84872 Federal Register / Vol. 89, No. 206 / Thursday, October 24, 2024 / Notices 

instructions were to improve the quality 

of information initially collected and to 

make the permit process more efficient. 

Affected Public: Individuals; Business 

or other for-profit organizations; Not-forprofit institutions; State, Local, or Tribal 

government; Federal Government. 

Frequency: On occasion. 

Respondent’s Obligation: Required to 

Obtain or Retain Benefits. 

Legal Authority: National Marine 

Sanctuaries Act, 16 U.S.C. 1431 et seq. 

This information collection request 

may be viewed at https://

www.reginfo.gov. Follow the 

instructions to view the Department of 

Commerce collections currently under 

review by OMB. 

Written comments and 

recommendations for the proposed 

information collection should be 

submitted within 30 days of the 

publication of this notice on the 

following website https://

www.reginfo.gov/public/do/PRAMain. 

Find this particular information 

collection by selecting ‘‘Currently under 

30-day Review—Open for Public 

Comments’’ or by using the search 

function and entering either the title of 

the collection or the OMB Control 

Number 0648–0141. 

Sheleen Dumas, 

Departmental PRA Clearance Officer, Office 

of the Under Secretary for Economic Affairs, 

Commerce Department. 

[FR Doc. 2024–24702 Filed 10–23–24; 8:45 am] 

BILLING CODE 3510–NK–P 

DEPARTMENT OF COMMERCE 

National Oceanic and Atmospheric 

Administration 

[RTID 0648–XD212] 

2024 Updated Guidance for Assessing 

the Effects of Anthropogenic Sound on 

Marine Mammal Hearing—Underwater 

and In-Air Criteria for Onset of 

Auditory Injury and Temporary 

Threshold Shifts (Version 3.0) 

AGENCY: National Marine Fisheries 

Service (NMFS), National Oceanic and 

Atmospheric Administration (NOAA), 

Commerce. 

ACTION: Notice. 

SUMMARY: The National Marine 

Fisheries Service (NMFS) announces the 

availability of our final 2024 Update to: 

Technical Guidance for Assessing the 

Effects of Anthropogenic Sound on 

Marine Mammal Hearing (Version 3.0): 

Underwater and In-Air Criteria for 

Onset of Auditory Injury and Temporary 

Threshold Shifts (2024 Updated 

Technical Guidance). The 2024 Updated 

Technical Guidance provides updated 

information, or acoustic criteria, to 

predict when individual marine 

mammals, both in-air and underwater, 

will experience changes in their hearing 

sensitivity (auditory injury or temporary 

threshold shift) from exposure to 

anthropogenic sound sources. The 2024 

Updated Technical Guidance replaces 

NMFS’s current 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 (2018 Revised Technical 

Guidance). 

ADDRESSES: The final 2024 Updated 

Technical Guidance is available in 

electronic form via the internet https:// 

www.fisheries.noaa.gov/national/ 

marine-mammal-protection/marinemammal-acoustic-technical-guidance. 

FOR FURTHER INFORMATION CONTACT: 

Amy R. Scholik-Schlomer, Office of 

Protected Resources, 301–427–8449, 

Amy.Scholik@noaa.gov. 

SUPPLEMENTARY INFORMATION: NMFS has 

updated its guidance for assessing the 

effects of anthropogenic sound on the 

hearing of marine mammal species 

under NMFS’s jurisdiction. Specifically, 

the 2024 Updated Technical Guidance 

identifies the received levels and 

auditory weighting functions, or 

‘‘acoustic criteria,’’ that describe the 

received levels (decibels (dB)) and 

frequencies (kilohertz (kHz)) where 

individual marine mammals are 

predicted to experience changes in their 

hearing sensitivity (auditory injury 

(AUD INJ) or temporary threshold shift 

(TTS)) from exposure to anthropogenic 

sound sources both in-air and 

underwater. This document is intended 

for use by NMFS analysts and managers 

and other relevant user groups and 

interested parties, including other 

Federal agencies, when seeking to 

determine whether and how their 

activities are expected to result in 

auditory impacts to marine mammals 

via acoustic exposure in-air and 

underwater. The 2024 Updated 

Technical Guidance outlines NMFS’s 

updated acoustic criteria and describes 

in detail how they were developed and 

how they will be updated in the future. 

For information on NMFS’ 2018 Revised 

and the original 2016 Technical 

Guidance, refer to our 2016 Federal 

Register notification (81 FR 51694, 

August 4, 2016). 

For the 2024 Updated Technical 

Guidance, NMFS again worked with the 

U.S. Navy (Navy), which recently 

updated its marine mammal AUD INJ 

and TTS criteria (Finneran 2024), to 

incorporate the best available science. 

NMFS conducted an independent peer 

review in October/November 2022. 

Details of the peer review, peer reviewer 

comments, and our response to these 

comments are available at the following 

website: https://www.noaa.gov/ 

information-technology/update-to20162018-technical-guidance-forassessing-effects-of-anthropogenicsound-on-marine-mammal. In May/June 

of 2023, NMFS solicited input from 

other relevant Federal agencies on the 

2024 Updated Technical Guidance. 

Federal agency comments and NMFS 

responses to those comments are 

available at the following website: 

https://www.fisheries.noaa.gov/ 

national/marine-mammal-protection/ 

marine-mammal-acoustic-technicalguidance. To complete the review 

process, NMFS solicited additional 

feedback from user groups and 

interested parties via a 45-day public 

comment period in May/June 2024. 

Comments received via the public 

comment period can be found at the 

following website: https://

www.regulations.gov/document/NOAANMFS-2024-0026-0001. 

It is important to note that the use of 

the acoustic criteria within the 2024 

Updated Technical Guidance should not 

be considered to represent the entirety 

of an impact assessment, but rather 

serve as one tool to help evaluate the 

effects of a proposed action. 

Furthermore, the 2024 Updated 

Technical Guidance does not create or 

confer any rights for or on any person, 

or operate to bind the public. For the 

purposes of assessing auditory impacts 

to marine mammals in support of 

regulatory processes under NMFS’ 

authority, an alternative approach that 

has undergone independent peer review 

may be proposed (by Federal agencies or 

prospective action proponents or 

applicants) and used if case-specific 

information/data indicate that the 

alternative approach is likely to produce 

a more accurate portrayal of auditory 

impacts (AUD INJ or TTS) for the 

project being evaluated, if NMFS 

determines the approach satisfies the 

requirements of the applicable statutes 

and regulations. 

The 2024 Updated Technical 

Guidance reflects 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 SEL24h criteria may extend 

beyond the capabilities of some action 

proponents. Thus, NMFS has developed 

an optional, alternative tool for those 


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who cannot fully incorporate these 

factors into their own analyses (See 

2024 Updated Technical Guidance’s 

companion optional User Spreadsheet 

tool; https://www.fisheries.noaa.gov/ 

national/marine-mammal-protection/ 

marine-mammal-acoustic-technicalguidance). 

Transitioning to 2024 Updated 

Technical Guidance 

NMFS has determined the updated 

thresholds and associated weighting 

functions in the 2024 Updated 

Technical Guidance represent the best 

available information for assessing 

whether exposure to specific activities 

is likely to result in changes in marine 

mammal hearing sensitivity (AUD INJ or 

TTS). Prospective applicants for 

incidental take authorizations under the 

Marine Mammal Protection Act 

(MMPA) and Federal agencies seeking 

Endangered Species Act (ESA) section 7 

consultations that have not yet started 

their acoustic analyses should begin 

using the 2024 Updated Technical 

Guidance immediately. At the same 

time, we recognize that for some 

proposed actions, analyses may have 

already substantially progressed using 

the existing criteria in the 2018 Revised 

Technical Guidance or other methods 

for assessing hearing effects, and it may 

be impractical to begin those analyses 

anew, taking into account timing 

constraints, expense, and other 

considerations. In such ‘‘pipeline’’ 

cases, the applicant or action agency 

should contact NMFS as soon as 

possible to discuss how to best include 

consideration of the 2024 Updated 

Technical Guidance to satisfy the 

applicable requirements. A nonexhaustive list of factors that could 

affect the extent to which the 2024 

Updated Technical Guidance will be 

quantitatively incorporated for an action 

include: The relative degree to which 

the 2024 Updated Technical Guidance 

is expected to affect the results of the 

acoustic impact analyses; how far in the 

process the application or prospective 

application has progressed; when the 

activity is scheduled to begin or other 

timing constraints; the complexity of the 

analyses and the cost and practicality of 

redoing them; and the temporal and 

spatial scope of anticipated effects. We 

anticipate that after the initial transition 

period, all applications for MMPA 

incidental take authorization and all 

requests for ESA section 7 consultations 

involving noise that may affect marine 

mammal hearing will include full 

consideration of the 2024 Updated 

Technical Guidance. 

Regulatory Context 

NMFS uses acoustic criteria to help 

quantify ‘‘take’’ and as part of more 

comprehensive effects analyses under 

several statutes. The 2024 Updated 

Technical Guidance’s acoustic criteria 

do not represent the entirety of the 

comprehensive effects analysis, but 

rather serve as one tool among others 

(e.g., behavioral impact criteria, 

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 findings required by NMFS’ 

various statutes. 

Under current agency practice, NMFS 

considers the onset of auditory injury as 

an example of ‘‘Level A Harassment’’ as 

defined in the MMPA and as ‘‘harm’’ as 

defined in ESA regulations, such that 

exposing an animal to weighted 

received sound levels at or above the 

indicated permanent threshold shift 

(PTS) threshold is predicted to result in 

these two types of ‘‘take’’ (i.e., Level A 

Harassment under the MMPA and harm 

under ESA). 

As explained below, NMFS does not 

consider a TTS to be an auditory injury 

under the MMPA or ESA, and thus it 

does not qualify as Level A harassment 

or harm. Nevertheless, TTS is an 

adverse effect that historically has been 

treated as ‘‘take’’ by ‘‘Level B 

Harassment’’ under the MMPA and 

‘‘harassment’’ under the ESA. 

Marine Mammal Protection Act 

The MMPA prohibits the take of 

marine mammals, with certain 

exceptions, one of which is the issuance 

of incidental take authorizations (ITAs). 

Sections 101(a)(5)(A) & (D) of the 

MMPA (16 U.S.C. 1361 et seq.) direct 

the Secretary of Commerce to allow, 

upon request, the incidental, but not 

intentional, taking of small numbers of 

marine mammals by U.S. citizens who 

engage in a specified activity (other than 

commercial fishing) within a specified 

geographical region if certain findings 

are made. Through delegation by the 

Secretary of Commerce, NMFS is 

required to authorize the incidental 

taking of marine mammals if the agency 

finds that the total taking will have a 

negligible impact on the species or 

stock(s) and will not have an 

unmitigable adverse impact on the 

availability of the species or stock(s) for 

certain subsistence uses. NMFS must 

also set forth the permissible methods of 

taking and requirements pertaining to 

the mitigation, monitoring, and 

reporting of such takings. (The ‘‘small 

numbers’’ and ‘‘specified geographical 

region’’ provisions do not apply to 

military readiness activities.) 

The term ‘‘take’’ means to harass, 

hunt, capture, or kill, or attempt to 

harass, hunt, capture or kill any marine 

mammal. 16 U.S.C. 1362(13). 

Except with respect to certain 

activities described below, 

‘‘harassment’’ means any act of pursuit, 

torment, or annoyance which: 

• Has the potential to injure a marine 

mammal or marine mammal stock in the 

wild (Level A Harassment); or 

• Has the potential to disturb a 

marine mammal or marine mammal 

stock in the wild by causing disruption 

of behavioral patterns, including, but 

not limited to, migration, breathing, 

nursing, breeding, feeding or sheltering 

(Level B Harassment). 

See id. at 1362(18)(A)(i) & (ii) 

(emphasis added). 

Congress amended the definition of 

‘‘harassment’’ as it applies to a ‘‘military 

readiness activity’’ or research 

conducted by or on behalf of the Federal 

government consistent with MMPA 

section 104(c)(3) as follows (section 

3(18)(B) of the MMPA): 

• Any act that injures or has the 

significant potential to injure a marine 

mammal or marine mammal stock in the 

wild (Level A Harassment); or 

• Any act that disturbs or is likely to 

disturb a marine mammal or marine 

mammal stock in the wild by causing 

disruption of natural behavioral 

patterns, including, but not limited to, 

migration, surfacing, nursing, breeding, 

feeding, or sheltering, to a point where 

such behavioral patterns are abandoned 

or significantly altered (Level B 

Harassment). 

See id. at 1362(18)(B)(i) & (ii) 

(emphasis added). 

The term ‘‘negligible impact’’ is 

defined as an impact resulting from the 

specified activity that cannot be 

reasonably expected to, and is not 

reasonably likely to, adversely affect the 

species or stock through effects on 

annual rates of recruitment or survival. 

50 CFR 216.103. 

In support of the analysis that is 

necessary to make the required statutory 

determinations, MMPA implementing 

regulations require ITA action 

proponents to provide NMFS with 

specific information. Although they may 

also be used to inform the development 

of mitigation measures, the updated 

acoustic criteria are particularly relevant 

to the following 2 of the 14 required 

pieces of information: 

• The type of incidental taking 

authorization that is being requested 

(i.e., takes by Level B Harassment only; 

Level A Harassment; or serious injury/ 


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mortality) and the method of incidental 

taking; and 

• By age, sex, and reproductive 

condition (if possible), the number of 

marine mammals (by species) that may 

be taken by each type of taking 

identified in paragraph (a)(5) of this 

section, and the number of times such 

takings by each type of taking are likely 

to occur. 50 CFR 216.104 (emphasis 

added). 

Endangered Species Act 

Section 9 of the ESA prohibits the 

take of ESA-listed species, with limited 

exceptions. Section 7 of the ESA 

requires that each Federal agency, in 

consultation with NMFS and/or the U.S. 

Fish and Wildlife Service (USFWS), 

ensure that any action authorized, 

funded, or carried out by the agency is 

not likely to jeopardize the continued 

existence of any endangered or 

threatened species or result in the 

destruction or adverse modification of 

designated critical habitat. See 16 U.S.C. 

1536(a)(2). Provided that NMFS or the 

USFWS reaches these conclusions 

through a ‘‘formal consultation’’ 

process, incidental take of ESA-listed 

species may be exempted from the 

section 9 take prohibition through an 

‘‘incidental take statement’’ that must 

specify the impact, i.e., the amount or 

extent, of the taking on the species. See 

id. at section 1536(b)(4). Incidental take 

statements must also include reasonable 

and prudent measures necessary or 

appropriate to minimize the impact, and 

the terms and conditions required to 

implement those measures. 

Under ESA, ‘‘take’’ means to harass, 

harm, pursue, hunt, shoot, wound, kill, 

trap, capture, or collect, or to attempt to 

engage in any such conduct. See id. at 

section 1532(19). ‘‘Harm’’ is defined in 

NMFS regulations as ‘‘an act which 

actually kills or injures fish or wildlife’’ 

(and can include significant habitat 

modification or degradation). See 50 

CFR 222.102. 

Under NMFS and the USFWS 

implementing regulations for section 7 

of the ESA, ‘‘jeopardize the continued 

existence of’’ means to engage in an 

action that reasonably would be 

expected, directly or indirectly, to 

reduce appreciably the likelihood of 

both the survival and recovery of a 

listed species in the wild by reducing 

the reproduction, numbers, or 

distribution of that species. See id. at 

§ 402.02. 

In support of the analysis necessary to 

conduct the consultation, the ESA 

implementing regulations state that in 

order to initiate formal consultation, the 

Federal action agency must submit a 

written request for formal consultation 

to the Director (of NMFS or the USFWS) 

that includes, among other things, a 

description of the manner in which the 

action may affect any listed species. See 

id. at § 402.14(c). 

Application of Acoustic Criteria for 

Auditory Injury 

The acoustic criterias for AUD INJ 

will be used in conjunction with sound 

source characteristics, environmental 

factors that influence sound 

propagation, anticipated marine 

mammal occurrence and behavior in the 

vicinity of the activity, as well as other 

available activity-specific factors, to 

quantitatively estimate (acknowledging 

the gaps in scientific knowledge and the 

inherent uncertainties in a marine 

environment) the takes of marine 

mammals (by Level A harassment and 

harm under the MMPA and ESA, 

respectively) and facilitate compliance 

with the MMPA and ESA, as described 

above. 

NMFS will use the same AUD INJ 

criteria in the identification and 

quantification of MMPA Level A 

harassment for both military readiness 

and non-military readiness activities. 

Because the acoustic criteria for AUD 

INJ predict the onset of AUD INJ, they 

are inclusive of the ‘‘potential’’ and 

‘‘significant potential’’ language in the 

two definitions of Level A harassment. 

The limited data now available do not 

support the parsing out of a meaningful 

quantitative difference between the 

‘‘potential’’ and ‘‘significant potential’’ 

for injury and, therefore, the designated 

AUD INJ criteria will be treated as onset 

of Level A harassment for both types of 

activities. 

Estimating the numbers of take by 

Level A harassment and harm is one 

component of the fuller analyses that 

inform NMFS’ ‘‘negligible impact’’ and 

‘‘jeopardy’’ determinations under the 

MMPA and ESA, respectively. Last, the 

AUD INJ criteria may be used to inform 

the development of mitigation and 

monitoring measures (such as shutdown zones) pursuant to the MMPA or 

ESA. 

When initiating any of the MMPA or 

ESA processes described above, 

agencies and other action proponents 

should utilize the AUD INJ criteria, in 

combination with activity-specific 

information, to predict whether, and if 

so how many, instances of AUD INJ are 

expected to occur. 

Application of Acoustic Criteria for 

Temporary Threshold Shift 

As previously stated, NMFS has not 

considered TTS an auditory injury for 

purposes of the MMPA and ESA, based 

on the work of a number of investigators 

that have measured TTS before and after 

exposure to intense sound. For example, 

Ward (1997) suggested that a TTS is 

within the normal bounds of 

physiological variability and tolerance 

and does not represent physical injury. 

In addition, Southall et al. (2007, 2019) 

indicate that although AUD INJ is a 

tissue injury, TTS is not because the 

reduced hearing sensitivity following 

exposure to intense sound results 

primarily from fatigue, not loss, of 

cochlear hair cells and supporting 

structures, and is reversible. TTS is not 

considered Level A harassment under 

the MMPA. However, given the 

associated disruptions of behavioral 

patterns anticipated to co-occur with 

TTS in some cases, it has been 

considered take by Level B harassment 

under the MMPA and harassment under 

the ESA, which will be the subject of 

future guidance. 

MMPA Level B harassment and ESA 

harassment are broad categories that 

encompass not only TTS but also other 

behaviorally related impacts that almost 

always involve a lower onset threshold 

than that for onset of TTS. In 

quantifying take by Level B harassment 

or harassment, NMFS considers all 

effects that fall into those categories of 

take, not just TTS. NMFS is in the 

process of developing updated acoustic 

criteria for the onset of behavioral 

effects and will further consider the best 

approach for considering TTS at that 

time. When that process is completed, 

NMFS will provide further guidance 

regarding how to best consider and/or 

quantify TTS for non-pulse and impulse 

sources that do not involve 

instantaneous explosives (see exception 

below for underwater explosives). In the 

meantime, except in the case of 

instantaneous underwater explosives 

(discussed next), action proponents do 

not need to quantify estimates of TTS 

separately from their overall behavioral 

harassment take calculations. NMFS 

will consider the TTS acoustic criteria 

in the 2024 Updated Technical 

Guidance as part of the larger 

comprehensive effects analyses under 

the MMPA and the ESA. 

With respect to instantaneous 

underwater explosives (as distinguished 

from repeated explosives such as 

gunnery exercises), NMFS already 

requires quantification of TTS estimates 

because instantaneous explosives do not 

have a separate behavioral component 

from a lower exposure threshold and 

there is no time accumulation involved. 

The rationale for calculating TTS for 

instantaneous explosives continues to 

apply with the 2024 Updated Technical 

Guidance. 


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The occurrence and estimated number 

of TTS takes is one component of the 

larger analysis that informs NMFS’s 

‘‘negligible impact’’ and ‘‘jeopardy’’ 

determinations under the MMPA and 

ESA, respectively. As with AUD INJ, 

TTS acoustic criteria also may be used 

to inform the development of mitigation 

and monitoring measures pursuant to 

the MMPA or ESA. 

Comments and Responses 

On May 3, 2024, NMFS published the 

draft 2024 Updated Technical Guidance 

for a 45-day public comment period (89 

FR 36762). During the public comment 

period, NMFS received 7 comments 

from individual members of the public, 

Fugro, EnerGeo Alliance and American 

Petroleum Institute, National Resources 

Defense Council, and Ocean 

Conservation Research. Six commenters 

(i.e., one commenter provided two 

separate comments) provided 

substantive comments addressing 

technical aspects or issues relating to 

the implementation of criteria. 

Some comments were similar to those 

received during the public comment 

periods for the 2016 Technical 

Guidance. For example, these similar 

comments addressed topics such as why 

NMFS does not consider TTS as injury, 

use of mean/medians, 

pseudoreplication, uncertainty, 

development of criteria for lowfrequency (LF) cetaceans, Tougaard et 

al. 2015, and Wright 2015. NMFS will 

not repeat our responses from 2016 here 

but instead refers readers to our 

previous Federal Register notification 

(81 FR 51694, August 4, 2016) that 

previously addressed these comment 

topics. 

2024 Updated Technical Guidance 

Scope 

Comment 1: One commenter stated 

that Sirenians should be included in the 

2024 Updated Technical Guidance. 

Response: The 2024 Updated 

Technical Guidance does not pertain to 

marine mammal species under the U.S. 

Fish and Wildlife Service’s jurisdiction 

(e.g., walrus, polar bears, manatees, 

dugongs, sea otters). Thus, Sirenians are 

not included in the main document. 

However, they are included in the 

Navy’s Technical Report, attached to the 

2024 Updated Technical Guidance as 

Appendix A. 

Peer Review Process 

Comment 2: One set of commenters 

stated that while the main sections of 

the 2024 Updated Technical Guidance 

was peer reviewed by experts, the 

Navy’s Technical Report does not seem 

to be. 

Response: The 2024 Updated 

Technical Guidance document, 

including the Navy’s Technical Report 

(Appendix A), completed all stages of 

the review process (i.e., the entire 

document underwent NMFS internal 

review, peer review, Federal agency 

preview, and public comment). 

Furthermore, during the peer review, 

federal agency preview, and public 

comment period, NMFS worked directly 

with the Navy to address some of the 

comments received. 

Marine Mammal Hearing 

Comment 3: To define a marine 

mammal hearing group’s generalized 

hearing range, one commenter asked 

whether the 65 dB level above the 

threshold of maximum hearing 

sensitivity was chosen arbitrarily (i.e., 

they asked for a reference that supports 

choosing a threshold specifically 5 dB 

wider than that in humans). 

Response: NMFS did not choose this 

level arbitrarily. We specifically chose 

the 65 dB threshold to be slightly wider 

than how the hearing range for humans 

is defined in order to encompass the 

general uncertainty of marine mammal 

hearing ranges, since we do not have 

hearing data for all species. 

Comment 4: One commenter’s letter 

stated that sperm whales are categorized 

as high-frequency (HF) cetaceans but 

produce lower frequency sounds and 

are expected to hear lower frequencies 

compared to smaller delphinids. The 

commenter pointed out that Southall et 

al. 2019 indicated that sperm whales, 

killer whales, and beaked whales may 

be separated from other HF cetaceans in 

the future (i.e., compose a midfrequency (MF) cetacean hearing group), 

but Appendix A (Finneran Technical 

Report) does not address this potential 

future hearing group. The comment also 

notes there is potential variation of 

phocid hearing that may necessitate 

splitting this hearing group in the 

future. In a related comment, another 

commenter questioned why killer whale 

hearing data were not used to define 

audiograms for a separate MF cetacean 

group. 

Response: While the potential to 

separate some marine mammal species 

into a separate MF cetacean hearing 

group is not directly mentioned in 

Appendix A (Finneran Technical 

Report), NMFS does address this in our 

main document. Specifically, table 1, 

footnote 1, says Southall et al. 2019 

indicates that as more data become 

available there may be separate hearing 

group designations for very lowfrequency cetaceans (blue, fin, right, and 

bowhead whales) and MF cetaceans 

(sperm, killer, and beaked whales). 

However, at this point, all baleen 

whales are part of the low-frequency 

(LF) cetacean hearing group, and sperm, 

killer, and beaked whales are part of the 

HF cetacean hearing group. 

Additionally, recent data indicate that 

as more data become available for 

Monachinae seals, separate hearing 

group designations may be appropriate 

for the two phocid subfamilies (Ruscher 

et al. 2021; Sills et al. 2021). NMFS 

concurs with the aforementioned 

studies that there are currently not 

enough data to further separate out MF 

cetaceans from HF cetaceans or further 

divide the phocid hearing group. 

Comment 5: One comment letter 

questioned why the LF cetacean 

generalized hearing range expanded by 

1 kHz, if there are no new data. 

Response: While there are no new 

data available for LF cetaceans 

specifically, the weighting function 

parameters slightly changed for all 

hearing groups as a result of 

maintaining consistency with other 

hearing groups. As a result, NMFS reexamined the generalized hearing range 

for all hearing groups. 

Comment 6: Numerous commenters 

inquired why auditory evoked potential 

(AEP) data are not being considered in 

deriving composite audiograms for 

various hearing groups and encouraged 

that all data be considered. Some 

commenters advocated for further 

research to focus on better integrating 

AEP data. 

Response: NMFS agrees that 

incorporating AEP data into composite 

audiograms would be preferred and 

would expand the number of species 

where hearing data are available. 

Nevertheless, there are some welldefined reasons this is not done. 

Behavioral techniques measure 

perception of sound by a receiver, while 

AEP methods measure only neural 

activity (Jewett and Williston 1971) (i.e., 

the two methodologies are not 

necessarily equivalent). Behavioral 

techniques, which are considered most 

representative (i.e., ‘‘gold standard’’ for 

measuring auditory sensitivity, 

consistently produce lower thresholds, 

which are indicative of greater 

sensitivity, than those obtained by AEPs 

(e.g., Szymanski et al. 1999; Yuen et al. 

2005; Houser and Finneran 2006). AEP 

data are considered if they are the only 

data available for a hearing group (e.g., 

LF cetaceans; See Response to next 

Comment). Currently, there are no 

established means for ‘‘correcting’’ AEP 

data so they are more comparable to 

behavioral data (Heffner and Heffner 

2003; Finneran 2015; Sisneros et al. 

2016; Erbe et al. 2016). NMFS is aware 

that the Navy’s Living Marine Resources 


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(LMR) Program is supporting a project 

entitled Standardizing Auditory Evoked 

Potential Hearing Thresholds with 

Behavioral Hearing Thresholds by 

Dorian Houser, National Marine 

Mammal Foundation, which may allow 

for the addition of AEP data to future 

versions of our Technical Guidance: 

https://exwc.navfac.navy.mil/Portals/ 

88/Documents/EXWC/Environmental_

Security/Living%20Marine%20

Resources/LMRFactSheet_Project47.pdf. 

NMFS also included this topic as a 

specific data gap in Appendix B to the 

2024 Updated Technical Guidance 

(‘‘Research Recommendations for 

Improved Criteria’’). 

Comment 7: Many commenters were 

interested in learning about recent AEP 

hearing measurements collected on 

minke whales by the National Marine 

Mammal Foundation. One commenter 

cautioned that the Balaenoptera (blue, 

fin, Rice’s, Bryde’s, minke, and sei 

whales) are just one genus of whale that 

use sounds in ways differently than 

Megaptera (humpback whales), 

Eschrichtius (gray whales), Balaena 

(bowhead whales), or Eubalaena (right 

whales) do. Similarly, another comment 

stated that NMFS should acknowledge 

that, given substantial differences 

among these LF cetacean species in 

their anatomy, sound production, and 

acoustic ecology, minke whales may not 

appropriately represent the hearing 

sensitivity of blue, fin, humpback, gray, 

and certain other baleen whales in the 

LF cetacean group; and that a more 

conservative approach to weighting in 

the very low frequencies may still be 

necessary. The commenter also 

remarked that NMFS should commit to 

a re-evaluation of LF cetacean group 

thresholds as soon as those data are 

published. 

Response: NMFS is aware that the 

National Marine Mammal Foundation 

successfully collected preliminary 

hearing data on two minke whales 

during their third field season (2023) in 

Norway. These data have implications 

for not only the generalized hearing 

range for LF cetaceans but also on their 

weighting function. However, at this 

time, no official results have been 

published. Furthermore, a fourth field 

season (2024) was recently completed, 

where more data were collected. Thus, 

it is premature for NMFS to propose any 

changes at this time. However, 

mysticete hearing data is identified as a 

special circumstance that could merit 

re-evaluating the acoustic criteria in the 

2024 Updated Technical Guidance, once 

the data from both field seasons are 

published. 

NMFS anticipates the publication of 

these AEP data from minke whales will 

help better inform the composite 

audiogram and associated weighting 

function for LF cetaceans. We agree that 

while having direct measurements of 

minke whale hearing would represent a 

significant milestone in better 

understanding mysticete hearing, these 

data will need to be considered 

carefully in the context of how they may 

or may not be appropriate to fill data 

gaps for other LF cetacean species. 

Comment 8: One commenter asserted 

that table A.3, which provides 

composite audiogram parameters, 

contains a number of errors. One error 

they purportedly identified is the use of 

hertz (Hz) instead of kHz (e.g., the F1

parameter for HF cetaceans is 9910 kHz 

and for Sirenians is 1680 kHz). Another 

example is the upper roll-off for the 

very-high frequency (VHF) cetaceans 

that begins below 100 kHz in Figure 

A.4, yet the value for the F2 parameter 

(132 kHz) in table A.3 fails to match this 

result. As a consequence, they assert, 

they were unable to assess NMFS’ use 

of DT values in extrapolating certain 

parameters across hearing groups. 

Response: Table A.3 is correct and 

does not contain any errors. This can be 

verified by calculating Eq. (3) (i.e., 

median threshold equation for 

composite audiogram) with the 

parameters from table A.3 and 

comparing the results to the composite 

audiograms. The F1 and F2 parameters 

in table A.3 are not roll-off frequencies, 

but instead are fitting parameters for use 

with Eq. (3) to best match the composite 

audiogram data. Because of the large 

number of fitting parameters, the values 

may not always make physical sense, 

especially for audiograms without a 

plateau region. This point is specifically 

made in the Finneran Technical Report 

(Appendix A, including the example 

cited by the reviewer) that the large 

number and possible high dependency 

of fitting parameters, in some cases the 

specific fitting parameter values may 

not make physical sense (e.g., HF group 

F1 = 9910 kHz), and the important point 

is how well the resulting curve fits the 

median threshold data. 

Comment 9: One commenter 

advocated that the F1 audiogram fitting 

parameter for LF cetaceans be changed 

from 412 Hz to 137 Hz. 

Response: NMFS disagrees that the F1

audiogram fitting parameter for LF 

cetaceans should be adjusted, since no 

new data have become available 

supporting this change. This parameter 

is the same as published in Southall et 

al. 2019, as well as what was in the 2018 

Revised Technical Guidance, and is 

appropriate based on our current 

understanding of LF cetacean hearing. 

Furthermore, when the new minke 

whale hearing data become available, it 

is likely that NMFS will begin the 

process of updating the acoustic criteria 

for LF cetaceans based on these data. 

Thus, the composite audiogram, 

thresholds, and weighting functions for 

this hearing group will all be reexamined and appropriate adjustments 

can be made. 

Weighting Functions 

Comment 10: A group of commenters 

requested that Appendix A (Finneran 

Technical Report) provide a detailed 

description of the methodology used to 

derive equations and criteria. On a few 

occasions, it is noted that mean values 

are calculated from data sets for 

deriving the weighting function, but the 

number of samples used to derive 

means or medians are not readily 

available. When available, this should 

be provided along with standard 

deviations. 

Response: Figures A14 through A17 

in Appendix A show the individual TTS 

onset values and the mean values used 

to fit the exposure functions. The 

number of samples and a sense of the 

variability can be determined from these 

plots. 

Comment 11: Several commenters had 

questions about the 2024 Updated 

Technical Guidance modifying the 

weighting function high-frequency 

exponent (b) from 2 to 5, which was 

done to fit better underwater otariid 

pinniped data. Many asked why this 

parameter was modified for all hearing 

groups and not just otariids. 

Response: This question was also 

asked during our Peer Review. In the 

2018 Technical Guidance (and Southall 

et al. 2019), the b parameter was the 

same for all hearing groups. Thus, the 

changes made to the 2024 Updated 

Technical Guidance are consistent 

keeping this parameter the same for all 

hearing groups. Increasing the b 

parameter from two to five was done to 

fit better the underwater otariid (OW) 

pinniped function without substantially 

affecting the other marine mammal 

hearing group fits. The decision to keep 

the same b parameter for all groups was 

made to try to reduce complexity where 

possible, and there are no data to 

currently suggest this parameter varies 

by marine mammal hearing group. 

Comment 12: A group of commenters 

asked for clarification on the R2 value 

for underwater phocid (PW) pinnipeds 

(i.e., ¥4.69) in table A.7 displaying 

weighting function parameters. 

Response: A similar question was also 

asked during our Peer Review. The 

negative R2 indicates the curve-fit does 

not follow the general trend in the data 

(i.e., the data would have fit better with 


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a flat line). This is a result of the 

assumption that the weighting function 

should be broader than the audiogram, 

thus F1 was decreased after fitting for 

the PW group to match the audiogram 

10-dB bandwidth. This prevents the 

weighting function from adjusting to 

best-fit the data points and causes the 

very low R2 value. 

Temporary Threshold Shifts 

Comment 13: A group of commenters 

stated that NMFS should clarify which 

TTS data in table 7 were collected using 

electrophysiological (AEP) methods vs. 

behavioral methods. They indicate that 

table 7 is misleading as it lists all the 

TTS studies available for integration, 

while only a small portion of these 

studies was used in the analysis. 

Response: NMFS agrees that this is 

important information to include and 

has updated table 7 to distinguish 

between which studies collected 

hearing measurements via behavioral 

methodology vs. AEPs. 

Comment 14: A group of commenters 

disagreed that impulsive sounds are 

more injurious than non-impulsive 

sounds. Specifically, their comment 

indicated that there are no direct or 

consistent data for marine mammals 

demonstrating that impulsive sounds 

are more injurious. They also indicated 

that marine mammals are able to selfmitigate, which might protect them from 

noise exposure. 

Response: While there are limited 

marine mammal TTS data associated 

with exposure to impulsive sound, there 

is a rich library of literature available for 

terrestrial mammals that indicates 

exposure to impulsive sounds more 

often leads 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). 

Additionally, inner ear anatomy is 

conserved among all mammals, 

including marine marine mammals 

(Grunstra et al. 2024). Thus, lessons 

learned from terrestrial mammals likely 

translate to marine mammals. 

Furthermore, the marine mammal TTS 

data currently available do support that 

TTS and AUD INJ onset thresholds are 

lower for impulsive sounds compared to 

non-impulsive sounds. 

Appendix B (Research 

Recommendations for Improved 

Criteria) in the 2024 Updated Technical 

Guidance acknowledges that 

odontocetes may have multiple means 

of reducing or ameliorating the effects of 

noise exposure. However, at this point, 

directly incorporating these 

mechanisms into our AUD INJ and TTS 

criteria and anticipating the likelihood 

of exposure ahead of an activity is 

difficult. More information on these 

mechanisms, especially associated with 

real-world exposure scenarios, would be 

useful. 

Comment 15: One commenter 

remarked that Southall et al. 2019 found 

an approximately +/¥6 dB difference in 

measured versus predicted TTS onset 

data. The commenter advocated there 

should be a similar measure of accuracy 

in Appendix A (Finneran Technical 

Report), but that the document provides 

no measure of natural variability or 

uncertainty, or any indication of 

predictability. Thus, they recommend 

that the agency implement a 6-dB 

reduction to its TTS and AUD INJ 

thresholds in line with the suggestions 

by Tougaard et al. 2015. 

Response: There are numerous figures 

showing TTS onset data and the 

relationship between the exposure 

functions and the TTS data. These 

graphs indicate the variability in the 

TTS data and the differences between 

the measurements of TTS onset and the 

predicted exposure functions. 

Furthermore, NMFS disagrees that a 6- 

dB reduction is necessary or justifiable 

(and despite Southall et al. 2019 

indicating variability in TTS data for 

VHF cetaceans, they did not alter their 

proposed TTS thresholds). 

Comment 16: A group of commenters 

noted that there are significant changes 

for HF cetaceans criteria compared to 

the 2018 Technical Guidance, based on 

data from Finneran et al. 2023, and 

indicated that these changes were not 

highlighted in the draft 2024 Updated 

Technical Guidance. The comment 

expressed concern that since numerous 

HF species travel in large groups, there 

is a potential that take will be 

overestimated, as the 2024 Updated 

Technical Guidance does not account 

for behavioral responses of the animals. 

They also noted that in Figure A.14 for 

2 kHz, it seems like the mean used for 

fitting value is much lower than the 

actual mean of the TTS onset values 

obtained by three studies (filled icons). 

Response: This change was 

highlighted in Section 1.3 of the draft 

2024 Updated Technical Guidance 

(Changes Associated with 2024 Updated 

Technical Guidance), specifically the 

fifth bullet: Lower TTS and AUD INJ 

thresholds ([cumulative sound exposure 

level metric] SEL24h metric) for HF 

cetaceans, below 10 kHz, based on new 

data (Finneran et al. 2023a). 

Furthermore, the behavioral response of 

marine mammals to anthropogenic 

sounds is outside the scope of the 2024 

Updated Technical Guidance. Finally, 

there are two TTS onset data points at 

2 kHz (brown triangles in Figure A.14). 

The mean value (large circle in Figure 

A.14, visually between the two data 

points) was used during curve-fitting. 

Comment 17: A group of commenters 

noted Appendix A (Navy’s Technical 

Report) indicates ‘‘For VHF, new data 

suggest substantially higher onset TTS 

SELs at frequencies above ∼10 kHz 

compared to the Phase 3 predictions, 

with high variability in the TTS onset 

data for harbor porpoises at 63 kHz (∼40 

dB difference in TTS onset for the two 

porpoises). Furthermore, the harbor 

porpoise behavioral TTS onset SELs are 

significantly higher than SELs resulting 

in large amounts (e.g., 23–45 dB) of AEP 

TTS in Yangtze finless porpoise (see 

Fig. A.8). Although some differences in 

AEP/behavioral TTS data are expected, 

these large differences indicate that 

caution is warranted in adopting the 

high-frequency behavioral TTS data at 

the present time. For this reason, the 

VHF behavioral TTS onset data at 

frequencies >10 kHz were not used 

during the exposure function fitting 

process.’’ They commented this is 

problematic as it deviates from the other 

species group and processes used 

throughout the document as behavioral 

methodology is preferred. 

Response: Numeric TTS onsets for the 

VHF cetaceans were derived using only 

behavioral data. For conditions where 

both behavioral and AEP data were 

available, the behavioral TTS data were 

used, because the relationship between 

AEP and behavioral TTS onsets is not 

clear. However, the AEP data cannot be 

completely ignored, and large 

differences between AEP and behavioral 

TTS onsets raise concerns. Because of 

the large difference in VHF cetacean 

behavioral TTS onset across individuals 

from the same study, and large 

differences between some of the 

behavioral and AEP data, the highest 

frequency VHF cetacean data were not 

used during the fitting process; only the 

lower frequency behavioral TTS data 

were used. This is consistent with the 

approach taken with other species 

groups, such as PW pinnipeds. 

Comment 18: A commenter noted the 

2024 Updated Technical Guidance 

generates notably higher TTS onset 

weighted exposure levels for harbor 

porpoise than the species-specific 

Tougaard et al. 2022 publication, even 

when accounting for different 

weightings. 

Response: Tougaard et al. 2022 

advocates examining harbor porpoise 

TTS data available since 2015 and calls 

for revisiting the synthesis culminating 

in Southall et al. 2019. NMFS’ 2024 

Updated Technical Guidance 

synthesizes all the same studies 

mentioned in Tougaard et al. 2022 (table 


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IV from that publication), including 

those since Southall et al. 2019. 

For impulsive sounds, compared to 

Southall et al. 2019 (which Tougaard et 

al. 2022 supports), the TTS SEL24h

thresholds in the 2024 Updated 

Technical Guidance are 4 dB higher. For 

non-impulsive sounds, compared to 

Southall et al. 2019 (which Tougaard et 

al. 2022 indicates updated data below 

10 kHz correspond well, with more 

differences above 10 kHz), the TTS 

SEL24h thresholds in the 2024 Updated 

Technical Guidance are 8 dB higher. 

However, it should be noted that the 

weighting function for VHF cetaceans 

has also shifted, making them more 

susceptible to noise-induced hearing 

loss below 10 kHz, where the majority 

of anthropogenic sound sources have 

their energy. Thus, both the thresholds 

and the weighting factors need to be 

considered in concert when evaluating 

the acoustic criteria for any marine 

mammal hearing group. 

Comment 19: A group of commenters 

noted that Appendix A (Finneran 

Technical Report) indicates that harbor 

seal TTS onset data below 2.5 kHz were 

excluded from the Phase 4 fitting 

process and asked how this data 

exclusion would affect potential 

applicants more concerned about 

Moanachinae vs Phocinae pinnipeds. 

Response: All phocids exposed in 

water are within the PW pinniped group 

and use the same criteria, therefore the 

exclusion affects Monachinae and 

Phocinae in the same way. 

Comment 20: A commenter 

questioned NMFS’ inclusion of a 132 dB 

data point in calculating the mean 

difference between TTS onset and the 

auditory threshold at f0. The commenter 

states that if 132 dB is not an outlier 

among the other cited values (116 dB, 

116 dB, and 118 dB), then they do not 

know what would count as one. More 

generally, the commenter states that a 

visual review of Figures A.14 to A.17 

indicates the presence of multiple 

apparent outliers, which collectively are 

likely to influence the fit of the 

exposure function. 

Response: In combining values or 

deriving central tendencies, the default 

approach was to use the mean. 

Identifying true outliers in the various 

datasets was difficult because the 

sample sizes were typically small, and 

in many cases, the underlying 

distributions were unknown. Even if 

individual species group distributions 

were Gaussian, it is probable that 

sampling from the different groups 

would result in a unique, non-Gaussian 

distribution, and thus a Gaussian 

distribution for purposes of statistically 

testing for outliers could not be 

assumed. Datasets were therefore 

considered on a case-by-case basis, 

taking into account not only the range 

of numeric values, but the specific 

circumstances under which the data 

were obtained. There were only four 

instances where changing from the 

mean to the median was warranted: 

(1) Estimating hearing thresholds for 

each group to create the composite 

audiograms. Here, the number of 

samples was relatively large, and there 

could be large fluctuations in thresholds 

across studies at any given frequency. 

Using the median value was the 

simplest way to estimate the composite 

audiogram, while reducing the 

influence of any outliers; 

(2) Calculating the parameter DT1. 

DT1 and DT2 (i.e., the amounts that the 

composite audiogram exceeded the 

minimum hearing threshold at the 

weighting function frequency 

parameters f1 and f2, respectively). 

Values of DT1 and DT2 were calculated 

for HF cetaceans, VHF cetaceans, OW 

pinnipeds, and PW pinnipeds. For the 

other species groups, the mean or 

median of these values was used to 

estimate f1 and f2 from their composite 

audiogram. DT1 values for groups HF 

cetaceans, VHF cetaceans, OW 

pinnipeds, and PW pinnipeds were 

36.8, 11.5, 3.9, 6.5 dB, with mean = 14.7 

and median = 9. The difference between 

36.8 and its nearest neighbor was 25.3, 

which was almost 10x larger than the 

smallest value. For this reason, the 

median was used rather than the mean. 

In contrast, for DT2, values were 38.6, 

22.7, 38.9, 39.4, with mean = 34.9 and 

median = 38.8. Here the mean was used 

rather than the median, despite a 

difference of 15.9 between 22.7 and its 

nearest neighbor; 

(3) Cumulative weighted impulse 

SEL-based TTS onset values for HF 

cetaceans. There were impulsive TTS 

onset data from four individuals in the 

HF cetacean group: 177, 178, 175, 188 

dB SEL (mean = 180, median = 178). 

The associated differences between 

steady-state and impulsive TTS onsets 

(Cs-Ci) were 4, 3, 6, and ¥7 dB (mean 

= 1.5, median = 3.5). Here, the median 

was used over concerns that the dolphin 

subject with the 188 dB onset may not 

be representative, based on his higher 

TTS onset and inverted relationship 

between steady-state and impulsive TTS 

onset compared to the other HF 

cetacean individuals. The inverted 

relationship between the steady-state 

and impulsive TTS onset values meant 

that including this subject would have 

made the impulsive TTS onsets more 

similar to steady-state onsets, which 

does not match our current 

understanding of TTS (impulsive noise 

is typically more hazardous); and 

(4) Estimating the audiogram function 

parameter B for mysticetes. To estimate 

B for LF cetaceans, the median of the B 

values from the composite audiograms 

for the other in-water species groups 

was used. The individual values were: 

1.66, 24.5, 2.5, 0.786, and 1.79 (mean = 

6.25, median = 1.79). The range of 

values here is extreme, with the largest 

value >31x the smallest and almost 10x 

larger than its nearest neighbor. For this 

reason, the median was used. 

In terms of the specific comments, the 

differences between hearing threshold 

and TTS onset at f0 (the frequency of 

best sensitivity) were 132, 118, 116, and 

118 dB for HF cetaceans, VHF 

cetaceans, OW pinnipeds, and PW 

pinnipeds (mean = 121, median = 118). 

The range of values and differences 

between neighbors is more similar to 

those for DT2, where the mean was 

used, compared to DT1, where the 

median was used. For this reason, the 

mean was used. Figures A.14 through 

A.17 show all available TTS data, 

regardless of the amount of TTS. These 

graphs therefore cannot be used to 

assess whether a data point is an 

‘‘outlier’’ or not. 

Comment 21: With the inclusion of 

in-air pinniped acoustic criteria in the 

2024 Updated Technical Guidance, a 

group of commenters asked how NMFS 

plans on managing pinnipeds entering 

and leaving the water (e.g., Does NMFS 

anticipate having animals 100 percent 

in air and/or 100 percent underwater 

during exposure calculations?). 

Response: The inclusion of the in-air 

pinniped criteria in our 2024 Updated 

Technical Guidance was to promote 

consistency with other documents that 

previously have included in-air criteria, 

such as Southall et al. 2007 and 

Southall et al. 2019. Their inclusion 

does not necessitate anything changing 

in terms of how previous analyses have 

been completed for pinnipeds. 

Recovery and Effective Quiet 

Comment 22: A group of commenters 

requested that recovery should be 

considered within the 2024 Updated 

Technical Guidance. They 

recommended that NMFS consider 

reviewing terrestrial data and comparing 

it to the cited two references (Finneran 

et al. 2010a and Finneran and Schlundt 

2013) that presented a model to 

approximate recovery in bottlenose 

dolphins. They stated that expansion to 

other odontocetes seems very reasonable 

and more supportable compared to 

some of the other decisions made in the 

2024 Updated Technical Guidance. 


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Response: NMFS acknowledges that 

after sound exposure ceases or between 

successive sound exposures, the 

potential for recovery from hearing loss 

exists, with AUD INJ resulting in 

incomplete recovery and TTS resulting 

in complete recovery. Nevertheless, 

predicting recovery from sound 

exposure can be complicated. Currently, 

recovery in wild marine mammals 

cannot be accurately quantified. As 

mentioned in the Comment, Finneran et 

al. 2010a and Finneran and Schlundt 

2013 proposed a model that 

approximates recovery in bottlenose 

dolphins exposed to tones. However, 

the applicability of this model to other 

species, other sound sources, and other 

exposure conditions has yet to be 

determined. As more data become 

available for a broader array of species 

and sound sources, the incorporation of 

recovery can be considered for future 

iterations of the Technical Guidance. 

Comment 23: A group of commenters 

indicated that it was unclear why 

effective quiet (i.e., the maximum sound 

pressure level that will fail to produce 

any significant threshold shift in 

hearing despite duration of exposure 

and amount of accumulation) was not 

integrated in the 2024 Updated 

Technical Guidance. 

Response: While NMFS agrees that 

effective quiet is an important 

consideration, there are limited data 

available to define effective quiet for 

marine mammals. As more data become 

available (identified as a data gap in 

Appendix B, Research 

Recommendations for Improved 

Criteria), they will be useful for a better 

understanding of appropriate 

accumulation periods for the weighted 

SEL24h metric and noise-induced 

hearing loss, as well as whether there is 

potential for low-level (e.g., Copping et 

al. 2014; Schuster et al. 2015; Copping 

and Hemery 2020; Tougaard et al. 2020; 

Sto ̈ber and Thomsen 2021; Kulkarni and 

Edwards 2022), continuously operating 

sources (e.g., alternative energy tidal, 

wave, or wind turbines) to result in 

noise-induced hearing loss or not (i.e., 

below effective quiet). 

Auditory Injury 

Comment 24: One commenter 

recommended that NMFS move away 

from establishing AUD INJ/TTS criteria 

and instead consider an ‘‘Auditory 

Damage Index,’’ which could include 

considerations of long-term hearing 

degeneration because of acute or 

chronic noise exposure and better allow 

for the assessment of a continuum of 

effects. 

Response: NMFS agrees that noiseinduced hearing loss follows a 

continuum (Houser 2021). However, to 

best quantify this continuum in a 

regulatory context, NMFS has 

established an onset criteria for both 

TTS and AUD INJ. 

Comment 25: A commenter noted that 

the definition of AUD INJ includes but 

is not limited to PTS. They commented 

that AUD INJ threshold levels in many 

cases are higher than previous PTS 

levels in the 2018 Technical Guidance 

and asked if it is possible to determine 

levels that will result in the ‘‘loss of 

cochlear neuron synapses or auditory 

neuropathy,’’ and if NMFS is expanding 

the range of auditory damage to be 

considered, whether threshold levels in 

all cases should be reduced. 

Another commenter had a similar 

comment, where they were concerned 

that this criterion is not conservative for 

purposes of representing directlyinduced AUD INJ. They indicated that 

40 dB TTS cannot continue to represent 

AUD INJ once indirect or accumulated 

injury is added. Conceptually, if 

directly-induced PTS alone equates to 

40 dB TTS, then the two processes 

together must equate to less than 40 dB 

TTS. Thus, levels of noise exposure that 

can result in auditory neuropathy are 

capable of inducing PTS or AUD INJ. 

Response: NMFS disagrees that based 

on our inclusion of AUD INJ, our 

thresholds should be adjusted or 

reduced. As stated in the 2024 Updated 

Technical Guidance, in situations where 

destruction of auditory tissue has 

occurred in terrestrial mammals, 

threshold shifts were 30 to 50 dB 

measured 24 hours after the exposure. 

There is no evidence that an exposure 

resulting in <40 dB TTS measured a few 

minutes after exposure can produce 

AUD INJ. Therefore, an exposure 

producing 40 dB of TTS measured a few 

minutes after exposure is used as an 

upper limit of a threshold shift to 

prevent AUD INJ (i.e., it is assumed that 

only exposures beyond those capable of 

causing 40 dB of TTS have the potential 

to result in AUD INJ, which may or may 

not result in PTS). 

Comment 26: A group of commenters 

requested clarification regarding use of 

the phrase a ‘‘few minutes’’ in Appendix 

A (Finneran Technical Report) where it 

talks about 40 dB of TTS, measured a 

few minutes after exposure, being used 

as a conservative estimate for the onset 

of PTS. The commenters indicated that 

this phrase was vague and should be 

clarified. 

Response: In this context, a ‘‘few 

minutes’’ means the range of time over 

which marine mammal TTS initial postexposure thresholds are obtained, 

typically 2 to 4 minutes. 

Metrics 

Comment 27: One commenter noted 

that 2024 Updated Technical Guidance 

indicates that SEL24h metric is not 

intended to estimate impact of noise 

exposure ‘‘over various spatial and 

temporal scales.’’ The comment asked if 

this means the SEL24h metric is not 

intended for accumulating exposures 

that occur at considerably different 

locations and times; and the reason for 

such a limitation if that is the case. The 

commenter asked if auditory recovery 

plays a role in the explanation. 

Response: As the 2024 Updated 

Technical Guidance indicates, current 

data available for deriving criteria using 

the SEL24h metric are based on exposure 

to only a single source and therefore 

may not be appropriate for situations 

where exposure to multiple sources is 

occurring. As more data become 

available, the use of this metric can be 

re-evaluated for application of exposure 

from multiple activities occurring in 

space and time. 

While auditory recovery is an 

important consideration, predicting 

recovery from sound exposure can be 

complicated. Currently, recovery in 

wild marine mammals cannot be 

accurately quantified. For the 2024 

Updated Technical Guidance criteria, 

for intermittent, repeated exposures 

within a 24-hour period, NMFS assumes 

there is no recovery between subsequent 

exposures, although auditory recovery 

has been demonstrated in terrestrial 

mammals (Clark et al. 1987; Ward 1991) 

and more recently in a marine mammal 

studies (Finneran et al. 2010b; Kastelein 

et al. 2014a; Kastelein et al. 2015b). As 

more data become available, this topic 

can be further evaluated and potentially 

considered in future versions of this 

guidance. 

Comment 28: A commenter 

recommended the incorporation and use 

of the kurtosis metric in the 2024 

Updated Technical Guidance. 

Response: NMFS agrees that kurtosis 

(i.e., a statistical quantity that represents 

the impulsiveness or ‘‘peakedness’’ of 

the event), can be a useful consideration 

for distinguishing between impulsive 

and non-impulsive sounds. However, 

there are questions of how to apply this 

metric to marine mammal acoustic 

criteria (Von Benda-Beckmann et al. 

2022). NMFS has identified kurtosis as 

a topic for further research in the 2024 

Updated Technical Guidance (Appendix 

B: Research Recommendations for 

Improved Criteria). While kurtosis may 

be useful in helping determine when 

impulsive vs. non-impulsive criteria 

might be applicable for a particular 

sound source in a specific situation, it 


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does not necessitate any changes to the 

criteria in the 2024 Updated Technical 

Guidance (i.e., kurtosis affects 

implementation of the acoustic criteria, 

not the criteria themselves). 

Comment 29: A group of commenters 

noted that for VHF cetaceans, there is 

one study (Kastelein et al. 2017c) where 

a higher peak sound pressure level (PK 

SPL) (199 dB) did not trigger TTS 

(maximum threshold shift of 3 to 5 dB), 

but Lucke et al. 2009 obtained 

significant TTS with a lower level PK 

SPL (195 dB) using AEP measurements. 

The commenters state these 

contradicting results highlight that PK 

SPL is currently not a robust and good 

predictor of TTS, and suggest that 

NMFS provide stronger reasoning on the 

choice of Lucke et al. 2009, while 

Kastelein et al. 2017c used behavioral 

methods (preferred method in Acoustic 

Guidance and Appendix A, Navy’s 

Technical Report). 

Response: NMFS acknowledges there 

are limited marine mammal data 

available for impulsive sounds reporting 

the PK SPL metric. However, we 

disagree that PK SPL is not a good 

predictor of TTS and believe it has 

inherent value in establishing marine 

mammal AUD INJ and TTS criteria. As 

stated in the 2024 Updated Technical 

Guidance, sound exposure containing 

transient components (e.g., short 

duration and high amplitude; impulsive 

sounds) can create a greater risk of 

causing direct mechanical fatigue to the 

inner ear (as opposed to strictly 

metabolic) compared to sounds that are 

strictly non-impulsive (Henderson and 

Hamernik 1986; Levine et al. 1998; 

Henderson et al. 2008). Often the risk of 

damage from these transient 

components does not depend on the 

duration of exposure. Thus, weighted 

SEL24h is not an appropriate metric to 

capture all the effects of impulsive 

sounds, which is why instantaneous PK 

SPL has also been chosen as part of 

NMFS’s dual metric criteria for 

impulsive sounds. Of note, human noise 

standards recognize and provide 

separate criteria for impulsive sound 

sources using the PK SPL metric 

(Occupational Safety and Health 

Administration 29 CFR 1910.95; Starck 

et al. 2003). 

As indicated in the document 

(Appendix A, Navy’s Technical Report), 

PK SPL thresholds for TTS were based 

on TTS data from single impulsive 

sound exposures that produced 6 dB or 

more TTS for the HF and VHF cetaceans 

(the only groups for which data are 

available). The PK SPL thresholds from 

these data were 224 and 196 dB, for HF 

and VHF cetaceans, respectively (table 

A.5, Finneran et al. 2002; Lucke et al. 

2009). The choice of relying on Lucke et 

al. 2009, even though it relies on AEP 

data, is due to the limited nature of the 

impulse TTS data for marine mammals 

and the likelihood that the VHF 

cetaceans are more susceptible than the 

HF cetaceans (i.e., use of the HF 

cetacean value is not appropriate). 

Based on the limited 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. Finally, 

Kastelein et al. 2017c is not used 

because it did not meet our definition of 

TTS as requiring a threshold shift of at 

least 6 dB. 

Future Updates to Technical Guidance 

Comment 30: A group of commenters 

stated it is unclear how/when NMFS 

will decide the appropriate timeline to 

next update the Technical Guidance. 

They also questioned how NMFS will 

integrate future data in future iterations 

and whether an update would require 

another Navy Technical Report or 

Southall et al. publication. 

Response: The 2024 Updated 

Technical Guidance provides a 

procedure and timeline for future 

updates in Section 3.1., where it 

indicates that NMFS will continue to 

monitor and evaluate new data as they 

become available and periodically 

convene staff from our various offices, 

regions, and science centers to revise 

the Updated Technical Guidance as 

appropriate (anticipating updates to 

occur on a three to five year cycle). A 

new Navy Technical Report and/or 

Southall et al. publication would be 

considered if either becomes available. 

Finally, as mentioned in an earlier 

response, NMFS is aware that the 

National Marine Mammal Foundation 

successfully collected preliminary 

hearing data on 2 minke whales during 

their third field season (2023) in 

Norway. However, at this time, no 

official results have been published. 

Furthermore, a fourth field season 

(2024) was recently completed, where 

more data were collected. Thus, it is 

premature for NMFS to propose any 

changes at this time. However, 

mysticete hearing data is identified as a 

special circumstance that could merit 

re-evaluating the acoustic criteria in the 

2024 Updated Technical Guidance, once 

the data from both field seasons are 

published. 

Miscellaneous Issues 

Comment 31: A group of commenters 

stated that the absence of consideration 

of ambient noise in measurements 

targeted at measuring a single source 

can be problematic, as certain 

environments have already elevated 

ambient noise levels even without the 

introduction of any specific source or 

activity. NMFS listed ‘‘Multiple 

sources’’ as a research priority in 

Appendix B (Research 

Recommendations for Improved 

Criteria), and while the commenters 

agree that information on multiple 

sources might be important to better 

characterize how the acoustic 

environment of animals might change, it 

is also critical to recognize the 

importance of ambient noise, 

particularly if NMFS recommends 

applicants consider recording 

broadband measurements. 

Response: NMFS agrees that 

characterizing the existing soundscape 

is an important consideration and has 

added it to the Appendix B (Research 

Recommendations for Improved 

Criteria) as suggested. 

Comment 32: Several commenters 

inquired about the status of NMFS 

updating behavioral disturbance criteria 

for marine mammals. 

Response: Behavioral disturbance 

criteria are outside the scope of the 2024 

Updated Technical guidance. However, 

NMFS is currently in the process of 

developing draft marine mammal 

behavioral disturbance criteria. To date, 

we have completed a NMFS internal 

review and have started the peer review 

via the Center for Independent Experts 

(July 2024). For more information on 

how this review is progressing, please 

see: https://www.noaa.gov/informationtechnology/national-marine-fisheriesservices-development-of-recommendedbehavioral-disturbance-criteria-for. 

Dated: October 21, 2024. 

Kimberly Damon-Randall, 

Director, Office of Protected Resources, 

National Marine Fisheries Service. 

[FR Doc. 2024–24748 Filed 10–23–24; 8:45 am] 

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