[Federal Register Volume 89, Number 206 (Thursday, October 24, 2024)]
[Notices]
[Pages 84872-84880]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2024-24748]
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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.
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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/marine-mammal-acoustic-technical-guidance.
FOR FURTHER INFORMATION CONTACT: Amy R. Scholik-Schlomer, Office of
Protected Resources, 301-427-8449, [email protected].
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-to-20162018-technical-guidance-for-assessing-effects-of-anthropogenic-sound-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-technical-guidance. 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/NOAA-NMFS-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
[[Page 84873]]
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-technical-guidance).
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 non-exhaustive 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/
[[Page 84874]]
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 Sec. 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 Sec. 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 shut-down
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.
[[Page 84875]]
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 low-frequency (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 mid-
frequency (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 low-frequency
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 re-examined 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 well-
defined 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
[[Page 84876]]
(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%20Resources/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 [Delta]T 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 re-examined 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
[[Page 84877]]
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 self-mitigate,
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
[[Page 84878]]
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.
[[Page 84879]]
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; St[ouml]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 noise-induced 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
directly-induced 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 post-exposure 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
[[Page 84880]]
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/information-technology/national-marine-fisheries-services-development-of-recommended-behavioral-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]
BILLING CODE 3510-22-P