Notice2022-20928
Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to a Geophysical Survey in the Ross Sea, Antarctica
Primary source
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Published
September 29, 2022
Issuing agencies
Commerce DepartmentNational Oceanic and Atmospheric Administration
Abstract
NMFS has received a request from the United States National Science Foundation (NSF) Office of Polar Programs for authorization to take marine mammals incidental to a geophysical survey in the Ross Sea, Antarctica. Pursuant to the Marine Mammal Protection Act (MMPA), NMFS is requesting comments on its proposal to issue an incidental harassment authorization (IHA) to incidentally take marine mammals during the specified activities. NMFS is also requesting comments on a possible one-year renewal that could be issued under certain circumstances and if all requirements are met, as described in Request for Public Comments at the end of this notice. NMFS will consider public comments prior to making any final decision on the issuance of the requested MMPA authorizations and agency responses will be summarized in the final notice of our decision.
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[Federal Register Volume 87, Number 188 (Thursday, September 29, 2022)]
[Notices]
[Pages 59204-59238]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2022-20928]
[[Page 59203]]
Vol. 87
Thursday,
No. 188
September 29, 2022
Part III
Department of Commerce
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National Oceanic and Atmospheric Administration
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Takes of Marine Mammals Incidental to Specified Activities; Taking
Marine Mammals Incidental to a Geophysical Survey in the Ross Sea,
Antarctica; Notice
Federal Register / Vol. 87 , No. 188 / Thursday, September 29, 2022 /
Notices
[[Page 59204]]
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DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
[RTID 0648-XC218]
Takes of Marine Mammals Incidental to Specified Activities;
Taking Marine Mammals Incidental to a Geophysical Survey in the Ross
Sea, Antarctica
AGENCY: National Marine Fisheries Service (NMFS), National Oceanic and
Atmospheric Administration (NOAA), Commerce.
ACTION: Notice; proposed incidental harassment authorization; request
for comments on proposed authorization and possible renewal.
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SUMMARY: NMFS has received a request from the United States National
Science Foundation (NSF) Office of Polar Programs for authorization to
take marine mammals incidental to a geophysical survey in the Ross Sea,
Antarctica. Pursuant to the Marine Mammal Protection Act (MMPA), NMFS
is requesting comments on its proposal to issue an incidental
harassment authorization (IHA) to incidentally take marine mammals
during the specified activities. NMFS is also requesting comments on a
possible one-year renewal that could be issued under certain
circumstances and if all requirements are met, as described in Request
for Public Comments at the end of this notice. NMFS will consider
public comments prior to making any final decision on the issuance of
the requested MMPA authorizations and agency responses will be
summarized in the final notice of our decision.
DATES: Comments and information must be received no later than October
31, 2022.
ADDRESSES: Comments should be addressed to Jolie Harrison, Chief,
Permits and Conservation Division, Office of Protected Resources,
National Marine Fisheries Service. Physical comments should be sent to
1315 East-West Highway, Silver Spring, MD 20910 and electronic comments
should be sent to <a href="/cdn-cgi/l/email-protection#a3eaf7f38debc2d1cfc2c0cbc6d1e3cdccc2c28dc4ccd5"><span class="__cf_email__" data-cfemail="6d24393d43250c1f010c0e05081f2d03020c0c430a021b">[email protected]</span></a>.
Instructions: NMFS is not responsible for comments sent by any
other method, to any other address or individual, or received after the
end of the comment period. Comments received electronically, including
all attachments, must not exceed a 25-megabyte file size. All comments
received are a part of the public record and will generally be posted
online at <a href="https://www.fisheries.noaa.gov/permit/incidental-take-authorizations-under-marine-mammal-protection-act">https://www.fisheries.noaa.gov/permit/incidental-take-authorizations-under-marine-mammal-protection-act</a> without change. All
personal identifying information (e.g., name, address) voluntarily
submitted by the commenter may be publicly accessible. Do not submit
confidential business information or otherwise sensitive or protected
information.
FOR FURTHER INFORMATION CONTACT: Jenna Harlacher, Office of Protected
Resources, NMFS, (301) 427-8401. Electronic copies of the application
and supporting documents, as well as a list of the references cited in
this document, may be obtained online at: <a href="https://www.fisheries.noaa.gov/permit/incidental-take-authorizations-under-marine-mammal-protection-act">https://www.fisheries.noaa.gov/permit/incidental-take-authorizations-under-marine-mammal-protection-act</a>. In case of problems accessing these
documents, please call the contact listed above.
SUPPLEMENTARY INFORMATION:
Background
The MMPA prohibits the ``take'' of marine mammals, with certain
exceptions. Sections 101(a)(5)(A) and (D) of the MMPA (16 U.S.C. 1361
et seq.) 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 issued or, if the taking is limited to harassment, a notice of a
proposed incidental take authorization may be provided to the public
for review.
Authorization for incidental takings shall be granted if NMFS finds
that the taking will have a negligible impact on the species or
stock(s) and will not have an unmitigable adverse impact on the
availability of the species or stock(s) for 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 the species or stocks for
taking for certain subsistence uses (referred to in shorthand as
``mitigation''); and requirements pertaining to the mitigation,
monitoring and reporting of the takings are set forth.
The definitions of all applicable MMPA statutory terms cited above
are included in the relevant sections below.
National Environmental Policy Act
To comply with the National Environmental Policy Act of 1969 (NEPA;
42 U.S.C. 4321 et seq.) and NOAA Administrative Order (NAO) 216-6A,
NMFS must review our proposed action (i.e., the issuance of an
incidental harassment authorization) with respect to potential impacts
on the human environment.
This action is consistent with categories of activities identified
in Categorical Exclusion B4 (incidental harassment authorizations with
no anticipated serious injury or mortality) of the Companion Manual for
NOAA Administrative Order 216-6A, which do not individually or
cumulatively have the potential for significant impacts on the quality
of the human environment and for which we have not identified any
extraordinary circumstances that would preclude this categorical
exclusion. Accordingly, NMFS has preliminarily determined that the
issuance of the proposed IHA qualifies to be categorically excluded
from further NEPA review.
Summary of Request
On May 26, 2022, NMFS received a request from NSF for an IHA to
take marine mammals incidental to conducting a low energy seismic
survey and icebreaking in the Ross Sea. The application was deemed
adequate and complete on July 22, 2022. NSF's request is for take of
small numbers of 17 species of marine mammals by Level B harassment
only. Neither NSF nor NMFS expects serious injury or mortality to
result from this activity and, therefore, an IHA is appropriate.
Description of Proposed Activity
Overview
Researchers from Louisiana State University, Texas A&M University,
University of Texas at Austin, University of West Florida, and Dauphin
Island Sea Lab, with funding from NSF, propose to conduct a two-part
low-energy seismic survey from the Research Vessel/Icebreaker (RVIB)
Nathaniel B. Palmer (NBP), in the Ross Sea during Austral Summer 2022-
2023. The two-part proposed survey would include the Ross Bank and the
Drygalski Trough areas. The proposed seismic survey would take place in
International waters of the Southern Ocean, in water depths ranging
from ~150 to 1100 meters (m).
The RVIB Palmer would deploy up to two 105-in\3\ generator injector
(GI) airguns at a depth of 1-4 m with a total maximum discharge volume
for the largest, two-airgun array of 210 in\3\ along predetermined
track lines. During the Ross Bank survey, ~1920km of seismic data would
be collected and
[[Page 59205]]
during the Drygalski Trough survey, ~1800 km of seismic acquisition
would occur, for a total of 3720 line km.
Although the proposed survey will occur in the Austral summer, some
icebreaking activities are expected to be required during the cruise.
The proposed Ross Bank portion of activity is to determine if, how,
when, and why the Ross Ice Shelf unpinned from Ross Bank in the recent
geologic past, to assess to what degree that event caused a re-
organization of ice sheet and ice shelf flow towards its current
configuration. The Drygalski Trough activities are proposed to examine
the gas hydrate contribution to the Ross Sea carbon budget. The
Drygalski Trough activities would examine the warming and carbon
cycling of the ephemeral reservoir of carbon at the extensive bottom
ocean layer-sediment interface of the Ross Sea. This large carbon
reserve appears to be sealed in the form of gas hydrate and is a
thermogenic carbon source and carbon storage in deep sediment hydrates.
The warming and ice melting coupled with high thermogenic gas hydrate
loadings suggest the Ross Sea is an essential environment to determine
contributions of current day and potential future methane, petroleum,
and glacial carbon to shallow sediment and water column carbon cycles.
Dates and Duration
The RVIB Palmer would likely depart from Lyttelton, New Zealand, on
December 18, 2022, and would return to McMurdo Station, Antarctica, on
January 18, 2023, after the program is completed. The cruise is
expected to consist of 31 days at sea, including approximately 19 days
of seismic operations (including 2 days of sea trials and/or
contingency), 1 day of ocean bottom seismometer (OBS) deployment/
recovery, and approximately 11 days of transit. Some deviation in
timing and ports of call could also result from unforeseen events such
as weather or logistical issues.
Specific Geographic Region
The proposed survey would take place in the Ross Sea, Antarctica
(continental shelf between ~75[deg]-77.7[deg] S and 171[deg] E-173[deg]
E and Drygalski Trough between ~74[deg]76.7[deg] S and 163.6[deg] E-
170[deg] E (Figure 1) in International waters of the Southern Ocean in
water depths ranging from approximately 150 to 1100 m. Representative
survey tracklines are shown in Figure 1; however, the actual survey
effort could occur anywhere within the outlined study area as shown.
The line locations for the survey area are preliminary and could be
refined in light of information from data collected during the study
and conditions within the survey area.
BILLING CODE 3510-22-P
[GRAPHIC] [TIFF OMITTED] TN29SE22.000
BILLING CODE 3510-22-C
[[Page 59206]]
Detailed Description of Specific Activity
The procedures to be used for the proposed survey would entail use
of conventional seismic methodology. The survey would involve one
source vessel, RVIB Palmer and the airgun array would be deployed at a
depth of approximately 1-4 m below the surface, spaced approximately
2.4 m apart for the two-gun array. Seismic acquisition is proposed to
begin with a standard sea trial to determine which configuration and
mode of GI airgun(s) provide the best reflection signals, which depends
on sea-state and subsurface conditions. A maximum of two GI airguns
would be used. Four GI configurations (each using one or two GI
airguns) would be tested during the sea trial (Table 1). The largest
volume airgun configuration (configuration 4) was carried forward in
our analysis and used for estimating the take numbers proposed for
authorization.
The RVIB Palmer would deploy two 105 in\3\ GI airguns as an energy
source with a total volume of ~210 in\3\. Seismic pulses would be
emitted at intervals of 5 to 10 seconds from the GI airgun. The
receiving system would consist of one hydrophone streamer, 75 m in
length, with the vessel traveling at 8.3 km/hr (4.5 knots (kn)) to
achieve high-quality seismic reflection data. As the airguns are towed
along the survey lines, the hydrophone streamer would receive the
returning acoustic signals and transfer the data to the on-board
processing system. If sea-ice conditions permit, a multi-channel
digital streamer would be used to improve signal-to-noise ratio by
digital data processing; if ice is present, a single-channel digital
steamer would be employed. When not towing seismic survey gear, the
RVIB Palmer has a maximum speed of 26.9 km/h (14.5 kn), but cruises at
an average speed of 18.7 km/h (10.1 kn). During the Ross Bank survey,
~1920km of seismic data would be collected and during the Drygalski
Trough survey, ~1800 km of seismic acquisition would occur, for a total
of 3720 line km.
During the Drygalski Trough survey, 2 deployments of 10 OBSs would
occur along 2 different seismic refraction lines (see Fig. 1 for
representative lines). Following refraction shooting of one line, OBSs
on that line would be recovered, serviced, and redeployed on a
subsequent refraction line. The spacing of OBSs on the initial
refraction line would be 5 km apart, but OBSs could be deployed as
close together as every 500 m on the subsequent refraction line. All
OBSs would be recovered at the end of the survey. To retrieve the OBSs,
the instrument is released via an acoustic release system to float to
the surface from the wire and/or anchor, which are not retrieved.
Table 1--Four GI Configurations (Each Using One or Two GI Airguns) Would Be Tested During the Sea Trial
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Airgun array total volume Frequency between
Configuration (GI configuration) seismic shots Streamer length
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1........................... 50 in\3\ Harmonic Mode 5-10 seconds........... 75 m.
configured as 25 in\3\
Generator + 25 Injector
in\3\.
2........................... 90 in\3\ Harmonic Mode 5-10 seconds...........
configured as 45 in\3\
Generator + 45 Injector
in\3\.
3........................... 50 in\3\ True-GI Mode 5-10 seconds...........
configured as 45 in\3\
Generator + 105 Injector
in\3\.
4........................... 210 in\3\ Harmonic Mode 5-10 seconds...........
configured as 105 in\3\
Generator + 105 Injector
in\3\.
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There could be additional seismic operations in the study area
associated with equipment testing, re-acquisition due to reasons such
as, but not limited to, equipment malfunction, data degradation during
poor weather, or interruption due to shut down or track deviation in
compliance with IHA requirements. To account for these additional
seismic operations, 25 percent has been added in the form of
operational days, which is equivalent to adding 25 percent to the
proposed line km to be surveyed.
Along with the airgun and OBS operations, additional acoustical
data acquisition systems and other equipment may be operated during the
seismic survey at any time to meet scientific objectives. The ocean
floor would be mapped with a Multibeam Ecosounder (MBES), Sub-bottom
Profiler (SBP), and/or Acoustic Doppler Current Profiler (ADCP). Data
acquisition in the survey area will occur in water depths ranging from
150 to 700 m. Take of marine mammals is not expected to occur
incidental to use of these other sources, whether or not the airguns
are operating simultaneously with the other sources. Given their
characteristics (e.g., narrow downward-directed beam), marine mammals
would experience no more than one or two brief ping exposures, if any
exposure were to occur. NMFS does not expect that the use of these
sources presents any reasonable potential to cause take of marine
mammals.
(1) Single Beam Echo Sounder (Knudsen 3260)--The hull-mounted
compressed high-intensity radiated pulse (CHIRP) sonar is operated at
12 kilohertz (kHz) for bottom-tracking purposes or at 3.5 kHz in the
sub-bottom profiling mode. The sonar emits energy in a 30[deg] beam
from the bottom of the ship and has a sound level of 224 dB re: 1
[mu]Pa m (rms).
(2) Multibeam Sonar (Kongsberg EM122)--The hull-mounted, multibeam
sonar operates at a frequency of 12 kHz, has an estimated maximum
source energy level of 242 dB re 1[mu]Pa (rms), and emits a very narrow
(<2[deg]) beam fore to aft and 150[deg] in cross-track. The multibeam
system emits a series of nine consecutive 15 millisecond (ms) pulses.
(3) Acoustic Doppler Current Profiler (ADCP) (Teledyne RDI VM-
150)--The hull-mounted ADCP operates at a frequency of 150 kHz, with an
estimated acoustic output level at the source of 223.6 dB re 1[mu]Pa
(rms). Sound energy from the ADCP is emitted as a 30[deg], conically
shaped beam.
(4) ADCP (Ocean Surveyor OS-38)--The characteristics of this
backup, hull-mounted ADCP unit are similar to the Teledyne VM-150. The
ADCP operates at a frequency of 150 kHz with an estimated acoustic
output level at the source of 223.6 dB re 1[mu]Pa (rms). Sound energy
from the ADCP is emitted as a 30[deg] conically-shaped beam.
(5) EK biological echo sounder (Simrad ES200-7C, ES38B, ES-120-
7C)--This echo sounder is a split-beam transducer with an estimated
acoustic output level at the source of 183-185 dB
[[Page 59207]]
re 1[mu]Pa and emits a 7[deg] beam. It can operate at 38 kHz, 120 kHz
and 200 kHz.
(6) Acoustic Release--To retrieve OBSs, an acoustic release
transponder (pinger) is used to interrogate the instrument at a
frequency of 8-11 kHz, and a response is received at a frequency of 7-
15 kHz. The burn-wire release assembly is then activated, and the
instrument is released to float to the surface from the wire and/or
anchor which are not retrieved.
(7) Oceanographic Sampling--during the Drygalski Trough study, the
researchers would also conduct opportunistic oceanographic sampling as
time and scheduling allows, including conductivity, temperature and
depth (CTD) measurements, box cores, and/or multi-cores.
Icebreaking
Icebreaking activities are expected to be limited during the
proposed survey. The Ross Sea is generally clear of ice January through
February, because of the large Ross Sea Polynya that occurs in front of
the Ross Ice Shelf. Heavy ice conditions would hamper the proposed
activities, as noise from icebreaking degrades the quality of the
geophysical data to be acquired. If the RVIB Palmer would find itself
in heavy ice conditions, it is unlikely that the airgun(s) and streamer
could be towed, as this could damage the equipment and generate noise
interference. The seismic survey could take place in low ice conditions
if the RVIB Palmer were able to generate an open path behind the
vessel. The RVIB Palmer is not rated for breaking multi-year ice and
generally avoids transiting through ice two years or older and more
than 1 m thick. If sea ice were to be encountered during the survey,
the RVIB Palmer would likely proceed through one-year sea ice, and new,
thin ice, but would follow leads wherever possible. Any time spent
icebreaking would take away time from the proposed research activities,
as the vessel would travel slower in ice-covered seas. Based on
estimated transit to the survey area, it is estimated that the RVIB
Palmer would break ice up to a distance of 500 km. Based on a ship
speed of 5 kn under moderate ice conditions, this distance represents
approximately 54 hours of icebreaking (or 2.2 days). Transit through
areas of primarily open water containing brash ice or pancake ice is
not considered icebreaking for the purposes of this assessment.
Proposed mitigation, monitoring, and reporting measures are
described in detail later in this document (please see Proposed
Mitigation and Proposed Monitoring and Reporting).
Description of Marine Mammals in the Area of Specified Activities
Sections 3 and 4 of the application summarize available information
regarding status and trends, distribution and habitat preferences, and
behavior and life history, of the potentially affected species.
Additional information about these species (e.g., physical and
behavioral descriptions) may be found on NMFS's website (<a href="https://www.fisheries.noaa.gov/find-species">https://www.fisheries.noaa.gov/find-species</a>).
The populations of marine mammals considered in this document do
not occur within the U.S. Exclusive Economic Zone (EEZ) and are
therefore not assigned to stocks and are not assessed in NMFS' Stock
Assessment Reports (SAR). As such, information on potential biological
removal (PBR; defined by the MMPA as the maximum number of animals, not
including natural mortalities, that may be removed from a marine mammal
stock while allowing that stock to reach or maintain its optimum
sustainable population) and on annual levels of serious injury and
mortality from anthropogenic sources are not available for these marine
mammal populations. Abundance estimates for marine mammals in the
survey location are lacking; therefore estimates of abundance presented
here are based on a variety of other sources including International
Whaling Commission (IWC) population estimates, the International Union
for Conservation of Nature's (IUCN) Red List of Threatened Species, and
various literature estimates (see IHA application for further detail),
as this is considered the best available information on potential
abundance of marine mammals in the area.
Seventeen species of marine mammals could occur in the Ross Sea,
including 5 mysticetes (baleen whales), 7 odontocetes (toothed whales)
and 5 pinniped species (Table 2). Another seven species occur in the
Sub-Antarctic but are unlikely to be encountered in the proposed survey
areas, as they generally occur farther to the north than the project
area. These species are not discussed further here but include: the
southern right whale (Eubalaena australis), common (dwarf) minke whale
(Balaenoptera acutorostrata), Cuvier's beaked (Ziphius cavirostris),
Gray's beaked (Mesoplodon grayi), Hector's beaked (Mesoplodon hectori),
and spade-toothed beaked (Mesoplodon traversii) whales, southern right
whale dolphin (Lissodelphis peronii), and spectacled porpoise (Phocoena
dioptrica). Table 2 lists all species with expected potential for
occurrence in the Ross Sea, Antarctica, and summarizes information
related to the population, including regulatory status under the MMPA
and ESA.
Table 2--Marine Mammal Species Potentially Present in the Project Area Expected To Be Affected by the Specified
Activities
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ESA/MMPA
status;
Common name Scientific name Stock\1\ strategic (Y/ Stock abundance
N) \2\
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Order Cetartiodactyla--Cetacea--Superfamily Mysticeti (baleen whales)
----------------------------------------------------------------------------------------------------------------
Family Balaenopteridae (rorquals):
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Blue whale................. Balaenoptera N/A E/D;Y 10,000-25,000.\5\
musculus. 1,700.\7\
Fin whale.................. Balaenoptera N/A E/D;Y 140,000.\5\
physalus. 38,200.\ 6\
Humpback whale............. Megaptera N/A .............. 90,000.-100,000.\5\
novaeangliae. 80,000.\10\
42,000.\11\
Antarctic minke whale\6\... Balaenoptera N/A .............. Several 100,000 \5\
bonaerensis. 515,000.\9\
[[Page 59208]]
Sei whale.................. Balaenoptera N/A E 70,000.\8\
borealis.
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Superfamily Odontoceti (toothed whales, dolphins, and porpoises)
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Family Physeteridae:
----------------------------------------------------------------------------------------------------------------
Sperm whale................ Physeter N/A E 360,000.\12\
macrocephalus. 12,069.\13\
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Family Ziphiidae (beaked whales):
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Arnoux's beaked whale...... Berardius arnuxii. N/A .............. 599,300.\14\
Strap-toothed beaked whale. Mesoplodon grayi.. N/A .............. 599,300.\14\
Southern bottlenose whale.. Hyperoodon N/A .............. 599,300.\14\
planifrons.
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Family Delphinidae:
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Killer whale............... Orcinus orca...... N/A .............. 50,000 \16\
25,000.\17\
Long-finned pilot whale.... Globicephala N/A .............. 200,000.\15\
macrorhynchus.
Hourglass dolphin.......... Lagenorhynchus NA .............. 144,300.\15\
cruciger.
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Family Phocidae (earless seals):
----------------------------------------------------------------------------------------------------------------
Crabeater seal............. Lobodon N/A .............. 5-10 million \18\
carcinophaga. 1.7 million.\19\
Leopard seal............... Hydrurga leptonyx. N/A .............. 222,000-440,00.\5\ \20\
Southern elephant seal..... Mirounga leonina.. N/A .............. 750,000.\23\
Ross seal.................. Ommatophoca rossii N/A .............. 250,000.\22\
Weddell seal............... Leptonychotes N/A .............. 1 million.\5\ \21\
weddellii.
----------------------------------------------------------------------------------------------------------------
N.A. = data not available.
\1\ Occurrence in area at the time of the proposed activities; based on professional opinion and available data.
\2\ U.S. Endangered Species Act: EN = endangered, NL = not listed.
\5\ Worldwide (Jefferson et al., 2015).
\6\ Antarctic (Aguilar and Garc[iacute]a-Vernet 2018).
\7\ Antarctic (Branch et al., 2007).
\8\ Southern Hemisphere (Horwood 2018).
\9\ Southern Hemisphere (IWC 2020).
\10\ Southern Hemisphere (Clapham 2018).
\11\ Antarctic feeding area (IWC 2020).
\12\ Worldwide (Whitehead 2002).
\13\ Antarctic south of 60[deg] S (Whitehead 2002).
\14\ All beaked whales south of the Antarctic Convergence; mostly southern bottlenose whales (Kasamatsu and
Joyce 1995).
\15\ Kasamatsu and Joyce (1995).
\16\ Worldwide (Forney and Wade 2006).
\17\ Minimum estimate for Southern Ocean (Branch and Butterworth 2001).
\18\ Worldwide (Bengtson and Stewart 2018).
\19\ Ross and Amundsen seas (Bengtson et al., 2011).
\20\ Rogers et al., 2018.
\21\ H[uuml]ckst[auml]dt 2018a.
\22\ Worldwide (Curtis et al., 2011 in H[uuml]ckst[auml]dt 2018b).
\23\ Total world population (Hindell et al., 2016).
All species that could potentially occur in the proposed survey
areas are included in Table 2. As described below, all 17 species
temporally and spatially co-occur with the activity to the degree that
take is reasonably likely to occur, and we have proposed authorizing
it.
We have reviewed NSF's species descriptions, including life history
information, distribution, regional distribution, diving behavior, and
acoustics and hearing, for accuracy and completeness. We refer the
reader to Section 4 of NSF's IHA application for a complete description
of the species, and offer a brief introduction to the species here, as
well as information regarding population trends and threats, and
describe information regarding local occurrence.
Mysticetes
Blue Whale
The blue whale has a cosmopolitan distribution, but tends to be
mostly pelagic, only occurring nearshore to feed and possibly breed
(Jefferson et al., 2015). It is most often found in cool, productive
waters where upwelling occurs (Reilly and Thayer 1990). The
distribution of the species, at least during times of the year when
feeding is a major activity, occurs in areas that provide large
seasonal concentrations of euphausiids (Yochem and Leatherwood 1985).
Seamounts and other deep ocean structures may be important habitat for
blue whales (Lesage et al., 2016).
[[Page 59209]]
Generally, blue whales are seasonal migrants between high latitudes in
summer, where they feed, and low latitudes in winter, where they mate
and give birth (Lockyer and Brown 1981).
Historically, blue whales were most abundant in the Southern Ocean.
Although, the population structure of the Antarctic blue whale
(Balaenoptera musculus intermedia) in the Southern Ocean is not well
understood, there is evidence of discrete feeding stocks (Sears &
Perrin 2018). Cooke (2018) explains that ``there are no complete
estimates of recent or current abundance for the other regions, but
plausible total numbers would be 1,000-3,000 in the North Atlantic,
3,000-5,000 in the North Pacific, and possibly 1,000-3,000 in the
eastern South Pacific. The number of Pygmy Blue whales is very
uncertain but may be in the range 2,000-5,000. Taken together with a
range of 5,000-8,000 in the Antarctic, the global population size in
2018 is plausibly in the range 10,000-25,000 total or 5,000-15,000
mature, compared with a 1926 global population of at least 140,000
mature.'' Blue whales begin migrating north out of the Antarctic to
winter breeding grounds earlier than fin and sei whales.
The Antarctic blue whale is typically found south of 55[deg] S
during summer, although some individuals do not migrate (Branch et al.,
2007a). The blue whale is considered to be rare in the Southern Ocean;
up to 360,000 blue whales were harvested in the Southern Hemisphere in
the early 20th century (Sears and Perrin 2018). Ainley (2010) noted
that they were extirpated from the Ross Sea shelf break front in the
1920s. Smith et al. (2012) estimated that 30 blue whales may occur in
the Ross Sea. Several sighting records were reported for the northern
Ross Sea between 1978 and 2005 (Kasamatsu et al., 1990; Nishiwaki et
al., 1997; Matsuoka et al., 2006; Ainley et al., 2010) as well as
during a 2008 survey (Baird and Mormede 2014). Acoustic detections were
also made in the northeastern Ross Sea between 1996 to 2010 (Shabangu
et al., 2018). Eight groups of 24 individuals were seen north of the
Ross Sea during summer surveys in 2002-2003 (Ensor et al., 2003). No
blue whales were seen during an NSF-funded seismic survey in the Ross
Sea in January-February 2015 (RPS 2015a).
Fin Whale
The fin whale is widely distributed in all the world's oceans
(Gambell 1985), although it is most abundant in temperate and cold
waters (Aguilar and Garc[iacute]a-Vernet 2018). Nonetheless, its
overall range and distribution is not well known (Jefferson et al.,
2015). Fin whales most commonly occur offshore, but can also be found
in coastal areas (Jefferson et al., 2015). Most populations migrate
seasonally between temperate waters where mating and calving occur in
winter, and polar waters where feeding occurs in the summer; they are
known to use the shelf edge as a migration route (Evans 1987). The
northern and southern fin whale populations likely do not interact
owing to their alternate seasonal migration; the resulting genetic
isolation has led to the recognition of two subspecies, B. physalus
quoyi and B. p. physalus in the Southern and Northern hemispheres,
respectively (Anguilar and Garc[iacute]a-Vernet 2018).
They likely migrate beyond 60[deg] S during the early to mid-
austral summer, arriving at southern feeding grounds after blue whales.
Overall, fin whale density tends to be higher outside the continental
slope than inside it. During the austral summer, the distribution of
fin whales ranges from 40[deg] S-60[deg] S in the southern Indian and
South Atlantic oceans and 50[deg] S-65[deg] S in the South Pacific.
Aguilar and Garc[iacute]a-Vernet (2018) found abundance estimates
resulted in 38,200 individuals in the Antarctic south of 307[deg] S.
Based on Edwards et al. (2015), densities in the Southern Ocean
south of 60[deg] S (including the northern part of the Ross Sea) are
highest during December-February, with non-zero densities <0.003
whales/km\2\. Pinkerton et al. (2010) assumed that ~200 fin whales use
the Ross Sea during summer. Fin whale sightings have been reported for
the Ross Sea by several authors (Nishiwaki et al., 1997; Matsuoka et
al., 2006; Ainley et al., 2010; Baird and Mormede 2014; MacDiarmid and
Stewart 2015). During an NSF-funded seismic survey in the Ross Sea in
January through February 2015, 13 sightings totaling 34 fin whales were
made, including within the proposed survey area (RPS 2015a). Ensor et
al. (2003) reported sightings north of the Ross Sea during summer
surveys in 2002-2003.
Humpback Whale
The humpback whale is found in all ocean basins (Clapham 2018).
Based on genetic data, there could be three subspecies, occurring in
the North Pacific, North Atlantic, and Southern Hemisphere (Jackson et
al., 2014). The humpback whale is highly migratory, undertaking one of
the world's longest mammalian migrations by traveling between mid- to
high-latitude waters where it feeds during spring to fall and low-
latitude wintering grounds over shallow banks, where it mates and
calves (Winn and Reichley 1985; Bettridge et al., 2015). Although
considered to be mainly a coastal species, it often traverses deep
pelagic areas while migrating (Baker et al., 1998; Garrigue et al.,
2002; Zerbini et al., 2011).
In the Southern Hemisphere, humpback whales migrate annually from
summer foraging areas in the Antarctic to breeding grounds in tropical
seas (Clapham 2018). The IWC recognizes seven breeding populations in
the Southern Hemisphere that are linked to six foraging areas in the
Antarctic (Bettridge et al., 2015; Clapham 2018). Humpbacks that occur
in the western Ross Sea (west of 170[deg] W) are part of the Area V
feeding stock (Schmitt et al., 2014); these individuals are from the
Oceania DPS that breeds in French Polynesia, Cook Islands, and Tonga,
and from the East Australia DPS (Schmitt et al., 2014; Bettridge et
al., 2015).
Humpback densities are high north of the Ross Sea (Branch 2011;
Matsuoka and Hakamada 2020), but not within it (Ropert-Coudert et al.,
2014). Pinkerton et al. (2010) estimated that <5 percent (150
individuals) of the Southern Ocean population occurs in the Ross Sea in
the austral summer. Humpback whales were seen in the northern Ross Sea
during surveys conducted between 1987 and 2009 (Baird and Mormede 2014;
MacDiarmid and Stewart 2015). However, none were seen in the Ross Sea
during the International Whaling Commission-Southern Ocean Whale and
Ecosystem Research (IDCR/SOWER) surveys from 1978/79 to 2004/05 (Branch
2011). During an NSF-funded seismic survey in the Ross Sea in January-
February 2015, two sightings totaling six individuals were made east of
the proposed survey areas (RPS 2015a). Acoustic detections were also
made in the northeastern Ross Sea between 1996 to 2010 (Shabangu et
al., 2018). Ensor et al. (2003) reported numerous humpback sightings
and acoustic detections north of the Ross Sea during summer surveys in
2002-2003.
Antarctic Minke Whale
The Antarctic minke whale has a circumpolar distribution in coastal
and offshore areas of the Southern Hemisphere from ~7 degrees S to the
ice edge (Jefferson et al., 2015). It is found between 60[deg] S and
the ice edge during the austral summer; in the austral winter, it is
mainly found at mid-latitude breeding grounds, including off western
South Africa and northeastern Brazil, where it is primarily oceanic,
[[Page 59210]]
occurring beyond the shelf break (Perrin et al., 2018). Antarctic minke
whale densities are highest near pack ice edges, although they are also
found amongst pack ice (Ainley et al., 2012; Williams et al., 2014),
where they feed almost entirely on krill (Tamura and Konishi 2009).
Murase et al. (2006, 2007) found that minke whale distribution was
related to krill density in the Ross Sea, with the greatest number of
pods in areas with a krill density of 1 g/m\2\.
Minke whales were harvested heavily in the Southern Ocean during
the 1970s and 1980s, with >13,000 harvested in the early 1980s; but the
hunt ceased in 1986 under an IWC moratorium (Ainley 2002). However,
Japanese whaling continued under scientific permit taking hundreds of
minke whales in the Ross Sea since the late 1980s (Ainley 2002). During
Japanese sighting surveys from 1976-1988, high encounter rates occurred
in the Ross Sea (Kasamatsu et al., 1996), where minke whales are known
to form feeding aggregations (Kasamatsu et al., 1998). Saino and
Guglielmo (2002) reported a mean density of 0.13 whales/km\2\ in the
western Ross Sea. The minke whale is the most abundant species
occupying the shelf waters in the Ross Sea (Waterhouse 2001; Smith et
al., 2007). Approximately six percent of Antarctic minke whales occur
in the Ross Sea (Ainley et a,l. 2010; Smith et al., 2012). The Ross Sea
population was estimated at 14,300 by Ainley (2002) and 87,643
individuals by Matsuoka et al., (2009).
Ainley et al. (2017) reported that minke whales started to arrive
in the southwestern Ross Sea in mid-November, with decreasing ice
conditions. Ainley et al. (2010, 2012) and Ballard et al. (2012)
reported sightings around the northwestern and northeastern periphery
of the proposed Ross Bank survey area and within the Drygalski Trough
survey area. Although minke whales have a high likelihood of occurrence
in the Ross Sea (e.g., Ainley et al., 2012; Ropert-Coudert et al.,
2014), habitat suitability for the proposed survey area in summer was
modeled as relatively low (Ballard et al., 2012). However, minke whales
were seen in the Ross Sea during surveys conducted between 1978 and
2009, including within the proposed survey area (Kasamatsu et al.,
1990; Baird and Mormede 2014; MacDiarmid and Stewart 2015). They were
also detected acoustically in the Ross Sea in 2004 (Dolman et al.,
2005). Minke whales were seen feeding (presumable on fish) in the
southwestern Ross Sea (Lauriano et al., 2007). During an NSF-funded
seismic survey in the Ross Sea in January-February 2015, 224 sightings
totaling 1023 minke whales were made, including within the proposed
survey area and in McMurdo Sound (RPS 2015a). Ensor et al. (2003)
reported numerous sightings north of the Ross Sea during summer surveys
in 2002-2003.
Sei Whale
The sei whale occurs in all ocean basins (Horwood 2018),
predominantly inhabiting deep waters throughout their range (Acevedo et
al., 2017a). It undertakes seasonal migrations to feed in sub-polar
latitudes during summer, returning to lower latitudes during winter to
calve (Horwood 2018). Recent observation records indicate that the sei
whale may utilize the Vit[oacute]ria-Trindade Chain off Brazil as
calving grounds (Heissler et al., 2016). In the Southern Hemisphere,
sei whales typically concentrate between the Subtropical and Antarctic
convergences during the summer (Horwood 2018) between 40[deg] S and
50[deg] S, with larger, older whales typically travelling into the
northern Antarctic zone while smaller, younger individuals remain in
the lower latitudes (Acevedo et al., 2017a). Pinkerton et al. (2010)
assumed that approximately 100 animals may occur in the Ross Sea. Ensor
et al. (2003) reported no sightings south of 54[deg] S during a summer
survey of the Southern Ocean in 2002-2003. No sei whales were seen
during an NSF-funded seismic survey in the Ross Sea in January-February
2015 (RPS 2015a).
Odontocetes
Sperm Whale
The sperm whale is widely distributed, occurring from the edge of
the polar pack ice to the Equator in both hemispheres, with the sexes
occupying different distributions (Whitehead 2018). In general, it is
distributed over large temperate and tropical areas that have high
secondary productivity and steep underwater topography, such as
volcanic islands (Jaquet and Whitehead 1996). Its distribution and
relative abundance can vary in response to prey availability, most
notably squid (Jaquet and Gendron 2002). Females generally inhabit
waters greater than 1,000 m deep at latitudes less than 40[deg] where
sea surface temperatures are less than 15 [deg]C; adult males move to
higher latitudes as they grow older and larger in size, returning to
warm-water breeding grounds according to an unknown schedule (Whitehead
2018).
Few sperm whales are thought to occur in the Ross Sea (Smith et
al., 2012), although Pinkerton et al. (2010) assumed that 800 sperm
whales could be using the Ross Sea. Sperm whales generally do not occur
south of approximately 73-74[deg] S in the Ross Sea (Matsuoka et al.,
1998; Ropert-Coudert et al., 2014). Nonetheless, sperm whales have been
reported there by several authors (Kasamatsu et al., 1990; Baird and
Mormede 2014). Ensor et al. (2003) reported numerous sightings and
acoustic detections north of the Ross Sea during summer surveys in
2002-2003. No sperm whales were seen during an NSF-funded seismic
survey in the Ross Sea in January through February 2015 (RPS 2015a).
Arnoux's Beaked Whale
Arnoux's beaked whale is distributed in deep, cold, temperate, and
subpolar waters of the Southern Hemisphere, occurring between 24[deg] S
and Antarctica (Thewissen 2018), as far south as the Ross Sea at
approximately 78[deg] S (Perrin et al,. 2009). Most records exist for
southeastern South America, Falkland Islands, Antarctic Peninsula,
South Africa, New Zealand, and southern Australia (MacLeod et al.,
2006; Jefferson et al., 2015).
Ainley et al. (2010) and Van Waerebeek et al. (2010), and Ropert-
Coudert et al. (2014) reported their occurrence in the Ross Sea.
Lauriano et al. (2011) reported two sightings of single individuals in
Terra Nova Bay, western Ross Sea, during summer 2004 surveys. There may
be 50 (Pinkerton et al., 2010) to 150 (Smith et al., 2012) Arnoux's
beaked whales in the Ross Sea. No Arnoux's beaked whales were seen
during an NSF-funded seismic survey in the Ross Sea in January through
February 2015 (RPS 2015a).
Southern Bottlenose Whale
The southern bottlenose whale is found throughout the Southern
Hemisphere from 30[deg] S to the ice edge, with most sightings reported
between approximately 57[deg] S and 70[deg] S (Jefferson et al., 2015;
Moors-Murphy 2018). Several sighting and stranding records exist for
southeastern South America, Falkland Islands, South Georgia Island,
southeastern Brazil, Argentina, South Africa, and numerous sightings
have been reported for the Southern Ocean (Findlay et al., 1992;
MacLeod et al. 2006; Riccialdelli et al., 2017). The population size of
southern bottlenose whales in the Ross Sea was assumed to be 500 by
Pinkerton et al. (2010). Ropert-Coudert et al. (2014) reported their
occurrence in the Ross Sea, and Kasamatsu et al. (1990) reported
sightings between 1978 and 1988. Southern bottlenose whales were also
sighted in the northern Ross Sea and
[[Page 59211]]
north of there during surveys of the Southern Ocean by Van Waerebeek et
al. (2010). Several unidentified beaked whales have also been reported
in the Ross Sea, including in the Ross Bank survey area and near the
Drygalski Trough survey area (Baird and Mormede 2014; MacDiarmid and
Stewart 2015; Matsuoka and Hakamada 2020). Ensor et al. (2003) and
Matsuoka and Hakamada (2020) reported numerous sightings of southern
bottlenose whales north of the Ross Sea. No bottlenose whales were seen
during an NSF-funded seismic survey in the Ross Sea in January-February
2015 (RPS 2015a).
Strap-Toothed Beaked Whale
The strap-toothed beaked whale is thought to have a circumpolar
distribution in temperate and subantarctic waters of the Southern
Hemisphere, mostly between 32[deg] and 63[deg] S (MacLeod et al., 2006;
Jefferson et al., 2015). It is likely quite common in the Southern
Ocean (Pitman 2018). It may undertake limited migration to warmer
waters during the austral winter (Pitman 2018). Strap-toothed beaked
whales are thought to migrate northward from Antarctic and subantarctic
latitudes during April-September (Sekiguchi et al,. 1995). One group of
three strap-toothed beaked whales was seen north of the Ross Sea, north
of 65[deg] S, during a 2002 through 2003 summer survey (Ensor et al.,
2003). No strap-toothed beaked whales were seen during an NSF-funded
seismic survey in the Ross Sea in January through February 2015 (RPS
2015a).
Killer Whale
The killer whale is cosmopolitan and globally abundant; it has been
observed in all oceans of the world (Ford 2018). It is very common in
temperate waters but also occurs in tropical waters (Heyning and
Dahlheim 1988) and inhabits coastal and offshore regions (Budylenko
1981). Mikhalev et al. (1981) noted that it appears to migrate from
warmer waters during the winter to higher latitudes during the summer.
In the Antarctic, it commonly occurs up to the pack ice edge but may
also find its way into ice-covered water (Ford 2018).
There are three ecotypes that occur in Antarctic waters: type A
hunts marine mammals in open water, mainly seeking minke whales, type B
hunt seals in loose pack ice, and type C feeds on fish in dense pack
ice (Pitman and Ensor 2003); these types are likely different species
(Morin et al., 2010; Pitman et al., 2017). Type D occurs in
subantarctic waters and is also likely a separate species (Pitman et
al., 2011). Type B travels widely to hunt its prey, whereas type C is
more resident (Andrews et al., 2008). In fact, type Cs (Ross Sea killer
whales) appear to have resident and transient groups in the Ross Sea
(e.g., Ainley et al., 2017). In the Ross Sea, abundance has been
estimated at 7500 individuals (Smith et al., 2007). Ainley et al.
(2010) and Smith et al. (2012) estimated that approximately 50 percent
of Ross Sea killer whales use the Ross Sea during summer foraging.
Smith et al. (2012) reported 3350 type C killer whales and 70 type A/B
killer whales in the Ross Sea. Pitman et al. (2017) reported only two
ecotypes in the Ross Sea (types B and C), but Ainley et al. (2010)
noted that type A could occur along the slope.
Ainley et al. (2017) reported that type C and B killer whales start
to arrive in the southwestern Ross Sea in mid-November, with decreasing
ice conditions, with type Bs arriving earlier than type Cs. Type C
killer whales have been seen feeding (presumable on fish) in the
southwestern Ross Sea (Lauriano et al., 2007), and type B and C killer
whales were reported during summer 2004 surveys in Terra Nova Bay,
western Ross Sea (Lauriano et al., 2011). Eisert et al. (2014) reported
Type C and B in McMurdo Sound. Type C killer whales have also been
detected acoustically in McMurdo Sound (Wellard et al., 2020). During
an NSF-funded seismic survey in the Ross Sea in January through
February 2015, 14 sightings totaling 254 killer whales were made,
including within the survey area and in McMurdo Sound (RPS 2015a).
Saino and Guglielmo (2002) reported a mean density of 0.05 whales/km\2\
in the western Ross Sea. However, numbers of type C killer whales have
apparently decreased in the southwestern Ross Sea, because of changes
in prey distribution (Antarctic toothfish) likely brought on by fishing
pressures (Ainley et al., 2009; Ainley and Ballard 2012). However,
Pitman et al. (2018) suggested that the presence of a mega-iceberg at
Ross Island may have also impeded killer whale movement, thereby
affecting the population size; they estimated a population size of 470
distinct individuals in McMurdo Sound. Type B killer whale numbers have
not changed in the southern Ross Sea, where they hunt Weddell seals and
emperor penguins (Ainley and Ballard 2012).
Type C killer whale appears to favor the Ross Sea shelf and slope
(Ballard et al., 2012). Sightings of type C killer whales within and
west of the proposed study area have been reported during summer
(Andrews et al., 2008; Ballard et al., 2012). The habitat suitability
for the proposed survey area in summer for type C killer whales was
modeled as relatively high, whereas it was lower for the Drygalski
Trough survey area (Ballard et al., 2012). Andrew et al. (2008)
documented movement of a tagged type B killer whale to the west of the
proposed study area. Aubrey et al. (1982) reported sightings of killer
whales in the Ross Sea off Cape Adare and over Pennell Banks, and noted
that killer whales were abundant off Ross Island. Killer whales were
also reported in the Ross Sea by several other authors (e.g., Kasamatsu
et al., 1990; Van Dam and Kooyman 2004; Van Waerebeek et al., 2010;
Baird and Mormede 2014; Ropert-Coudert et al., 2014). Acoustic
detections were also made in the northeastern Ross Sea between 1996 to
2010 (Shabangu et al., 2018). Ensor et al. (2003) reported numerous
sightings and acoustic detections north of the Ross Sea during summer
surveys in 2002-2003.
Long-Finned Pilot Whales
The long-finned pilot whale is distributed antitropically in cold
temperate waters, including the Southern Ocean, whereas the short-
finned pilot whale is found in tropical and warm temperate waters
(Olson 2018). The ranges of the two species show little overlap (Olson
2018). Long-finned pilot whales are geographically isolated and
separated into two subspecies, G. melas melas and G. melas edwardii in
the Northern and Southern hemispheres, respectively (Olson 2018). In
the Southern Hemisphere, their range extends to the Antarctic
Convergence and sometimes as far south as 68[deg] S (Jefferson et al.,
2015). Although generally not seen south of 68[deg] S, long-finned
pilot whales were reported in the Ross Sea during observations from
longliners between 1997 and 2009 (Baird and Mormede 2014). During
summer surveys in 2002-2003, several sightings were made north of the
Ross Sea (Ensor et al., 2003). They were also reported north of the
Ross Sea during surveys by Van Waerebeek et al. (2010). No pilot whales
were seen during an NSF-funded seismic survey in the Ross Sea in
January-February 2015 (RPS 2015a).
Hourglass Dolphin
The hourglass dolphin occurs in the Southern Ocean, with most
sightings between approximately 45[deg] S and 60[deg] S (Cipriano
2018). However, some sightings have been made as far north as 33[deg] S
(Jefferson et al., 2015). Hourglass dolphins were sighted near 45[deg]
S, north of the Ross Sea, during surveys of the Southern Ocean (Van
Waerebeek et al.,
[[Page 59212]]
2010). Although it is pelagic, it is also sighted near banks and
islands (Cipriano 2018). Ensor et al. (2003) reported numerous
sightings of hourglass dolphins north of the Ross Sea, north of 65[deg]
S, during a summer survey in 2002-2003. No hourglass dolphins were seen
during an NSF-funded seismic survey in the Ross Sea in January through
February 2015 (RPS 2015a).
Phocids
Crabeater Seal
The crabeater seal has a circumpolar distribution off Antarctica
and is the most abundant seal in the region, sometimes congregating in
the hundreds (Bengtson and Stewart 2018). It generally spends the
entire year in the advancing and retreating pack ice (Bengtson and
Stewart 2018). However, outside of the breeding season, crabeater seals
spend ~14 percent of their time in open water (reviewed in Southwell et
al., 2012); they mainly forage on krill. During the breeding season,
crabeater seals are most likely to be present within 5[deg] or less
(~550 km) of the shelf break; non-breeding animals range farther north
(Southwell et al., 2012). Pupping season peaks in mid- to late-October,
and adults are observed with their pups as late as mid-December
(Bengtson and Stewart 2018).
Crabeater seals are most common in the pack ice of the northern
Ross Sea (Waterhouse 2001). A population of approximately 204,000 has
been estimated for the Ross Sea (Waterhouse 2001; Ainley 2002, 2010;
Pinkerton and Bradford-Grieve 2010; Smith et al., 2012). Crabeater
seals have been reported for the Ross Sea by several authors (Stirling
1969; Van Dam and Kooyman 2004; Bester and Stewart 2006; Baird and
Mormede 2014; Ropert-Coudert et al., 2014). Crabeater seals have been
sighted within the proposed survey area (e.g., Saino and Guglielmo
2000; Ainley et al., 2010; Ballard et al., 2012), with greater habitat
suitability in summer in the Drygalski Trough survey area than in the
Ross Bank survey area (Ballard et al., 2012). Similarly, Bengtson et
al. (2011) reported relatively low densities in the Ross Bank area and
higher densities in the Drygalski Trough area. Saino and Guglielmo
(2002) showed increasing densities with increasing pack ice and
distance from shore, with a mean density of 0.49 seals/km\2\, in the
western Ross Sea. In contrast, Bengtson et al. (2011) reported the
highest density (1.3 seals/km\2\) on the shelf at distances up to 200
km from the ice edge during surveys of the Ross and Amundsen seas;
densities in the proposed survey area were estimated to be low. During
an NSF-funded seismic survey in the Ross Sea in January through
February 2015, 9 sightings of 14 individuals were made (RPS 2015a).
Leopard Seal
The leopard seal has a circumpolar distribution around the
Antarctic continent where it is solitary and widely dispersed at low
densities (Rogers 2018). It primarily occurs in pack ice, but when the
sea ice extent is reduced, it can be found in coastal habitats (Meade
et al., 2015). Leopard seals are top predators, consuming everything
from krill and fish to penguins and other seals (e.g., Hall-Aspland and
Rogers 2004). Pups are born during October to mid-November and weaned
~one month later (Rogers 2018). Mating occurs in the water during
December and January. A population of ~8000 is thought to occur in the
Ross Sea (Waterhouse 2001; Ainley 2002, 2010; Pinkerton and Bradford-
Grieve 2010; Smith et al., 2012). Bengtson et al. (2011) reported an
abundance of 15,000 leopard seals for the Ross and Amundsen seas.
Densities were highest (0.024 seals/km\2\) in water <3000 m deep and
<100 km from the ice edge; very low densities were estimated for the
southern portion of the Ross Bank survey area, with low densities in
the rest of the survey area and in the Drygalski Trough survey area
(Bengtson et al., 2011). Leopard seals have been documented to take
Ad[eacute]lie penguins at several colonies in the Ross Sea, including
Cape Crozier (south of the proposed survey areas), and in McMurdo Sound
(Ainley et al., 2005). Leopard seals have been reported within and near
the Drygalski Trough survey area, no sightings have been reported
within the Ross Bank survey area (Stirling 1969; Ackley et al., 2003;
Van Dam and Kooyman 2004; Bester and Stewart 2006; Ainley et al., 2010;
Baird and Mormede 2014; Ropert-Coudert et al., 2014). No leopard seals
were sighted during an NSF-funded seismic survey in the Ross Sea in
January-February 2015 (RPS 2015a).
Southern Elephant Seal
The southern elephant seal has a near circumpolar distribution in
the Southern Hemisphere (Jefferson et al., 2015), with breeding sites
located on islands throughout the subantarctic (Hindell 2018). Breeding
colonies are generally island-based, with the occasional exception of
the Antarctic mainland (Hindell 2018).
When not breeding (September-October) or molting (November-April),
southern elephant seals range throughout the Southern Ocean from areas
north of the Antarctic Polar Front to the pack ice of the Antarctic,
spending >80 percent of their time at sea each year, up to 90 percent
of which is spent submerged while hunting, travelling, and resting in
water depths >=200 m (Hindell 2018). Males generally feed in
continental shelf waters, while females preferentially feed in ice-free
Antarctic Polar Front waters or the marginal ice zone in accordance
with winter ice expansion (Hindell 2018). Southern elephant seals
tagged at South Georgia showed long-range movements from ~April through
October into the open Southern Ocean and to the shelf of the Antarctic
Peninsula (McConnell and Fedak 1996). Their occurrence in the Ross Sea
is rare and only during the summer (Waterhouse 2001; Pinkerton and
Bradford-Grieve 2010). The population size in the Ross Sea is estimated
to number <100 individuals (Ainley 2010; Smith et al., 2012). Ropert-
Coudert et al. (2014) reported one record in the Ross Sea, in McMurdo
Sound. No southern elephant seals were seen during an NSF-funded
seismic survey in the Ross Sea in January-February 2015 (RPS 2015a)
Ross Seal
Ross seals are considered the rarest of all Antarctic seals; they
are the least documented because they are infrequently observed. Ross
seals have a circumpolar Antarctic distribution. They are pelagic
through most of the year.
The population in the Ross Sea may number 500 (Smith et al,. 2012)
to 5000 individuals (Waterhouse 2001; Ainley 2010; Pinkerton and
Bradford-Grieve 2010). According to surveys by Bester et al. (2006),
Ross seals are relatively abundant in the Ross Sea. Based on surveys of
the Ross and Amundsen seas, Bengtson et al. (2011) estimated an
abundance of 22,600, with the highest density (0.032 seals/km\2\) in
deep water (greater than 3000 m) within 200 km from the ice edge; low
densities were estimated for the proposed survey area. Ross seals were
seen in the western (Stirling 1969) and eastern Ross Sea during surveys
(Stirling 1969; Ackley et al., 2003; Bester and Stewart 2006). During
an NSF-funded seismic survey in the Ross Sea in January through
February 2015, two sightings of single Ross seals were made to the east
of the proposed survey area (RPS 2015a).
Weddell Seal
The Weddell seal is the second most abundant species of Antarctic
seal (H[uuml]ckst[auml]dt 2018a). It occurs in the fast
[[Page 59213]]
and pack ice around all of Antarctica, as well as on land along the
coast, but is rarely found in ice-free water (H[uuml]ckst[auml]dt
2018a). It occurs on the Ross Sea shelf and slope (Ballard et al.,
21012). It is the most southerly breeding mammal in the world,
occurring as far south as the RIS (H[uuml]ckst[auml]dt 2018a). Unlike
other Antarctic ice seals, Weddell seals form colonies (Cameron et al.,
2007). There are numerous pupping locations throughout the western Ross
Sea, including around Ross Island (Ainley et al., 2010). Juveniles tend
to disperse widely, resulting in genetic diversity in the population
(H[uuml]ckst[auml]dt 2018a). Seals outfitted with tags in the western
Ross Sea were documented to disperse hundreds of kilometers, making
their way into the proposed survey areas (Ainley et al., 2010; Goetz
2015). However, some small colonies have been isolated from open water
by ice sheets and therefore show inbreeding depression (Gelatt et al.,
2010). Weddell seals primarily feed on fish. Pups are born from October
through November and are weaned after ~six to eight weeks
(H[uuml]ckst[auml]dt 2018a). Paterson et al. (2015) suggested that the
timing of reproduction by Weddell seals in Erebus Bay, McMurdo Sound,
is coupled with periods of high productivity in Ross Bay. After the
breeding season, the ice breaks down and seals disperse into the sea to
forage for one to two months and return to ice or land to molt in
January and February (H[uuml]ckst[auml]dt 2018a).
Ainley et al. (2010) estimated that 50 to 72 percent of the South
Pacific sector of Weddell seals occur in the Ross Sea. The population
in the Ross Sea has been estimated between 32,000 and 50,000
individuals (e.g., Ainley 2002, 2010; Pinkerton and Bradford-Grieve
2010; Smith et al., 2012). Bengtson et al. (2011) estimated the
population in the Ross and Amundsen seas at 330,000 seals. The highest
densities (up to 0.173 seals/km\2\) were observed in water less than
3000 m deep; densities in the proposed survey area were estimated to be
lower (Bengtson et al., 2011). Populations at McMurdo Sound were
permanently reduced by sealing in the 20th century (Ainley 2010).
Sightings within the Ross Sea, including within and near the proposed
survey area, have been reported by several sources (Stirling 1969;
Saino and Guglielmo 2002; Ackley et al., 2003; Van Dam and Kooyman
2004; Bester and Stewart 2006; Ainley et al., 2010; Ropert-Coudert et
al., 2014; Baird and Mormede 2014). Ballard et al. (2012) relatively
low habitat suitability for Weddell seals in the majority of the Ross
Bank survey area, with higher suitability in the eastern portion of the
Ross Bank survey area and within the Drygalski Trough survey area.
During an NSF-funded seismic survey in the Ross Sea in January through
February 2015, 17 sightings of Weddell seals were made, including
within the proposed survey area (RPS 2015a).
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
decibel (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. Marine mammal hearing
groups and their associated hearing ranges are provided in Table 3.
Table 3--Marine Mammal Hearing Groups (NMFS, 2018)
------------------------------------------------------------------------
Hearing group Generalized hearing range *
------------------------------------------------------------------------
Low-frequency (LF) cetaceans 7 Hz to 35 kHz.
(baleen whales).
Mid-frequency (MF) cetaceans 150 Hz to 160 kHz.
(dolphins, toothed whales, beaked
whales, bottlenose whales).
High-frequency (HF) cetaceans (true 275 Hz to 160 kHz.
porpoises, Kogia, river dolphins,
cephalorhynchid, Lagenorhynchus
cruciger & L. australis).
Phocid pinnipeds (PW) (underwater) 50 Hz to 86 kHz.
(true seals).
Otariid pinnipeds (OW) (underwater) 60 Hz to 39 kHz.
(sea lions and fur seals).
------------------------------------------------------------------------
* Represents the generalized hearing range for the entire group as a
composite (i.e., all species within the group), where individual
species' hearing ranges are typically not as broad. Generalized
hearing range chosen based on ~65 dB threshold from normalized
composite audiogram, with the exception for lower limits for LF
cetaceans (Southall et al., 2007) and PW pinniped (approximation).
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 & Holt,
2013).
For more detail concerning these groups and associated frequency
ranges, please see NMFS (2018) for a review of available information.
Potential Effects of Specified Activities on Marine Mammals and Their
Habitat
This section includes a summary and discussion of the ways that
components of the specified activity may impact marine mammals and
their habitat. The Estimated Take section later in this document
includes a quantitative analysis of the number of individuals that are
expected to be taken by this activity. The Negligible Impact Analysis
and Determination section considers the content of this section, the
Estimated Take section, and the Proposed Mitigation section, to draw
conclusions regarding the likely impacts of these activities on the
reproductive success or survivorship of individuals and how those
impacts on individuals are likely to impact marine mammal species or
stocks.
[[Page 59214]]
Description of Active Acoustic Sound Sources
This section contains a brief technical background on sound, the
characteristics of certain sound types, and on metrics used in this
proposal in as much as the information is relevant to the specified
activity and to a discussion of the potential effects of the specified
activity on marine mammals found later in this document.
Sound travels in waves, the basic components of which are
frequency, wavelength, velocity, and amplitude. Frequency is the number
of pressure waves that pass by a reference point per unit of time and
is measured in hertz (Hz) or cycles per second. Wavelength is the
distance between two peaks or corresponding points of a sound wave
(length of one cycle). Higher frequency sounds have shorter wavelengths
than lower frequency sounds, and typically attenuate (decrease) more
rapidly, except in certain cases in shallower water. Amplitude is the
height of the sound pressure wave or the ``loudness'' of a sound and is
typically described using the relative unit of the dB. A sound pressure
level (SPL) in dB is described as the ratio between a measured pressure
and a reference pressure (for underwater sound, this is one microPascal
([mu]Pa)) and is a logarithmic unit that accounts for large variations
in amplitude; therefore, a relatively small change in dB corresponds to
large changes in sound pressure. The source level (SL) represents the
SPL referenced at a distance of one m from the source (referenced to
one [mu]Pa) while the received level is the SPL at the listener's
position (referenced to one [mu]Pa).
Root mean square (rms) is the quadratic mean sound pressure over
the duration of an impulse. Root mean square is calculated by squaring
all of the sound amplitudes, averaging the squares, and then taking the
square root of the average (Urick 1983). Root mean square accounts for
both positive and negative values; squaring the pressures makes all
values positive so that they may be accounted for in the summation of
pressure levels (Hastings & Popper, 2005). This measurement is often
used in the context of discussing behavioral effects, in part because
behavioral effects, which often result from auditory cues, may be
better expressed through averaged units than by peak pressures.
Sound exposure level (SEL; represented as dB re 1 [mu]Pa\2\-s)
represents the total energy contained within a pulse and considers both
intensity and duration of exposure. Peak sound pressure (also referred
to as zero-to-peak sound pressure or 0-p) is the maximum instantaneous
sound pressure measurable in the water at a specified distance from the
source and is represented in the same units as the rms sound pressure.
Another common metric is peak-to-peak sound pressure (pk-pk), which is
the algebraic difference between the peak positive and peak negative
sound pressures. Peak-to-peak pressure is typically approximately six
dB higher than peak pressure (Southall et al., 2007).
When underwater objects vibrate or activity occurs, sound-pressure
waves are created. These waves alternately compress and decompress the
water as the sound wave travels. Underwater sound waves radiate in a
manner similar to ripples on the surface of a pond and may be either
directed in a beam or beams or may radiate in all directions
(omnidirectional sources), as is the case for pulses produced by the
airgun arrays considered here. The compressions and decompressions
associated with sound waves are detected as changes in pressure by
aquatic life and man-made sound receptors such as hydrophones.
Even in the absence of sound from the specified activity, the
underwater environment is typically loud due to ambient sound. Ambient
sound is defined as environmental background sound levels lacking a
single source or point (Richardson et al., 1995), and the sound level
of a region is defined by the total acoustical energy being generated
by known and unknown sources. These sources may include physical (e.g.,
wind and waves, earthquakes, ice, atmospheric sound), biological (e.g.,
sounds produced by marine mammals, fish, and invertebrates), and
anthropogenic (e.g., vessels, dredging, construction) sound. A number
of sources contribute to ambient sound, including the following
(Richardson et al., 1995):
(1) Wind and waves: The complex interactions between wind and water
surface, including processes such as breaking waves and wave-induced
bubble oscillations and cavitation, are a main source of naturally
occurring ambient sound for frequencies between 200 Hz and 50 kHz
(Mitson, 1995). In general, ambient sound levels tend to increase with
increasing wind speed and wave height. Surf sound becomes important
near shore, with measurements collected at a distance of 8.5 km from
shore showing an increase of 10 dB in the 100 to 700 Hz band during
heavy surf conditions;
(2) Precipitation: Sound from rain and hail impacting the water
surface can become an important component of total sound at frequencies
above 500 Hz, and possibly down to 100 Hz during quiet times;
(3) Biological: Marine mammals can contribute significantly to
ambient sound levels, as can some fish and snapping shrimp. The
frequency band for biological contributions is from approximately 12 Hz
to over 100 kHz; and
(4) Anthropogenic: Sources of ambient sound related to human
activity include transportation (surface vessels), dredging and
construction, oil and gas drilling and production, seismic surveys,
sonar, explosions, and ocean acoustic studies. Vessel noise typically
dominates the total ambient sound for frequencies between 20 and 300
Hz. In general, the frequencies of anthropogenic sounds are below one
kHz and, if higher frequency sound levels are created, they attenuate
rapidly. Sound from identifiable anthropogenic sources other than the
activity of interest (e.g., a passing vessel) is sometimes termed
background sound, as opposed to ambient sound.
The sum of the various natural and anthropogenic sound sources at
any given location and time--which comprise ``ambient'' or
``background'' sound--depends not only on the source levels (as
determined by current weather conditions and levels of biological and
human activity) but also on the ability of sound to propagate through
the environment. In turn, sound propagation is dependent on the
spatially and temporally varying properties of the water column and sea
floor, and is frequency-dependent. As a result of the dependence on a
large number of varying factors, ambient sound levels can be expected
to vary widely over both coarse and fine spatial and temporal scales.
Sound levels at a given frequency and location can vary by 10-20 dB
from day to day (Richardson et al., 1995). The result is that,
depending on the source type and its intensity, sound from a given
activity may be a negligible addition to the local environment or could
form a distinctive signal that may affect marine mammals. Details of
source types are described in the following text.
Sounds are often considered to fall into one of two general types:
pulsed and non-pulsed (defined in the following). The distinction
between these two sound types is important because they have differing
potential to cause physical effects, particularly with regard to
hearing (e.g., Ward, 1997 in Southall et al., 2007). Please see
Southall et al. (2007) for an in-depth discussion of these concepts.
Pulsed sound sources (e.g., airguns, explosions, gunshots, sonic
booms,
[[Page 59215]]
impact pile driving) produce signals that are brief (typically
considered to be less than one second), broadband, atonal transients
(ANSI, 1986, 2005; Harris, 1998; NIOSH, 1998; ISO, 2003) and occur
either as isolated events or repeated in some succession. Pulsed sounds
are all characterized by a relatively rapid rise from ambient pressure
to a maximal pressure value followed by a rapid decay period that may
include a period of diminishing, oscillating maximal and minimal
pressures, and generally have an increased capacity to induce physical
injury as compared with sounds that lack these features.
Non-pulsed sounds can be tonal, narrowband, or broadband, brief or
prolonged, and may be either continuous or non-continuous (ANSI, 1995;
NIOSH, 1998). Some of these non-pulsed sounds can be transient signals
of short duration but without the essential properties of pulses (e.g.,
rapid rise time). Examples of non-pulsed sounds include those produced
by vessels, aircraft, machinery operations such as drilling or
dredging, vibratory pile driving, and active sonar systems (such as
those used by the U.S. Navy). The duration of such sounds, as received
at a distance, can be greatly extended in a highly reverberant
environment.
Airgun arrays produce pulsed signals with energy in a frequency
range from about 10-2,000 Hz, with most energy radiated at frequencies
below 200 Hz. The amplitude of the acoustic wave emitted from the
source is equal in all directions (i.e., omnidirectional), but airgun
arrays do possess some directionality due to different phase delays
between guns in different directions. Airgun arrays are typically tuned
to maximize functionality for data acquisition purposes, meaning that
sound transmitted in horizontal directions and at higher frequencies is
minimized to the extent possible.
As described above, hull-mounted MBESs, SBP, and ADCPs would also
be operated from vessel continuously throughout the seismic surveys.
Given the higher frequencies and relatively narrow beampatterns
associated with these sources, in context of the movement and speed of
the vessel, exposures of marine mammals are considered unlikely and,
therefore, we do not expect take of marine mammals to result from use
of these sources and do not consider them further in this analysis.
Acoustic Effects
Here, we discuss the effects of active acoustic sources on marine
mammals.
Potential Effects of Underwater Sound--Please refer to the
information given previously (Description of Active Acoustic Sound
Sources section) regarding sound, characteristics of sound types, and
metrics used in this document. 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 potentially result in
one or more of the following: temporary or permanent hearing
impairment, non-auditory physical or physiological effects, behavioral
disturbance, 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). 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 will occur almost exclusively for noise
within an animal's hearing range. We first describe specific
manifestations of acoustic effects before providing discussion specific
to the use of airgun arrays.
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 or other 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 describe the more severe effects of certain non-auditory
physical or physiological effects only briefly as we do not expect that
use of airgun arrays are reasonably likely to result in such effects
(see below for further discussion). 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) caused by exposure to sound include neurological effects,
bubble formation, resonance effects, and other types of organ or tissue
damage (Cox et al., 2006; Southall et al., 2007; Zimmer & Tyack, 2007;
Tal et al., 2015). The survey activities considered here do not involve
the use of devices such as explosives or mid-frequency tactical sonar
that are associated with these types of effects.
Threshold Shift--Marine mammals exposed to high-intensity sound, or
to lower-intensity sound for prolonged periods, can experience hearing
threshold shift (TS), which is the loss of hearing sensitivity at
certain frequency ranges (Finneran, 2015). TS 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). Repeated sound exposure that
leads to TTS could cause 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). 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.
Relationships between TTS and PTS thresholds have not been studied
in marine mammals, and there is no PTS data for cetaceans but such
relationships are assumed to be similar to those in humans and other
terrestrial mammals. PTS typically occurs at exposure levels at least
several dBs above (a 40-dB threshold shift approximates PTS onset;
e.g., Kryter et al., 1966; Miller, 1974) that inducing mild TTS (a 6-dB
threshold shift approximates TTS onset;
[[Page 59216]]
e.g., Southall et al., 2007). Based on data from terrestrial mammals, a
precautionary assumption is that the PTS thresholds for impulse sounds
(such as airgun pulses as received close to the source) are at least 6
dB higher than the TTS threshold on a peak-pressure basis and PTS
cumulative sound exposure level thresholds are 15 to 20 dB higher than
TTS cumulative sound exposure level thresholds (Southall et al., 2007).
Given the higher level of sound or longer exposure duration necessary
to cause PTS as compared with TTS, it is considerably less likely that
PTS could occur.
For mid-frequency cetaceans in particular, potential protective
mechanisms may help limit onset of TTS or prevent onset of PTS. Such
mechanisms include dampening of hearing, auditory adaptation, or
behavioral amelioration (e.g., Nachtigall and Supin, 2013; Miller et
al., 2012; Finneran et al., 2015; Popov et al., 2016).
TTS is the mildest form of hearing impairment that can occur during
exposure to sound (Kryter, 1985). While experiencing TTS, the hearing
threshold rises, and a sound must be at a higher level in order to be
heard. In terrestrial and marine mammals, TTS can last from minutes or
hours to days (in cases of strong TTS). In many cases, hearing
sensitivity recovers rapidly after exposure to the sound ends. Few data
on sound levels and durations necessary to elicit mild TTS have been
obtained for marine mammals.
Marine mammal hearing plays a critical role in communication with
conspecifics, and 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. 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 occurs 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 time when
communication is critical for successful mother/calf interactions could
have more serious impacts.
Finneran et al. (2015) measured hearing thresholds in three captive
bottlenose dolphins before and after exposure to ten pulses produced by
a seismic airgun in order to study TTS induced after exposure to
multiple pulses. Exposures began at relatively low levels and gradually
increased over a period of several months, with the highest exposures
at peak SPLs from 196 to 210 dB and cumulative (unweighted) SELs from
193-195 dB. No substantial TTS was observed. In addition, behavioral
reactions were observed that indicated that animals can learn behaviors
that effectively mitigate noise exposures (although exposure patterns
must be learned, which is less likely in wild animals than for the
captive animals considered in this study). The authors note that the
failure to induce more significant auditory effects is likely due to
the intermittent nature of exposure, the relatively low peak pressure
produced by the acoustic source, and the low-frequency energy in airgun
pulses as compared with the frequency range of best sensitivity for
dolphins and other mid-frequency cetaceans.
Currently, TTS data only exist for four species of cetaceans
(bottlenose dolphin, beluga whale, harbor porpoise, and Yangtze finless
porpoise) exposed to a limited number of sound sources (i.e., mostly
tones and octave-band noise) in laboratory settings (Finneran, 2015).
In general, harbor porpoises have a lower TTS onset than other measured
cetacean species (Finneran, 2015). Additionally, the existing marine
mammal TTS data come from a limited number of individuals within these
species. There are no data available on noise-induced hearing loss for
mysticetes.
Critical questions remain regarding the rate of TTS growth and
recovery after exposure to intermittent noise and the effects of single
and multiple pulses. Data at present are also insufficient to construct
generalized models for recovery and determine the time necessary to
treat subsequent exposures as independent events. More information is
needed on the relationship between auditory evoked potential and
behavioral measures of TTS for various stimuli. For summaries of data
on TTS in marine mammals or for further discussion of TTS onset
thresholds, please see Southall et al. (2007), Finneran and Jenkins
(2012), Finneran (2015), and NMFS (2018).
Behavioral Effects--Behavioral disturbance may include a variety of
effects, including subtle changes in behavior (e.g., minor or brief
avoidance of an area or changes in vocalizations), more conspicuous
changes in similar behavioral activities, and more sustained and/or
potentially severe reactions, such as displacement from or abandonment
of high-quality habitat. Behavioral responses to sound are highly
variable and context-specific and any reactions depend on numerous
intrinsic and extrinsic factors (e.g., species, state of maturity,
experience, current activity, reproductive state, auditory sensitivity,
time of day), as well as the interplay between factors (e.g.,
Richardson et al., 1995; Wartzok et al., 2003; Southall et al., 2007;
Weilgart, 2007; Archer et al., 2010). Behavioral reactions can vary not
only among individuals but also within an individual, depending on
previous experience with a sound source, context, and numerous other
factors (Ellison et al., 2012), and can vary depending on
characteristics associated with the sound source (e.g., whether it is
moving or stationary, number of sources, distance from the source).
Please see Appendices B-C of Southall et al. (2007) for a review of
studies involving marine mammal behavioral responses to sound.
Habituation can occur when an animal's response to a stimulus wanes
with repeated exposure, usually in the absence of unpleasant associated
events (Wartzok et al., 2003). Animals are most likely to habituate to
sounds that are predictable and unvarying. It is important to note that
habituation is appropriately considered as a ``progressive reduction in
response to stimuli that are perceived as neither aversive nor
beneficial,'' rather than as, more generally, moderation in response to
human disturbance (Bejder et al., 2009). The opposite process is
sensitization, when an unpleasant experience leads to subsequent
responses, often in the form of avoidance, at a lower level of
exposure. As noted, behavioral state may affect the type of response.
For example, animals that are resting may show greater behavioral
change in response to disturbing sound levels than animals that are
highly motivated to remain in an area for feeding (Richardson et al.,
1995; NRC, 2003; Wartzok et al., 2003). Controlled experiments with
captive marine mammals have shown pronounced behavioral reactions,
including avoidance of loud sound sources (Ridgway et al., 1997).
Observed responses of wild marine mammals to loud pulsed sound sources
(typically seismic airguns or acoustic harassment devices) have been
varied but often consist of avoidance behavior or other behavioral
changes suggesting discomfort (Morton & Symonds, 2002; see also
Richardson et al., 1995; Nowacek et al., 2007). However, many
delphinids approach acoustic source vessels with no apparent discomfort
or
[[Page 59217]]
obvious behavioral change (e.g., Barkaszi et al., 2012).
Available studies show wide variation in response to underwater
sound; therefore, it is difficult to predict specifically how any given
sound in a particular instance might affect marine mammals perceiving
the signal. If a marine mammal does react briefly to an underwater
sound by changing its behavior or moving a small distance, the impacts
of the change are unlikely to be significant to the individual, let
alone the stock or population. However, if a sound source displaces
marine mammals from an important feeding or breeding area for a
prolonged period, impacts on individuals and populations could be
significant (e.g., Lusseau & Bejder, 2007; Weilgart, 2007; NRC, 2005).
However, there are broad categories of potential response, which we
describe in greater detail here, that include alteration of dive
behavior, alteration of foraging behavior, effects to breathing,
interference with or alteration of vocalization, avoidance, and flight.
Changes in dive behavior can vary widely, and 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
& Clark, 2000; Ng & Leung, 2003; Nowacek et al., 2004; Goldbogen et
al., 2013a, b). Variations in dive behavior may reflect interruptions
in biologically significant activities (e.g., foraging) or they may be
of little biological significance. The impact of an alteration to dive
behavior 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.
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; Nowacek et al.; 2004; Madsen et al., 2006; 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.
Visual tracking, passive acoustic monitoring, and movement
recording tags were used to quantify sperm whale behavior prior to,
during, and following exposure to airgun arrays at received levels in
the range 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.,
2006; 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 airguns 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 seismic 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).
Variations in respiration naturally vary with different behaviors
and alterations to breathing rate as a function of acoustic exposure
can be expected to co-occur with other behavioral reactions, such as a
flight response or an alteration in diving. However, respiration rates
in and of themselves may be representative of annoyance or an acute
stress response. Various studies have shown that respiration rates may
either be unaffected or could increase, depending on the species and
signal characteristics, again highlighting the importance in
understanding species differences in the tolerance of underwater noise
when determining the potential for impacts resulting from anthropogenic
sound exposure (e.g., Kastelein et al., 2001, 2005, 2006; Gailey et
al., 2007, 2016).
Marine mammals vocalize for different purposes and across multiple
modes, such as whistling, echolocation click production, calling, and
singing. Changes in vocalization behavior in response to anthropogenic
noise can occur for any of these modes and may result from a need to
compete with an increase in background noise or may reflect increased
vigilance or a startle response. For example, in the presence of
potentially masking signals, humpback whales and killer whales have
been observed to increase the length of their songs (Miller et al.,
2000; Fristrup et al., 2003; Foote et al., 2004), while right whales
have been 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). In some cases, animals may cease sound
production during production of aversive signals (Bowles et al., 1994).
Cerchio et al. (2014) used passive acoustic monitoring to document
the presence of singing humpback whales off the coast of northern
Angola and to opportunistically test for the effect of seismic survey
activity on the number of singing whales. Two recording units were
deployed between March and December 2008 in the offshore environment;
numbers of singers were counted every hour. Generalized Additive Mixed
Models were used to assess the effect of survey day (seasonality), hour
(diel variation), moon phase, and received levels of noise (measured
from a single pulse during each 10 minute sampled period) on singer
number. The number of singers significantly decreased with increasing
received level of noise, suggesting that humpback whale breeding
activity was disrupted to some extent by the survey activity.
Castellote et al. (2012) reported acoustic and behavioral changes
by fin whales in response to shipping and airgun noise. Acoustic
features of fin whale song notes recorded in the Mediterranean Sea and
northeast Atlantic Ocean were compared for areas with different
shipping noise levels and traffic intensities and during a seismic
airgun survey. During the first 72 h of the survey, a steady decrease
in song received levels and bearings to singers indicated that whales
moved away from the acoustic source and out of the study area. This
displacement persisted for a time period well beyond the 10-day
duration of seismic airgun activity, providing evidence that fin whales
may avoid an area for an extended period in the presence of increased
noise. The authors hypothesize that fin whale acoustic communication is
modified to compensate for increased background noise and that a
sensitization process may play a role in the observed temporary
displacement.
Seismic pulses at average received levels of 131 dB re 1
[micro]Pa\2\-s caused blue whales to increase call production (Di Iorio
and Clark, 2010). In contrast, McDonald et al. (1995) tracked a blue
whale with seafloor seismometers and reported that it stopped
vocalizing and changed its travel direction at a range of 10 km from
the acoustic source vessel (estimated received level 143 dB pk-pk).
Blackwell et al. (2013) found that
[[Page 59218]]
bowhead whale call rates dropped significantly at onset of airgun use
at sites with a median distance of 41-45 km from the survey. Blackwell
et al. (2015) expanded this analysis to show that whales actually
increased calling rates as soon as airgun signals were detectable
before ultimately decreasing calling rates at higher received levels
(i.e., 10-minute SEL<INF>cum</INF> of ~127 dB). Overall, these results
suggest that bowhead whales may adjust their vocal output in an effort
to compensate for noise before ceasing vocalization effort and
ultimately deflecting from the acoustic source (Blackwell et al., 2013,
2015). These studies demonstrate that even low levels of noise received
far from the source can induce changes in vocalization and/or behavior
for mysticetes.
Avoidance is the displacement of an individual from an area or
migration path as a result of the presence of a sound or other
stressors, and is one of the most obvious manifestations of disturbance
in marine mammals (Richardson et al., 1995). For example, gray whales
are known to change direction--deflecting from customary migratory
paths--in order to avoid noise from seismic surveys (Malme et al.,
1984). Humpback whales showed avoidance behavior in the presence of an
active seismic array during observational studies and controlled
exposure experiments in western Australia (McCauley et al., 2000).
Avoidance may be short-term, with animals returning to the area once
the noise has ceased (e.g., Bowles et al., 1994; Goold, 1996; Stone et
al., 2000; Morton and Symonds, 2002; Gailey et al., 2007). Longer-term
displacement is possible, however, which may lead to changes in
abundance or distribution patterns of the affected species in the
affected region if habituation to the presence of the sound does not
occur (e.g., Bejder et al., 2006; Teilmann et al., 2006).
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 &
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, marine mammal strandings
(Evans & England, 2001). However, it should be noted that response to a
perceived predator does not necessarily invoke flight (Ford & Reeves,
2008), and whether individuals are solitary or in groups may influence
the response.
Behavioral disturbance can also impact marine mammals in more
subtle ways. Increased vigilance may result in costs related to
diversion of focus and attention (i.e., when a response consists of
increased vigilance, it may come at the cost of decreased attention to
other critical behaviors such as foraging or resting). These effects
have generally not been demonstrated for marine mammals, but studies
involving fish and terrestrial animals have shown that increased
vigilance may substantially reduce feeding rates (e.g., Beauchamp &
Livoreil, 1997; Fritz et al., 2002; Purser & Radford, 2011). In
addition, chronic disturbance can cause population declines through
reduction of fitness (e.g., decline in body condition) and subsequent
reduction in reproductive success, survival, or both (e.g., Harrington
& Veitch, 1992; Daan et al., 1996; Bradshaw et al., 1998). However,
Ridgway et al. (2006) reported that increased vigilance in bottlenose
dolphins exposed to sound over a five-day period did not cause any
sleep deprivation or stress effects.
Many animals perform vital functions, such as feeding, resting,
traveling, and socializing, on a diel cycle (24-hour cycle). Disruption
of such functions resulting from reactions to stressors such as sound
exposure are more likely to be significant if they last more than one
diel cycle or recur on subsequent days (Southall et al., 2007).
Consequently, a behavioral response lasting less than one day and not
recurring on subsequent days is not considered particularly severe
unless it could directly affect reproduction or survival (Southall et
al., 2007). Note that there is a difference between multi-day
substantive behavioral reactions and multi-day anthropogenic
activities. For example, just because an activity lasts for multiple
days does not necessarily mean that individual animals are either
exposed to activity-related stressors for multiple days or, further,
exposed in a manner resulting in sustained multi-day substantive
behavioral responses.
Stone (2015) reported data from at-sea observations during 1,196
seismic surveys from 1994 to 2010. When large arrays of airguns
(considered to be 500 in\3\ or more) were firing, lateral displacement,
more localized avoidance, or other changes in behavior were evident for
most odontocetes. However, significant responses to large arrays were
found only for the minke whale and fin whale. Behavioral responses
observed included changes in swimming or surfacing behavior, with
indications that cetaceans remained near the water surface at these
times. Cetaceans were recorded as feeding less often when large arrays
were active. Behavioral observations of gray whales during a seismic
survey monitored whale movements and respirations pre-, during and
post-seismic survey (Gailey et al., 2016). Behavioral state and water
depth were the best `natural' predictors of whale movements and
respiration and, after considering natural variation, none of the
response variables were significantly associated with seismic survey or
vessel sounds.
Stress Responses--An animal's perception of a threat may be
sufficient to trigger stress responses consisting of some combination
of behavioral responses, autonomic nervous system responses,
neuroendocrine responses, or immune responses (e.g., Seyle, 1950;
Moberg, 2000). In many cases, an animal's first and sometimes most
economical (in terms of energetic costs) response is behavioral
avoidance of the potential stressor. Autonomic nervous system responses
to stress typically involve changes in heart rate, blood pressure, and
gastrointestinal activity. These responses have a relatively short
duration and may or may not have a significant long-term effect on an
animal's fitness.
Neuroendocrine stress responses often involve the hypothalamus-
pituitary-adrenal system. Virtually all neuroendocrine 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, altered metabolism, reduced immune
competence, and behavioral disturbance (e.g., Moberg, 1987; Blecha,
2000). Increases in the circulation of glucocorticoids are also equated
with stress (Romano et al., 2004).
The primary distinction between stress (which is adaptive and does
not normally place an animal at risk) and ``distress'' is the 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 functions. This state of
distress will last
[[Page 59219]]
until the animal replenishes its energetic reserves sufficiently to
restore normal function.
Relationships between these physiological mechanisms, animal
behavior, and the costs of stress responses are well-studied through
controlled experiments and for both laboratory and free-ranging animals
(e.g., Holberton et al., 1996; Hood et al., 1998; Jessop et al., 2003;
Krausman et al., 2004; Lankford et al., 2005). Stress responses due to
exposure to anthropogenic sounds or other stressors and their effects
on marine mammals have also been reviewed (Fair & 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).
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, navigation) (Richardson et al., 1995; 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. 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.
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 or altering critical behaviors. It is important to
distinguish TTS and PTS, which persist after the sound exposure, from
masking, which occurs during the sound exposure. Because masking
(without resulting in TS) is not associated with abnormal physiological
function, it is not considered a physiological effect, but rather a
potential behavioral effect.
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) 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).
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 vessel traffic),
contribute to elevated ambient sound levels, thus intensifying masking.
Masking effects of pulsed sounds (even from large arrays of
airguns) on marine mammal calls and other natural sounds are expected
to be limited, although there are few specific data on this. Because of
the intermittent nature and low duty cycle of seismic pulses, animals
can emit and receive sounds in the relatively quiet intervals between
pulses. However, in exceptional situations, reverberation occurs for
much or all of the interval between pulses (e.g., Simard et al., 2005;
Clark & Gagnon 2006), which could mask calls. Situations with prolonged
strong reverberation are infrequent. However, it is common for
reverberation to cause some lesser degree of elevation of the
background level between airgun pulses (e.g., Gedamke 2011; Guerra et
al., 2011, 2016; Klinck et al., 2012; Guan et al., 2015), and this
weaker reverberation presumably reduces the detection range of calls
and other natural sounds to some degree. Guerra et al. (2016) reported
that ambient noise levels between seismic pulses were elevated as a
result of reverberation at ranges of 50 km from the seismic source.
Based on measurements in deep water of the Southern Ocean, Gedamke
(2011) estimated that the slight elevation of background levels during
intervals between pulses reduced blue and fin whale communication space
by as much as 36-51 percent when a seismic survey was operating 450-
2,800 km away. Based on preliminary modeling, Wittekind et al. (2016)
reported that airgun sounds could reduce the communication range of
blue and fin whales 2000 km from the seismic source. Nieukirk et al.
(2012) and Blackwell et al. (2015) noted the potential for masking
effects from seismic surveys on large whales.
Some baleen and toothed whales are known to continue calling in the
presence of seismic pulses, and their calls usually can be heard
between the pulses (e.g., Nieukirk et al., 2012; Thode et al., 2012;
Br[ouml]ker et al., 2013; Sciacca et al., 2016). As noted above,
Cerchio et al. (2014) suggested that the breeding display of humpback
whales off Angola could be disrupted by seismic sounds, as singing
activity declined with increasing received levels. In addition, some
cetaceans are known to change their calling rates, shift their peak
frequencies, or otherwise modify their vocal behavior in response to
airgun sounds (e.g., Di Iorio and Clark 2010; Castellote et al., 2012;
Blackwell et al., 2013, 2015). The hearing systems of baleen whales are
undoubtedly more sensitive to low-frequency sounds than are the ears of
the small odontocetes that have been studied directly (e.g.,
MacGillivray et al., 2014). The sounds important to small odontocetes
are
[[Page 59220]]
predominantly at much higher frequencies than are the dominant
components of airgun sounds, thus limiting the potential for masking.
In general, masking effects of seismic pulses are expected to be minor,
given the normally intermittent nature of seismic pulses.
Icebreaking
Icebreakers produce more noise while breaking ice than ships of
comparable size due, primarily, to the sounds of propeller cavitation
(Richardson et al., 1995). Icebreakers commonly back and ram into heavy
ice until losing momentum to make way. The highest noise levels usually
occur while backing full astern in preparation to ram forward through
the ice. Overall the noise generated by an icebreaker pushing ice was
10 to 15 dB greater than the noise produced by the ship underway in
open water (Richardson et al., 1995). In general, the Antarctic and
Southern Ocean is a noisy environment. Calving and grounding icebergs
as well as the break-up of ice sheets, can produce a large amount of
underwater noise. Little information is available about the increased
sound levels due to icebreaking.
Cetaceans--Few studies have been conducted to evaluate the
potential interference of icebreaking noise with marine mammal
vocalizations. Erbe and Farmer (1998) measured masked hearing
thresholds of a captive beluga whale. They reported that the recording
of a Canadian Coast Guard Ship (CCGS) Henry Larsen, ramming ice in the
Beaufort Sea, masked recordings of beluga vocalizations at a noise to
signal pressure ratio of 18 dB, when the noise pressure level was eight
times as high as the call pressure. Erbe and Farmer (2000) also
predicted when icebreaker noise would affect beluga whales through
software that combined a sound propagation model and beluga whale
impact threshold models. They again used the data from the recording of
the Henry Larsen in the Beaufort Sea and predicted that masking of
beluga whale vocalizations could extend between 40 and 71 km (21.6 and
38.3 nmi) near the surface. Lesage et al. (1999) report that beluga
whales changed their call type and call frequency when exposed to boat
noise. It is possible that the whales adapt to the ambient noise levels
and are able to communicate despite the sound. Given the documented
reaction of belugas to ships and icebreakers it is highly unlikely that
beluga whales would remain in the proximity of vessels where
vocalizations would be masked.
Beluga whales have been documented swimming rapidly away from ships
and icebreakers in the Canadian high Arctic when a ship approaches to
within 35 to 50 km (18.9 to 27 nmi), and they may travel up to 80 km
(43.2 nmi) from the vessel's track (Richardson et al., 1995). It is
expected that belugas avoid icebreakers as soon as they detect the
ships (Cosens and Dueck, 1993). However, the reactions of beluga whales
to ships vary greatly and some animals may become habituated to high
levels of ambient noise (Erbe and Farmer, 2000).
There is little information about the effects of icebreaking ships
on baleen whales. Migrating bowhead whales appeared to avoid an area
around a drill site by greater than 25 km (13.5 mi) where an icebreaker
was working in the Beaufort Sea. There was intensive icebreaking daily
in support of the drilling activities (Brewer et al., 1993). Migrating
bowheads also avoided a nearby drill site at the same time of year
where little icebreaking was being conducted (LGL and Greeneridge,
1987). It is unclear as to whether the drilling activities, icebreaking
operations, or the ice itself might have been the cause for the whale's
diversion. Bowhead whales are not expected to occur in the proximity of
the proposed action area.
Pinnipeds--Brueggeman et al. (1992) reported on the reactions of
seals to an icebreaker during activities at two prospects in the
Chukchi Sea. Reactions of seals to the icebreakers varied between the
two prospects. Most (67 percent) seals did not react to the icebreaker
at either prospect. Reaction at one prospect was greatest during
icebreaking activity (running/maneuvering/jogging) and was 0.23 km
(0.12 nmi) of the vessel and lowest for animals beyond 0.93 km (0.5
nmi). At the second prospect however, seal reaction was lowest during
icebreaking activity with higher and similar levels of response during
general (non-icebreaking) vessel operations and when the vessel was at
anchor or drifting. The frequency of seal reaction generally declined
with increasing distance from the vessel except during general vessel
activity where it remained consistently high to about 0.46 km (0.25
nmi) from the vessel before declining.
Similarly, Kanik et al. (1980) found that ringed (Pusa hispida) and
harp seals (Pagophilus groenlandicus) often dove into the water when an
icebreaker was breaking ice within 1 km (0.5 nmi) of the animals. Most
seals remained on the ice when the ship was breaking ice 1 to 2 km (0.5
to 1.1 nmi) away.
Sea ice is important for pinniped life functions such as resting,
breeding, and molting. Icebreaking activities may damage seal breathing
holes and would also reduce the haulout area in the immediate vicinity
of the ship's track. Icebreaking along a maximum of 500 km of
tracklines would alter local ice conditions in the immediate vicinity
of the vessel. This has the potential to temporarily lead to a
reduction of suitable seal haulout habitat. However, the dynamic sea-
ice environment requires that seals be able to adapt to changes in sea,
ice, and snow conditions, and they therefore create new breathing holes
and lairs throughout the winter and spring (Hammill and Smith, 1989).
In addition, seals often use open leads and cracks in the ice to
surface and breathe (Smith and Stirling, 1975). Disturbance of the ice
would occur in a very small area relative to the Southern Ocean ice-
pack and no significant impact on marine mammals is anticipated by
icebreaking during the proposed low-energy seismic survey.
Ship Noise
Vessel noise from the RVIB Palmer could affect marine animals in
the proposed survey areas. Houghton et al. (2015) proposed that vessel
speed is the most important predictor of received noise levels, and
Putland et al. (2017) also reported reduced sound levels with decreased
vessel speed. Sounds produced by large vessels generally dominate
ambient noise at frequencies from 20 to 300 Hz (Richardson et al.,
1995). However, some energy is also produced at higher frequencies
(Hermannsen et al., 2014); low levels of high-frequency sound from
vessels has been shown to elicit responses in harbor porpoise (Dyndo et
al., 2015). Increased levels of ship noise have been shown to affect
foraging by porpoise (Teilmann et al., 2015; Wisniewska et al., 2018);
Wisniewska et al. (2018) suggest that a decrease in foraging success
could have long-term fitness consequences.
Ship noise, through masking, can reduce the effective communication
distance of a marine mammal if the frequency of the sound source is
close to that used by the animal, and if the sound is present for a
significant fraction of time (e.g., Richardson et al., 1995; Clark et
al,. 2009; Jensen et al., 2009; Gervaise et al., 2012; Hatch et al.,
2012; Rice et al., 2014; Dunlop 2015; Erbe et al., 2016; Jones et al,.
2017; Putland et al., 2017). In addition to the frequency and duration
of the masking sound, the strength, temporal pattern, and location of
the introduced sound also play a role in the extent of the masking
(Branstetter et al., 2013, 2016; Finneran and Branstetter 2013; Sills
et al., 2017). Branstetter et al. (2013)
[[Page 59221]]
reported that time-domain metrics are also important in describing and
predicting masking. In order to compensate for increased ambient noise,
some cetaceans are known to increase the source levels of their calls
in the presence of elevated noise levels from shipping, shift their
peak frequencies, or otherwise change their vocal behavior (e.g., Parks
et al., 2011, 2012, 2016a,b; Castellote et al., 2012; Melc[oacute]n et
al., 2012; Azzara et al., 2013; Tyack and Janik 2013; Lu[iacute]s et
al., 2014; Sairanen 2014; Papale et al., 2015; Bittencourt et al.,
2016; Dahlheim and Castellote 2016; Gospi[cacute] and Picciulin 2016;
Gridley et al., 2016; Heiler et al., 2016; Martins et al., 2016;
O'Brien et al., 2016; Tenessen & Parks 2016). Harp seals did not
increase their call frequencies in environments with increased low-
frequency sounds (Terhune and Bosker 2016). Holt et al. (2015) reported
that changes in vocal modifications can have increased energetic costs
for individual marine mammals. A negative correlation between the
presence of some cetacean species and the number of vessels in an area
has been demonstrated by several studies (e.g., Campana et al., 2015;
Culloch et al., 2016).
Baleen whales are thought to be more sensitive to sound at these
low frequencies than are toothed whales (e.g., MacGillivray et al.,
2014), possibly causing localized avoidance of the proposed survey area
during seismic operations. Reactions of gray and humpback whales to
vessels have been studied, and there is limited information available
about the reactions of right whales and rorquals (fin, blue, and minke
whales). Reactions of humpback whales to boats are variable, ranging
from approach to avoidance (Payne 1978; Salden 1993). Baker et al.
(1982, 1983) and Baker and Herman (1989) found humpbacks often move
away when vessels are within several kilometers. Humpbacks seem less
likely to react overtly when actively feeding than when resting or
engaged in other activities (Krieger and Wing 1984, 1986). Increased
levels of ship noise have been shown to affect foraging by humpback
whales (Blair et al., 2016). Fin whale sightings in the western
Mediterranean were negatively correlated with the number of vessels in
the area (Campana et al., 2015). Minke whales and gray seals have shown
slight displacement in response to construction-related vessel traffic
(Anderwald et al., 2013).
Many odontocetes show considerable tolerance of vessel traffic,
although they sometimes react at long distances if confined by ice or
shallow water, if previously harassed by vessels, or if they have had
little or no recent exposure to ships (Richardson et al., 1995).
Dolphins of many species tolerate and sometimes approach vessels (e.g.,
Anderwald et al., 2013). Some dolphin species approach moving vessels
to ride the bow or stern waves (Williams et al., 1992). Pirotta et al.
(2015) noted that the physical presence of vessels, not just ship
noise, disturbed the foraging activity of bottlenose dolphins.
Sightings of striped dolphin, Risso's dolphin, sperm whale, and
Cuvier's beaked whale in the western Mediterranean were negatively
correlated with the number of vessels in the area (Campana et al.,
2015).
There are few data on the behavioral reactions of beaked whales to
vessel noise, though they seem to avoid approaching vessels (e.g.,
W[uuml]rsig et al., 1998) or dive for an extended period when
approached by a vessel (e.g., Kasuya 1986). Based on a single
observation, Aguilar Soto et al. (2006) suggest foraging efficiency of
Cuvier's beaked whales may be reduced by close approach of vessels.
Sounds emitted by the Palmer are low frequency and continuous, but
would be widely dispersed in both space and time. Project vessel sounds
would not be at levels expected to cause anything more than possible
localized and temporary behavioral changes in marine mammals, and would
not be expected to result in significant negative effects on
individuals or at the population level. In addition, in all oceans of
the world, large vessel traffic is currently so prevalent that it is
commonly considered a usual source of ambient sound (NSF-USGS 2011).
In summary, project vessel sounds would not be at levels expected
to cause anything more than possible localized and temporary behavioral
changes in marine mammals, and would not be expected to result in
significant negative effects on individuals or at the population level.
Ship Strike
Vessel collisions with marine mammals, or ship strikes, can result
in death or serious injury of the animal. Wounds resulting from ship
strike may include massive trauma, hemorrhaging, broken bones, or
propeller lacerations (Knowlton and Kraus, 2001). An animal at the
surface may be struck directly by a vessel, a surfacing animal may hit
the bottom of a vessel, or an animal just below the surface may be cut
by a vessel's propeller. Superficial strikes may not kill or result in
the death of the animal. These interactions are typically associated
with large whales (e.g., fin whales), which are occasionally found
draped across the bulbous bow of large commercial ships upon arrival in
port. Although smaller cetaceans are more maneuverable in relation to
large vessels than are large whales, they may also be susceptible to
strike. The severity of injuries typically depends on the size and
speed of the vessel, with the probability of death or serious injury
increasing as vessel speed increases (Knowlton and Kraus, 2001; Laist
et al., 2001; Vanderlaan and Taggart, 2007; Conn and Silber, 2013).
Impact forces increase with speed, as does the probability of a strike
at a given distance (Silber et al., 2010; Gende et al., 2011).
Pace and Silber (2005) also found that the probability of death or
serious injury increased rapidly with increasing vessel speed.
Specifically, the predicted probability of serious injury or death
increased from 45 to 75 percent as vessel speed increased from 10 to 14
kn, and exceeded 90 percent at 17 kn. Higher speeds during collisions
result in greater force of impact, but higher speeds also appear to
increase the chance of severe injuries or death through increased
likelihood of collision by pulling whales toward the vessel (Clyne,
1999; Knowlton et al., 1995). In a separate study, Vanderlaan and
Taggart (2007) analyzed the probability of lethal mortality of large
whales at a given speed, showing that the greatest rate of change in
the probability of a lethal injury to a large whale as a function of
vessel speed occurs between 8.6 and 15 kn. The chances of a lethal
injury decline from approximately 80 percent at 15 kn to approximately
20 percent at 8.6 kn. At speeds below 11.8 kn, the chances of lethal
injury drop below 50 percent, while the probability asymptotically
increases toward one hundred percent above 15 kn.
The RVIB Palmer travels at a speed of 4.5 kn (8.3 km/hour) when
towing seismic survey gear, or at an average speed of 18.7 km/h (10.1
kn) while cruising. At these speeds, both the possibility of striking a
marine mammal and the possibility of a strike resulting in serious
injury or mortality are discountable. At average transit speed, the
probability of serious injury or mortality resulting from a strike is
less than 50 percent. However, the likelihood of a strike actually
happening is again discountable. Ship strikes, as analyzed in the
studies cited above, generally involve commercial shipping, which is
much more common in both space and time than is geophysical survey
activity. Jensen and Silber (2004) summarized ship strikes of large
whales worldwide from 1975-2003 and found that most collisions occurred
in the
[[Page 59222]]
open ocean and involved large vessels (e.g., commercial shipping). No
such incidents were reported for geophysical survey vessels during that
time period.
It is possible for ship strikes to occur while traveling at slow
speeds. For example, a hydrographic survey vessel traveling at low
speed (5.5 kn) while conducting mapping surveys off the central
California coast struck and killed a blue whale in 2009. The State of
California determined that the whale had suddenly and unexpectedly
surfaced beneath the hull, with the result that the propeller severed
the whale's vertebrae, and that this was an unavoidable event. This
strike represents the only such incident in approximately 540,000 hours
of similar coastal mapping activity (p = 1.9 x 10<SUP>-</SUP>\6\; 95
percent CI = 0-5.5 x 10<SUP>-</SUP>\6\; NMFS, 2013b). In addition, a
research vessel reported a fatal strike in 2011 of a dolphin in the
Atlantic, demonstrating that it is possible for strikes involving
smaller cetaceans to occur. In that case, the incident report indicated
that an animal apparently was struck by the vessel's propeller as it
was intentionally swimming near the vessel. While indicative of the
type of unusual events that cannot be ruled out, neither of these
instances represents a circumstance that would be considered reasonably
foreseeable or that would be considered preventable.
Although the likelihood of the vessel striking a marine mammal is
low, we require a robust ship strike avoidance protocol (see Proposed
Mitigation), which we believe eliminates any foreseeable risk of ship
strike. We anticipate that vessel collisions involving a seismic data
acquisition vessel towing gear, while not impossible, represent
unlikely, unpredictable events for which there are no preventive
measures. Given the required mitigation measures, the relatively slow
speed of the vessel towing gear, the presence of bridge crew watching
for obstacles at all times (including marine mammals), and the presence
of marine mammal observers, we believe that the possibility of ship
strike is discountable and, further, that were a strike of a large
whale to occur, it would be unlikely to result in serious injury or
mortality. No incidental take resulting from ship strike is
anticipated, and this potential effect of the specified activity will
not be discussed further in the following analysis.
Stranding--When a living or dead marine mammal swims or floats onto
shore and becomes ``beached'' or incapable of returning to sea, the
event is a ``stranding'' (Geraci et al., 1999; Perrin and Geraci, 2002;
Geraci and Lounsbury, 2005; NMFS, 2007). The legal definition for a
``stranding'' under the MMPA is an event in the wild in which (A) a
marine mammal is dead and is (i) on a beach or shore of the United
States; or (ii) in waters under the jurisdiction of the United States
(including any navigable waters); or (B) a marine mammal is alive and
is (i) on a beach or shore of the United States and unable to return to
the water; (ii) on a beach or shore of the United States and, although
able to return to the water, is in need of apparent medical attention;
or (iii) in the waters under the jurisdiction of the United States
(including any navigable waters), but is unable to return to its
natural habitat under its own power or without assistance (16 U.S.C.
1421h(3)).
Marine mammals strand for a variety of reasons, such as infectious
agents, biotoxicosis, starvation, fishery interaction, ship strike,
unusual oceanographic or weather events, sound exposure, or
combinations of these stressors sustained concurrently or in series.
However, the cause or causes of most strandings are unknown (Geraci et
al., 1976; Eaton, 1979; Odell et al., 1980; Best, 1982). Numerous
studies suggest that the physiology, behavior, habitat relationships,
age, or condition of cetaceans may cause them to strand or might pre-
dispose them to strand when exposed to another phenomenon. These
suggestions are consistent with the conclusions of numerous other
studies that have demonstrated that combinations of dissimilar
stressors commonly combine to kill an animal or dramatically reduce its
fitness, even though one exposure without the other does not produce
the same result (Chrousos, 2000; Creel, 2005; DeVries et al., 2003;
Fair & Becker, 2000; Foley et al., 2001; Moberg, 2000; Relyea, 2005a;
2005b, Romero, 2004; Sih et al., 2004).
There is no conclusive evidence that exposure to airgun noise
results in behaviorally-mediated forms of injury. Behaviorally-mediated
injury (i.e., mass stranding events) has been primarily associated with
beaked whales exposed to mid-frequency active (MFA) naval sonar.
Tactical sonar and the alerting stimulus used in Nowacek et al. (2004)
are very different from the noise produced by airguns. One should
therefore not expect the same reaction to airgun noise as to these
other sources. As explained below, military MFA sonar is very different
from airguns, and one should not assume that airguns will cause the
same effects as MFA sonar (including strandings).
To understand why Navy MFA sonar affects beaked whales differently
than airguns do, it is important to note the distinction between
behavioral sensitivity and susceptibility to auditory injury. To
understand the potential for auditory injury in a particular marine
mammal species in relation to a given acoustic signal, the frequency
range the species is able to hear is critical, as well as the species'
auditory sensitivity to frequencies within that range. Current data
indicate that not all marine mammal species have equal hearing
capabilities across all frequencies and, therefore, species are grouped
into hearing groups with generalized hearing ranges assigned on the
basis of available data (Southall et al., 2007, 2019). Hearing ranges
as well as auditory sensitivity/susceptibility to frequencies within
those ranges vary across the different groups. For example, in terms of
hearing range, the high-frequency cetaceans (e.g., Kogia spp.) have a
generalized hearing range of frequencies between 275 Hz and 160 kHz,
while mid-frequency cetaceans--such as dolphins and beaked whales--have
a generalized hearing range between 150 Hz to 160 kHz. Regarding
auditory susceptibility within the hearing range, while mid-frequency
cetaceans and high-frequency cetaceans have roughly similar hearing
ranges, the high-frequency group is much more susceptible to noise-
induced hearing loss during sound exposure, i.e., these species have
lower thresholds for these effects than other hearing groups (NMFS,
2018). Referring to a species as behaviorally sensitive to noise simply
means that an animal of that species is more likely to respond to lower
received levels of sound than an animal of another species that is
considered less behaviorally sensitive. So, while dolphin species and
beaked whale species--both in the mid-frequency cetacean hearing
group--are assumed to generally hear the same sounds equally well and
be equally susceptible to noise-induced hearing loss (auditory injury),
the best available information indicates that a beaked whale is more
likely to behaviorally respond to that sound at a lower received level
compared to an animal from other mid-frequency cetacean species that
are less behaviorally sensitive. This distinction is important because,
while beaked whales are more likely to respond behaviorally to sounds
than are many other species (even at lower levels), they cannot hear
the predominant, lower frequency sounds from seismic airguns as well as
sounds that have more energy at frequencies that beaked whales can hear
better (such as military MFA sonar).
[[Page 59223]]
Navy MFA sonar affects beaked whales differently than airguns do
because it produces energy at different frequencies than airguns. Mid-
frequency cetacean hearing is generically thought to be best between
8.8 to 110 kHz, i.e., these cutoff values define the range above and
below which a species in the group is assumed to have declining
auditory sensitivity, until reaching frequencies that cannot be heard
(NMFS, 2018). However, beaked whale hearing is likely best within a
higher, narrower range (20-80 kHz, with best sensitivity around 40
kHz), based on a few measurements of hearing in stranded beaked whales
(Cook et al., 2006; Finneran et al., 2009; Pacini et al., 2011) and
several studies of acoustic signals produced by beaked whales (e.g.,
Frantzis et al., 2002; Johnson et al., 2004, 2006; Zimmer et al.,
2005). While precaution requires that the full range of audibility be
considered when assessing risks associated with noise exposure
(Southall et al., 2007, 2019a, 2019), animals typically produce sound
at frequencies where they hear best. More recently, Southall et al.
(2019) suggested that certain species in the historical mid-frequency
hearing group (beaked whales, sperm whales, and killer whales) are
likely more sensitive to lower frequencies within the group's
generalized hearing range than are other species within the group, and
state that the data for beaked whales suggest sensitivity to
approximately 5 kHz. However, this information is consistent with the
general conclusion that beaked whales (and other mid-frequency
cetaceans) are relatively insensitive to the frequencies where most
energy of an airgun signal is found. Military MFA sonar is typically
considered to operate in the frequency range of approximately 3-14 kHz
(D'Amico et al., 2009), i.e., outside the range of likely best hearing
for beaked whales but within or close to the lower bounds, whereas most
energy in an airgun signal is radiated at much lower frequencies, below
500 Hz (Dragoset, 1990).
It is important to distinguish between energy (loudness, measured
in dB) and frequency (pitch, measured in Hz). In considering the
potential impacts of mid-frequency components of airgun noise (1-10
kHz, where beaked whales can be expected to hear) on marine mammal
hearing, one needs to account for the energy associated with these
higher frequencies and determine what energy is truly ``significant.''
Although there is mid-frequency energy associated with airgun noise (as
expected from a broadband source), airgun sound is predominantly below
1 kHz (Breitzke et al., 2008; Tashmukhambetov et al., 2008; Tolstoy et
al., 2009). As stated by Richardson et al. (1995), ``[. . .] most
emitted [seismic airgun] energy is at 10-120 Hz, but the pulses contain
some energy up to 500-1,000 Hz.'' Tolstoy et al. (2009) conducted
empirical measurements, demonstrating that sound energy levels
associated with airguns were at least 20 decibels (dB) lower at 1 kHz
(considered ``mid-frequency'') compared to higher energy levels
associated with lower frequencies (below 300 Hz) (``all but a small
fraction of the total energy being concentrated in the 10-300 Hz
range'' [Tolstoy et al., 2009]), and at higher frequencies (e.g., 2.6-4
kHz), power might be less than 10 percent of the peak power at 10 Hz
(Yoder, 2002). Energy levels measured by Tolstoy et al. (2009) were
even lower at frequencies above 1 kHz. In addition, as sound propagates
away from the source, it tends to lose higher-frequency components
faster than low-frequency components (i.e., low-frequency sounds
typically propagate longer distances than high-frequency sounds)
(Diebold et al., 2010). Although higher-frequency components of airgun
signals have been recorded, it is typically in surface-ducting
conditions (e.g., DeRuiter et al., 2006; Madsen et al., 2006) or in
shallow water, where there are advantageous propagation conditions for
the higher frequency (but low-energy) components of the airgun signal
(Hermannsen et al., 2015). This should not be of concern because the
likely behavioral reactions of beaked whales that can result in acute
physical injury would result from noise exposure at depth (because of
the potentially greater consequences of severe behavioral reactions).
In summary, the frequency content of airgun signals is such that beaked
whales will not be able to hear the signals well (compared to MFA
sonar), especially at depth where we expect the consequences of noise
exposure could be more severe.
Aside from frequency content, there are other significant
differences between MFA sonar signals and the sounds produced by
airguns that minimize the risk of severe behavioral reactions that
could lead to strandings or deaths at sea, e.g., significantly longer
signal duration, horizontal sound direction, typical fast and
unpredictable source movement. All of these characteristics of MFA
sonar tend towards greater potential to cause severe behavioral or
physiological reactions in exposed beaked whales that may contribute to
stranding. Although both sources are powerful, MFA sonar contains
significantly greater energy in the mid-frequency range, where beaked
whales hear better. Short-duration, high energy pulses--such as those
produced by airguns--have greater potential to cause damage to auditory
structures (though this is unlikely for mid-frequency cetaceans, as
explained later in this document), but it is longer duration signals
that have been implicated in the vast majority of beaked whale
strandings. Faster, less predictable movements in combination with
multiple source vessels are more likely to elicit a severe, potentially
anti-predator response. Of additional interest in assessing the
divergent characteristics of MFA sonar and airgun signals and their
relative potential to cause stranding events or deaths at sea is the
similarity between the MFA sonar signals and stereotyped calls of
beaked whales' primary predator: the killer whale (Zimmer and Tyack,
2007). Although generic disturbance stimuli--as airgun noise may be
considered in this case for beaked whales--may also trigger
antipredator responses, stronger responses should generally be expected
when perceived risk is greater, as when the stimulus is confused for a
known predator (Frid and Dill, 2002). In addition, because the source
of the perceived predator (i.e., MFA sonar) will likely be closer to
the whales (because attenuation limits the range of detection of mid-
frequencies) and moving faster (because it will be on faster-moving
vessels), any antipredator response would be more likely to be severe
(with greater perceived predation risk, an animal is more likely to
disregard the cost of the response; Frid and Dill, 2002). Indeed, when
analyzing movements of a beaked whale exposed to playback of killer
whale predation calls, Allen et al. (2014) found that the whale engaged
in a prolonged, directed avoidance response, suggesting a behavioral
reaction that could pose a risk factor for stranding. Overall, these
significant differences between sound from MFA sonar and the mid-
frequency sound component from airguns and the likelihood that MFA
sonar signals will be interpreted in error as a predator are critical
to understanding the likely risk of behaviorally-mediated injury due to
seismic surveys.
The available scientific literature also provides a useful contrast
between airgun noise and MFA sonar regarding the likely risk of
behaviorally-mediated injury. There is strong evidence for the
association of beaked whale stranding events with MFA sonar use, and
particularly detailed accounting of several events is available (e.g.,
a 2000 Bahamas stranding event for which
[[Page 59224]]
investigators concluded that MFA sonar use was responsible; Evans and
England, 2001). D'Amico et al. (2009) reviewed 126 beaked whale mass
stranding events over the period from 1950 (i.e., from the development
of modern MFA sonar systems) through 2004. Of these, there were two
events where detailed information was available on both the timing and
location of the stranding and the concurrent nearby naval activity,
including verification of active MFA sonar usage, with no evidence for
an alternative cause of stranding. An additional ten events were at
minimum spatially and temporally coincident with naval activity likely
to have included MFA sonar use and, despite incomplete knowledge of
timing and location of the stranding or the naval activity in some
cases, there was no evidence for an alternative cause of stranding. The
U.S. Navy has publicly stated agreement that five such events since
1996 were associated in time and space with MFA sonar use, either by
the U.S. Navy alone or in joint training exercises with the North
Atlantic Treaty Organization. The U.S. Navy additionally noted that, as
of 2017, a 2014 beaked whale stranding event in Crete coincident with
naval exercises was under review and had not yet been determined to be
linked to sonar activities (U.S. Navy, 2017). Separately, the
International Council for the Exploration of the Sea reported in 2005
that, worldwide, there have been about 50 known strandings, consisting
mostly of beaked whales, with a potential causal link to MFA sonar
(ICES, 2005). In contrast, very few such associations have been made to
seismic surveys, despite widespread use of airguns as a geophysical
sound source in numerous locations around the world.
A more recent review of possible stranding associations with
seismic surveys (Castellote and Llorens, 2016) states plainly that,
``[s]peculation concerning possible links between seismic survey noise
and cetacean strandings is available for a dozen events but without
convincing causal evidence.'' The authors' ``exhaustive'' search of
available information found ten events worth further investigation via
a ranking system representing a rough metric of the relative level of
confidence offered by the data for inferences about the possible role
of the seismic survey in a given stranding event. Only three of these
events involved beaked whales. Whereas D'Amico et al. (2009) used a 1-5
ranking system, in which ``1'' represented the most robust evidence
connecting the event to MFA sonar use, Castellote and Llorens (2016)
used a 1-6 ranking system, in which ``6'' represented the most robust
evidence connecting the event to the seismic survey. As described
above, D'Amico et al. (2009) found that two events were ranked ``1''
and ten events were ranked ``2'' (i.e., 12 beaked whale stranding
events were found to be associated with MFA sonar use). In contrast,
Castellote and Llorens (2016) found that none of the three beaked whale
stranding events achieved their highest ranks of 5 or 6. Of the ten
total events, none achieved the highest rank of 6. Two events were
ranked as 5: one stranding in Peru involving dolphins and porpoises and
a 2008 stranding in Madagascar. This latter ranking can only broadly be
associated with the survey itself, as opposed to use of seismic
airguns. An exhaustive investigation of this stranding event, which did
not involve beaked whales, concluded that use of a high-frequency
mapping system (12-kHz multibeam echosounder) was the most plausible
and likely initial behavioral trigger of the event, which was likely
exacerbated by several site- and situation-specific secondary factors.
The review panel found that seismic airguns were used after the initial
strandings and animals entering a lagoon system, that airgun use
clearly had no role as an initial trigger, and that there was no
evidence that airgun use dissuaded animals from leaving (Southall et
al., 2013).
However, one of these stranding events, involving two Cuvier's
beaked whales, was contemporaneous with and reasonably associated
spatially with a 2002 seismic survey in the Gulf of California
conducted by Lamont-Doherty Earth Observatory (L-DEO), as was the case
for the 2007 Gulf of Cadiz seismic survey discussed by Castellote and
Llorens (also involving two Cuvier's beaked whales). However, neither
event was considered a ``true atypical mass stranding'' (according to
Frantzis [1998]) as used in the analysis of Castellote and Llorens
(2016). While we agree with the authors that this lack of evidence
should not be considered conclusive, it is clear that there is very
little evidence that seismic surveys should be considered as posing a
significant risk of acute harm to beaked whales or other mid-frequency
cetaceans. We have considered the potential for the proposed survey to
result in marine mammal stranding and have concluded that, based on the
best available information, stranding is not expected to occur.
Use of military tactical sonar has been implicated in a majority of
investigated stranding events. Most known stranding events have
involved beaked whales, though a small number have involved deep-diving
delphinids or sperm whales (e.g., Mazzariol et al., 2010; Southall et
al., 2013). In general, long duration (approximately 1 second) and
high-intensity sounds (greater than 235 dB SPL) have been implicated in
stranding events (Hildebrand, 2004). With regard to beaked whales, mid-
frequency sound is typically implicated (when causation can be
determined) (Hildebrand, 2004). Although seismic airguns create
predominantly low-frequency energy, the signal does include a mid-
frequency component. We have considered the potential for the proposed
survey to result in marine mammal stranding and have concluded that,
based on the best available information, stranding is not expected to
occur.
Entanglement--Entanglements occur when marine mammals become
wrapped around cables, lines, nets, or other objects suspended in the
water column. During seismic operations, numerous cables, lines, and
other objects primarily associated with the airgun array and hydrophone
streamers will be towed behind the Palmer near the water`s surface. No
incidents of entanglement of marine mammals with seismic survey gear
have been documented in over 54,000 kt (100,000 km) of previous NSF-
funded seismic surveys when observers were aboard (e.g., Smultea and
Holst 2003; Haley and Koski 2004; Holst 2004; Smultea et al., 2004;
Holst et al., 2005a; Haley and Ireland 2006; SIO and NSF 2006b; Hauser
et al., 2008; Holst and Smultea 2008). Although entanglement with the
streamer is theoretically possible, it has not been documented during
tens of thousands of miles of NSF-sponsored seismic cruises or, to our
knowledge, during hundreds of thousands of miles of industrial seismic
cruises. There are a relative few deployed devices, and no interaction
between marine mammals and any such device has been recorded during
prior NSF surveys using the devices. There are no meaningful
entanglement risks posed by the proposed survey, and entanglement risks
are not discussed further in this document.
Anticipated Effects on Marine Mammal Habitat
Physical Disturbance--Sources of seafloor disturbance related to
geophysical surveys that may impact marine mammal habitat include
placement of anchors, nodes, cables, sensors, or other equipment on or
in the seafloor for various activities. Equipment deployed on the
seafloor has
[[Page 59225]]
the potential to cause direct physical damage and could affect bottom-
associated fish resources.
Placement of equipment, such as the heat flow probe in the
seafloor, could damage areas of hard bottom where direct contact with
the seafloor occurs and could crush epifauna (organisms that live on
the seafloor or surface of other organisms). Damage to unknown or
unseen hard bottom could occur, but because of the small area covered
by most bottom-founded equipment and the patchy distribution of hard
bottom habitat, contact with unknown hard bottom is expected to be rare
and impacts minor. Seafloor disturbance in areas of soft bottom can
cause loss of small patches of epifauna and infauna due to burial or
crushing, and bottom-feeding fishes could be temporarily displaced from
feeding areas. Overall, any effects of physical damage to habitat are
expected to be minor and temporary.
Effects to Prey--Marine mammal prey varies by species, season, and
location and, for some, is not well documented. Fish react to sounds
which are especially strong and/or intermittent low-frequency sounds.
Short duration, sharp sounds can cause overt or subtle changes in fish
behavior and local distribution. Hastings and Popper (2005) identified
several studies that suggest fish may relocate to avoid certain areas
of sound energy. Additional studies have documented effects of pulsed
sound on fish, although several are based on studies in support of
construction projects (e.g., Scholik and Yan, 2001, 2002; Popper and
Hastings, 2009). Sound pulses at received levels of 160 dB may cause
subtle changes in fish behavior. SPLs of 180 dB may cause noticeable
changes in behavior (Pearson et al., 1992; Skalski et al., 1992). SPLs
of sufficient strength have been known to cause injury to fish and fish
mortality. The most likely impact to fish from survey activities at the
project area would be temporary avoidance of the area. The duration of
fish avoidance of a given area after survey effort stops is unknown,
but a rapid return to normal recruitment, distribution and behavior is
anticipated.
Marine mammal prey varies by species, season, and location and, for
some, is not well documented. Fish react to sounds which are especially
strong and/or intermittent low-frequency sounds, and behavioral
responses such as flight or avoidance are the most likely effects.
However, the reaction of fish to airguns depends on the physiological
state of the fish, past exposures, motivation (e.g., feeding, spawning,
migration), and other environmental factors. Several studies have
demonstrated that airgun sounds might affect the distribution and
behavior of some fishes, potentially impacting foraging opportunities
or increasing energetic costs (e.g., Fewtrell and McCauley, 2012;
Pearson et al., 1992; Skalski et al., 1992; Santulli et al., 1999;
Paxton et al., 2017), though the bulk of studies indicate no or slight
reaction to noise (e.g., Miller and Cripps, 2013; Dalen and Knutsen,
1987; Pena et al., 2013; Chapman and Hawkins, 1969; Wardle et al.,
2001; Sara et al., 2007; Jorgenson and Gyselman, 2009; Blaxter et al.,
1981; Cott et al., 2012; Boeger et al., 2006), and that, most commonly,
while there are likely to be impacts to fish as a result of noise from
nearby airguns, such effects will be temporary. For example,
investigators reported significant, short-term declines in commercial
fishing catch rate of gadid fishes during and for up to five days after
seismic survey operations, but the catch rate subsequently returned to
normal (Engas et al., 1996; Engas and Lokkeborg, 2002). Other studies
have reported similar findings (Hassel et al., 2004). Skalski et al.,
(1992) also found a reduction in catch rates--for rockfish (Sebastes
spp.) in response to controlled airgun exposure--but suggested that the
mechanism underlying the decline was not dispersal but rather decreased
responsiveness to baited hooks associated with an alarm behavioral
response. A companion study showed that alarm and startle responses
were not sustained following the removal of the sound source (Pearson
et al., 1992). Therefore, Skalski et al. (1992) suggested that the
effects on fish abundance may be transitory, primarily occurring during
the sound exposure itself. In some cases, effects on catch rates are
variable within a study, which may be more broadly representative of
temporary displacement of fish in response to airgun noise (i.e., catch
rates may increase in some locations and decrease in others) than any
long-term damage to the fish themselves (Streever et al., 2016).
SPLs of sufficient strength have been known to cause injury to fish
and fish mortality and, in some studies, fish auditory systems have
been damaged by airgun noise (McCauley et al., 2003; Popper et al.,
2005; Song et al., 2008). However, in most fish species, hair cells in
the ear continuously regenerate and loss of auditory function likely is
restored when damaged cells are replaced with new cells. Halvorsen et
al. (2012b. (2012) showed that a TTS of 4-6 dB was recoverable within
24 hours for one species. Impacts would be most severe when the
individual fish is close to the source and when the duration of
exposure is long--both of which are conditions unlikely to occur for
this survey that is necessarily transient in any given location and
likely result in brief, infrequent noise exposure to prey species in
any given area. For this survey, the sound source is constantly moving,
and most fish would likely avoid the sound source prior to receiving
sound of sufficient intensity to cause physiological or anatomical
damage. In addition, ramp-up may allow certain fish species the
opportunity to move further away from the sound source.
A recent comprehensive review (Carroll et al., 2017) found that
results are mixed as to the effects of airgun noise on the prey of
marine mammals. While some studies suggest a change in prey
distribution and/or a reduction in prey abundance following the use of
seismic airguns, others suggest no effects or even positive effects in
prey abundance. As one specific example, Paxton et al. (2017), which
describes findings related to the effects of a 2014 seismic survey on a
reef off of North Carolina, showed a 78 percent decrease in observed
nighttime abundance for certain species. It is important to note that
the evening hours during which the decline in fish habitat use was
recorded (via video recording) occurred on the same day that the
seismic survey passed, and no subsequent data is presented to support
an inference that the response was long-lasting. Additionally, given
that the finding is based on video images, the lack of recorded fish
presence does not support a conclusion that the fish actually moved
away from the site or suffered any serious impairment. In summary, this
particular study corroborates prior studies indicating that a startle
response or short-term displacement should be expected.
Available data suggest that cephalopods are capable of sensing the
particle motion of sounds and detect low frequencies up to 1-1.5 kHz,
depending on the species, and so are likely to detect airgun noise
(Kaifu et al., 2008; Hu et al., 2009; Mooney et al., 2010; Samson et
al., 2014). Auditory injuries (lesions occurring on the statocyst
sensory hair cells) have been reported upon controlled exposure to low-
frequency sounds, suggesting that cephalopods are particularly
sensitive to low-frequency sound (Andre et al., 2011; Sole et al.,
2013). Behavioral responses, such as inking and jetting, have also been
reported upon exposure to low-frequency sound (McCauley et al., 2000b;
Samson et al., 2014). Similar to fish, however, the transient nature of
[[Page 59226]]
the survey leads to an expectation that effects will be largely limited
to behavioral reactions and would occur as a result of brief,
infrequent exposures.
With regard to potential impacts on zooplankton, McCauley et al.
(2017) found that exposure to airgun noise resulted in significant
depletion for more than half the taxa present and that there were two
to three times more dead zooplankton after airgun exposure compared
with controls for all taxa, within 1 km of the airguns. However, the
authors also stated that in order to have significant impacts on r-
selected species (i.e., those with high growth rates and that produce
many offspring) such as plankton, the spatial or temporal scale of
impact must be large in comparison with the ecosystem concerned, and it
is possible that the findings reflect avoidance by zooplankton rather
than mortality (McCauley et al., 2017). In addition, the results of
this study are inconsistent with a large body of research that
generally finds limited spatial and temporal impacts to zooplankton as
a result of exposure to airgun noise (e.g., Dalen and Knutsen, 1987;
Payne, 2004; Stanley et al., 2011). Most prior research on this topic,
which has focused on relatively small spatial scales, has showed
minimal effects (e.g., Kostyuchenko, 1973; Booman et al., 1996;
S[aelig]tre and Ona, 1996; Pearson et al., 1994; Bolle et al., 2012).
A modeling exercise was conducted as a follow-up to the McCauley et
al. (2017) study (as recommended by McCauley et al.), in order to
assess the potential for impacts on ocean ecosystem dynamics and
zooplankton population dynamics (Richardson et al., 2017). Richardson
et al. (2017) found that for copepods with a short life cycle in a
high-energy environment, a full-scale airgun survey would impact
copepod abundance up to three days following the end of the survey,
suggesting that effects such as those found by McCauley et al. (2017)
would not be expected to be detectable downstream of the survey areas,
either spatially or temporally.
Notably, a recently described study produced results inconsistent
with those of McCauley et al. (2017). Researchers conducted a field and
laboratory study to assess if exposure to airgun noise affects
mortality, predator escape response, or gene expression of the copepod
Calanus finmarchicus (Fields et al., 2019). Immediate mortality of
copepods was significantly higher, relative to controls, at distances
of 5 m or less from the airguns. Mortality one week after the airgun
blast was significantly higher in the copepods placed 10 m from the
airgun but was not significantly different from the controls at a
distance of 20 m from the airgun. The increase in mortality, relative
to controls, did not exceed 30 percent at any distance from the airgun.
Moreover, the authors caution that even this higher mortality in the
immediate vicinity of the airguns may be more pronounced than what
would be observed in free-swimming animals due to increased flow speed
of fluid inside bags containing the experimental animals. There were no
sublethal effects on the escape performance or the sensory threshold
needed to initiate an escape response at any of the distances from the
airgun that were tested. Whereas McCauley et al. (2017) reported an SEL
of 156 dB at a range of 509-658 m, with zooplankton mortality observed
at that range, Fields et al. (2019) reported an SEL of 186 dB at a
range of 25 m, with no reported mortality at that distance. Regardless,
if we assume a worst-case likelihood of severe impacts to zooplankton
within approximately 1 km of the acoustic source, the typically wide
dispersal of survey vessels and brief time to regeneration of the
potentially affected zooplankton populations does not lead us to expect
any meaningful follow-on effects to the prey base for odontocete
predators.
A recent review article concluded that, while laboratory results
provide scientific evidence for high-intensity and low-frequency sound-
induced physical trauma and other negative effects on some fish and
invertebrates, the sound exposure scenarios in some cases are not
realistic to those encountered by marine organisms during routine
seismic operations (Carroll et al., 2017). The review finds that there
has been no evidence of reduced catch or abundance following seismic
activities for invertebrates, and that there is conflicting evidence
for fish with catch observed to increase, decrease, or remain the same.
Further, where there is evidence for decreased catch rates in response
to airgun noise, these findings provide no information about the
underlying biological cause of catch rate reduction (Carroll et al.,
2017).
In summary, impacts of the specified activity on marine mammal prey
species will likely be limited to behavioral responses, the majority of
prey species will be capable of moving out of the area during the
survey, a rapid return to normal recruitment, distribution, and
behavior for prey species is anticipated, and, overall, impacts to prey
species will be minor and temporary. Prey species exposed to sound
might move away from the sound source, experience TTS, experience
masking of biologically relevant sounds, or show no obvious direct
effects. Mortality from decompression injuries is possible in close
proximity to a sound, but only limited data on mortality in response to
airgun noise exposure are available (Hawkins et al., 2014). The most
likely impacts for most prey species in the survey area would be
temporary avoidance of the area. The proposed survey would move through
an area relatively quickly, limiting exposure to multiple impulsive
sounds. In all cases, sound levels would return to ambient once the
survey moves out of the area or ends and the noise source is shut down
and, when exposure to sound ends, behavioral and/or physiological
responses are expected to end relatively quickly (McCauley et al.,
2000b). The duration of fish avoidance of a given area after survey
effort stops is unknown, but a rapid return to normal recruitment,
distribution, and behavior is anticipated. While the potential for
disruption of spawning aggregations or schools of important prey
species can be meaningful on a local scale, the mobile and temporary
nature of this survey and the likelihood of temporary avoidance
behavior suggest that impacts would be minor.
In general, impacts to marine mammal prey are expected to be
limited due to the relatively small temporal and spatial overlap
between the proposed survey and any areas used by marine mammal prey
species. The proposed use of airguns as part of an active seismic array
survey would occur over a relatively short time period (approximately
25 days at sea) and would occur over a very small area relative to the
area available as marine mammal habitat in the Ross Sea. We believe any
impacts to marine mammals due to adverse effects to their prey would be
insignificant due to the limited spatial and temporal impact of the
proposed survey. However, adverse impacts may occur to a few species of
fish and to zooplankton.
Acoustic Habitat--Acoustic habitat is the soundscape--which
encompasses all of the sound present in a particular location and time,
as a whole--when considered from the perspective of the animals
experiencing it. Animals produce sound for, or listen for sounds
produced by, conspecifics (communication during feeding, mating, and
other social activities), other animals (finding prey or avoiding
predators), and the physical environment (finding suitable habitats,
navigating). Together, sounds made by animals and the geophysical
environment (e.g., produced by earthquakes, lightning, wind, rain,
[[Page 59227]]
waves) make up the natural contributions to the total acoustics of a
place. These acoustic conditions, termed acoustic habitat, are one
attribute of an animal's total habitat.
Soundscapes are also defined by, and acoustic habitat influenced
by, the total contribution of anthropogenic sound. This may include
incidental emissions from sources such as vessel traffic, or may be
intentionally introduced to the marine environment for data acquisition
purposes (as in the use of airgun arrays). Anthropogenic noise varies
widely in its frequency content, duration, and loudness and these
characteristics greatly influence the potential habitat-mediated
effects to marine mammals (please see also the previous discussion on
masking under Acoustic Effects), which may range from local effects for
brief periods of time to chronic effects over large areas and for long
durations. Depending on the extent of effects to habitat, animals may
alter their communications signals (thereby potentially expending
additional energy) or miss acoustic cues (either conspecific or
adventitious). For more detail on these concepts see, e.g., Barber et
al., 2010; Pijanowski et al., 2011; Francis and Barber, 2013; Lillis et
al., 2014.
Problems arising from a failure to detect cues are more likely to
occur when noise stimuli are chronic and overlap with biologically
relevant cues used for communication, orientation, and predator/prey
detection (Francis and Barber, 2013). Although the signals emitted by
seismic airgun arrays are generally low frequency, they would also
likely be of short duration and transient in any given area due to the
nature of these surveys. As described previously, exploratory surveys
such as this one cover a large area but would be transient rather than
focused in a given location over time and therefore would not be
considered chronic in any given location.
Based on the information discussed herein, we conclude that impacts
of the specified activity are not likely to have more than short-term
adverse effects on any prey habitat or populations of prey species.
Further, any impacts to marine mammal habitat are not expected to
result in significant or long-term consequences for individual marine
mammals, or to contribute to adverse impacts on their populations.
Estimated Take
This section provides an estimate of the number of incidental takes
proposed for authorization through this IHA, which will inform both
NMFS' consideration of ``small numbers'' and the negligible impact
determination.
Harassment is the only type of take expected to result from these
activities. Except with respect to certain activities not pertinent
here, section 3(18) of the MMPA defines ``harassment'' as any act of
pursuit, torment, or annoyance, which (i) has the potential to injure a
marine mammal or marine mammal stock in the wild (Level A harassment);
or (ii) has the potential to disturb a marine mammal or marine mammal
stock in the wild by causing disruption of behavioral patterns,
including, but not limited to, migration, breathing, nursing, breeding,
feeding, or sheltering (Level B harassment).
All proposed takes are by Level B harassment, involving temporary
changes in behavior. No Level A harassment is expected or proposed for
authorization. In the sections below, we describe methods to estimate
the number of Level B harassment events. The main sources of
distributional and numerical data used in deriving the estimates are
summarized below.
Generally speaking, we estimate take by considering: (1) acoustic
thresholds above which NMFS believes the best available science
indicates marine mammals will be behaviorally harassed or incur some
degree of hearing impairment; (2) the area or volume of water that will
be ensonified above these levels in a day; (3) the density or
occurrence of marine mammals within these ensonified areas; and (4) the
number of days of activities. We note that while these basic factors
can contribute to a basic calculation to provide an initial prediction
of takes, additional information that can qualitatively inform take
estimates is also sometimes available (e.g., previous monitoring
results or average group size). Below, we describe the factors
considered here in more detail and present the proposed take estimate.
Acoustic Thresholds
NMFS recommends the use of acoustic thresholds that identify the
received level of underwater sound above which exposed marine mammals
would be reasonably expected to be behaviorally harassed (equated to
Level B harassment) or to incur PTS of some degree (equated to Level A
harassment).
Level B Harassment for non-explosive sources--Though significantly
driven by received level, the onset of behavioral disturbance from
anthropogenic noise exposure is also informed to varying degrees by
other factors related to the source (e.g., frequency, predictability,
duty cycle), the environment (e.g., bathymetry), and the receiving
animals (hearing, motivation, experience, demography, behavioral
context) and can be difficult to predict (Southall et al., 2007,
Ellison et al., 2012). Based on what the available science indicates
and the practical need to use a threshold based on a factor that is
both predictable and measurable for most activities, NMFS uses a
generalized acoustic threshold based on received level to estimate the
onset of behavioral harassment. NMFS predicts that marine mammals are
likely to be behaviorally harassed in a manner we consider Level B
harassment when exposed to underwater anthropogenic noise above
received levels of 120 dB re 1 [mu]Pa (rms) for continuous (e.g.,
vibratory pile-driving, drilling) and above 160 dB re 1 [mu]Pa (rms)
for non-explosive impulsive (e.g., seismic airguns) or intermittent
(e.g., scientific sonar) sources.
The proposed activities include the use of continuous icebreaking
and impulsive seismic sources and, and therefore the 120 and 160 dB re
1 [mu]Pa (rms) are applicable.
Level A harassment for non-explosive sources--NMFS' Technical
Guidance for Assessing the Effects of Anthropogenic Sound on Marine
Mammal Hearing (Version 2.0) (Technical Guidance, 2018) identifies dual
criteria to assess auditory injury (Level A harassment) to five
different marine mammal groups (based on hearing sensitivity) as a
result of exposure to noise from two different types of sources
(impulsive or non-impulsive). The proposed activity includes the use of
impulsive seismic and continuous non-impulsive icebreaking sources.
These thresholds are provided in the table below. The references,
analysis, and methodology used in the development of the thresholds are
described in NMFS 2018 Technical Guidance, which may be accessed at
<a href="https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance">https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance</a>.
[[Page 59228]]
Table 4--Thresholds Identifying the Onset of Permanent Threshold Shift
----------------------------------------------------------------------------------------------------------------
PTS onset acoustic thresholds * (received level)
Hearing group ------------------------------------------------------------------------
Impulsive Non-impulsive
----------------------------------------------------------------------------------------------------------------
Low-Frequency (LF) Cetaceans........... Cell 1: Lpk,flat: 219 dB; Cell 2: LE,LF,24h: 199 dB.
LE,LF,24h: 183 dB.
Mid-Frequency (MF) Cetaceans........... Cell 3: Lpk,flat: 230 dB; Cell 4: LE,MF,24h: 198 dB.
LE,MF,24h: 185 dB.
High-Frequency (HF) Cetaceans.......... Cell 5: Lpk,flat: 202 dB; Cell 6: LE,HF,24h: 173 dB.
LE,HF,24h: 155 dB.
Phocid Pinnipeds (PW) (Underwater)..... Cell 7: Lpk,flat: 218 dB; Cell 8: LE,PW,24h: 201 dB.
LE,PW,24h: 185 dB.
Otariid Pinnipeds (OW) (Underwater).... Cell 9: Lpk,flat: 232 dB; Cell 10: LE,OW,24h: 219 dB.
LE,OW,24h: 203 dB.
----------------------------------------------------------------------------------------------------------------
* Dual metric acoustic thresholds for impulsive sounds: Use whichever results in the largest isopleth for
calculating PTS onset. If a non-impulsive sound has the potential of exceeding the peak sound pressure level
thresholds associated with impulsive sounds, these thresholds should also be considered.
Note: Peak sound pressure (Lpk) has a reference value of 1 [micro]Pa, and cumulative sound exposure level (LE)
has a reference value of 1[micro]Pa\2\s. In this Table, thresholds are abbreviated to reflect American
National Standards Institute standards (ANSI 2013). However, peak sound pressure is defined by ANSI as
incorporating frequency weighting, which is not the intent for this Technical Guidance. Hence, the subscript
``flat'' is being included to indicate peak sound pressure should be flat weighted or unweighted within the
generalized hearing range. The subscript associated with cumulative sound exposure level thresholds indicates
the designated marine mammal auditory weighting function (LF, MF, and HF cetaceans, and PW and OW pinnipeds)
and that the recommended accumulation period is 24 hours. The cumulative sound exposure level thresholds could
be exceeded in a multitude of ways (i.e., varying exposure levels and durations, duty cycle). When possible,
it is valuable for action proponents to indicate the conditions under which these acoustic thresholds will be
exceeded.
Ensonified Area
Here, we describe operational and environmental parameters of the
activity that will feed into identifying the area ensonified above the
acoustic thresholds, which include source levels and transmission loss
coefficient.
When the NMFS Technical Guidance (2016) was published, in
recognition of the fact that ensonified area/volume could be more
technically challenging to predict because of the duration component in
the new thresholds, we developed a User Spreadsheet that includes tools
to help predict a simple isopleth that can be used in conjunction with
marine mammal density or occurrence to help predict takes. We note that
because of some of the assumptions included in the methods used for
these tools, we anticipate that isopleths produced are typically going
to be overestimates of some degree, which may result in some degree of
overestimate of Level A harassment take. However, these tools offer the
best way to predict appropriate isopleths when more sophisticated 3D
modeling methods are not available, and NMFS continues to develop ways
to quantitatively refine these tools, and will qualitatively address
the output where appropriate. For mobile sources (e.g., icebreaking),
the User Spreadsheet predicts the closest distance at which a
stationary animal would not incur PTS if the sound source traveled by
the animal in a straight line at a constant speed.
The proposed survey would entail the use of a 2-airgun array with a
total discharge of 210 in\3\ at a tow depth of 1-4 m (with the worst-
case scenario of 4 m assumed for purposes of modeling). L-DEO model
results are used to determine the 160 dB<INF>rms</INF> radius for the
2-airgun array water depth ranging from 150-700 m. Received sound
levels were predicted by L-DEO's model (Diebold et al., 2010) as a
function of distance from the airguns, for the two 105 in\3\ airguns.
This modeling approach uses ray tracing for the direct wave traveling
from the array to the receiver and its associated source ghost
(reflection at the air-water interface in the vicinity of the array),
in a constant-velocity half-space (infinite homogenous ocean layer,
unbounded by a seafloor). In addition, propagation measurements of
pulses from a 36-airgun array at a tow depth of 6 m have been reported
in deep water (~1,600 m), intermediate water depth on the slope (~600-
1,100 m), and shallow water (~50 m) in the Gulf of Mexico in 2007-2008
(Tolstoy et al., 2009; Diebold et al., 2010).
For deep and intermediate water cases, the field measurements
cannot be used readily to derive the Level A and Level B harassment
isopleths, as at those sites the calibration hydrophone was located at
a roughly constant depth of 350-550 m, which may not intersect all the
SPL isopleths at their widest point from the sea surface down to the
maximum relevant water depth (~2,000 m) for marine mammals. At short
ranges, where the direct arrivals dominate and the effects of seafloor
interactions are minimal, the data at the deep sites are suitable for
comparison with modeled levels at the depth of the calibration
hydrophone. At longer ranges, the comparison with the model--
constructed from the maximum SPL through the entire water column at
varying distances from the airgun array--is the most relevant.
In deep and intermediate water depths at short ranges, sound levels
for direct arrivals recorded by the calibration hydrophone and L-DEO
model results for the same array tow depth are in good alignment (see
Figures 12 and 14 in Appendix H of NSF-USGS 2011). Consequently,
isopleths falling within this domain can be predicted reliably by the
L-DEO model, although they may be imperfectly sampled by measurements
recorded at a single depth. At greater distances, the calibration data
show that seafloor-reflected and sub-seafloor-refracted arrivals
dominate, whereas the direct arrivals become weak and/or incoherent
(see Figures 11, 12, and 16 in Appendix H of NSF-USGS 2011). Aside from
local topography effects, the region around the critical distance is
where the observed levels rise closest to the model curve. However, the
observed sound levels are found to fall almost entirely below the model
curve. Thus, analysis of the Gulf of Mexico calibration measurements
demonstrates that although simple, the L-DEO model is a robust tool for
conservatively estimating isopleths.
The proposed survey would acquire data with two 105-in\3\ guns at a
tow depth of 1-4 m. For deep water (>1000 m), we use the deep-water
radii obtained from L-DEO model results down to a maximum water depth
of 2,000 m for the airgun array. The radii for intermediate water
depths (100-1,000 m) are derived from the deep-water ones by applying a
correction factor (multiplication) of 1.5, such that observed levels at
very near offsets fall below the corrected mitigation curve (see Figure
16 in Appendix H of NSF-USGS 2011).
L-DEO's modeling methodology is described in greater detail in
NSF's IHA application. The estimated distances to the Level B
harassment isopleth for the
[[Page 59229]]
proposed airgun configuration are shown in Table 5.
Table 5--Predicted Radial Distances From the RVIB Palmer Seismic Source
to Isopleths Corresponding to Level B Harassment Threshold
------------------------------------------------------------------------
Predicted
distances (m)
Airgun configuration Water depth to 160 dB
(m) \a\ received sound
level
------------------------------------------------------------------------
Two 105-in\3\ GI guns................... >1,000 726 \b\
100-1,000 1,089 \c\
------------------------------------------------------------------------
\a\ No survey effort would occur in water >1000 m; the distance for this
water depth is included for informational purposes only.
\b\ Distance is based on L-DEO model results.
\c\ Distance is based on L-DEO model results with a 1.5 x correction
factor between deep and intermediate water depths.
Table 6 presents the modeled PTS isopleths for each marine mammal
hearing group based on the L-DEO modeling incorporated in the companion
User Spreadsheet (NMFS 2018).
Table 6--Modeled Radial Distances to Isopleths Corresponding to Level A Harassment Thresholds
----------------------------------------------------------------------------------------------------------------
SEL cumulative SEL cumulative Pk PTS Pk PTS
Hearing group PTS threshold PTS distance threshold (dB) distance (m)
(dB) \1\ (m) \1\ \1\ \1\
----------------------------------------------------------------------------------------------------------------
Low-frequency cetaceans......................... 183 25.4 219 6.69
Mid-frequency cetaceans......................... 185 0.0 230 1.50
High-frequency cetaceans........................ 155 0.0 202 47.02
Phocid pinnipeds................................ 185 0.3 218 7.53
Otariid pinnpeds................................ 203 0.0 232 0.92
----------------------------------------------------------------------------------------------------------------
\1\ Cumulative sound exposure level for PTS (SELcumPTS) or Peak (SPLflat) resulting in Level A harassment (i.e.,
injury). Based on 2018 NMFS Acoustic Technical Guidance (NMFS 2018).
Predicted distances to Level A harassment isopleths, which vary
based on marine mammal hearing groups, were calculated based on
modeling performed by L-DEO using the Nucleus software program and the
NMFS User Spreadsheet, described below. The acoustic thresholds for
impulsive sounds (e.g., airguns) contained in the Technical Guidance
were presented as dual metric acoustic thresholds using both
SEL<INF>cum</INF> and peak sound pressure metrics (NMFS 2016a). As dual
metrics, NMFS considers onset of PTS (Level A harassment) to have
occurred when either one of the two metrics is exceeded (i.e., metric
resulting in the largest isopleth). The SEL<INF>cum</INF> metric
considers both level and duration of exposure, as well as auditory
weighting functions by marine mammal hearing group. In recognition of
the fact that the requirement to calculate Level A harassment
ensonified areas could be more technically challenging to predict due
to the duration component and the use of weighting functions in the new
SEL<INF>cum</INF> thresholds, NMFS developed an optional User
Spreadsheet that includes tools to help predict a simple isopleth that
can be used in conjunction with marine mammal density or occurrence to
facilitate the estimation of take numbers.
The SEL<INF>cum</INF> for the two-GI airgun array is derived from
calculating the modified farfield signature. The farfield signature is
often used as a theoretical representation of the source level. To
compute the farfield signature, the source level is estimated at a
large distance (right) below the array (e.g., 9 km), and this level is
back projected mathematically to a notional distance of 1 m from the
array's geometrical center. However, it has been recognized that the
source level from the theoretical farfield signature is never
physically achieved at the source when the source is an array of
multiple airguns separated in space (Tolstoy et al., 2009). Near the
source (at short ranges, distances <1 km), the pulses of sound pressure
from each individual airgun in the source array do not stack
constructively as they do for the theoretical farfield signature. The
pulses from the different airguns spread out in time such that the
source levels observed or modeled are the result of the summation of
pulses from a few airguns, not the full array (Tolstoy et al., 2009).
At larger distances, away from the source array center, sound pressure
of all the airguns in the array stack coherently, but not within one
time sample, resulting in smaller source levels (a few dB) than the
source level derived from the farfield signature. Because the farfield
signature does not take into account the interactions of the two
airguns that occur near the source center and is calculated as a point
source (single airgun), the modified farfield signature is a more
appropriate measure of the sound source level for large arrays. For
this smaller array, the modified farfield changes will be
correspondingly smaller as well, but this method is used for
consistency across all array sizes.
The Level B harassment estimates are based on a consideration of
the number of marine mammals that could be within the area around the
operating airgun array where received levels of sound >=160 dB re 1
[micro]Parms are predicted to occur (see Table 1). The estimated
numbers are based on the densities (numbers per unit area) of marine
mammals expected to occur in the area in the absence of seismic
surveys. To the extent that marine mammals tend to move away from
seismic sources before the sound level reaches the criterion level and
tend not to approach an operating airgun array, these estimates likely
overestimate the
[[Page 59230]]
numbers actually exposed to the specified level of sound.
Marine Mammal Occurrence
In this section we provide the information about the presence,
density, or group dynamics of marine mammals that will inform the take
calculations.
For the proposed survey area, NSF provided density data for marine
mammal species that might be encountered in the project area. NMFS
concurred that these data are the best available. Sightings data from
the 2002-2003 (IWC-SOWER) Circumpolar Cruise, Area V (Ensor et al.
2003) were used to estimate densities for four mysticete (i.e.,
humpback whale, Antarctic minke whale, fin whale, and blue whale) and
six odontocete species (i.e., sperm whale, southern bottlenose whale,
strap-toothed beaked whale, killer whale, long-finned pilot whale and
hourglass dolphin). Densities for sei and Arnoux's beaked whales were
based on those reported in the Naval Marine Species Density Database
(NMSDD) (Department of Navy 2012). NMFS finds NMSDD a reasonable
representation of the lower likelihood of encountering these species,
as evidenced by previous monitoring reports from projects in the same
or similar area (85 FR 5619; January 31, 2020 & 0648-XD705;January 29,
2015) and primary literature on whale species density distribution in
the Antarctic (Cetacean Population Studies Vol.2, 2020). Densities of
pinnipeds were estimated using best available data (Waterhouse 2001;
Pinkerton and Bradford-Grieve 2010) and dividing the estimated
population of pinnipeds (number of animals) by the area of the Ross Sea
(300,000 km\2\). Estimated densities used and Level B harassment
ensonified areas to inform take estimates are presented in Table 7.
Table 7--Marine Mammal Densities and Total Ensonified Area of Activities in the Proposed Survey Area
----------------------------------------------------------------------------------------------------------------
Ross bank Drygalski Icebreaking
Estimated level B tough level B level B
Species density (#/ ensonified ensonified ensonified
km\2\) area (km\2\) area (km\2\) area (km\2\)
----------------------------------------------------------------------------------------------------------------
Fin whale....................................... 0.0306570 .............. .............. ..............
Blue whale...................................... 0.0065132 .............. .............. ..............
Sei whale....................................... 0.0046340 .............. .............. ..............
Antarctic minke whale........................... 0.0845595 .............. .............. ..............
Humpback whale.................................. 0.0321169 .............. .............. ..............
Sperm whale..................................... 0.0098821 .............. .............. ..............
Southern bottlenose whale....................... 0.0117912 .............. .............. ..............
Arnoux's beaked whale........................... 0.0134420 .............. .............. ..............
Strap-toothed beaked whale...................... 0.0044919 5,272 4,942 8,278
Killer whale.................................... 0.0208872 .............. .............. ..............
Long-finned pilot whale......................... 0.0399777 .............. .............. ..............
Hourglass dolphin............................... 0.0189782 .............. .............. ..............
Crabeater seal.................................. 0.6800000 .............. .............. ..............
Leopard seal.................................... 0.0266700 .............. .............. ..............
Ross seal....................................... 0.0166700 .............. .............. ..............
Weddell seal.................................... 0.1066700 .............. .............. ..............
Southern elephant seal.......................... 0.0001300 .............. .............. ..............
----------------------------------------------------------------------------------------------------------------
Take Calculation and Estimation
Here we describe how the information provided above is brought
together to produce a quantitative take estimate.
Seismic Surveys
In order to estimate the number of marine mammals predicted to be
exposed to sound levels that would result in Level B harassment, the
radial distance from the airgun array to the predicted isopleth
corresponding to the Level B harassment threshold is calculated, as
described above. The radial distance is then used to calculate the area
around the airgun array predicted to be ensonified to the sound level
that exceed the Level B harassment threshold. The area estimated to be
ensonified in a single day of the survey is then calculated (Table 8),
based on the area predicted to be ensonified around the array and the
estimated trackline distance traveled per day. The daily ensonified
area was then multiplied by the number of estimated seismic acquisition
days -9.6 days for the Ross Bay survey and 9 days for the Drygalski
Trough survey. The product is then multiplied by 1.25 to account for
the additional 25 percent contingency, as described above. This results
in an estimate of the total area (km\2\) expected to be ensonified to
the Level B harassment threshold.
Table 8--Area (km\2\) To Be Ensonified to the Level B Harassment Threshold
--------------------------------------------------------------------------------------------------------------------------------------------------------
Daily
Distance/day Threshold ensonified Number of Plus 25% Total
Survey area (km) distance (km) area with survey days (contingency) ensonified
endcap (km\2\) area (km\2\)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Ross Bank............................................... 200 1.089 439 9.6 12 5,272
Drygaiski Trough........................................ 200 1.089 439 9 11.25 4,942
--------------------------------------------------------------------------------------------------------------------------------------------------------
Based on the small Level A harassment isopleths (as shown in Table
6) and in consideration of the proposed mitigation measures (see
Proposed Mitigation section below), take by Level A harassment is not
expected to occur and is not proposed for authorization.
[[Page 59231]]
The marine mammals predicted to occur within the respective areas,
based on estimated densities (Table 7), are assumed to be incidentally
taken. Estimated take, and percentages of the stocks estimated to be
taken, for the proposed survey are shown in Table 10.
Icebreaking
Applying the maximum estimated amount of icebreaking expected by
NSF, i.e., 500 km, we calculate the total ensonified area of
icebreaking (Table 9). Estimates of exposures assume that there would
be approximately 2 days of icebreaking activities; the calculated takes
have been increased by 25 percent (2.75 days).
Table 9--Ensonified Area for Icebreaking Activities
--------------------------------------------------------------------------------------------------------------------------------------------------------
Daily
Distance/day Threshold ensonified area Number of Plus 25% Total
Criteria (km) distance (km) with endcap survey days (contingency) ensonified area
(km\2\) (km\2\)
--------------------------------------------------------------------------------------------------------------------------------------------------------
120 dB............................................ 223 6,456 3,010 2.2 2.75 8,278
--------------------------------------------------------------------------------------------------------------------------------------------------------
Estimated take from icebreaking for the proposed survey are shown
in Table 10. As most cetaceans do not occur in pack ice, the estimates
of the numbers of marine mammal
[…truncated; see source link]Indexed from Federal Register on September 29, 2022.
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