Notice2022-00455
Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to Geophysical Surveys of the Guerrero Gap in the Eastern Tropical Pacific
Primary source
Metadata and text below are from the Federal Register, a public-domain U.S. government work. Always verify the official published version before relying on it for any legal matter.
Published
January 12, 2022
Issuing agencies
Commerce DepartmentNational Oceanic and Atmospheric Administration
Abstract
NMFS has received a request from the Lamont-Doherty Earth Observatory (L-DEO) for authorization to take marine mammals incidental to geophysical surveys of the Guerrero Gap off the coast of Mexico in the Eastern Tropical Pacific. 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-time, 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 authorization and agency responses will be summarized in the final notice of our decision.
Full Text
<html>
<head>
<title>Federal Register, Volume 87 Issue 8 (Wednesday, January 12, 2022)</title>
</head>
<body><pre>
[Federal Register Volume 87, Number 8 (Wednesday, January 12, 2022)]
[Notices]
[Pages 1992-2025]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2022-00455]
[[Page 1991]]
Vol. 87
Wednesday,
No. 8
January 12, 2022
Part IV
Department of Commerce
-----------------------------------------------------------------------
National Oceanic and Atmospheric Administration
-----------------------------------------------------------------------
Takes of Marine Mammals Incidental to Specified Activities; Taking
Marine Mammals Incidental to Geophysical Surveys of the Guerrero Gap in
the Eastern Tropical Pacific; Notice
Federal Register / Vol. 87 , No. 8 / Wednesday, January 12, 2022 /
Notices
[[Page 1992]]
-----------------------------------------------------------------------
DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
[RTID 0648-XB628]
Takes of Marine Mammals Incidental to Specified Activities;
Taking Marine Mammals Incidental to Geophysical Surveys of the Guerrero
Gap in the Eastern Tropical Pacific
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.
-----------------------------------------------------------------------
SUMMARY: NMFS has received a request from the Lamont-Doherty Earth
Observatory (L-DEO) for authorization to take marine mammals incidental
to geophysical surveys of the Guerrero Gap off the coast of Mexico in
the Eastern Tropical Pacific. 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-time, 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 authorization and agency
responses will be summarized in the final notice of our decision.
DATES: Comments and information must be received no later than February
11, 2022.
ADDRESSES: Comments should be addressed to Jolie Harrison, Chief,
Permits and Conservation Division, Office of Protected Resources,
National Marine Fisheries Service submitted via email to
<a href="/cdn-cgi/l/email-protection#19504d49375f766e757c6b5977767878377e766f"><span class="__cf_email__" data-cfemail="a2ebf6f28ce4cdd5cec7d0e2cccdc3c38cc5cdd4">[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, 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="http://www.fisheries.noaa.gov/permit/incidental-take-authorizations-under-marine-mammal-protection-act">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: Amy Fowler, 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 proposed or, if the taking is limited to harassment, a notice of a
proposed incidental harassment authorization is 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 IHA)
with respect to potential impacts on the human environment.
Accordingly, NMFS plans to adopt the National Science Foundation's
(NSF's) Environmental Assessment (EA), provided our independent
evaluation of the document finds that it includes adequate information
analyzing the effects on the human environment of issuing the IHA. The
NSF's EA is available 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>.
We will review all comments submitted in response to this notice
prior to concluding our NEPA process or making a final decision on the
IHA request.
Summary of Request
On August 21, 2021, NMFS received a request from L-DEO for an IHA
to take marine mammals incidental to geophysical surveys of the
Guerrero Gap off the coast of Mexico in the Eastern Tropical Pacific
(ETP). The application was deemed adequate and complete on December 14,
2021. L-DEO's request is for take of a small number of 30 species of
marine mammals by Level B harassment and, for two of those species, by
Level A harassment. Neither L-DEO 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 L-DEO, University of Texas Institute of Geophysics
(UTIG), and Northern Arizona University (NAU), with funding from the
NSF, and in collaboration with researchers from the National Autonomous
University of Mexico (Universidad Nacional Autonoma de Mexico or UNAM)
and Kyoto University, propose to conduct high-energy seismic surveys
from the research vessel (R/V) Marcus G. Langseth (Langseth) in and
around the Guerrero Gap off western Mexico, in the ETP. The proposed
study would use two-dimensional (2-D) seismic surveying to quantify
incoming plate hydration and examine the role of fluids on megathrust
slip behavior in and around the Guerrero Gap of the Middle America
Trench. This is one of the best-known examples in the world of along-
strike variations in slip behavior of the plate boundary. L-DEO
proposes to conduct two different methods of seismic acquisition,
multi-channel seismic (MCS) using a hydrophone streamer and refraction
surveys using ocean bottom seismometers (OBSs). The
[[Page 1993]]
surveys would use a 36-airgun towed array with a total discharge volume
of ~6600 cubic inches (in\3\) as an acoustic source, acquiring return
signals using both a towed streamer as well as OBSs. The majority of
the proposed 2-D seismic surveys would occur within the Exclusive
Economic Zone (EEZ) of Mexico, including territorial seas, and a small
portion would occur in International Waters.
Dates and Duration
The proposed research cruise would be expected to last for 48 days,
including approximately 20 days of seismic survey operations, 3 days of
transit to and from the survey area, 19 days for equipment deployment/
recovery, and 6 days of contingency time for poor weather, etc. The R/V
Langseth would likely leave out of and return to port in Manzanillo,
Mexico, during spring 2022. The proposed IHA would be valid from March
1, 2022 through February 28, 2023.
Specific Geographic Region
The proposed surveys would occur within the area of approximately
14-18.5[deg]N and approximately 99-105[deg]W. Representative survey
tracklines are shown in Figure 1. Some deviation in actual track lines,
including the order of survey operations, could be necessary for
reasons such as science drivers, poor data quality, inclement weather,
or mechanical issues with the research vessel and/or equipment. The
majority of the proposed surveys would occur within the EEZ of Mexico,
including territorial seas, and a small portion would occur in
International Waters. The surveys would occur in waters up to 5,560
meters (m) deep. Most of the survey effort (94 percent) would occur in
deep water (>1000 m), and 6 percent would occur in intermediate water
(100-1000 m deep); no effort would occur in shallow water (<100 m
deep). A total of 3,600 kilometers (km) of transect lines would be
surveyed (2,230 km of 2-D MCS reflection data and 1,370 km of OBS
refraction data).
Approximately 6 percent of the total survey effort would occur in
Mexican territorial waters. Note that the MMPA does not apply in
Mexican territorial waters. L-DEO is subject only to Mexican law in
conducting that portion of the survey. However, NMFS has calculated the
expected level of incidental take in the entire activity area
(including Mexican territorial waters) as part of the analysis
supporting our determination under the MMPA that the activity will have
a negligible impact on the affected species (see Estimated Take and
Negligible Impact Analysis and Determination).
BILLING CODE 3510-22-P
[GRAPHIC] [TIFF OMITTED] TN12JA22.027
[[Page 1994]]
BILLING CODE 3510-22-C
Detailed Description of Specific Activity
The procedures to be used for the proposed marine geophysical
surveys would be similar to those used during previous surveys by L-DEO
that received incidental take authorizations from NMFS (e.g., 85 FR
55645; September 9, 2020, 84 FR 35073; July 22, 2019) and would use
conventional seismic methodology. The survey would involve one source
vessel, R/V Langseth, which would tow a 36-airgun array with a
discharge volume of ~6600 in\3\ at a depth of 12 m. The array consists
of 36 elements, including 20 Bolt 1500LL airguns with volumes of 180 to
360 in\3\ and 16 Bolt 1900LLX airguns with volumes of 40 to 120 in\3\.
The airgun array configuration is illustrated in Figure 2-11 of NSF and
the U.S. Geological Survey's (USGS's) Programmatic Environmental Impact
Statement (PEIS; NSF-USGS, 2011). (The PEIS is available online at:
<a href="http://www.nsf.gov/geo/oce/envcomp/usgs-nsf-marine-seismic-research/nsf-usgs-final-eis-oeis-with-appendices.pdf">www.nsf.gov/geo/oce/envcomp/usgs-nsf-marine-seismic-research/nsf-usgs-final-eis-oeis-with-appendices.pdf</a>).
The proposed surveys consist of eight MCS lines, of which six are
coincident OBS refraction lines that are located perpendicular to the
margin; these six lines would therefore be acquired twice.
Approximately 62 percent of the total survey effort would be MCS
surveys, with the remaining 38 percent using OBSs. There could be
additional seismic survey operations associated with turns, airgun
testing, and repeat coverage of any areas where initial data quality is
sub-standard, and 25 percent has been added to the assumed survey line-
kms to account for this potential. NMFS considers this a conservative
approach to estimating potential acoustic exposures.
The vessel speed during seismic survey operations would be ~4.1
knots (~7.6 km/hour) during MCS reflection surveys and 5 knots (~9.3
km/hour) during OBS refraction surveys. The airguns would fire at a
shot interval of 50 m (approximately 24 seconds) during MCS surveys
with the hydrophone streamer and at a 400-m (155 seconds) interval
during refraction surveys to OBSs. The receiving system would consist
of a 15-km long hydrophone streamer and short-period OBSs. As the
airgun arrays are towed along the survey lines, the OBSs would receive
and store the returning acoustic signals internally for later analysis,
and the hydrophone streamer would transfer the data to the on-board
processing system.
The seismometers would consist of 33 OBSs, which would be deployed
at a total of 124 sites. The instruments would be deployed by R/V
Langseth and spaced 10 or 12 km apart. Following refraction shooting of
one line, short-period instruments on that line would be recovered,
serviced, and redeployed on a subsequent refraction line while MCS data
are acquired. The OBSs have a height and diameter of approximately 1 m
and an anchor weighing roughly 80 kilograms (kg). OBS sample rate would
be set at 200 hertz (Hz). All OBSs would be recovered by the end of the
survey.
To retrieve OBSs, an acoustic release transponder (pinger) is used
to interrogate the instrument at a frequency of 8-11 kilohertz (kHz),
and a response is received at a frequency of 11.5-13 kHz. The burn-wire
release assembly is then activated, and the instrument is released to
float to the surface from the anchor which is not retrieved. Take of
marine mammals is not expected to occur incidental to L-DEO's use of
OBSs.
In addition to the operations of the airgun array, a multibeam
echosounder (MBES), a sub-bottom profiler (SBP), and an Acoustic
Doppler Current Profiler (ADCP) would be operated from R/V Langseth
continuously during the seismic surveys, but not during transit to and
from the survey area. Take of marine mammals is not expected to occur
incidental to use of the MBES, SBP, or ADCP as, due to these sources'
characteristics (e.g., narrow downward-directed beam), marine mammals
would experience no more than one or two brief ping exposures from
them, if any exposure were to occur. Accordingly, the use of MBES, SBP,
and ADCP are not analyzed further in this document.
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. Brief
discussions of some species and stocks is presented below. For all
other species, we refer the reader to the descriptions in L-DEO's IHA
application, incorporated here by reference, instead of reprinting the
information. Additional information regarding population trends and
threats may be found in NMFS's Stock Assessment Reports (SARs; <a href="https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments">https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments</a>) and more general 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>).
Table 1 lists all species or stocks for which take is expected and
proposed to be authorized for this action, and summarizes information
related to the population or stock, including regulatory status under
the MMPA and Endangered Species Act (ESA) and potential biological
removal (PBR), where known. For taxonomy, we follow Committee on
Taxonomy (2021). PBR is 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 (as described in NMFS's SARs). While no
serious injury or mortality is anticipated or proposed for
authorization here, PBR and annual serious injury and mortality from
anthropogenic sources are included here as gross indicators of the
status of the species and other threats.
Marine mammal abundance estimates presented in this document
represent the total number of individuals that make up a given stock or
the total number estimated within a particular study or survey area.
NMFS's stock abundance estimates for most species represent the total
estimate of individuals within the geographic area, if known, that
comprises that stock. For some species, this geographic area may extend
beyond U.S. waters. All managed stocks in this region are assessed in
NMFS's U.S. Pacific SARs. All values presented in Table 1 are the most
recent available at the time of publication and are available in the
2020 SARs (Carretta et al., 2021) and draft 2021 SARs (available online
at: <a href="https://www.fisheries.noaa.gov/national/marine-mammal-protection/draft-marine-mammal-stock-assessment-reports">https://www.fisheries.noaa.gov/national/marine-mammal-protection/draft-marine-mammal-stock-assessment-reports</a>). Where available,
abundance and status information is also presented for marine mammals
in the Pacific waters of Mexico and/or the greater ETP region. Table 1
denotes the status of species and stocks under the U.S. MMPA and ESA.
We note also that the Guadalupe fur seal is classified as ``En peligro
de extinci[oacute]n'' (in danger of extinction) under the Norma Oficial
Mexicana NOM-059-SEMARNAT-2010 and all other marine mammal species
listed in Table 1, with the exception of Longman's beaked whales and
Deraniyagala's beaked whales, are listed as ``Sujetas a
protecci[oacute]n especial'' (subject to special protection).
[[Page 1995]]
Table 1--Marine Mammals That Could Occur in the Survey Area
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Stock abundance (CV,
Common name Scientific name Stock ESA/MMPA status; Nmin, most recent PBR Annual M/SI\3\ ETP abundance Mexico Pacific
strategic (Y/N) \1\ abundance survey) \2\ \4\ abundance \5\
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Order Cetartiodactyla--Cetacea--Superfamily Mysticeti (baleen whales)
Family Balaenopteridae (rorquals)
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Humpback Whale.................... Megaptera Central N -, -, Y.............. 10,103 (0.3, 7,890, 83................... 26 2,566 ..............
novaeangliae. Pacific 2006).
Minke whale....................... Balaenoptera N/A -, -, N.............. N/A.................. N/A.................. N/A 115 ..............
acutorostrata.
Bryde's whale..................... Balaenoptera edeni... Eastern Tropical -, -, N.............. Unknown (Unknown, Undetermined......... Unknown 10,411 649
Pacific Unknown, N/A).
Sei whale......................... Balaenoptera borealis Eastern N E, D, Y.............. 519 (0.4, 374, 2014). 0.75................. >=0.2 0 ..............
Pacific
Fin whale......................... Balaenoptera physalus N/A E, D, Y.............. N/A.................. N/A.................. N/A 574 145
Blue whale........................ Balaenoptera musculus Eastern N E, D, Y.............. 1,898 (0.085, 1,767, 4.1.................. >=19.4 1,415 773
Pacific 2018).
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Superfamily Odontoceti (toothed whales, dolphins, and porpoises)
Family Physeteridae
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Sperm whale....................... Physeter N/A E, D, Y.............. N/A.................. N/A.................. N/A 4,145 2810
macrocephalus.
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Family Kogiidae
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Dwarf Sperm Whale................. Kogia sima........... N/A N/A.................. N/A.................. N/A.................. N/A \6\ 11,200 ..............
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Family Ziphiidae (beaked whales)
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Cuvier's Beaked Whale............. Ziphius cavirostris.. N/A -, -, N.............. N/A.................. N/A.................. N/A \7\ 20,000 \8\ 68,828
Longman's beaked whale............ Indopacetus pacificus N/A -, -, N.............. N/A.................. N/A.................. N/A 1,007 ..............
Blainville's beaked whale......... Mesoplodon N/A -, -, N.............. N/A.................. N/A.................. N/A \9\ 25,300 \8\ 68,828
densirostris.
Ginkgo-toothed beaked whale....... M. ginkgodens........ N/A -, -, N.............. N/A.................. N/A.................. N/A \9\ 25,300 \8\ 68,828
Deraniyagala's beaked whale....... M. hotaula........... N/A -, -, N.............. N/A.................. N/A.................. N/A \9\ 25,300 \8\ 68,828
Pygmy beaked whale................ M. peruvianus........ N/A -, -, N.............. N/A.................. N/A.................. N/A \9\ 25,300 \8\ 68,828
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Family Delphinidae
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Risso's dolphin................... Grampus griseus...... N/A -, -, N.............. N/A.................. N/A.................. N/A 110,457 24,084
Rough-toothed dolphin............. Steno bredanensis.... N/A -, -, N.............. N/A.................. N/A.................. N/A 107,663 37,511
Common bottlenose dolphin......... Tursiops truncatus... N/A -, -, N.............. N/A.................. N/A.................. N/A 335,834 61,536
Pantropical spotted dolphin....... Stenella attenuata... N/A\10\ -, D, N.............. N/A.................. N/A.................. N/A \11\ 1,297,091 146,296
Spinner dolphin................... Stenella longirostris N/A \10\ -, D, N.............. N/A.................. N/A.................. N/A \11\ 2,075,871 186,906
Striped dolphin................... Stenella coeruleoalba N/A -, -, N.............. N/A.................. N/A.................. N/A 964,362 128,867
Short-beaked common dolphin....... Delphinus delphis.... N/A -, -, N.............. N/A.................. N/A.................. N/A 3,127,203 283196
Fraser's dolphin.................. Lagenodelphis hosei.. N/A -, -, N.............. N/A.................. N/A.................. N/A \7\ 289,300 ..............
Short-finned pilot whale.......... Globicephala N/A -, -, N.............. N/A.................. N/A.................. N/A \12\ 589,315 3,348
macrorhynchus.
Killer whale...................... Orcinus orca......... N/A -, -, N.............. N/A.................. N/A.................. N/A \7\ 8,500 852
False killer whale................ Pseudorca crassidens. N/A -, -, N.............. N/A.................. N/A.................. N/A \7\ 39,800
Pygmy killer whale................ Feresa attenuata..... N/A -, -, N.............. N/A.................. N/A.................. N/A \7\ 38,900 ..............
Melon-headed whale................ Peponocephala electra N/A -, -, N.............. N/A.................. N/A.................. N/A \7\ 45,400 ..............
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Order Carnivora--Superfamily Pinnipedia
Family Otariidae (eared seals and sea lions)
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Guadalupe fur seal................ Arctocephalus Mexico T, D, Y.............. 34,187 (N/A, 31,019, 1062................. >=3.8 .............. ..............
townsendi. 2013).
[[Page 1996]]
California sea lion............... Zalophus U.S. -, -, N.............. 257,606 (N/A,233,515, 14011................ >320 105,000 ..............
californianus. 2014).
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Endangered Species Act (ESA) status: Endangered (E), Threatened (T)/MMPA status: Depleted (D). A dash (-) indicates that the species is not listed under the ESA or designated as depleted
under the MMPA. Under the MMPA, a strategic stock is one for which the level of direct human-caused mortality exceeds PBR or which is determined to be declining and likely to be listed under
the ESA within the foreseeable future. Any species or stock listed under the ESA is automatically designated under the MMPA as depleted and as a strategic stock.
\2\ NMFS marine mammal stock assessment reports online at: <a href="https://www.fisheries.noaa.gov/national/marine-mammal-protection/draft-marine-mammal-stock-assessment-reports">https://www.fisheries.noaa.gov/national/marine-mammal-protection/draft-marine-mammal-stock-assessment-reports</a> . CV is coefficient of
variation; Nmin is the minimum estimate of stock abundance. In some cases, CV is not applicable.
\3\ These values, found in NMFS's SARs, represent annual levels of human-caused mortality plus serious injury from all sources combined (e.g., commercial fisheries, ship strike). Annual M/SI
often cannot be determined precisely and is in some cases presented as a minimum value or range. A CV associated with estimated mortality due to commercial fisheries is presented in some
cases.
\4\ From NMFS (2015b) unless otherwise noted.
\5\ Pacific Mexico excluding the Gulf of California (from Gerrodette and Palacios (1996) unless otherwise noted).
\6\ Estimate for ETP is mostly for K. sima but may also include some K. breviceps (Wade and Gerrodette 1993).
\7\ Wade and Gerrodette 1993.
\8\ Abundance for all ziphiids.
\9\ This estimate for the ETP includes all species of the genus Mesoplodon.
\10\ Several stocks of these species, while not classified as such in the U.S. SARs, are considered depleted due to historical interactions with tuna fisheries in the area. Please see below
for a discussion of these stocks.
\11\ Includes abundance of several stocks added together.
\12\ Based on surveys in 2000 (Gerrodette and Forcada 2002).
As indicated above, all 30 species (with six managed stocks) in
Table 1 temporally and spatially co-occur with the activity to the
degree that take is reasonably likely to occur, and we have proposed
authorizing it. As the planned survey lines are outside of the U.S.
EEZ, they do not directly overlap with the defined ranges for most U.S.
managed stocks (Carretta et al., 2021). For some species (e.g., Bryde's
whale, Guadalupe fur seal; see Table 1), animals encountered during the
surveys could be from a defined stock under the MMPA but most marine
mammals in the survey area do not belong to any defined stock. Species
that could potentially occur in the proposed research area but are not
likely to be encountered due to the rarity of their occurrence (i.e.,
are considered extralimital or rare visitors to the coastal waters of
Mexico in the Eastern Tropical Pacific) are described briefly but
omitted from further analysis. These generally include species that do
not normally occur in the area but for which there are one or more
occurrence records that are considered beyond the normal range of the
species. These species include the gray whale (Eschrichtius robustus),
Hubbs' beaked whale (Mesoplodon carlhubbsi), Stejneger's beaked whale
(M. stejnegeri), Perrin's beaked whale (M. perrini), Baird's beaked
whale (Berardius bairdii), pygmy sperm whale (Kogia breviceps), long-
finned pilot whale (Globicephala melas), Dall's porpoise (Phocoenoides
dalli), Pacific white-sided dolphin (Lagenorhynchus obliquidens), and
northern right whale dolphin (Lissodelphis borealis), which all
generally occur well north of the proposed survey area (e.g, north of
the Baja peninsula). Five additional pinniped species are known to
occur in the ETP but are considered extralimital in the proposed survey
area: The Gal[aacute]pagos sea lion (Zalophus wollebaeki),
Gal[aacute]pagos fur seal (Arctocephalus galapagoensis), South American
fur seal (A. australis), and the South American sea lion (Otaria
flavescens), which all occur south of the survey area, and the northern
elephant seal (Mirounga angustirostris) which is found north of the
survey area.
Prior to 2016, humpback whales were listed under the ESA as an
endangered species worldwide. Following a 2015 global status review
(Bettridge et al., 2015), NMFS delineated 14 distinct population
segments (DPSs) with different listing statuses (81 FR 62259; September
8, 2016) pursuant to the ESA. The DPSs that occur in U.S. waters do not
necessarily equate to the existing stocks designated under the MMPA and
shown in Table 1. The threatened Mexico DPS and endangered Central
America DPS may occur within the proposed survey area. However, due to
the expected timing of the proposed survey (spring), most humpbacks
from the Mexico DPS will have begun their migration north toward the
feeding grounds off of the U.S. west coast and are likely to be outside
of the survey area. Humpbacks from the Central America DPS will likely
be migrating northward through the survey area at the time of the
proposed survey. Therefore, we assume that most humpback whales taken
by the proposed survey activities will be from the Central America DPS.
The pantropical spotted dolphin is one of the most abundant
cetaceans and is distributed worldwide in tropical and some subtropical
waters, between ~40[deg]N and 40[deg]S (Jefferson et al., 2015). In the
ETP, this species ranges from 25[deg] N off the Baja California
Peninsula to 17[deg] S, off southern Peru (Perrin and Hohn, 1994).
There are two forms of pantropical spotted dolphin (Perrin 2018a):
Coastal (Stenella attenuata graffmani) and offshore (S. a. attenuata),
both of which could occur within the proposed survey area. Along the
coast of Latin America, the coastal form typically occurs within 20 km
from shore (Urb[aacute]n 2008 in Heckel et al., 2020). There are
currently three recognized stocks of spotted dolphins in the ETP: The
coastal stock and two offshore stocks--the northeast and the west/south
stocks (Wade and Gerrodette 1993; Leslie et al., 2019). Much of what is
known about the pantropical spotted dolphin in the ETP is related to
the historical tuna purse-seine fishery in that area (Perrin and Hohn
1994). There was an overall stock decline of spotted dolphins from
1960-1980 because of the fishery (Allen 1985). In 1979, the population
size of spotted dolphins in the ETP was estimated at 2.9-3.3 million
(Allen 1985). For 1986-1990, Wade and Gerrodette (1993) reported an
estimate of 2.1 million. Gerrodette and Forcada (2005) noted that the
population of offshore northeastern spotted dolphins had not yet
recovered from the earlier population declines; possible reasons for
the lack of growth were attributed to unreported bycatch, effects of
fishing activity on survival and reproduction, and long-term changes in
the ecosystem. The abundance estimate for 2006 was ~857,884
northeastern offshore spotted
[[Page 1997]]
dolphins, and 439,208 western-southern offshore spotted dolphins; the
coastal subspecies was estimated at 278,155 and was less affected by
fishing activities (Gerrodette et al., 2008). In 2004, the mortality
rate in the tuna fishery was estimated at 0.03 percent (Bayliff 2004).
Perrin (2018a) noted that for the last few years, hundreds of spotted
dolphins have been taken in the fishery. Currently, there are ~640,000
northeastern offshore spotted dolphins inhabiting the ETP (Perrin
2018a). This stock is still considered depleted and may be slow to
recover due to continued chase and encirclement by the tuna fishery,
which may in turn affect reproductive rates (Cramer et al., 2008;
Kellar et al., 2013). The northeastern offshore and coastal stocks of
pantropical spotted dolphins are likely to be encountered during the
proposed surveys.
The spinner dolphin is pantropical in distribution, including
oceanic tropical and sub-tropical waters between 40[deg] N and 40[deg]
S (Jefferson et al., 2015). It is generally considered a pelagic
species, but it can also be found in coastal waters (Perrin 2018b). In
the ETP, three types of spinner dolphins have been identified and two
of those are recognized as subspecies: The eastern spinner dolphin
(Stenella longirostris orientalis), considered an offshore species, the
Central American spinner (S.l. centroamericana; also known as the Costa
Rican spinner), considered a coastal species occurring from southern
Mexico to Costa Rica (Perrin 1990; Dizon et al., 1991), and the
`whitebelly' spinner which is thought to be a hybrid of the eastern
spinner and Gray's spinner (S.l. longirostris). Gray's spinner dolphin
is not expected to occur within the proposed study area. Although there
is a great deal of overlap between the ranges of eastern and whitebelly
spinner dolphins, the eastern form generally occurs in the northeastern
portion of the ETP, whereas the whitebelly spinner occurs in the
southern portion of the ETP, ranging farther offshore (Wade and
Gerrodette 1993; Reilly and Fiedler 1994). Reilly and Fiedler (1994)
noted that eastern spinners are associated with waters that have high
surface temperatures and chlorophyll and shallow thermoclines, whereas
whitebelly spinners are associated with cooler surface temperatures,
lower chlorophyll levels, and deeper thermoclines. The eastern spinner
dolphins are the most likely to occur in the proposed survey area (see
Ferguson and Barlow 2001; Heckel et al., 2020), as this subspecies
occurs in the ETP, east of 145[deg] W, between 24[deg] N off the Baja
California Peninsula and 10[deg] S off Peru (Perrin 1990). Wade and
Gerrodette (1993) reported an abundance estimate of 1.7 million, and
Gerrodette et al. (2005) estimated the abundance at 1.1 million for
2003. Gerrodette and Forcada (2005) noted that the population of
eastern spinner dolphins had not yet recovered from the earlier
population declines due to the tuna fishery. The population estimate
for eastern spinner dolphins in 2003 was 612,662 (Gerrodette et al.,
2005). In 2000, the whitebelly dolphin was estimated to number 801,000
in the ETP (Gerrodette et al., 2005). Bayliff (2004) noted a spinner
dolphin mortality rate in the tuna fishery of 0.03 percent for 2004.
Possible reasons why the population has not recovered include under-
reported bycatch, effects of fishing activity on survival and
reproduction, and long-term changes in the ecosystem (Gerrodette and
Forcada, 2005). The continued chase and encirclement by the tuna
fishery may be affecting the reproductive rates of the eastern spinner
dolphin (Cramer et al., 2008).
The common dolphin is found in oceanic and nearshore waters of
tropical and warm temperate oceans around the world, ranging from
~60[deg] N to ~50[deg] S (Jefferson et al., 2015). There are two
subspecies of common dolphins that occur in the eastern Pacific Ocean,
the short-beaked form (Delphinus delphis delphis) and the long-beaked
form (D. delphis bairdii). The long-beaked form generally prefers
shallower water (Perrin 2018c), typically occurring within 180 km from
shore (Jefferson et al., 2015). The short-beaked form occurs along the
entire coast of Mexico and has been sighted near the proposed survey
area off Nayarit, Michoac[aacute]n, and Guerrero; the long-beaked form
occurs off the Baja California Peninsula and the Gulf of California
(Heckel et al., 2020). The southern limit of the long-beaked form
appears to be 22[deg] N (Urb[aacute]n 2008), and no sightings in
Mexican waters have been made to the south of that. Thus, only the
short-beaked form is expected to occur within the study area.
Unusual Mortality Events (UME)
A UME is defined under the MMPA as ``a stranding that is
unexpected; involves a significant die-off of any marine mammal
population; and demands immediate response.'' For more information on
UMEs, please visit: <a href="http://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-unusual-mortality-events">www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-unusual-mortality-events</a>.
Increased strandings of Guadalupe fur seals have occurred along the
entire coast of California. Guadalupe fur seal strandings began in
January 2015 and were eight times higher than the historical average.
Strandings have continued since 2015 and have remained well above
average through 2019. Strandings are seasonal and generally peak in
April through June of each year. Strandings in Oregon and Washington
became elevated starting in 2019 and have continued to present.
Strandings in these two states in 2019 are five times higher than the
historical average. As of December 2021, a total of 724 Guadalupe fur
seals have stranded and are considered part of the UME (542 in
California and 182 in Oregon and Washington). Stranded Guadalupe fur
seals are mostly weaned pups and juveniles (1-2 years old). The
majority of stranded animals showed signs of malnutrition with
secondary bacterial and parasitic infections. For more information,
please visit <a href="https://www.fisheries.noaa.gov/national/marine-life-distress/2015-2021-guadalupe-fur-seal-unusual-mortality-event-california">https://www.fisheries.noaa.gov/national/marine-life-distress/2015-2021-guadalupe-fur-seal-unusual-mortality-event-california</a>.
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 2.
[[Page 1998]]
Table 2--Marine Mammal Hearing Groups
[NMFS, 2018]
------------------------------------------------------------------------
Hearing group Generalized hearing range *
------------------------------------------------------------------------
Low-frequency (LF) cetaceans (baleen 7 Hz to 35 kHz.
whales).
Mid-frequency (MF) cetaceans (dolphins, 150 Hz to 160 kHz.
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) (true 50 Hz to 86 kHz.
seals).
Otariid pinnipeds (OW) (underwater) (sea 60 Hz to 39 kHz.
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 and Holt,
2013).
For more detail concerning these groups and associated frequency
ranges, please see NMFS (2018) for a review of available information.
30 marine mammal species (28 cetacean and two pinniped (both otariid)
species) have the reasonable potential to co-occur with the proposed
survey activities. Please refer to Table 1. Of the cetacean species
that may be present, six are classified as low-frequency cetaceans
(i.e., all mysticete species), 20 are classified as mid-frequency
cetaceans (i.e., all delphinid and ziphiid species and the sperm
whale), and two are classified as high-frequency cetaceans (i.e.,
harbor porpoise and Kogia spp.).
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.
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 inasmuch 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 1 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 1 m from the source (referenced to 1
[mu]Pa) while the received level is the SPL at the listener's position
(referenced to 1 [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 and 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 6 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.,
[[Page 1999]]
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):
<bullet> 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;
<bullet> 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;
<bullet> 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
<bullet> 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 1 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, 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.
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'') regarding sound, characteristics of sound types, and metrics
used in this document. Note that, in the following discussion, we refer
in many cases to a review article concerning studies of noise-induced
hearing loss conducted from 1996-2015 (i.e., Finneran, 2015). For
study-specific citations, please see that work. 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
[[Page 2000]]
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 and 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; 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 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 (Delphinapterus leucas), harbor
porpoise (Phocoena phocoena), and Yangtze finless porpoise (Neophocaena
asiaeorientalis)) 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
[[Page 2001]]
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, 2019), 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,
2019; 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 showed 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 and Symonds, 2002; see also
Richardson et al., 1995; Nowacek et al., 2007). However, many
delphinids approach acoustic source vessels with no apparent discomfort
or obvious behavioral change (e.g., Barkaszi et al., 2012; Barkaszi and
Kelly, 2018).
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 and 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
and Clark, 2000; Ng and 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.
Of note for one of the species that occur in the survey area,
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 6 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
[[Page 2002]]
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 or amplitude of
calls (Miller et al., 2000; Fristrup et al., 2003; Foote et al., 2004;
Holt et al., 2012), 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 hours 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 [mu]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 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 SELcum 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).
Forney et al. (2017) detail the potential effects of noise on
marine mammal populations with high site fidelity, including
displacement and auditory masking, noting that a lack of observed
response does not imply absence of fitness costs and that apparent
tolerance of disturbance may have population-level impacts that are
less obvious and difficult to document. Forney et al. (2017) state
that, for these animals, remaining in a disturbed area may reflect a
lack of alternatives rather than a lack of effects. The authors discuss
several case studies, including western Pacific gray whales, which are
a small population of mysticetes believed to be adversely affected by
oil and gas development off Sakhalin Island, Russia (Weller et al.,
2002; Reeves et al., 2005). Western gray whales display a high degree
of interannual site fidelity to the area for foraging purposes, and
observations in the area during airgun surveys has shown the potential
for harm caused by displacement from such an important area (Weller et
al., 2006; Johnson et al., 2007). Forney et al. (2017) also discuss
beaked whales, noting that anthropogenic effects in areas where they
are resident could cause severe biological consequences, in part
because displacement may adversely affect foraging rates, reproduction,
or health, while an overriding instinct to remain could lead to more
severe acute effects.
A flight response is a dramatic change in normal movement to a
directed and rapid movement away from the perceived location of a sound
source. The flight response differs from other avoidance responses in
the intensity of the response (e.g., directed movement, rate of
travel). Relatively little information on flight responses of marine
mammals to anthropogenic signals exist, although observations of flight
responses to the presence of predators have occurred (Connor and
Heithaus, 1996). The result of a flight response could range from
brief, temporary exertion and displacement from the area where the
signal provokes flight to, in extreme cases, marine mammal strandings
(Evans and England, 2001). However, it should be noted that response to
a perceived predator does not necessarily invoke flight (Ford and
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
[[Page 2003]]
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 and Livoreil, 1997; Fritz et al., 2002; Purser and 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 and 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 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 and Becker, 2000;
Romano et al., 2002b) and, more rarely, studied in wild populations
(e.g., Romano et al., 2002a). For example, Rolland et al. (2012) found
that noise reduction from reduced ship traffic in the Bay of Fundy was
associated with decreased stress in North Atlantic right whales. These
and other studies lead to a reasonable expectation that some marine
mammals will experience physiological stress responses upon exposure to
acoustic stressors and that it is possible that some of these would be
classified as ``distress.'' In addition, any animal experiencing TTS
would likely also experience stress responses (NRC, 2003).
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
[[Page 2004]]
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 and 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. (2013) 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 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.
Vessel Noise
Vessel noise from the Langseth 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. 2015; 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) 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. 2016a,b; 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 and Parks 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).
[[Page 2005]]
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 (e.g., fin, blue,
minke, humpback, sei, and Bryde's 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
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 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 Langseth are low frequency and continuous,
but would be widely dispersed in both space and time. Vessel traffic
associated with the proposed survey is of low density compared to
traffic associated with commercial shipping, industry support vessels,
or commercial fishing vessels, and would therefore be expected to
represent an insignificant incremental increase in the total amount of
anthropogenic sound input to the marine environment, and the effects of
vessel noise described above are not expected to occur as a result of
this survey. 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. 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).
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
resulting from a strike increased from 45 to 75 percent as vessel speed
increased from 10 to 14 knots, and exceeded 90 percent at 17 knots.
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 knots. The
chances of a lethal injury decline from approximately 80 percent at 15
knots to approximately 20 percent at 8.6 knots. At speeds below 11.8
knots, the chances of lethal injury drop below 50 percent, while the
probability asymptotically increases toward 100 percent above 15 knots.
The vessel speed during seismic survey operations would be
approximately 4.1 knots (7.6 km/h) during MCS reflection surveys and 5
knots (9.3 km/h) during OBS refraction surveys. At this speed, both the
possibility of striking a marine mammal and the possibility of a strike
resulting in serious injury or mortality are so low as to be
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 low.
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. Commercial shipping vessels are
also generally much larger than typical geophysical survey vessels
(e.g., up to 360 m long cargo vessels compared to the 71-m R/V
Langseth). Jensen and Silber (2004) summarized ship strikes of large
whales worldwide from 1975-2003 and found that most collisions occurred
in the open ocean and involved large vessels (e.g., commercial shipping
vessels). 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 knots) 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
[[Page 2006]]
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 during transit. 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 that ``(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 is 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.''
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 (Chroussos, 2000; Creel, 2005; DeVries et al., 2003;
Fair and 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).
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
[[Page 2007]]
audibility be considered when assessing risks associated with noise
exposure (Southall et al., 2007, 2019), animals typically produce sound
at frequencies where they hear best. More recently, Southall et al.
(2019) suggested that certain species amongst 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 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., what is actually a MFA sonar signal)
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 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
[[Page 2008]]
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 10 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 10
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 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 surveys 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 survey operations, numerous cables, lines,
and other objects primarily associated with the airgun array and
hydrophone streamers will be towed behind the Langseth near the water`s
surface. However, we are not aware of any cases of entanglement of
mysticetes in seismic survey equipment. No incidents of entanglement of
marine mammals with seismic survey gear have been documented in over
54,000 nmi (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., 2005; Haley and
Ireland 2006; SIO and NSF 2006; 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. Entanglement in
OBSs and ocean bottom nodes (OBNs) is also not expected to occur. 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 the potential to cause direct physical damage and could
affect bottom-associated fish resources.
Placement of OBSs on 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,
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.,
[[Page 2009]]
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 5 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
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 more recent 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,
[[Page 2010]]
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 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 marine mammals.
A 2017 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 survey 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.
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,
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 these 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
analysis and 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).
Authorized takes would primarily be by Level B harassment, as use
of seismic airguns has the potential to result in disruption of
behavioral patterns for individual marine mammals. There is also some
potential for auditory injury (Level A harassment) for mysticetes and
high frequency cetaceans (i.e.,
[[Page 2011]]
porpoises, Kogia spp.). The proposed mitigation and monitoring measures
are expected to minimize the severity of such taking to the extent
practicable.
As noted previously, no serious injury or mortality is anticipated
or proposed to be authorized for this activity. Below we describe how
the take is estimated.
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 permanent 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. L-DEO's proposed activity includes
the use of impulsive seismic sources. Therefore, the 160 dB re 1 [mu]Pa
(rms) threshold is applicable for analysis of Level B harassment.
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). L-DEO's proposed seismic survey includes
the use of impulsive (seismic airguns) 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>.
Table 3--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.
The proposed 2-D survey would acquire data using the 36-airgun
array with a total discharge of 6,600 in\3\ at a maximum tow depth of
12 m. L-DEO model results are used to determine the 160-dBrms radius
for the 36-airgun array in deep water (>1,000 m) down to a maximum
water depth of 2,000 m. Received sound levels were predicted by L-DEO's
model (Diebold et al., 2010) which 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 homogeneous ocean
layer, unbounded by a seafloor). In addition, propagation measurements
of pulses from the 36-airgun array at a tow depth of 6 m have been
reported in deep water (approximately 1,600 m), intermediate water
depth on the slope (approximately 600-1,100 m), and shallow water
(approximately 50 m) in the Gulf of Mexico in 2007-2008 (Tolstoy et al.
2009; Diebold et al. 2010).
[[Page 2012]]
For deep and intermediate-water cases, the field measurements
cannot be used readily to derive Level A and Level B harassment
isopleths, as at those sites the calibration hydrophone was located at
a roughly constant depth of 350-500 m, which may not intersect all the
SPL isopleths at their widest point from the sea surface down to the
maximum relevant water depth for marine mammals of ~2,000 m. At short
ranges, where the direct arrivals dominate and the effects of seafloor
interactions are minimal, the data recorded at the deep and slope 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, comparisons at short ranges
between sound levels for direct arrivals recorded by the calibration
hydrophone and model results for the same array tow depth are in good
agreement (Fig. 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. 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.
For deep water (>1,000 m), L-DEO used the deep-water radii obtained
from model results down to a maximum water depth of 2,000 m. The radii
for intermediate water depths (100-1,000 m) were 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 Fig. 16 in Appendix H of NSF-USGS, 2011).
L-DEO's modeling methodology is described in greater detail in
their IHA application. The estimated distances to the Level B
harassment isopleths for the array are shown in Table 4. Please note
that no survey effort will occur in waters <100 m deep. The estimated
isopleth distance specific to shallow water depths are provided for
reference only.
Table 4--Predicted Radial Distances to Isopleths Corresponding to Level B Harassment Threshold
----------------------------------------------------------------------------------------------------------------
Level B
Source and volume Tow depth (m) Water depth harassment
(m) zone (m)
----------------------------------------------------------------------------------------------------------------
36 airgun array; 6,600 in\3\.................................... 12 >1,000 \1\ 6,733
100-1,000 \2\ 10,100
\3\ <100 \4\ 25,494
----------------------------------------------------------------------------------------------------------------
\1\ Distance based on L-DEO model results.
\2\ Distance is based on L-DEO model results with a 1.5 x correction factor between deep and intermediate water
depths.
\3\ No survey effort will occur in waters <100 m deep.
\4\ Distance is based on empirically derived measurements in the Gulf of Mexico (GoM) with scaling applied to
account for differences in tow depth.
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 source modeling 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
2018). 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 values for SEL<INF>cum</INF> and peak SPL for the Langseth
airgun arrays were derived from calculating the modified far-field
signature. The far-field signature is often used as a theoretical
representation of the source level. To compute the far-field signature,
the source level is estimated at a large distance 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,
when the source is an array of multiple airguns separated in space, the
source level from the theoretical far-field signature is not
necessarily the best measurement of the source level that is physically
achieved at the source (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 far-field 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 far-field signature. Because the far-field signature
does not take into account the large array effect near the source and
is calculated as a point source, the modified far-field signature is a
more appropriate measure of the sound source level for distributed
sound sources, such as airgun arrays. L-DEO used the acoustic modeling
methodology as used for estimating Level B harassment distances with a
small grid step of 1 m in both the inline and depth directions. The
propagation modeling takes into account all airgun
[[Page 2013]]
interactions at short distances from the source, including interactions
between subarrays, which are modeled using the NUCLEUS software to
estimate the notional signature and MATLAB software to calculate the
pressure signal at each mesh point of a grid.
In order to more realistically incorporate the Technical Guidance's
weighting functions over the seismic array's full acoustic band,
unweighted spectrum data for the Langseth's airgun array (modeled in 1
Hz bands) was used to make adjustments (dB) to the unweighted spectrum
levels, by frequency, according to the weighting functions for each
relevant marine mammal hearing group. These adjusted/weighted spectrum
levels were then converted to pressures ([mu]Pa) in order to integrate
them over the entire broadband spectrum, resulting in broadband
weighted source levels by hearing group that could be directly
incorporated within the User Spreadsheet (i.e., to override the
Spreadsheet's more simple weighting factor adjustment). Using the User
Spreadsheet's ``safe distance'' methodology for mobile sources
(described by Sivle et al., 2014) with the hearing group-specific
weighted source levels, and inputs assuming spherical spreading
propagation and information specific to the planned survey (i.e., the
2.2 m/s source velocity and (worst-case) 50-m shot interval, equivalent
to a repetition rate of 23.1 seconds), potential radial distances to
auditory injury zones were then calculated for SEL<INF>cum</INF>
thresholds.
Inputs to the User Spreadsheets in the form of estimated source
levels are shown in Appendix A of L-DEO's application. User
Spreadsheets used by L-DEO to estimate distances to Level A harassment
isopleths for the airgun arrays are also provided in Appendix A of the
application. Outputs from the User Spreadsheets in the form of
estimated distances to Level A harassment isopleths for the survey are
shown in Table 5. As described above, NMFS considers onset of PTS
(Level A harassment) to have occurred when either one of the dual
metrics (SEL<INF>cum</INF> and Peak SPL<INF>flat</INF>) is exceeded
(i.e., metric resulting in the largest isopleth). L-DEO proposes to
conduct two different methods of seismic acquisition, MCS using a
hydrophone streamer (approximately 62 percent of the total survey
effort) and refraction surveys using OBSs (approximately 38 percent of
the total survey effort). The airguns would fire at a shot interval of
50 m (repetition rate of 23 seconds) during MCS surveys and at a 400-m
interval (repetition rate of 155 seconds) during refraction surveys to
OBSs. The distances presented in Table 5 were calculated using the MCS
survey inputs as using the 50-m shot interval provides more
conservative distances than the 400-m shot interval.
Table 5--Modeled Radial Distances (m) to Isopleths Corresponding to Level A Harassment Thresholds
----------------------------------------------------------------------------------------------------------------
Level A harassment zone (m)
Source (volume) Threshold ---------------------------------------------------------------
LF cetaceans MF cetaceans HF cetaceans Otariids
----------------------------------------------------------------------------------------------------------------
36-airgun array (6,600 SELcum............ 320.2 0 1.0 0
in\3\).
Peak.............. 8.9 13.9 268.3 10.6
----------------------------------------------------------------------------------------------------------------
Note that because of some of the assumptions included in the
methods used (e.g., stationary receiver with no vertical or horizontal
movement in response to the acoustic source), isopleths produced may be
overestimates to some degree, which will ultimately result in some
degree of overestimation of Level A harassment. However, these tools
offer the best way to predict appropriate isopleths when more
sophisticated 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,
such as the proposed seismic survey, 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.
Auditory injury is unlikely to occur for mid-frequency cetaceans
and otariid pinnipeds, given very small modeled zones of injury for
those species (all estimated zones less than 15 m for mid-frequency
cetaceans and otariid pinnipeds), in context of distributed source
dynamics. The source level of the array is a theoretical definition
assuming a point source and measurement in the far-field of the source
(MacGillivray, 2006). As described by Caldwell and Dragoset (2000), an
array is not a point source, but one that spans a small area. In the
far-field, individual elements in arrays will effectively work as one
source because individual pressure peaks will have coalesced into one
relatively broad pulse. The array can then be considered a ``point
source.'' For distances within the near-field, i.e., approximately 2-3
times the array dimensions, pressure peaks from individual elements do
not arrive simultaneously because the observation point is not
equidistant from each element. The effect is destructive interference
of the outputs of each element, so that peak pressures in the near-
field will be significantly lower than the output of the largest
individual element. Here, the relevant peak isopleth distances would in
all cases be expected to be within the near-field of the array where
the definition of source level breaks down. Therefore, actual locations
within this distance of the array center where the sound level exceeds
the relevant peak SPL thresholds would not necessarily exist. In
general, Caldwell and Dragoset (2000) suggest that the near-field for
airgun arrays is considered to extend out to approximately 250 m.
In order to provide quantitative support for this theoretical
argument, we calculated expected maximum distances at which the near-
field would transition to the far-field (Table 5). For a specific array
one can estimate the distance at which the near-field transitions to
the far-field by:
[GRAPHIC] [TIFF OMITTED] TN12JA22.028
with the condition that D >> [lambda], and where D is the distance,
L is the longest dimension of the array, and [lambda] is the
wavelength of the signal (Lurton, 2002).
Given that [lambda] can be defined by:
[GRAPHIC] [TIFF OMITTED] TN12JA22.029
where f is the frequency of the sound signal and v is the speed of
the sound in the medium of interest, one can rewrite the equation
for D as:
[GRAPHIC] [TIFF OMITTED] TN12JA22.030
and calculate D directly given a particular frequency and known speed
[[Page 2014]]
of sound (here assumed to be 1,500 meters per second in water, although
this varies with environmental conditions).
To determine the closest distance to the arrays at which the source
level predictions in Table 5 are valid (i.e., maximum extent of the
near-field), we calculated D based on an assumed frequency of 1 kHz. A
frequency of 1 kHz is commonly used in near-field/far-field
calculations for airgun arrays (Zykov and Carr, 2014; MacGillivray,
2006; NSF and USGS, 2011), and based on representative airgun spectrum
data and field measurements of an airgun array used on the Langseth,
nearly all (greater than 95 percent) of the energy from airgun arrays
is below 1 kHz (Tolstoy et al., 2009). Thus, using 1 kHz as the upper
cut-off for calculating the maximum extent of the near-field should
reasonably represent the near-field extent in field conditions.
If the largest distance to the peak sound pressure level threshold
was equal to or less than the longest dimension of the array (i.e.,
under the array), or within the near-field, then received levels that
meet or exceed the threshold in most cases are not expected to occur.
This is because within the near-field and within the dimensions of the
array, the source levels specified in Appendix A of L-DEO's application
are overestimated and not applicable. In fact, until one reaches a
distance of approximately three or four times the near-field distance
the average intensity of sound at any given distance from the array is
still less than that based on calculations that assume a directional
point source (Lurton, 2002). The 6,600-in\3\ airgun array planned for
use during the proposed survey has an approximate diagonal of 28.8 m,
resulting in a near-field distance of 138.7 m at 1 kHz (NSF and USGS,
2011). Field measurements of this array indicate that the source
behaves like multiple discrete sources, rather than a directional point
source, beginning at approximately 400 m (deep site) to 1 km (shallow
site) from the center of the array (Tolstoy et al., 2009), distances
that are actually greater than four times the calculated 140-m near-
field distance. Within these distances, the recorded received levels
were always lower than would be predicted based on calculations that
assume a directional point source, and increasingly so as one moves
closer towards the array (Tolstoy et al., 2009). Given this, relying on
the calculated distance (138.7 m) as the distance at which we expect to
be in the near-field is a conservative approach since even beyond this
distance the acoustic modeling still overestimates the actual received
level. Within the near-field, in order to explicitly evaluate the
likelihood of exceeding any particular acoustic threshold, one would
need to consider the exact position of the animal, its relationship to
individual array elements, and how the individual acoustic sources
propagate and their acoustic fields interact. Given that within the
near-field and dimensions of the array source levels would be below
those assumed here, we believe exceedance of the peak pressure
threshold would only be possible under highly unlikely circumstances.
In consideration of the received sound levels in the near-field as
described above, we expect the potential for Level A harassment of mid-
frequency cetaceans, otariid pinnipeds, and phocid pinnipeds to be de
minimis, even before the likely moderating effects of aversion and/or
other compensatory behaviors (e.g., Nachtigall et al., 2018) are
considered. We do not believe that Level A harassment is a likely
outcome for any mid-frequency cetacean, otariid pinniped, or phocid
pinniped and do not propose to authorize any Level A harassment for
these species.
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.
L-DEO used habitat-based stratified marine mammal densities for
summer for the ETP when available (Barlow et al., 2009), and densities
for the ETP from NMFS (2015b) for all other species (Table 6). Barlow
et al. (2009) used data from 16 NMFS Southwest Fisheries Science Center
(SWFSC) ship-based cetacean and ecosystem assessment surveys between
1986 and 2006 to develop habitat models to predict density for 15
cetacean species in the ETP. Model predictions were then used in
standard line-transect formulae to estimate density for each transect
segment for each survey year. Predicted densities for each year were
smoothed with geospatial methods to obtain a continuous grid of density
estimates for the surveyed area in the ETP. These annual grids were
then averaged to obtain a composite grid that represents our best
estimates of cetacean density over the past 20 years in the ETP. The
models developed by Barlow et al. (2009) have been incorporated into a
web-based GIS software system developed by Duke University's Strategic
Environmental Research and Development Program. The habitat-based
density models consist of 100 km x 100 km grid cells. Densities in the
grid cells that overlapped the survey area were averaged for each of
the three water depth categories (shallow, intermediate, deep).
The NMFS SWFSC also developed density estimates for species in the
ETP that may be affected by their own fisheries research activities
(NMFS 2015b). These estimates were derived from abundance estimates
using ship-based surveys of marine mammals in the ETP, as reported by
Gerrodette et al. (2008). While the SWFSC developed volumetric density
estimates (animals/km\3\) to account for typical dive depth of each
species (0-200 m and >200 m), L-DEO used the area density (animals/
km\2\) to represent expected density across all water depth strata.
For the sei whale, for which NMFS (2015b) reported a density of
zero, L-DEO used the spring density for Baja from U.S. Navy (2017b). No
regional density estimates are available for Guadalupe fur seals in the
ETP; therefore, NMFS (2015b) used the density of Guadalupe fur seals in
the California Current Ecosystem (CCE) as a proxy. However, as the
survey area is south of the typical range of Guadalupe fur seals (Ortiz
et al., 2019), the density from the CCE is likely an overestimate. In
the survey area, Guadalupe fur seals are extremely unlikely to occur in
waters over the continental shelf under 2,000 m (T. Norris, pers.
comm.). NMFS has therefore assumed that the density of Guadalupe fur
seals in water depths under 2,000 m is zero animals per square km, and
have retained the CCE density estimate for waters over 2,000 m deep
(Table 6).
[[Page 2015]]
Table 6--Estimated Densities of Marine Mammals in the Proposed Survey Area
----------------------------------------------------------------------------------------------------------------
Density (#/km\2\) in survey area
-----------------------------------------------
Species Intermediate
Shallow water water (100- Deep water
(<100 m) 1,000 m) (>1,000 m)
----------------------------------------------------------------------------------------------------------------
Humpback whale.................................................. \1\ 0.00013 \1\ 0.00013 \1\ 0.00013
Minke whale..................................................... \1\ 0.00001 \1\ 0.00001 \1\ 0.00001
Bryde's whale................................................... \2\ 0.000486 \2\ 0.000489 \2\ 0.000451
Fin whale....................................................... \1\ 0.00003 \1\ 0.00003 \1\ 0.00003
Sei whale....................................................... \3\ 0.00005 \3\ 0.00005 \3\ 0.00005
Blue whale...................................................... \2\ 0.00010 \2\ 0.00009 \2\ 0.00008
Sperm whale..................................................... \1\ 0.00019 \1\ 0.00019 \1\ 0.00019
Cuvier's beaked whale........................................... \2\ 0.00105 \2\ 0.00106 \2\ 0.00107
Longman's beaked whale.......................................... \1\ 0.00004 \1\ 0.00004 \1\ 0.00004
Mesoplodon spp \4\.............................................. \2\ 0.00032 \2\ 0.00033 \2\ 0.00036
Risso's dolphin................................................. \1\ 0.00517 \1\ 0.00517 \1\ 0.00517
Rough-toothed dolphin........................................... \2\ 0.00880 \2\ 0.00891 \2\ 0.00945
Common bottlenose dolphin....................................... \2\ 0.04809 \2\ 0.04502 \2\ 0.03557
Pantropical spotted dolphin..................................... \1\ 0.12263 \1\ 0.12263 \1\ 0.12263
Spinner dolphin (whitebelly).................................... \2\ 0.00148 \2\ 0.00155 \2\ 0.00193
Spinner dolphin (eastern)....................................... \2\ 0.13182 \2\ 0.12989 \2\ 0.12791
Striped dolphin................................................. \2\ 0.02800 \2\ 0.02890 \2\ 0.03516
Short-beaked common dolphin..................................... \2\ 0.04934 \2\ 0.04881 \2\ 0.04435
Fraser's dolphin................................................ \1\ 0.01355 \1\ 0.01355 \1\ 0.01355
Short-finned pilot whale \5\.................................... \2\ 0.00346 \2\ 0.00344 \2\ 0.00382
Killer whale.................................................... \1\ 0.0004 \1\ 0.0004 \1\ 0.0004
False killer whale.............................................. \1\ 0.00186 \1\ 0.00186 \1\ 0.00186
Pygmy killer whale.............................................. \1\ 0.00183 \1\ 0.00183 \1\ 0.00183
Melon-headed whale.............................................. \1\ 0.00213 \1\ 0.00213 \1\ 0.00213
Kogia spp....................................................... \1\ 0.00053 \1\ 0.00053 \1\ 0.00053
Guadalupe fur seal.............................................. 0 \1\ \6\ \1\ 0.00741
0.00741
California sea lion............................................. \1\ 0.16262 \1\ 0.16262 \7\ 0
----------------------------------------------------------------------------------------------------------------
\1\ Density in greater ETP (NMFS 2015b).
\2\ Density in proposed survey area (Barlow et al., 2009).
\3\ Density for Baja (U.S. Navy 2017b).
\4\ Density for Mesoplodon species guild (Blainville's beaked whale, Gingko-toothed beaked whale, Deraniyagala's
beaked whale, and pygmy beaked whale).
\5\ Density for Globicephala species guild.
\6\ Density is assumed to be zero in waters <2,000 m.
\7\ Density is assumed to be zero in deep water (>1,000 m).
Take Calculation and Estimation
Here we describe how the information provided above is brought
together to produce a quantitative take estimate.
In order to estimate the number of marine mammals predicted to be
exposed to sound levels that would result in Level A or Level B
harassment, radial distances from the airgun array to predicted
isopleths corresponding to the Level A harassment and Level B
harassment thresholds are calculated, as described above. Those radial
distances are then used to calculate the area(s) around the airgun
array predicted to be ensonified to sound levels that exceed the Level
A and Level B harassment thresholds. L-DEO identified specific seismic
survey trackline(s) that could be surveyed on one day of research; in
this case, a representative 182-km MCS line and a 222-km long OBS line
were chosen. The distances to the 160-dB Level B harassment threshold
and PTS (Level A harassment) thresholds (based on L-DEO model results)
were used to draw a buffer around every transect line in GIS to
determine the daily ensonified area in each depth category. The
ensonified areas were then multiplied by the number of survey days (7
days for OBS survey effort; 13 days for MCS survey effort) increased by
25 percent. As noted previously, L-DEO has added 25 percent in the form
of operational days, which is equivalent to adding 25 percent to the
proposed line kilometers to be surveyed. This accounts for the
possibility that additional operational days are required, but likely
results in an overestimate of actual exposures. For additional details
regarding calculations of ensonified area, please see Appendix D of L-
DEO's application. L-DEO's estimated incidents of exposure above Level
A and Level B harassment criteria are presented in Table 7.
As previously noted, NMFS does not have authority under the MMPA
within the territorial seas of foreign nations (from 0-12 nmi (22.2 km)
from shore), as the MMPA does not apply in those waters, and therefore
does not authorize incidental take that may occur as a result of
activities occurring within territorial waters. However, NMFS has still
calculated the estimated level of incidental take in the entire
activity area (including Mexican territorial waters) as part of the
analysis supporting our determination under the MMPA that the activity
will have a negligible impact on the affected species. The total
estimated take in U.S. and Mexican waters is presented in Table 8 (see
Negligible Impact Analysis and Determination).
L-DEO generally assumed that their estimates of marine mammal
exposures above harassment thresholds to equate to take and requested
authorization of those takes. Those estimates in turn form the basis
for our proposed take authorization numbers. For the species for which
NMFS does not expect there to be a reasonable potential for take by
Level A harassment to occur, i.e., mid-frequency cetaceans and all
pinnipeds, we have added L-DEO's estimated exposures above Level A
harassment thresholds (and requests for take by Level A harassment) to
their estimated exposures above the Level B harassment threshold to
produce a total number of incidents of take by Level B harassment
[[Page 2016]]
that is proposed for authorization. Estimated exposures and proposed
take numbers for authorization are shown in Table 7.
Table 7--Estimated and Proposed Take by Level A and Level B Harassment, and Percentage of Population
--------------------------------------------------------------------------------------------------------------------------------------------------------
Estimated Estimated Proposed takes Proposed takes Regional
Species takes by Level takes by Level by Level B by Level A Total proposed population Percent of
B harassment A harassment harassment harassment take size population
--------------------------------------------------------------------------------------------------------------------------------------------------------
Humpback whale.......................... 8 0 8 0 8 \a\ 2,566 0.31
Minke whale............................. 1 0 \b\ 2 0 \b\ 2 115 1.74
Bryde's whale........................... 27 1 27 1 28 \a\ 649 4.31
Fin whale............................... 2 0 2 0 2 \a\ 145 1.38
Sei whale............................... 3 0 3 0 3 \c\ 29,600 0.01
Blue whale.............................. 5 0 5 0 5 773 0.65
Sperm whale............................. 12 0 12 0 12 2,810 0.43
Cuvier's beaked whale................... 69 0 69 0 69 \c\ 20,000 0.35
Longman's beaked whale.................. 3 0 3 0 3 \c\ 1,007 0.30
Mesoplodon spp.......................... 23 0 23 0 23 \c\ 25,300 0.09
Risso's dolphin......................... 327 1 328 0 328 \a\ 24,084 1.36
Rough-toothed dolphin................... 596 1 597 0 597 \a\ 37,511 1.59
Common bottlenose dolphin............... 2,268 6 2274 0 2274 \a\ 61,536 3.70
Pantropical spotted dolphin............. 7,973 15 7988 0 7988 \a\ 146,296 5.46
Spinner dolphin (whitebelly)............ 121 0 121 0 121 \a\ 186,906 0.06
Spinner dolphin (eastern)............... 8,173 16 8,189 0 8189 \a\ 186,906 4.38
Striped dolphin......................... 2,209 3 2212 0 2212 \a\ 128,867 1.72
Short-beaked common dolphin............. 2,812 6 2818 0 2818 \a\ 283,196 1.00
Fraser's dolphin........................ 856 2 858 0 858 \c\ 289,300 0.30
Short-finned pilot whale................ 244 0 244 0 244 \a\ 3,348 7.29
Killer whale............................ 25 0 25 0 25 \a\ 852 2.93
False killer whale...................... 118 0 118 0 118 \c\ 39,600 0.30
Pygmy killer whale...................... 116 0 116 0 116 \c\ 38,900 0.30
Melon-headed whale...................... 135 0 135 0 135 \c\ 45,400 0.30
Kogia spp............................... 33 1 33 1 34 \c\ \d\ 11,200 0.30
Guadalupe fur seal...................... 415 1 416 0 416 \c\ 34,187 1.22
California sea lion..................... 349 16 365 0 365 \c\ 105,000 0.35
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ Estimated population in Pacific waters of Mexico (Gerrodette and Palacios (1996)).
\b\ Proposed take increased to maximum group size.
\c\ Population in ETP or wider Pacific (NMFS 2015b).
\d\ Population of Kogia species guild.
Proposed Mitigation
In order to issue an IHA under section 101(a)(5)(D) of the MMPA,
NMFS must set forth the permissible methods of taking pursuant to the
activity, and other means of effecting the least practicable impact on
the species or stock and its habitat, paying particular attention to
rookeries, mating grounds, and areas of similar significance, and on
the availability of the species or stock for taking for certain
subsistence uses (latter not applicable for this action). NMFS
regulations require applicants for incidental take authorizations to
include information about the availability and feasibility (economic
and technological) of equipment, methods, and manner of conducting the
activity or other means of effecting the least practicable adverse
impact upon the affected species or stocks and their habitat (50 CFR
216.104(a)(11)).
In evaluating how mitigation may or may not be appropriate to
ensure the least practicable adverse impact on species or stocks and
their habitat, as well as subsistence uses where applicable, we
carefully consider two primary factors:
(1) The manner in which, and the degree to which, the successful
implementation of the measure(s) is expected to reduce impacts to
marine mammals, marine mammal species or stocks, and their habitat.
This considers the nature of the potential adverse impact being
mitigated (likelihood, scope, range). It further considers the
likelihood that the measure will be effective if implemented
(probability of accomplishing the mitigating result if implemented as
planned) and the likelihood of effective implementation (probability
implemented as planned); and
(2) The practicability of the measures for applicant
implementation, which may consider such things as cost, impact on
operations, and, in the case of a military readiness activity,
personnel safety, practicality of implementation, and impact on the
effectiveness of the military readiness activity.
In order to satisfy the MMPA's least practicable adverse impact
standard, NMFS has evaluated a suite of basic mitigation protocols for
seismic surveys that are required regardless of the status of a stock.
Additional or enhanced protections may be required for species whose
stocks are in particularly poor health and/or are subject to some
significant additional stressor that lessens that stock's ability to
weather the effects of the specified activities without worsening its
status. We reviewed seismic mitigation protocols required or
recommended elsewhere
[[Page 2017]]
(e.g., HESS, 1999; DOC, 2013; IBAMA, 2018; Kyhn et al., 2011; JNCC,
2017; DEWHA, 2008; BOEM, 2016; DFO, 2008; GHFS, 2015; MMOA, 2016;
Nowacek et al., 2013; Nowacek and Southall, 2016), recommendations
received during public comment periods for previous actions, and the
available scientific literature. We also considered recommendations
given in a number of review articles (e.g., Weir and Dolman, 2007;
Compton et al., 2008; Parsons et al., 2009; Wright and Cosentino, 2015;
Stone, 2015b). This exhaustive review and consideration of public
comments regarding previous, similar activities has led to development
of the protocols included here.
Vessel-Based Visual Mitigation Monitoring
Visual monitoring requires the use of trained observers (herein
referred to as visual protected species observers (PSOs)) to scan the
ocean surface for the presence of marine mammals. The area to be
scanned visually includes primarily the exclusion zone (EZ), within
which observation of certain marine mammals requires shutdown of the
acoustic source, but also a buffer zone and, to the extent possible
depending on conditions, the surrounding waters. The buffer zone means
an area beyond the EZ to be monitored for the presence of marine
mammals that may enter the EZ. During pre-start clearance monitoring
(i.e., before ramp-up begins), the buffer zone also acts as an
extension of the EZ in that observations of marine mammals within the
buffer zone would also prevent airgun operations from beginning (i.e.,
ramp-up). The buffer zone encompasses the area at and below the sea
surface from the edge of the 0-500 m EZ, out to a radius of 1,000 m
from the edges of the airgun array (500-1,000 m). This 1,000-m zone (EZ
plus buffer) represents the pre-start clearance zone. Visual monitoring
of the EZ and adjacent waters is intended to establish and, when visual
conditions allow, maintain zones around the sound source that are clear
of marine mammals, thereby reducing or eliminating the potential for
injury and minimizing the potential for more severe behavioral
reactions for animals occurring closer to the vessel. Visual monitoring
of the buffer zone is intended to (1) provide additional protection to
marine mammals that may be in the vicinity of the vessel during pre-
start clearance, and (2) during airgun use, aid in establishing and
maintaining the EZ by alerting the visual observer and crew of marine
mammals that are outside of, but may approach and enter, the EZ.
L-DEO must use dedicated, trained, NMFS-approved PSOs. The PSOs
must have no tasks other than to conduct observational effort, record
observational data, and communicate with and instruct relevant vessel
crew with regard to the presence of marine mammals and mitigation
requirements. PSO resumes shall be provided to NMFS for approval.
At least one of the visual and two of the acoustic PSOs (discussed
below) aboard the vessel must have a minimum of 90 days at-sea
experience working in those roles, respectively, with no more than 18
months elapsed since the conclusion of the at-sea experience. One
visual PSO with such experience shall be designated as the lead for the
entire protected species observation team. The lead PSO shall serve as
primary point of contact for the vessel operator and ensure all PSO
requirements per the IHA are met. To the maximum extent practicable,
the experienced PSOs should be scheduled to be on duty with those PSOs
with appropriate training but who have not yet gained relevant
experience.
During survey operations (e.g., any day on which use of the
acoustic source is planned to occur, and whenever the acoustic source
is in the water, whether activated or not), a minimum of two visual
PSOs must be on duty and conducting visual observations at all times
during daylight hours (i.e., from 30 minutes prior to sunrise through
30 minutes following sunset). Visual monitoring of the pre-start
clearance zone must begin no less than 30 minutes prior to ramp-up, and
monitoring must continue until one hour after use of the acoustic
source ceases or until 30 minutes past sunset. Visual PSOs shall
coordinate to ensure 360[deg] visual coverage around the vessel from
the most appropriate observation posts, and shall conduct visual
observations using binoculars and the naked eye while free from
distractions and in a consistent, systematic, and diligent manner.
PSOs shall establish and monitor the exclusion and buffer zones.
These zones shall be based upon the radial distance from the edges of
the acoustic source (rather than being based on the center of the array
or around the vessel itself). During use of the acoustic source (i.e.,
anytime airguns are active, including ramp-up), detections of marine
mammals within the buffer zone (but outside the EZ) shall be
communicated to the operator to prepare for the potential shutdown of
the acoustic source. Visual PSOs will immediately communicate all
observations to the on duty acoustic PSO(s), including any
determination by the PSO regarding species identification, distance,
and bearing and the degree of confidence in the determination. Any
observations of marine mammals by crew members shall be relayed to the
PSO team. During good conditions (e.g., daylight hours; Beaufort sea
state (BSS) 3 or less), visual PSOs shall conduct observations when the
acoustic source is not operating for comparison of sighting rates and
behavior with and without use of the acoustic source and between
acquisition periods, to the maximum extent practicable.
Visual PSOs may be on watch for a maximum of 4 consecutive hours
followed by a break of at least one hour between watches and may
conduct a maximum of 12 hours of observation per 24-hour period.
Combined observational duties (visual and acoustic but not at same
time) may not exceed 12 hours per 24-hour period for any individual
PSO.
Passive Acoustic Monitoring
Acoustic monitoring means the use of trained personnel (sometimes
referred to as passive acoustic monitoring (PAM) operators, herein
referred to as acoustic PSOs) to operate PAM equipment to acoustically
detect the presence of marine mammals. Acoustic monitoring involves
acoustically detecting marine mammals regardless of distance from the
source, as localization of animals may not always be possible. Acoustic
monitoring is intended to further support visual monitoring (during
daylight hours) in maintaining an EZ around the sound source that is
clear of marine mammals. In cases where visual monitoring is not
effective (e.g., due to weather, nighttime), acoustic monitoring may be
used to allow certain activities to occur, as further detailed below.
PAM would take place in addition to the visual monitoring program.
Visual monitoring typically is not effective during periods of poor
visibility or at night, and even with good visibility, is unable to
detect marine mammals when they are below the surface or beyond visual
range. Acoustic monitoring can be used in addition to visual
observations to improve detection, identification, and localization of
cetaceans. The acoustic monitoring would serve to alert visual PSOs (if
on duty) when vocalizing cetaceans are detected. It is only useful when
marine mammals vocalize, but it can be effective either by day or by
night, and does not depend on good visibility. It would be monitored in
real time so that the visual observers can be advised when cetaceans
are detected.
The R/V Langseth will use a towed PAM system, which must be
monitored
[[Page 2018]]
by at a minimum one on duty acoustic PSO beginning at least 30 minutes
prior to ramp-up and at all times during use of the acoustic source.
Acoustic PSOs may be on watch for a maximum of 4 consecutive hours
followed by a break of at least one hour between watches and may
conduct a maximum of 12 hours of observation per 24-hour period.
Combined observational duties (acoustic and visual but not at same
time) may not exceed 12 hours per 24-hour period for any individual
PSO.
Survey activity may continue for 30 minutes when the PAM system
malfunctions or is damaged, while the PAM operator diagnoses the issue.
If the diagnosis indicates that the PAM system must be repaired to
solve the problem, operations may continue for an additional 5 hours
without acoustic monitoring during daylight hours only under the
following conditions:
<bullet> Sea state is less than or equal to BSS 4;
<bullet> No marine mammals (excluding delphinids) detected solely
by PAM in the applicable EZ in the previous 2 hours;
<bullet> NMFS is notified via email as soon as practicable with the
time and location in which operations began occurring without an active
PAM system; and
<bullet> Operations with an active acoustic source, but without an
operating PAM system, do not exceed a cumulative total of 5 hours in
any 24-hour period.
Establishment of Exclusion and Pre-Start Clearance Zones
An EZ is a defined area within which occurrence of a marine mammal
triggers mitigation action intended to reduce the potential for certain
outcomes, e.g., auditory injury, disruption of critical behaviors. The
PSOs would establish a minimum EZ with a 500-m radius. The 500-m EZ
would be based on radial distance from the edge of the airgun array
(rather than being based on the center of the array or around the
vessel itself). With certain exceptions (described below), if a marine
mammal appears within or enters this zone, the acoustic source would be
shut down.
The pre-start clearance zone is defined as the area that mus
[…truncated; see source link]Indexed from Federal Register on January 12, 2022.
This is legal information, not legal advice. Laws vary by jurisdiction and change frequently. Always verify current law with official sources and consult a licensed attorney in your jurisdiction for advice on your specific situation.