Proposed Rule2022-16509
Taking and Importing Marine Mammals; Taking Marine Mammals Incidental to the U.S. Navy Training Activities in the Gulf of Alaska Study Area
Primary source
Metadata and text below are from the Federal Register, a public-domain U.S. government work. Always verify the official published version before relying on it for any legal matter.
Published
August 11, 2022
Issuing agencies
Commerce DepartmentNational Oceanic and Atmospheric Administration
Abstract
NMFS has received a request from the U.S. Navy (Navy) to take marine mammals incidental to training activities conducted in the Gulf of Alaska (GOA) Study Area (hereafter referred to as the GOA Study Area). Pursuant to the Marine Mammal Protection Act (MMPA), NMFS is requesting comments on its proposal to issue regulations and a subsequent Letter of Authorization (LOA) to the Navy to incidentally take marine mammals during the specified activities. NMFS will consider public comments prior to issuing any final rule and making final decisions on the issuance of the requested LOA. Agency responses to public comments will be provided in the notice of the final decision. The Navy's activities qualify as military readiness activities pursuant to the MMPA, as amended by the National Defense Authorization Act for Fiscal Year 2004 (2004 NDAA).
Full Text
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[Federal Register Volume 87, Number 154 (Thursday, August 11, 2022)]
[Proposed Rules]
[Pages 49656-49765]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2022-16509]
[[Page 49655]]
Vol. 87
Thursday,
No. 154
August 11, 2022
Part II
Department of Commerce
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National Oceanic and Atmospheric Administration
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50 CFR Part 218
Taking and Importing Marine Mammals; Taking Marine Mammals Incidental
to the U.S. Navy Training Activities in the Gulf of Alaska Study Area;
Proposed Rule
Federal Register / Vol. 87 , No. 154 / Thursday, August 11, 2022 /
Proposed Rules
[[Page 49656]]
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DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
50 CFR Part 218
[Docket No. 220726-0163]
RIN 0648-BK46
Taking and Importing Marine Mammals; Taking Marine Mammals
Incidental to the U.S. Navy Training Activities in the Gulf of Alaska
Study Area
AGENCY: National Marine Fisheries Service (NMFS), National Oceanic and
Atmospheric Administration (NOAA), Commerce.
ACTION: Proposed rule; request for comments and information.
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SUMMARY: NMFS has received a request from the U.S. Navy (Navy) to take
marine mammals incidental to training activities conducted in the Gulf
of Alaska (GOA) Study Area (hereafter referred to as the GOA Study
Area). Pursuant to the Marine Mammal Protection Act (MMPA), NMFS is
requesting comments on its proposal to issue regulations and a
subsequent Letter of Authorization (LOA) to the Navy to incidentally
take marine mammals during the specified activities. NMFS will consider
public comments prior to issuing any final rule and making final
decisions on the issuance of the requested LOA. Agency responses to
public comments will be provided in the notice of the final decision.
The Navy's activities qualify as military readiness activities pursuant
to the MMPA, as amended by the National Defense Authorization Act for
Fiscal Year 2004 (2004 NDAA).
DATES: Comments and information must be received no later than
September 26, 2022.
ADDRESSES: Submit all electronic public comments via the Federal e-
Rulemaking Portal. Go to <a href="https://www.regulations.gov">https://www.regulations.gov</a> and enter NOAA-
NMFS-2022-0060 in the Search box. Click on the ``Comment'' icon,
complete the required fields, and enter or attach your comments.
Instructions: Comments sent by any other method, to any other
address or individual, or received after the end of the comment period,
may not be considered by NMFS. All comments received are a part of the
public record and will generally be posted for public viewing on
<a href="http://www.regulations.gov">www.regulations.gov</a> without change. All personal identifying
information (e.g., name, address), confidential business information,
or otherwise sensitive information submitted voluntarily by the sender
will be publicly accessible. NMFS will accept anonymous comments (enter
``N/A'' in the required fields if you wish to remain anonymous).
Attachments to electronic comments will be accepted in Microsoft Word,
Excel, or Adobe PDF file formats only.
A copy of the Navy's application and other supporting documents and
documents cited herein may be obtained online at: <a href="https://www.fisheries.noaa.gov/action/incidental-take-authorization-us-navy-training-activities-gulf-alaska-temporary-maritime-0">https://www.fisheries.noaa.gov/action/incidental-take-authorization-us-navy-training-activities-gulf-alaska-temporary-maritime-0</a>. In case of
problems accessing these documents, please use the contact listed here
(see FOR FURTHER INFORMATION CONTACT).
FOR FURTHER INFORMATION CONTACT: Leah Davis, Office of Protected
Resources, NMFS, (301) 427-8401.
SUPPLEMENTARY INFORMATION:
Purpose of Regulatory Action
These proposed regulations, issued under the authority of the MMPA
(16 U.S.C. 1361 et seq.), would provide the framework for authorizing
the take of marine mammals incidental to the Navy's training activities
(which qualify as military readiness activities), including the use of
sonar and other transducers, and in-air detonations at or near the
surface (within 10 m above the water surface) in the GOA Study Area.
The GOA Study Area is comprised of three areas: the Temporary Maritime
Activities Area (TMAA), a warning area, and the Western Maneuver Area
(WMA) (see Figure 1). The TMAA and WMA are temporary areas established
within the GOA for ships, submarines, and aircraft to conduct training
activities. The warning area overlaps and extends slightly beyond the
northern corner of the TMAA. The WMA is located south and west of the
TMAA and provides additional surface, sub-surface, and airspace in
which to maneuver in support of activities occurring within the TMAA.
The use of sonar and other transducers, and explosives would not occur
within the WMA.
NMFS received an application from the Navy requesting 7-year
regulations and an authorization to incidentally take individuals of
multiple species of marine mammals (``Navy's rulemaking/LOA
application'' or ``Navy's application''). Take is anticipated to occur
by Level A harassment and Level B harassment incidental to the Navy's
training activities. No lethal take is anticipated or proposed for
authorization.
Background
The MMPA prohibits the ``take'' of marine mammals, with certain
exceptions. Sections 101(a)(5)(A) and (D) of the MMPA direct the
Secretary of Commerce (as delegated to NMFS) 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 and either regulations are proposed or, if the taking
is limited to harassment, the public is provided with notice of the
proposed incidental take authorization and provided the opportunity to
review and submit comments.
An authorization for incidental takings shall be granted if NMFS
finds that the taking will have a negligible impact on the species or
stocks and will not have an unmitigable adverse impact on the
availability of the species or stocks for taking for subsistence uses
(where relevant). Further, NMFS must prescribe the permissible methods
of taking and other means of effecting the least practicable adverse
impact on the affected species or stocks and their habitat, paying
particular attention to rookeries, mating grounds, and areas of similar
significance, and on the availability of such species or stocks for
taking for certain subsistence uses (referred to in this rule as
``mitigation measures''); and requirements pertaining to the monitoring
and reporting of such takings. The MMPA defines ``take'' to mean to
harass, hunt, capture, or kill, or attempt to harass, hunt, capture, or
kill any marine mammal. The Preliminary Analysis and Negligible Impact
Determination section below discusses the definition of ``negligible
impact.''
The NDAA for Fiscal Year 2004 (2004 NDAA) (Pub. L. 108-136) amended
section 101(a)(5) of the MMPA to remove the ``small numbers'' and
``specified geographical region'' provisions indicated above and
amended the definition of ``harassment'' as applied to a ``military
readiness activity.'' The definition of harassment for military
readiness activities (Section 3(18)(B) of the MMPA) is (i) 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 (ii) 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
[[Page 49657]]
point where such behavioral patterns are abandoned or significantly
altered (Level B harassment). In addition, the 2004 NDAA amended the
MMPA as it relates to military readiness activities such that the least
practicable adverse impact analysis shall include consideration of
personnel safety, practicality of implementation, and impact on the
effectiveness of the military readiness activity.
More recently, Section 316 of the NDAA for Fiscal Year 2019 (2019
NDAA) (Pub. L. 115-232), signed on August 13, 2018, amended the MMPA to
allow incidental take rules for military readiness activities under
section 101(a)(5)(A) to be issued for up to 7 years. Prior to this
amendment, all incidental take rules under section 101(a)(5)(A) were
limited to 5 years.
Summary and Background of Request
On October 9, 2020, NMFS received an adequate and complete
application from the Navy requesting authorization for take of marine
mammals, by Level A harassment and Level B harassment, incidental to
training from the use of active sonar and other transducers and
explosives (in-air, occurring at or above the water surface) in the
TMAA over a 7-year period beginning when the current authorization
expires. On March 12, 2021, the Navy submitted an updated application
that provided revisions to the Northern fur seal take estimate and
incorporated additional best available science. In August 2021, the
Navy communicated to NMFS that it was considering an expansion of the
GOA Study Area and an expansion of the Portlock Bank Mitigation Area
proposed in its previous applications. On February 2, 2022, the Navy
submitted a second updated application that described the addition of
the WMA to the GOA Study Area (which previously just consisted of the
TMAA) and the replacement of the Portlock Bank Mitigation Area with the
Continental Shelf and Slope Mitigation Area. The Navy is not planning
to conduct any testing activities.
On January 8, 2021 (86 FR 1483), we published a notice of receipt
(NOR) of application in the Federal Register, requesting comments and
information related to the Navy's request for 30 days. We received one
comment on the NOR that was non-substantive in nature.
The following types of training, which are classified as military
readiness activities pursuant to the MMPA, as amended by the 2004 NDAA,
would be covered under the regulations and LOA (if issued): surface
warfare (detonations at or above the water surface) and anti-submarine
warfare (sonar and other transducers). The Navy is also conducting Air
Warfare, Electronic Warfare, Naval Special Warfare, Strike Warfare, and
Support Operations, but these activities do not involve sonar and other
transducers, detonations at or above the water surface, or any other
stressors that could result in the take of marine mammals. (See the
2020 GOA Draft SEIS/OEIS for more detail on those activities). The
activities would not include in-water explosives, pile driving/removal,
or use of air guns.
This would be the third time NMFS has promulgated incidental take
regulations pursuant to the MMPA relating to similar military readiness
activities in the GOA, following those effective beginning May 4, 2011
(76 FR 25479; May 4, 2011) and April 26, 2017 (82 FR 19530; April 27,
2017).
The Navy's mission is to organize, train, equip, and maintain
combat-ready naval forces capable of winning wars, deterring
aggression, and maintaining freedom of the seas. This mission is
mandated by Federal law (10 U.S.C. 8062), which requires the readiness
of the naval forces of the United States. The Navy executes this
responsibility by establishing and executing training programs,
including at-sea training and exercises, and ensuring naval forces have
access to the ranges, operating areas (OPAREA), and airspace needed to
develop and maintain skills for conducting naval activities.
The Navy has conducted training activities in the TMAA portion of
the GOA Study Area since the 1990s. Since the 1990s, the Department of
Defense has conducted a major joint training exercise in Alaska and off
the Alaskan coast that involves the Departments of the Navy, Army, Air
Force, and Coast Guard participants reporting to a unified or joint
commander who coordinates the activities. These activities are planned
to demonstrate and evaluate the ability of the services to engage in a
conflict and successfully carry out plans in response to a threat to
national security. The Navy's planned activities for the period of this
proposed rule would be a continuation of the types and level of
training activities that have been ongoing for more than a decade.
While the specified activities have not changed, there are changes in
the platforms and systems used in those activities, as well as changes
in the bins (source classifications) used to analyze the activities.
(For example, two new sonar bins were added (MF12 and ASW1) and another
bin was eliminated (HF6). This was due to changes in platforms and
systems.) Further, the Navy expanded the GOA Study Area to include the
WMA, though the vast majority of the training activities would still
occur only in the TMAA.
The Navy's rulemaking/LOA application reflects the most up-to-date
compilation of training activities deemed necessary by senior Navy
leadership to accomplish military readiness requirements. The types and
numbers of activities included in the proposed rule account for
fluctuations in training in order to meet evolving or emergent military
readiness requirements. These proposed regulations would become
effective in December of 2022 and would cover training activities that
would occur for a 7-year period following the expiration of the current
MMPA authorization for the GOA, which expired on April 26, 2022.
Description of the Specified Activity
The Navy requests authorization to take marine mammals incidental
to conducting training activities. The Navy has determined that
acoustic and explosives stressors are most likely to result in impacts
on marine mammals that could rise to the level of harassment, and NMFS
concurs with this determination. Detailed descriptions of these
activities are provided in Chapter 2 of the 2020 GOA Draft Supplemental
Environmental Impact Statement (SEIS)/Overseas EIS (OEIS) (2020 GOA
DSEIS/OEIS) (<a href="https://www.goaeis.com/">https://www.goaeis.com/</a>) and in the Navy's rulemaking/LOA
application (<a href="https://www.fisheries.noaa.gov/action/incidental-take-authorization-us-navy-training-activities-gulf-alaska-temporary-maritime-0">https://www.fisheries.noaa.gov/action/incidental-take-authorization-us-navy-training-activities-gulf-alaska-temporary-maritime-0</a>) and are summarized here.
Dates and Duration
Training activities would be conducted intermittently in the GOA
Study Area over a maximum time period of up to 21 consecutive days
annually from April to October to support a major joint training
exercise in Alaska and off the Alaskan coast that involves the
Departments of the Navy, Army, Air Force, and Coast Guard. The
participants report to a unified or joint commander who coordinates the
activities planned to demonstrate and evaluate the ability of the
services to engage in a conflict and carry out plans in response to a
threat to national security. The specified activities would occur over
a maximum time period of up to 21 consecutive days each year during the
7-year period of validity of the regulations. The proposed number of
training activities are described in the Detailed Description of
Proposed Activities section (Table 3) of this proposed rule.
[[Page 49658]]
Geographical Region
The GOA Study Area (see Figure 1 below and Figure ES-1 of the 2022
Supplement to the 2020 GOA DSEIS/OEIS) is entirely at sea and is
comprised of the TMAA and a warning area in the Gulf of Alaska, and the
WMA. The term ``at-sea'' refers to training activities in the Study
Area (both the TMAA and WMA) that occur (1) on the ocean surface, (2)
beneath the ocean surface, and (3) in the air above the ocean surface.
Navy training activities occurring on or over the land outside the GOA
Study Area are not included in this proposed rule, and are covered
under separate environmental documentation prepared by the U.S. Air
Force and the U.S. Army. As depicted in Figure 1 of this proposed rule,
the TMAA is a polygon roughly resembling a rectangle oriented from
northwest to southeast, approximately 300 nmi (556 km) in length by 150
nmi (278 km) in width, located south of Montague Island and east of
Kodiak Island. The GOA Study Area boundary was intentionally designed
to avoid ESA-designated Steller sea lion critical habitat. The WMA is
located south and west of the TMAA, and provides an additional 185,806
nmi\2\ of surface, sub-surface, and airspace training to support
activities occurring within the TMAA (Figure 1). The boundary of the
WMA follows the bottom of the slope at the 4,000 m contour line, and
was configured to avoid overlap and impacts to ESA-designated critical
habitat, biologically important areas (BIAs), migration routes, and
primary fishing grounds. The WMA provides additional airspace and sea
space for aircraft and vessels to maneuver during training activities
for increased training complexity. The TMAA and WMA are temporary areas
established within the GOA for ships, submarines, and aircraft to
conduct training activities.
Additional detail can be found in Chapter 2 of the Navy's
rulemaking/LOA application.
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Primary Mission Areas
The Navy categorizes many of its training activities into
functional warfare areas called primary mission areas. The Navy's
planned activities for the GOA Study Area generally fall into the
following six primary mission areas: Air Warfare; Surface Warfare;
Anti-Submarine Warfare; Electronic Warfare; Naval Special Warfare; and
Strike Warfare. Most activities conducted in the GOA are categorized
under one of these primary mission areas; activities that do not fall
within one of these areas are listed as ``support operations'' or
``other training activities.'' Each warfare community (aviation,
surface, and subsurface) may train in some or all of these primary
mission areas. A description of the sonar, munitions, targets, systems,
and other materials used during training activities within these
primary mission areas is provided in Appendix A (Navy Activities
Descriptions) of the 2020 GOA DSEIS/OEIS and section ES.2.2 (Proposed
Activities in the Western Maneuver Area) of the 2022 Supplement to the
2020 GOA DSEIS/OEIS.
The Navy describes and analyzes the effects of its training
activities within the 2020 GOA DSEIS/OEIS and 2022 Supplement to the
2020 GOA DSEIS/OEIS. In its assessment, the Navy concluded that of the
activities to be conducted within the GOA Study Area, sonar use and in-
air explosives occurring at or above the water surface were the
stressors resulting in impacts on marine mammals that could rise to the
level of harassment as defined under the MMPA. (The Navy is not
proposing to conduct any activities that use in-water or underwater
explosives.) Further, these activities are limited to the TMAA. No
activities involving sonar use or explosives would occur in the WMA or
the portion of the warning area that extends beyond the TMAA.
Therefore, the Navy's rulemaking/LOA application provides the Navy's
assessment of potential effects from sonar use and explosives occurring
at or above the water surface in terms of the various warfare mission
areas they are associated with. Those mission areas include the
following:
<bullet> surface warfare (in-air detonations at or above the water
surface); \1\ and
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\1\ Defined herein as being within 10 meters of the ocean
surface.
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<bullet> anti-submarine warfare (sonar and other transducers).
The Navy's activities in Air Warfare, Electronic Warfare, Naval
Special Warfare, Strike Warfare, Support Operations, and Other Training
Activities do not involve sonar and other transducers, detonations at
or near the surface, or any other stressors that could result in
harassment, serious injury, or mortality of marine mammals. Therefore,
the activities in these warfare areas are not discussed further in this
proposed rule, but are analyzed fully in the 2020 GOA DSEIS/OEIS and
2022 Supplement to the 2020 GOA DSEIS/OEIS. The specific acoustic
sources analyzed in this proposed rule are contained in the 2020 GOA
DSEIS/OEIS and are presented in the following sections based on the
primary mission areas.
Surface Warfare
The mission of surface warfare (named anti-surface warfare in the
2011 GOA Final Environmental Impact Statement (FEIS)/Overseas
Environmental Impact Statement (OEIS) and 2016 GOA Final Supplemental
Environmental Impact Statement (FSEIS)/OEIS, but since changed by the
Navy to ``Surface Warfare'') is to obtain control of sea space from
which naval forces may operate, which entails offensive action against
surface targets while also defending against enemy forces. In surface
warfare, aircraft use guns, air-launched cruise missiles, or other
precision-guided munitions; ships employ naval guns and surface-to-
surface missiles; and submarines attack surface ships using anti-ship
cruise missiles.
Anti-Submarine Warfare
The mission of anti-submarine warfare is to locate, neutralize, and
defeat hostile submarine forces that threaten Navy surface forces.
Anti-submarine warfare can involve various assets such as aircraft,
ships, and submarines which all search for hostile submarines. These
forces operate together or independently to gain early warning and
detection, and to localize, track, target, and attack submarine
threats.
Anti-submarine warfare training addresses basic skills such as
detecting and classifying submarines, as well as evaluating sounds to
distinguish between enemy submarines and friendly submarines, ships,
and marine life. These integrated anti-submarine warfare training
exercises are conducted in coordinated, at-sea training events
involving submarines, ships, and aircraft.
Overview of the Major Training Exercise Within the GOA Study Area
The training activities in the GOA Study Area are considered to be
a major training exercise (MTE). A MTE, for purposes of this
rulemaking, is comprised of several unit-level activities conducted by
several units operating together, commanded and controlled by a single
Commander, and potentially generating more than 100 hours of active
sonar. These exercises typically employ an exercise scenario developed
to train and evaluate the exercise participants in tactical and
operational tasks. In a MTE, most of the activities being directed and
coordinated by the Commander in charge of the exercise are identical in
nature to the activities conducted during individual, crew, and smaller
unit-level training events. In a MTE, however, these disparate training
tasks are conducted in concert, rather than in isolation. At most, only
one MTE would occur in the GOA Study Area per year (over a maximum of
21 days).
Description of Stressors
The Navy uses a variety of sensors, platforms, weapons, and other
devices, including ones used to ensure the safety of Sailors and
Marines, to meet its mission. Training with these systems may introduce
sound and energy into the environment. The proposed training activities
were evaluated to identify specific components that could act as
stressors by having direct or indirect impacts on the environment. This
analysis included identification of the spatial variation of the
identified stressors. The following subsections describe the acoustic
and explosive stressors for marine mammals and their habitat (including
prey species) within the GOA Study Area. Each description contains a
list of activities that may generate the stressor. Stressor/resource
interactions that were determined to have de minimis or no impacts
(e.g., vessel noise, aircraft noise, weapons noise, and high-altitude
(greater than 10 m above the water surface) explosions) were not
carried forward for analysis in the Navy's rulemaking/LOA application.
The Navy fully considered the possibility of vessel strike, conducted
an analysis, and determined that requesting take of marine mammals by
vessel strike was not warranted. Although the Navy did not request take
for vessel strike, NMFS also fully analyzed the potential for vessel
strike of marine mammals as part of this rulemaking. Therefore, this
stressor is discussed in detail below. No Sinking Exercise (SINKEX)
events are proposed in the GOA Study Area for this rulemaking, nor is
establishment and use of a Portable Undersea Tracking Range (PUTR)
proposed. NMFS reviewed the Navy's analysis and conclusions on de
minimis and no-impact sources, included in Section 3.8.3 (Environmental
Consequences) of
[[Page 49661]]
the 2020 GOA DSEIS/OEIS and finds them complete and supportable.
Acoustic Stressors
Acoustic stressors include acoustic signals emitted into the water
for a specific purpose, such as sonar, other transducers (devices that
convert energy from one form to another--in this case, into sound
waves), incidental sources of broadband sound produced as a byproduct
of vessel movement, aircraft transits, and use of weapons or other
deployed objects. Explosives also produce broadband sound but are
characterized separately from other acoustic sources due to their
unique hazardous characteristics. Characteristics of each of these
sound sources are described in the following sections.
In order to better organize and facilitate the analysis of
approximately 300 sources of underwater sound used by the Navy,
including sonar and other transducers and explosives, a series of
source classifications, or source bins, were developed. The source
classification bins do not include the broadband noise produced
incidental to vessel movement, aircraft transits, and weapons firing.
Noise produced from vessel movement, aircraft transits, and use of
weapons or other deployed objects is not carried forward because those
activities were found to have de minimis or no impacts, as described
above.
The use of source classification bins provides the following
benefits:
<bullet> Provides the ability for new sensors or munitions to be
covered under existing authorizations, as long as those sources fall
within the parameters of a ``bin;''
<bullet> Improves efficiency of source utilization data collection
and reporting requirements anticipated under the MMPA authorizations;
<bullet> Ensures a precautionary approach to all impact estimates,
as all sources within a given class are modeled as the most impactful
source (highest source level, longest duty cycle, or largest net
explosive weight) within that bin;
<bullet> Allows analyses to be conducted in a more efficient
manner, without any compromise of analytical results; and
<bullet> Provides a framework to support the reallocation of source
usage (hours/explosives) between different source bins, as long as the
total numbers of takes remain within the overall analyzed and
authorized limits. This flexibility is required to support evolving
Navy training and testing requirements, which are linked to real world
events.
Sonar and Other Transducers
Active sonar and other transducers emit non-impulsive sound waves
into the water to detect objects, navigate safely, and communicate.
Passive sonars differ from active sound sources in that they do not
emit acoustic signals; rather, they only receive acoustic information
about the environment, or listen. In this proposed rule, the terms
sonar and other transducers will be used to indicate active sound
sources unless otherwise specified.
The Navy employs a variety of sonars and other transducers to
obtain and transmit information about the undersea environment. Some
examples are mid-frequency hull-mounted sonars used to find and track
enemy submarines; high-frequency small object detection sonars used to
detect mines; high-frequency underwater modems used to transfer data
over short ranges; and extremely high-frequency (greater than 200
kilohertz (kHz)) doppler sonars used for navigation, like those used on
commercial and private vessels. The characteristics of these sonars and
other transducers, such as source level, beam width, directivity, and
frequency, depend on the purpose of the source. Higher frequencies can
carry more information or provide more information about objects off
which they reflect, but attenuate more rapidly. Lower frequencies
attenuate less rapidly, so they may detect objects over a longer
distance, but with less detail.
Propagation of sound produced underwater is highly dependent on
environmental characteristics such as bathymetry, bottom type, water
depth, temperature, and salinity. The sound received at a particular
location will be different than near the source due to the interaction
of many factors, including propagation loss; how the sound is
reflected, refracted, or scattered; the potential for reverberation;
and interference due to multi-path propagation. In addition, absorption
greatly affects the distance over which higher-frequency sounds
propagate. The effects of these factors are explained in Appendix B
(Acoustic and Explosive Concepts) of the 2020 GOA DSEIS/OEIS. Because
of the complexity of analyzing sound propagation in the ocean
environment, the Navy relies on acoustic models in its environmental
analyses that consider sound source characteristics and varying ocean
conditions across the TMAA. As noted above, the Navy does not propose
to use sonar and other transducers within the WMA.
The sound sources and platforms typically used in naval activities
analyzed in the Navy's rulemaking/LOA application are described in
Appendix A (Navy Activities Descriptions) of the 2020 GOA DSEIS/OEIS.
Sonars and other transducers used to obtain and transmit information
underwater during Navy training activities generally fall into several
categories of use described below.
Anti-Submarine Warfare
Sonar used during anti-submarine warfare would impart the greatest
amount of acoustic energy of any category of sonar and other
transducers analyzed in this proposed rule. Types of sonars used to
detect potential enemy vessels include hull-mounted, towed, line array,
sonobuoy, and helicopter dipping sonars. In addition, acoustic targets
and decoys (countermeasures) may be deployed to emulate the sound
signatures of vessels or repeat received signals.
Most anti-submarine warfare sonars are mid-frequency (1-10 kHz)
because mid-frequency sound balances sufficient resolution to identify
targets with distance over which threats can be identified. However,
some sources may use higher or lower frequencies. Duty cycles can vary
widely, from rarely used to continuously active. For example, anti-
submarine warfare sonars can be wide angle in a search mode or highly
directional in a track mode.
Most anti-submarine warfare activities involving submarines or
submarine targets would occur in waters greater than 600 feet (ft; 183
m) deep due to safety concerns about running aground at shallower
depths.
Navigation and Safety
Similar to commercial and private vessels, Navy vessels employ
navigational acoustic devices, including speed logs, Doppler sonars for
ship positioning, and fathometers. These may be in use at any time for
safe vessel operation. These sources are typically highly directional
to obtain specific navigational data.
Communication
Sound sources used to transmit data (such as underwater modems),
provide location (pingers), or send a single brief release signal to
bottom-mounted devices (acoustic release) may be used throughout the
TMAA. These sources typically have low duty cycles and are usually only
used when it is desirable to send a detectable acoustic message.
Classification of Sonar and Other Transducers
Sonars and other transducers are grouped into classes that share an
[[Page 49662]]
attribute, such as frequency range or purpose. As detailed below,
classes are further sorted by bins based on the frequency or bandwidth;
source level; and, when warranted, the application for which the source
would be used. Unless stated otherwise, a reference distance of 1 meter
(m) is used for sonar and other transducers.
<bullet> Frequency of the non-impulsive acoustic source:
[cir] Low-frequency sources operate below 1 kHz;
[cir] Mid-frequency sources operate at and above 1 kHz, up to and
including 10 kHz;
[cir] High-frequency sources operate above 10 kHz, up to and
including 100 kHz; and
[cir] Very-high-frequency sources operate above 100 kHz but below
200 kHz.
<bullet> Sound pressure level:
[cir] Greater than 160 decibels (dB) referenced to 1 micropascal
(re: 1 [micro]Pa), but less than 180 dB re: 1 [micro]Pa;
[cir] Equal to 180 dB re: 1 [micro]Pa and up to and including 200
dB re: 1 [micro]Pa; and
[cir] Greater than 200 dB re: 1 [micro]Pa.
<bullet> Application for which the source would be used:
[cir] Sources with similar functions that have similar
characteristics, such as pulse length (duration of each pulse), beam
pattern, and duty cycle.
The bins used for classifying active sonars and transducers that
are quantitatively analyzed in the TMAA are shown in Table 1. While
general parameters or source characteristics are shown in the table,
actual source parameters are classified.
Table 1--Sonar and Other Transducers Quantitatively Analyzed in the TMAA
----------------------------------------------------------------------------------------------------------------
For annual training activities
-----------------------------------------------------------------------------------------------------------------
Source class category Bin Description Units Annual 7-Year total
----------------------------------------------------------------------------------------------------------------
Mid-Frequency (MF) Tactical MF1 Hull-mounted H 271 1,897
and non-tactical sources surface ship
that produce signals from 1 sonars (e.g.,
to 10 kHz. AN/SQS-53C and
AN/SQS-60).
MF3 Hull-mounted H 25 175
submarine
sonars (e.g.,
AN/BQQ-10).
MF4 Helicopter- H 27 189
deployed
dipping sonars
(e.g., AN/AQS-
22).
MF5 Active acoustic I 126 882
sonobuoys
(e.g., DICASS).
MF6 Active I 14 98
underwater
sound signal
devices (e.g.,
MK 84).
MF11 Hull-mounted H 42 294
surface ship
sonars with an
active duty
cycle greater
than 80%.
MF12 Towed array H 14 98
surface ship
sonars with an
active duty
cycle greater
than 80%.
High-Frequency (HF) Tactical HF1 Hull-mounted H 12 84
and non-tactical sources submarine
that produce signals greater sonars (e.g.,
than 10 kHz but less than AN/BQQ-10).
100 kHz.
Anti-Submarine Warfare (ASW) ASW1 MF systems H 14 98
Tactical sources used during operating
ASW training activities. above 200 dB.
ASW2 MF Multistatic H 42 294
Active
Coherent
sonobuoy
(e.g., AN/SSQ-
125).
ASW3 MF towed active H 273 1,911
acoustic
countermeasure
systems (e.g.,
AN/SLQ-25).
ASW4 MF expendable I 7 49
active
acoustic
device
countermeasure
s (e.g., MK3).
----------------------------------------------------------------------------------------------------------------
Notes: H = hours, I = count (e.g., number of individual pings or individual sonobuoys), DICASS = Directional
Command Activated Sonobuoy System.
Explosive Stressors
The near-instantaneous rise from ambient to an extremely high peak
pressure is what makes an explosive shock wave potentially damaging.
Farther from an explosive, the peak pressures decay and the explosive
waves propagate as an impulsive, broadband sound. Several parameters
influence the effect of an explosive: the weight of the explosive in
the warhead, the type of explosive material, the boundaries and
characteristics of the propagation medium, and the detonation depth in
water. The net explosive weight, which is the explosive power of a
charge expressed as the equivalent weight of trinitrotoluene (TNT),
accounts for the first two parameters. The effects of these factors are
explained in Appendix B (Acoustic and Explosive Concepts) of the 2020
GOA DSEIS/OEIS.
Explosive Use
Explosive detonations during training activities are from the use
of explosive bombs, and naval gun shells; however, no in-water
explosive detonations are included as part of the training activities.
For purposes of the analysis in this proposed rule, detonations
occurring in air at a height of 33 ft (10 m) or less above the water
surface, and detonations occurring directly on the water surface, were
modeled to detonate at a depth of 0.3 ft (0.1 m) below the water
surface since there is currently no other identified methodology for
modeling potential effects to marine
[[Page 49663]]
mammals that are underwater as a result of detonations occurring in-air
at or above the surface of the ocean (within 10 m above the surface).
This conservative approach over-estimates the potential underwater
impacts due to low-altitude and surface explosives by assuming that all
explosive energy is released and remains under the water surface.
Explosive stressors resulting from the detonation of some
munitions, such as missiles and gun rounds used in air-air and surface-
air scenarios, occur at high altitude. The resulting sound energy from
those detonations in air would not impact marine mammals. The explosive
energy released by detonations in air has been well studied, and basic
methods are available to estimate the explosive energy exposure with
distance from the detonation (e.g., U.S. Department of the Navy
(1975)). In air, the propagation of impulsive noise from an explosion
is highly influenced by atmospheric conditions, including temperature
and wind. While basic estimation methods do not consider the unique
environmental conditions that may be present on a given day, they do
allow for approximation of explosive energy propagation under neutral
atmospheric conditions. Explosions that occur during Air Warfare would
typically be at a sufficient altitude that a large portion of the sound
refracts upward due to cooling temperatures with increased altitude.
Based on an understanding of the explosive energy released by
detonations in air, detonations occurring in air at altitudes greater
than 10 m above the surface of the ocean are not likely to result in
acoustic impacts on marine mammals; therefore, these types of explosive
activities will not be discussed further in this document. (Note that
most of these in-air detonations would occur at altitudes substantially
greater than 10 m above the surface of the ocean, as described in
further detail in section 3.0.4.2.2 (Explosions in Air) of the 2020 GOA
DSEIS/OEIS.) Activities such as air-surface bombing or surface-surface
gunnery scenarios may involve the use of explosive munitions that
detonate upon impact with targets at or above the water surface (within
10 m above the surface). For these activities, acoustic effects
modeling was undertaken as described below.
In order to organize and facilitate the analysis of explosives,
explosive classification bins were developed. The use of explosive
classification bins provides the same benefits as described for
acoustic source classification bins in the Acoustic Stressors section,
above.
The explosive bin types and the number of explosives detonating at
or above the water surface in the TMAA are shown in Table 2.
Table 2--Explosive Sources Quantitatively Analyzed That Detonate At or Above the Water Surface in the TMAA
----------------------------------------------------------------------------------------------------------------
Number of explosives
Explosives (source class and net explosive weight (NEW)) Number of explosives with the specified
(lb.) * with the specified activity (7-year
activity (annually) total)
----------------------------------------------------------------------------------------------------------------
E5 (>5-10 lb. NEW)............................................ 56 392
E9 (>100-250 lb. NEW)......................................... 64 448
E10 (>250-500 lb. NEW)........................................ 6 42
E12 (>650-1,000 lb. NEW)...................................... 2 14
----------------------------------------------------------------------------------------------------------------
* All of the E5, E9, E10, and E12 explosives would occur in-air, at or above the surface of the water, and would
also occur offshore away from the continental shelf and slope beyond the 4,000-meter isobath.
Propagation of explosive pressure waves in water is highly
dependent on environmental characteristics such as bathymetry, bottom
type, water depth, temperature, and salinity, which affect how the
pressure waves are reflected, refracted, or scattered; the potential
for reverberation; and interference due to multi-path propagation. In
addition, absorption greatly affects the distance over which higher-
frequency components of explosive broadband noise can propagate.
Appendix B (Acoustic and Explosive Concepts) of the 2020 GOA DSEIS/OEIS
explains the characteristics of explosive detonations and how the above
factors affect the propagation of explosive energy in the water.
Because of the complexity of analyzing sound propagation in the ocean
environment, the Navy relies on acoustic models in its environmental
analyses that consider sound source characteristics and varying ocean
conditions across the TMAA.
For in-air explosives detonating at or above the water surface, the
model estimating acoustic impacts assumes that all acoustic energy from
the detonation is underwater with no loss of sound or energy into the
air. Important considerations must be factored into the analysis of
results with these modeling assumptions, given that the peak pressure
and sound from a detonation in air significantly decreases across the
air-water interface as it is partially reflected by the water's surface
and partially transmitted underwater, as detailed in the following
paragraphs.
Detonation of an explosive in air creates a supersonic high
pressure shock wave that expands outward from the point of detonation
(Kinney and Graham, 1985; Swisdak, 1975). The near-instantaneous rise
from ambient to an extremely high peak pressure is what makes the
explosive shock wave potentially injurious to an animal experiencing
the rapid pressure change (U.S. Department of the Navy, 2017a). As the
shock wave-front travels away from the point of detonation, it slows
and begins to behave as an acoustic wave-front travelling at the speed
of sound. Whereas a shock wave from a detonation in-air has an abrupt
peak pressure, that same pressure disturbance when transmitted through
the water surface results in an underwater pressure wave that begins
and ends more gradually compared with the in-air shock wave, and
diminishes with increasing depth and distance from the source (Bolghasi
et al., 2017; Chapman and Godin, 2004; Cheng and Edwards, 2003; Moody,
2006; Richardson et al., 1995; Sawyers, 1968; Sohn et al., 2000;
Swisdak, 1975; Waters and Glass, 1970; Woods et al., 2015). The
propagation of the shock wave in-air and then transitioning underwater
is very different from a detonation occurring deep underwater where
there is little interaction with the surface. In the case of an
underwater detonation occurring just below the surface, a portion of
the energy from the detonation would be released into the air (referred
to as surface blow off), and at greater depths a pulsating, air-filled
cavitation bubble would form, collapse, and reform around the
detonation point (Urick, 1983). The Navy's acoustic effects model for
analyzing underwater impacts on marine species does not account for the
loss of energy due to surface blow-
[[Page 49664]]
off or cavitation at depth. Both of these phenomena would diminish the
magnitude of the acoustic energy received by an animal under real-world
conditions (U.S. Department of the Navy, 2018b).
To more completely analyze the results predicted by the Navy's
acoustic effects model from detonations occurring in-air above the
ocean surface, it is necessary to consider the transfer of energy
across the air-water interface. Much of the scientific literature on
the transferal of shock wave impulse across the air-water interface has
focused on energy from sonic booms created by fast moving aircraft
flying at low altitudes above the ocean (Chapman and Godin, 2004; Cheng
and Edwards, 2003; Moody, 2006; Sawyers, 1968; Waters and Glass, 1970).
The shock wave created by a sonic boom is similar to the propagation of
a pressure wave generated by an explosion (although having a
significantly slower rise in peak pressure) and investigations of sonic
booms are somewhat informative. Waters and Glass (1970) were also
investigating sonic booms, but their methodology involved actual in-air
detonations. In those experiments, they detonated blasting caps
elevated 30 ft (9 m) above the surface in a flooded quarry and measured
the resulting pressure at and below the surface to determine the
penetration of the shock wave across the air-water interface.
Microphones above the water surface recorded the peak pressure in-air,
and hydrophones at various shallow depths underwater recorded the
unreflected remainder of the pressure wave after transition across the
air-water interface. The peak pressure measurements were compared and
the results supported the theoretical expectations for the penetration
of a pressure wave from air into water, including the predicted
exponential decay of energy with distance from the source underwater.
In effect, the air-water interface acted as a low-pass filter
eliminating the high-frequency components of the shock wave. At
incident angles greater than 14 degrees perpendicular to the surface,
most of the shock wave from the detonation was reflected off the water
surface, which is consistent with results from similar research (Cheng
and Edwards, 2003; Moody, 2006; Yagla and Stiegler, 2003). Given that
marine mammals spend, on average, up to 90 percent of their time
underwater (Costa, 1993; Costa and Block, 2009), and the shock wave
from a detonation is only a few milliseconds in duration, marine
mammals are unlikely to be exposed in-air when surfaced.
Vessel Strike
NMFS also considered the chance that a vessel utilized in training
activities could strike a marine mammal in the GOA Study Area,
including both the TMAA and WMA portions of the Study Area. Vessel
strikes have the potential to result in incidental take from serious
injury and/or mortality. Vessel strikes are not specific to any
particular training activity, but rather are a limited, sporadic, and
incidental result of Navy vessel movement within a study area. Vessel
strikes from commercial, recreational, and military vessels are known
to seriously injure and occasionally kill cetaceans (Abramson et al.,
2011; Berman-Kowalewski et al., 2010; Calambokidis, 2012; Douglas et
al., 2008; Laggner, 2009; Lammers et al., 2003; Van der Hoop et al.,
2012; Van der Hoop et al., 2013), although reviews of the literature on
ship strikes mainly involve collisions between commercial vessels and
whales (Jensen and Silber, 2003; Laist et al., 2001). Vessel speed,
size, and mass are all important factors in determining both the
potential likelihood and impacts of a vessel strike to marine mammals
(Conn and Silber, 2013; Gende et al., 2011; Silber et al., 2010;
Vanderlaan and Taggart, 2007; Wiley et al., 2016). For large vessels,
speed and angle of approach can influence the severity of a strike.
Navy vessels transit at speeds that are optimal for fuel
conservation and to meet training requirements. Vessels used as part of
the proposed specified activities include ships, submarines, unmanned
vessels, and boats ranging in size from small, 22 ft (7 m) rigid hull
inflatable boats to aircraft carriers with lengths up to 1,092 ft (333
m). The average speed of large Navy ships ranges between 10 and 15
knots (kn; 19-28 km/hr), and submarines generally operate at speeds in
the range of 8 to 13 kn (15 to 24 km/hr), while a few specialized
vessels can travel at faster speeds. Small craft (for purposes of this
analysis, less than 18 m in length) have much more variable speeds (0
to 50+ kn (0 to 93+ km/hr)), dependent on the activity), but generally
range from 10 to 14 kn (19-26 km/hr). From unpublished Navy data,
average median speed for large Navy ships in the other Navy ranges from
2011-2015 varied from 5 to 10 kn (9 to 19 km/hr) with variations by
ship class and location (i.e., slower speeds close to the coast).
Similar patterns would occur in the GOA Study Area. A full description
of Navy vessels that are used during training activities can be found
in Section 1.2.1 and Section 2.4.2.1 of the 2011 GOA FEIS/OEIS.
While these speeds are representative of most events, some vessels
need to temporarily operate outside of these parameters for certain
times or during certain activities. For example, to produce the
required relative wind speed over the flight deck, an aircraft carrier
engaged in flight operations must adjust its speed through the water
accordingly. Also, there are other instances, such as launch and
recovery of a small rigid hull inflatable boat; vessel boarding,
search, and seizure training events; or retrieval of a target when
vessels would be dead in the water or moving slowly ahead to maintain
steerage.
Large Navy vessels (greater than 18 m in length) within the
offshore areas of range complexes operate differently from commercial
vessels in ways that may reduce potential whale collisions. Surface
ships operated by or for the Navy have multiple personnel assigned to
stand watch at all times when a ship or surfaced submarine is moving
through the water (underway). A primary duty of personnel standing
watch on surface ships is to detect and report all objects and
disturbances sighted in the water that may indicate a threat to the
vessel and its crew, such as debris, a periscope, surfaced submarine,
or surface disturbance. Per vessel safety requirements, personnel
standing watch also report any marine mammals sighted in the path of
the vessel as a standard collision avoidance procedure. All vessels
proceed at a safe speed so they can take proper and effective action to
avoid a collision with any sighted object or disturbance, and can be
stopped within a distance appropriate to the prevailing circumstances
and conditions.
Detailed Description of Proposed Activities
Proposed Training Activities
The Navy proposes to conduct a single carrier strike group (CSG)
exercise which would last for a maximum of 21 consecutive days in a
year. The CSG exercise is comprised of several individual training
activities. Table 3 lists and describes those individual activities
that may result in takes of marine mammals. The events listed would
occur intermittently during the 21 days and could be simultaneous and
in the same general area within the TMAA or could be independent and
spatially separate from other ongoing activities. The table is
organized according to primary mission areas and includes the activity
name, associated stressor(s), description and duration of the activity,
sound source bin, the areas
[[Page 49665]]
where the activities are conducted in the GOA Study Area, the maximum
number of events per year in the 21-day period, and the maximum number
of events over 7 years. Not all sound sources are used with each
activity. The ``Annual # of Events'' column indicates the maximum
number of times that activity could occur during any single year. The
``7-Year # of Events'' is the maximum number of times an activity would
occur over the 7-year period of the proposed regulations if the
training occurred each year and at the maximum levels requested. The
events listed would occur intermittently during the exercise over a
maximum of 21 days. The maximum number of activities may not occur in
some years, and historically, training has occurred only every other
year. However, to conduct a conservative analysis, NMFS analyzed the
maximum times these activities could occur over one year and 7 years.
The 2020 GOA DSEIS/OEIS includes more detailed activity descriptions.
(Note the Navy proposes no low-frequency active sonar (LFAS) use for
the activities in this rulemaking.)
Table 3--Proposed Training Activities Analyzed for the 7-Year Period in the GOA Study Area
----------------------------------------------------------------------------------------------------------------
Annual # of 7-year # of
Stressor category Activity Description Source bin events events
----------------------------------------------------------------------------------------------------------------
Surface Warfare
----------------------------------------------------------------------------------------------------------------
Explosive.................... Gunnery Surface ship E5............. 6 42
Exercise, crews fire
Surface-to- inert small-
Surface (GUNEX- caliber, inert
S-S). medium-
caliber, or
large-caliber
explosive
rounds at
surface
targets.
Explosive.................... Bombing Fixed-wing E9, E10, E12... 18 126
Exercise (Air- aircraft
to-Surface) conduct
(BOMBEX [A-S]). bombing
exercises
against
stationary
floating
targets, towed
targets, or
maneuvering
targets.
----------------------------------------------------------------------------------------------------------------
Anti-Submarine Warfare (ASW)
----------------------------------------------------------------------------------------------------------------
Acoustic..................... Tracking Helicopter MF4, MF5, MF6.. 22 154
Exercise--Heli crews search
copter for, track,
(TRACKEX--Helo and detect
). submarines.
Acoustic..................... Tracking Maritime patrol MF5, MF6, ASW2. 13 91
Exercise--Mari aircraft crews
time Patrol search for,
Aircraft track, and
(TRACKEX--MPA). detect
submarines.
Acoustic..................... Tracking Surface ship ASW1, ASW3, 2 14
Exercise--Ship crews search MF1, MF11,
(TRACKEX--Ship for, track, MF12.
). and detect
submarines.
Acoustic..................... Tracking Submarine crews ASW4, HF1, MF3. 2 14
Exercise--Subm search for,
arine track, and
(TRACKEX--Sub). detect
submarines.
----------------------------------------------------------------------------------------------------------------
Notes: S-S = Surface to Surface, A-S = Air to Surface.
Standard Operating Procedures
For training to be effective, personnel must be able to safely use
their sensors and weapon systems as they are intended to be used in
military missions and combat operations and to their optimum
capabilities. Standard operating procedures applicable to training have
been developed through years of experience, and their primary purpose
is to provide for safety (including public health and safety) and
mission success. Because standard operating procedures are essential to
safety and mission success, the Navy considers them to be part of the
proposed specified activities, and has included them in the analysis.
In many cases, there are benefits to natural and cultural resources
resulting from standard operating procedures. Standard operating
procedures that are recognized as having a potential benefit to marine
mammals during training activities are noted below and discussed in
more detail within the 2020 GOA DSEIS/OEIS.
<bullet> Vessel Safety;
<bullet> Weapons Firing Procedures;
<bullet> Target Deployment and Retrieval Safety; and
<bullet> Towed In-Water Device Procedures.
Standard operating procedures (which are implemented regardless of
their secondary benefits) are different from mitigation measures (which
are designed entirely for the purpose of avoiding or reducing impacts).
Information on mitigation measures is provided in the Proposed
Mitigation Measures section below. Additional information on standard
operating procedures is presented in Section 2.3.2 (Standard Operating
Procedures) in the 2020 GOA DSEIS/OEIS.
Description of Marine Mammals and Their Habitat in the Area of the
Specified Activities
Marine mammal species and their associated stocks that have the
potential to occur in the GOA Study Area are presented in Table 4 along
with each stock's ESA and MMPA statuses, abundance estimate and
associated coefficient of variation value, minimum abundance estimate,
and expected occurrence in the GOA Study Area. The Navy requested
authorization to take individuals of 16 marine mammal species by Level
A harassment and Level B harassment, and NMFS has conservatively
analyzed and proposes to authorize incidental take of two additional
species. The Navy does not request authorization for any serious
injuries or mortalities of marine mammals, and NMFS agrees that serious
injury and mortality is unlikely to occur from the Navy's activities.
NMFS recently designated critical habitat under the Endangered Species
Act (ESA) for humpback whales in the TMAA portion of the GOA Study
Area, and this designated critical habitat is considered below (86 FR
21082; April 21, 2021). The WMA portion of the GOA Study Area does not
overlap ESA-designated critical habitat for humpback whales or any
other species.
Information on the status, distribution, abundance, population
trends, habitat, and ecology of marine mammals in the GOA Study Area
may be found in Chapter 4 of the Navy's rulemaking/LOA application.
NMFS has reviewed this information and found it
[[Page 49666]]
to be accurate and complete. Additional information on the general
biology and ecology of marine mammals is included in the 2020 GOA
DSEIS/OEIS. Table 4 incorporates the best available science, including
data from the 2020 U.S. Pacific and the Alaska Marine Mammal Stock
Assessment Reports (SARs; Carretta et al., 2021; Muto et al., 2021),
2021 draft U.S. Pacific and Alaska Marine Mammal SARs, as well as
monitoring data from the Navy's marine mammal research efforts.
To better define marine mammal occurrence in the TMAA, the portion
of the GOA Study Area where take of marine mammals is anticipated to
occur, four regions within the TMAA were defined (and are depicted in
Figure 3-1 of the Navy's rulemaking/LOA application), consistent with
the survey strata used by Rone et al. (2017) during the most recent
marine mammal surveys in the TMAA. The four regions are: inshore,
slope, seamount, and offshore.
Species Not Included in the Analysis
There has been no change in the species unlikely to be present in
the GOA Study Area since the last MMPA rulemaking process (82 FR 19530;
April 27, 2017). The species carried forward for analysis are those
likely to be found in the GOA Study Area based on the most recent data
available and do not include species that may have once inhabited or
transited the area but have not been sighted in recent years (e.g.,
species which were extirpated from factors such as 19th and 20th
century commercial exploitation). Several species and stocks that may
be present in the northeast Pacific Ocean generally have an extremely
low probability of presence in the GOA Study Area. These species and
stocks are considered extralimital (may be sightings, acoustic
detections, or stranding records, but the GOA Study Area is outside the
species' range of normal occurrence) or rare (occur in the GOA Study
Area sporadically, but sightings are rare). These species and stocks
include the Eastern North Pacific Northern Resident and the West Coast
Transient stocks of killer whale (Orcinus orca), beluga whale
(Delphinapterus leucas), false killer whale (Pseudorca crassidens),
short-finned pilot whale (Globicephala macrorhynchus), northern right
whale dolphin (Lissodelphis borealis), and Risso's dolphin (Grampus
griseus).
The Eastern North Pacific Northern Resident and the West Coast
Transient stocks of killer whale are considered extralimital in the GOA
Study Area. Given the paucity of any beluga whale sightings in the GOA
(Laidre et al. 2000), the occurrence of this species within the GOA
Study Area is considered extralimital. The GOA Study Area is also
outside of the normal range of the false killer whale's distribution in
the Pacific Ocean, and despite rare stranding or sighting reports, the
GOA Study Area is outside of the normal range of the short-finned pilot
whale as well. There are two sighting records of northern right whale
dolphins in the Gulf of Alaska, but these are considered extremely rare
(U.S. Department of the Navy 2006; NOAA 2012) and extralimital in the
GOA Study Area. There are a few records of Risso's dolphins near the
GOA Study Area; however, their occurrence within the GOA Study Area is
rare, and therefore Risso's dolphin is considered extralimital. NMFS
agrees with the Navy's assessment that these species are unlikely to
occur in the GOA Study Area and they are not discussed further.
One species of marine mammal, the Northern sea otter, occurs in the
Gulf of Alaska but is managed by the U.S. Fish and Wildlife Service and
is not considered further in this document.
Table 4--Marine Mammal Occurrence Within the GOA Study Area
--------------------------------------------------------------------------------------------------------------------------------------------------------
Stock abundance
ESA status, (CV, Nmin, year of
Common name Scientific name Stock MMPA status, most recent PBR Annual M/ Occurrence in GOA
strategic (Y/ abundance survey) SI \3\ study area \4\
N) \1\ \2\
--------------------------------------------------------------------------------------------------------------------------------------------------------
Order Cetacea--Suborder Mysticeti (baleen whales)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Family Balaenidae (right
whales):
North Pacific right whale... Eubalaena japonica. Eastern North E, D, Y 31 (0.226, 26, \5\ 0.05 0 Rare.
Pacific. 2008).
Family Balaenopteridae
(rorquals):
Humpback whale.............. Megaptera Central North -, -, Y 10,103 (0.3, 83 26 Seasonal; highest
novaeangliae. Pacific \6\. 7,891, 2006). likelihood June
to September.
California, Oregon, -, -, Y 4,973 (0.05, 28.7 >=48.6 Seasonal; highest
and Washington \6\. 4,776, 2018). likelihood June
to September.
Western North E, D, Y 1,107 (0.3, 865, 3 2.8 Seasonal; highest
Pacific. 2006). likelihood June
to September.
Blue whale.................. Balaenoptera Eastern North E, D, Y 1,898 (0.085, 4.1 >=19.4 Seasonal; highest
musculus. Pacific. 1,767, 2018). likelihood June
to December.
Central North E, D, Y 133 (1.09, 63, 0.1 0 Seasonal; highest
Pacific. 2010). likelihood June
to December.
Fin whale................... Balaenoptera Northeast Pacific.. E, D, Y 3,168 (0.26, 5.1 0.6 Likely.
physalus. 2,554, 2013) \7\.
Sei whale................... Balaenoptera Eastern North E, D, Y 519 (0.4, 374, 0.75 >=0.2 Rare.
borealis. Pacific \8\. 2014).
Minke whale................. Balaenoptera Alaska............. -, -, N UNK............... UND 0 Likely.
acutorostrata.
Family Eschrichtiidae (gray
whale):
Gray whale.................. Eschrichtius Eastern North -, -, N 26,960 (0.05, 801 131 Likely: Highest
robustus. Pacific. 25,849, 2016). numbers during
seasonal
migrations (fall,
winter, spring).
[[Page 49667]]
Western North E, D, Y 290 (N/A, 271, 0.12 UNK Rare: Individuals
Pacific. 2016). migrate through
GOA.
--------------------------------------------------------------------------------------------------------------------------------------------------------
Order Cetacea--Suborder Odontoceti (toothed whales)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Family Physeteridae (sperm
whale):
Sperm whale................. Physeter North Pacific...... E, D, Y 345 (0.43, 244, UND 3.5 Likely; More
macrocephalus. 2015) \9\. likely in waters
>1,000 m depth,
most often >2,000
m.
Family Delphinidae (dolphins):
Killer whale................ Orcinus orca....... Eastern North -, -, N \10\ 2,347 (N/A, 24 1 Likely.
Pacific Alaska 2,347, 2012).
Resident.
Eastern North -, -, N 300 (0.1, 276, 2.8 0 Likely.
Pacific Offshore. 2012).
AT1 Transient...... -, D, Y \10\ 7 (N/A, 7, 0.01 0 Rare; more likely
2018). inside Prince
William Sound and
Kenai Fjords.
Eastern North -, -, N \10\ 587 (N/A, 5.87 0.8 Likely.
Pacific GOA, 587, 2012).
Aleutian Island,
and Bering Sea
Transient.
Pacific white-sided dolphin. Lagenorhynchus North Pacific...... -, -, N 26,880 (N/A, N/A, UND 0 Likely.
obliquidens. 1990).
Family Phocoenidae (porpoises):
Harbor porpoise............. Phocoena phocoena.. GOA................ -, -, Y 31,046 (0.21, N/A, UND 72 Rare; Inshore and
1998). Slope Regions, if
present.
Southeast Alaska... -, -, Y 1,354 (0.12, 12 34 Rare.
1,224, 2012).
Dall's porpoise............. Phocoenoides dalli. Alaska............. -, -, N 83,400 (0.097, UND 37 Likely.
3,110, 2015).
Family Ziphiidae (beaked
whales):
Cuvier's beaked whale....... Ziphius cavirostris Alaska............. -, -, N UNK............... UND 0 Likely.
Baird's beaked whale........ Berardius bairdii.. Alaska............. -, -, N UNK............... UND 0 Likely.
Stejneger's beaked whale.... Mesoplodon Alaska............. -, -, N UNK............... UND 0 Likely.
stejnegeri.
--------------------------------------------------------------------------------------------------------------------------------------------------------
Order Carnivora--Suborder Pinnipedia \8\
--------------------------------------------------------------------------------------------------------------------------------------------------------
Family Otarieidae (fur seals and
sea lions):
Steller sea lion............ Eumetopias jubatus. Eastern U.S........ -, -, N \11\ 43,201 (N/A, 2,592 112 Rare.
43,201, 2017).
Western U.S........ E, D, Y \11\ 52,932 (N/A, 318 254 Likely; Inshore
52,932, 2013). region.
California sea lion......... Zalophus U.S................ -, -, N 257,606 (N/A, 14,011 >320 Rare (highest
californianus. 233,515, 2014). likelihood April
and May).
Northern fur seal........... Callorhinus ursinus Eastern Pacific.... -, D, Y 626,618 (0.2, 11,403 373 Likely.
530,376, 2019).
California......... -, D, N 14,050 (N/A, 451 1.8 Rare.
7,524, 2013).
Family Phocidae (true seals):
Northern elephant seal...... Mirounga California Breeding -, -, N 187,386 (N/A, 5,122 5.3 Seasonal (highest
angustirostris. 85,369, 2013). likelihood July-
September).
Harbor seal................. Phoca vitulina..... N Kodiak........... -, -, N 8,677 (N/A, 7,609, 228 38 Likely; Inshore
2017). region.
S Kodiak........... -, -, N 26,448 (N/A, 939 127 Likely; Inshore
22,351, 2017). region.
Prince William -, -, N 44,756 (N/A, 1,253 413 Likely; Inshore
Sound. 41,776, 2015). region.
Cook Inlet/Shelikof -, -, N 28,411 (N/A, 807 107 Likely; Inshore
26,907, 2018). region.
Ribbon seal................. Histriophoca Unidentified....... -, -, N 184,697 (N/A, 9,785 163 Rare.
fasciata. 163,086, 2013).
--------------------------------------------------------------------------------------------------------------------------------------------------------
Notes: CV = coefficient of variation, ESA = Endangered Species Act, GOA = Gulf of Alaska, m = meter(s), MMPA = Marine Mammal Protection Act, N/A = not
available, U.S. = United States, M/SI = mortality and serious injury, UNK = unknown, UND = undetermined.
[[Page 49668]]
\1\ Endangered Species Act (ESA) status: Endangered (E), Threatened (T)/MMPA status: Depleted (D). A dash (-) indicates that the species is not listed
under the ESA or designated as depleted under the MMPA. Under the MMPA, a strategic stock is one for which the level of direct human-caused mortality
exceeds potential biological removal (PBR) or which is determined to be declining and likely to be listed under the ESA within the foreseeable future.
Any species or stock listed under the ESA is automatically designated under the MMPA as depleted and as a strategic stock.
\2\ The stocks and stock abundance number are as provided in Carretta et al., 2021 and Muto et al., 2021. Nmin is the minimum estimate of stock
abundance. In some cases, CV is not applicable. NMFS marine mammal stock assessment reports online at: <a href="https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessment-reports-region">https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessment-reports-region</a>.
\3\ These values, found in NMFS' SARs, represent annual levels of human-caused mortality and serious injury (M/SI) from all sources combined (e.g.,
commercial fisheries, ship strike). Annual mortality and serious injury (M/SI) often cannot be determined precisely and is in some cases presented as
a minimum value or range. A CV associated with estimated mortality due to commercial fisheries is presented in some cases.
\4\ RARE: The distribution of the species is near enough to the GOA Study Area that the species could occur there, or there are a few confirmed
sightings. LIKELY: Year-round sightings or acoustic detections of the species in the GOA Study Area, although there may be variation in local
abundance over the year. SEASONAL: Species absence and presence as documented by surveys or acoustic monitoring. Regions within the GOA Study Area
follow those presented in Rone et al. (2015); Rone et al. (2009); Rone et al. (2014); Rone et al. (2017): inshore, slope, seamount, and offshore.
\5\ See SAR for more details
\6\ Humpback whales in the Central North Pacific stock and the California, Oregon, and Washington stock are from three Distinct Population Segments
based on animals identified in breeding areas in Hawaii, Mexico, and Central America (Carretta et al., 2021; Muto et al., 2021; National Marine
Fisheries Service, 2016c).
\7\ The SAR reports this stock abundance assessment as provisional and notes that it is an underestimate for the entire stock because it is based on
surveys which covered only a small portion of the stock's range.
\8\ This analysis assumes that these individuals are from the Eastern North Pacific stock; however, they are not discussed in the West Coast or the
Alaska Stock Assessment Reports (Carretta et al., 2021; Muto et al., 2021).
\9\ The SAR reports that this is an underestimate for the entire stock because it is based on surveys of a small portion of the stock's extensive range
and it does not account for animals missed on the trackline or for females and juveniles in tropical and subtropical waters.
\10\ Stock abundance is based on counts of individual animals identified from photo-identification catalogues. Surveys for abundance estimates of these
stocks are conducted infrequently.
\11\ Stock abundance is the best estimate of pup and non-pup counts, which have not been corrected to account for animals at sea during abundance
surveys.
Below, we consider additional information about the marine mammals
in the area of the specified activities that informs our analysis, such
as identifying known areas of important habitat or behaviors, or where
Unusual Mortality Events (UME) have been designated.
Critical Habitat
On April 21, 2021 (86 FR 21082), NMFS published a final rule
designating critical habitat for the endangered Western North Pacific
DPS, the endangered Central America DPS, and the threatened Mexico DPS
of humpback whales, including specific marine areas located off the
coasts of California, Oregon, Washington, and Alaska. Based on
consideration of national security, economic impacts, and data
deficiency in some areas, NMFS excluded certain areas from the
designation for each DPS.
NMFS identified prey species, primarily euphausiids and small
pelagic schooling fishes (see the final rule for particular prey
species identified for each DPS; 86 FR 21082; April 21, 2021) of
sufficient quality, abundance, and accessibility within humpback whale
feeding areas to support feeding and population growth, as an essential
habitat feature. NMFS, through a critical habitat review team (CHRT),
also considered inclusion of migratory corridors and passage features,
as well as sound and the soundscape, as essential habitat features.
However, NMFS did not include either, as the CHRT concluded that the
best available science did not allow for identification of any
consistently used migratory corridors or definition of any physical,
essential migratory or passage conditions for whales transiting between
or within habitats of the three DPSs. The best available science also
currently does not enable NMFS to identify a sound-related habitat
feature that is essential to the conservation of humpback whales.
NMFS considered the co-occurrence of this designated humpback whale
critical habitat and the GOA Study Area. Figure 4-1 of the Navy's
rulemaking/LOA application shows the overlap of the humpback whale
critical habitat with the TMAA. As shown in the Navy's rulemaking/LOA
application, the TMAA overlaps with humpback whale critical habitat
Unit 5 (destination for whales from the Hawaii, Mexico, and Western
North Pacific DPSs; Calambokidis et al., 2008) and Unit 8 (destination
for whales from the Hawaii and Mexico DPSs (Baker et al., 1986,
Calambokidis et al., 2008); Western North Pacific DPS whales have not
been photo-identified in this specific area, but presence has been
inferred based on available data indicating that humpback whales from
Western North Pacific wintering areas occur in the Gulf of Alaska (NMFS
2020, Table C5)). Approximately 4 percent of the humpback whale
critical habitat in the GOA region overlaps with the TMAA, and
approximately 2 percent of critical habitat in both the GOA and U.S.
west coast regions combined overlaps with the TMAA. The WMA portion of
the GOA Study Area does not overlap ESA-designated critical habitat for
humpback whales.
As noted above in the Geographical Region section, the TMAA
boundary was intentionally designed to avoid ESA-designated Western DPS
(MMPA Western U.S. stock) Steller sea lion critical habitat.
Biologically Important Areas
BIAs include areas of known importance for reproduction, feeding,
or migration, or areas where small and resident populations are known
to occur (Van Parijs, 2015). Unlike ESA critical habitat, these areas
are not formally designated pursuant to any statute or law, but are a
compilation of the best available science intended to inform impact and
mitigation analyses. An interactive map of BIAs may be found here:
<a href="https://cetsound.noaa.gov/biologically-important-area-map">https://cetsound.noaa.gov/biologically-important-area-map</a>.
The WMA does not overlap with any known BIAs. BIAs in the GOA that
overlap portions of the TMAA include the following feeding and
migration areas: North Pacific right whale feeding BIA (June-
September); Gray whale migratory corridor BIA (November-January,
southbound; March-May, northbound) (Ferguson et al., 2015). Fin whale
feeding areas (east, west, and southwest of Kodiak Island) occur to the
west of the TMAA and gray whale feeding areas occur both east
(Southeast Alaska) and west (Kodiak Island) of the TMAA; however, these
feeding areas are located well outside of (> 20 nmi (37 km)) the TMAA
and beyond the Navy's estimated range to effects for take by Level A
harassment and Level B harassment.
A portion of the North Pacific right whale feeding BIA overlaps
with the western side of the TMAA by approximately 2,051 square
kilometers (km\2\; approximately 1.4 percent of the TMAA, and 7 percent
of the feeding BIA). A small portion of the gray whale migration
corridor BIA also overlaps with the western side of the TMAA by
approximately 1,582 km\2\ (approximately 1 percent of the TMAA, and 1
percent of the migration corridor BIA). To mitigate impacts to marine
mammals in these BIAs, the Navy would implement several procedural
mitigation measures and mitigation areas (described in the Proposed
Mitigation Measures section).
[[Page 49669]]
Unusual Mortality Events (UMEs)
A UME is defined under Section 410(6) of the MMPA as a stranding
that is unexpected; involves a significant die-off of any marine mammal
population; and demands immediate response. There is one UME that is
applicable to our evaluation of the Navy's activities in the GOA Study
Area. The gray whale UME along the west coast of North America is
active and involves ongoing investigations in the GOA that inform our
analysis are discussed below.
Gray Whale UME
Since January 1, 2019, elevated gray whale strandings have occurred
along the west coast of North America, from Mexico to Canada. As of
June 3, 2022, there have been a total of 578 strandings along the
coasts of the United States, Canada, and Mexico, with 278 of those
strandings occurring along the U.S. coast. Of the strandings on the
U.S. coast, 118 have occurred in Alaska, 66 in Washington, 14 in
Oregon, and 80 in California. Full or partial necropsy examinations
were conducted on a subset of the whales. Preliminary findings in
several of the whales have shown evidence of emaciation. These findings
are not consistent across all of the whales examined, so more research
is needed. As part of the UME investigation process, NOAA has assembled
an independent team of scientists to coordinate with the Working Group
on Marine Mammal Unusual Mortality Events to review the data collected,
sample stranded whales, consider possible causal-linkages between the
mortality event and recent ocean and ecosystem perturbations, and
determine the next steps for the investigation. Please refer to:
<a href="https://www.fisheries.noaa.gov/national/marine-life-distress/2019-2022-gray-whale-unusual-mortality-event-along-west-coast-and">https://www.fisheries.noaa.gov/national/marine-life-distress/2019-2022-gray-whale-unusual-mortality-event-along-west-coast-and</a> for more
information on this UME.
Marine Mammal Hearing
Hearing is the most important sensory modality for marine mammals
underwater, and exposure to anthropogenic sound can have deleterious
effects. To appropriately assess the potential effects of exposure to
sound, it is necessary to understand the frequency ranges marine
mammals are able to hear. Current data indicate that not all marine
mammal species have equal hearing capabilities (e.g., Richardson et
al., 1995; Wartzok and Ketten, 1999; Au and Hastings, 2008). To reflect
this, Southall et al. (2007) recommended that marine mammals be divided
into functional hearing groups based on directly measured or estimated
hearing ranges on the basis of available behavioral response data,
audiograms derived using auditory evoked potential techniques,
anatomical modeling, and other data. Note that no direct measurements
of hearing ability have been successfully completed for mysticetes
(i.e., low-frequency cetaceans). Subsequently, NMFS (2018) described
generalized hearing ranges for these marine mammal hearing groups.
Generalized hearing ranges were chosen based on the approximately 65 dB
threshold from the normalized composite audiograms, with the exception
for lower limits for low-frequency cetaceans where the lower bound was
deemed to be biologically implausible and the lower bound from Southall
et al. (2007) retained. The functional groups and the associated
frequencies are indicated below (note that these frequency ranges
correspond to the range for the composite group, with the entire range
not necessarily reflecting the capabilities of every species within
that group):
<bullet> Low-frequency cetaceans (mysticetes): generalized hearing
is estimated to occur between approximately 7 Hz and 35 kHz;
<bullet> Mid-frequency cetaceans (larger toothed whales, beaked
whales, and most delphinids): generalized hearing is estimated to occur
between approximately 150 Hz and 160 kHz;
<bullet> High-frequency cetaceans (porpoises, river dolphins, and
members of the genera Kogia and Cephalorhynchus; including two members
of the genus Lagenorhynchus, on the basis of recent echolocation data
and genetic data): generalized hearing is estimated to occur between
approximately 275 Hz and 160 kHz;
<bullet> Pinnipeds in water; Phocidae (true seals): generalized
hearing is estimated to occur between approximately 50 Hz to 86 kHz;
and
<bullet> Pinnipeds in water; Otariidae (eared seals): generalized
hearing is estimated to occur between 60 Hz and 39 kHz.
The pinniped functional hearing group was modified from Southall et
al. (2007) on the basis of data indicating that phocid species have
consistently demonstrated an extended frequency range of hearing
compared to otariids, especially in the higher frequency range
(Hemil[auml] et al., 2006; Kastelein et al., 2009; Reichmuth and Holt,
2013).
For more details concerning these groups and associated frequency
ranges, please see NMFS (2018) for a review of the available
information.
Potential Effects of Specified Activities on Marine Mammals and Their
Habitat
This section includes a discussion of the ways that components of
the specified activity may impact marine mammals and their habitat. The
Estimated Take of Marine Mammals section later in this rule includes a
quantitative analysis of the number of instances of take that could
occur from these activities. The Preliminary Analysis and Negligible
Impact Determination section considers the content of this section, the
Estimated Take of Marine Mammals section, and the Proposed Mitigation
Measures section to draw conclusions regarding the likely impacts of
these activities on the reproductive success or survivorship of
individuals and whether those impacts on individuals are likely to
adversely affect the species through effects on annual rates of
recruitment or survival.
The Navy has requested authorization for the take of marine mammals
that may occur incidental to training activities in the GOA Study Area.
The Navy analyzed potential impacts to marine mammals in its
rulemaking/LOA application. NMFS carefully reviewed the information
provided by the Navy along with independently reviewing applicable
scientific research and literature and other information to evaluate
the potential effects of the Navy's activities on marine mammals, which
are presented in this section. (As noted above, activities that would
result in take of marine mammals would only occur in the TMAA portion
of the GOA Study Area.)
Other potential impacts to marine mammals from training activities
in the GOA Study Area were analyzed in the Navy's rulemaking/LOA
application as well as in the 2020 GOA DSEIS/OEIS and 2022 Supplement
to the 2020 GOA DSEIS/OEIS, in consultation with NMFS as a cooperating
agency, and determined to be unlikely to result in marine mammal take.
These include incidental take from vessel strike and serious injury or
mortality from explosives. Therefore, the Navy did not request
authorization for incidental take of marine mammals by vessel strike or
serious injury or mortality from explosives from its proposed specified
activities. NMFS has carefully considered the information in the 2020
GOA DSEIS/OEIS, the 2022 Supplement to the 2020 GOA DSEIS/OEIS, and all
other pertinent information and agrees that incidental take is unlikely
to occur from these sources. NMFS conducted a detailed analysis of the
potential for vessel strike, and based on that analysis,
[[Page 49670]]
NMFS does not anticipate vessel strikes of large whales or smaller
marine mammals in the GOA Study Area. In this proposed rule, NMFS
analyzes the potential effects of the Navy's activities on marine
mammals in the GOA Study Area, focusing primarily on the activity
components that may cause the take of marine mammals: exposure to
acoustic or explosive stressors including non-impulsive (sonar and
other transducers) and impulsive (explosives) stressors.
For the purpose of MMPA incidental take authorizations, NMFS'
effects assessments serve four primary purposes: (1) to determine
whether the specified activities would have a negligible impact on the
affected species or stocks of marine mammals (based on whether it is
likely that the activities would adversely affect the species or stocks
through effects on annual rates of recruitment or survival); (2) to
determine whether the specified activities would have an unmitigable
adverse impact on the availability of the species or stocks for
subsistence uses; (3) to prescribe the permissible methods of taking
(i.e., Level B harassment (behavioral disturbance and temporary
threshold shift (TTS)), Level A harassment (permanent threshold shift
(PTS) and non-auditory injury), serious injury, or mortality),
including identification of the number and types of take that could
occur by harassment, serious injury, or mortality, and to prescribe
means of effecting the least practicable adverse impact on the species
or stocks and their habitat (i.e., mitigation measures); and (4) to
prescribe requirements pertaining to monitoring and reporting.
In this section, NMFS provides a description of the ways marine
mammals potentially could be affected by these activities in the form
of mortality, physical trauma, sensory impairment (permanent and
temporary threshold shifts and acoustic masking), physiological
responses (particularly stress responses), behavioral disturbance, or
habitat effects. The Estimated Take of Marine Mammals section discusses
how the potential effects on marine mammals from non-impulsive and
impulsive sources relate to the MMPA definitions of Level A Harassment
and Level B Harassment, and quantifies those effects that rise to the
level of a take. The Preliminary Analysis and Negligible Impact
Determination section assesses whether the proposed authorized take
would have a negligible impact on the affected species and stocks.
Potential Effects of Underwater Sound
Anthropogenic sounds cover a broad range of frequencies and sound
levels and can have a range of highly variable impacts on marine life,
from none or minor to potentially severe responses, depending on
received levels, duration of exposure, behavioral context, and various
other factors. The potential effects of underwater sound from active
acoustic sources can possibly result in one or more of the following:
temporary or permanent hearing impairment, non-auditory physical or
physiological effects, behavioral response, stress, and masking
(Richardson et al., 1995; Gordon et al., 2004; Nowacek et al., 2007;
Southall et al., 2007; G[ouml]tz et al., 2009, Southall et al., 2019a).
The degree of effect is intrinsically related to the signal
characteristics, received level, distance from the source, and duration
of the sound exposure. In general, sudden, high level sounds can cause
hearing loss, as can longer exposures to lower level sounds. Temporary
or permanent loss of hearing can occur after exposure to noise, and
occurs almost exclusively for noise within an animal's hearing range.
Note that in the following discussion, we refer in many cases to a
review article concerning studies of noise-induced hearing loss
conducted from 1996-2015 (i.e., Finneran, 2015). For study-specific
citations, please see that work. We first describe general
manifestations of acoustic effects before providing discussion specific
to the Navy's activities.
Richardson et al. (1995) described zones of increasing intensity of
effect that might be expected to occur, in relation to distance from a
source and assuming that the signal is within an animal's hearing
range. First is the area within which the acoustic signal would be
audible (potentially perceived) to the animal, but not strong enough to
elicit any overt behavioral or physiological response. The next zone
corresponds with the area where the signal is audible to the animal and
of sufficient intensity to elicit behavioral or physiological
responsiveness. Third is a zone within which, for signals of high
intensity, the received level is sufficient to potentially cause
discomfort or tissue damage to auditory systems. Overlaying these zones
to a certain extent is the area within which masking (i.e., when a
sound interferes with or masks the ability of an animal to detect a
signal of interest that is above the absolute hearing threshold) may
occur; the masking zone may be highly variable in size.
We also describe more severe potential effects (i.e., certain non-
auditory physical or physiological effects). Potential effects from
impulsive sound sources can range in severity from effects such as
behavioral disturbance or tactile perception to physical discomfort,
slight injury of the internal organs and the auditory system, or
mortality (Yelverton et al., 1973). Non-auditory physiological effects
or injuries that theoretically might occur in marine mammals exposed to
high level underwater sound or as a secondary effect of extreme
behavioral reactions (e.g., change in dive profile as a result of an
avoidance reaction) include neurological effects, bubble formation,
resonance effects, and other types of organ or tissue damage (Cox et
al., 2006; Southall et al., 2007; Zimmer and Tyack, 2007; Tal et al.,
2015).
Acoustic Sources
Direct Physiological Effects
Non-impulsive sources of sound can cause direct physiological
effects including noise-induced loss of hearing sensitivity (or
``threshold shift''), nitrogen decompression, acoustically-induced
bubble growth, and injury due to sound-induced acoustic resonance. Only
noise-induced hearing loss is anticipated to occur due to the Navy's
activities. Acoustically-induced (or mediated) bubble growth and other
pressure-related physiological impacts are addressed below, but are not
expected to result from the Navy's activities. Separately, an animal's
behavioral reaction to an acoustic exposure might lead to physiological
effects that might ultimately lead to injury or death, which is
discussed later in the Stranding and Mortality subsection.
Hearing Loss--Threshold Shift
Marine mammals exposed to high-intensity sound, or to lower-
intensity sound for prolonged periods, can experience hearing threshold
shift, which is the loss of hearing sensitivity at certain frequency
ranges after cessation of sound (Finneran, 2015). Threshold shift can
be permanent (PTS), in which case the loss of hearing sensitivity is
not fully recoverable, or temporary (TTS), in which case the animal's
hearing threshold would recover over time (Southall et al., 2007). TTS
can last from minutes or hours to days (i.e., there is recovery back to
baseline/pre-exposure levels), can occur within a specific frequency
range (i.e., an animal might only have a temporary loss of hearing
sensitivity within a limited frequency band of its auditory
[[Page 49671]]
range), and can be of varying amounts (e.g., an animal's hearing
sensitivity might be reduced by only 6 dB or reduced by 30 dB). While
there is no simple functional relationship between TTS and PTS or other
auditory injury (e.g., neural degeneration), as TTS increases, the
likelihood that additional exposure sound pressure level (SPL) or
duration will result in PTS or other injury also increases (see also
the 2020 GOA DSEIS/OEIS for additional discussion). Exposure thresholds
for the onset of PTS or other auditory injury are defined by the amount
of sound energy that results in 40 dB of TTS. This value is informed by
experimental data, and is used as a proxy for the onset of auditory
injury; i.e., it is assumed that exposures beyond those capable of
causing 40 dB of TTS have the potential to result in PTS or other
auditory injury (e.g., loss of cochlear neuron synapses, even in the
absence of PTS). In severe cases of PTS, there can be total or partial
deafness, while in most cases the animal has an impaired ability to
hear sounds in specific frequency ranges (Kryter, 1985).
When PTS occurs, there is physical damage to the sound receptors in
the ear (i.e., tissue damage), whereas TTS represents primarily tissue
fatigue and is reversible (Southall et al., 2007). PTS is permanent
(i.e., there is incomplete recovery back to baseline/pre-exposure
levels), but also can occur in a specific frequency range and amount as
mentioned above for TTS. In addition, other investigators have
suggested that TTS is within the normal bounds of physiological
variability and tolerance and does not represent physical injury (e.g.,
Ward, 1997). Therefore, NMFS does not consider TTS to constitute
auditory injury.
The following physiological mechanisms are thought to play a role
in inducing auditory threshold shift: effects to sensory hair cells in
the inner ear that reduce their sensitivity; modification of the
chemical environment within the sensory cells; residual muscular
activity in the middle ear; displacement of certain inner ear
membranes; increased blood flow; and post-stimulatory reduction in both
efferent and sensory neural output (Southall et al., 2007). The
amplitude, duration, frequency, temporal pattern, and energy
distribution of sound exposure all can affect the amount of associated
threshold shift and the frequency range in which it occurs. Generally,
the amount of threshold shift, and the time needed to recover from the
effect, increase as amplitude and duration of sound exposure increases.
Human non-impulsive noise exposure guidelines are based on the
assumption that exposures of equal energy (the same sound exposure
level (SEL)) produce equal amounts of hearing impairment regardless of
how the sound energy is distributed in time (NIOSH, 1998). Previous
marine mammal TTS studies have also generally supported this equal
energy relationship (Southall et al., 2007). However, some more recent
studies concluded that for all noise exposure situations the equal
energy relationship may not be the best indicator to predict TTS onset
levels (Mooney et al., 2009a and 2009b; Kastak et al., 2007). These
studies highlight the inherent complexity of predicting TTS onset in
marine mammals, as well as the importance of considering exposure
duration when assessing potential impacts. Generally, with sound
exposures of equal energy, those that were quieter (lower SPL) with
longer duration were found to induce TTS onset at lower levels than
those of louder (higher SPL) and shorter duration. Less threshold shift
will occur from intermittent sounds than from a continuous exposure
with the same energy (some recovery can occur between intermittent
exposures) (Kryter et al., 1966; Ward, 1997; Mooney et al., 2009a,
2009b; Finneran et al., 2010). For example, one short but loud (higher
SPL) sound exposure may induce the same impairment as one longer but
softer (lower SPL) sound, which in turn may cause more impairment than
a series of several intermittent softer sounds with the same total
energy (Ward, 1997). Additionally, though TTS is temporary, very
prolonged or repeated exposure to sound strong enough to elicit TTS, or
shorter-term exposure to sound levels well above the TTS threshold can
cause PTS, at least in terrestrial mammals (Kryter, 1985; Lonsbury-
Martin et al., 1987).
PTS is considered auditory injury (Southall et al., 2007).
Irreparable damage to the inner or outer cochlear hair cells may cause
PTS; however, other mechanisms are also involved, such as exceeding the
elastic limits of certain tissues and membranes in the middle and inner
ears and resultant changes in the chemical composition of the inner ear
fluids (Southall et al., 2007).
The NMFS Acoustic Technical Guidance (NMFS, 2018), which was used
in the assessment of effects for this rule, compiled, interpreted, and
synthesized the best available scientific information for noise-induced
hearing effects for marine mammals to derive updated thresholds for
assessing the impacts of noise on marine mammal hearing. More recently,
Southall et al. (2019a) evaluated Southall et al. (2007) and used
updated scientific information to propose revised noise exposure
criteria to predict onset of auditory effects in marine mammals (i.e.,
PTS and TTS onset). Southall et al. (2019a) note that the quantitative
processes described and the resulting exposure criteria (i.e.,
thresholds and auditory weighting functions) are largely identical to
those in Finneran (2016) and NMFS (2018). They only differ in that the
Southall et al. (2019a) exposure criteria are more broadly applicable
as they include all marine mammal species (rather than only those under
NMFS jurisdiction) for all noise exposures (both in air and underwater
for amphibious species) and, while the hearing group compositions are
identical, they renamed the hearing groups. Southall et al. (2021)
updated the behavioral response severity criteria laid out in Southall
et al. (2007) and included recommendations on how to present and score
behavioral responses in future work.
Many studies have examined noise-induced hearing loss in marine
mammals (see Finneran (2015) and Southall et al. (2019a) for
summaries), however for cetaceans, published data on the onset of TTS
are limited to the captive bottlenose dolphin, beluga, harbor porpoise,
and Yangtze finless porpoise, and for pinnipeds in water, measurements
of TTS are limited to harbor seals, elephant seals, and California sea
lions. These studies examine hearing thresholds measured in marine
mammals before and after exposure to intense sounds. The difference
between the pre-exposure and post-exposure thresholds can then be used
to determine the amount of threshold shift at various post-exposure
times. NMFS has reviewed the available studies, which are summarized
below (see also the 2020 GOA DSEIS/OEIS which includes additional
discussion on TTS studies related to sonar and other transducers).
<bullet> The method used to test hearing may affect the resulting
amount of measured TTS, with neurophysiological measures producing
larger amounts of TTS compared to psychophysical measures (Finneran et
al., 2007; Finneran, 2015).
<bullet> The amount of TTS varies with the hearing test frequency.
As the exposure SPL increases, the frequency at which the maximum TTS
occurs also increases (Kastelein et al., 2014b). For high-level
exposures, the maximum TTS typically occurs one-half to one octave
above the exposure frequency (Finneran et al., 2007; Mooney et al.,
2009a; Nachtigall et al., 2004; Popov et al., 2011; Popov et al., 2013;
Schlundt et al., 2000;
[[Page 49672]]
Kastelein et al., 2021b; Kastelien et al., 2022). The overall spread of
TTS from tonal exposures can therefore extend over a large frequency
range (i.e., narrowband exposures can produce broadband (greater than
one octave) TTS).
<bullet> The amount of TTS increases with exposure SPL and duration
and is correlated with SEL, especially if the range of exposure
durations is relatively small (Kastak et al., 2007; Kastelein et al.,
2014b; Popov et al., 2014). As the exposure duration increases,
however, the relationship between TTS and SEL begins to break down.
Specifically, duration has a more significant effect on TTS than would
be predicted on the basis of SEL alone (Finneran et al., 2010a; Kastak
et al., 2005; Mooney et al., 2009a). This means if two exposures have
the same SEL but different durations, the exposure with the longer
duration (thus lower SPL) will tend to produce more TTS than the
exposure with the higher SPL and shorter duration. In most acoustic
impact assessments, the scenarios of interest involve shorter duration
exposures than the marine mammal experimental data from which impact
thresholds are derived; therefore, use of SEL tends to over-estimate
the amount of TTS. Despite this, SEL continues to be used in many
situations because it is relatively simple, more accurate than SPL
alone, and lends itself easily to scenarios involving multiple
exposures with different SPL.
<bullet> Gradual increases of TTS may not be directly observable
with increasing exposure levels, before the onset of PTS (Reichmuth et
al., 2019). Similarly, PTS can occur without measurable behavioral
modifications (Reichmuth et al., 2019).
<bullet> The amount of TTS depends on the exposure frequency.
Sounds at low frequencies, well below the region of best sensitivity,
are less hazardous than those at higher frequencies, near the region of
best sensitivity (Finneran and Schlundt, 2013). The onset of TTS--
defined as the exposure level necessary to produce 6 dB of TTS (i.e.,
clearly above the typical variation in threshold measurements)--also
varies with exposure frequency. At low frequencies, onset-TTS exposure
levels are higher compared to those in the region of best sensitivity.
For example, for harbor porpoises exposed to one-sixth octave noise
bands at 16 kHz (Kastelein et al., 2019f), 32 kHz (Kastelein et al.,
2019d), 63 kHz (Kastelein et al., 2020a), and 88.4 kHz (Kastelein et
al., 2020b), less susceptibility to TTS was found as frequency
increased, whereas exposure frequencies below ~6.5 kHz showed an
increase in TTS susceptibility as frequency increased and approached
the region of best sensitivity. Kastelein et al. (2020b) showed a much
higher onset of TTS for a 88.5 kHz exposure as compared to lower
exposure frequencies (i.e., 16 kHz (Kastelein et al., 2019) 1.5 kHz and
6.5 kHz (Kastelein et al., 2020a)). For the 88.4 kHz test frequency, a
185 dB re 1 micropascal squared per second ([micro]Pa\2\-s) exposure
resulted in 3.6 dB of TTS, and a 191 dB re 1 [micro]Pa\2\-s exposure
produced 5.2 dB of TTS at 100 kHz and 5.4 dB of TTS at 125 kHz.
Together, these new studies demonstrate that the criteria for high-
frequency (HF) cetacean auditory impacts is likely to be conservative.
<bullet> TTS can accumulate across multiple exposures, but the
resulting TTS will be less than the TTS from a single, continuous
exposure with the same SEL (Finneran et al., 2010a; Kastelein et al.,
2014b; Kastelein et al., 2015b; Mooney et al., 2009b). This means that
TTS predictions based on the total, cumulative SEL will overestimate
the amount of TTS from intermittent exposures such as sonars and
impulsive sources. The importance of duty cycle in predicting the
likelihood of TTS is demonstrated further in Kastelein et al. (2021b).
The authors found that reducing the duty cycle of a sound generally
reduced the potential for TTS in California sea lions, and that,
further, California sea lions are more susceptible to TTS than
previously believed at the 2 and 4 kHz frequencies tested.
<bullet> The amount of observed TTS tends to decrease with
increasing time following the exposure; however, the relationship is
not monotonic (i.e., increasing exposure does not always increase TTS).
The time required for complete recovery of hearing depends on the
magnitude of the initial shift; for relatively small shifts recovery
may be complete in a few minutes, while large shifts (e.g.,
approximately 40 dB) may require several days for recovery. Recovery
times are consistent for similar-magnitude TTS, regardless of the type
of fatiguing sound exposure (impulsive, continuous noise band, or
sinusoidal wave; (Kastelein et al., 2019e)). Under many circumstances
TTS recovers linearly with the logarithm of time (Finneran et al.,
2010a, 2010b; Finneran and Schlundt, 2013; Kastelein et al., 2012a;
Kastelein et al., 2012b; Kastelein et al., 2013a; Kastelein et al.,
2014b; Kastelein et al., 2014c; Popov et al., 2011; Popov et al., 2013;
Popov et al., 2014). This means that for each doubling of recovery
time, the amount of TTS will decrease by the same amount (e.g., 6 dB
recovery per doubling of time). Please see Section 3.8.3.1.1.2 of the
2020 GOA DSEIS/OEIS for discussion of additional threshold shift
literature.
Nachtigall et al. (2018) and Finneran (2018) describe the
measurements of hearing sensitivity of multiple odontocete species
(bottlenose dolphin, harbor porpoise, beluga, and false killer whale)
when a relatively loud sound was preceded by a warning sound. These
captive animals were shown to reduce hearing sensitivity when warned of
an impending intense sound. Based on these experimental observations of
captive animals, the authors suggest that wild animals may dampen their
hearing during prolonged exposures or if conditioned to anticipate
intense sounds. Another study showed that echolocating animals
(including odontocetes) might have anatomical specializations that
might allow for conditioned hearing reduction and filtering of low-
frequency ambient noise, including increased stiffness and control of
middle ear structures and placement of inner ear structures (Ketten et
al., 2021). Finneran recommends further investigation of the mechanisms
of hearing sensitivity reduction in order to understand the
implications for interpretation of existing TTS data obtained from
captive animals, notably for considering TTS due to short duration,
unpredictable exposures.
Marine mammal hearing plays a critical role in communication with
conspecifics and in interpretation of environmental cues for purposes
such as predator avoidance and prey capture. Depending on the degree
(elevation of threshold in dB), duration (i.e., recovery time), and
frequency range of TTS, and the context in which it is experienced, TTS
can have effects on marine mammals ranging from discountable to
serious, similar to those discussed in auditory masking below. For
example, a marine mammal may be able to readily compensate for a brief,
relatively small amount of TTS in a non-critical frequency range that
takes place during a time where ambient noise is lower and there are
not as many competing sounds present. Alternatively, a larger amount
and longer duration of TTS sustained during a time when communication
is critical for successful mother/calf interactions could have more
serious impacts if it were in the same frequency band as the necessary
vocalizations and of a severity that impeded communication. Animals
exposed to high levels of sound that would be expected to result in
this physiological response would also be expected to have behavioral
responses of a
[[Page 49673]]
comparatively more severe or sustained nature, which is potentially
more significant than simple existence of a TTS. However, it is
important to note that TTS could occur due to longer exposures to sound
at lower levels so that a behavioral response may not be elicited.
Depending on the degree and frequency range, the effects of PTS on
an animal could also range in severity, although it is considered
generally more serious than TTS because it is a permanent condition. Of
note, reduced hearing sensitivity as a simple function of aging has
been observed in marine mammals, as well as humans and other taxa
(Southall et al., 2007), so we can infer that strategies exist for
coping with this condition to some degree, though likely not without
some cost to the animal.
Acoustically-Induced Bubble Formation Due to Sonars and Other Pressure-
Related Impacts
One theoretical cause of injury to marine mammals is rectified
diffusion (Crum and Mao, 1996), the process of increasing the size of a
bubble by exposing it to a sound field. This process could be
facilitated if the environment in which the ensonified bubbles exist is
supersaturated with gas. Repetitive diving by marine mammals can cause
the blood and some tissues to accumulate gas to a greater degree than
is supported by the surrounding environmental pressure (Ridgway and
Howard, 1979). The deeper and longer dives of some marine mammals (for
example, beaked whales) are theoretically predicted to induce greater
supersaturation (Houser et al., 2001b). If rectified diffusion were
possible in marine mammals exposed to high-level sound, conditions of
tissue supersaturation could theoretically speed the rate and increase
the size of bubble growth. Subsequent effects due to tissue trauma and
emboli would presumably mirror those observed in humans suffering from
decompression sickness.
It is unlikely that the short duration (in combination with the
source levels) of sonar pings would be long enough to drive bubble
growth to any substantial size, if such a phenomenon occurs. However,
an alternative but related hypothesis has also been suggested: stable
bubbles could be destabilized by high-level sound exposures such that
bubble growth then occurs through static diffusion of gas out of the
tissues. In such a scenario the marine mammal would need to be in a
gas-supersaturated state for a long enough period of time for bubbles
to become of a problematic size. Recent research with ex vivo
supersaturated bovine tissues suggested that, for a 37 kHz signal, a
sound exposure of approximately 215 dB referenced to (re) 1 [mu]Pa
would be required before microbubbles became destabilized and grew
(Crum et al., 2005). Assuming spherical spreading loss and a nominal
sonar source level of 235 dB re: 1 [mu]Pa at 1 m, a whale would need to
be within 10 m (33 ft) of the sonar dome to be exposed to such sound
levels. Furthermore, tissues in the study were supersaturated by
exposing them to pressures of 400-700 kilopascals for periods of hours
and then releasing them to ambient pressures. Assuming the
equilibration of gases with the tissues occurred when the tissues were
exposed to the high pressures, levels of supersaturation in the tissues
could have been as high as 400-700 percent. These levels of tissue
supersaturation are substantially higher than model predictions for
marine mammals (Houser et al., 2001; Saunders et al., 2008). It is
improbable that this mechanism is responsible for stranding events or
traumas associated with beaked whale strandings because both the degree
of supersaturation and exposure levels observed to cause microbubble
destabilization are unlikely to occur, either alone or in concert.
Yet another hypothesis (decompression sickness) has speculated that
rapid ascent to the surface following exposure to a startling sound
might produce tissue gas saturation sufficient for the evolution of
nitrogen bubbles (Jepson et al., 2003; Fernandez et al., 2005;
Fern[aacute]ndez et al., 2012). In this scenario, the rate of ascent
would need to be sufficiently rapid to compromise behavioral or
physiological protections against nitrogen bubble formation.
Alternatively, Tyack et al. (2006) studied the deep diving behavior of
beaked whales and concluded that: ``Using current models of breath-hold
diving, we infer that their natural diving behavior is inconsistent
with known problems of acute nitrogen supersaturation and embolism.''
Collectively, these hypotheses can be referred to as ``hypotheses of
acoustically mediated bubble growth.''
Although theoretical predictions suggest the possibility for
acoustically mediated bubble growth, there is considerable disagreement
among scientists as to its likelihood (Piantadosi and Thalmann, 2004;
Evans and Miller, 2003; Cox et al., 2006; Rommel et al., 2006). Crum
and Mao (1996) hypothesized that received levels would have to exceed
190 dB in order for there to be the possibility of significant bubble
growth due to supersaturation of gases in the blood (i.e., rectified
diffusion). Work conducted by Crum et al. (2005) demonstrated the
possibility of rectified diffusion for short duration signals, but at
SELs and tissue saturation levels that are highly improbable to occur
in diving marine mammals. To date, energy levels (ELs) predicted to
cause in vivo bubble formation within diving cetaceans have not been
evaluated (NOAA, 2002b). Jepson et al. (2003, 2005) and Fernandez et
al. (2004, 2005, 2012) concluded that in vivo bubble formation, which
may be exacerbated by deep, long-duration, repetitive dives may explain
why beaked whales appear to be relatively vulnerable to MF/HF sonar
exposures. It has also been argued that traumas from some beaked whale
strandings are consistent with gas emboli and bubble-induced tissue
separations (Jepson et al., 2003); however, there is no conclusive
evidence of this (Rommel et al., 2006). Based on examination of sonar-
associated strandings, Bernaldo de Quiros et al. (2019) list diagnostic
features, the presence of all of which suggest gas and fat embolic
syndrome for beaked whales stranded in association with sonar exposure.
As described in additional detail in the Nitrogen Decompression
subsection of the 2020 GOA DSEIS/OEIS, marine mammals generally are
thought to deal with nitrogen loads in their blood and other tissues,
caused by gas exchange from the lungs under conditions of high ambient
pressure during diving, through anatomical, behavioral, and
physiological adaptations (Hooker et al., 2012). Although not a direct
injury, variations in marine mammal diving behavior or avoidance
responses have been hypothesized to result in nitrogen off-gassing in
super-saturated tissues, possibly to the point of deleterious vascular
and tissue bubble formation (Hooker et al., 2012; Jepson et al., 2003;
Saunders et al., 2008) with resulting symptoms similar to decompression
sickness, however the process is still not well understood.
Fahlman et al. (2021) explained how stress can have a critical role
in causing the gas emboli present in stranded cetaceans. The authors
review decompression theory and the mechanisms dolphins have evolved to
prevent high N<INF>2</INF> levels and gas emboli in normal conditions,
and describe how, in times of high stress, the selective gas exchange
hypothesis states that this mechanism can break down. In addition,
circulating microparticles may be a useful biomarker for decompression
stress in cetaceans. Velazquez-Wallraf et al. (2021) found that
individual variation also has an essential role in
[[Page 49674]]
this condition. To validate decompression sickness observations in
certain stranded cetaceans found coincident with naval activities, the
study used rabbits as an experimental pathological model and found that
rabbit mortalities during or immediately following decompression showed
systematically distributed gas bubbles (microscopic and macroscopic),
as well as emphysema and hemorrhages in multiple organs, similar to
observations in the stranded cetacean mortalities. Similar findings
were not found in almost half the rabbits that survived at least one
hour after decompression, revealing individual variation has an
essential role in this condition.
In 2009, Hooker et al. tested two mathematical models to predict
blood and tissue tension N<INF>2</INF> (P<INF>N2</INF>) using field
data from three beaked whale species: northern bottlenose whales,
Cuvier's beaked whales, and Blainville's beaked whales. The researchers
aimed to determine if physiology (body mass, diving lung volume, and
dive response) or dive behavior (dive depth and duration, changes in
ascent rate, and diel behavior) would lead to differences in
P<INF>N2</INF> levels and thereby decompression sickness risk between
species. In their study, they compared results for previously published
time depth recorder data (Hooker and Baird, 1999; Baird et al., 2006,
2008) from Cuvier's beaked whale, Blainville's beaked whale, and
northern bottlenose whale. They reported that diving lung volume and
extent of the dive response had a large effect on end-dive
P<INF>N2</INF>. Also, results showed that dive profiles had a larger
influence on end-dive P<INF>N2</INF> than body mass differences between
species. Despite diel changes (i.e., variation that occurs regularly
every day or most days) in dive behavior, P<INF>N2</INF> levels showed
no consistent trend. Model output suggested that all three species live
with tissue P<INF>N2</INF> levels that would cause a significant
proportion of decompression sickness cases in terrestrial mammals. The
authors concluded that the dive behavior of Cuvier's beaked whale was
different from both Blainville's beaked whale and northern bottlenose
whale, and resulted in higher predicted tissue and blood N<INF>2</INF>
levels (Hooker et al., 2009). They also suggested that the prevalence
of Cuvier's beaked whales stranding after naval sonar exercises could
be explained by either a higher abundance of this species in the
affected areas or by possible species differences in behavior and/or
physiology related to MF active sonar (Hooker et al., 2009).
Bernaldo de Quiros et al. (2012) showed that, among stranded
whales, deep diving species of whales had higher abundances of gas
bubbles compared to shallow diving species. Kvadsheim et al. (2012)
estimated blood and tissue P<INF>N2</INF> levels in species
representing shallow, intermediate, and deep diving cetaceans following
behavioral responses to sonar and their comparisons found that deep
diving species had higher end-dive blood and tissue N<INF>2</INF>
levels, indicating a higher risk of developing gas bubble emboli
compared with shallow diving species. Fahlmann et al. (2014) evaluated
dive data recorded from sperm, killer, long-finned pilot, Blainville's
beaked and Cuvier's beaked whales before and during exposure to low-
frequency (1-2 kHz), as defined by the authors, and mid-frequency (2-7
kHz) active sonar in an attempt to determine if either differences in
dive behavior or physiological responses to sonar are plausible risk
factors for bubble formation. The authors suggested that CO<INF>2</INF>
may initiate bubble formation and growth, while elevated levels of
N<INF>2</INF> may be important for continued bubble growth. The authors
also suggest that if CO<INF>2</INF> plays an important role in bubble
formation, a cetacean escaping a sound source may experience increased
metabolic rate, CO<INF>2</INF> production, and alteration in cardiac
output, which could increase risk of gas bubble emboli. However, as
discussed in Kvadsheim et al. (2012), the actual observed behavioral
responses to sonar from the species in their study (sperm, killer,
long-finned pilot, Blainville's beaked, and Cuvier's beaked whales) did
not imply any significantly increased risk of decompression sickness
due to high levels of N<INF>2.</INF> Therefore, further information is
needed to understand the relationship between exposure to stimuli,
behavioral response (discussed in more detail below), elevated
N<INF>2</INF> levels, and gas bubble emboli in marine mammals. The
hypotheses for gas bubble formation related to beaked whale strandings
is that beaked whales potentially have strong avoidance responses to MF
active sonars because they sound similar to their main predator, the
killer whale (Cox et al., 2006; Southall et al., 2007; Zimmer and
Tyack, 2007; Baird et al., 2008; Hooker et al., 2009). Further
investigation is needed to assess the potential validity of these
hypotheses.
To summarize, while there are several hypotheses, there is little
data directly connecting intense, anthropogenic underwater sounds with
non-auditory physical effects in marine mammals. The available data do
not support identification of a specific exposure level above which
non-auditory effects can be expected (Southall et al., 2007) or any
meaningful quantitative predictions of the numbers (if any) of marine
mammals that might be affected in these ways. In addition, such
effects, if they occur at all, would be expected to be limited to
situations where marine mammals are exposed to high powered sounds at
very close range over a prolonged period of time, which is not expected
to occur based on the speed of the vessels operating sonar in
combination with the speed and behavior of marine mammals in the
vicinity of sonar.
Injury Due to Sonar-Induced Acoustic Resonance
An object exposed to its resonant frequency will tend to amplify
its vibration at that frequency, a phenomenon called acoustic
resonance. Acoustic resonance has been proposed as a potential
mechanism by which a sonar or sources with similar operating
characteristics could damage tissues of marine mammals. In 2002, NMFS
convened a panel of government and private scientists to investigate
the potential for acoustic resonance to occur in marine mammals (NOAA,
2002). They modeled and evaluated the likelihood that Navy mid-
frequency sonar (2-10 kHz) caused resonance effects in beaked whales
that eventually led to their stranding. The workshop participants
concluded that resonance in air-filled structures was not likely to
have played a primary role in the Bahamas stranding in 2000. They
listed several reasons supporting this finding including (among
others): tissue displacements at resonance are estimated to be too
small to cause tissue damage; tissue-lined air spaces most susceptible
to resonance are too large in marine mammals to have resonant
frequencies in the ranges used by mid-frequency or low-frequency sonar;
lung resonant frequencies increase with depth, and tissue displacements
decrease with depth so if resonance is more likely to be caused at
depth it is also less likely to have an affect there; and lung tissue
damage has not been observed in any mass, multi-species stranding of
beaked whales. The frequency at which resonance was predicted to occur
in the animals' lungs was 50 Hz, well below the frequencies used by the
mid-frequency sonar systems associated with the Bahamas event. The
workshop participants focused on the March 2000 stranding of beaked
whales in the Bahamas as high-quality data were available, but the
workshop report notes that the results apply to other sonar-related
stranding events. For the reasons given by the
[[Page 49675]]
2002 workshop participants, we do not anticipate injury due to sonar-
induced acoustic resonance from the Navy's planned activities.
Physiological Stress
There is growing interest in monitoring and assessing the impacts
of stress responses to sound in marine animals. Classic stress
responses begin when an animal's central nervous system perceives a
potential threat to its homeostasis. That perception triggers stress
responses regardless of whether a stimulus actually threatens the
animal; the mere perception of a threat is sufficient to trigger a
stress response (Moberg, 2000; Sapolsky et al., 2005; Seyle, 1950).
Once an animal's central nervous system perceives a threat, it mounts a
biological response or defense that consists of a combination of the
four general biological defense responses: behavioral responses,
autonomic nervous system responses, neuroendocrine responses, or immune
responses.
According to Moberg (2000), in the case of many stressors, an
animal's first and sometimes most economical (in terms of biotic costs)
response is behavioral avoidance of the potential stressor or avoidance
of continued exposure to a stressor. An animal's second line of defense
to stressors involves the sympathetic part of the autonomic nervous
system and the classical ``fight or flight'' response which includes
the cardiovascular system, the gastrointestinal system, the exocrine
glands, and the adrenal medulla to produce changes in heart rate, blood
pressure, and gastrointestinal activity that humans commonly associate
with ``stress.'' These responses have a relatively short duration and
may or may not have significant long-term effect on an animal's
welfare.
An animal's third line of defense to stressors involves its
neuroendocrine systems or sympathetic nervous systems; the system that
has received the most study has been the hypothalmus-pituitary-adrenal
system (also known as the HPA axis in mammals or the hypothalamus-
pituitary-interrenal axis in fish and some reptiles). Unlike stress
responses associated with the autonomic nervous system, virtually all
neuro-endocrine functions that are affected by stress--including immune
competence, reproduction, metabolism, and behavior--are regulated by
pituitary hormones. Stress-induced changes in the secretion of
pituitary hormones have been implicated in failed reproduction (Moberg,
1987; Rivier and Rivest, 1991), altered metabolism (Elasser et al.,
2000), reduced immune competence (Blecha, 2000), and behavioral
disturbance (Moberg, 1987; Blecha, 2000). Increases in the circulation
of glucocorticosteroids (cortisol, corticosterone, and aldosterone in
marine mammals; see Romano et al., 2004) have been equated with stress
for many years.
The primary distinction between stress (which is adaptive and does
not normally place an animal at risk) and distress is the biotic cost
of the response. During a stress response, an animal uses glycogen
stores that can be quickly replenished once the stress is alleviated.
In such circumstances, the cost of the stress response would not pose
serious fitness consequences. However, when an animal does not have
sufficient energy reserves to satisfy the energetic costs of a stress
response, energy resources must be diverted from other biotic
functions, which impairs those functions that experience the diversion.
For example, when a stress response diverts energy away from growth in
young animals, those animals may experience stunted growth. When a
stress response diverts energy from a fetus, an animal's reproductive
success and its fitness will suffer. In these cases, the animals will
have entered a pre-pathological or pathological state which is called
``distress'' (Seyle, 1950) or ``allostatic loading'' (McEwen and
Wingfield, 2003). This pathological state of distress will last until
the animal replenishes its energetic reserves sufficiently to restore
normal function. Note that these examples involved a long-term (days or
weeks) stress response exposure to stimuli.
Relationships between these physiological mechanisms, animal
behavior, and the costs of stress responses are well-studied through
controlled experiments in both laboratory and free-ranging animals (for
examples see, Holberton et al., 1996; Hood et al., 1998; Jessop et al.,
2003; Krausman et al., 2004; Lankford et al., 2005; Reneerkens et al.,
2002; Thompson and Hamer, 2000). However, it should be noted (and as is
described in additional detail in the 2020 GOA DSEIS/OEIS) that our
understanding of the functions of various stress hormones (for example,
cortisol), is based largely upon observations of the stress response in
terrestrial mammals. Atkinson et al., 2015 note that the endocrine
response of marine mammals to stress may not be the same as that of
terrestrial mammals because of the selective pressures marine mammals
faced during their evolution in an ocean environment. For example, due
to the necessity of breath-holding while diving and foraging at depth,
the physiological role of epinephrine and norepinephrine (the
catecholamines) in marine mammals might be different than in other
mammals.
Marine mammals naturally experience stressors within their
environment and as part of their life histories. Changing weather and
ocean conditions, exposure to disease and naturally occurring toxins,
lack of prey availability, and interactions with predators all
contribute to the stress a marine mammal experiences (Atkinson et al.,
2015). Breeding cycles, periods of fasting, and social interactions
with members of the same species are also stressors, although they are
natural components of an animal's life history. Anthropogenic
activities have the potential to provide additional stressors beyond
those that occur naturally (Fair et al., 2014; Meissner et al., 2015;
Rolland et al., 2012). Anthropogenic stressors potentially include such
things as fishery interactions, pollution, tourism, and ocean noise.
Acoustically induced stress in marine mammals is not well
understood. There are ongoing efforts to improve our understanding of
how stressors impact marine mammal populations (e.g., King et al.,
2015; New et al., 2013a; New et al., 2013b; Pirotta et al., 2015a),
however little data exist on the consequences of sound-induced stress
response (acute or chronic). Factors potentially affecting a marine
mammal's response to a stressor include the individual's life history
stage, sex, age, reproductive status, overall physiological and
behavioral plasticity, and whether they are na[iuml]ve or experienced
with the sound (e.g., prior experience with a stressor may result in a
reduced response due to habituation (Finneran and Branstetter, 2013;
St. Aubin and Dierauf, 2001). Stress responses due to exposure to
anthropogenic sounds or other stressors and their effects on marine
mammals have been reviewed (Fair and Becker, 2000; Romano et al.,
2002b) and, more rarely, studied in wild populations (e.g., Romano et
al., 2002a). For example, Rolland et al. (2012) found that noise
reduction from reduced ship traffic in the Bay of Fundy was associated
with decreased stress in North Atlantic right whales. These and other
studies lead to a reasonable expectation that some marine mammals will
experience physiological stress responses upon exposure to acoustic
stressors and that it is possible that some of these would be
classified as ``distress.'' In addition, any animal experiencing TTS
would likely also experience stress responses (NRC, 2003).
[[Page 49676]]
Other research has also investigated the impact from vessels (both
whale-watching and general vessel traffic noise), and demonstrated
impacts do occur (Bain, 2002; Erbe, 2002; Lusseau, 2006; Williams et
al., 2006; Williams et al., 2009; Noren et al., 2009; Read et al.,
2014; Rolland et al., 2012; Skarke et al., 2014; Williams et al., 2013;
Williams et al., 2014a; Williams et al., 2014b; Pirotta et al., 2015b).
This body of research has generally investigated impacts associated
with the presence of chronic stressors, which differ significantly from
the proposed Navy training activities in the GOA Study Area. For
example, in an analysis of energy costs to killer whales, Williams et
al. (2009) suggested that whale-watching in Canada's Johnstone Strait
resulted in lost feeding opportunities due to vessel disturbance, which
could carry higher costs than other measures of behavioral change might
suggest. Ayres et al. (2012) reported on research in the Salish Sea
(Washington state) involving the measurement of southern resident
killer whale fecal hormones to assess two potential threats to the
species recovery: lack of prey (salmon) and impacts to behavior from
vessel traffic. Ayres et al. (2012) suggested that the lack of prey
overshadowed any population-level physiological impacts on southern
resident killer whales from vessel traffic. In a conceptual model
developed by the Population Consequences of Acoustic Disturbance (PCAD)
working group, serum hormones were identified as possible indicators of
behavioral effects that are translated into altered rates of
reproduction and mortality (NRC, 2005). The Office of Naval Research
hosted a workshop (Effects of Stress on Marine Mammals Exposed to
Sound) in 2009 that focused on this topic (ONR, 2009). Ultimately, the
PCAD working group issued a report (Cochrem, 2014) that summarized
information compiled from 239 papers or book chapters relating to
stress in marine mammals and concluded that stress responses can last
from minutes to hours and, while we typically focus on adverse stress
responses, stress response is part of a natural process to help animals
adjust to changes in their environment and can also be either neutral
or beneficial.
Most sound-induced stress response studies in marine mammals have
focused on acute responses to sound either by measuring catecholamines
or by measuring heart rate as an assumed proxy for an acute stress
response. Belugas demonstrated no catecholamine response to the
playback of oil drilling sounds (Thomas et al., 1990) but showed a
small but statistically significant increase in catecholamines
following exposure to impulsive sounds produced from a seismic water
gun (Romano et al., 2004). A bottlenose dolphin exposed to the same
seismic water gun signals did not demonstrate a catecholamine response,
but did demonstrate a statistically significant elevation in
aldosterone (Romano et al., 2004), albeit the increase was within the
normal daily variation observed in this species (St. Aubin et al.,
1996). Increases in heart rate were observed in bottlenose dolphins to
which known calls of other dolphins were played, although no increase
in heart rate was observed when background tank noise was played back
(Miksis et al., 2001). Unfortunately, in this study, it cannot be
determined whether the increase in heart rate was due to stress or an
anticipation of being reunited with the dolphin to which the
vocalization belonged. Similarly, a young beluga's heart rate was
observed to increase during exposure to noise, with increases dependent
upon the frequency band of noise and duration of exposure, and with a
sharp decrease to normal or below normal levels upon cessation of the
exposure (Lyamin et al., 2011). Spectral analysis of heart rate
variability corroborated direct measures of heart rate (Bakhchina et
al., 2017). This response might have been in part due to the conditions
during testing, the young age of the animal, and the novelty of the
exposure; a year later the exposure was repeated at a slightly higher
received level and there was no heart rate response, indicating the
beluga whale may have acclimated to the noise exposure. Kvadsheim et
al. (2010) measured the heart rate of captive hooded seals during
exposure to sonar signals and found an increase in the heart rate of
the seals during exposure periods versus control periods when the
animals were at the surface. When the animals dove, the normal dive-
related bradycardia (decrease in heart rate) was not impacted by the
sonar exposure. Elmegaard et al. (2021) found that sonar sweeps did not
elicit a startle response in captive harbor porpoises, but initial
exposures induced bradycardia, whereas impulse exposures induced
startle responses without a change in heart rate. The authors suggested
that the parasympathetic cardiac dive response may override any
transient sympathetic response, or that diving mammals may not have the
cardiac startle response seen in terrestrial mammals in order to
maintain volitional cardiovascular control at depth. Similarly,
Thompson et al. (1998) observed a rapid but short-lived decrease in
heart rates in harbor and grey seals exposed to seismic air guns (cited
in Gordon et al., 2003). Williams et al. (2017) monitored the heart
rates of narwhals released from capture and found that a profound dive
bradycardia persisted, even though exercise effort increased
dramatically as part of their escape response following release. Thus,
although some limited evidence suggests that tachycardia might occur as
part of the acute stress response of animals that are at the surface,
the dive bradycardia persists during diving and might be enhanced in
response to an acute stressor. Yang et al. (2021) measured cortisol
concentrations in two bottlenose dolphins and found significantly
higher concentrations after exposure to 140 dB re 1 [micro]Pa impulsive
noise playbacks. Two out of six tested indicators of immune system
function underwent acoustic dose-dependent changes, suggesting that
repeated exposures or sustained stress response to impulsive sounds may
increase an affected individual's susceptibility to pathogens. However,
exposing dolphins to a different acoustic stressor yielded contrasting
results. Houser et al. (2020) measured cortisol and epinephrine
obtained from 30 bottlenose dolphins exposed to simulated U.S. Navy
mid-frequency sonar and found no correlation between SPL and stress
hormone levels. In the same experiment (Houser et al., 2013b),
behavioral responses were shown to increase in severity with increasing
received SPLs. These results suggest that behavioral reactions to sonar
signals are not necessarily indicative of a hormonal stress response.
Houser et al. (2020) notes that additional research is needed to
determine the relationship between behavioral responses and
physiological responses.
Despite the limited amount of data available on sound-induced
stress responses for marine mammals exposed to anthropogenic sounds,
studies of other marine animals and terrestrial animals would also lead
us to expect that some marine mammals experience physiological stress
responses and, perhaps, physiological responses that would be
classified as ``distress'' upon exposure to high-frequency, mid-
frequency, and low-frequency sounds. For example, Jansen (1998)
reported on the relationship between acoustic exposures and
physiological responses that are indicative of stress responses in
humans (e.g., elevated respiration and increased heart rates). Jones
(1998) reported on reductions in human performance when faced with
acute,
[[Page 49677]]
repetitive exposures to acoustic disturbance. Trimper et al. (1998)
reported on the physiological stress responses of osprey to low-level
aircraft noise while Krausman et al. (2004) reported on the auditory
and physiological stress responses of endangered Sonoran pronghorn to
military overflights. However, take due to aircraft noise is not
anticipated as a result of the Navy's activities. Smith et al. (2004a,
2004b) identified noise-induced physiological transient stress
responses in hearing-specialist fish (i.e., goldfish) that accompanied
short- and long-term hearing losses. Welch and Welch (1970) reported
physiological and behavioral stress responses that accompanied damage
to the inner ears of fish and several mammals.
Auditory Masking
Sound can disrupt behavior through masking, or interfering with, an
animal's ability to detect, recognize, or discriminate between acoustic
signals of interest (e.g., those used for intraspecific communication
and social interactions, prey detection, predator avoidance, or
navigation) (Richardson et al., 1995; Erbe and Farmer, 2000; Tyack,
2000; Erbe et al., 2016). Masking occurs when the receipt of a sound is
interfered with by another coincident sound at similar frequencies and
at similar or higher intensity, and may occur whether the sound is
natural (e.g., snapping shrimp, wind, waves, precipitation) or
anthropogenic (e.g., shipping, sonar, seismic exploration) in origin.
As described in detail in the 2020 GOA DSEIS/OEIS, the ability of a
noise source to mask biologically important sounds depends on the
characteristics of both the noise source and the signal of interest
(e.g., signal-to-noise ratio, temporal variability, direction), in
relation to each other and to an animal's hearing abilities (e.g.,
sensitivity, frequency range, critical ratios, frequency
discrimination, directional discrimination, age, or TTS hearing loss),
and existing ambient noise and propagation conditions. Masking these
acoustic signals can disturb the behavior of individual animals, groups
of animals, or entire populations. Masking can lead to behavioral
changes including vocal changes (e.g., Lombard effect, increasing
amplitude, or changing frequency), cessation of foraging, and leaving
an area, to both signalers and receivers, in an attempt to compensate
for noise levels (Erbe et al., 2016).
In humans, significant masking of tonal signals occurs as a result
of exposure to noise in a narrow band of similar frequencies. As the
sound level increases, though, the detection of frequencies above those
of the masking stimulus decreases also. This principle is expected to
apply to marine mammals as well because of common biomechanical
cochlear properties across taxa.
Under certain circumstances, marine mammals experiencing
significant masking could also be impaired from maximizing their
performance fitness in survival and reproduction. Therefore, when the
coincident (masking) sound is man-made, it may be considered harassment
when disrupting natural behavioral patterns to the point where the
behavior is abandoned or significantly altered. It is important to
distinguish TTS and PTS, which persist after the sound exposure, from
masking, which only occurs during the sound exposure. Because masking
(without resulting in threshold shift) is not associated with abnormal
physiological function, it is not considered a physiological effect,
but rather a potential behavioral effect.
Richardson et al. (1995b) argued that the maximum radius of
influence of an industrial noise (including broadband low-frequency
sound transmission) on a marine mammal is the distance from the source
to the point at which the noise can barely be heard. This range is
determined by either the hearing sensitivity (including critical
ratios, or the lowest signal-to-noise ratio in which animals can detect
a signal, Finneran and Branstetter, 2013; Johnson et al., 1989;
Southall et al., 2000) of the animal or the background noise level
present. Industrial masking is most likely to affect some species'
ability to detect communication calls and natural sounds (i.e., surf
noise, prey noise, etc.; Richardson et al., 1995).
The frequency range of the potentially masking sound is important
in determining any potential behavioral impacts. For example, low-
frequency signals may have less effect on high-frequency echolocation
sounds produced by odontocetes but are more likely to affect detection
of mysticete communication calls and other potentially important
natural sounds such as those produced by surf and some prey species.
The masking of communication signals by anthropogenic noise may be
considered as a reduction in the communication space of animals (e.g.,
Clark et al., 2009; Matthews et al., 2016) and may result in energetic
or other costs as animals change their vocalization behavior (e.g.,
Miller et al., 2000; Foote et al., 2004; Parks et al., 2007; Di Iorio
and Clark, 2009; Holt et al., 2009). Masking can be reduced in
situations where the signal and noise come from different directions
(Richardson et al., 1995), through amplitude modulation of the signal,
or through other compensatory behaviors (Houser and Moore, 2014).
Masking can be tested directly in captive species (e.g., Erbe, 2008),
but in wild populations it must be either modeled or inferred from
evidence of masking compensation. There are few studies addressing
real-world masking sounds likely to be experienced by marine mammals in
the wild (e.g., Branstetter et al., 2013).
The echolocation calls of toothed whales are subject to masking by
high-frequency sound. Human data indicate low-frequency sound can mask
high-frequency sounds (i.e., upward masking). Studies on captive
odontocetes by Au et al. (1974, 1985, 1993) indicate that some species
may use various processes to reduce masking effects (e.g., adjustments
in echolocation call intensity or frequency as a function of background
noise conditions). There is also evidence that the directional hearing
abilities of odontocetes are useful in reducing masking at the high-
frequencies these cetaceans use to echolocate, but not at the low-to-
moderate frequencies they use to communicate (Zaitseva et al., 1980). A
study by Nachtigall and Supin (2018) showed that false killer whales
adjust their hearing to compensate for ambient sounds and the intensity
of returning echolocation signals.
Impacts on signal detection, measured by masked detection
thresholds, are not the only important factors to address when
considering the potential effects of masking. As marine mammals use
sound to recognize conspecifics, prey, predators, or other biologically
significant sources (Branstetter et al., 2016), it is also important to
understand the impacts of masked recognition thresholds (often called
``informational masking''). Branstetter et al., 2016 measured masked
recognition thresholds for whistle-like sounds of bottlenose dolphins
and observed that they are approximately 4 dB above detection
thresholds (energetic masking) for the same signals. Reduced ability to
recognize a conspecific call or the acoustic signature of a predator
could have severe negative impacts. Branstetter et al., 2016 observed
that if ``quality communication'' is set at 90 percent recognition the
output of communication space models (which are based on 50 percent
detection) would likely result in a significant decrease in
communication range.
As marine mammals use sound to recognize predators (Allen et al.,
2014; Cummings and Thompson, 1971; Cur[eacute]
[[Page 49678]]
et al., 2015; Fish and Vania, 1971), the presence of masking noise may
also prevent marine mammals from responding to acoustic cues produced
by their predators, particularly if it occurs in the same frequency
band. For example, harbor seals that reside in the coastal waters off
British Columbia are frequently targeted by mammal-eating killer
whales. The seals acoustically discriminate between the calls of
mammal-eating and fish-eating killer whales (Deecke et al., 2002), a
capability that should increase survivorship while reducing the energy
required to attend to all killer whale calls. Similarly, sperm whales
(Cur[eacute] et al., 2016; Isojunno et al., 2016), long-finned pilot
whales (Visser et al., 2016), and humpback whales (Cur[eacute] et al.,
2015) changed their behavior in response to killer whale vocalization
playbacks; these findings indicate that some recognition of predator
cues could be missed if the killer whale vocalizations were masked. The
potential effects of masked predator acoustic cues depends on the
duration of the masking noise and the likelihood of a marine mammal
encountering a predator during the time that detection and recognition
of predator cues are impeded.
Redundancy and context can also facilitate detection of weak
signals. These phenomena may help marine mammals detect weak sounds in
the presence of natural or manmade noise. Most masking studies in
marine mammals present the test signal and the masking noise from the
same direction. The dominant background noise may be highly directional
if it comes from a particular anthropogenic source such as a ship or
industrial site. Directional hearing may significantly reduce the
masking effects of these sounds by improving the effective signal-to-
noise ratio.
Masking affects both senders and receivers of acoustic signals and
can potentially have long-term chronic effects on marine mammals at the
population level as well as at the individual level. Low-frequency
ambient sound levels have increased by as much as 20 dB (more than
three times in terms of SPL) in the world's ocean from pre-industrial
periods, with most of the increase from distant commercial shipping
(Hildebrand, 2009). All anthropogenic sound sources, but especially
chronic and lower-frequency signals (e.g., from commercial vessel
traffic), contribute to elevated ambient sound levels, thus
intensifying masking.
Impaired Communication
In addition to making it more difficult for animals to perceive and
recognize acoustic cues in their environment, anthropogenic sound
presents separate challenges for animals that are vocalizing. When they
vocalize, animals are aware of environmental conditions that affect the
``active space'' (or communication space) of their vocalizations, which
is the maximum area within which their vocalizations can be detected
before it drops to the level of ambient noise (Brenowitz, 2004; Brumm
et al., 2004; Lohr et al., 2003). Animals are also aware of
environmental conditions that affect whether listeners can discriminate
and recognize their vocalizations from other sounds, which is more
important than simply detecting that a vocalization is occurring
(Brenowitz, 1982; Brumm et al., 2004; Dooling, 2004, Marten and Marler,
1977; Patricelli et al., 2006). Anthropogenic sounds that reduce the
signal-to-noise ratio of animal vocalizations, increase the masked
auditory thresholds of animals listening for such vocalizations, or
reduce the active space of an animal's vocalizations, impair
communication between animals. Most species that vocalize have evolved
with an ability to make adjustments to their vocalizations to increase
the signal-to-noise ratio, active space, and recognizability/
distinguishability of their vocalizations in the face of temporary
changes in background noise (Brumm et al., 2004; Patricelli et al.,
2006). Vocalizing animals can make adjustments to vocalization
characteristics such as the frequency structure, amplitude, temporal
structure, and temporal delivery (repetition rate), or may cease to
vocalize.
Many animals will combine several of these strategies to compensate
for high levels of background noise. Although the fitness consequences
of vocal adjustments are not directly known in all instances, like most
other trade-offs animals must make, some of these strategies probably
come at a cost (Patricelli et al., 2006). Shifting songs and calls to
higher frequencies may also impose energetic costs (Lambrechts, 1996).
For example, in birds, vocalizing more loudly in noisy environments may
have energetic costs that decrease the net benefits of vocal adjustment
and alter a bird's energy budget (Brumm, 2004; Wood and Yezerinac,
2006).
Marine mammals are also known to make vocal changes in response to
anthropogenic noise. In cetaceans, vocalization changes have been
reported from exposure to anthropogenic noise sources such as sonar,
vessel noise, and seismic surveying (see the following for examples:
Gordon et al., 2003; Di Iorio and Clark, 2010; Hatch et al., 2012; Holt
et al., 2008; Holt et al., 2011; Lesage et al., 1999; McDonald et al.,
2009; Parks et al., 2007, Risch et al., 2012, Rolland et al., 2012), as
well as changes in the natural acoustic environment (Caruso et al.,
2020; Dunlop et al., 2014; Helble et al., 2020). Vocal changes can be
temporary, or can be persistent. For example, model simulation suggests
that the increase in starting frequency for the North Atlantic right
whale upcall over the last 50 years resulted in increased detection
ranges between right whales. The frequency shift, coupled with an
increase in call intensity by 20 dB, led to a call detectability range
of less than 3 km to over 9 km (Tennessen and Parks, 2016). Holt et al.
(2008) measured killer whale call source levels and background noise
levels in the one to 40 kHz band and reported that the whales increased
their call source levels by one dB SPL for every one dB SPL increase in
background noise level. Similarly, another study on St. Lawrence River
belugas reported a similar rate of increase in vocalization activity in
response to passing vessels (Scheifele et al., 2005). Di Iorio and
Clark (2010) showed that blue whale calling rates vary in association
with seismic sparker survey activity, with whales calling more on days
with surveys than on days without surveys. They suggested that the
whales called more during seismic survey periods as a way to compensate
for the elevated noise conditions.
In some cases, these vocal changes may have fitness consequences,
such as an increase in metabolic rates and oxygen consumption, as
observed in bottlenose dolphins when increasing their call amplitude
(Holt et al., 2015). A switch from vocal communication to physical,
surface-generated sounds such as pectoral fin slapping or breaching was
observed for humpback whales in the presence of increasing natural
background noise levels, indicating that adaptations to masking may
also move beyond vocal modifications (Dunlop et al., 2010).
While these changes all represent possible tactics by the sound-
producing animal to reduce the impact of masking, the receiving animal
can also reduce masking by using active listening strategies such as
orienting to the sound source, moving to a quieter location, or
reducing self-noise from hydrodynamic flow by remaining still. The
temporal structure of noise (e.g., amplitude modulation) may also
provide a considerable release from masking through comodulation
masking release (a reduction of masking that occurs when broadband
noise, with a frequency spectrum wider than an animal's auditory filter
bandwidth at the
[[Page 49679]]
frequency of interest, is amplitude modulated) (Branstetter and
Finneran, 2008; Branstetter et al., 2013). Signal type (e.g., whistles,
burst-pulse, sonar clicks) and spectral characteristics (e.g.,
frequency modulated with harmonics) may further influence masked
detection thresholds (Branstetter et al., 2016; Cunningham et al.,
2014).
Masking Due to Sonar and Other Transducers
The functional hearing ranges of mysticetes, odontocetes, and
pinnipeds underwater overlap the frequencies of the sonar sources used
in the Navy's low-frequency active sonar (LFAS)/mid-frequency active
sonar (MFAS)/high-frequency active sonar (HFAS) training exercises
(though the Navy proposes no LFAS use for the activities in this
rulemaking). Additionally, almost all affected species' vocal
repertoires span across the frequencies of these sonar sources used by
the Navy. The closer the characteristics of the masking signal to the
signal of interest, the more likely masking is to occur. Masking by
mid-frequency active sonar (MFAS) with relatively low-duty cycles is
not anticipated (or would be of very short duration) for most cetaceans
as sonar signals occur over a relatively short duration and narrow
bandwidth (overlapping with only a small portion of the hearing range).
While dolphin whistles and MFAS are similar in frequency, masking is
not anticipated (or would be of very short duration) due to the low-
duty cycle of most sonars.
As described in the 2020 GOA DSEIS/OEIS, newer high-duty cycle or
continuous active sonars have more potential to mask vocalizations.
These sonars transmit more frequently (greater than 80 percent duty
cycle) than traditional sonars, but at a substantially lower source
level. HFAS, such as pingers that operate at higher repetition rates
(e.g., 2-10 kHz with harmonics up to 19 kHz, 76 to 77 pings per minute)
(Culik et al., 2001), also operate at lower source levels and have
faster attenuation rates due to the higher frequencies used. These
lower source levels limit the range of impacts, however compared to
traditional sonar systems, individuals close to the source are likely
to experience masking at longer time scales. The frequency range at
which high-duty cycle systems operate overlaps the vocalization
frequency of many mid-frequency cetaceans. Continuous noise at the same
frequency of communicative vocalizations may cause disruptions to
communication, social interactions, acoustically mediated cooperative
behaviors, and important environmental cues. There is also the
potential for the mid-frequency sonar signals to mask important
environmental cues (e.g., predator or conspecific acoustic cues),
possibly affecting survivorship for targeted animals. Masking due to
high duty cycle sonars is likely analogous to masking produced by other
continuous sources (e.g., vessel noise and low-frequency cetaceans),
and would likely have similar short-term consequences, though longer in
duration due to the duration of the masking noise. A study by von
Benda-Beckmann et al. (2021) modeled the effect of pulsed and
continuous 1-2 kHz active sonar on sperm whale echolocation clicks, and
found that the presence of upper harmonics in the sonar signal
increased masking of clicks produced in the search phase of foraging
compared to buzz clicks produced during prey capture. Different levels
of sonar caused intermittent to continuous masking (120 to 160 dB re 1
[mu]Pa2, respectively), but varied based on click level, whale
orientation, and prey target strength. Continuous active sonar resulted
in a greater percentage of time that echolocation clicks were masked
compared to pulsed active sonar. Other short-term consequences may
include changes to vocalization amplitude and frequency (Brumm and
Slabbekoorn, 2005; Hotchkin and Parks, 2013) and behavioral impacts
such as avoidance of the area and interruptions to foraging or other
essential behaviors (Gordon et al., 2003; Isojunno et al., 2021). Long-
term consequences could include changes to vocal behavior and
vocalization structure (Foote et al., 2004; Parks et al., 2007),
abandonment of habitat if masking occurs frequently enough to
significantly impair communication (Brumm and Slabbekoorn, 2005), a
potential decrease in survivorship if predator vocalizations are masked
(Brumm and Slabbekoorn, 2005), and a potential decrease in recruitment
if masking interferes with reproductive activities or mother-calf
communication (Gordon et al., 2003).
Masking Due to Vessel Noise
Masking is more likely to occur in the presence of broadband,
relatively continuous noise sources such as vessels. Several studies
have shown decreases in marine mammal communication space and changes
in behavior as a result of the presence of vessel noise. For example,
right whales were observed to shift the frequency content of their
calls upward while reducing the rate of calling in areas of increased
anthropogenic noise (Parks et al., 2007) as well as increasing the
amplitude (intensity) of their calls (Parks, 2009; Parks et al., 2011).
Fournet et al. (2018) observed that humpback whales in Alaska responded
to increasing ambient sound levels (natural and anthropogenic) by
increasing the source levels of their calls (non-song vocalizations).
Clark et al. (2009) also observed that right whales communication space
decreased by up to 84 percent in the presence of vessels (Clark et al.,
2009). Cholewiak et al. (2018) also observed loss in communication
space in Stellwagen National Marine Sanctuary for North Atlantic right
whales, fin whales, and humpback whales with increased ambient noise
and shipping noise. Gabriele et al. (2018) modeled the effects of
vessel traffic sound on communication space in Glacier Bay National
Park in Alaska and found that typical summer vessel traffic in the
National Park causes losses of communication space to singing whales
(reduced by 13-28 percent), calling whales (18-51 percent), and roaring
seals (32-61 percent), particularly during daylight hours and even in
the absence of cruise ships. Dunlop (2019) observed that an increase in
vessel noise reduced modelled communication space and resulted in
significant reduction in group social interactions in Australian
humpback whales. However, communication signal masking did not fully
explain this change in social behavior in the model, indicating there
may also be an additional effect of the physical presence of the vessel
on social behavior (Dunlop, 2019). Although humpback whales off
Australia did not change the frequency or duration of their
vocalizations in the presence of ship noise, their source levels were
lower than expected based on source level changes to wind noise,
potentially indicating some signal masking (Dunlop, 2016). Multiple
delphinid species have also been shown to increase the minimum or
maximum frequencies of their whistles in the presence of anthropogenic
noise and reduced communication space (for examples see: Holt et al.,
2008; Holt et al., 2011; Gervaise et al., 2012; Williams et al., 2013;
Hermannsen et al., 2014; Papale et al., 2015; Liu et al., 2017; Pine et
al., 2021).
Behavioral Response/Disturbance
Behavioral responses to sound are highly variable and context-
specific. Many different variables can influence an animal's perception
of and response to (nature and magnitude) an acoustic event. An
animal's prior experience with a sound or sound source affects whether
it is less likely (habituation) or more likely (sensitization) to
respond to certain sounds in the future (animals
[[Page 49680]]
can also be innately predisposed to respond to certain sounds in
certain ways) (Southall et al., 2007). Related to the sound itself, the
perceived nearness of the sound, bearing of the sound (approaching vs.
retreating), the similarity of a sound to biologically relevant sounds
in the animal's environment (i.e., calls of predators, prey, or
conspecifics), and familiarity of the sound may affect the way an
animal responds to the sound (Southall et al., 2007; DeRuiter et al.,
2013). Individuals (of different age, gender, reproductive status,
etc.) among most populations will have variable hearing capabilities,
and differing behavioral sensitivities to sounds that will be affected
by prior conditioning, experience, and current activities of those
individuals. Often, specific acoustic features of the sound and
contextual variables (i.e., proximity, duration, or recurrence of the
sound, or the current behavior that the marine mammal is engaged in or
its prior experience), as well as entirely separate factors such as the
physical presence of a nearby vessel, may be more relevant to the
animal's response than the received level alone. For example, Goldbogen
et al. (2013) demonstrated that individual behavioral state was
critically important in determining response of blue whales to sonar,
noting that some individuals engaged in deep (>50 m) feeding behavior
had greater dive responses than those in shallow feeding or non-feeding
conditions. Some blue whales in the Goldbogen et al. (2013) study that
were engaged in shallow feeding behavior demonstrated no clear changes
in diving or movement even when received levels (RLs) were high (~160
dB re: 1[micro]Pa) for exposures to 3-4 kHz sonar signals, while others
showed a clear response at exposures at lower received levels of sonar
and pseudorandom noise.
Studies by DeRuiter et al. (2012) indicate that variability of
responses to acoustic stimuli depends not only on the species receiving
the sound and the sound source, but also on the social, behavioral, or
environmental contexts of exposure. Another study by DeRuiter et al.
(2013) examined behavioral responses of Cuvier's beaked whales to MF
sonar and found that whales responded strongly at low received levels
(RL of 89-127 dB re: 1[micro]Pa) by ceasing normal fluking and
echolocation, swimming rapidly away, and extending both dive duration
and subsequent non-foraging intervals when the sound source was 3.4-9.5
km away. Importantly, this study also showed that whales exposed to a
similar range of received levels (78-106 dB re: 1 [micro]Pa) from
distant sonar exercises (118 km away) did not elicit such responses,
suggesting that context may moderate reactions.
Ellison et al. (2012) outlined an approach to assessing the effects
of sound on marine mammals that incorporates contextual-based factors.
The authors recommend considering not just the received level of sound,
but also the activity the animal is engaged in at the time the sound is
received, the nature and novelty of the sound (i.e., is this a new
sound from the animal's perspective), and the distance between the
sound source and the animal. They submit that this ``exposure
context,'' as described, greatly influences the type of behavioral
response exhibited by the animal. Forney et al. (2017) also point out
that an apparent lack of response (e.g., no displacement or avoidance
of a sound source) may not necessarily mean there is no cost to the
individual or population, as some resources or habitats may be of such
high value that animals may choose to stay, even when experiencing
stress or hearing loss. Forney et al. (2017) recommend considering both
the costs of remaining in an area of noise exposure such as TTS, PTS,
or masking, which could lead to an increased risk of predation or other
threats or a decreased capability to forage, and the costs of
displacement, including potential increased risk of vessel strike,
increased risks of predation or competition for resources, or decreased
habitat suitable for foraging, resting, or socializing. This sort of
contextual information is challenging to predict with accuracy for
ongoing activities that occur over large spatial and temporal expanses.
However, distance is one contextual factor for which data exist to
quantitatively inform a take estimate, and the method for predicting
Level B harassment in this rule does consider distance to the source.
Other factors are often considered qualitatively in the analysis of the
likely consequences of sound exposure, where supporting information is
available.
Friedlaender et al. (2016) provided the first integration of direct
measures of prey distribution and density variables incorporated into
across-individual analyses of behavior responses of blue whales to
sonar, and demonstrated a five-fold increase in the ability to quantify
variability in blue whale diving behavior. These results illustrate
that responses evaluated without such measurements for foraging animals
may be misleading, which again illustrates the context-dependent nature
of the probability of response.
Exposure of marine mammals to sound sources can result in, but is
not limited to, no response or any of the following observable
responses: increased alertness; orientation or attraction to a sound
source; vocal modifications; cessation of feeding; cessation of social
interaction; alteration of movement or diving behavior; habitat
abandonment (temporary or permanent); and, in severe cases, panic,
flight, stampede, or stranding, potentially resulting in death
(Southall et al., 2007; Southall et al., 2021). A review of marine
mammal responses to anthropogenic sound was first conducted by
Richardson (1995). More recent reviews (Nowacek et al., 2007; DeRuiter
et al., 2012 and 2013; Ellison et al., 2012; Gomez et al., 2016)
address studies conducted since 1995 and focused on observations where
the received sound level of the exposed marine mammal(s) was known or
could be estimated. Gomez et al. (2016) conducted a review of the
literature considering the contextual information of exposure in
addition to received level and found that higher received levels were
not always associated with more severe behavioral responses and vice
versa. Southall et al. (2016) states that results demonstrate that some
individuals of different species display clear yet varied responses,
some of which have negative implications, while others appear to
tolerate high levels, and that responses may not be fully predictable
with simple acoustic exposure metrics (e.g., received sound level).
Rather, the authors state that differences among species and
individuals along with contextual aspects of exposure (e.g., behavioral
state) appear to affect response probability.
Sperm whales were exposed to pulsed active sonar (1-2 kHz) at
moderate source levels and high source levels, as well as continuously
active sonar at moderate levels for which the summed energy (SEL)
equaled the summed energy of the high source level pulsed sonar
(Isojunno et al., 2020). Foraging behavior did not change during
exposures to moderate source level sonar, but non-foraging behavior
increased during exposures to high source level sonar and to the
continuous sonar, indicating that the energy of the sound (the SEL) was
a better predictor of response than SPL. However, the time of day of
the exposure was also an important covariate in determining the amount
of non-foraging behavior, as were order effects (e.g. the SEL of the
previous exposure). Isojunno et al. (2021) found that higher SELs
reduced
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sperm whale buzzing (i.e., foraging). Duration of continuous sonar
activity also appears to impact sperm whale displacement and foraging
activity (Stanistreet, 2022). During long bouts of sonar lasting up to
13 consecutive hours, occurring repeatedly over an 8 day naval exercise
(median and maximum SPL = 120 dB and 164 dB), sperm whales
substantially reduced how often they produced clicks during sonar,
indicating a decrease or cessation in foraging behavior. Few previous
studies have shown sustained changes in sperm whales, but there was an
absence of sperm whale clicks for 6 consecutive days of sonar activity.
Cur[eacute] et al. (2021) also found that sperm whales exposed to
continuous and pulsed active sonar were more likely to produce low or
medium severity responses with higher cumulative SEL. Specifically, the
probability of observing a low severity response increased to 0.5 at
approximately 173 dB SEL and observing a medium severity response
reached a probability of 0.35 at cumulative SELs between 179 and 189
dB. These results again demonstrate that the behavioral state and
environment of the animal mediates the likelihood of a behavioral
response, as do the characteristics (e.g., frequency, energy level) of
the sound source itself.
The following subsections provide examples of behavioral responses
that provide an idea of the variability in behavioral responses that
would be expected given the differential sensitivities of marine mammal
species to sound and the wide range of potential acoustic sources to
which a marine mammal may be exposed. Behavioral responses that could
occur for a given sound exposure should be determined from the
literature that is available for each species, or extrapolated from
closely related species when no information exists, along with
contextual factors.
Flight Response
A flight response is a dramatic change in normal movement to a
directed and rapid movement away from the perceived location of a sound
source. The flight response differs from other avoidance responses in
the intensity of the response (e.g., directed movement, rate of
travel). Relatively little information on flight responses of marine
mammals to anthropogenic signals exist, although observations of flight
responses to the presence of predators have occurred (Connor and
Heithaus, 1996). The result of a flight response could range from
brief, temporary exertion and displacement from the area where the
signal provokes flight to, in extreme cases, being a component of
marine mammal strandings associated with sonar activities (Evans and
England, 2001). If marine mammals respond to Navy vessels that are
transmitting active sonar in the same way that they might respond to a
predator, their probability of flight responses should increase when
they perceive that Navy vessels are approaching them directly, because
a direct approach may convey detection and intent to capture (Burger
and Gochfeld, 1981, 1990; Cooper, 1997, 1998). There are limited data
on flight response for marine mammals in water; however, there are
examples of this response in species on land. For instance, the
probability of flight responses in Dall's sheep Ovis dalli dalli (Frid,
2001), hauled-out ringed seals Phoca hispida (Born et al., 1999),
Pacific brant (Branta bernicl nigricans), and Canada geese (B.
canadensis) increased as a helicopter or fixed-wing aircraft more
directly approached groups of these animals (Ward et al., 1999). Bald
eagles (Haliaeetus leucocephalus) perched on trees alongside a river
were also more likely to flee from a paddle raft when their perches
were closer to the river or were closer to the ground (Steidl and
Anthony, 1996).
Response to Predator
As discussed earlier, evidence suggests that at least some marine
mammals have the ability to acoustically identify potential predators.
For example, harbor seals that reside in the coastal waters off British
Columbia are frequently targeted by certain groups of killer whales,
but not others. The seals discriminate between the calls of threatening
and non-threatening killer whales (Deecke et al., 2002), a capability
that should increase survivorship while reducing the energy required
for attending to and responding to all killer whale calls. The
occurrence of masking or hearing impairment provides a means by which
marine mammals may be prevented from responding to the acoustic cues
produced by their predators. Whether or not this is a possibility
depends on the duration of the masking/hearing impairment and the
likelihood of encountering a predator during the time that predator
cues are impeded.
Alteration of Diving or Movement
Changes in dive behavior can vary widely. They may consist of
increased or decreased dive times and surface intervals as well as
changes in the rates of ascent and descent during a dive (e.g., Frankel
and Clark, 2000; Ng and Leung, 2003; Nowacek et al. 2004; Goldbogen et
al., 2013a, 2013b). Variations in dive behavior may reflect
interruptions in biologically significant activities (e.g., foraging)
or they may be of little biological significance. Variations in dive
behavior may also expose an animal to potentially harmful conditions
(e.g., increasing the chance of ship-strike) or may serve as an
avoidance response that enhances survivorship. The impact of a
variation in diving resulting from an acoustic exposure depends on what
the animal is doing at the time of the exposure and the type and
magnitude of the response.
Nowacek et al. (2004) reported disruptions of dive behaviors in
foraging North Atlantic right whales when exposed to an alerting
stimulus, an action, they noted, that could lead to an increased
likelihood of ship strike. However, the whales did not respond to
playbacks of either right whale social sounds or vessel noise,
highlighting the importance of the sound characteristics in producing a
behavioral reaction. Conversely, Indo-Pacific humpback dolphins have
been observed to dive for longer periods of time in areas where vessels
were present and/or approaching (Ng and Leung, 2003). In both of these
studies, the influence of the sound exposure cannot be decoupled from
the physical presence of a surface vessel, thus complicating
interpretations of the relative contribution of each stimulus to the
response. Indeed, the presence of surface vessels, their approach, and
speed of approach, seemed to be significant factors in the response of
the Indo-Pacific humpback dolphins (Ng and Leung, 2003). Arranz et al.
(2021) attempted to distinguish effects of vessel noise from vessel
presence by conducting a noise exposure experiment which compared
behavioral reactions of resting short-finned pilot whale mother-calf
pairs during controlled approaches by a tour boat with two electric
(136-140 dB) or petrol engines (139-150 dB). Approach speed (<4 knots),
distance of passes (60 m), and vessel features other than engine noise
remained the same between the two experimental conditions. Behavioral
data was collected via unmanned aerial vehicle and activity budgets
were calculated from continuous focal follows. Mother pilot whales
rested less and calves nursed less in response to both types of boat
engines compared to control conditions (vessel >300 m, stationary in
neutral). However, they found no significant impact on whale behaviors
when the boat approached with the quieter electric engine, while
resting
[[Page 49682]]
behavior decreased 29 percent and nursing decreased 81 percent when the
louder petrol engine was installed in the same vessel. Low-frequency
signals of the Acoustic Thermometry of Ocean Climate (ATOC) sound
source were not found to affect dive times of humpback whales in
Hawaiian waters (Frankel and Clark, 2000) or to overtly affect elephant
seal dives (Costa et al., 2003). They did, however, produce subtle
effects that varied in direction and degree among the individual seals,
illustrating the equivocal nature of behavioral effects and consequent
difficulty in defining and predicting them. Lastly, as noted
previously, DeRuiter et al. (2013) noted that distance from a sound
source may moderate marine mammal reactions in their study of Cuvier's
beaked whales, which showed the whales swimming rapidly and silently
away when a sonar signal was 3.4-9.5 km away while showing no such
reaction to the same signal when the signal was 118 km away even though
the received levels were similar.
Foraging
Disruption of feeding behavior can be difficult to correlate with
anthropogenic sound exposure, so it is usually inferred by observed
displacement from known foraging areas, the appearance of secondary
indicators (e.g., bubble nets or sediment plumes), or changes in dive
behavior. As for other types of behavioral response, the frequency,
duration, and temporal pattern of signal presentation, as well as
differences in species sensitivity, are likely contributing factors to
differences in response in any given circumstance (e.g., Croll et al.,
2001; Harris et al., 2017; Madsen et al., 2006a; Nowacek et al.; 2004;
Yazvenko et al., 2007). A determination of whether foraging disruptions
incur fitness consequences would require information on or estimates of
the energetic requirements of the affected individuals and the
relationship between prey availability, foraging effort and success,
and the life history stage of the animal.
Southall et al. (2019a) found that prey availability was higher in
the western area of the Southern California Offshore Range where
Cuvier's beaked whales preferentially occurred, while prey resources
were lower in the eastern area and moderate in the area just north of
the Range. This high prey availability may indicate that fewer foraging
dives are needed to meet metabolic energy requirements than would be
needed in another area with fewer resources. Benoit-Bird et al. (2020)
demonstrated that differences in squid distribution could be a
substantial factor for beaked whales' habitat preference. The
researchers suggest that this be considered when comparing beaked whale
habitat use both on and off Navy ranges.
Noise from seismic surveys was not found to impact the feeding
behavior in western grey whales off the coast of Russia (Yazvenko et
al., 2007). Visual tracking, passive acoustic monitoring, and movement
recording tags were used to quantify sperm whale behavior prior to,
during, and following exposure to air gun arrays at received levels in
the range of 140-160 dB at distances of 7-13 km, following a phase-in
of sound intensity and full array exposures at 1-13 km (Madsen et al.,
2006a; Miller et al., 2009). Sperm whales did not exhibit horizontal
avoidance behavior at the surface. However, foraging behavior may have
been affected. The sperm whales exhibited 19 percent less vocal (buzz)
rate during full exposure relative to post exposure, and the whale that
was approached most closely had an extended resting period and did not
resume foraging until the air guns had ceased firing. The remaining
whales continued to execute foraging dives throughout exposure;
however, swimming movements during foraging dives were six percent
lower during exposure than control periods (Miller et al., 2009). These
data raise concerns that air gun surveys may impact foraging behavior
in sperm whales, although more data are required to understand whether
the differences were due to exposure or natural variation in sperm
whale behavior (Miller et al., 2009).
Balaenopterid whales exposed to moderate low-frequency signals
similar to the ATOC sound source demonstrated no variation in foraging
activity (Croll et al., 2001), whereas five out of six North Atlantic
right whales exposed to an acoustic alarm interrupted their foraging
dives (Nowacek et al., 2004). Although the received SPLs were similar
in the latter two studies, the frequency, duration, and temporal
pattern of signal presentation were different. These factors, as well
as differences in species sensitivity, are likely contributing factors
to the differential response. Blue whales exposed to mid-frequency
sonar in the Southern California Bight were less likely to produce low
frequency calls usually associated with feeding behavior (Melc[oacute]n
et al., 2012). However, Melc[oacute]n et al. (2012) were unable to
determine if suppression of low frequency calls reflected a change in
their feeding performance or abandonment of foraging behavior and
indicated that implications of the documented responses are unknown.
Further, it is not known whether the lower rates of calling actually
indicated a reduction in feeding behavior or social contact since the
study used data from remotely deployed, passive acoustic monitoring
buoys. In contrast, blue whales increased their likelihood of calling
when ship noise was present, and decreased their likelihood of calling
in the presence of explosive noise, although this result was not
statistically significant (Melc[oacute]n et al., 2012). Additionally,
the likelihood of an animal calling decreased with the increased
received level of mid-frequency sonar, beginning at a SPL of
approximately 110-120 dB re: 1 [micro]Pa (Melc[oacute]n et al., 2012).
Results from behavioral response studies in Southern California waters
indicated that, in some cases and at low received levels, tagged blue
whales responded to mid-frequency sonar but that those responses were
generally brief, of low to moderate severity, and highly dependent on
exposure context (Southall et al., 2011; Southall et al., 2012b;
Southall et al., 2019b). Information on or estimates of the energetic
requirements of the individuals and the relationship between prey
availability, foraging effort and success, and the life history stage
of the animal will help better inform a determination of whether
foraging disruptions incur fitness consequences. Surface feeding blue
whales did not show a change in behavior in response to mid-frequency
simulated and real sonar sources with received levels between 90 and
179 dB re: 1 [micro]Pa, but deep feeding and non-feeding whales showed
temporary reactions including cessation of feeding, reduced initiation
of deep foraging dives, generalized avoidance responses, and changes to
dive behavior. The behavioral responses the researchers observed were
generally brief, of low to moderate severity, and highly dependent on
exposure context (behavioral state, source-to-whale horizontal range,
and prey availability) (DeRuiter et al., 2017; Goldbogen et al., 2013b;
Sivle et al., 2015). Goldbogen et al. (2013b) indicate that disruption
of feeding and displacement could impact individual fitness and health.
However, for this to be true, we would have to assume that an
individual whale could not compensate for this lost feeding opportunity
by either immediately feeding at another location, by feeding shortly
after cessation of acoustic exposure, or by feeding at a later time.
There is no indication this is the case, particularly since unconsumed
prey would likely still be available in the environment in most cases
following the cessation of acoustic exposure.
[[Page 49683]]
Similarly, while the rates of foraging lunges decrease in humpback
whales due to sonar exposure, there was variability in the response
across individuals, with one animal ceasing to forage completely and
another animal starting to forage during the exposure (Sivle et al.,
2016). In addition, almost half of the animals that exhibited avoidance
behavior were foraging before the exposure but the others were not; the
animals that exhibited avoidance behavior while not feeding responded
at a slightly lower received level and greater distance than those that
were feeding (Wensveen et al., 2017). These findings indicate that the
behavioral state of the animal plays a role in the type and severity of
a behavioral response. In fact, when the prey field was mapped and used
as a covariate in similar models looking for a response in the same
blue whales, the response in deep-feeding behavior by blue whales was
even more apparent, reinforcing the need for contextual variables to be
included when assessing behavioral responses (Friedlaender et al.,
2016).
Breat
[…truncated; see source link]Indexed from Federal Register on August 11, 2022.
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