Technical Guidance for Assessing the Effects of Anthropogenic Sound on Marine Mammal Hearing-Underwater Acoustic Thresholds for Onset of Permanent and Temporary Threshold Shifts, 51693-51724 [2016-18462]

Agencies

• DEPARTMENT OF COMMERCE
• National Oceanic and Atmospheric Administration

[Federal Register Volume 81, Number 150 (Thursday, August 4, 2016)]
[Notices]
[Pages 51693-51724]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2016-18462]



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Vol. 81

Thursday,

No. 150

August 4, 2016

Part IV





Department of Commerce





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National Oceanic and Atmospheric Administration





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

Federal Register / Vol. 81 , No. 150 / Thursday, August 4, 2016 / 
Notices

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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

RIN 0648-XC969


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

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 its final Technical Guidance for Assessing the Effects 
of Anthropogenic Sound on Marine Mammal Hearing--Underwater Acoustic 
Thresholds for Onset of Permanent and Temporary Threshold Shifts 
(Technical Guidance or Guidance) that provides updated received levels, 
or acoustic thresholds, above which individual marine mammals under 
NMFS' jurisdiction are predicted to experience changes in their hearing 
sensitivity (either temporary or permanent) for all underwater 
anthropogenic sound sources.

ADDRESSES: The Technical Guidance is available in electronic form via 
the Internet at https://www.nmfs.noaa.gov/pr/acoustics/.

FOR FURTHER INFORMATION CONTACT: Amy R. Scholik-Schlomer, Office of 
Protected Resources, 301-427-8449, Amy.Scholik@noaa.gov.

SUPPLEMENTARY INFORMATION: The National Marine Fisheries Service in 
consultation with the National Ocean Service has developed Technical 
Guidance to help assess the effects of underwater anthropogenic sound 
on marine mammal species under NMFS' jurisdiction. Specifically, the 
Guidance identifies the received levels, or acoustic thresholds, above 
which individual marine mammals are predicted to experience changes in 
their hearing sensitivity (either temporary or permanent) for all 
underwater anthropogenic sound sources. NMFS compiled, interpreted, and 
synthesized scientific literature to produce updated acoustic 
thresholds for the onset of both temporary (TTS) and permanent 
threshold shifts (PTS). This is the first time NMFS has presented this 
information in a single, comprehensive document. This Technical 
Guidance is intended for use by NMFS analysts and managers and other 
relevant user groups and stakeholders, including other federal 
agencies, when seeking to determine whether and how their activities 
are expected to result in hearing impacts to marine mammals via 
acoustic exposure.
    The main body of the document contains NMFS' updated acoustic 
thresholds for onset of PTS for marine mammals exposed to underwater 
sound and NMFS' plan for periodically updating acoustic thresholds. 
Other information such as details on the development marine mammal 
auditory weighting functions and acoustic thresholds, research 
recommendations, alternative methodology (formerly referred to as a 
User Guide), the peer review and public comment process, and a glossary 
of acoustic terms can be found in the Technical Guidance appendices.
    These thresholds update those currently in use by NMFS. Updates 
include a protocol for deriving PTS and TTS onset levels for impulsive 
(e.g., airguns, impact pile drivers) and non-impulsive (e.g., tactical 
sonar, vibratory pile drivers) sound sources and the formation of 
marine mammal hearing groups (low- (LF), mid- (MF), and high-frequency 
(HF) cetaceans and otariid (OW) and phocid (PW) pinnipeds in water) and 
associated auditory weighting functions. Acoustic thresholds are 
presented using the dual metrics of cumulative sound exposure level 
(SELcum) and peak sound pressure level (PK) for impulsive 
sounds and the SELcum metric for non-impulsive sounds. While 
the updated acoustic thresholds are more complex than what has been in 
use by NMFS and regulated entities, they more accurately reflect the 
current state of scientific knowledge regarding the characteristics of 
sound that have the potential to impact marine mammal hearing 
sensitivity. Given the specific nature of these updates, it is not 
possible to generally or directly compare the updated acoustic 
thresholds presented in this document with the thresholds they will 
replace because outcomes will depend on project-specific 
specifications.
    Although NMFS has updated the acoustic thresholds, and these 
changes may necessitate new methodologies for calculating impacts, the 
application of the thresholds in the regulatory context of applicable 
statutes (Marine Mammal Protection Act (MMPA), Endangered Species Act 
(ESA), and National Marine Sanctuaries Act (NMSA)) remains consistent 
with current NOAA practice (see Regulatory Context in this Federal 
Register Notice). It is important to emphasize that these updated 
acoustic thresholds do not represent the entirety of an impact 
assessment, but rather serve as one tool (in addition to behavioral 
impact thresholds, auditory masking assessments, evaluations to help 
understand the ultimate effects of any particular type of impact on an 
individual's fitness, population assessments, etc.), to help evaluate 
the effects of a proposed action.
    NMFS recognizes that action proponents may have varying abilities 
to model and estimate exposure and that the Technical Guidance may be 
more complex than some action proponents are able to incorporate. Thus, 
NMFS has provided alternative methodology and an associated User 
Spreadsheet to aid action proponents with SELcum thresholds 
and marine mammal auditory weighting functions (https://www.nmfs.noaa.gov/pr/acoustics/).
    The Technical Guidance is classified as a Highly Influential 
Scientific Assessment (HISA) by the Office of Management and Budget. As 
such, three independent peer reviews were undertaken, at three 
different stages of the development of the Technical Guidance, 
including a follow-up to one of the peer reviews, prior to broad public 
dissemination by the Federal Government. Details of each peer review 
can be found within the Technical Guidance (Appendix C) and at the 
following Web site: https://www.nmfs.noaa.gov/pr/acoustics/. NMFS 
acknowledges and thanks the Marine Mammal Commission (Commission) and 
the Acoustical Society of America's Underwater Technical Council for 
nominating peer reviewers and thanks the peer reviewers for their time 
and expertise in reviewing this document.
    In additional to three independent peer reviews, the Technical 
Guidance was the subject of three public comment periods. NMFS 
evaluated all substantive comments made during each public comment 
period to determine their relevance to the Technical Guidance as it was 
revised. Public comments made on aspects of the Technical Guidance that 
are no longer relevant have not been included here. Substantive and 
relevant comments and NMFS' responses are included below (see Comments 
and Responses).
    The Technical Guidance does not create or confer any rights for or 
on any person, or operate to bind the public. An alternative approach 
that has undergone independent peer review may be proposed (by federal 
agencies or prospective action proponents) and used if case-specific 
information/data indicate that the alternative approach is likely to 
produce a more accurate

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portrayal of take for the project being evaluated, if NOAA determines 
the approach satisfies the requirements of the applicable statutes and 
regulations.

Transitioning to the Technical Guidance

    NMFS considers the updated thresholds and associated weighting 
functions in the Technical Guidance to be the best available 
information for assessing whether exposure to specific activities is 
likely to result in changes in marine mammal hearing sensitivity 
(temporary or permanent). Prospective applicants for incidental take 
authorizations under the MMPA and federal agencies seeking ESA section 
7 consultations that have not yet started their acoustic analyses 
should begin using the new Technical Guidance immediately. At the same 
time, we recognize that for some proposed actions, analyses may have 
already substantially progressed using the existing thresholds 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 Technical Guidance to 
satisfy the applicable requirements. A non-exhaustive list of factors 
that could affect the extent to which the Technical Guidance will be 
considered for an action include: The relative degree to which the 
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 (ITA) 
and all requests for ESA section 7 consultations involving noise that 
may affect marine mammals will include full consideration of the 
Technical Guidance.

National Environmental Policy Act (NEPA)

    In 2005, NMFS published a Federal Register Notice of Public Scoping 
and Intent to Prepare an EIS for a similar action (70 FR 1871, January 
11, 2005). The nature of the Guidance has evolved significantly since 
then. After evaluating the contents of the Technical Guidance and the 
standards for a categorical exclusion under NAO 216-6, sec. 6.03c.3(i), 
we have determined the Technical Guidance is categorically excluded 
from further NEPA review.
    NAO 216-6, sec. 6.03c.3(i), provides that a categorical exclusion 
is appropriate for ``policy directives, regulations, and guidelines of 
an administrative, technical, or procedural nature, or the 
environmental effects of which are too broad, speculative or 
conjectural to lend themselves to meaningful analysis and will be 
subject later to the NEPA process, either collectively or case by 
case.''
    Although changes to the PTS and TTS thresholds will likely change 
the take estimates for at least some portion of activities, any 
environmental effects of the draft guidance alone, without reference to 
a specific activity, are too speculative or conjectural to lend 
themselves to meaningful analysis at this stage. Effects analyses under 
the MMPA, ESA, and NMSA (and appropriate mitigation and monitoring) are 
activity-specific exercises that cannot be conducted absent some level 
of specificity regarding the nature of the proposed activity, the 
general location, and the time and duration. Moreover, direct 
comparisons cannot be made between the thresholds currently used and 
the updated thresholds, due to the different metrics and taxa-specific 
frequency weighting used in the new thresholds.
    Any environmental effects from application of the updated PTS and 
TTS thresholds will flow from future actions that are the subject of 
ITAs under the MMPA and related consultations under the ESA or NMSA. 
The nature and magnitude of such effects will depend on the specific 
actions themselves, each of which would be subject to the NEPA process.
    Because any effects from the Technical Guidance are speculative and 
conjectural, NOAA has determined it cannot meaningfully analyze 
potential effects in the manner contemplated by NEPA, which is to 
inform agency decisions about the effects of an action (and reasonable 
alternatives) on the environment. Any changes in future effects 
analyses resulting from the Guidance will be part of the NEPA and other 
statutorily-required analyses conducted for specific actions in the 
future.
    Finally, the proposed action does not trigger any of the exceptions 
for categorical exclusions described in section 5.05c of NAO 216-6. It 
does not involve a geographic area with unique characteristics, is not 
a subject of public controversy due to potential environmental 
consequences, have uncertain environmental impacts or unique or unknown 
risks, establish a precedent or decision in principle about future 
proposals, result in cumulatively significant impacts, or have any 
adverse effects upon endangered or threatened species or their 
habitats.

Regulatory Context

    NMFS uses acoustic thresholds to help quantify ``take'' and as part 
of more comprehensive effects analyses under several statutes. The 
Technical Guidance's updated acoustic thresholds do not represent the 
entirety of the comprehensive effects analysis, but rather serve as one 
tool among others (e.g., behavioral impact thresholds, auditory masking 
assessments, evaluations to help understand the ultimate effects of any 
particular type of impact on an individual's fitness, population 
assessments, etc.) to help evaluate the effects of a proposed action 
and make findings required by NOAA's various statutes.
    Under current agency practice, NMFS considers the onset of PTS, 
which is an 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 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. The broad definition 
of ``injury'' under the NMSA regulations includes both PTS and TTS (as 
well as other adverse changes in physical or behavioral characteristics 
that are not addressed in the Technical Guidance).

Marine Mammal Protection Act

    The MMPA prohibits the take of marine mammals, with certain 
exceptions, one of which is the issuance of 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

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required to authorize the incidental taking of marine mammals if it 
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 thresholds are particularly relevant to the 
following two of the fourteen 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/mortality) and the method of 
incidental taking;
     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).

National Marine Sanctuaries Act

    Section 304(d) of the NMSA requires federal agencies whose actions 
are likely to destroy, cause the loss of, or injure a sanctuary 
resource to consult with the Office of National Marine Sanctuaries 
(ONMS) before taking the action. See 16 U.S.C. 1434(d)(1). The NMSA 
defines sanctuary resource as ``any living or nonliving resource of a 
national marine sanctuary that contributes to the conservation, 
recreational, ecological, historical, educational, cultural, 
archeological, scientific, or aesthetic value of the sanctuary.''16 
U.S.C. 1432(8). Through the sanctuary consultation process, ONMS may 
recommend reasonable and prudent alternatives that will protect 
sanctuary resources. Recommended alternatives may include alternative 
locations, timing, and/or methods for conducting the proposed action. 
See id.at Sec.  1434(d)(2). Monitoring may also be recommended to 
better characterize impacts to sanctuary resources or accompany 
mitigation.
    The term ``injure'' is defined in the ONMS implementing regulations 
as to ``change adversely, either in the short or long term, a chemical, 
biological or physical attribute of, or the viability of.'' 15 CFR 
922.3.
    In support of the analysis necessary to conduct the consultation, 
the NMSA requires that any federal agency proposing an action that may 
injure a sanctuary resource provide ONMS with a written statement 
(``sanctuary resource statement'') describing the action and its 
potential effects on sanctuary resources. See 16 U.S.C. 1434(d)(1)(B).

Application of Acoustic Thresholds for Permanent Threshold Shift

    The acoustic thresholds for PTS 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

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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, ESA, and NMSA as 
described above.
    NMFS will use the same PTS acoustic thresholds in the 
identification and quantification of MMPA Level A harassment for both 
military readiness and non-military readiness activities. Because the 
acoustic thresholds for PTS predict the onset of PTS, 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 PTS acoustic thresholds will be 
treated as 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, as well as ``likely to injure'' or ``may affect'' 
determinations under the NMSA. Last, the PTS acoustic thresholds may be 
used to inform the development of mitigation and monitoring measures 
(such as shut-down zones) pursuant to the MMPA, ESA, or NMSA.
    When initiating any of the MMPA, ESA, or NMSA processes described 
above, agencies and other action proponents should utilize the PTS 
acoustic thresholds, in combination with activity-specific information, 
to predict whether, and if so how many, instances of PTS are expected 
to occur.

Application of Acoustic Thresholds 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) 
indicates that although PTS 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. Accordingly, TTS has been considered 
take by Level B harassment under the MMPA and harassment under the ESA, 
which will be the subject of future guidance. However, TTS is 
considered injury under the broad definition of the term ``injury'' in 
NMSA regulations (along with PTS and behavioral impacts). For now, NMFS 
will continue the practice of requiring applicants to estimate take by 
TTS for explosive sources.
    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 will be developing updated acoustic thresholds 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 not involving instantaneous 
explosives (see exception below for underwater explosives). In the 
meantime, action proponents not using instantaneous explosives do not 
need to quantify estimates of TTS separately from their overall 
behavioral harassment take calculations. For now, the TTS acoustic 
thresholds presented in the Technical Guidance will be considered as 
part of the larger comprehensive effects analyses under the MMPA and 
the ESA.
    With respect to instantaneous explosives (as distinguished from 
repeated explosives such as gunnery exercises), NMFS already requires 
quantification of TTS estimates because an instantaneous explosive will 
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 updated TTS thresholds for explosives.
    NMFS is aware of studies by Kujawa and Liberman (2009) and Lin et 
al. (2011), which found that despite completely reversible TS that 
leave cochlear sensory cells intact, large (but temporary) TS could 
cause synaptic level changes and delayed cochlear nerve degeneration in 
mice and guinea pigs. However, the large TS (i.e., maximum 40 decibel 
dB) that led to the synaptic changes shown in these studies are in the 
range of the large shifts used by Southall et al. (2007) and in the 
Technical Guidance to define PTS onset (i.e., 40 dB). It is unknown 
whether smaller levels of TTS would lead to similar changes or the 
long-term implications of irreversible neural degeneration. The effects 
of sound exposure on the nervous system are complex, and this will be 
re-examined as more data become available.
    The occurrence of, 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 well as ``likely to injure'' or ``may affect'' 
determinations under the NMSA. As with PTS, TTS acoustic thresholds 
also may be used to inform the development of mitigation and monitoring 
measures pursuant to the MMPA, ESA, or NMSA.
Comments and Responses
    On December 27, 2013, NMFS published the initial Draft Guidance for 
Assessing the Effects of Anthropogenic Sound on Marine Mammals: 
Acoustic Thresholds for Onset of Permanent and Temporary Threshold 
Shifts for a 30-day public comment period (78 FR 78822), which was 
extended an additional 45-days (79 FR 4672; January 29, 2014) based on 
public request. During the public comment period, NMFS received 
comments from U.S. Representatives from Congress, Federal agencies, an 
international government agency, state governments, Alaskan native 
groups, industry groups, and non-governmental organizations, individual 
subject matter experts, a professional society, a regulatory watchdog 
group, and 89 private citizens.
    After the close of the initial public comment period, as NMFS was 
addressing public comments and working towards finalizing the Guidance, 
a new methodology for identifying marine mammal auditory weighting 
functions and acoustic thresholds was developed by the U.S. Navy (Dr. 
James Finneran, SPAWAR Systems Center Pacific) based on new science. 
Additionally, NMFS re-evaluated its methods for defining threshold 
usage for sources characterized as impulsive or non-impulsive based on 
comments received during the initial public comment period. 
Incorporating these updated methodologies resulted in substantial 
changes to the Guidance, necessitating additional peer review, as well 
as another public comment period. As a result, NMFS solicited public 
comment on a revised Draft Guidance (July 2015) via a second 45-day 
public comment period (80 FR 45642, July 31, 2015). During the second 
public comment period, NMFS received 20 comments from Federal agencies, 
industry groups, environmental consultants, Alaskan native groups, non-
governmental

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organizations, individual subject matter experts, a professional 
society, a regulatory watchdog group, and two private citizens.
    While NMFS was working to address public comments from the second 
public comment period and finalize the Guidance, NMFS and the Navy (Dr. 
James Finneran, SPAWAR Systems Center Pacific) further evaluated 
certain aspects of the U.S. Navy's methodology. As a result of the 
Navy's and NMFS' review, several focused recommendations/modifications 
were suggested, which did not change the overall methodology provided 
in the July 2015 Draft Guidance (the primary changes were related to 
deriving a composite audiogram for LF cetaceans). After consideration 
of these recommendations, NMFS updated sections of the July 2015 Draft 
Guidance to reflect the suggested changes and solicited public comment 
on those focused revisions via a focused 14-day public comment period 
(81 FR 14095, March 16, 2016). During this third public comment period, 
NMFS received 20 comments from Federal agencies, industry groups, non-
governmental organizations, individual subject matter experts, a 
professional society, and a private citizen. Please refer to these 
Federal Register Notices for additional background about the 2013 and 
2015 Draft Guidance, as well as the document containing proposed 
changes to the Draft Guidance during the public comment period in 2016.
    During these three public comment periods several commenters' 
remarks pertained to topics beyond the scope of the final Technical 
Guidance (e.g., impacts beyond hearing: Non-auditory injury, mortality, 
gas emboli, stranding events, masking, stress, cumulative effects, 
ecosystem-wide effects, behavioral disturbance; activity-specific 
issues associated with specific permit/authorization; effects of 
airborne noise on pinniped hearing; effects of noise on fishes and sea 
turtles; propagation modeling; animal distribution/density; data or 
modeling requirements; take estimation methodology). NMFS did not 
address comments outside the scope of this document. Additionally, in 
re-evaluating substantive public comments made during the first (2013/
2014), second (2015), and third (2016) public comment periods, those 
earlier comments pertaining to sections of the document no longer 
included in the final Technical Guidance are not addressed (e.g., 
proposed 1-hour accumulation period, transition range methodology, 
alternative thresholds).
Technical Guidance Scope
    Comment 1: Several commenters were concerned about the potential 
impacts of sound on polar bear, sea otter, and walrus and asked if NMFS 
coordinated with the USFWS or other branches of NMFS when evaluating 
and establishing thresholds in the Guidance.
    Response: The Technical Guidance only addresses the effects of 
underwater anthropogenic sound on marine mammal species under NMFS' 
jurisdiction. The Technical Guidance does not pertain to marine mammal 
species under the USFWS's jurisdiction (e.g., walrus, polar bears, 
manatees, sea otters). The USFWS is aware of this document and was 
provided an opportunity to comment. NMFS Headquarters, Regions, and 
Science Centers coordinated in the development this Guidance, as did 
the National Ocean Service.
    Comment 2: Multiple commenters, citing the technical complexity of 
the Draft Guidance, requested an extension during all three public 
comment periods. Additionally, multiple commenters expressed concern 
that the public comment period associated with the March 2016 Proposed 
Changes document was rushed, resulted in arbitrary decisions, and did 
not allow for meaningful input from those action proponents most 
impacted by changes (i.e., activities producing low-frequency sound). 
These commenters advocated that instead of NMFS adopting the changes in 
the March 2016 document, the July 2015 Draft Guidance instead be 
finalized.
    Response: NMFS extended the initial 30-day public comment period on 
the 2013 Draft Guidance by an additional 45 days (79 FR 4672, January 
29, 2014). In consideration of an appropriate duration for the 2015 
Draft Guidance public comment period (80 FR 45642, July 31, 2015), NMFS 
chose a 45-day (opposed to 30 days) public comment period, based on the 
extent of changes from the Draft 2013 Guidance, but did not extend that 
public comment period. Regarding the third public comment period, due 
to the focused nature of the most recent proposed revision, presented 
in a standalone 24-page document, and significant previous 
opportunities for public comment, NMFS deemed a 14-day public comment 
period appropriate (81 FR, 14095, March 16, 2016) and did not extend 
public comment period in response to requests. Based on input received 
during the robust review process (i.e., three public comment periods 
and three peer reviews, as well as follow-up peer review), NMFS does 
not believe additional or extended public comment periods were 
necessary to finalize the Technical Guidance.
    NMFS disagrees that the March 2016 public comment period was rushed 
or resulted in arbitrary decisions. The March 2016 public comment 
period was the third opportunity given to the public to review our 
Draft Guidance (following the 75-day first public comment period and 
45-day second public comment period). Previous versions of the Draft 
Guidance had already been revised based upon peer review and public 
input. Due to the focused nature of the proposed changes since the 
prior draft (which were described in a 24-page standalone document) and 
balanced against the lengthy process to date and need for updated 
thresholds, NMFS determined a 14-day public comment period was 
appropriate.
    Comment 3: A few commenters indicated that the 2015 Draft Guidance 
and the 2016 Proposed Changes document was incomplete and the Guidance 
should not be finalized until the public has an opportunity to comment 
on the following missing sections: Agency response to comments made 
during the initial and second public comment periods; optional User 
Spreadsheet for determining isopleths; and references associated with 
sirenian data used in the March 2016 Proposed Changes document.
    Response: NMFS disagrees that the 2015 Draft Guidance and 2016 
Proposed Changes document were incomplete for public comment. In 
finalizing the Technical Guidance (via this Federal Register Notice), 
NMFS has addressed to substantive comments provided during all three 
public comment periods, except those no longer relevant due to 
subsequent changes to the Draft Guidance. Both the 2015 Draft Guidance 
and the 2016 Proposed Changes document encompassed modifications based 
on comments received during the first and second public comment 
periods.
    NMFS disagrees that the User Spreadsheet associated with the 
Technical Guidance's alternative methodology requires public comment. 
This spreadsheet precisely follows the alternative methodology provided 
in the Technical Guidance (Appendix D), which was available for public 
comment. There is nothing additional or new provided by this 
spreadsheet.
    As for the sirenian data used in the March 2016 Proposed Changes 
document, in response to this comment, these references (Gerstein et 
al., 1999; Mann et al., 2009) have been included in the finalized 
Technical Guidance. However, NMFS does not believe additional public 
review is necessary.

[[Page 51699]]

    Comment 4: A few commenters requested clarification as to how the 
Technical Guidance will be used in management decisions (i.e., is the 
Technical Guidance's use a requirement? Is the Technical Guidance a 
rule?).
    Response: The Technical Guidance provides a robust assessment and 
synthesis of a body of scientifically complex information to assess 
impacts of sound on marine mammal hearing. Although its use is not a 
binding requirement, it currently reflects the agency's expert 
assessment of the scientific literature and represents what the agency 
believes is the best approach for assessing auditory impacts. The 
Guidance allows for an alternative approach if case-specific 
information/data indicate that such an approach is likely, in NMFS' 
view following peer review, to produce an equally or a more accurate 
estimate of auditory impacts.
    Comment 5: Multiple commenters requested NMFS include a brief 
statement in the Guidance about what standards are currently in use and 
why they need to be updated. Additionally, the Commission requested 
that the Guidance include updated explosive thresholds for mortality 
(extensive lung injury) and injury (slight lung and gastrointestinal 
(G.I.) tract).
    Response: A new section has been added to the Technical Guidance 
(see Section 1.1 of Main Document) to explain the justification for the 
updated acoustic thresholds for PTS and TTS. The Technical Guidance 
explicitly indicates that the thresholds within the document are meant 
to update all thresholds currently in use by NMFS for assessing PTS 
onset, including generic injury thresholds (i.e., root mean square 
sound pressure level (RMS SPL) thresholds of 180/190 dB), and PTS/TTS 
thresholds for explosives.
    NMFS acknowledges that future Technical Guidance is needed for non-
auditory impacts, but is planning on addressing this in a separate 
guidance document and recommends current non-auditory thresholds for 
explosives remain in use until updates can be completed via the 
appropriate processes.
    Comment 6: Multiple commenters requested clarification on the 
applicability the National Environmental Policy Act (NEPA) to the 
Guidance.
    Response: NMFS determined that the Technical Guidance satisfies the 
standards for a categorical exclusion under NAO 216-6. NAO 216-6, sec. 
6.03c.3(i), which provides that a categorical exclusion is appropriate 
for ``policy directives, regulations, and guidelines of an 
administrative, technical, or procedural nature, or the environmental 
effects of which are too broad, speculative or conjectural to lend 
themselves to meaningful analysis and will be subject later to the NEPA 
process, either collectively or case by case.'' See the section 
addressing NEPA earlier in this Notice.
    Comment 7: The Center for Regulatory Effectiveness (CRE) indicated 
that any use of the Guidance by NMFS in rules would have to be 
supported by cost-benefit analyses because it ``could have a potential 
impact of more than $500 million in any one year on either the public 
or private sector; or . . . the dissemination is novel, controversial, 
or precedent-setting; or . . . [it has] significant interagency 
interest.''
    Response: The Technical Guidance is not a regulatory action subject 
to a cost-benefit analysis under Executive Orders 12866 and 13563. The 
Technical Guidance was classified as a HISA because it was novel and 
precedent setting, not due to the potential financial implications. The 
Technical Guidance will inform assessments of activities that occur in 
a regulatory context as they arise. The Technical Guidance does not 
address or change NMFS' application of the thresholds in the regulatory 
context, under applicable statutes. Any required cost-benefit 
considerations will take place during future actions that are the 
subject of regulatory action, such as ITAs under the MMPA. The nature 
and magnitude of such effects will depend on the specific actions 
themselves. Because any direct effects from the Technical Guidance are 
speculative and conjectural, NMFS cannot meaningfully analyze potential 
effects by a cost-benefit analysis.
    Comment 8: The CRE states that NMFS needs to prepare and obtain 
Office of Management and Budget (OMB) approval of a new Paperwork 
Reduction Act (PRA) Information Collection Request (ICR) in compliance 
with Information Quality Act (IQA) Guidelines before they can use the 
Technical Guidance for any sound source.
    Response: There is no collection of information requirement 
associated with the Technical Guidance. However, NMFS' information 
collection for Applications and Reporting Requirements for Incidental 
Taking of Marine Mammals by Specified Activities Under the Marine 
Mammal Protection Act, OMB approval number 0648-0151, could be affected 
by applicants using the Technical Guidance, possibly in added response 
time to prepare applications using the Guidance. The current approval 
expires in March 2017 and will require renewal before then with an 
opportunity for public comment. In preparation for that renewal, NMFS 
will consider the effect of the Technical Guidance, specifically 
whether a revision in the burden hour estimates is appropriate, and 
invite public comment on its assessment. NMFS has complied with the IQA 
Guidelines with the development of the Guidance.
    Comment 9: A commenter requested that NMFS provide more information 
how the Guidance's updated thresholds would be applied in conjunction 
with thresholds used to assess MMPA Level B behavioral harassment.
    Response: The Technical Guidance does not provide updated acoustic 
thresholds for levels that could result in behavioral effects. NMFS' 
current acoustic thresholds for these impacts are not affected by the 
Technical Guidance. NMFS recognizes the Technical Guidance provides 
updated metrics that are different than those used for estimating 
behavioral harassment. Accordingly, where calculations or modeling 
suggest that some animals will be exposed to sound levels that are at 
or above the relevant PTS threshold under the Technical Guidance but 
behavioral harassment under the current behavioral harassment 
thresholds, an individual should be counted ``taken'' one time, by the 
more severe impact (i.e., PTS onset). However, the qualitative and 
contextual analysis of the likely impacts on that animal, at these 
exposure levels, will consider both the impacts of the likely PTS as 
well as anticipated behavioral responses.
    Comment 10: During the third public comment period, the Commission 
recommended that NMFS review and revise this document every two years 
via a small expert panel, as opposed to the proposed three to five year 
schedule. Revising the Guidance on a two-year basis was also supported 
by other commenters. Additionally, the Commission recommended that 
rather than developing independent guidance, NMFS instead incorporate 
by reference technical reports and peer-reviewed literature already 
summarizing the best available science.
    Response: NMFS will continue to monitor and evaluate new data as 
they become available and will periodically convene staff from our 
various offices, regions, and science centers, and to update the 
Guidance as appropriate (anticipating updates to occur on a three to 
five year cycle). NMFS believes this timeline is appropriate and does 
not need to be modified.

[[Page 51700]]

    NMFS disagrees with the Commission's recommendation to incorporate 
by reference other reports or peer-reviewed literature and believes the 
process of developing Technical Guidance requires a more thorough 
evaluation of the science in the context of NOAA statutory 
requirements. Public comment would also be needed.
    Comment 11: Several commenters expressed uncertainty and requested 
clarification as to how the Guidance would apply to mitigation and 
monitoring requirements (e.g., exclusion zones), often prescribed by 
the conditions of an MMPA permit or authorization.
    Response: Mitigation and monitoring requirements associated with an 
MMPA authorization or ESA consultation or permit are independent 
management decisions made in accordance with statutory and regulatory 
standards in the context of a proposed activity and comprehensive 
effects analysis, and are beyond the scope of the Technical Guidance. 
NMFS acknowledges that in practice, exclusion zones and monitoring 
zones have often corresponded to acoustic impact thresholds, but that 
is not a legal requirement, and the updated thresholds may make such a 
simple correlation more challenging, given their greater complexity. 
The Technical Guidance will be used with other relevant information to 
inform impact assessments, and that in turn will be considered in the 
development of mitigation and monitoring.
Peer Review Process
    Comment 12: One commenter expressed concerned about the peer review 
process and choice of peer reviewers, particularly in regards to 
potential financial ties to NMFS.
    Response: NMFS adhered to appropriate procedures in the selection 
of the peer reviewers to prevent any real or perceived conflicts of 
interest. The Commission, specifically their Commissioners and members 
of their Committee of Scientific Advisors, nominated the peer reviewers 
for each of the three peer reviews. Additionally, the Acoustical 
Society of America's Underwater Technical Council nominated some of the 
peer reviewers in association with the third peer review. Each peer 
reviewer, for all three reviews, submitted a conflict of interest form. 
None of the Technical Guidance's reviewers indicated having a conflict 
of interest, defined as ``any financial or other interest which 
conflicts with the service of the individual because it (1) could 
significantly impair the individual's objectivity, or (2) could create 
an unfair competitive advantage for any person or organization.''
    Comment 13: Several commenters expressed concern that the March 
2016 Proposed Changes document did not undergo peer review and believed 
peer review would result in significant changes to the Guidance 
necessitating the need for a fourth public comment period. If NMFS does 
not conduct a fourth public comment period, the commenters advocated 
that NMFS retract its March 2016 Proposed Changes document and proceed 
with issuing the July 2015 Draft Guidance (modified based on public 
comments from the first and second public comment period) as its 
finalized Guidance.
    Response: The comments are incorrect. NMFS conducted a follow-up 
peer review concurrent with the third public comment period. NMFS 
disagrees with the recommendation to retract the March 2016 Proposed 
Changes document and that a fourth public comment period is needed 
based on comments made by the peer reviewers during this follow-up 
review. The follow-up peer review report is publicly available via: 
https://www.cio.noaa.gov/services_programs/prplans/ID43.html and was 
available before the Guidance was finalized (May 2016).
    Comment 14: One commenter indicated that Guidance should not be 
used until NMFS addresses all the peer reviewers' comments from its 
three peer reviews, and that failing to doing so would cause the 
finalized Guidance to be IQA non-compliant.
    Response: NMFS adhered to IQA procedures and NOAA's IQG, making the 
finalized Technical Guidance IQA compliant. NMFS received valuable 
input from the peer reviewers and made changes to the Technical 
Guidance based on their comments during all three peer reviews, as well 
as during the follow-up review. The peer reviewers' comments greatly 
improved the Technical Guidance before it was available for public 
comment during the initial and second public comment periods. The 
manner in which NMFS addressed the peer reviewers' comments, from all 
three peer reviews, as well as the follow-up review, appear within our 
Peer Review Reports: https://www.cio.noaa.gov/services_programs/prplans/ID43.html.
    Comment 15: A commenter considered NMFS' treatment and peer review 
of the Finneran Technical Report, associated with the July 2015 Draft 
Guidance (Appendix A), as inconsistent, asserting the Finneran 
Technical Report should have been treated similarly to other 
publications that did not undergo formal peer review associated with 
publication in a scientific journal. The commenter questioned why the 
methodology from the Finneran and Jenkins (2012) technical report was 
not subjected to an independent peer review by NMFS but was used in its 
2013 Draft Guidance.
    Response: NMFS disagrees that there was an inconsistency in its 
treatment of Finneran Technical Report (the methodology used for Navy's 
``Phase 3'' environmental compliance analyses in any of the versions of 
our Technical Guidance. NMFS considered Finneran and Jenkins (2012) in 
the development of the 2013 Draft Guidance. However, that particular 
technical report served as a summary of methodology and previously 
published data on impacts of sound on protected species (i.e., it did 
not contain any new data). Although Finneran and Jenkins (2012) was not 
published, the portions used directly in the 2013 Draft Guidance were 
supported by peer reviewed publications. A separate peer review of 
Finneran and Jenkins (2012) was neither necessary nor required under 
HISA requirements.
    For the 2015 Draft Guidance, the Finneran Technical Report, used to 
derive updated marine mammal auditory weighting functions and 
thresholds for the Navy's Phase 3 analyses, was directly incorporated 
into the Guidance via Appendix A. This was the first time the Finneran 
Technical Report was made public, and thus, was subject to HISA 
requirements for inclusion in the Technical Guidance, including peer 
review. We also note that after the July 2015 public comment period, 
part of the Finneran Technical Report, specifically a summary of 
available data on noise-induced hearing loss in marine mammals, was 
published in a peer reviewed journal (Finneran et al., 2015).
    Comment 16: Several commenters expressed concerns over NMFS 
adopting the Finneran Technical Report within the Guidance. One 
commenter specifically stated that the Guidance ``effectively results 
in the US Navy writing its own regulations'' and recommended that the 
entire Guidance process be reconvened using a fully independent panel 
of experts.
    Response: NMFS disagrees with the commenters' assessment. The 
author of the Finneran Technical Report that was incorporated into 
Technical Guidance (Appendix A) is a well-respected and recognized 
scientist with over 50 peer reviewed publications on marine mammal 
hearing and has served on the Southall et al., 2007 expert panel, as 
well as the current Southall panel that

[[Page 51701]]

is updating their 2007 publication. Additionally, this methodology 
underwent an independent peer review convened by NMFS and was evaluated 
internally within NMFS before it was incorporated into our Technical 
Guidance. NMFS believes the Finneran Technical Report represents the 
best available science, which is why we incorporated it in the 
Technical Guidance.
    Comment 17: One commenter requested that the NMFS share their 
original documents and peer reviews from the first peer review (2013), 
in order to facilitate common understanding as to those aspects of 
science related to marine mammal behavior that may be limiting NMFS' 
ability to establish guidance and promote studies that would address 
significant data gaps.
    Response: As noted in the first peer review report (2013), in light 
of the peer reviewers' comments and based upon internal discussions, 
NMFS decided to re-evaluate its proposed methodology for deriving 
acoustic thresholds for behavior and, therefore, included only 
thresholds for PTS and TTS onset in the Draft Technical Guidance (i.e., 
Draft 2013 and 2015 and 2016 Proposed Changes public comment versions). 
NMFS did not include peer reviewer comments on proposed behavioral 
thresholds in the peer review report because they were no longer 
relevant to the scope of the Draft Guidance contents. NMFS will publish 
this information, if relevant, once we re-evaluate our approach for 
establishing updated guidance for behavior effects.
Use of Published Versus Unpublished Data
    Comment 18: Several commenters remarked on the use of published and 
unpublished literature in the Guidance and sought clarification 
regarding the sources considered in the development of the Guidance.
    Response: Not all data considered in the development of the 
Technical Guidance have been published in a peer review journal. For 
the development of PTS and TTS onset acoustic thresholds and marine 
mammal auditory weighting functions, NMFS primarily relied on published 
data. The scientific aspects of the Technical Guidance underwent some 
form of peer review, either via formal publication in a scientific 
journal and/or via the HISA process.
    Comment 19: Several commenters recommended that unpublished 
information from more recent scientific conferences should be 
considered in the Guidance. One commenter specifically indicated 
Southall et al. (2007) will be updated in the near future and that the 
Guidance's finalization should be delayed for this publication or NMFS 
should commit to updating its Guidance within six months of the 
finalization of the updated Southall et al. (2007) publication.
    Response: NMFS notes that when these more recent studies become 
available, they can be considered and incorporated into future updates 
of the Technical Guidance. NMFS is aware that Southall et al. (2007) is 
being updated. We anticipate that the methodology in the Technical 
Guidance will be similar to that provided in the updated publication 
(the author of the Navy's Finneran Technical Report is also on the 
panel updating Southall et al., 2007). NMFS will evaluate and consider 
the updated Southall et al. publication when it becomes available and 
does not believe delaying the Technical Guidance is necessary. 
Regarding the request to update the Technical Guidance within six 
months of the updated Southall et al. (2007) publication, NMFS will 
evaluate the Southall update and consider next steps at the time rather 
than commit to any timeframe in advance.
    Comment 20: One commenter suggested that the Verboom and 
Kastelein's (2005) unpublished report, specifically the ``discomfort 
threshold,'' be included for consideration in the Guidance.
    Response: NMFS reviewed Verboom and Kastelein (2005) and concluded 
the data are more relevant for consideration in future behavioral 
effects guidance.
Sound Sources
    Comment 21: Some commenters indicated that the Guidance appears to 
focus on five sound sources (i.e., underwater detonations, seismic 
airguns, impact pile drivers, vibratory pile drivers, and sonar). They 
recommended the document consider other sound sources that have the 
potential to result in noise-induced hearing loss and provide a list of 
these potential sources within the Technical Guidance, so that other 
sounds sources are given explicit recognition.
    Response: The Technical Guidance identifies the received levels, or 
thresholds, above which individual marine mammals are predicted to 
experience changes in their hearing sensitivity for acute, incidental 
exposure to all underwater anthropogenic sound sources. NMFS believes 
providing a list of all potential sounds sources within the Technical 
Guidance is unnecessary and would limit the document's utility (e.g., 
if there was a new source that was not specifically listed).
    Comment 22: Multiple commenters remarked that the Guidance's 
definitions of ``non-impulsive'' and ``impulsive'' sounds are vague 
(i.e., NMFS does not define what is meant by ``high peak sound pressure 
level'' or ``rapid rise time'') and do not objectively distinguish 
between these two types of sound. The commenters recommended that 
clear, technical definitions be included. Further, commenters noted 
that impulsive sounds become increasingly continuous with distance, due 
to multipath arrivals and other factors, and may have continuous 
components even at short distances due to reverberation and requested 
NMFS also consider waveform data at the location of the marine mammal 
to categorize sound sources.
    Response: The Technical Guidance relied on defining sound sources 
based on previously established definitions and standards (i.e., 
American National Standards Institute (ANSI)). NMFS categorized sound 
sources as impulsive or non-impulsive based on temporal characteristics 
of the sound at the source. The definition of an impulsive sound source 
in the Technical Guidance relates specifically to noise-induced hearing 
loss and specifies the physical characteristics of an impulsive sound 
source, which likely gives impulsive sounds a higher potential to cause 
auditory injury than non-impulsive sounds. Unfortunately, these 
standards do not provide quantitative definitions for terms like 
``high'' peak sound pressure level and ``rapid'' rise time, especially 
in the context of underwater sources.
    NMFS acknowledges that sound propagation is complex and the 
physical property of sounds change as they travel through the 
environment. The July 2015 Draft Guidance proposed a methodology for 
examining when impulsive sounds are less likely to possess the physical 
characteristics that make them more injurious (i.e., peak sound 
pressure level and pulse duration). This proposed methodology underwent 
an independent peer review (Guidance's third peer review). However, 
based on comments received during the public comment period for the 
2015 Draft Guidance, NMFS decided the proposed methodology would 
benefit from by further research, removed the proposed methodology from 
main Guidance document, and highlighted it in the Research 
Recommendations, Appendix B. Included in the Technical Guidance's 
Research Recommendations is a call to identify sound characteristics 
associated with injury, which may allow for more

[[Page 51702]]

detailed definitions in future iterations of this Guidance.
    Comment 23: One commenter suggested that the Guidance definition of 
impulsive sound sources as those with signals less than one second in 
duration could possibly capture sources that are not truly impulsive 
and recommended that impulsive sources be defined as those which exceed 
some threshold of impulse, defined as ``the time integral of a force 
over the time that the force is applied (ANSI 1994).'' Another 
commenter suggested characterizing impulsive sources based on metrics 
which consider rise time, crest factor, or the signal kurtosis (i.e., 
statistical quantity that represents the impulsiveness ``peakedness'' 
of the event). A follow-up comment acknowledged that kurtosis in the 
time domain may not be practical and suggested considering kurtosis in 
the frequency domain.
    Response: The terms impulsive and non-impulsive as defined in the 
Technical Guidance are based on several ANSI standards. If action 
proponents are unclear which category their source might fit, they may 
contact NMFS for further discussion. NMFS acknowledges that the 
additional factors suggested by the commenters could be useful for 
defining source types. However, these are not currently commonly used 
descriptors by action proponents or those conducting marine mammal 
noise-induced hearing loss studies (i.e., data are not typically 
collected and published using these metrics), and would not be easily 
implementable at this time. Additional metrics can be considered as 
more data become available in a broader array of metrics. A better 
understanding of appropriate metrics has been identified as an area for 
recommended research in Appendix B of the Technical Guidance. In 
regards to using kurtosis in the frequency domain, NMFS re-examined 
this metric based on the comment received. However, upon evaluation, it 
was determined that this metric is still not currently practical to 
implement.
    Comment 24: The Commission recommended that the 2015 Finneran 
Technical Report definitions of impulsive and non-impulsive sounds be 
adopted by NMFS and used in all contexts, including MMPA Level B 
behavioral harassment.
    Response: The Technical Guidance definitions of impulsive and non-
impulsive sounds comply with ANSI definitions and were subject to 
independent peer review (third peer review). These specific definitions 
were chosen to capture those physical characteristics that make a sound 
more or less injurious in terms of noise-induced hearing loss. The 
Technical Guidance does not address direct behavioral impacts from 
sound and so does not adopt definitions that bear on behavior. 
Classification of sound sources in terms of behavioral harassment will 
be examined when we develop guidance for these types of impacts.
    Comment 25: Multiple commenters expressed concern that seismic 
waterguns produce higher frequency sounds than seismic airguns and 
should not be used to set thresholds for airguns.
    Response: NMFS established Technical Guidance for all impulsive 
sounds based on the currently available data, which may not include 
every potential sound source to which a marine mammal could be exposed. 
Watergun data were used to represent airguns, as well as impact pile 
driving for most hearing groups. However it should be noted that the HF 
cetacean TTS onset impulsive thresholds are derived directly from data 
obtained from a harbor porpoise exposed to a single airgun. 
Incorporating marine mammal auditory weighting functions into exposure 
models allows for the consideration that airguns predominantly produce 
lower frequencies compared to waterguns.
    Comment 26: A group of commenters expressed concern the Guidance 
will restrict the use of marine vibrators, which are designed to be 
more environmentally friendly by avoiding the generation of sound in 
the ``best hearing'' range of most marine animals, and generate a 
significantly lower overall sound pressure level throughout the 
frequency band relative to seismic airguns.
    Response: The Technical Guidance does not restrict or allow any 
activity. It sets out science-based thresholds for the onset of 
auditory impacts based on our evaluation and synthesis of available 
data. Decisions about various sound-generating activities are outside 
the scope of the Technical Guidance.
    Comment 27: A commenter noted that when considering sound source 
characterization, recording equipment can be limited in bandwidth and 
dynamic range (i.e., equipment may not be able to accurately 
characterize the sound source).
    Response: NMFS agrees that fully characterizing the complete 
spectrum of a sound source, within the hearing ranges of marine 
mammals, is essential to accurately assess potential impacts, as is 
ensuring that sources meet manufacturer specifications (i.e., sometimes 
sources are capable of producing sounds outside their specified bands, 
which have the potential to fall within the hearing range of marine 
mammals; Deng et al., 2014; Hastie et al., 2014). This factor is 
important in considering the potential of a sound source to impact a 
specific hearing group, and text addressing this point has been added 
to the Technical Guidance.
    Comment 28: One commenter remarked that the Guidance was unclear 
whether NMFS will require sound source verification (SSV), associated 
with the application of the Guidance's acoustic thresholds. The comment 
noted that conducting a SSV poses a complicated and unnecessary burden 
on operations because the results are highly variable due to constantly 
changing conditions in the environment.
    Response: The Technical Guidance does not impose any such 
requirements. NMFS has added text to the introduction of the Technical 
Guidance to clarify this point.
Metrics
    Comment 29: One commenter recommended additional clarification on 
various sound metrics to prevent confusion between the peak sound 
pressure level (PK) used in the current Guidance and maximum RMS SPL 
used to describe prior NMFS thresholds.
    Response: NMFS agrees and added clarification to the Technical 
Guidance to distinguish between metrics used in this document and those 
associated with previous thresholds, as well as including definitions 
of these metrics in the Glossary (Appendix E).
    Comment 30: One commenter requested clarity on the definition of 
``peak pressure'' used in the Guidance, which the commenter assumes to 
be the equivalent of a ``zero-to-peak'' value. This commenter further 
indicated that the Guidance has been inconsistent in converting between 
``peak-to-peak'' and RMS values to ``zero-to-peak'' values.
    Response: NMFS has defined peak sound pressure level in the 
Glossary (Appendix E) and has clarified the definition in the Technical 
Guidance to indicate a zero-to-peak value. NOAA disagrees that there 
are inconsistencies in the Technical Guidance because there have been 
no conversions made between zero-to-peak and peak-to-peak sound 
pressure levels or from RMS sound pressure to any other metric anywhere 
in this document.
    Comment 31: To match what was provided in the Finneran Technical 
Report (Appendix A of July 2015 Draft Guidance), the Commission and 
some other commenters recommended that NMFS only provide dual metrics 
for PTS onset for impulsive sources (i.e.,

[[Page 51703]]

remove peak pressure metric threshold for non-impulsive sources). 
Conversely, a commenter was not supportive of removing the peak 
pressure thresholds for non-impulsive sources, as was suggested in the 
2016 Proposed Changes document. Finally, there was some confusion as to 
how and when the PK threshold needs to be considered based on the 
updates in the 2016 Proposed Changes document.
    Response: Upon further evaluation, NMFS agrees and has removed the 
PK thresholds for non-impulsive source in the Technical Guidance, since 
it is highly unlikely that the dominant metric for non-impulsive 
sources will be the peak sound pressure level. However, the Technical 
Guidance caveats that if a non-impulsive sound has the potential of 
exceeding the PK threshold associated with impulsive sources, these 
thresholds should still be considered. Thus, in the Technical Guidance, 
there remain dual criteria associated with impulsive sources (i.e., 
applicant should consider whichever threshold results in the largest 
effect distance (isopleth)).
    Comment 32: A few commenters remarked SELcum is not a 
standardized acoustic notation and that the Guidance should adhere to 
existing standards in terms of terminology, definitions, symbols, and 
acronyms in order to promote clarity and reduce confusion. It was also 
recommended that NMFS work with standards-setting bodies to develop a 
consistent system of notation for marine bioacoustics applications 
(e.g., ANSI or International Organization for Standardization (ISO)).
    Response: NMFS acknowledges that neither the 2013 nor the 2015 
Draft Guidance documents consistently used notations complying with 
available standards. The final Technical Guidance has been revised to 
better reflect ANSI standards (e.g., terminology, abbreviation, and 
symbols). Further, NMFS is aware of the work of ISO 18405 to develop 
standards specifically for underwater acoustics and will re-evaluate 
the Guidance's notations in future updates once the ISO work becomes 
finalized.
    Comment 33: One commenter noted an inconsistency in the Guidance 
with both PK and SELcum acoustic thresholds being derived 
from the same study. The commenter noted that if the energy from a 
transmission does not cause an impact at a given frequency because of 
an animal's reduced sensitivity (or capability) to hear that signal, 
then the ability to be impacted by the PK should also be reduced for 
that frequency.
    Response: NMFS does not agree there is an inconsistency in how data 
were assessed. Data from Lucke et al. (2009) were used to derive both 
thresholds for HF cetaceans exposed to impulsive sources. For MF 
cetaceans, both thresholds come from belugas exposed to waterguns 
(Finneran et al., 2002). For both the Lucke et al. (2009) and Finneran 
et al. (2002) study, TTS onset was recorded in multiple metrics, with 
two of these metrics (i.e., PK and SELcum) directly used in 
the Technical Guidance. NMFS disagrees that auditory weighting 
functions are appropriate for use with the PK metric, as direct 
mechanical damage associated with sounds having high peak sound 
pressures typically does not strictly reflect the frequencies an 
individual species hears best (i.e., why PK thresholds should be 
considered unweighted/flat-weighted within the entire frequency band of 
a hearing group).
    Comment 34: Multiple commenters noted that the SELcum 
metric within the Guidance is used under the assumption that a low 
amplitude/long signal having an equal SELcum, as a high 
amplitude/short signal, will have the same effects on the auditory 
system (i.e., the Equal Energy Hypothesis (EEH)). A commenter further 
stated that the EEH may be correct in certain conditions, but that an 
increasing body of evidence indicates that the EEH does not hold true 
for most marine mammal sound exposures. It was suggested that as more 
data become available, NMFS should perform more analyses to determine 
what model or equation best fits the EEH and revise the acoustic 
thresholds to more accurately reflect the potential for TTS changes 
with duration and amplitude.
    Response: NMFS agrees that EEH may not be valid for all exposure 
situations. However, the Technical Guidance provides acoustic 
thresholds in the SELcum metric, based on the belief that 
the EEH is the best means of incorporating this metric (also 
recommended by Southall et al., 2007). NMFS maintains that despite the 
shortcomings, having a metric that includes the duration of exposure is 
critical for predicting effects of noise on marine mammal hearing. The 
evaluation of appropriate metrics and EEH has specifically been 
identified as an area where more research is needed (Guidance Appendix 
B).
    Comment 35: One commenter indicated since ``SEL'' is the 
accumulated acoustic energy in a signal and cumulative by definition, 
whether calculated over one second or a single pulse event, the 
Guidance's use of ``SELcum'' to describe cumulative sound 
exposure is unnecessary. The commenter suggested NMFS should simply use 
the abbreviation ``SEL''.
    Response: NMFS agrees that the SEL implies accumulation. The ANSI 
definition indicates that accumulation occurs over a stated time 
interval, which is typically referenced to one second. In order to 
clarify that the duration of accumulation in the Guidance is not one 
second (i.e., 24 hours), NMFS chose to use the notation 
SELcum.
Use of Data From Captive Marine Mammals
    Comment 36: Multiple commenters indicated that the use of data from 
captive individuals was a poor proxy (e.g., over-estimate TTS onset or 
hearing thresholds, may be habituated or have different survival 
tactics) for their free-ranging counterparts and suggested that data 
from captive bottlenose dolphins be adjusted to be more representative.
    Response: NMFS acknowledges that captive individuals may be 
habituated to their test environment, making them less than ideal 
proxies for their free-ranging counterparts for studying behavioral 
reactions to noise. However, we believe habituation has minimal effects 
on testing auditory capabilities and the impacts of noise on hearing, 
which is the focus of this Technical Guidance.
    For example, NMFS notes that data from Castellote et al. (2014), 
from free-ranging belugas in Alaska, indicate of the seven healthy 
individuals tested (3 females/4 males; 1 subadult/6 adults), all had 
hearing abilities ``similar to those of belugas measured in zoological 
settings.'' Thus, from this one study, it appears that for baseline 
hearing measurements, captive individuals might be an appropriate 
surrogate for free-ranging animals. However, this is currently the only 
study of its kind, and more research is needed to examine if this trend 
applies to other species (see Appendix B: Research Recommendations).
    NMFS also finds an adjustment to bottlenose dolphin data is 
unnecessary. The Technical Guidance methodology for deriving marine 
mammal auditory weighting functions incorporates data from a multitude 
of species (~20 species), beyond just bottlenose dolphins, and is 
considered representative based on the best available science.
    Comment 37: Several commenters expressed concern over the ages of 
many of the captive individuals used in TTS studies as not being 
representative (e.g., thresholds obtained from younger bottlenose 
dolphin in Johnson 1968 are on average 10 dB lower than from older 
individuals) and considers them sources of uncertainty. Many commenters 
suggested that data from older

[[Page 51704]]

individuals should either be adjusted or excluded from consideration.
    Response: NMFS disagrees that data from older individuals needs to 
be excluded or adjusted and notes that Houser and Finneran (2006) did a 
comprehensive study on the hearing sensitivity of the Navy bottlenose 
dolphin population (i.e., tested 42 individuals from age 4 to 47 years; 
28 males/14 females) and found that high-frequency hearing loss 
typically began between the ages of 20 and 30 years. For example, at 
frequencies where this species is most susceptible to noise-induced 
hearing loss (i.e., 10 to 30 kilohertz (kHz)), these are the 
frequencies where there is the lowest variability in mean thresholds 
between individuals of different ages. Additionally, for harbor seals, 
similar levels of TTS onset were found in Kastelein et al. (2012a) for 
individuals of 4 to 5 years of age compared to the individual from in 
Kastak et al. (2005), which was 14 years old. For belugas similar 
levels of TTS were measured in Popov et al. (2014) for an individual 2 
years old compared to those used in Schlundt et al. (2000), which were 
20 to 22 years old or 29 to 31 years old.
    Further, Houser and Finneran 2006 attribute the lower thresholds 
recorded by the individual from Johnson (1968) to differences in 
methodology (i.e., Johnson (1968) used behavioral protocol to test 
hearing versus electrophysiological methodology by Houser and Finneran 
(2006)). The Technical Guidance relies primarily on behavioral data 
associated with hearing and threshold shift measurements, as opposed to 
those obtained via other means (e.g., auditory evoked potentials (AEP)) 
because we consider these data to be most representative of hearing 
ability and noise-induced hearing loss, which further eliminates the 
need for any adjustment.
    Comment 38: One commenter indicated that studies show that marine 
mammals tend to avoid disruptive sound sources, which could 
significantly diminish the potential for noise-induced hearing loss. 
Therefore, the commenter suggests that the data collected in laboratory 
experiments are likely to result in overestimates of exposure because 
the subjects are exposed to longer and louder sounds than they would be 
in the natural environment.
    Response: NMFS agrees that when considering exposure durations for 
animals under realistic exposure conditions, generally, it is predicted 
that most individuals will only be in the closest ranges to a sound 
source/activity for a minimal amount of time (e.g., animals are capable 
of moving horizontally and vertically in the water column to reduce 
exposure, and/or individuals are exposed to mobile sources). Thus, 
using laboratory data from animals exposed to unusually long, 
continuous durations of sound (i.e., animals cannot leave exposure 
scenario and the level during exposure remains constant) may not best 
reflect scenarios expected to be encountered by wild individuals, when 
exposed to sound over long periods of time. However, measurements of 
TTS from laboratory studies are the only data currently available, and 
they remain informative regarding sound exposure that may impact marine 
mammal hearing. Appendix B of the Guidance recommends future TTS 
studies to address exposures animals are likely to receive in the 
natural environment and provide more representative results.
Marine Mammal Hearing Ranges
    Comment 39: One commenter noted that the establishment of hearing 
groups is fundamentally flawed because it is based on the assumption 
that similar exposures will result in similar effects in all group 
members. The commenter believes it is important to consider species 
differences in behavior (e.g., movement away from the noise source) 
when calculating cumulative exposure associated with PTS onset.
    Response: NMFS agrees that marine mammal behavioral responses could 
result in differences in noise exposures and accumulation scenarios 
(i.e., SELcum). However, NMFS disagrees that such responses 
necessarily indicate that hearing physiology is dissimilar or that 
levels causing noise-induced threshold shifts are dissimilar between 
species within a hearing group. Further, differences in behavioral 
responses to sound will be considered in the development of behavioral 
effects thresholds.
    Comment 40: One commenter indicated that the method for determining 
the limits of the functional hearing ranges was not clearly indicated 
in the Guidance and suggests that NMFS should indicate how the limits 
were obtained for each group. Another commenter indicated that the term 
``functional hearing range'' is intended to convey the range over which 
the majority of the species' hearing ability is found. However, there 
are at least two examples of a species' ability to hear a signal 
outside its functional hearing range (i.e., false killer whale and 
Risso's dolphin (Au et al., 1997)).
    Response: Based on the revised methodology for establishing marine 
mammal auditory weighting functions (Appendix A), NMFS has replaced the 
concept of functional hearing range with the establishment of what the 
Technical Guidance terms ``generalized hearing range'' for each hearing 
group. The latter is recommended for consideration associated with flat 
weighting for PK thresholds and when determining general risk of 
auditory impacts from noise. The generalized hearing ranges were chosen 
based on the approximate 65 dB threshold from the normalized composite 
audiogram. NMFS believes that outside the generalized hearing range, 
the risk of auditory impacts from sounds (i.e., TTS or PTS) is 
considered to be either zero or very low (the exception would be if a 
sound above/below this range was determined to have the potential to 
cause physical injury, i.e., lung or gastrointestinal tract injury from 
explosives) and added additional information to clarify this in the 
Technical Guidance.
    NMFS is aware of the Au et al. (1997) paper, which examines the 
effect of the 75 Hz acoustic thermometry of ocean climate (ATOC) signal 
on hearing sensitivity of a single false killer whale and single 
Risso's dolphin, both mid-frequency (MF) cetaceans. Hearing thresholds 
for both species, from this study, were 139 dB or higher (false killer 
whale: Thomas et al., 1988; Risso's dolphin: Nachtigall et al., 1995). 
Thus, this ATOC signal is considered beyond the generalized hearing 
range of MF cetaceans.
    Comment 41: Several commenters questioned the justification used to 
support the PW and OW pinnipeds' upper hearing limit in the Technical 
Guidance. The commenters noted that newer studies have consistently 
shown that 75 kHz is a more reasonable upper cutoff for PW pinnipeds 
underwater. These commenters recommended that NMFS choose the median 
value, not the most conservative value, for the PW pinniped upper 
hearing range limit. For OW pinnipeds, the 2013 Draft Guidance does not 
clearly explain why 40 kHz was selected as a high-frequency cut-off for 
OW pinnipeds instead of 50 kHz reported in Finneran and Jenkins (2012).
    Response: As indicated in the previous comment/response, NMFS has 
provided generalized hearing ranges by marine mammal hearing group. The 
generalized hearing ranges are supported by available pinniped 
audiogram data that were used to derive the composite audiogram for 
this group (Terhune 1988; Kastak and Schusterman 1999; Kastelein et 
al., 2009; Reichmuth et al., 2013; Sills et al., 2014; and Sills et 
al., 2015). The generalized frequency ranges are intended to be broad 
enough to encompass the hearing range of the

[[Page 51705]]

entire hearing group (i.e., choice of using 65 dB threshold compared to 
60 dB threshold typically used to define human and other terrestrial 
mammal hearing ranges). Thus, NMFS disagrees that using a median is 
preferred. For PW and OW pinnipeds, the upper range based in the 
finalized Technical Guidance is 86 kHz and 39 kHz, respectively.
    Comment 42: One commenter noted that current ESA and MMPA analyses 
are based on data collected while monitoring previous activities, with 
little of that data having been analyzed by hearing group. The 
commenter suggested that until more data are available, it will be 
difficult to find data upon which to base the analyses.
    Response: NMFS disagrees that it will be difficult to complete 
analyses and believes that hearing group data and marine mammal 
auditory weighting functions provided in the Technical Guidance are 
based on the best available science and can be applied to any source. 
Additionally, the Technical Guidance states that the application of 
marine mammal auditory weighting functions should be completed after 
data collection (i.e., auditory weighting functions should not be 
applied beforehand), with the total spectrum of sound preserved for 
later analysis (i.e., if weighting functions are updated or if there is 
interest in additional species, data can still be used).
General Auditory Weighting Functions
    Comment 43: NMFS' exclusion of AEP data in establishing marine 
mammal composite audiograms and auditory weighting functions was 
criticized by several commenters. These commenters noted that by 
including AEP datasets, the statistical power of the assessment would 
be improved.
    Response: In deriving marine mammal composite audiograms, NMFS 
established an informal data hierarchy in terms of assessing these 
types of data. Specifically, audiograms obtained via behavioral 
methodology provide the most representative presentation (most 
sensitive) on hearing ability, followed by AEP data, lastly by 
mathematical models for species where no data are available (i.e., low-
frequency or LF cetaceans). Thus, the highest quality data available 
for a specific hearing group should be used, which for all hearing 
groups, except LF cetaceans, is behavioral. Additional clarifying text 
on this informal data hierarchy has been provided in the Technical 
Guidance.
    It also should be noted that marine mammal AEP audiograms have been 
based almost exclusively on measurements of the auditory brainstem 
response, and thus do not take into account contributions to hearing 
from higher centers of the brain and auditory nervous system, and no 
means have been established for ``correcting'' AEP data so that they 
may be more comparable to those obtained via behavioral methods. AEP 
thresholds are typically elevated compared to behavioral thresholds in 
a frequency-dependent manner, especially at lower frequencies (e.g., 
Szymanski et al., 1999; Yuen et al., 2005; Houser and Finneran 2006); 
therefore including the low-frequency AEP data in the composite 
audiogram would cause an artificial increase in audiogram low-frequency 
slope and cause the resulting weighting function to be more narrow at 
low frequencies.
    Despite not directly including AEP audiograms in the development of 
a hearing groups' composite audiogram, these data were evaluated to 
ensure species were placed within the appropriate hearing group and to 
ensure that a species for which only AEP data were available were 
within the bounds of the composite audiogram for that hearing group. 
Further, AEP TTS data are presented within the Guidance for comparative 
purposes alongside TTS data collected by behavioral methods 
illustrating that the AEP TTS data are within the bounds (the majority 
of the time above) of those collected by behavioral methods (i.e., 
Figures A18 and A19).
    Comment 44: One commenter remarked that the Guidance may change as 
improved information becomes available, which means that auditory 
weighting functions may also change. The commenter suggested that NMFS 
develop a mechanism for allowing updates until a widely-accepted 
weighting procedure for marine mammals is standardized by expert 
consensus (e.g., through the ANSI or ISO standardization processes).
    Response: NMFS agrees that as additional data become available, the 
auditory weighting functions, among other factors, may require 
modification. For that reason, NMFS has added specifications to the 
Technical Guidance indicating that auditory weighting functions should 
be applied after data are collected (i.e., during data collection, the 
complete spectrum of sound should be collected) to ensure they are 
available for re-analysis if updated weighting functions become 
available. The Technical Guidance also establishes protocols for 
evaluating new data and updating the document.
    Comment 45: Multiple commenters noted that each of Guidance's 
hearing groups contains species whose sound production and regions of 
best hearing sensitivity do not overlap to a high degree. A few 
commenters further added that applying results from one or two aging 
bottlenose dolphins to all members of a hearing group is inadequate.
    Response: The auditory weighting functions are meant to assess risk 
of noise-induced hearing loss and not necessarily encompass the entire 
range of best hearing for every species within the hearing group. NMFS' 
use of auditory weighting functions is consistent with how weighting 
functions are used in human noise standards, which is to assess the 
overall hazard of noise on hearing. Specifically, the human auditory 
weighting function provides a ``rating that indicates the injurious 
effects of noise on human hearing'' (OSHA 2013). While these weighting 
functions are based on regions of equal loudness and best hearing, they 
are meant to reflect the susceptibility of the ear to noise-induced 
threshold shifts, and as such, the region of enhanced susceptibility to 
noise exposure may not perfectly mirror a species' region of best 
hearing (e.g., TTS data from bottlenose dolphin, belugas, and Yangtze 
finless porpoise support this).
    Further, updated methodology in the July 2015 revised Draft 
Guidance used composite audiograms based on multiple species to derive 
marine mammal auditory weighting functions. Thus, data from more than 
just bottlenose dolphins were used to derive these functions (i.e., MF 
cetacean composite audiograms are derived using data from eight 
different species).
    As for how animal age could impact hearing susceptibility, please 
see Response to Comment 37.
    Comment 46: Multiple commenters expressed concern that the 
Guidance's marine mammal auditory weighting functions are invalid, 
since they are based on assumptions that have not been subject to 
uncertainty analysis for frequencies below 3 kHz.
    Response: NMFS disagrees that there is greater uncertainty for 
frequencies below 3 kHz, since audiogram data were collected for 
frequencies below 3 kHz for a multitude of species in the MF and HF 
cetacean and PW and OW pinniped hearing groups (e.g., see Figure A5 in 
Technical Guidance). Further, low-frequency data from the composite 
audiogram is used to directly determine the slope of the weighting 
function.
    Comment 47: A commenter requested clarification on what NMFS 
intended by the term ``smaller isopleth'' in discussing the effects 
marine mammal

[[Page 51706]]

auditory weighting functions have on exposure modeling results.
    Response: The Technical Guidance thresholds associated with a 
hearing group themselves do not change depending on how much a sound 
may overlap a group's most susceptible frequency range. Instead, how 
weighting functions affect exposure modeling/analysis is related to the 
size of the isopleth (area) associated with the threshold based on how 
susceptible that particular hearing group is to the particular sound 
being modeled. For example, a hearing group could have different size 
isopleths associated with the same threshold, if one sound was within 
its most susceptible frequency range and the other was not (i.e., sound 
in the most susceptible hearing range will result in larger isopleth 
compared to sound outside the most susceptible hearing range). We have 
provided additional text in the Technical Guidance to clarify this 
concept.
    Comment 48: One commenter expressed concern as to the practicality 
of obtaining and maintaining modeled sound field results for broadband 
sources (e.g., airguns or impact pile drivers) in order for weighting 
functions (current or revised) to be applied at a later date.
    Response: The Technical Guidance recommends that marine mammal 
auditory weighting functions be applied after sound field measurements 
have been obtained (i.e., post-processing; auditory weighting functions 
should not be applied beforehand), with the total spectrum of sound 
preserved for later analysis (i.e., if weighting functions are updated 
or if there is interest in additional species, data can still be used). 
This recommendation applies to actual field measurements and not 
modeling results. The final Technical Guidance includes additional text 
to clarify this point.
Uncertainty and Statistical Analyses Associated With Auditory Weighting 
Functions
    Comment 49: Several commenters expressed concern about uncertainty 
in the development of the marine mammal auditory weighting functions 
and acoustic thresholds, especially because of the reliance on mean and 
median values without reporting variation (i.e., methodology does not 
account for variability/confidence intervals associated with small 
sample sizes). Alternative methodologies to account for uncertainty 
were suggested for consideration (e.g., inverse Bayesian formulations 
with Markov-chain Monte Carlo and Metropolis-Hastings sampling methods; 
Wright 2015; Potential Biological Removal (PBR); human noise standards 
(NIOSH 1998)).
    Further, Wright (2015) claimed that inconsistencies within the 
methodology used to establish the auditory weighting functions and 
acoustic thresholds contributed to uncertainty; namely, that: (a) The 
hearing threshold (audiogram)-to-TTS onset component, on a per 
individual basis, is neglected (recommends calculating audiogram-to-TTS 
onset for each individual); (b) it is inappropriate for non-adjusted 
(non-normalized) TTS onset data points for individuals to be fit to 
composite audiograms; and (c) there is a discrepancy between the 
frequency of best sensitivity for the composite audiogram and exposure 
function, which results in the weighting/exposure function gain 
parameters (i.e., parameters ``K'' and ``C'') underestimating TTS 
onset.
    Finally, it was requested that NMFS (1) provide the underlying data 
used to derive the weighting functions so that uncertainty and 
statistical analyses can be evaluated by those outside NMFS and (2) 
delay the Guidance's finalization until this outside process can be 
completed.
    Response: NMFS acknowledges the small sample size associated with 
the available marine mammal data used to derive weighting functions and 
thresholds presents challenges. However, the Technical Guidance's 
methodology is designed to predict the mostly likely (realistic) 
outcome using the central tendencies (means/median) associated with the 
best available science. The intent is not to predict the worst-case-
scenario by relying on the lowest limits for every possible step in the 
methodology (i.e., Technical Guidance is for accurately predicting 
exposures and not for establishing ``safe limits,'' where there is 
limited to no risk). Despite not using statistical methodology to 
report variability, Appendix A provides the full suite of available 
data for consideration and comparison to the values used in the 
Technical Guidance (e.g., Figures A5 and A6 for audiogram data and 
Figures A18-A20 for TTS data). With respect to data used to derive 
composite audiograms, auditory thresholds are typically defined by the 
50 percent detection threshold (ANSI 2009), and equal loudness contours 
used to derive human weighting functions are derived using averages 
(e.g., Fletcher and Munson 1933), as opposed to relying on the lowest 
value (i.e., there is a precedence for using medians/means). 
Additionally, it is important to remember that the derived weighting 
functions are based on more than the just the composite audiogram 
(i.e., the audiogram shapes are adjusted to best fit the existing TTS 
data) resulting in a function that is always broader than the composite 
audiogram (e.g., Figure A17).
    Human noise risk assessments (NIOSH 1998) are not equivalent (or 
applicable) to thresholds provided in the Technical Guidance, since 
they are used to predict hearing loss based on a daily 8-h exposure 
over 40 years (i.e., current marine mammal TTS are only available to 
predict exposure periods of 24 h or less and cannot be used to assess 
or predict risk associated with a lifetime of exposure; See Response to 
Comment 79) and are based on larger sample sizes of human listeners 
(e.g., NIOSH 1972 and 1997 risk assessments were based on a sample size 
of 1,172 people). As pointed out in Wright 2015, NIOSH criteria provide 
a 95 percent confidence interval for their human noise standards but 
also allows for an excess risk of material hearing impairment, defined 
as an average threshold elevation for both ears that exceeds 25 dB, of 
eight percent (i.e., human noise standards limits do allow for some 
risk; risk is not zero percent and specifically that eight percent of 
the population is still capable of developing noise-induced hearing 
loss exceeding 25 dB when exposed to the 85 dB NIOSH level). For how 
the Technical Guidance's TTS thresholds encompass available data, see 
Response to Comment 72 and Appendix A, Figures A18-A20, which provide 
all available marine mammal TTS data collected via both behavioral and 
AEP techniques). Additionally, methodology associated with the 
calculation of PBR (i.e., use of twentieth percentile) was based on 
simulations specific to a particular dataset (Wade 1998) and is not 
applicable to the Technical Guidance.
    With respect to specific comments made in Wright (2015), NMFS 
disagrees there are inconsistencies in the methodology in the Technical 
Guidance. Specifically related to the assertion in part (a) of the 
comment that NMFS neglected the hearing threshold (audiogram)-to-TTS 
onset component: In re-examining available data sets, in terms of 
offset between hearing threshold and TTS onset, only six individuals 
(three MF cetacean, one OW pinniped, and two PW pinnipeds) have 
measurements available for both hearing threshold and TTS onset. 
Differences in TTS onset at frequency of best hearing (from the 
exposure function) and threshold at frequency of best hearing (from the 
composite audiogram) are reflected by hearing group in the Technical 
Guidance in Table A7 (Appendix A, ``Difference'' column).

[[Page 51707]]

Unfortunately, comparisons between the difference hearing thresholds 
and TTS onset from the same individual to differences depicted in Table 
A7 are difficult, since none of the individual TTS data occur in the 
frequency of best hearing. However, TTS onset (SELcum 
metric) predicted from the exposure function is within 1 dB or lower 
compared to TTS onset based on these five individuals. Further, this 
specific recommendation from Wright (2015), to consider data from 
individual audiograms, counters other recommendations made elsewhere in 
that paper that data from the same species should be considered 
correlated and combined to reduce issues associated pseudoreplication 
(See Response to Comments 53).
    As for non-adjusted TTS data points being fit to normalized 
composite audiograms (point b), the Guidance's methodology examines the 
best fit of TTS data points to both original (non-normalized) and 
normalized composite audiogram data to establish the ``delta T'' 
parameter (i.e., both non-normalized and normalized data are used to 
derive delta T). Additionally, the ``K'' parameter is derived using the 
original (non-normalized) audiogram data and is defined to minimize the 
square error between the exposure function and TTS data for each 
hearing group.
    As to point (c), NMFS acknowledges that there is a shift 
(discrepancy) in frequency between the best sensitivity in terms of the 
composite audiogram and resulting exposure function for a hearing 
group, but disagrees that this leads to an underestimation of TTS 
onset. Any difference in minimum value between the exposure function 
and audiogram is an outcome of the fitting process used to fit the 
exposure function to the available TTS data, and thus, reflects the 
underlying TTS data. This shift in minimal value results in an 
identical (PW and OW pinnipeds) or lower TTS onset threshold (MF and HF 
cetaceans) than predicted by considering the composite audiogram alone 
(See Table A7 vs. A8 in Technical Guidance). Further, the ``C'' 
parameter results in a minimal adjustment to the final TTS onset 
threshold (maximum 1 dB; See Table A8 in Appendix A).
    Finally, NMFS believes it is unnecessary to provide underlying 
datasets associated with the Technical Guidance and delay publication, 
since the majority of the underlying data (with a few exceptions) are 
published and freely available.
    Comment 50: Commenters indicated that sound reception is an 
essential ability of marine mammals, particularly cetaceans, for 
survival, and these commenters, citing Nowacek et al. (2007), indicated 
that PTS can lead in many cases to mortality of individuals which may 
have serious consequences for the survival of populations.
    Response: NMFS agrees that the ability to accurately interpret the 
surrounding environment via hearing is essential for marine mammals. 
However, NMFS' review of Nowacek et al. (2007) as well as all other 
available information did not locate any statements that PTS can result 
in mortality.
    Comment 51: Some commenters recommended that audiograms from 
individuals of the same species should be treated as correlated in the 
determination of composite audiograms. Further, in order to determine a 
conservative representative sensitivity for each hearing group, the 
highest measured sensitivity, lowest threshold (behavioral or AEP), per 
frequency per species should be assessed. Commenters indicated that 
this would be a more cautionary approach than relying on the mean.
    Response: NMFS does not disagree that audiograms from individuals 
of the same species may be correlated but disagrees with the 
recommendation to collapse available audiograms, so that there is only 
one per species. Employing this recommendation would further reduce 
already limited data sets (see Response to Comment 53 regarding 
pseudoreplication recommending a similar procedure and similar issue 
with data limitations) For NMFS' response relating to the use of AEP 
data, see Response to Comment 43, and for our response regarding 
relying on the lowest threshold, see Response to Comment 49. NMFS 
believes that the Guidance's current approach maximizes the use of the 
best available science.
    That said, based on this comment, NMFS re-evaluated AEP data 
available for consideration in the development of composite audiograms. 
The inclusion of AEP resulted in only minimal changes to the composite 
audiogram (i.e., majority of AEP audiogram data had equal, if not 
higher thresholds, than those collected by behavioral methods, which 
would only result in a less conservative composite audiogram).
    Comment 52: Based on Wright 2015, commenters recommended that NMFS 
develop marine mammal auditory weighting functions based on envelope 
functions, which incorporate all available audiogram points. 
Additionally, these same commenters objected to NMFS' comparison 
between the Guidance's weighting functions and inverted audiograms 
(i.e., Guidance's weighting functions are broader than inverted 
audiograms that have been suggested). The commenters stressed that 
inverted audiograms have only been recommended for individual species 
and not entire hearing groups.
    Response: NMFS disagrees with this recommendation (See Response to 
Comment 49). As far as comparing the Technical Guidance's weighting 
functions to inverted audiograms, NMFS agrees that the comparison to 
inverse audiograms may not have been applicable and removed it from the 
Technical Guidance. Nevertheless, the point that the Technical Guidance 
auditory weighting functions are broader than the corresponding hearing 
group's composite audiogram, as well as any audiogram associated with 
an individual species, is still valid.
    Comment 53: Pseudoreplication was highlighted as a significant 
deficiency of the Guidance by several commenters. It was recommended 
that NMFS evaluate TTS on a species-by-species basis, rather than on an 
individual basis.
    Response: NMFS understands the concerns regarding 
pseudoreplication. However, marine mammal hearing and noise-induced 
hearing loss data are limited, not only in the number of species but 
also in the number of individuals available. Unfortunately, any means 
of minimizing pseudoreplication would further reduce these already 
limited data sets. Specifically, with marine mammal behavioral TTS 
studies, behaviorally-derived data are only available for two MF 
cetacean species (i.e., bottlenose dolphin, beluga) and two PW pinniped 
species (i.e., harbor seal and northern elephant seal), with OW 
pinnipeds and HF cetaceans only having behaviorally-derived data from 
one species. Thus, NMFS believes that the current approach makes the 
best use of the given data (See Response to Comment 72 for more 
information on the inclusion of available TTS data). Appropriate means 
of reducing pseudoreplication may be considered in the future, if more 
data become available.
    Comment 54: Several commenters requested that a list of data gaps 
and research recommendations should be included in the Guidance to 
inform funding groups and the research community of critical data 
needs.
    Response: NMFS agrees and has identified several data gaps and 
added a Research Recommendations Appendix (B) to the Technical 
Guidance.
Low-Frequency Cetacean Hearing and Auditory Weighting Functions
    Comment 55: Several commenters questioned the justification for

[[Page 51708]]

expanding the upper hearing limit of LF cetaceans beyond that proposed 
in Southall et al. (2007) in the 2013 Draft Guidance (i.e., 22 kHz to 
30 kHz).
    Response: NMFS has replaced the use of functional hearing range 
with generalized hearing range, which is derived based upon more 
consistent methodology (See Response to Comment 40).
    Comment 56: One commenter indicated that recent data suggest that 
within the LF cetacean hearing group, new divisions are appropriate to 
consider (e.g., Ultra Low: blue and fin whales; Low: bowhead and right 
whales; Low to Mid: humpback and gray whales; and Mid: minke whale 
groups).
    Response: NMFS acknowledges that as more data become available, 
marine mammal hearing ranges may warrant modification, or that it may 
be appropriate to divide LF cetaceans into subdivisions. However, NMFS 
does not believe there currently are enough data to support further LF 
cetacean divisions and subsequent auditory weighting functions, 
especially since so little direct information on hearing is available 
for this hearing group.
    Comment 57: Several commenters questioned the sufficiency of data 
to support the LF cetacean auditory weighting function provided in 
various versions of the Draft Guidance. Some recommended using the M-
weighting function provided by Southall et al. (2007) until more data 
could be collected or developing a LF cetacean weighting function based 
on the known low-frequency vocal range of this hearing group, ensuring 
that the weighting function encompasses ultra-low-frequencies (i.e., 
<30 Hz) used by blue and fin whales. One commenter further suggested 
that the LF cetacean weighting function be flat down to 0 Hz to ensure 
low-frequency sound does not compromise critical communication signals.
    Counter to those recommendations, other commenters expressed 
concern that the low-frequency slope parameter (``a'' parameter) of the 
LF weighting function (i.e., 20 dB/decade) was not scientifically 
supportable and should be more reflective of mammalian data (30 to 40 
dB/decade). Furthermore, the selection of this parameter was criticized 
because it resulted in an exposure function that predicts an 
unrealistically low-frequency hearing (80 dB threshold above best 
hearing occurring well below 1 Hz; e.g., only a -26 dB weighting 
function amplitude at 10 Hz), which is not reflective of what is known 
about other low-frequency specialist mammals, like humans and kangaroo 
rats. Additionally, these same commenters commended NMFS for not using 
vocalizations, especially frequencies associated with blue and fin 
whales, as a direct means for deriving the LF cetacean predicted 
audiogram.
    Finally, NMFS received a comment from a group of subject matter 
experts offering information on ambient noise levels below 2 kHz from 
Clark and Ellison (2004) as additional scientific justification for the 
LF cetacean weighting function contained in the March 2016 Proposed 
Changes.
    Response: NMFS acknowledges the limited data predicting LF cetacean 
hearing sensitivity but disagrees that utilizing the M-weighting 
functions from Southall et al. (2007) or creating a weighting function 
that is flat to 0 Hz reflects the best available science. Via the 
Technical Guidance public comment and peer review processes, NMFS 
determined that the methodology in the March 2016 Proposed Changes 
document best reflects the currently available data for deriving marine 
mammal auditory weighting/exposure functions, including those methods 
to derive surrogate parameters for LF cetaceans.
    Regarding the appropriateness of using vocal range to establish 
weighting functions, see Response to Comment 45. As for the frequencies 
used by fin and blue whales, NMFS acknowledges that the weighting 
function amplitude is >-16 dB at frequencies below 30 Hz. However, 
predicted hearing sensitivity for LF cetaceans based on ambient noise 
levels from Clark and Ellison (2004) offer additional scientific 
support to NMFS' weighting function below 2 kHz (for direct comparison 
to the 2016 LF cetacean weighting function see: https://www.regulations.gov/#!documentDetail;D=NOAA-NMFS-2013-0177-0155). 
Additionally, Cranford and Krysl (2015) predicted that since low-
frequency sound propagates further than those containing higher 
frequencies, this might explain the potential mismatch between the 
frequencies associated with best hearing and vocalizations for LF 
cetaceans. Furthermore, creating a weighting function to ensure 
communication signals are not compromised is beyond the scope of this 
document (the Technical Guidance weighting functions are meant to 
reflect a hearing group's susceptibility to noise-induced hearing 
loss).
    As for the low-frequency slope associated with the LF cetacean 
weighting function, NMFS believes it is reflective of currently 
available predictive data for this hearing group. For example, 
predictive audiograms based on anatomical modeling for minke whale 
(Tubelli et al., 2012), fin whale (Cranford and Krysl 2015), and 
humpback whale (Houser et al., 2001) all indicate this hearing group 
may have a shallower low-frequency slope compared to other terrestrial 
and marine mammals. Specifically, Tubelli et al. (2012) offers that the 
``extra'' 20 dB difference in the low-frequency slope between other 
cetaceans (HF and MF cetaceans) may be a result of the inner ear 
anatomy of this hearing group (i.e., open auditory bulla and the 
resulting pressure differences along the ``glove finger''). Finally, 
ambient noise levels with slopes ~20 dB/decade support the predicted 
low-frequency slope for this hearing group (Wenz 1962).
    Comment 58: Multiple commenters indicated the LF cetacean exposure 
function's ``K'' parameter, which the commenters classified as a metric 
of dynamic range, was arbitrary and inappropriately based on data from 
a beluga and a harbor porpoise for impulsive sounds.
    Response: NMFS disagrees with the commenters' classification of the 
exposure function's ``K'' parameter as a metric of dynamic range and 
the criticism. This parameter is set to match the weighted threshold 
for TTS or PTS onset based on available data in the SELcum 
metric (i.e., NMFS' dynamic range methodology is for deriving PK 
thresholds; See Response to Comment 87). NMFS agrees that for impulsive 
sounds, TTS data are extremely limited (i.e., beluga data from Finneran 
et al. (2002) and harbor porpoise data from Lucke et al. (2009)). 
Nevertheless, the methodology for establishing a surrogate value for 
this parameter for hearing groups where no data are available is 
consistent with the derivation of other surrogate parameters within the 
Technical Guidance.
    Comment 59: Numerous commenters, including the Commission, 
identified an inconsistency in how NMFS derived the ``F2'' parameter, 
which predicts the high-frequency portion of the composite audiogram 
for LF cetaceans. Specifically, this parameter was adjusted to achieve 
a threshold at 30 kHz of 40 dB relative to the lowest threshold. 
However, in earlier discussions of the low-frequency parameter ``F1,'' 
the March 2016 Proposed Changes document mentioned predictive modeling 
of LF cetacean hearing indicating 40 dB of best sensitivity occurring 
at ~25 kHz (i.e., not 30 kHz). Commenters were unclear if this was an 
error or if 30 kHz was chosen deliberately and if so, why.
    Response: NMFS acknowledges the potential for confusion and chose 
to

[[Page 51709]]

adjust the ``F2'' parameter to achieve a threshold value at 30 kHz of 
40 dB relative to the lowest threshold as a means to account for 
uncertainty associated with this hearing group and to avoid too gradual 
of a cutoff at the high-frequency end (i.e., decision to adjust 
parameter at 30 kHz vs. 25 kHz). Additional text was added to the final 
Technical Guidance for more clarity on this decision.
    Comment 60: Numerous commenters criticized the potential for 
``takes''/isopleths/mitigation ranges to increase dramatically based on 
updated weighting functions/thresholds for LF cetacean hearing group 
(i.e., comparison between 2015 Draft Guidance and 2016 Proposed Changes 
document).
    Response: NMFS acknowledges that the LF cetacean predicted 
weighting function and PTS onset thresholds in the 2016 Proposed 
Changes document/Technical Guidance are more conservative than those 
presented in the 2015 Draft Guidance. However, in our judgement, the 
changes reflect the best available science and account for uncertainty 
associated with this particular hearing group where data are limited. 
In response to how the Technical Guidance could impact mitigation 
ranges, see Response to Comment 11.
Mid- and High-Frequency Cetacean Hearing and Auditory Weighting 
Functions
    Comment 61: Multiple commenters indicated that the Guidance's 
auditory weighting functions do not represent the hearing sensitivities 
of all included species, indicating that bottlenose dolphins are not 
appropriate surrogates for killer whales or sperm whales, which are 
known to have regions of greatest hearing sensitivities at much lower 
frequencies, and that harbor porpoises and finless porpoise may not 
represent the auditory ability of Irrawaddy, Ganges River, Commerson's, 
and Peale's dolphins.
    Response: See Response to Comment 45. In the Guidance, a broader 
range of species were considered in the development of the MF auditory 
weighting function via the composite audiogram. Specifically, for MF 
cetaceans, the composite audiograms are derived from data compiled from 
eight species (bottlenose dolphins, beluga, false killer whale, Risso's 
dolphin, striped dolphin, and tucuxi) and 22 individuals of these 
species, of which only six individuals are bottlenose dolphins. 
Further, two individuals of these are killer whales, which from these 
available audiogram data indicate thresholds consistent with other MF 
cetaceans (i.e., current audiograms do not indicate this species has 
better low-frequency hearing than other MF cetaceans). Currently, there 
are no direct measurements available on sperm whale hearing (only an 
incomplete audiogram exists for a stranded sperm whale neonate from 
Ridgway and Carder (2001)). NMFS considers sperm whale placement within 
MF cetaceans appropriate based on Ketten (2000), which classified sperm 
whales as having Type I cochlea, similar to other MF cetaceans and 
considers the MF cetacean auditory weighting function representative of 
all species within this hearing group based on the best available 
science.
    For HF cetaceans, composite audiograms are derived from more 
limited data (i.e., four individuals from two species: harbor porpoise 
and Amazon River dolphin; AEP data are only available for Yangtze 
finless porpoise). Thus, it is unclear how these two species represent 
others in this hearing group, since no other data are available (i.e., 
no data on hearing ability of Irrawaddy, Ganges River, Commerson's and 
Peale's dolphins). The need for additional audiograms, particularly 
from the HF cetacean hearing group was added as a Research 
Recommendation (Appendix B) in the Technical Guidance.
    Comment 62: One commenter noticed an error in the audiograms used 
to construct the composite audiogram for HF cetacean in the July 2015 
Draft Guidance. They indicated that the harbor porpoise audiogram by 
Kastelein et al. (2002), was later revised due to a problem with the 
analysis of the sound stimuli, with the correct audiogram found in 
Kastelein et al. (2010). Thus, it is recommended that NMFS use the 2010 
data, instead of the 2002 data.
    Response: NMFS re-evaluated the data used to construct the 
composite audiogram for HF cetaceans and confirmed the assertion made 
by the commenter that the wrong data set was initially used. This error 
has been corrected for in the final Technical Guidance.
    Comment 63: Several commenters, including the Commission, were in 
support of moving the white-beaked dolphin from MF cetaceans to HF 
cetaceans.
    However, numerous other commenters indicated that moving this 
species to a new hearing group was not scientifically supported. The 
Navy specifically recommended that this species remain in the MF 
cetacean hearing group based upon the following scientific support: (1) 
A hearing threshold comparison between white-beaked dolphin (Nachtigall 
et al., 2008), bottlenose dolphin (Johnson 1967), and harbor porpoise 
(Kastelein et al., 2002; Kastelein et al., 2010) indicating white-
beaked dolphin do not have significantly better high-frequency hearing 
than the bottlenose dolphin (for figure depicting comparison see: 
https://www.regulations.gov/#!documentDetail;D=NOAA-NMFS-2013-0177-
0152); (2) white-beaked dolphin echolocation are more similar to those 
of bottlenose dolphins (i.e., resembling broadband, exponentially-
damped sinusoids containing only a few cycles; Au 1980; Rasmussen and 
Miller 2002) in contrast to echolocation emissions for harbor porpoises 
and other species placed into the HF cetacean hearing group (e.g., 
Cephalorhynchus sp., Lagenorhynchus australis) (i.e., more narrowband, 
longer in duration, and contain mostly high-frequency energy; Tougaard 
and Kyhn 2010); and (3) Ketten's (2000) categorization of the cochlea 
of white-beaked dolphin and bottlenose dolphin as ``Type II,'' while 
the harbor porpoise cochlea is categorized as ``Type I'' (i.e., 
reinforcing the idea that the white-beaked dolphin is acoustically 
more-closely related to the bottlenose dolphin than to porpoises).
    Response: Upon re-evaluation, NMFS concurs that based on currently 
available data, it is more appropriate for the white-beaked dolphin to 
remain in the MF cetacean hearing group. The scientific support to move 
this species from MF to HF cetaceans is not to the level of that of two 
other members of the genus Lagenorhynchus Peale's and hourglass 
dolphins. (Note: In the Navy's justification above, Ketten (2000) did 
not analyze white-beaked dolphin cochlea but instead Pacific and 
Atlantic white-sided dolphins (also members of the genus 
Lagenorhynchus)).
    Comment 64: The Commission supported NMFS' decision to include the 
newly published audiogram of a harbor porpoise (Kastelein et al., 2015) 
in the March 2016 Proposed Changes document. However, other commenters 
indicated that NMFS provided incomplete information on this dataset 
making it impossible to conduct a meaningful comparison to the July 
2015 Draft Guidance.
    Response: NMFS disagrees that incomplete information was provided 
in the March 2016 Proposed Changes document associated with the 
addition of a newly published harbor porpoise audiogram (Kastelein et 
al., 2015). The addition of this audiogram did not change the 
fundamental methodology associated with the Guidance (i.e., Appendix 
A), rather it only added a

[[Page 51710]]

newly available dataset, as will be the case as new data become 
available in the future.
Pinniped Hearing and Auditory Weighting Functions
    Comment 65: NMFS received a comment indicating that there are not 
enough data to establish two separate weighting functions for 
pinnipeds.
    Response: NMFS disagrees. There are audiogram data available from 
three species (eight individuals) of OW pinnipeds and four species 
(eight individuals) of PW pinnipeds. Further, based on NMFS' review of 
the literature, phocid species have consistently demonstrated an 
extended frequency range of hearing compared to otariids, especially in 
the higher frequency range. This is believed to be because phocid ears 
are anatomically distinct from otariid ears in that phocids have 
larger, more dense middle ear ossicles, inflated auditory bulla, and 
larger portions of the inner ear (i.e., tympanic membrane, oval window, 
and round window), which make them more adapted for underwater hearing. 
If one examines the composite audiograms for these two pinniped groups, 
distinct differences appear, supporting NMFS' decision to establish two 
distinct pinniped hearing groups.
    Comment 66: Numerous commenters questioned the justification for 
the removal of some of the pinniped datasets based on non-
representative hearing in the March 2016 Proposed Changes document. The 
commenters noted that masking is a common issue with obtaining 
audiogram data for animals in captivity and indicated that NMFS must 
provide a specific explanation for why these particular datasets 
contain unique masking problems that are unlike the other datasets used 
in the Guidance. An additional commenter requested NMFS provide the 
exact procedures as to how and why it removed unrepresentative or 
outlier data from its datasets and consider that one reason for 
unrepresentative data is due to exposure to anthropogenic sound. Other 
commenters, including the Commission, were in favor of removing these 
datasets.
    Response: Decisions to exclude data were based on comparison of the 
individual published audiograms and ambient noise characteristics with 
those for other individuals of the same or closely related species. The 
most common reasons for excluding an individual's data were abnormal 
audiograms featuring high-frequency hearing loss (typically seen in 
older animals) or ``notches'' in the audiogram, or data collected in 
the presence of relatively high ambient noise which resulted in 
elevated thresholds. Excluding these data ensured that the composite 
audiograms were not artificially elevated, which could result in 
unrealistically high impact thresholds. NMFS disagrees that previous 
exposure to anthropogenic sources is the basis for deeming the datasets 
unrepresentative, since currently available audiograms are derived from 
captive individuals (i.e., there is no indication that anthropogenic 
sound in captivity is directly impacting auditory thresholds, other 
than via possible masking).
    Comment 67: NMFS received several comments indicating that the 
proposed changes to the PW pinniped ``a'' parameter, which defines the 
slope of the low-frequency portion of the weighting function, were 
arbitrary and unsupported. Additionally, a commenter noted an 
inconsistency in this parameter (i.e., ``a'' parameter value provided 
did not seem to match what was depicted on the PW pinniped weighting 
function). Finally, the commenters criticized that the March 2016 
Proposed Changes document illustrated (Figure PC5) that the PW exposure 
functions was only based on one data point.
    Response: The PW pinniped ``a'' parameter is directly derived from 
PW pinniped behavioral audiograms (8 individuals of 4 species). 
Additionally, the 2016 Proposed Changes document removed 
unrepresentative datasets, which resulted in a steeper slope (``a'' = 
1.0) compared to the 2015 Draft Guidance (``a'' = 0.8).
    Upon re-evaluation, NMFS agrees that there was a slight discrepancy 
with the ``a'' parameter depicted in the weighting function provided 
for PW pinnipeds in the March 2016 Proposed Changes document. This has 
been remedied with the correct value portrayed for this hearing group's 
auditory weighting function.
    Finally, the March 2016 Proposed Changes document (Figure PC5) 
illustrates available TTS data for all hearing groups. NMFS agrees that 
data are limited particularly for PW pinnipeds (i.e., two TTS onset 
data points). Nevertheless, it should be noted that the exposure/
weighting functions are not merely based on TTS onset data but also 
incorporate available audiogram data each for hearing group.
    Comment 68: A commenter questioned if there was an error in 
Appendix A, specifically with the best-fit parameters associated with 
the derivation of the composite audiogram (original and normalized 
data) for PW pinnipeds in Table A4. These tables indicate an unusually 
high ``F1'' value (excess of 300 kHz) and an anomalous 
``T0'' value of negative decibels.
    Response: Upon re-evaluation, NMFS determined that the best-fit 
parameters for PW are not anomalous or in error. These parameters 
mentioned by the commenter are merely fitting parameters for equation 9 
in Appendix A and do not directly correspond to a particular feature of 
the audiogram (i.e., F1 does not represent the frequency at which the 
audiogram reaches a specific value). The value for F1 
influences the frequency at which thresholds begin to plateau near the 
best sensitivity. Very large values for F1 (and the 
accompanying small value for T0) simply reflect little or no 
plateau in the thresholds in the region of best sensitivity. In many 
respects, the specific numeric values applied to Equation 9 in Appendix 
A of Technical Guidance are not key; what matters are the resulting 
shapes of the composite audiograms and how well they match the 
underlying threshold data.
    Comment 69: One commenter suggested that the two species of PW 
pinnipeds (i.e., harbor seal and northern elephant seal) mentioned in 
the Guidance are commonly found in close proximity to human population 
centers and are not good proxies for Arctic and Antarctic seals.
    Response: The Technical Guidance relies on more data than from 
harbor seal and northern elephant seal. Additionally data from two 
Arctic species (spotted seal from Sills et al. (2014) and ringed seal 
from Sills et al. (2015)) were used to derive composite audiogram for 
PW pinnipeds. Thus, data from four different PW pinniped species were 
used to derive composite audiograms for this hearing group. NMFS 
believes currently available data are representative of all PW 
pinnipeds, including polar species.
Application of Auditory Weighting Functions
    Comment 70: One commenter requested that NMFS provide additional 
clarification as how the auditory weighting functions were applied to 
the data used to develop acoustic thresholds (e.g., were the auditory 
weighting functions applied to the entire raw data before calculating 
the SELcum) and examples of software that could be used to 
apply these weighting functions.
    Response: Marine mammal auditory weighting were directly 
incorporated in the derivation of thresholds associated with non-
impulsive sounds and then were directly applied in the derivation of 
impulsive thresholds, since only limited data are available (Details in

[[Page 51711]]

Appendix A). Section 2.2.4 of the Technical Guidance (Main Document) 
provides more detail on how to implement/apply these weighting 
functions. For a source consisting of a single tone, the application of 
auditory weighting functions is a straight forward process (i.e., only 
single frequency to consider). For broadband sounds, the application is 
more complicated (i.e., must consider multiple frequencies), which is 
why NMFS included alternative weighting factor adjustments for when 
frequency weighting functions cannot be fully incorporated (Appendix 
D).
    Comment 71: One commenter noted that the LF cetacean acoustic 
thresholds do not appear to be adjusted based on the LF cetacean 
auditory weighting functions and asked whether the threshold for LF 
cetaceans exposed to an airgun/watergun with most of its energy in 
their primary hearing band as measured in the experiment should be 
adjusted.
    Response: Marine mammal TTS data for impulsive sources exist only 
for two hearing groups (i.e., MF and HF cetaceans). For other groups, 
alternative methodology was developed using MF and HF cetaceans as 
surrogate data and assuming the relationship between impulsive and non-
impulsive thresholds is conserved among hearing groups (i.e., 
methodology resulted in a TTS onset threshold for impulsive sources 
that is 11 dB lower than the TTS threshold onset for non-impulsive 
sources). NMFS disagrees that any adjustment needs to be made to the LF 
cetacean acoustic thresholds. Weighting functions are also implemented 
in exposure modeling, which will take into account whether or not a 
sound falls within a hearing group's most susceptible frequency range.
    Comment 72: A few commenters indicated that Tougaard et al. (2013) 
note that auditory weighing functions cannot themselves be 
``conservative'' if applied in establishing and then implementing 
acoustic thresholds. To achieve a conservative approach, the commenters 
suggested the application of a more tailored function at the acoustic 
threshold determination stage in combination with a wider and more 
energy-inclusive function at the implementation stage. The commenters 
suggested that NMFS use a function normalized to a lower level (e.g., -
3 dB) for establishing acoustic thresholds, while using functions 
normalized to a higher level (e.g., 0 dB) for estimating the number of 
``takes'' when implementing these thresholds. The commenters provided 
the example that JASCO Applied Sciences typically incorporates a 3-dB 
precautionary adjustment in their propagation modeling to account for 
uncertainty.
    Response: The Technical Guidance explains that auditory weighting 
functions are considered within both the data evaluation and 
implementation processes, as pointed out by Tougaard et al. (2013) (now 
published Tougaard et al., 2015). NMFS acknowledges that adjustments 
during the data evaluation process that result in a lower threshold 
could potentially translate to smaller isopleths, if a source has 
energy in frequencies outside a hearing groups most susceptible hearing 
range (i.e., weighting functions are essentially filters; their 
application results either in the same size or in smaller isopleths or 
the same or lower thresholds). Tougaard et al. (2015) provide some 
important factors for consideration when applying weighting functions 
in both the context of data evaluation and implementation. However, 
NMFS does not find it appropriate to normalize the Technical Guidance's 
acoustic thresholds, as suggested by the commenters, as there are no 
data to support doing so. Further, several conservative assumptions 
were applied to the derivation of acoustic thresholds to account for 
uncertainty and limited data (see Response to Comment 77). Finally, 
NMFS' application of auditory weighting functions is consistent with 
what has been done for humans (i.e., A-weighted thresholds used in 
conjunction with A-weighting during implementation).
    As for the 3-dB adjustment JASCO Applied Sciences makes to the 
results of their propagation models, this adjustment is based on their 
best fit analysis, where 90 percent of all their measured values fall 
within 3 dB of the mean level (e.g., see any recent SSV reports from 
JASCO Applied Sciences, like Beland et al. (2013), for more details). 
NMFS used this same premise to re-examine the TTS onset thresholds for 
non-impulsive sources for data collected via both the preferred 
behavioral technique as well as AEP methodology, the next tier in our 
data hierarchy (the same analysis could not be done for impulsive 
sources, where data are limited to two studies). It was found that for 
all hearing groups, except PW pinnipeds, the TTS onset thresholds 
encompassed more than 90 percent of available TTS data (MF cetaceans, 
only two points below the onset threshold, with maximum point only 2 dB 
below), and in some situations 100 percent of TTS data (i.e., OW and HF 
cetaceans; although both these groups are data limited). For PW, which 
are also data limited, only one of the five available data points was 
below the TTS onset threshold (i.e., 1 dB below the threshold). Thus, 
NMFS believes any further adjustments to the thresholds are unnecessary 
and that they provide realistic predictions, based on currently 
available data, of noise-induced hearing loss in marine mammals.
Temporary Threshold Shifts
    Comment 73: One commenter cautioned that a 6 dB threshold shift may 
be appropriate for testing TTS but should not be confused with the 
level that is biologically important (e.g., 6 dB corresponds to a 
roughly 8-fold decrease in the volume in which biologically significant 
sounds can be detected through passive listening).
    Response: The Technical Guidance considers a threshold shift of 6 
dB the minimum threshold shift clearly larger than any day-to-day or 
session-to-session variation in a subject's normal hearing ability and 
is typically the minimum amount of threshold shift that can be 
differentiated in most experimental conditions (Schlundt et al., 2000; 
Finneran et al., 2000; Finneran et al., 2002). Similarly, for humans, 
NIOSH (1998) regards the range of audiometric testing variability to be 
approximately 5 dB. Because the Technical Guidance does not address the 
biological significance of passive listening, NMFS has set the onset of 
TTS at the lowest level that exceeds recorded variation and could be 
considered biologically significant.
    Comment 74: One commenter noted that the Guidance appeared to use 
temporary threshold shift (TTS) when it may mean threshold shift (TS) 
and suggested that NMFS use terms consistently and clearly.
    Another commenter requested the Guidance make clear that a 
threshold shift is a symptom of noise exposure rather than an impact 
(i.e., a manifestation of an anatomical alteration that deters or 
eliminates auditory responses). The commenter emphasized that 
impairments arise from other acoustic features associated with what the 
ear receives (i.e., not necessarily characteristics associated with the 
source), and there are multiple components to any received sound (e.g., 
received level, timing, intensity, sensitivity, time course, recovery 
period), all of which may act singly or in concert to impact an ear at 
any frequency and for any species, whether in air or water. As such, 
the commenter suggested the Guidance include a brief statement 
indicating the choice of using a threshold shift to assess the effects 
of noise on hearing is one driven by practicality (i.e., Guidance does 
not address all critical features associated

[[Page 51712]]

with impacts from sound, but there is an awareness and expectation that 
other features require investigation and that these may ultimately 
alter the thresholds according to their interplay and relative 
potential for harm).
    Response: NMFS has revised the Technical Guidance to clearly 
distinguish between a threshold shift (temporary or permanent) as a 
term which indicates the increase in threshold of audibility (i.e., 6 
dB for onset of TTS and 40 dB for onset of PTS) versus the exposure 
level (i.e., acoustic threshold) associated with that shift.
    NMFS agrees that a threshold shift is a ``symptom'' rather than an 
``impact.'' However, in the context of the Technical Guidance and in 
terms of how the acoustic thresholds will be used, the term/concept of 
``impact'' is one that readers of the document will be more familiar 
with. NMFS also agrees that features of the signal at the receiver are 
most important, but are often most difficult to determine. The 
Technical Guidance includes more information explaining when choices 
are based on considerations of practicality because of complexity and 
makes various research recommendations to address these issues 
(Appendix B).
    Comment 75: Several commenters requested clarification on the 
application of TTS onset acoustic thresholds presented in the Guidance 
under NMFS' relevant statutes, including the Commission, which 
recommended all applicants be required to use the Guidance's TTS onset 
thresholds. The Commission requested further clarification on how the 
Guidance's TTS thresholds are to be implemented in conjunction with 
NMFS' generic RMS SPL 120/160 dB behavioral thresholds.
    Response: The Technical Guidance sets forth the levels at which TTS 
and PTS onset are likely to occur. In this Federal Register Notice 
(Regulatory Context), we describe our current agency practice for 
assessing take and refer readers to that section (this information 
previously appeared in the Draft Guidance Regulatory Context section). 
In short, PTS onset is treated as Level A harassment under the MMPA and 
harm under the ESA (as well as injury under NMSA as administered by 
NOS' National Marine Sanctuary Program), and NMFS recommends using the 
Technical Guidance to estimate take from PTS exposures in regulatory 
compliance documents.
    Regarding TTS, with the exception of underwater explosives (see 
Regulatory Context), NMFS does not currently recommend calculations of 
TTS exposures separate from assessments of Level B harassment or ESA 
harassment using the prior existing thresholds for enumerating 
behavioral takes. NMFS is in the process of evaluating behavioral 
effects thresholds and intends to develop related guidance for use in 
its regulatory processes. Because the effects in consideration when TTS 
is incurred are behavioral and temporary in nature, much like 
behavioral responses, we intend to address those effects in the context 
of regulatory compliance at that time.
    Comment 76: Multiple commenters indicated an inconsistency in the 
Guidance in the characterization of TTS among NOAA's various statutes 
(i.e., NMFS collectively does not consider TTS an auditory injury, but 
TTS is considered injury under the broad definition of the NMSA) and 
suggested NOAA implement a consistent regulatory interpretation of the 
term injure when addressing acoustic exposures on marine mammals.
    Response: The Guidance is a technical document that compiles, 
interprets, and synthesizes the scientific literature, to produce 
updated, scientifically-based, impact thresholds for assessing the 
effects of noise on hearing. Although these changes may necessitate new 
methodologies for calculating impacts, the application of the 
thresholds under applicable statutes remains consistent with past and 
current NMFS practice. See Regulatory Context section in this Federal 
Register Notice. That information was moved out of the main body of the 
Guidance to emphasize the distinction between the scientific exercise 
of developing updated thresholds, which is science-based, and the 
application of thresholds in the regulatory arena, which is also 
informed by policy and legal considerations.
    Comment 77: Multiple commenters recommended that NMFS consider 
threshold shifts requiring extended recovery periods (e.g., in excess 
of 24 hours), as well as nerve and other related damage, to be included 
in the definition of injury. The commenters expressed concern that NMFS 
did not consider the results of Kujawa and Liberman (2009) and Lin et 
al. (2011), and suggested the Guidance state that the PTS acoustic 
thresholds will be conservatively revised in the future to reflect any 
new evidence showing correlations of injurious effects of TTS below 
these new acoustic thresholds.
    Response: NMFS recognizes this is an area where additional study is 
needed. NMFS has included several conservative assumptions in its 
protocol for examining marine mammal hearing loss data (e.g., using a 6 
dB threshold shift to represent TTS onset, not directly accounting for 
exposure levels that did not result in threshold shifts, assuming there 
is no recovery with the 24-h baseline accumulation period or between 
intermittent exposures, etc.).
    The Technical Guidance includes information from Kujawa and 
Liberman (2009) and Lin et al. (2011) as a way to illustrate the 
complexity associated with noise-induced hearing loss and as an area 
where more research is needed (Appendix B). NMFS finds that these 
studies would be informative for use as qualitative considerations 
within the comprehensive effects analysis. NMFS acknowledges the 
complexity of sound exposure on the nervous system, and will re-examine 
this issue as more data become available.
    Comment 78: One commenter indicated that in Germany, TTS is 
considered the onset of injury. The commenter suggested that since many 
countries may adopt this Guidance rather than developing their own, 
NMFS make clear that choosing PTS as onset for injury is based on U.S. 
legal considerations.
    Response: This Federal Register Notice contains a section 
explaining the current U.S. regulatory context for using the acoustic 
thresholds contained in the Technical Guidance.
    Comment 79: Several commenters indicated that chronic, repeated 
exposures to levels capable of inducing TTS can lead to PTS and 
recommended that NMFS consider cumulative effects of all anthropogenic 
sound sources in terms of long-term exposure in the development of the 
Guidance's acoustic thresholds, as well as within the context of NEPA. 
Specifically, it was suggested that, apart from the accumulation time 
applied to any single activity (i.e., acoustic thresholds), NMFS add 
repeated, intermittent exposure to multiple acoustic activities to its 
table of ``qualitative factors for consideration.''
    Response: NMFS acknowledges that cumulative effects and long-term 
exposure of noise are important considerations in understanding the 
impacts of sound on marine mammals and that repeated exposures 
initially resulting in TTS have the potential to result in PTS. 
However, they are beyond the scope of this document, in terms of 
developing quantitative acoustic thresholds and are being considered by 
other mechanisms within or supported by NOAA (e.g., NOAA Ocean Noise 
Strategy and CetSound Projects; National Research Council's Ocean 
Studies Board's Cumulative Effects of Human Activities on Marine Mammal 
Populations Study). The Technical Guidance focuses on acute exposures 
to

[[Page 51713]]

noise and threshold shifts associated with these types of exposures. 
Additionally, the TTS data currently available for marine mammals only 
support deriving thresholds for these types of short-term exposures, 
rather than long-term/chronic exposure. Having data to address more 
realistic exposure scenarios, including repeated exposures, have been 
identified within our Research Recommendation Appendix (Appendix B).
    NMFS has added cumulative exposures to its recommended qualitative 
factors to consider within a comprehensive effects analysis. The 
discussion of qualitative factors has been moved from the main Guidance 
document to Appendix B (See Response to Comment 130).
    Comment 80: One commenter recommended that since seismic activities 
do not cause PTS and TTS ``during realistic field conditions,'' there 
is no need to apply the new PTS and TTS acoustic thresholds levels in 
the Guidance to these activities.
    Response: NMFS notes that the only marine mammal TTS data available 
are from laboratory studies, and that there are no TTS data available 
for any sound source in more realistic field conditions. Nevertheless, 
marine mammal laboratory studies offer vital information on exposure 
situations that can result in noise-induced threshold shifts, and NMFS 
used this information to establish acoustic thresholds for free-ranging 
animals exposed to anthropogenic sound sources in their natural 
environment. NMFS is not aware of any evidence to indicate that seismic 
sound sources should be treated differently than any other 
anthropogenic sound source.
Uncertainty and Statistical Analyses Associated With Temporary 
Threshold Shift Data
    Comment 81: Several commenters suggested that where a potential for 
uncertainty exists NMFS should proceed cautiously and consider 
adjustments to thresholds that are most protective of the animals. One 
commenter specifically urged NMFS to consider the precautionary 
principle within the Guidance and NOAA's need to comply with its own 
statutes.
    Response: The Technical Guidance identifies areas of uncertainty 
and data limitations (Appendix A) and has made several conservative 
assumptions to account for this (e.g., defining TTS onset as the level 
just above where individual variability in hearing occurs, not 
accounting for exposures where TTS onset did not occur, etc.). See 
Response to Comment 49 for more details on the issue of uncertainty. 
Additionally, a Research Recommendations section has been added to 
identify data gaps (Appendix B). As more data become available, NMFS 
can explore more sophisticated means of analysis.
    As previously indicated, the acoustic thresholds do not represent 
the entirety of an effects analysis, but rather serve as one tool to 
help evaluate the effects of a proposed action and make findings 
required by NOAA's various statutes. Further, other measures can be 
employed to account for uncertainty beyond considerations within the 
Technical Guidance (e.g., mitigation/monitoring requirements).
    Comment 82: Multiple commenters recommended that the procedures for 
establishing acoustic thresholds be revised to use the lowest available 
value or correction factor to account for the full representation of 
the distribution of TTS/PTS onset in a population rather than using the 
median value if five or more data points are available. Specifically, 
commenters expressed concern that NMFS is producing a threshold closer 
to the population mean (i.e., the point at which the first ``take'' is 
estimated to occur is roughly 50 percent of any given population will 
have already experienced a threshold shift) by relying on the median 
value. These commenters suggested that NMFS investigate statistical 
methods that deal with probabilities and distributions (e.g., Bayesian 
statistics), which particularly account for individual variability and 
uncertainty over the mean of threshold shift onset. These commenters 
further indicated that these statistical methods or a simple less 
precise alternative where the lowest reported TTS onset value was 
always selected (instead of the median) would likely provide a more 
appropriate estimation of TTS/PTS onset for a given proportion of the 
population.
    Contrary to the comments above, another commenter cautioned against 
relying on the lowest onset with limited data because these data could 
be outliers and result in overly conservative acoustic thresholds. The 
commenter further indicated that overly conservative thresholds could 
result in unrealistic exposure estimates and suggested NMFS' protocol 
be modified to examine the distribution of the data and make a reasoned 
decision about whether the lowest threshold might be an outlier and 
whether (and how) it should be included in the determination of a 
threshold.
    Response: NMFS incorporated several conservative assumptions into 
the derivation of the acoustic thresholds to account for uncertainty 
and variability (see Response to Comment 77). The comment's reference 
to use of a median value if five or more data points are available 
refers to proposed methodology from the 2013 Draft Guidance. The 2015 
Draft Guidance contained updated methodology for deriving TTS/PTS onset 
acoustic thresholds which better account for available marine mammal 
data (see Response to Comment 72).
    NMFS used the best available science to develop the Technical 
Guidance. As more data are collected, NMFS will be better able to 
identify outliers (e.g., one individual has an unusually high or low 
threshold or testing procedures led to flawed results) and consider 
necessary adjustments (i.e., removal of an outlier datum).
    Comment 83: Multiple commenters expressed concern associated with 
the Guidance's low acoustic thresholds for the HF cetacean hearing 
group. Specifically, the commenters indicated that for impulsive sound, 
the thresholds are based on data from a single study involving a single 
animal (harbor porpoise) (Lucke et al., 2009), and for non-impulsive 
sound, the threshold is based on a single study involving only two 
animals (Popov et al., 2011). The commenters remarked that both studies 
have potential biases and uncertainty and urged NMFS to allow for 
flexibility in the implementation of acoustic thresholds in future 
regulatory processes.
    Response: NMFS acknowledges that, for most hearing groups, data are 
available only from a limited number of species and a limited number of 
individuals within that species. The need for more data from all 
species is highlighted in the newly added Research Recommendation 
section of the Technical Guidance (Appendix B).
    In addition, new data have become available since the NMFS received 
this comment during the first public comment period. As indicated in 
the Technical Guidance, the acoustic threshold (SELcum 
metric) for HF cetaceans exposed to non-impulsive sound was derived 
using data from three studies (i.e., Kastelein et al., 2012, Kastelein 
et al., 2014a, and Kastelein et al., 2014b, not Popov et al., 2011a, 
which did not derive TTS onset and relied on AEP methodology). These 
new studies support results from Lucke et al. 2009 indicating that 
harbor porpoises have a lower TTS onset than other cetaceans (i.e., 
reason for separating MF and HF cetaceans into separate hearing 
groups).
    NMFS recognizes that acoustic thresholds for HF cetaceans, which 
are based exclusively from harbor porpoise

[[Page 51714]]

data, are much lower than other hearing groups, and therefore some 
additional considerations may be warranted on a case-by-case basis. 
However, it also should be noted that auditory weighting functions 
should be considered when evaluating impacts of sound on HF cetaceans, 
which are most susceptible to injury from higher frequency sounds 
(e.g., 25 to 60 kHz).
    Comment 84: Multiple commenters recommended a precautionary 
approach (i.e., more conservative thresholds) when applying the 
Guidance to activities and species in the Arctic.
    Response: NMFS recognizes that marine mammals in the Arctic are 
experiencing increasing pressures from human activities (e.g., climate 
change, increased commercial activities). However, NMFS does not find 
that there are data to indicate greater susceptibility of Arctic 
species to noise-induced hearing loss compared to non-Arctic species. 
Data from two Arctic species (spotted seal from Sills et al., 2014 and 
ringed seal from Sills et al., 2015) were used to derive composite 
audiograms for PW pinnipeds. Additionally, measured underwater hearing 
of two captive spotted seals (Sills et al., 2014) and two captive 
ringed seals (Sills et al., 2015) found these species' hearing 
abilities are comparable to harbor seals. Thus, harbor seals (i.e., 
only phocid with TTS data are available) are believed to be an 
appropriate surrogate for ice seal species.
    Further, audiogram data from belugas (n=9; more individuals of this 
species than any other) were specifically used to derive composite 
audiograms for MF cetaceans. In addition, recent data from Castellote 
et al. (2014), from free-ranging belugas in Alaska, indicate of the 
seven individuals tested (3 females/4 males; 1 subadult/6 adults), all 
had hearing abilities ``similar to those of belugas measured in 
zoological settings.'' Thus, from this study, it appears that for 
baseline hearing measurements, captive individuals are an appropriate 
surrogate for free-ranging animals. The Technical Guidance also 
incorporates TTS data (i.e., TTS onset and TTS growth rate) are 
available from four individual belugas (e.g., Schlundt et al., 2000; 
Popov et al., 2014)
    Thus, data from Arctic species are directly incorporated into 
numerous aspects of the Technical Guidance's methodology. These data 
indicate additional conservative adjustments in determining thresholds 
unnecessary. Precautionary adjustments may be made elsewhere (e.g., 
applied in a specific regulatory context of fully evaluating effects, 
authorizing, and developing mitigation for an action).
Cetacean Temporary Threshold Shift Data
    Comment 85: There was concerned expressed that the low TTS onset 
thresholds for HF cetaceans exposed to impulsive sources results from a 
AEP study, opposed to one using behavioral methods, and that this 
violates the methodology of only using behavioral data stipulated in 
Appendix A of the Guidance. Contrary to this comment, multiple 
commenters advocated for the inclusion of TTS data derived using AEPs 
into the Guidance's methodology.
    Response: As mentioned in earlier, NMFS established an informal 
data hierarchy in consideration of the development of the Technical 
Guidance's composite audiograms and acoustic thresholds (see Response 
to Comment 43), with the best-representative data being used over other 
sources. In the case of deriving TTS acoustic thresholds for HF 
cetaceans, only one dataset is currently available (Lucke et al., 
2009), which relies on AEP measurements. Appendix A specifically 
addresses this issue: ``Note that the data from Lucke et al. (2009) are 
based on AEP measurements and may thus under-estimate TTS onset; 
however, they are used here because of the very limited nature of the 
impulse TTS data for marine mammals and the likelihood that the high-
frequency cetaceans are more susceptible than the mid-frequency 
cetaceans (i.e., use of the mid-frequency cetacean value is not 
appropriate).''
    There have been limited comparisons of TTS data collected via 
behavioral versus AEP methods for any marine mammals, especially marine 
mammals. There is only one available marine mammal study (Finneran et 
al., 2007) that found threshold shifts of 40 to 45 dB associated with 
AEP methods and 19 to 33 dB thresholds shifts measured via behavioral 
methods. These two methodologies do not provide the same results (i.e., 
AEP methods consistently produce higher thresholds compared to 
behavioral techniques), and there is currently no accurate means 
available to ``correct'' AEP data so that it can be more comparable to 
those obtained via behavioral techniques.
    Comment 86: One commenter requested the Guidance provide additional 
clarification on the TTS PK acoustic threshold of 224 dB for MF 
cetaceans and suggested a 226 dB value be used instead, as is cited in 
Finneran et al. (2002).
    Response: NMFS notes the Guidance's MF cetacean TTS onset PK 
threshold is based on the pressure levels originally expressed as 
pounds per square inch (psi) presented in Finneran et al. (2002). This 
value was then converted from psi to peak pressure levels (i.e., 23 psi 
is equivalent to PK 224 dB). The PK 226 dB, referred to by the 
commenter, was a peak-to-peak pressure level and not a peak pressure 
level (i.e., different metric), which was why it was not directly 
applied to the Technical Guidance.
    Comment 87: The Commission recommended that instead of using the MF 
cetaceans' PK thresholds as surrogates for other hearing groups where 
no data are available that NMFS consider dynamic range (i.e., 
difference between threshold at frequency of best hearing sensitivity 
and peak pressure threshold) for deriving peak pressure thresholds, as 
has been used for humans (e.g., 140 dB from Occupational Safety and 
Health Administration, OSHA). The Commission specifically suggested 
NMFS apply the measured dynamic range from HF cetaceans to the derive 
thresholds for LF cetaceans, PW pinnipeds, and OW pinnipeds.
    Contrary to the Commission's recommendation, several commenters 
criticized NMFS' use of dynamic range to predict PK thresholds. 
Specifically, commenters questioned NMFS use of onset TTS to define 
dynamic range, since the onset of TTS is not equivalent to the 
threshold of pain and therefore overly conservative (i.e., different 
between TTS onset and PTS is approximately 40 dB). Additionally, these 
commenters indicated that dynamic range data are available for both 
pinniped hearing groups (Kastak et al., 2005) and should be used 
instead of surrogate data from MF and HF cetaceans.
    Additionally, one group of commenters requested NMFS provide more 
information on why the median dynamic range for MF and HF cetaceans was 
used as a surrogate for LF cetaceans.
    Response: NMFS evaluated the Commission's recommendation of an 
alternative methodology for deriving PK thresholds using dynamic range 
and determined that it is a more valid approach to approximating PK 
thresholds for hearing groups where no data exist. However, NMFS 
determined that using the dynamic range for HF cetaceans for other 
hearing groups was not appropriate and instead used the median of the 
dynamic range from both MF and HF cetaceans to derive PK thresholds for 
PW and OW pinnipeds and LF cetaceans.
    As for comments criticizing the Technical Guidance's methodology 
for establishing PK thresholds based on dynamic range, NMFS notes that

[[Page 51715]]

``dynamic range'' can have many connotations. In the Technical 
Guidance, we relate hearing threshold and TTS onset levels, and 
therefore define dynamic range based on hearing threshold and TTS 
onset. Furthermore, NMFS does consider a 40 dB threshold shift to 
represent the PTS onset and uses this value to approximate PTS onset 
thresholds from available TTS onset data (i.e., TTS growth rate data). 
NMFS re-evaluated data within Kastak et al. (2005) to consider for 
establishing PK pressure thresholds for pinnipeds, rather than using 
surrogate MF and HF cetacean data. Within this publication, NMFS could 
not find any information on dynamic range for pinnipeds or any other 
publication that provides impulsive data for pinnipeds. Therefore, 
dynamic range cannot be directly calculated for pinnipeds and surrogate 
data had to be used.
    As for the request for more information on why a surrogate dynamic 
range from MF and HF cetacean data was used for LF cetaceans, NMFS 
relied on the methodology used in other situations to derive surrogate 
values for species groups where data do not exist (i.e., use data from 
other hearing groups, assuming groups where data are not available fall 
within the bounds of existing marine mammal data). Until data become 
available for these hearing groups, NMFS believes this method is an 
appropriate means of deriving surrogate values.
    Comment 88: Multiple commenters expressed concern that the Guidance 
excludes studies in which TTS was not induced, and that, as a result, 
the acoustic thresholds could represent exposure scenarios that will 
not necessarily result in TTS under all conditions. The commenters 
suggested that Guidance's thresholds should only be used to estimate 
the number of animals that could potentially experience TTS (i.e., 
acoustic exposure levels describe potential and not actual TTS onset 
for all exposure scenarios) and that exposures not inducing TTS be 
directly included and used to develop the Guidance's acoustic 
thresholds. The commenters stressed that this distinction is important 
because the Draft Guidance defines TTS, not ``potential TTS,'' as Level 
B harassment and that how Level B harassment is estimated has important 
relevance to the ``small numbers'' and ``negligible impact'' 
determinations that must be made in support of MMPA incidental take 
authorizations.
    Response: The Technical Guidance itself does not rely upon or 
address regulatory practice or interpretations. The section of the 
Draft Guidance that discussed application of thresholds in the 
regulatory context for informational purposes has been more 
appropriately placed in this Federal Register Notice (see Regulatory 
Context). However, to account for uncertainty and limited data, the 
Technical Guidance used a conservative protocol to estimate the onset 
of TTS (see Response to Comment 77). NMFS agrees that exposure 
scenarios where TTS could not be induced are not directly accounted for 
in the development of the quantitative acoustic thresholds. 
Nevertheless, in some situations, studies where TTS could not be 
induced are used to evaluate (cross-check) the Guidance thresholds 
(e.g., HF cetacean pile driving data; MF cetacean seismic airgun data, 
MF cetacean explosion simulator data). As more data become available, 
NMFS may explore alternative means of deriving acoustic thresholds 
(e.g., protocol that directly accounts for scenarios when threshold 
shifts do and do not occur).
    Comment 89: The Commission indicated that TTS data have not been 
collected for either HF or MF cetaceans below 1 kHz. Further, they 
recommend that measurements of TTS frequencies lower than 1 kHz and TTS 
measurements associated with exposure to multiple pulses/hammers 
strikes be added the Guidance's Research Recommendations (Appendix B).
    Response: Although limited, TTS data have been collected at 
frequencies below 1 kHz for HF and MF cetaceans. Finneran et al. (2015) 
exposed bottlenose dolphins (MF cetaceans) to multiple impulses from 
seismic airguns measured TTS at a range of frequencies (0.5 to 64 kHz) 
for three individuals (see Figure 6 in Finneran et al., 2015b). 
Additionally, Kastelein et al. (2015) exposed a harbor porpoise (HF 
cetacean) to playbacks of offshore pile driving and measured TTS at a 
range of frequencies from 0.5 to 125 kHz. Finally, Kastelein et al. 
(2014) exposed harbor porpoise (HF cetaceans) to 1 to 2 kHz sonar 
sweeps and measured TTS at 1.5 kHz. NMFS agrees with the Commission's 
recommendations for additional research and has added them to Appendix 
B of the Guidance (i.e., Sound Exposure to More Realistic Scenarios).
Pinniped Temporary Threshold Shift Data
    Comment 90: One commenter remarked that pinnipeds are likely to be 
less sensitive to noise compared to cetaceans and expressed concern 
that the Guidance's extrapolations using cetaceans as surrogates for 
pinnipeds may be flawed. Given the current lack of information, the 
commenter suggested the highest threshold values from any of the 
cetacean hearing groups (and not any higher) be used to establish the 
underwater acoustic thresholds for pinnipeds.
    Response: In establishing the pinniped thresholds, NMFS used the 
best available data (i.e., non-impulsive TTS thresholds are based on 
measurements collected from three individual harbor seals and a single 
California sea lion) and acknowledges that in some situations where no 
pinniped data were available, cetacean data were used as surrogate data 
to derive acoustic thresholds for pinnipeds. As an example, for PK 
thresholds, data from MF cetaceans and HF cetaceans were used to 
determine an appropriate dynamic range for pinnipeds, but this 
surrogate dynamic range was then combined with direct data on hearing 
thresholds from pinnipeds to derive these thresholds (i.e., combination 
of pinniped and other marine mammal data). As more direct pinniped data 
become available, NMFS will re-evaluate these acoustic thresholds. This 
has specifically been identified as a data gap within the Research 
Recommendation Appendix (Appendix B) of the Technical Guidance.
    Comment 91: A commenter expressed concern that the thresholds for 
OW pinnipeds were much higher than other hearing groups, especially 
that the SELcum thresholds are not much lower than the PK 
threshold. It was indicated that these values appear anomalous and 
should be verified.
    Response: NMFS re-evaluated the data used to derive the OW pinniped 
acoustic thresholds. There are only limited data available for this 
hearing group, with TTS onset thresholds for non-impulsive sources 
coming from a single California sea lion. This threshold is 18 dB 
higher than that for PW pinnipeds and at least 20+ dB higher than the 
thresholds for the cetacean hearing group. Additionally, with the 
updated methodology to estimate PK thresholds using dynamic range (2016 
Proposed Changes document), the OW pinniped PK thresholds have 
increased by 2 dB compared to the thresholds in the 2015 Draft 
Guidance. Due to lack of data for OW pinnipeds, surrogate datasets or 
methodologies to approximate TTS onset for impulsive sounds and PTS 
onset levels had to be used. These approximations build upon the one 
data set available for OW pinnipeds. Thus, all the resulting thresholds 
are higher than those of other hearing groups. This has been 
highlighted within the Technical

[[Page 51716]]

Guidance's Appendix B: Research Recommendations.
Alternative Acoustic Thresholds (Optional Means To Incorporate 
Weighting Functions)
    Comment 92: One commenter suggested that there is no justification 
or explanation for the process for alternative acoustic thresholds 
within the 2015 Draft Guidance and that attempts to compare the results 
of using these alternative thresholds seem to produce conservative 
(i.e., higher) levels of exposure when compared to the thresholds the 
encompass the full auditory weighting function.
    Response: Based on public comment, NMFS re-evaluated its proposed 
alternative acoustic thresholds and replaced this methodology with 
optional weighting factor adjustments (WFAs) that more realistically 
incorporate marine mammal auditory weighting functions for all hearing 
groups (not just HF and MF cetaceans) and allow for all action 
proponents to use the same acoustic thresholds.
    NMFS has included additional explanation in the final Technical 
Guidance's Appendix D. For situations where the full auditory weighting 
functions cannot be incorporated, updated weighting factor adjustments 
are provided, which are based on broader, simpler consideration of 
weighting functions (i.e., relies on using a single frequency that best 
represents where a particular sound has energy). Incorporating optional 
WFAs should result in similar if not identical isopleths for narrowband 
sources and slightly more conservative isopleths (albeit more realistic 
than the previous alternative threshold methodology) for broadband 
sources compared to those action proponents that can fully incorporate 
the Technical Guidance's auditory weighting functions.
    Comment 93: The Commission questioned the utility of two sets of 
thresholds in the Guidance (i.e., weighted and unweighted), noting that 
if an action proponent can calculate or determine the isopleths 
(distances) to the relevant thresholds (weighted or unweighted) then 
that same action proponent should be able to apply the auditory 
weighting functions. The Commission suggested that NMFS require action 
proponents to use the best available science, including auditory 
weighting functions and relevant weighted thresholds, rather than give 
action proponents the choice of using unweighted thresholds.
    Response: NMFS notes that the updated optional WFAs, which replace 
the Draft Guidance alternative thresholds, are provided for action 
proponents unable to fully incorporate auditory weighting functions. 
This is because, especially for broadband sources (which most 
anthropogenic sources are), this incorporation is not a simple 
calculation (i.e., it depends upon the spectrum of the source). NMFS 
regards the practicality of applying more complex, updated thresholds 
an important consideration. This is why NMFS has provided the simpler 
optional WFA approach, which allows action proponents to apply 
weighting in a simpler manner (i.e., most appropriate single 
frequency). The use of WFAs results in all action proponents using on 
the same thresholds.
    Comment 94: Several commenters suggested that the Guidance provide 
clear direction on which thresholds should be used and under what 
specific circumstances. Further, multiple commenters noted that the 
Guidance's alternative thresholds (updated WFAs in final Technical 
Guidance) represent a simple and conservative way to present the 
thresholds and recommended that they be applied to all action 
proponents. Doing so, the commenters suggested, would simplify 
implementation for all authorization action proponents, as well as 
those processing and reviewing the applications, including the 
associated public comment by increasing transparency and reducing 
application processing time.
    Response: As indicated in the Response to the previous comment, 
alternative thresholds have been removed from the final Technical 
Guidance, such that all action proponents are using identical 
thresholds, regardless of their ability to incorporated marine mammal 
weighting functions. NMFS appreciates the need for clarity and has 
included more information in the final Technical Guidance's Appendix D 
regarding when optional WFAs should be used. Specifically, text has 
been added to indicate that NMFS recognizes that the implementation of 
marine mammal auditory weighting functions represents a new and 
complicating factor for consideration, which may extend beyond the 
capabilities of some action proponents and that NMFS has developed 
optional WFAs for those who cannot fully apply weighting functions 
associated with the SELcum metric. Action proponents are 
encouraged to incorporate as many factors, like full auditory weighting 
functions, into their exposure models as possible.
    Comment 95: One commenter suggested that NMFS include a more 
detailed definition of the term ``narrowband,'' one that includes 
explanatory text with regard to the derivation, terms and application 
within the Guidance. Additionally, it was pointed out that NMFS is 
incorrect to assume that narrowband sources will precisely adhere to 
manufacture specifications and that harmonics or subharmonics are 
unusual occurrences with these sources.
    Response: NMFS agrees and has included additional clarification in 
the Technical Guidance regarding the derivation and application of WFAs 
in Appendix D (see Response to Comment 70). The term ``bandwidth'' is 
defined in the Glossary (Appendix E). Additionally, based on this 
comment, NMFS has revised the Technical Guidance to indicate harmonics 
and sub-harmonics are almost always present and should be considered 
when evaluating a source. The terms ``harmonics'' and ``sub-harmonics'' 
have also been added to the Glossary (Appendix E) of the Technical 
Guidance.
24-Hour Accumulation Period
    Comment 96: One commenter suggested the Guidance's 
SELcum metric should require that the accumulation period be 
based on the time an animal is or could be exposed to the sound and not 
necessarily the time the noise occurs.
    Along these same lines, the Commission noted that the accumulation 
period should account for the biology, ecology, and ecological setting 
(e.g., semi-enclosed bay, steep-sided underwater canyon) of the 
affected animals and recommended that for activities that last at least 
24 hours, NMFS consult with scientists and acousticians regarding the 
applicability of an accumulation time for species that occur in a 
confined or small geographic area during an extended period of time and 
for activities that may affect resident populations or marine mammals 
involved in certain behavior states (e.g., feeding, breeding/nursing, 
socializing). Several other commenters provided similar examples and 
made similar recommendations.
    Response: NMFS agrees that the accumulation time associated with 
SELcum metric should be based on the time the animal is 
exposed, but notes that this can be exceedingly difficult if not 
impossible or practical to determine (i.e., an animal's movement can 
vary over space and time).
    Further, NMFS acknowledges for exposure scenarios that occur in 
confined geographic areas with resident populations, case-specific 
modifications can be made, if appropriate, to the accumulation period 
to capture the

[[Page 51717]]

potential for extended exposure periods for these populations. Various 
factors could be considered, including consulting with scientists, if 
appropriate.
    Comment 97: One commenter expressed concern that implementing a 
fixed accumulation period that is not based on physiology could have 
unintended consequences. The commenter provided the example of when an 
operation lasts for more than 24 hours, the use of a fixed 24-h 
accumulation period may result in animals being ``taken'' multiple 
times and that this may skew the risk assessment.
    Response: The Technical Guidance focuses on predicting onset of PTS 
and TTS, including consideration of energy accumulation. In the 
regulatory context, NMFS acknowledges that the application of the 
updated acoustic thresholds for quantifying take could result in 
scenarios where an animal could be ``taken'' on multiple days (i.e., a 
stationary source near resident animals; mobile source continuing over 
multiple days), but this is no different from how take calculations are 
done under the current thresholds, nor should it skew the broader 
effects analysis. Ultimately, other factors would have to be taken into 
consideration within a comprehensive effect analysis, including if the 
same animals are exposed or ``taken'' on multiple days.
    Comment 98: Several commenters recommended that the accumulation 
period encompass the entire duration of an activity and suggested NMFS 
revise the Technical Guidance to allow for the option of 
SELcum modeling for the duration of the activity, in order 
to allow action proponents the ability to utilize the approach with the 
smallest estimated number of marine mammal exposures.
    Response: NMFS determined the data currently available for deriving 
acoustic thresholds do not support an accumulation period beyond 24 
hours (e.g., available marine mammal TTS data are only available for 
shorter duration exposures). Further, a key consideration in accurately 
accumulating exposure beyond the recommended 24-h period is the ability 
to accurately predict the location of the receiver relative to the 
source. Again, the understanding of marine mammal distribution and 
movement, especially during periods of sound exposure, is limited. 
These data limitations hamper the ability to make realistic exposure 
predictions for longer duration exposures. However, NMFS acknowledges 
that there may be specific exposure situations where this accumulation 
period requires adjustment and will work with action proponents to make 
these adjustments (e.g., a resident population found in a small and/or 
confined area; continuous stationery activity nearby an area where 
marine mammals congregate, like a pinniped pupping beach). Finally, 
NMFS recommends use of the approach that produces the most accurate 
results for an activity (i.e., not necessarily the one that produces 
the smallest or largest number of exposures).
    Comment 99: Multiple commenters requested clarification as to 
whether the Guidance accounts for the accumulation of sound from 
multiple activities in the same area and multiple sources/phases 
associated with a single activity. The commenters requested that an 
alternative method/metric be developed for multiple sources active in 
the same area at the same time (i.e., to better address cumulative 
exposure associated with the entire soundscape). Specifically, the 
Commission recommended that NMFS require action proponents use the 
Guidance thresholds for determining the relevant isopleths associated 
with activities that use multiple sound sources in the same area during 
the same timeframe (e.g., multibeam echosounders and sub-bottom 
profilers simultaneously with airguns during a seismic survey, various 
types of sonar and/or impulsive sources used simultaneously during a 
military exercise), rather than requiring action proponents to apply 
the thresholds to discrete sources used during a specific activity.
    Response: The Technical Guidance recommends application of the 
SELcum metric to assess the impacts of noise on hearing for 
individual activities/sources. Because current data available for 
deriving acoustic thresholds are based on exposure to only a single 
source, this metric is not intended for accumulating sound exposure 
from multiple activities occurring within the same area or over the 
same time or for multiple sources within a single activity. Currently, 
NMFS is unaware of alternative metrics available to assess the impacts 
of noise on hearing from multiple sound sources. As more data become 
available, NMFS can re-evaluate the use of this metric for application 
of exposure from multiple activities occurring in space and time. In 
other contexts, such as masking, which is expected to occur at much 
lower levels and much more likely to result from the contributions of 
multiple sources, NMFS is supporting efforts to better assess the 
impact of multiple sound sources on marine mammals (e.g., NOAA Ocean 
Noise Strategy and CetSound Projects; National Research Council's Ocean 
Studies Board's Cumulative Effects of Human Activities on Marine Mammal 
Populations Study).
    Comment 100: The Commission requested that NMFS provide additional 
guidance on how action proponents unable to incorporate moving sources 
should determine the total ensonified area (and consequently the number 
of ``takes'') and recommended that action proponents unable to model 
moving receivers and/or sources determined the total ensonified area 
based on a model accumulating the energy for 24 hours and then 
multiplying that ensonified area by the marine mammal density to 
determine the total number of ``takes.'' The Commission's approach does 
not assume a constant distance from the source, but rather a total 
ensonified area associated with activity lasting 24 hours (or less if 
appropriate) and a uniform density.
    Response: Instead of the approach recommended by the Commission, 
NMFS created a simple User Spreadsheet (released with Technical 
Guidance) to aid action proponents in determining the isopleth 
associated with their particular activity, if they are unable to employ 
more sophisticated modeling techniques. The updated simple methodology 
is based on the concept of ``safe distance'' presented in Sivle et al. 
(2014) for moving sources, with more details presented in Appendix D of 
the Guidance. The ``safe distance'' is equivalent to isopleths 
applicants have calculated in the past, with area and marine mammal 
exposures calculated by the same means (i.e., multiply isopleth times 
marine mammal density) applicants have used with NMFS' current 
thresholds (e.g., generic RMS SPL 180/190 dB).
    Comment 101: One commenter requested clarification on several 
questions related to the modeling of exposures using more and less 
sophisticated methods: (1) Must a model be able to incorporate the 
movement of both the source and the receivers or at least the receiver? 
(2) How will NMFS determine whether an action proponent has the ability 
to model moving receivers or not? (3) What will be the difference 
between an action proponent employing more sophisticated modeling 
capabilities versus those with less sophisticated capabilities?
    Response: An action proponent is responsible for determining their 
own modeling capabilities and, depending on the source and/or receiver, 
this might include movement or not in order to recreate the most 
realistic source-receiver separation (i.e., variation in spacing 
between source and receiver over space and time). While NMFS does

[[Page 51718]]

not require any particular models be used, they do evaluate the 
appropriateness of models and associated methodologies used in 
estimating acoustic exposures on a case-by-case basis in the context of 
a proposed activity. NMFS has provided an optional User Spreadsheet for 
action proponents unable to employ more sophisticated modeling on their 
own. Generally speaking, because it intentionally includes multiple 
conservative assumptions, we expect the simple, alternative method 
generally will result in higher estimates of PTS-level exposure (which 
in turn will translate into higher take estimates). A comprehensive 
effects analysis for an action would take into consideration the fact 
that the alternative method results in overestimates.
    Comment 102: Several commenters indicated that the Guidance needs 
to better address the potential of noise-induced hearing loss from more 
continuous sources that operate 24 hours a day for multiple days (e.g., 
renewable energy wind farms/tidal operations; communication/navigation 
beacons). Additionally, a commenter urged NMFS to consider 
complementary devices operating synchronously in arrays as a continuous 
sound source, rather than discrete sources. This same commenter 
requested consideration for continuous noise sources having the 
potential to displace an animal from critical feeding habitat.
    Response: In U.S. waters, NMFS is aware of very few sources with 
the potential of operating continuously (i.e., 24 hours a day, 7 days a 
week, year-round). However, renewable energy platforms have the 
capabilities for these types of continuous operations. NMFS 
acknowledges that continuous operations can result in higher potential 
for exposure accumulation, but the majority of renewable energy 
operations produce relatively low levels of sound (i.e., close to 
ambient, especially in environments conducive to wave or tidal devices; 
e.g., Coping et al., 2014; Schuster et al., 2015) that even over an 
accumulation period of 24-h are unlikely to exceed the PTS onset 
thresholds. As for the operation of communication/navigation beacons, 
these types of sources have a multitude of characteristics (e.g., 
source level, duty cycle, frequency band, beam width/orientation) but 
generally have relatively short pulse lengths and produce higher 
frequencies (i.e., greater ability for sound to attenuate) reducing the 
likelihood of exposure resulting in cumulative effects. Finally, 
regarding the comment about displacing an animal from critical feeding 
habitat, the Technical Guidance focuses on the effects of noise on 
marine mammal hearing and does not address displacement.
    As previously addressed in a prior comment, because a sound 
operates 24-h a day does not necessarily mean a receiver is exposed to 
that source for that entire period (i.e., marine mammals are capable of 
moving vertically or horizontally in the water column) or that it is 
exposed to levels capable of inducing noise induced threshold shifts. 
In other words, having an accurate understanding of the spatial and 
temporal overlap between a source and receiver is important in being 
able to accurately predict exposures.
Recovery
    Comment 103: Multiple commenters recommended that the Guidance 
consider data on marine mammal recovery from noise exposure. 
Specifically, one commenter suggested the use of a ``leaky-integrator 
model'' that accumulates sound energy and account for potential 
physiological recovery in a time-dependent manner (described by a time 
constant). The commenter indicated that the value of the time 
constant(s) is not known but could be conservatively estimated.
    Contrary to this comment, another commenter cautioned that recovery 
times have generally been measured only during quiet periods within 
laboratory settings and that in the open ocean, it is likely that free-
ranging animals will be exposed to sound during the recovery period.
    Response: Recovery is an important consideration in assessing the 
effects of noise on marine mammals, and the Technical Guidance includes 
general information on recovery. We also agree recovery in the open 
ocean is more complex than measured in a laboratory setting. Currently, 
there are not enough data to directly take recovery into consideration 
in the development of acoustic thresholds (and this is specifically 
identified as a research recommendation in Appendix B), including the 
integration of a ``leaky-integrator model.'' As more data become 
available, NMFS can re-evaluate this issue. NMFS has provided 
additional text in the Technical Guidance to address why recovery was 
not directly considered in a quantitative manner. NMFS has also 
provided more clarification in the text regarding recovery and the 
Technical Guidance baseline accumulation period.
    Comment 104: One commenter suggested that the Guidance's 
accumulation period be ``reset'' to zero only when there has been a 
sufficiently long silent period (i.e., not automatically after 24 
hours). The commenter referred to NMFS' interim injury impact pile 
driving criteria for fishes, which assumes that accumulation from zero 
occurs only after a recovery period of 12 hours without sound exposure.
    Response: NMFS' interim injury criteria for fishes pertain to 
smaller pile driving activities (i.e., primarily associated with 
construction) that only occur during daylight hours, where resetting 
the accumulation period and allowing for a 12-h recovery period is 
possible. However, some activities covered by the scope of this 
Technical Guidance continue for longer than 24 hours (e.g., seismic 
survey) and only resetting the accumulation after a sufficiently long 
silent period (i.e., 12 to 24 hours) is not feasible. The data 
currently available for deriving acoustic thresholds do not support an 
accumulation period beyond 24 hours, and accumulating over the entire 
activity duration (i.e., beyond 24 hours) could result in unrealistic 
exposure results (e.g., difficult to predict the temporal and spatial 
variability of a receivers over multiple days; see Response to Comment 
79).
    Comment 105: One commenter noted that if TTS and/or PTS are caused 
by build-up of free radicals in the hair cell synapses (e.g., McFadden 
et al., 2005), then exposure over extended periods must take the 
clearance rate of the free radicals into consideration. The commenter 
indicated that a 24-h period might be a reasonable approach based on 
human audiometry but that given the absence of sufficient marine mammal 
data, it may be necessary to consider SELcum over periods of 
greater than 24 hours in situations where sources are loudest (e.g., 
large seismic airgun surveys) and propagation loss is lowest.
    Response: NMFS acknowledges there are a multitude of factors that 
affect recovery from noise-induced hearing loss, including clearance of 
free radicals, making recovery complex. Further, there is a lack of 
data, especially for marine mammals. That said, NMFS acknowledges there 
may be some situations where the accumulation period needs to be 
extended beyond 24 hours depending on case-specific scenarios. However, 
these should be exceptions and not the norm (i.e., proposed 
accumulations periods represent the typical exposure scenario; see 
Response to Comment 79).
    Comment 106: Multiple commenters expressed concern that several of 
the recovery time lengths in the marine mammal TTS literature have been 
reported to exceed 24 hours and

[[Page 51719]]

indicate the Guidance's acoustic thresholds may not be sufficiently 
conservative. Further, several commenters requested that NMFS consider 
recovery in terms of exposure to other stressors, since these stressors 
may exacerbate threshold shifts and/or recovery.
    Response: NMFS acknowledges that recovery from noise exposure is 
extremely complex and depends on a multitude of factors, which is why 
recovery was not directly integrated into the Technical Guidance's 
recommended accumulation period or into the acoustic thresholds. As 
NMFS notes in the Technical Guidance, threshold shifts on the order of 
the established PTS onset (i.e., 40 dB) recorded in marine mammal 
laboratory studies have still resulted in recovery. Additionally, NMFS 
has made several conservative assumptions in the development of its 
acoustic thresholds (see Response to Comment 77). NMFS has added a 
research recommendation relating to examining noise under realistic 
exposure scenarios, including consideration of other stressors.
    Comment 107: Several commenters suggested that the accumulation 
period allow for the consideration of periods of reduced or no sound 
(e.g., power-downs and line turns during seismic activities).
    Response: NMFS agrees that power-downs associated with line turns 
(not associated with mitigation, which can be unpredictable) should be 
accounted for in modeling, particularly with the accumulation period 
(i.e., total exposure period within a 24-h period, excluding periods 
when there is no exposure).
Appendix D: Alternative Methodology (Formerly Identified as the User 
Guide)
    Comment 108: Several commenters indicated that the Guidance should 
not be finalized until the public has been given the opportunity to 
evaluate NMFS' user tools (i.e., having these tools is necessary to 
perform a thorough analysis of the Guidance).
    Response: NMFS disagrees. See Response to Comment 3.
    Comment 109: It was suggested by a commenter that an alternative 
method is unnecessary, as it is unlikely animals will remain close 
enough to a source to exceed the Guidance's SELcum 
thresholds (i.e., PK is anticipated to be the dominant metric, 
resulting in the largest isopleth for most, if not all situations).
    Response: NMFS disagrees that the PK should be assumed to be the 
threshold resulting in the most conservative (i.e., largest) isopleth 
for most sources. Furthermore, as a result of public comment, NMFS 
decided to remove the PK thresholds for non-impulsive sounds. For 
impulsive sounds, NMFS recommends an action proponent fully evaluate 
their sound source to determine which metric would be dominant. NMFS 
agrees it may be unlikely that animals would remain close to a source 
for extended periods of time in most exposure situations. However, 
predicting animal movement and distribution, especially during sound 
exposure scenarios, is difficult. Finally, NMFS recognizes that in 
updating our acoustic thresholds to reflect the best available science, 
they have become more complex. Thus, Appendix D provides a set of 
tools, examples, and weighting factor adjustments to allow action 
proponents with different levels of exposure modeling capabilities to 
reasonably approximate PTS onset, using the updated acoustic 
thresholds, for all sound sources.
    Comment 110: Several commenters requested NMFS explain how the 
SELcum acoustic threshold should be used to determine if an 
auditory impact would occur. Commenters recommended more guidance on 
how this would be implemented for a couple of example projects (i.e. 
stationary source such as pile driving, and moving source such as 
seismic).
    Response: Due to the diverse array of potential sound sources, it 
is impractical for NMFS to provide specific, detailed example 
calculations within the Technical Guidance. However, NMFS is providing 
a simple optional User Spreadsheet to aid action proponents unable to 
perform more sophisticated exposure modeling. This spreadsheet 
specifically provides a means of applying the Technical Guidance's 
thresholds and simplified weighting (WFAs) and calculates isopleths 
associated with thresholds expressed as SELcum. Thus, 
example calculations can be completed by using the optional User 
Spreadsheet. Those using more sophisticated models (e.g., animats) 
would presumably have some other means of accounting for cumulative 
exposure, like an ``acoustic dosimeter,'' and would not necessarily 
need to determine a SELcum threshold distance (see Response 
to Comment 114).
    Comment 111: Concern was expressed by several commenters that the 
alternative methodology provided in Appendix D would limit flexibility 
to assess the impacts of noise on marine mammal hearing.
    Response: Action proponents are not obligated to use the 
alternative methodology and may perform more sophisticated modeling or 
consider additional action- or location-specific factors, if able. 
Thus, action proponents are given flexibility in terms of their 
exposure modeling.
    Comment 112: Several commenters were concerned that the highly 
technical nature of the Guidance does not lend itself to direct and 
consistent application, particularly by non-experts and indicated that 
alternative methodology could result in more restrictive acoustic 
criteria for the smaller action proponents.
    Response: NMFS has produced an associated simple optional User 
Spreadsheet that has been finalized with the Technical Guidance to 
assist stakeholders in applying the updated acoustic thresholds 
associated with the more complex SELcum thresholds, 
including tools to help those that cannot incorporate more complicated 
auditory weighting functions (see Response to Comments 70 and 100).
    NMFS acknowledges that less sophisticated exposure models may 
result in higher exposure estimates because these models do not 
incorporate as many factors as more sophisticated models. Action 
proponents are encouraged to incorporate as many appropriate factors 
into their modeling as possible. An action proponent is not obligated 
to use the simpler tools provided by NMFS, if they can provide equally 
or more realistic exposure modeling on their own.
    Comment 113: One commenter noted that the NMFS' West Coast Region 
provides a SELcum calculator for estimating impacts to 
fishes during impact pile driving, including the incorporation of an 
``effective quiet'' value, and requested a similar calculator be 
provided for marine mammals. The commenter recommended a consistent 
process for accumulating energy and assessing impacts to all species 
under NMFS' purview.
    Response: The Technical Guidance provides a similar 
SELcum calculator for marine mammals, but effective quiet 
will not be directly incorporated into the marine mammal calculator 
because NMFS determined there are not enough data at this time to do 
so. NMFS believes it is consistent in how it assesses acoustic impacts 
for the various species under its jurisdiction but, there may be 
exceptions that depend on various factors (e.g., species-specific 
considerations, data availability, etc.).
Model Specifications
    Comment 114: Multiple commenters indicated that the Guidance 
suggests that a variety of model approaches could be employed in 
applying the Guidance's acoustic thresholds. Instead, the commenters 
suggested that NMFS

[[Page 51720]]

recommended standardized computer models or modeling requirements, 
which would allow regulators, industry, and the public to run 
repeatable analysis to verify acoustic data based on NMFS' 
recommendations. The commenters expressed concern that it is likely 
that both the current range of modeling vendor choices and their 
capacity will be inadequate to fulfill the agency's requirements, which 
could lead to unwarranted permitting delays or costs, and suggested a 
transition period to necessitate the expansion of the pool of adequate 
modeling expertise and vendors. Finally, a commenter recommended that 
NMFS undertake model validation/verification as part of the process of 
developing the final acoustic criteria.
    Response: Providing standard computer models for analysis or 
modeling requirements associated with the application of the Technical 
Guidance's acoustic thresholds and/or auditory weighting functions, as 
well as model validation/verification, is beyond the scope of this 
exercise. The adequacy of models will depend on a multitude of factors, 
including the activity (source) and potential receivers. Because the 
updated acoustic thresholds are more complex, simpler alternatives have 
been provided (e.g., User Spreadsheet with weighting factor adjustments 
for those unable to fully incorporate auditory weighting functions), 
which can be used until the pool of adequate modeling expertise is 
expanded. Further, NMFS recognizes there will be a transition period 
before the Guidance is fully used. (See previous section in this Notice 
on Transitioning to the Technical Guidance).
    Comment 115: The Commission recommended that the Guidance provide 
specifications necessary to perform exposure modeling. They indicate 
that it is NMFS' responsibility, as a regulatory agency, to make 
required findings and direct action proponents to the appropriate types 
of models, including inputs and appropriate factors to be considered 
within those models.
    Response: NMFS does not currently provide modeling specifications 
and has no current plans to do so. NMFS will provide some technical 
assistance to prospective applicants who request it and will continue 
to evaluate the models that are used in submitted compliance documents 
to ensure they are adequate and appropriate.
    Comment 116: The Commission commented on the two alternative models 
(i.e., one for moving sources and one for stationary sources) provided 
in the 2015 Draft Guidance Appendix D. Specifically, the Commission 
requested that more information be provided whether the 3-D ``safe 
distance'' methodology of Sivle et al. (2014) for moving sources is 
applicable to NMFS' 2-D application specified in the Guidance. The 
Commission requests this aspect be submitted for peer review.
    BOEM expressed concern that the methodology of Sivle et al. (2014) 
is not appropriate for directional sources or for receivers that are 
not at the same depth as the source (e.g., sperm whales). The Guidance 
states that this methodology is independent of exposure duration, and 
BOEM states this is inconsistent with the document's recommendation of 
a 24-h baseline accumulation period. Further, BOEM recommended that 
this method include a representative depth typical of the species being 
modeled.
    Response: NMFS reiterates that the two models referred by the 
Commission are alternative methods. Action proponents are not obligated 
to use these methods. Although Sivle et al. (2014) accounted for the 
depth of herring to determine the percent of the winter and summer 
populations exceeding the ``safe distance'' associated with exposure to 
naval sonar, the calculation of ``safe distance'' (i.e., equations in 
the Technical Guidance) makes minimal assumptions associated with the 
receiver (i.e., the receiver is stationary and does not exhibit 
avoidance or attraction to the source) and does not directly account 
for receiver depth or density. It only provides the distance from the 
source (i.e., isopleth) beyond which a threshold is exceeded. Thus, 
NMFS believes that this methodology is appropriate for 2-D 
applications. NMFS has added information about the assumptions 
associated with the receiver within the Technical Guidance for clarity. 
NMFS does not believe additional peer review is need for this aspect of 
the Technical Guidance because the methodology (Sivle et al., 2014) has 
already undergone peer review as part of its publication in ICES 
Journal of Marine Science.
    Addressing concerns raised by BOEM, it is correct that the methods 
of Sivle et al. (2014) may not be representative for directional 
sources and are likely to result in more conservative exposures (i.e., 
model does not account for source directivity and isopleths produced 
assume an omnidirectional source; meaning that it produces an isopleth 
equal in all directions). However for directional sources, the source 
level parameter associated with this methodology assumes the values 
provided are those relating to the direction producing the maximum 
level. Again, this optional methodology does not make any assumptions 
about the depth of the receiver: it only provides an isopleth 
associated with a particular acoustic threshold. It is possible that 
the depth of the receiver can accounted for in terms of depth-dependent 
density (i.e., percentage of time species is located at a particular 
depth). However, accounting for specific characteristics associated 
with the receiver (e.g., depth distribution, density, behavioral 
response, etc.) is beyond the scope of this document.
    Finally, the reason this optional methodology is independent of 
exposure duration is because it only considers one pass of the source 
relative to receiver, with the closest points of approach incurring the 
greatest accumulation (i.e., once the source moves past the closest 
point of approach accumulation is only further reduced as the source 
moves farther and farther away). Accumulating past the recommended 24-h 
accumulation period does not result in the addition of any significant 
amount to the cumulative sound exposure of the receiver. The model can 
be adjusted to account for shorter accumulation periods. However, the 
equations become more complex and more difficult to implement.
    Comment 117: Several commenters expressed concerns over a potential 
short-coming associated with the optional ``safe distance'' method 
(Sivle et al., 2014) accounting for cumulative exposure for moving 
sources, specifically its ability to allow only for the inclusion of 
spherical spreading as a propagation model. It was suggested that other 
propagation models, especially those more conservative spreading models 
associated with shallow water, need to be incorporated into this 
methodology. Related to this, BOEM indicated that the Guidance's 
``source factor'' definitions closely resembled cylindrical spreading 
(10\TL\/\10\), rather than spherical spreading 
(10\TL\/\20\) and expressed a concern over whether Mean 
Squared Pressure (MSP) or Equivalent Plane Wave Intensity (EPWI) terms 
were used, and that the terms ``S,'' ``SE,'' and ``E0'' in the Guidance 
appear to have similar units, but they do not.
    Additionally, these commenters provided an example to assess the 
appropriateness of the ``safe distance'' methodology by examining the 
modeled radii from four parallel passes, within a 24-h period, from a 
3300 cubic inch airgun. Based on their modeling, it was suggested that 
NMFS lower thresholds for LF cetacean and PW pinnipeds, raise 
thresholds for HF cetaceans, and adjust the same distance methodology 
to

[[Page 51721]]

account for the number of passes within an area during a 24-h period. 
There was no detail provided by the commenter on what these adjustments 
should be.
    Response: NMFS acknowledges the concerns and potential limitations 
of the optional ``safe distance'' methodology but believes other 
assumptions associated with this methodology ensure as a whole it 
remains precautionary. The incorporation of other types of spreading 
models results in a more complicated equation making the methodology 
less easy to implement. However, many mobile sources, like seismic 
airguns or sonar, produce sound that is highly-directional (i.e., most 
of time sound source is directed to the ocean floor, with less sound 
propagating horizontally, compared to the vertical direction), and 
directionality is not accounted for with this methodology (see Response 
to previous comment). Additionally, many higher-frequency sounds, like 
sonar, are also attenuated by absorption, which is also not taken into 
account in this methodology. Thus, there are other considerations 
beyond spherical spreading, including other conservative factors (i.e., 
simplified incorporation of auditory weighting factors, the receiver 
does not avoid the source, etc.) to consider when assessing whether the 
use of this optional methodology will result in a potential 
underestimate of exposure. Thus, despite these simple assumptions, NMFS 
believes the optional ``safe distance'' approach offers a better 
approximation of the source-receiver distance over space and time for 
various mobile sources than choosing a set accumulation period for all 
sources, which assumes a fixed source-receiver distance over that time, 
and encourages the development/validation of alternative models, 
including the assessment optional models provided in the Technical 
Guidance (see Appendix B: Research Recommendations).
    As for BOEM's comments regarding MSP vs. EPWI terms, by following 
ANSI definitions within the Guidance, NMFS is implicitly using MSP 
terms. The term ``source factor'' within the Guidance is based on a 
source level being defined as pressure squared, which why it may appear 
to resemble cylindrical spreading, rather than spherical spreading. 
This additional information was added to provide clarity. BOEM is 
correct that the terms ``S,'' ``SE,'' and ``E0'' that appear in the 
Technical Guidance do not have identical units. NMFS understands the 
potential confusion, since this information was not included in the 
2015 July Draft Guidance. A section has been added in Appendix D 
providing these units in the Technical Guidance (i.e., See section 
3.2.1.1 Linear Equivalents).
    In response to the commenter's modeled example, NMFS disagrees with 
the appropriateness of this comparison. One of the assumptions 
associated with the optional ``safe distance'' methodology is that the 
source moves at a constant speed and in a constant direction. Thus, 
this model is not sophisticated enough to account for situations for 
multiple passes and should not be used for these situations (i.e., NMFS 
would recommend an action proponent in this situation to find a more 
appropriate means of modeling exposure, or work with NMFS to determine 
if the ``safe distance'' methodology can be appropriately modified to 
account for multiple passes from a source). Thus, it is not unexpected 
that there are several discrepancies between the commenter's modeled 
isopleths and those provided by the ``safe distance'' method, including 
the use of different weighting functions and thresholds, by the 
commenter, compared to those in the Technical Guidance. NMFS believes 
the Technical Guidance represents the best available science and 
disagrees that adjustments to the document's acoustic thresholds is 
supported.
Technical Guidance Implementation and Regulatory Context
    Comment 118: One commenter recommended that the Guidance solely 
focus on providing the technical basis for acoustic thresholds (i.e., 
best available science) rather than containing substantial 
implementation language in the document. The commenter indicated that 
limiting the purpose of the Guidance to solely providing technical 
background would allow flexibility to incorporate new technologies and 
information as they become available.
    Response: NMFS agrees and revised the title of the Guidance to 
reflect its technical, scientific nature. The Technical Guidance is a 
compilation, interpretation, and synthesis of the available literature. 
Application of the updated acoustic thresholds remains consistent with 
current NMFS practice. That information on regulatory context has been 
moved to this Notice. Any changes to application in the regulatory 
context are separate from the basis for updating the thresholds 
themselves, where advances in scientific knowledge are the drivers.
    Comment 119: One commenter requested the Technical Guidance provide 
a brief reference to its use in the current 14-question MMPA incidental 
take application.
    Response: The Technical Guidance is a compilation, interpretation, 
and synthesis of the scientific literature on the impacts of sound on 
marine mammal hearing. There is no change to the use of thresholds in 
the regulatory context. No specific reference is required in our 
implementing regulations.
    Comment 120: One commenter noted that the MMPA mandates that 
``Level A'' harassment includes not only the actual or likely onset of 
injury, but also the potential for injury and that the ESA definition 
of ``harm'' encompasses temporary injuries or impairments that impact 
essential behavior. The commenter expressed concern that setting the 
threshold for ``Level A'' harassment under the MMPA and ``harm'' under 
the ESA at the actual onset of injury is inconsistent with the 
statutory mandates, which seek to protect against the risk of, or 
potential for, injury and recommended that NMFS must set a protective 
threshold in order to comply with its statutory mandates (i.e., one 
that interprets the existing literature conservatively enough to 
reflect the potentiality of harm).
    Response: The Technical Guidance auditory impact thresholds were 
based on scientifically-based judgments, including accounting for 
uncertainty and variability, developed to stand independent of 
interpretations of statutory terms such as ``take,'' ``harm,'' and 
``harassment.'' At the same time, the thresholds were designed for use 
in NMFS' regulatory analyses.
    NMFS incorporated several conservative assumptions in the 
development of the PTS onset thresholds to account for the potential 
for PTS onset (see Response to Comment 77). Further, there are several 
examples of marine mammal exposure exceeding the Guidance's PTS 
thresholds, where recovery has occurred (see recent review in Finneran 
2015).
    Comment 121: Several commenters provided examples of how the 
weighting function and thresholds compare to data collected in the 
field during SSV measurements (e.g., seismic and impact piled driving). 
The commenters' analysis operated on the assumption that the weighting 
functions and thresholds should provide equal results when compared to 
the weighting functions and thresholds in Southall et al. (2007), and 
argued that results stemming from the Guidance ``did not yield the most 
reliable or cautionary results.'' In one example, it is stated that 
these comparisons are ``at odds with the

[[Page 51722]]

reports of the sensitivity of beaked whales to pulsed sounds.''
    Response: NMFS appreciates the commenter's efforts to provide 
examples and comparisons using the Technical Guidance. However, we 
disagree that the Technical Guidance must yield similar results to 
those provided in Southall et al. (2007), since available data and 
methodology has significantly evolved since 2007. For example, marine 
mammal weighting functions (M-weighting) from Southall et al. (2007) 
were derived in a more simplistic manner than the updated methodology 
provided in Appendix A, which directly uses audiogram and TTS data to 
derive weighting functions. Thus, the Southall et al. (2007) M-
weighting functions are broader than those provided in the Technical 
Guidance and would inherently result in larger, more conservative 
isopleths. Although the isopleths derived using the Technical Guidance 
results are smaller in comparison to those from Southall et al. (2007), 
they are not necessarily unreliable.
    In addition, NMFS is aware that the Southall et al. (2007) panel is 
in the process of updating its paper. It is anticipated that their 
proposed weighting functions will not be as broad (most susceptible 
frequency range) as their original M-weighting functions (i.e., they 
will be more aligned with those presented in the Technical Guidance). 
Regarding beaked whale sensitivity, NMFS agrees these species are often 
classified as a ``particularly sensitive'' group, but in the context of 
behavioral responses. The Technical Guidance does not pertain to 
behavioral responses, only effects of noise on hearing. The assumption 
that this enhanced sensitivity carries over to hearing and 
susceptibility to noise-induced hearing loss is currently unsupported 
by beaked whale AEP measurements (e.g., Finneran et al., 2009; Pacini 
et al.. 2011) or transmission pathway modeling (e.g., Cranford et al., 
2008) .
    Comment 122: Several commenters remarked that the Guidance does not 
explain the anticipated impact of the acoustic thresholds on the 
regulated community. Because the Guidance will be applied in a range of 
regulatory actions, it was recommended that NMFS undertake a study 
comparing the assessment approach described in the Guidance with the 
current assessment methods to demonstrate the regulatory implications 
of the proposed acoustic thresholds.
    Response: The Technical Guidance represents the culmination of a 
robust assessment of the scientific literature to derive updated, 
science-based auditory impact thresholds for marine mammals. The 
overall assessment approach in the regulatory context has not changed 
from current agency practice.
    The acoustic thresholds presented in the Technical Guidance use 
different metrics compared to the current thresholds. In some 
situations, depending on the sound source, species of interest, and 
duration of exposure, application of the updated acoustic thresholds 
may result in greater estimates of PTS (and therefore more ``takes'') 
than under the existing thresholds, while in other situations the 
opposite result may occur. Examining all possible scenarios associated 
with the wide range of potential activities is not feasible.
    Comment 123: Multiple commenters expressed concern that the 
Guidance will unnecessarily result in an increased burden to action 
proponents during the permitting process and would lead to an increased 
number of shutdowns or longer survey duration, with increased costs and 
safety risks.
    Response: NMFS recognizes the advancing science on auditory impacts 
has led to more complex set of thresholds and methodology for 
evaluating impacts and has provided a simplified alternative 
methodology to alleviate some of the burden associated with applying 
the more complex acoustic thresholds and auditory weighting functions.
    In terms of effects on activities themselves, the Guidance does not 
address consequences for mitigation requirements in a regulatory 
context. This will depend on the particular aspects of an action, 
taking into account the comprehensive effects analysis and regulatory 
considerations. NMFS notes that there are no requirements that 
mitigation measures directly correspond to acoustic thresholds (See 
Response to Comment 11).
    Comment 124: One commenter expressed concern that applying the 
alternative methods provided in the Guidance could result in 
unrealistically high exposure estimates. The commenter recommended that 
the Guidance include more explanation to inform action proponents about 
the potential costs, benefits, and consequences of methodologies that 
directly use auditory weighting functions and those that do not 
(alternative methods).
    Response: NMFS notes it will be an action proponent's decision as 
to how they model and estimate their potential impacts to marine 
mammals. Analyzing the potential cost/benefits of the methodologies 
applied is beyond the scope of the document and will vary depending on 
the activity/sound source and species impacted. The optional WFAs 
provided in the Technical Guidance should assist action proponents with 
incorporating auditory weighting functions and should provide very 
similar (if not identical) results for narrow-band sources and larger 
isopleths for broadband sources, depending on how much information the 
action proponent can provide regarding the frequency composition of 
their source (i.e., can provide the 95 percent frequency contour 
percentile or rely on the more conservative default WFA values).
    Comment 125: Multiple commenters requested more information on how 
NMFS will transition from previously applied thresholds to the acoustic 
thresholds provided in the Guidance (e.g., how will it affect 
applications/consultations completed, in process and beyond) and 
expressed concerned over the potential for delays and NMFS' time 
requirements to process permits based on the Guidance.
    Further, one commenter remarked that NMFS' intention to update the 
acoustic thresholds based on newly available information is valid from 
a scientific point of view, but from a practical aspect could be 
confusing, could promote regulatory uncertainty, and has the potential 
to affect permitting timelines. The commenter indicated that planning 
for certain activities can take multiple years to complete, with the 
introduction of additional uncertainty potentially adversely affecting 
the ability of action proponents to plan for and comply with the 
Guidance.
    Similarly, several commenters requested clarification as to how the 
Guidance would be implemented in (a) the context of a five-year 
incidental take regulation (ITR) (with specific take authorizations by 
letters of authorization (LOA)) and (b) when numerous IHAs are issued 
for a given area in the absence of an ITR. Specifically, a commenter 
asked if different methods will be used to estimate the amount of 
authorized incidental ``take'' in each of these contexts and how, if at 
all, will authorized ``take'' be allocated over certain periods of time 
in one or both of these contexts?
    Response: NMFS acknowledges there will be some lag between updates 
in the best available information and the ability to incorporate that 
new information into ongoing processes. We refer readers to the section 
of this Notice addressing Transitioning to the

[[Page 51723]]

Technical Guidance for more information.
    Comment 126: One commenter suggested that the Guidance provides an 
opportunity for NMFS to clarify its policy on ``takes'' vs. ``animals 
taken.'' The commenter indicated that just because an animal is 
``exposed'' to a sound source does not necessarily equate to a ``take'' 
or an impact as defined in the MMPA and provided the following example 
with migratory (e.g., 50 takes with individuals being taken once) vs. 
resident species (e.g., 50 takes with ten individuals being taken five 
time each). Similarly, a commenter requested that NMFS should clarify 
that, in estimating numbers of auditory impacts for management 
purposes, take numbers will be calculated for each day of exposure and 
then added to obtain the total estimate. For example, assuming an equal 
daily risk of eight exposures that exceed PTS thresholds for some 
species over a 10-day pile-driving project, the total potential PTS-
level take would be 80 animals. The Navy has long employed this method 
of calculation, but its use by other applicants (e.g., seismic 
operators) has been inconsistent. Notably, this method would not 
account for multiple takes of individual marine mammals and the 
cumulative impact on hearing that would result from those takes.
    Response: The Technical Guidance is designed for assessing the 
impact of underwater noise on marine mammal hearing by providing 
scientifically-based auditory weighting functions and acoustic 
thresholds. It does not address how to calculate takes in various 
situations. Those considerations are case-specific and based on 
multiple considerations, including spatial and temporal overlap between 
the sound source and a receiver). Moreover, factors like whether a 
marine mammal species or stock is migratory or resident (among numerous 
other factors), are considered within a broader comprehensive effects 
analysis when such information is available.
    Comment 127: The Commission commented that the Guidance states that 
an alternative approach may be proposed (by federal agencies or other 
action proponents) and used if case-specific information or data 
indicate that the alternative approach is likely to produce a more 
accurate estimate of Level A Harassment, harm, or auditory injury for 
the proposed activities. Such a proposed alternative approach may be 
used if NMFS determines that the approach satisfies the requirements of 
the applicable statutes and regulations. The Commission noted that NMFS 
has not provided any criteria under which such an exception could be 
invoked and is allowing action proponents to waive the Guidance's 
acoustic thresholds. The Commission does not support this approach and 
recommends that NMFS require all action proponents to implement the 
final acoustic thresholds until such time that they are amended or 
revised by NMFS.
    Similar to the Commission's concerns, another commenter indicated 
any alternative approach must be at least as protective as methods 
prescribed in the Guidance, which have at least undergone peer review 
and public notice and comment. Alternatively, the commenter suggested 
that more conservative approaches should be used if a project's 
circumstances require a lower threshold for ``take'' based on specific 
factors, such as geographic region, oceanographic conditions, low 
abundance, species site fidelity, prey impacts or cumulative impacts.
    Contrary to the comments above, a few commenters indicated that 
they welcome the opportunity for action proponents to propose 
alternative approaches to those presented in the Guidance. The 
commenters noted that this flexibility will enable innovation within 
the bounds of regulatory compliance and that are appropriate and 
justified (e.g., there are many ways to estimate potential exposures of 
marine mammals to various sound levels).
    Response: The Technical Guidance is not a regulation or rule. It 
does not create or confer any rights for or on any person, or operate 
to bind the public. However, it is NMFS' assessment of the best 
available information for determining auditory impacts from exposure to 
anthropogenic sound and it has undergone extensive peer and public 
review. With that in mind, NMFS agrees with the comment that any 
alternative approach should be peer reviewed before it is used instead 
of the updated thresholds in the Technical Guidance (or the alternative 
methodology). With that addition to NMFS' statement in the Draft 
Guidance, an alternative approach that has undergone independent peer 
review may be proposed if in NMFS' view it ``is likely to produce an 
equally or more accurate estimate of auditory impacts for the project 
being evaluated, if NMFS determines the approach satisfies the 
requirements of the applicable statutes and regulations.'' NMFS 
believes this sets a fairly high bar as to what type of data/
alternative approach would justify a departure from the Guidance's 
auditory weighting functions and/or acoustic thresholds, especially in 
terms of the HISA standards to which this Guidance adheres. 
Additionally, action proponents are afforded flexibility for factors 
beyond the Guidance's auditory weighting functions and/or acoustic 
thresholds (e.g., propagation modeling, exposure modeling) as a means 
to accurately predict and assess the effects of noise on marine 
mammals.
    Comment 128: Multiple commenters requested flexibility associated 
with the accumulation period, especially for projects with a stationary 
source and for action proponents with limited ability to conduct 
detailed modeling (e.g., pile driving projects). The commenters 
recommended that NMFS allow for the flexibility to make project-
specific adjustments based on physical or biological factors associated 
with the activity.
    Response: NMFS acknowledges that all action proponents may not have 
the same level capabilities to apply the Technical Guidance and has 
provided an optional User Spreadsheet for action proponents that wish 
to avail themselves of it. Additionally, NMFS recognizes there may be 
some situations where project-specific modification may be necessary 
(i.e., action proponent should contact NMFS to discuss project-specific 
issues that are beyond scope of Technical Guidance).
    Comment 129: One commenter expressed concern that the updated 
acoustic thresholds could underestimate instances of PTS/TTS from 
permitted activities because marine mammals can be elusive and 
observations from protected species observers are few in relation to 
the estimated abundance. Similarly, one commenter asked how the 
acoustic thresholds would be used to calculate ``take'' after an 
activity is completed.
    Response: The acoustic thresholds are just one tool used to predict 
``take'' calculations. Other factors (e.g., sound propagation or marine 
mammal density/occurrence) contribute to these calculations though they 
are beyond the scope of the Technical Guidance. NMFS notes that the 
Technical Guidance's intended purpose is as a tool for predicting 
potential impacts of noise on hearing before an activity occurs (and 
perhaps afterward).
    Comment 130: The Commission requested clarification on how and when 
action proponents should use the qualitative factors identified within 
the Guidance and expressed concern that these factors could be used to 
allow for a reduction in ``take'' estimates based on subjective 
judgments rather than best available science. The Commission 
recommended that NMFS remove the list of qualitative factors listed and 
incorporate it by reference in the text and not allow action proponents 
to use

[[Page 51724]]

those factors to modify isopleths or numbers of ``takes'' resulting 
from the quantitative thresholds.
    Response: NMFS' intent of providing qualitative factors for 
consideration was to acknowledge that when additional data may become 
available in the future; these additional factors may be incorporated 
with quantitative PTS onset thresholds. At this time, however, it is 
not NMFS' intent for these factors to reduce quantitative exposure 
estimates based on subjective judgment. The Technical Guidance 
acknowledges that these factors are important for consideration within 
the comprehensive effects analysis on a qualitative basis. To avoid 
confusion, NMFS removed the list of qualitative factors from the 
threshold tables and placed this information in Appendix B: Research 
Recommendations.
Miscellaneous Issues
    Comment 131: One commenter requested clarification was on how much 
an acoustic threshold would need to change to update the Technical 
Guidance and suggested updates only occur when thresholds change by at 
least 5 dB.
    Response: NMFS has provided a procedure and timeline for updating 
the Guidance (Section III of main Guidance document) and will evaluate 
new studies as they become available, including in the context of 
existing data, before determining the impact to the acoustic 
thresholds.
    Comment 132: One commenter recommended the Guidance include a table 
indicating a species' hearing ability, sound production 
characteristics, and genetic relatedness to other species in order to 
determine when there are enough individuals of a particular species or 
genus to warrant species- or genus-specific acoustic thresholds, rather 
than relying on hearing group thresholds.
    Response: NMFS has used the best available science to support the 
division marine mammals into five hearing groups, including the 
derivation of composite audiograms based on available hearing data, and 
declines to include the requested table as it goes beyond the scope of 
the Technical Guidance. As science progresses (i.e., more data on 
hearing, sound production, genetics become available), NMFS will 
determine if further refinements of hearing groups and their associated 
auditory thresholds are needed.
    Comment 133: Several commenters requested that additional terms be 
better defined in the Guidance (e.g., isopleth, narrowband, roll-off, 
equal latency).
    Response: NMFS has added and defined these terms in the Glossary 
(Appendix E) and/or provided more clarification within the Technical 
Guidance.
    Comment 134: A few commenters suggested improvements to the 
Guidance, including technical editing, literature citation 
verification, and the inclusion of more plain language.
    Response: NMFS has verified that all references used in the 
Technical Guidance appear in the Literature Cited section and has 
included more plain language, when possible. However, NMFS notes this 
is a highly technical document, with most of the terms not easily 
subjected to plain language revisions without altering the accepted 
meaning of those terms. Additionally, definitions for technical terms 
used in this document are defined in the Glossary (Appendix E).

    Dated: July 29, 2016.
Donna S. Wieting,
Director, Office of Protected Resources, National Marine Fisheries 
Service.
[FR Doc. 2016-18462 Filed 8-3-16; 8:45 am]
 BILLING CODE 3510-22-P