C was determined bysubstituting 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, andthe 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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Page 77

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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Page 78

---

'

''

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 parametersspecified 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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Page 79

7

--

210

'

(/)

N

'1 T 11~I
I
I
I~4.311

ro0.. 200
::i

I

T"""

[>o,3,

Q)
L.

I

m 190

--.....

T




()

~

!I<1"

'"O
Q)

•

(/)

c:: 180

0

I>

0

Cf)

II-

.

*0

170

Schlund! 2000
Nachtigall 2003
Nachtigall 2004
Finneran 2005
Finneran 2007 (behav)
Finneran 2007 (AEP)
Mooney 2009aMooney 2009b
Finneran 201 Oa
Finneran 201 Ob
Popov 2011aFinnera n 2013
Popov 2013
Popov 2014 (F)Popov 2014 (M)Popov 2015

Exposure function• • • • Phase 2 function- - Composite audiogram

160
1

Figure A18.

10frequen cy (kHz)100

Mid-frequency cetacean exposure function, (normalized) composite audiogram, andPhase 2 exposure functions compared to mid-frequency cetacean TTS data. Largesymbols 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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Page 80

()

-

190

Cl')

N

C'Cl

i

a..

::i 180

.....
Q)
'--

en 170--......

........... .....................

"O

ci35

"

cJ8

C:

0
Cf)

~

... ...

160*i

cJ5 cJ3
cJ3
cJ5

0 18

Popov (2011)in (2012a)
 Kastele
Kastele in (2013b)

T Kastele in (2014a) - 6.5 kHz

030037<:Js <:JO

Q)

Cl')

0

d sd o cJ5

()

I

[I

<>

Kastele in (2014a) - 9.2 kHz
Kastele in (2014b) . 100%
Kastele in (2014b) - 10%
Kastele in (2015a) - 100%
Kastele in (2015a) - 10%- E xposure function• • • • Phase 2 function- - Composite aud iogram

150

140
0.5

Figure A19.

1

10frequency (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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Page 81N''

en 210roa..
:::i..
T"""

ID 200
I...

I
I

'

''

''

k 2005
 Kasta
Kaslele in 20 12 (sea l 01 )

'

''

T SO+

'

ID
en 190
C

0

...

I

.A 44

''

•?

I
I
I

- Exposure function• • • • Phase 2 func tion
- - Composite audiogram

I

''

'

,,

•.

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, andPhase 2 exposure functions compared to phocid TTS data. Large symbols with nonumeric values indicate onset TTS exposures. Smaller symbols represent specificamounts of TTS observed, with numeric values giving the amount (or range) or
measured TTS.

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Page 82

X.

PTS EXPOSURE FUNCTIONSFUNCTIONS 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 forcetaceans and a 14-dB difference for phocids, otariids, odobenids, mustelids, ursids, andsirenians (Finneran and Jenkins, 2012). The 20-dB value was based on human data (Wardet al., 1958) and the available marine mammal data, essentially following theextrapolation 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 inair.
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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Page 83

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 inconjunction 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 soundexposures 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 byapplying 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 Luckeet al. (2009), the SEL-based weighted TTS thresholds are 170 and 140 dB re 1 μPa2s forthe 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 thehigh-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 thisspectrum 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 threshold2018 REVISION TO: TECHNICAL GUIDANCE FOR ASSESSING THE EFFECTS OF ANTHROPOGENIC SOUND ON MARINE MAMMALHEARING (VERSION 2.0)
Page 84

and the impulse TTS weighted threshold for the groups for which data exist (the mid- andhigh-frequency cetaceans):
,

(A11)

where G indicates thresholds for a species group for which impulse TTS data are notavailable, C indicates the median threshold for the groups for which data exist, thesubscript 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 therelationship 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 eachof 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- andhigh-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 inchinchillas. 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
thresholdPTS
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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Page 86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. -40

E

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 tounderwater sound. Parameters required to generate the functions are provided inTable A10.

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Page 87

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
thresholdPTS
threshold

Impulse
TTS
thresholdPTS
threshold

Grou
a
p

b

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

LF

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

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

1

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Page 88

To properly compare the TTS/PTS criteria and thresholds used by Navy for Phase 2 andPhase 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 thresholdat the most susceptible frequency (based on the relevant weighting function). Since theexposure 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 thefollowing:(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 usedin Phase 2. In Phase 2, the TTS onset for the otariids was taken directly from thepublished literature (Kastak et al., 2005); for Phase 3, the actual TTS data from Kastak etal. (2005) were fit by a TTS growth curve using identical methods as those used with theother 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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Page 89

·· ·· ·· ·~
\

--

.

.:

~

180

(/)

N

co

'3_ 160

LF

Q)
,._

CD

,:,

--w

140

0.01

MF
0.1

1

10

10

100

1

10

100

_J

en 220200'

180-- - - - - - - - -

'

,

ow

SI

0.1

10

100

0.1

PW
1

10

100

0 .1

10

100

frequency (kHz)- - Phase 2 - TTS Exposure function· · · · · · Phase 2 - PTS Exposure function
Phase 3 - TTS Exposure function
Phase 3 - PTS Exposure function

Figure A22.

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

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Page 90

.//, '·· ·•······........
... ~

180

'

'

,'/

--

I

I

,

en 160Nroa..:::t

140

LF

MF

~

Q}
,_

co 220

0.01

--w
-0

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 2 - TTS Exposu re function· · · · · · Phase 2 - PTS Exposu re func tion
Phase 3 - TTS Exposu re function
Phase 3 - PTS Exposu re func tion

TTS and PTS exposure functions for explosives, impact pile driving, air guns, andother 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 dashedlines — Navy Phase 2 PTS exposure functions.

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Page 91

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 ofbasilar 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 andfrequency 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, additionalsources 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 descriptionof the mathematical process by which frequency-place maps based on anatomicalmeasurements 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, thevalidity 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 headto the ear of the fin whale, but does not include the sensory receptors of thecochlea. There is therefore no way to properly predict the upper cutoff of2018 REVISION TO: TECHNICAL GUIDANCE FOR ASSESSING THE EFFECTS OF ANTHROPOGENIC SOUND ON MARINE MAMMALHEARING (VERSION 2.0)
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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 anindividual 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 datafrom other mammals with normal hearing. Given these considerations, theproposed 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 inconspecific 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 ensurethat 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 thecontext 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 10l 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 smallerand 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 ‑AdB/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

H(f)

in 50

--

"C
"C

40

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), (dashedline).

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 thelowest 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, thelowest LF cetacean threshold is defined to match the median threshold of the in-water
marine mammal species groups (MF cetaceans, HF cetaceans, sirenians, otariids andother 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 theaudiogram, 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 thelower 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, withthresholds within 3 dB of best sensitivity from ~1.4 to 7.8 kHz. For right whales, Parks etal. (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 theregion 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-dBof 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, andthresholds 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 thelowest 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 thatthresholds are ≤ 3 dB relative to the lowest threshold when the frequency is within theregion 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 thecomposite audiograms for the other in-water marine mammal species groups (MFcetaceans, HF cetaceans, sirenians, otariids and other marine carnivores in water, andphocids in water). This results in B = 3.2 for the LF cetaceans. Once B is defined, F2 isadjusted 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, predictedaudiograms 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, andthresholds are within 1 dB of the lowest threshold from ~1.8 to 11 kHz, and within 3 dBof 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 inmysticete conspecific vocal communication signals. While some species (e.g., blue
whales) produce some extremely low (e.g., 10 Hz) frequency call components, themajority of mysticete social calls occur in the few tens of Hz to few kHz range,
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Page 96overlapping reasonably well with the predicted auditory sensitivity shown in thecomposite 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 phocidseals (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

7060---~ 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 byanatomical and finite-element models.

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XIII.

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Moore, P.W.B. and Schusterman, R.J. (1987). “Audiometric assessment of northern fur seals,
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Mulsow, J., Schlundt, C.E., Brandt, L., and Finneran, J.J. (2015). “Equal latency contours for bottlenose
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Parks, S.E., Ketten, D.R., O’Malley, J.T., and Arruda, J. (2007). “Anatomical predictions of hearing in the
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Popov, V.V., Nechaev, D.I., Sysueva, E.V., Rozhnov, V.V., and Supin, A.Y. (2015). “Spectrum pattern
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Popov, V.V., Supin, A.Y., Pletenko, M.G., Tarakanov, M.B., Klishin, V.O., Bulgakova, T.N., andRosanova, E.I. (2007). “Audiogram variability in normal bottlenose dolphins (Tursiops
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Reichmuth, C. and Southall, B.L. (2012). “Underwater hearing in California sea lions (Zalophus
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Reichmuth, C., Ghoul, A., Rouse, A., Sills, J., and Southall, B. (2016). “Temporary threshold shift notmeasured in spotted or ringed seals exposed to single airgun impulses,” J. Acoust. Soc. Am. (inreview).
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2250- 2259.
Southall, B.L., Bowles, A.E., Ellison, W.T., Finneran, J.J., Gentry, R.L., Greene Jr., C.R., Kastak, D.,
Ketten, D.R., Miller, J.H., Nachtigall, P.E., Richardson, W.J., Thomas, J.A., and Tyack, P.L.
(2007). “Marine mammal noise exposure criteria: initial scientific recommendations,” Aquatic
Mammal. 33, 411-521.
Stebbins, W.C. (1966). “Auditory reaction time and the derivation of equal loudness contours for themonkey,” Journal of the Experimental Analysis of Behavior 9, 135-142.
Szymanski, M.D., Bain, D.E., Kiehl, K., Pennington, S., Wong, S., and Henry, K.R. (1999). “Killer whale(Orcinus orca) hearing: Auditory brainstem response and behavioral audiograms,” J. Acoust.
Soc. Am. 106, 1134-1141.
Terhune, J.M. (1988). “Detection thresholds of a harbour seal to repeated underwater highfrequency, short-duration sinusoidal pulses,” Canadian Journal of Zoology 66, 15781582.
Thomas, J., Chun, N., Au, W., and Pugh, K. (1988). “Underwater audiogram of a false killer whale(Pseudorca crassidens),” J. Acoust. Soc. Am. 84, 936-940.
Tremel, D.P., Thomas, J.A., Ramierez, K.T., Dye, G.S., Bachman, W.A., Orban, A.N., and Grimm, K.K.
(1998). “Underwater hearing sensitivity of a Pacific white-sided dolphin, Lagenorhynchus
obliquidens,” Aquatic Mammal. 24, 63-69.
Tubelli, A.A., Zosuls, A., Ketten, D.R., Yamato, M., and Mountain, D.C. (2012). “A prediction of theminke whale (Balaenoptera acutorostrata) middle-ear transfer function,” J. Acoust. Soc. Am.
132, 3263-3272.
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Tyack, P.L. and Clark, C.W. (2000). “Communication and acoustic behavior of dolphins and whales,”in Hearing by Whales and Dolphins, edited by W.W.L. Au, A.N. Popper, and R.R. Fay(Springer, New York), pp. 156-224.
Ward, W.D. (1960). “Recovery from high values of temporary threshold shift,” J. Acoust. Soc. Am. 32,
497-500.
Ward, W.D. (1997). “Effects of high-intensity sound,” in Encyclopedia of Acoustics, edited by M.J.
Crocker (Wiley, New York, NY), pp. 1497-1507.
Ward, W.D., Glorig, A., and Sklar, D.L. (1958). “Dependence of temporary threshold shift at 4 kc on
intensity and time,” J. Acoust. Soc. Am. 30, 944-954.
Ward, W.D., Glorig, A., and Sklar, D.L. (1959). “Temporary Threshold Shift from Octave-Band Noise:
Applications to Damage-Risk Criteria,” J. Acoust. Soc. Am. 31, 522-528.
Wartzok, D. and Ketten, D. (1999). “Marine mammal sensory systems,” in The Biology of Marine
Mammals, edited by J.E. Reynolds and S.A. Rommel (Smithsonian Institution Press,
Washington, DC).
Wensveen, P.J., Huijser, L.A.E., Hoek, L., and Kastelein, R.A. (2014). “Equal latency contours andauditory weighting functions for the harbour porpoise (Phocoena phocoena),” J. Exp. Biol.
217, 359-369.
White, M.J., Norris, J., Ljungblad, D.K., Baron, K., and di Sciara, G.N. (1978). “Auditory thresholds oftwo beluga whales (Delphinapterus leucas),” (Hubbs Sea World Research Institute, San
Diego).

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DO0UMEiNTATl:ON PAGE

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APPENDIX B:

RESEARCH RECOMMENDATIONSRECOM ENDATIONS FOR
FOR IMPROVED
I PROVEDTHRESHOLDS

In compiling, interpreting, and synthesizing the scientific literature to produce thresholds for thisTechnical Guidance, it is evident that additional data would be useful for future iterations of thisdocument, since many data gaps still exist (Table B1). The need for the Technical Guidance toidentify critical data gaps was also recommended during the initial peer review and publiccomment period.
Table B1:

Summary of currently available marine mammal data.

Hearing GroupLF Cetaceans

MF Cetaceans
HF Cetaceans
PW Pinnipeds
OW Pinnipeds

Audiogram
Data/Number ofSpecies
Predictivemodeling/2
species

TTS
Data/Number ofSpecies

Sound Sources for TTS Studies

None/0 species

None

Behavioral/8
species

Behavioral/2
species

Behavioral/2
species
Behavioral/5
species
Behavioral/3
species

Behavioral/1
species
Behavioral/2
species
Behavioral/1
species

Octave-band noise; Tones; Midfrequency sonar; Explosion
simulator; Watergun; Airgun
Tones, Mid-frequency sonar;
Impact pile driver; Airgun*
Octave-band noise; Impact piledriverOctave-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 otherpublications/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 enoughinformation to allow for quantifiable modifications to thresholds associated with many of theserecommendations, does not mean these recommendations cannot be incorporated as qualitative
considerations within the comprehensive effects analysis.

I.
1.1

SUMMARY OF RESEARCHRESEARCH RECOMMENDATIONSLOW-FREQUENCY CETACEAN HEARINGAs 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, additional38

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, predictivemodels 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 Krysl2014).

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, arethere 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 alower hearing threshold compared to all other hearing groups.
Additionally, having a more complete understanding of how sound enters the heads/bodies ofmarine mammals and its implication on hearing and impacts of noise among various species isanother 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 etal. 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 sevenhealthy 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 andfemales; subadult and adults) had “the shape of the hearing curve is generally similar topreviously published results from behavioral trials.” Thus, from these studies, it appears that forbaseline hearing measurements, captive individuals may be appropriate surrogates for freeranging animals. Additionally, Mulsow et al. (2011) measured aerial hearing abilities of sevenstranded 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 thistrend 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, andheredity, 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 andother 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 thepotential impact of aging on hearing ability and TSs:•

Houser and Finneran (2006) conducted a comprehensive study of the hearing sensitivityof 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 typicallybegan between the ages of 20 and 30 years. However, the frequencies where thisspecies is most susceptible to noise-induced hearing loss (i.e., 10 to 30 kHz) are thefrequencies where the lowest variability exists in mean thresholds between individuals ofdifferent 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, fromage one to 26 years, and found that only the two 26-year old individuals had hearingclassified 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 thatused 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, whichwere 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 termsof assessing TSs for animals of different ages. Nevertheless, additional data are needed toconfirm if these data are representative for all species (Lucke et al. 2016).
1.4

ADDITIONAL TTS MEASUREMENTS WITH MORE SPECIES AND/OR INDIVIDUALSCurrently, 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 etal. 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 ofsound sources (i.e., mostly tones and octave-band noise 42) in laboratory settings. Measurementsfrom 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 noiseoccurs) are needed.

1.5.1

Frequency and Duration of Exposure

In addition to received level, NMFS recognizes that other factors, such as frequency and durationof 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 thepotential 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 anotherimportant 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, aswell 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 soundsources) 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 toinduce a TS compared to continuous exposures of the same duration (e.g., Mooney etal. 2009a; Finneran et al. 2010b; Kastelein et al. 2014a)2) Violation of EEH: Exposures of longer duration and lower levels induce a TTS at alower 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 etal. 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 awarning signal. Nachtigall and Supin (2014) reported a similar finding in a bottlenose dolphin, abeluga (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 andSupin 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 etal. (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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Page 112during prolonged stimulation. The authors also caution that adaptation will vary with soundparameters. Finneran (2018) confirmed that bottlenose dolphins can “self mitigate” when warnedof 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. Moreinformation 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 causedelayed cochlear nerve degeneration in mice. Further, Lin et al. (2011) reported a similar patternof 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 neuraldiscrimination 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 andMerzenich 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 anadaptation to living in a noisy environment (e.g., noise exposed rats performed tasks better innoisy 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 inmarine 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 ismore 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 to2018 REVISION TO: TECHNICAL GUIDANCE FOR ASSESSING THE EFFECTS OF ANTHROPOGENIC SOUND ON MARINE MAMMALHEARING (VERSION 2.0)
Page 113decline.” The number of individuals exposed and the location and duration of exposure areimportant factors, as well. To determine whether a TS will result in a fitness consequencerequires one to consider several factors.
First, one has to consider the likelihood an individual would be exposed for a long enoughduration 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 areexperiencing situations where TSs are likely from individual sources (Richardson et al.1995; Erbeand 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 torecovery (seconds to minutes or hours to days), the frequency range of the exposure, thefrequency range of hearing and vocalization for the particular species (i.e., how animal usessound in the frequency range of anthropogenic noise exposure; e.g., Kastelein et al. 2014b), andtheir 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 whichmarine 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 fromsevere 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 ahearing 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 abetter understanding of the impacts of repeated exposures. As Kight and Swaddle (2011) indicate“Perhaps the most important unanswered question in anthropogenic noise research – and inanthropogenic 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, whicharise 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 soundsource, hearing sensitivity, sex, age, reproductive status, geographic location, season, health,social behavior, or context.
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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. Theremay 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 toanthropogenic 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 abetter understanding as to how sounds could possess less injurious characteristics further fromthe source (e.g., transition range).
Further, validation and/or comparison of various propagation and exposure models for a variety ofsources would be useful to regulators, who with thresholds that are more complex will be facedwith 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 adetermination of how precautionary these methodologies are under various scenarios and allow
for potential refinement.
1.9

NOISE-INDUCED THRESHOLD SHIFT GROWTH RATES AND RECOVERYTS 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 bevaluable.
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 TERMINOLOGYSound 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 whencomparing 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 beinaccurate 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 theinteraction 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 thecontext 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 toadopt 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 ofappropriate 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 importantconsideration for the onset TTS and PTS thresholds expressed by the weighted SELcum metricbecause if not taken into consideration unrealistically low levels of exposure with long enoughexposure durations could accumulate to exceed current weighted SELcum thresholds, when thelikelihood 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 understandingof appropriate accumulations periods for the weighted SELcum metric and NIHL, as well as thepotential 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 preferredstandard 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 importantconsideration. As more is learned about the potential effects of sound on marine mammals, themore 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 thisdocument, 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 createdadditional challenges for implementation. Practical application always needs to be weighedagainst making thresholds overly complicated (cost vs. benefit considerations). The creation oftools 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 thebackground tools and knowledge to be able to implement the Technical Guidance is critical to thisdocument being a useful and effective tool in assessing the effects of noise on marine mammal
hearing.

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Page 117APPENDIX C:TECHNICAL GUIDANCE REVIEW PROCESSES: PEER
REVIEW, PUBLICU DER
PUBLIC COMMENT,CO ME T, AND REVIEW UNDEREXECUTIVE 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 PROCESSThe President’s Office Management and Budget (OMB 2005) states, “Peer review is one of theimportant procedures used to ensure that the quality of published information meets thestandards 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 definedwithin 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 soundand 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 aHighly 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 apeer review is based on expertise, with due consideration of independence and conflict ofinterest.”
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 theentire 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 initialpublic comment period, which focused on a particular technical section relating to the proposed
application of impulsive and non-impulsive PTS onset thresholds based on physicalcharacteristics at the source and how those characteristics change with range. 47 Upon completionof 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 steeringcommittee 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 tocomplete an individual review (Table C1). The focus of the peer review was on thescientific/technical studies that have been applied and the manner that they have been applied inthis 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 technicalreport, 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 toincorporate 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 nominated48

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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Page 119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 thisappendix), a follow-up peer review was conducted. The focus of this peer review was whether the2016 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. Peerreviewers’ 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 assound 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 onparticular 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 soundexperiences as it propagates through the environment, the Acoustical Society of America’s
Underwater Technical Council was asked to nominate peer reviewers with expertise inunderwater sound propagation and physical characteristics of impulsive sources, especially highexplosives, 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 ofexpertise 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, tworeviewers volunteered, were available, had no conflicts of interest, and had the appropriate areaof 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 theindividual 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 toreview information subject to the OMB Peer Review Bulletin if the individual has a conflict ofinterest that is relevant to the functions to be performed.
The following website contains information on the peer review process including: the charge topeer reviewers, peer reviewers’ names, peer reviewers’ individual reports, and NMFS’ responseto 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 thescience 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 mostscientifically sound product for review and comment. A third public focused comment period washeld 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 TECHNICALGUIDANCE)

A public meeting/webinar was held to inform interested parties and solicit comments on the firstpublicly 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 andtranscript 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 publiccomment 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; eightstate/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 theimplementation of thresholds, which were addressed in the Final Technical Guidance or relatedFederal Register Notice. 52
Of those not mentioned above, an additional 101 comments were submitted in the form of a letteror individual comment. Twelve of these comments specifically requested an extension of theoriginal 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 militaryactivities) 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 theTechnical Guidance) and one commenter submitted their comments twice. In addition, one comment was not included inthis 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 thecomments 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 TECHNICALGUIDANCE)

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 summerof 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 agroup/organization/affiliation (some submitted on behalf of an organization and/or as anindividual). Those commenting included: two federal agencies; four industry groups; sevensubject matter experts; a scientific professional organization; seven non-governmentalorganizations; 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 letteror 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 theTechnical Guidance (e.g., general concern over impacts of noise on marine mammals fromvarious industry or military activities) and were not further addressed. Specific comments can beviewed 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 FROMDRAFT 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 evaluatedinternally 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 andweighting/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 anyof 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, thisspecies remains a MF cetacean.

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Page 123•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 agroup/organization/affiliation (some submitted on behalf of an organization and/or as anindividual). Those commenting included: two federal agencies; seven industry groups; threesubject matter experts; a scientific professional organization; and nine non-governmentalorganizations. 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 werefrom 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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Page 124•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 EXECUTIVEEXECUTIVE 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 UnitedStates 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 andresilience for the benefit of the American people, while ensuring that any such activity is safe andenvironmentally 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 orrevise 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 publiccomment 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 (approximately70%) 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, andmembers of the public (Table C4).
Table C4:

Summary of commenters

Commenter
Category
U.S. Federal
agencies
Members ofCongress*
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 GeophysicalContractors/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 ResearchCenter for Regulatory EffectivenessJoint 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 theTechnical 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 publiccomments 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, vialetter, 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 expectedFederal 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 wereappreciative 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 asafe and environmentally responsible manner. Our development and implementation of theTechnical Guidance are consistent with allowing activities vital to our nation’s security andeconomy to proceed, including those mentioned in EO 13795, and allows for decisions to bemade based upon the best available information.
The EO 13795 review process provided NMFS the opportunity to acquire valuable feedback fromthe 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 the2016 Technical Guidance (NMFS 2016a) be rescinded. Most comments were supportive of thethresholds and auditory weighting functions within 2016 Technical Guidance. Of those providing
comments, most offered recommendations for improving the clarity of the document andfacilitating 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) theneed 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 futureneeds.
NMFS’ evaluation of comments received during this process affirms that the Technical Guidanceis 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 insection 2 of EO. 13795 (as reflected in this 2018 Technical Guidance, Version 2.0):

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Page 127•To promote a more realistic assessment of the potential impacts of sound on marine
mammal hearing, using the Technical Guidance, NMFS will re-evaluate implementationof the default 24-h accumulation period and plans to convene a working group later in2018 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 aworking 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 fromstakeholders and inform future versions of the User Manual.

•

NMFS issued an updated optional User Spreadsheet tool to provide PTS onset isoplethsassociated 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 forvibratory pile driving activities to facilitate the ease of assessing PTS onset for thiscommonly 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 morereflective of the International Organization for Standardization (ISO) 2017 Underwater
Acoustics – Terminology standard (ISO 18405), which was specifically developed forunderwater 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 anddetermining the best way to address them via other means outside this review.

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Page 128APPENDIX D:

I.

ALTERNATIVE METHODOLOGYETHODOLOGYINTRODUCTION

This Appendix is provided to assist action proponents in the application of thresholds presented inthis 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 theeffects 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 scienceand 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 beable to apply NMFS’ thresholds for the onset of PTS for all sound sources. These tools areincorporated 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 moresophisticated 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 andauditory weighting function associated with the SELcum metric. NMFS recognizes that theimplementation of marine mammal auditory weighting functions represents a new factor forconsideration, 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 bemade 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 SOUNDSFor narrowband sources, the selection of the appropriate frequency for consideration associatedwith 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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Page 129function amplitude, for each hearing group, associated with the particular frequency of interestand 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 (mostsusceptible 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 morenegative WFA that results will lead to a smaller effect distance (isopleth) compared to a lessnegative 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 tozero (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 isnarrowband or not, please consult with NMFS.

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Page 130

WiFA
0

,__
i:i:l

"C
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-10

/

II)

/

"C

-~

t<

-20

.!=

-30

C

/

-

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-

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LF
MF

• • • HF

C

;:)

i:...
0/J

-40

.5

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~

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.

.
.. ...

-10

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.
.
.
...

-20

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-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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Page 131

'\

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 dashedgreen 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 SOUNDSFor broadband sources, the selection of the appropriate frequency for consideration associatedwith WFAs is more complicated. The selection of WFAs associated with broadband sources issimilar 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 (Madsen2005) but considered in the frequency domain, rather than the time domain. This is typicallyreferred 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 haveprovided representative “default” values for various broadband sources (see associated User
Spreadsheet tool and User Manual for User Spreadsheet tool).

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Page 132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 inevery 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 amplitudeis 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 essentiallyunweighted; 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

~ -40

r--:---~~---+~-----------;---1-1
Appropriate frequencies
Inappropriat
to use WFA

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 ofweighting 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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Page 133

Table D1:Applicability of weighting factor adjustments for frequencies associatedwith 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 anauditory 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 anaction 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 asound sources’ spectrum will result in more realistic (i.e., likely smaller) isopleths. NMFS iscurrently evaluating whether surrogate spectrum are available and applicable for particular soundsources, 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

~: 14010

Figure D4:

_ _J

100
1000
Frequency (Hz),Maximum one-third octave band source level in the horizontal plane for ageneric 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 the2018 REVISION TO: TECHNICAL GUIDANCE FOR ASSESSING THE EFFECTS OF ANTHROPOGENIC SOUND ON MARINE MAMMALHEARING (VERSION 2.0)
Page 134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.

WeightingDefault WFA(1 kHz)Seismic array spectrum(BOEM 2017)*

LF
cetaceanMF
cetacean

HF
cetaceanPW
pinnipedOW
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 theirtime in the closest ranges to a sound source/activity and that exposures at the closest point ofapproach are the primary exposures contributing to a receiver’s accumulated level (Gedamke etal. 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 thereceiver), 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 thecharacteristics of the receiver (i.e., swim speed and whether species is transient or resident to thearea 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 orfor 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 thismetric 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 eachmodeled 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 anarea where marine mammals congregate, like a pinniped pupping beach.

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Page 135

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 ofindividuals, swim speeds for transient species, or specific times when activity temporarily
ceases). Alternatively, there may be case-specific circumstances where the accumulation timeneeds 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, andspecies-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 acontinuous stationery activity nearby a pinniped pupping beach).

3.2

LESS SOPHISTICATED MODELSFor action proponents unable to incorporate animal and/or source movement, it may not berealistic 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 beused 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 forstationary 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 (𝑝𝑝SL/(10dB)• Source factor (S) = 10μPa2m264• Energy source factor (SE) = 10SL𝐸𝐸 /(10 dB) μPa2 m2sBoth source level and energy source level (and their corresponding factors) are evaluated andreported 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 radiantintensity 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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Page 1363.2.1.2 “Safe Distance” Methodology
Cumulative sound exposure can be computed using a simple equation, assuming a constantreceived 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 aconstant direction, then exposure changes over space and time (i.e., greatest rate ofaccumulation 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 athreshold 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 apredetermined 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:::estPomtof 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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Page 137

a

𝑅𝑅0 =

For impulsive sources, SD is replaced with SE/τ:bwhere:

𝑅𝑅0 =

π
𝑆𝑆𝑆𝑆
𝐸𝐸0 𝑣𝑣Equations D2a,b

π 𝑆𝑆𝐸𝐸𝐸𝐸0 𝑣𝑣 𝜏𝜏S = 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 havepreviously used (e.g., determine area covered over a 24-h period multiplied by the density of amarine 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 orvice versa; a faster transit speed results in less energy within a unit of time and leads to alower 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 toexceed 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 moreaccurately modeling exposure.

2018 REVISION TO: TECHNICAL GUIDANCE FOR ASSESSING THE EFFECTS OF ANTHROPOGENIC SOUND ON MARINE MAMMALHEARING (VERSION 2.0)
Page 138•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 aconstant direction). Caution is recommended if the source has the potential to move in amanner where the same group of receivers could be exposed to multiple passes from thesource.

•Minimal assumptions are made about the receivers. They are considered stationary andassumed to not move up or down within the water column. There is no avoidance and thereceiver accumulates sound via one pass of the source (i.e., receiver is not exposed tomultiple passes from the source). Because this methodology only examines one pass ofthe 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).
oThese assumptions are appropriate for sources that are expected to move much
faster than the receiver does. Further, assuming receivers do not avoid thesource or change position vertically or horizontally in the water column will resultin more exposures exceeding the thresholds compared to those receivers thatwould 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 soundsource.

•Distance (i.e., velocity x change over time) between “pulses” for intermittent sources issmall 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 noabsorption). 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 inthese 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 isdirected to the ocean floor, with less sound propagating horizontally, compared to the vertical direction), which is notaccounted for with this methodology. Additionally, many higher-frequency sounds, like sonar, are also attenuated byabsorption, which is also taken into account in this model. These, among other factors, are recommended forconsideration when evaluating whether spherical spreading is potentially resulting in an underestimation of exposure.

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Page 139

Ainslie and Von Benda-Beckmann (2013) investigated the effect various factors had on thederivation 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 thesource), 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 thatcharacteristics 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 witheach 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 athreshold) will remain there for the entire time of the activity.
For stationary, impulsive sources with high source levels (i.e., impulsive pile driving associatedwith 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 theUser 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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Page 140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 permanentthreshold shift).
Ambient noise: All-encompassing sound at a given place, usually a composite of sound frommany 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

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••

Cl

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...::::,
Cl

•··•
••

' - - - - - - - - - - A u dible - - - - - - - - • •••••••••(above line)•• • • • • •

•~

11'1
11'1
Cl

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::::,

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.•

•
••

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en
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Inaudible (below line)
Low

Figure E1.

I

:
.
•••

••

•••••••••••••••••••••••

Inaudible (below line)------------ --- -- --- ---------------- --------------- ----------------• HighFrequency (kHz)Example audiogram.

Auditory adaptation: Temporary decrease in hearing sensitivity occurring during thepresentation 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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Page 141

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 canbe applied to a sound-level measurement to account for frequency-dependent hearing (i.e.,. anexpression 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 theimportance 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), whilenarrowband or tonal sources produce sounds over a more narrow frequency range, typically witha 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 mechanicalvibration 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 twocochlea 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 andAmazon river dolphin, which produce high-frequency echolocation signals. Cochlea type II isfound 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 moremechanical; e.g., short duration of impulse can be less than the ear’s integration time, leading forthe 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 thebase ten of the ratio of a given time integral of squared instantaneous frequency-weighted soundpressure over a stated time interval or event to the reference sound exposure (ANSI 1995; ANSI2013). 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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Page 142

Decibel (dB): One-tenth of a bel. Unit of level when the base of the logarithm is the tenth root often, 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 increasein 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 ora 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 equalrisk for hearing loss (i.e., if the cumulative energy of two sources are similar, a sound from alower 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 soundpressure 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 soundpressure 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 soundpressure decreases linearly with increasing distance (neglecting reflections, refraction, andabsorption) (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 thefundamental 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 orexposure 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 tolevel 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 (lessthan 1 second), broadband, and consist of high peak sound pressure with rapid rise time andrapid 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 piledrivers.
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, andintegrity 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 criticalamount of energy. The process of summing the power to generate the required energy iscompleted 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 theear (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 amore 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 etal. 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 theimportation 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 similarfrequencies (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 soundpressure, 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, andright 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 themarine 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 beendelegated 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. andincludes ten National Standards to guide fishery conservation and management. One of thesestandards, referred to as National Standard 2 (NS2), guides scientific integrity and states“(fishery) conservation and management measures shall be based upon the best scientificinformation 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 peaksound pressure with rapid rise time that impulsive sounds do. Examples of non-impulsive soundsources 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, dolphinsand 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 isdesigned to be as small as possible).
One-third octave (base 10): The frequency ratio corresponding to a decidecade or one tenth ofa 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 specificfrequency 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 ofaudibility 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 indecibels (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 statedpoints in a transmission system (for example the reduction in the magnitude of a signal between asource 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, normallymeasured 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 thebase 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 anindividual 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 accountthe 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 pressurecomponent of sound. Ten times the logarithm to the base 10 of the ratio of time-mean-squarepressure of a sound in a stated frequency band to the square of the reference pressure (1 µPa inwater) (ANSI 2013).
Source Level (SL): Sound pressure level measured in a given radian direction, corrected forabsorption, and scaled to a reference distance (Morfey 2001). For underwater sources, the soundpressure level of is measured in the far-field and scaled to a standard reference distance (1meter) 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 afunction 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 widthof the band (ANSI 2013).
Subharmonic: Sinusoidal quantity having a frequency that is an integral submultiple of thefundamental 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 establishedreference 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 thanany 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 asound sensation characterized by a single pitch (one frequency). A complex tone is a soundsensation 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; Cohenet 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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