Notice2023-12040
Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to a Marine Geophysical Survey of the Blake Plateau in the Northwest Atlantic Ocean
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
June 7, 2023
Issuing agencies
Commerce DepartmentNational Oceanic and Atmospheric Administration
Abstract
NMFS has received a request from Lamont-Doherty Earth Observatory (L-DEO) for authorization to take marine mammals incidental to a marine geophysical survey of the Blake Plateau in the northwest Atlantic Ocean. 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, 1-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.
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[Federal Register Volume 88, Number 109 (Wednesday, June 7, 2023)]
[Notices]
[Pages 37390-37422]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2023-12040]
[[Page 37389]]
Vol. 88
Wednesday,
No. 109
June 7, 2023
Part III
Department of Commerce
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National Oceanic and Atmospheric Administration
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Takes of Marine Mammals Incidental to Specified Activities; Taking
Marine Mammals Incidental to a Marine Geophysical Survey of the Blake
Plateau in the Northwest Atlantic Ocean; Notice
Federal Register / Vol. 88, No. 109 / Wednesday, June 7, 2023 /
Notices
[[Page 37390]]
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DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
[RTID 0648-XC877]
Takes of Marine Mammals Incidental to Specified Activities;
Taking Marine Mammals Incidental to a Marine Geophysical Survey of the
Blake Plateau in the Northwest Atlantic Ocean
AGENCY: National Marine Fisheries Service (NMFS), National Oceanic and
Atmospheric Administration (NOAA), Commerce.
ACTION: Notice; proposed incidental harassment authorization; request
for comments on proposed authorization and possible renewal.
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SUMMARY: NMFS has received a request from Lamont-Doherty Earth
Observatory (L-DEO) for authorization to take marine mammals incidental
to a marine geophysical survey of the Blake Plateau in the northwest
Atlantic Ocean. 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, 1-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 July 7,
2023.
ADDRESSES: Comments should be addressed to Jolie Harrison, Chief,
Permits and Conservation Division, Office of Protected Resources, NMFS,
and should be submitted via email to <a href="/cdn-cgi/l/email-protection#aae3fefa84c2cbd8c6cbc9c2cfd8eac4c5cbcb84cdc5dc"><span class="__cf_email__" data-cfemail="e4adb0b4ca8c85968885878c8196a48a8b8585ca838b92">[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), confidential business information,
or otherwise sensitive information voluntarily submitted by the
commenter may be publicly accessible. Do not submit confidential
business information or otherwise sensitive or protected information.
FOR FURTHER INFORMATION CONTACT: Jenna Harlacher, Office of Protected
Resources, NMFS, (301) 427-8401.
Electronic copies of the application and supporting documents, as
well as a list of the references cited in this document, may be
obtained online at: <a href="http://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-research-and-other-activities">www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-research-and-other-activities</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. Section 101(a)(5)(A) and (D) of the MMPA (16 U.S.C. 1361 et
seq.) directs 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 IHA 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 (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) Environmental Assessment (EA), as we have preliminarily
determined that it includes adequate information analyzing the effects
on the human environment of issuing the IHA. NSF's draft EA is
available at <a href="https://www.nsf.gov/geo/oce/envcomp/blake-plateau-2023/Blake-Plateau-Rev-Draft-EA-12-Jan.pdf">https://www.nsf.gov/geo/oce/envcomp/blake-plateau-2023/Blake-Plateau-Rev-Draft-EA-12-Jan.pdf</a>.
Summary of Request
On November 22, 2022, NMFS received a request from L-DEO for an IHA
to take marine mammals incidental to a marine geophysical survey of the
Blake Plateau in the northwest Atlantic Ocean. The application was
deemed adequate and complete on February 1, 2023. L-DEO's request is
for take of 29 marine mammal species by Level B harassment, and for 4
of these species, by Level A harassment. Neither L-DEO nor NMFS expect
serious injury or mortality to result from this activity and,
therefore, an IHA is appropriate.
Description of Proposed Activity
Overview
Researchers from the University of Texas Institute of Geophysics
(UTIG) and L-DEO, with funding from the NSF, propose to conduct
research, including high-energy seismic surveys using airguns as the
acoustic source, from the research vessel (R/V) Marcus G. Langseth
(Langseth). The surveys would occur in the Blake Plateau in the
northwestern Atlantic Ocean during summer or fall 2023. The proposed
multi-channel seismic (MCS) reflection and Ocean Bottom Seismometers
(OBS) seismic refraction surveys would occur within the Exclusive
Economic Zone (EEZ) of the United States and Bahamas and in
international waters, in depths ranging from >100 to 5,200 meters (m).
To complete this survey, the R/V Langseth would tow a 36-airgun array
consisting of a mixture of Bolt airguns ranging from 40-360 cubic
inches (in\3\) (1-9.1 m\3\) each on 4 strings spaced 16 m apart, with a
total discharge volume of 6,600 in\3\ (167.6 m\3\). The acoustic source
would be towed at 10-12 m deep along the survey lines, while the
receiving systems for the different survey segments would consist of a
15 kilometer (km) long solid-state hydrophone streamer and
approximately 40 OBS, respectively.
[[Page 37391]]
The proposed study would acquire two-dimensional (2-D) seismic
reflection and seismic refraction data to examine the structure and
evolution of the rifted margins of the southeastern United States,
including the rift dynamics during the formation of the Carolina Trough
and Blake Plateau. Additional data would be collected using a multibeam
echosounder (MBES), a sub-bottom profiler (SBP), and an Acoustic
Doppler Current Profiler (ADCP), which would be operated from R/V
Langseth continuously during the seismic surveys, including during
transit. No take of marine mammals is expected to result from use of
this equipment.
Dates and Duration
The proposed survey is expected to last for approximately 61 days,
spread between two operational legs, with 40 days of seismic
operations. One leg would include 32 days of MCS seismic operations and
4 days of transit time, whereas the other leg would consist of 8 days
of seismic operations with OBSs, 13 days of OBS deployment, and 4 days
of transit. R/V Langseth would likely leave from and return to port in
Jacksonville, Florida during summer or fall 2023.
Specific Geographic Region
The proposed survey would occur within approximately 27.5-33.5[deg]
N, 74-80[deg] W off the coasts of South Carolina to northern Florida in
the northwest Atlantic Ocean. The distances to all state waters would
be >80 km, and to the coast would be ~90 km off Georgia, ~98 km off
Florida, and ~107 km off South Carolina. The region where the survey is
proposed to occur is depicted in Figure 1; the tracklines could occur
anywhere within the polygon shown in Figure 1. Representative survey
tracklines are shown, however, some deviation in actual tracklines,
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
surveys are proposed to occur within the EEZs of the United States and
Bahamas and in international waters, in depths ranging from >100-5,200
m deep.
[GRAPHIC] [TIFF OMITTED] TN07JN23.000
[[Page 37392]]
Detailed Description of the Specified Activity
The procedures to be used for the proposed surveys would be similar
to those used during previous seismic surveys by L-DEO and would use
conventional seismic methodology. The surveys would involve one source
vessel, R/V Langseth, which is owned and operated by L-DEO. During MCS
seismic reflection and OBS seismic refraction surveys, R/V Langseth
would tow 4 strings with 36 airguns, consisting of a mixture of Bolt
1500LL and Bolt 1900LLX. During the surveys, all 4 strings, totaling 36
active airguns with a total discharge volume of 6,600 in\3\, would be
used. The four airgun strings would be spaced 16 m apart, distributed
across an area of approximately 24 m x 16 m behind the R/V Langseth,
and would be towed approximately 140 m behind the vessel. The array
would be towed at a depth of 10-12 m, and the shot interval would be 50
m (~24 seconds (s)) during MCS seismic reflection surveys and 200 m
(~78 s) during OBS seismic refraction surveys. The airgun array
configuration is illustrated in Figure 2-13 of NSF and 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 receiving system for the MCS survey would consist of a 15-km long
solid-state hydrophone streamer (solid flexible polymer) and ~40 OBSs
for the OBS portion of the survey. As the airgun arrays are towed along
the survey lines, the hydrophone streamer would transfer the data to
the on-board processing system for the MCS survey, and the OBSs would
receive and store the returning acoustic signals internally for later
analysis for the OBS survey.
Approximately 6,682 km of seismic acquisition are proposed: 5,730
km of 2-D MCS seismic reflection data and 952 km of OBS refraction
data. Overall, just over half (55 percent) of all survey effort would
occur in intermediate water (100-1,000 m deep), and 45 percent would
occur in deep water (>1,000 m deep); no seismic acquisition would take
place in shallow water (<100 m). When only MCS reflection surveys are
considered, most of the effort (58 percent) would occur in
intermediate-depth water, and 42 percent of effort would occur in deep
water. When only refraction surveys with OBSs are considered, most of
that effort (60 percent) would occur in deep water, and 40 percent
would occur in intermediate-depth water. Refraction surveys with OBSs
would be acquired along two lines--one 456-km long line across the
southern Carolina Trough (32 OBS drops) and a 496-km long line across
Blake Plateau (39 OBS drops). Following refraction shooting of one
line, OBSs on that line would be recovered, serviced, and redeployed on
a subsequent refraction line. In addition to the operations of the
airgun array, the ocean floor would be mapped with the Kongsberg EM 122
MBES and a Knudsen Chirp 3260 SBP. A Teledyne RDI 75 kHz Ocean Surveyor
ADCP would be used to measure water current velocities.
All planned geophysical data acquisition activities would be
conducted by L-DEO with on-board assistance by the scientists who have
proposed the studies. The vessel would be self-contained, and the crew
would live aboard the vessel. Take of marine mammals is not expected to
occur incidental to use of the MBES, SBP, and ADCP, whether or not the
airguns are operating simultaneously with the other sources. Given
their characteristics (e.g., narrow downward-directed beam), marine
mammals would experience no more than one or two brief ping exposures,
if any exposure were to occur. NMFS does not expect that the use of
these sources presents any reasonable potential to cause take of marine
mammals.
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 L-DEO's application summarize available
information regarding status and trends, distribution and habitat
preferences, and behavior and life history, of the potentially affected
species. Additional information regarding population trends and threats
may be found in NMFS' Stock Assessment Reports (SARs;
<a href="http://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments">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'
website (<a href="http://www.fisheries.noaa.gov/find-species">www.fisheries.noaa.gov/find-species</a>). NMFS refers the reader
to the application and to the aforementioned sources for general
information regarding the species listed in Table 1.
Table 1 lists all species or stocks for which take is expected and
proposed to be authorized for this activity, 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. 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'
SARs). While no serious injury or mortality is expected to occur, PBR
and annual serious injury and mortality from anthropogenic sources are
included here as gross indicators of the status of the species or
stocks 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' 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 stocks managed under the MMPA in this region
are assessed in NMFS' U.S. Atlantic and Gulf of Mexico SARs (e.g.,
Hayes et al., 2019, 2020, 2022). All values presented in Table 1 are
the most recent available (including the draft 2022 SARs) at the time
of publication and are available online at: <a href="http://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments">www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments</a>.
[[Page 37393]]
Table 1--Species Likely Impacted by the Specified Activities
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ESA/MMPA Stock abundance
status; (CV, Nmin, most Modeled Annual M/
Common name Scientific name Stock strategic (Y/N) recent abundance abundance PBR SI \3\
\1\ survey) \2\ \5\
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Order Cetartiodactyla--Cetacea--Superfamily Mysticeti (baleen whales)
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Family Balaenopteridae (rorquals):
Humpback whale................ Megaptera Gulf of Maine........ -/-; N 1,396 (0; 1,380; \7\ 2,259 22 12.15
novaeangliae. 2016).
Fin whale..................... Balaenoptera physalus Western North E/D; Y 6,802 (0.24; 5,573; \6\ 3,587 11 1.8
Atlantic. 2016).
Sei whale..................... Balaenoptera borealis Nova Scotia.......... E/D; Y 6,292 (1.02; 3,098; \6\ 1,043 6.2 0.8
2016).
Minke whale................... Balaenoptera Canadian East Coast.. -/-; N 21,968 (0.31; \6\ 4,044 170 10.6
acutorostrata. 17,002; 2016).
Blue whale.................... Balaenoptera musculus Western North E/D;Y unk (unk; 402; 1980- \7\ 33 0.8 0
Atlantic. 2008).
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Superfamily Odontoceti (toothed whales, dolphins, and porpoises)
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Family Physeteridae:
Sperm whale................... Physeter North Atlantic....... E/D;Y 4,349 (0.28; 3,451; \6\ 6,576 3.9 0
macrocephalus. 2016).
Family Kogiidae:
Pygmy sperm whale............. Kogia breviceps...... Western North -/-; N 7,750 (0.38; 5,689; \7\ 7,980 46 0
Atlantic. 2016).
Dwarf sperm whale................. Kogia sima........... Western North -/-; N
Atlantic.
Family Ziphiidae (beaked whales):
Cuvier's beaked Whale......... Ziphius cavirostris.. Western North -/-; N 5,744 (0.36, 4,282, \7\ 5,588 43 0.2
Atlantic. 2016).
Blainville's beaked Whale..... Mesoplodon Western North -/-; N 10,107 (0.27; 8,085; \7\ 6,526 \4\ 81 \4\ 0
densirostris. Atlantic. 2016) \4\.
True's beaked whale........... Mesoplodon mirus..... Western North -/-; N
Atlantic.
Gervais' beaked whale......... Mesoplodon europaeus. Western North -/-; N
Atlantic.
Family Delphinidae:
Long-finned pilot whale....... Globicephala melas... Western North -/-; N 39,215 (0.30; 7 8 306 9
Atlantic. 30,627; 2016). 23,905
Short finned pilot whale...... Globicephala Western North -/-;Y 28,924 (0.24; 236 136
macrorhynchus. Atlantic. 23,637; 2016).
Rough-toothed dolphin......... Steno bredanensis.... Western North -/-; N 136 (1.0; 67; 2016). \7\ 1,011 0.7 0
Atlantic.
Bottlenose dolphin............ Tursiops truncatus... Western North -/-; N 62,851 (0.23; \6\ 519 28
Atlantic Offshore. 51,914, 2016). 68,739
Pantropical spotted dolphin... Stenella attenuata... Western North -/-; N 6,593 (0.52; 4,367; \7\ 1,403 44 0
Atlantic. 2016).
Atlantic spotted dolphin...... Stenella frontalis... Western North -/-; N 39,921 (0.27; \6\ 320 0
Atlantic. 32,032; 2016). 39,352
Spinner dolphin............... Stenella longirostris Western North -/-; N 4,102 (0.99; 2,045; \7\ 885 21 0
Atlantic. 2016).
Clymene dolphin............... Stenella clymene..... Western North -/-; N 4,237 (1.03; 2,071; \7\ 8,576 21 0
Atlantic. 2016).
Striped dolphin............... Stenella coeruleoalba Western North -/-; N 67,036 (0.29; \7\ 529 0
Atlantic. 52,939; 2016). 54,707
Fraser's dolphin.............. Lagenodelphis hosei.. Western North -/-; N unk................. \7\ 658 unk 0
Atlantic.
Risso's dolphin............... Grampus griseus...... Western North -/-; N 35,215(0.19; 30,051; \6\ 301 34
Atlantic. 2016). 24,260
Common dolphin................ Delphinus delphis.... Western North -/-; N 172,947 (0.21; \6\ 1,452 390
Atlantic. 145,216; 2016). 144,036
Melon-headed whale............ Peponocephala electra Western North -/-; N unk................. \7\ 618 unk 0
Atlantic.
Pygmy killer whale............ Feresa attenuate..... Western North -/-; N unk................. \7\ 68 unk 0
Atlantic.
False killer whale............ Pseudorca crassidens. Western North -/-; N 1,791 (0.56; 1,154; \7\ 139 12 0
Atlantic. 2016).
Killer whale.................. Orcinus orca......... Western North -/-; N unk................. \7\ 73 unk 0
Atlantic.
Family Phocoenidae (porpoises):
Harbor porpoise............... Phocoena phocoena.... Gulf of Maine/Bay of -/-; N 95,543 (0.31; \7\ 851 164
Fundy. 74,034; 2016). 55,049
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\1\ 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/marine-mammal-stock-assessment-reports-region/">https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessment-reports-region/</a>. CV is coefficient of variation; Nmin is the minimum estimate of stock abundance; unknown (unk).
\3\ These values, found in NMFS' SARs, represent annual levels of human-caused mortality plus serious injury from all sources combined (e.g., commercial
fisheries, ship strike). Annual mortality or serious injury (M/SI) often cannot be determined precisely and is in some cases presented as a minimum
value or range.
\4\ The values for Mesoplodont beaked whales would also represent Sowerby's beaked whales, which are not expected to occur in the survey area.
\5\ Modeled abundance from Roberts and Halpin (2022).
\6\ Averaged monthly (May-Oct) abundance.
\7\ Only single annual abundance given.
\8\ Modeled abundance for pilot whale is grouped together for both short-finned and long-finned pilot whales.
In Table 1 above, NMFS reports two sets of abundance estimates:
Those from NMFS' SARs and those predicted by Roberts and Halpin
(2022)--for the latter, we provide both the mean of monthly (May-
October) abundance and
[[Page 37394]]
the single annual abundance (where applicable). Please see footnotes 6-
7 of Table 1 for more detail. NMFS' SAR estimates are typically
generated from the most recent shipboard and/or aerial surveys
conducted. The spatial scale of the survey area along the Atlantic
coast is small relative to the ability of most cetacean species to
travel within their ranges. As an example, only one sighting of rough-
toothed dolphin occurred in the last two dedicated cetacean abundance
surveys near L-DEO's proposed survey area during 2011 or 2016. The SAR
states that the abundance estimate listed (136) was based on a single
sighting and therefore the abundance estimate is highly uncertain.
Additionally, multiple species with modeled take proposed for
authorization do not have a population abundance listed in the SAR's
even though the last surveys were conducted on these species in 2019.
Studies based on abundance and distribution surveys restricted to U.S.
waters are unable to detect temporal shifts in distribution beyond U.S.
waters that might account for any changes in abundance within U.S.
waters. NMFS' SAR estimates also typically do not incorporate
correction for detection bias. Therefore, they should generally be
considered underestimates, especially for cryptic or long-diving
species (e.g., beaked whales, Kogia spp., sperm whales). Dias and
Garrison (2016) state, for example, that current abundance estimates
for Kogia spp. may be considerably underestimated due to the cryptic
behavior of these species and difficulty of detection in Beaufort sea
state greater than one, and density estimates for certain species
derived from long-term passive acoustic monitoring are much higher than
are estimates derived from visual observations (Mullin and Fulling,
2004; Mullin, 2007; Hildebrand et al., 2012).
The Roberts and Halpin (2022) abundance estimates represent the
output of predictive models derived from multi-year observations and
associated environmental parameters and which incorporate corrections
for detection bias. Incorporating more data over multiple years of
observation can yield different results in either direction, as the
result is not as readily influenced by fine-scale shifts in species
habitat preferences or by the absence of a species in the study area
during a given year. NMFS' abundance estimates show substantial year-
to-year variability in some cases. For these reasons, the Roberts and
Halpin (2022) estimates are generally more realistic and, for these
purposes, represent the best available information. For purposes of
assessing estimated exposures relative to abundance--used in this case
to understand the scale of the predicted takes compared to the
population--NMFS generally believes that the Roberts and Halpin (2022)
abundance predictions are most appropriate because they were used to
generate the exposure estimates and therefore provide the most relevant
comparison. Roberts and Halpin (2022) represents the best available
scientific information regarding marine mammal occurrence and
distribution in the Blake Plateau.
As indicated above, all 29 species in Table 1 temporally and
spatially co-occur with the activity to the degree that take is
reasonably likely to occur. Species that could potentially occur in the
proposed research area but are not likely to be harassed due to the
rarity of their occurrence (i.e., are considered extralimital or rare
visitors to the waters off southeast U.S.), or because their known
migration through the area does not align with the proposed survey
dates, are 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 northern bottlenose whales
(Hyperoodon ampullatus), Sowerby's beaked whales (Mesoplodon bidens),
Atlantic white-sided dolphin (Lagenorhynchus acutus), white-beaked
dolphins (Lagenorhynchus albirostris), harp seals (Pagophilus
groenlandicus), hooded seals (Cystophora cristata), gray seals
(Halichoerus grypus), and harbor seals (Phoca vitulina), which are all
typically distributed further north on the eastern coast of the United
States. In addition to what is included in Sections 3 and 4 of the
application, the SARs, and NMFS' website, further detail informing the
baseline for select species of particular or unique vulnerability
(i.e., information regarding current Unusual Mortality Events (UME) and
important habitat areas) is provided below.
This also includes the North Atlantic right whale (Eubalaena
glacialis), as their migration through waters directly adjacent to the
study area does not align with the proposed survey dates. Based on the
timing of migratory behavior relative to the proposed survey, in
conjunction with the location of the survey in primarily deep waters
beyond the shelf, no right whales would be expected to be subject to
take incidental to the survey. A quantitative, density-based analysis
confirms these conclusions (see Estimated Take, later in this notice).
Elevated North Atlantic right whale mortalities have occurred since
June 7, 2017, along the U.S. and Canadian coast. This event has been
declared an Unusual Mortality Event (UME), with human interactions,
including entanglement in fixed fishing gear and vessel strikes,
implicated in at least 20 of the mortalities thus far. As of May 22,
2023, a total of 36 confirmed dead stranded whales (21 in Canada; 15 in
the United States) have been documented. The cumulative total number of
animals in the North Atlantic right whale UME has been updated to 69
individuals to include both the confirmed mortalities (dead stranded or
floaters) (n=36) and seriously injured free-swimming whales (n=33) to
better reflect the confirmed number of whales likely removed from the
population during the UME and more accurately reflect the population
impacts. More information is available online at:
<a href="http://www.fisheries.noaa.gov/national/marine-life-distress/2017-2022-north-atlantic-right-whale-unusual-mortality-event">www.fisheries.noaa.gov/national/marine-life-distress/2017-2022-north-atlantic-right-whale-unusual-mortality-event</a>.
During 2016, NMFS designated 102,084 km\2\ of combined critical
habitat for North Atlantic right whales in the Gulf of Maine and
Georges Bank region (Unit 1) and off the southeast U.S. coast (Unit 2)
(NMFS 2016b). The 2016 final rule incorporated a southward extension of
Unit 2 such that it now includes nearshore and offshore waters from
Cape Fear to south of Cape Canaveral, Florida (81 FR 4837, January 27,
2016). Unit 2 has been recognized as critical for calving right whales,
and mother-calf pairs are consistently observed there, particularly
during January and February. Unit 2 of the calving critical habitat
occurs more than 50 km west of the proposed survey area in water <100 m
deep.
The proposed survey area is also adjacent to the migratory corridor
Biologically Important Area (BIA) identified for North Atlantic right
whales that extends from Massachusetts to Florida in March-April and
November-December (LeBrecque et al., 2015). This important migratory
area is approximately 269,488 km\2\ and is comprised of the waters of
the continental shelf offshore the East Coast of the United States.
Right whales occur here during seasonal movements north or south
between their feeding and breeding grounds (Firestone et al., 2008;
Knowlton et al., 2002). During their migration, North Atlantic right
whales prefer shallower waters, with the majority of sightings
occurring within 56 km of the coast and in water depths shallower than
45 m (Knowlton et al.,
[[Page 37395]]
2002). When whales are seen further offshore, it is in the northern
part of their migratory path south of New England. Comparatively, L-
DEO's survey would occur at a minimum of 80 km off the coast in water
depths ranging from >100 m to 5,200 m.
Right whales have been observed in or near Georgia waters from
September through April, which coincides with the migratory timeframe
for this species (Knowlton et al., 2002). They have been acoustically
detected throughout the winter months from late October through early
April in the southeastern U.S. (Hodge et al., 2015). They are typically
most common in the spring (late March) when they are migrating north
and in the winter during their southbound migration to the calving
grounds (NOAA Fisheries 2017).
Acoustic detections have been made off the southeastern U.S. in all
seasons with peak occurrence during winter (November-February); fewer
detections were made the rest of the year (Hodge et al., 2015; Davis et
al., 2017; Palka et al., 2021). On WhaleMap (<a href="https://whalemap.org/">https://whalemap.org/</a>),
there are ~2,000 records for the waters off the southeastern U.S.
between 2010 and 2022; all sightings were made between November and
March, but no detections were made in the proposed survey area (Johnson
et al. 2021). Similarly, Hayes et al. (2022) showed numerous sightings
on the shelf off Georgia and Florida for 2015-2019, but no sightings
within the proposed survey area. DoN (2008c) showed peak occurrence on
the shelf off the southeastern U.S. during winter, including some along
the western edge of the proposed survey area; fewer sightings were
reported during fall, and nearly no sightings during spring and summer
(DoN 2008c). Additionally, there are no Ocean Biodiversity Information
System (OBIS) records of right whales for the proposed survey area of
the Blake Plateau (OBIS 2022).
All vessels 65 feet (19.8 meters) or longer must travel at 10 knots
or less in certain locations (called Seasonal Management Areas (SMA))
along the U.S. east coast at certain times of the year to reduce the
threat of vessel collisions with endangered North Atlantic right
whales. The purpose of this mandatory regulation is to reduce the
likelihood of deaths and serious injuries to these endangered whales
that result from collisions with vessels. There are no SMAs designated
within the proposed survey area, however there is a SMA adjacent to the
survey area near Jacksonville, Florida. This SMA is in effect from
November 15 through April 15, requiring vessel speed be restricted in
the area bounded to the north by latitude 31[deg]27' N; to the south by
latitude 29[deg]45' N; and to the east by longitude 080[deg]51'36'' W.
L-DEO intends to complete the survey before November 1, 2023, and NMFS
proposes that use of airguns be limited to the period May 1 through
October 31. Additional restrictions in higher density areas of the
survey area in October are also proposed (see Proposed Mitigation
section). The regulations identifying SMAs (50 CFR 224.105) also
establish a process under which dynamic management areas (DMA) can be
established based on North Atlantic right whale sightings. NMFS
established a Slow Zone program in 2020 that notifies vessel operators
of areas where maintaining speeds of 10 knots (kn; 18.5 km per hour) or
less can help protect North Atlantic right whales from vessel
collisions. Right Whale Slow Zones are established around areas where
right whales have been recently detected; these areas are identical to
DMAs when triggered by right whale visual sightings but they can also
be established when right whale detections are confirmed from acoustic
receivers. More information on SMAs, DMAs, and Slow Zones can be found
at: https://www.fisheries.noaa.gov/national/endangered-species-
conservation/reducing-vessel-strikes-north-atlantic-right-
whales#:~:text=Right%20Whale%20Slow%20Zones%20is,right%20whales%20have%2
0been%20detected.
On August 1, 2022, NMFS announced proposed changes to the existing
North Atlantic right whale vessel speed regulations to further reduce
the likelihood of mortalities and serious injuries to endangered right
whales from vessel collisions, which are a leading cause of the
species' decline and a primary factor in an ongoing UME (87 FR 46921).
Should a final vessel speed rule be issued and become effective during
the effective period of this IHA (or any other MMPA incidental take
authorization), the authorization holder would be required to comply
with any and all applicable requirements contained within the final
rule. Specifically, where measures in any final vessel speed rule are
more protective or restrictive than those in this or any other MMPA
authorization, authorization holders would be required to comply with
the requirements of the rule. Alternatively, where measures in this or
any other MMPA authorization are more restrictive or protective than
those in any final vessel speed rule, the measures in the MMPA
authorization would remain in place. The responsibility to comply with
the applicable requirements of any vessel speed rule would become
effective immediately upon the effective date of any final vessel speed
rule and, when notice is published of the effective date, NMFS would
also notify L-DEO if the measures in the speed rule were to supersede
any of the measures in the MMPA authorization such that they were no
longer applicable.
Humpback Whale
In the western North Atlantic, humpback whales feed during spring,
summer, and fall over a geographic range encompassing the eastern coast
of the United States (including the Gulf of Maine), the Gulf of St.
Lawrence, Newfoundland/Labrador, and western Greenland (Katona and
Beard 1990). The whales that feed on the eastern coast of the United
States are recognized as a distinct feeding stock, known as the Gulf of
Maine stock (Palsb[oslash]ll et al. 2001; Vigness-Raposa et al. 2010).
During winter, these whales mate and calve in the West Indies, where
spatial and genetic mixing among feeding stocks occurs (Katona and
Beard 1990; Clapham et al. 1993; Palsb[oslash]ll et al. 1997; Stevick
et al. 1998; Kennedy et al. 2013).
Humpback whales were listed as endangered under the Endangered
Species Conservation Act (ESCA) in June 1970. In 1973, the ESA replaced
the ESCA, and humpbacks continued to be listed as endangered. NMFS re-
evaluated the status of the species in 2015, and on September 8, 2016,
divided the species into 14 distinct population segments (DPS), removed
the current species-level listing, and in its place listed 4 DPSs as
endangered and 1 DPS as threatened (81 FR 62259, September 8, 2016).
The remaining nine DPSs were not listed. Only one DPS occurs in the
proposed survey area, the West Indies DPS, which is not listed under
the ESA.
The Gulf of Maine stock of humpback whales, a feeding population of
the West Indies DPS, occurs primarily in the southern Gulf of Maine and
east of Cape Cod during summers to feed (Clapham et al. 1993; Hayes et
al. 2020). Off the southeastern U.S., most sightings have been reported
for winter and mostly nearshore (DoN 2008c; Conley et al. 2017); there
were fewer sightings in fall and spring, and no sightings during summer
(DoN 2008c). Similarly, summer surveys by the Northeast Fisheries
Science Center (NEFSC) and Southeast Fisheries Science Center (SEFSC)
showed no sightings off the southeastern U.S. (Hayes et al. 2020). One
satellite-tagged humpback whale was reported near the northern portion
[[Page 37396]]
of the survey area during January 2021 (DoN 2022). Davis et al. (2020)
detected humpback whales acoustically off the southeastern U.S. during
winter (November-February) and spring (March-April), with few
detections during summer (May-July), and no detections during fall
(August-October). Kowarski et al. (2022) reported acoustic detections
on the Blake Plateau during summer. There are no records in the OBIS
database for the proposed survey area (OBIS 2022). The humpback whales
that could occur in the survey area are of the West Indies breeding
population, but not necessarily from the Gulf of Maine feeding
population.
Since January 2016, elevated humpback whale mortalities have
occurred along the Atlantic coast from Maine to Florida. Partial or
full necropsy examinations have been conducted on approximately half of
the 194 known cases. Of the whales examined, about 50 percent had
evidence of human interaction, either ship strike or entanglement.
While a portion of the whales have shown evidence of pre-mortem vessel
strike, this finding is not consistent across all whales examined and
more research is needed. NMFS is consulting with researchers that are
conducting studies on the humpback whale populations, and these efforts
may provide information on changes in whale distribution and habitat
use that could provide additional insight into how these vessel
interactions occurred. Three additional UMEs involving humpback whales
have occurred since 2000, in 2003, 2005, and 2006. More information is
available at: <a href="http://www.fisheries.noaa.gov/national/marine-life-distress/2016-2021-humpback-whale-unusual-mortality-event-along-atlantic-coast">www.fisheries.noaa.gov/national/marine-life-distress/2016-2021-humpback-whale-unusual-mortality-event-along-atlantic-coast</a>.
Minke Whale
In the Northern Hemisphere, the minke whale is usually seen in
coastal areas, but can also be seen in pelagic waters during its
northward migration in spring and summer and southward migration in
autumn (Stewart and Leatherwood, 1985). The Canadian East Coast stock
can be found in the area from the western half of the Davis Strait
(45[deg] W) to the Gulf of Mexico (Hayes et al., 2020). Minke whales in
the Atlantic have a strong seasonal component to their distribution,
with acoustic detections indicating that they migrate south in mid-
October to early November, and return from wintering grounds starting
in March through early April (Hayes et al., 2020). Northward migration
appears to track the warmer waters of the Gulf Stream along the
continental shelf, while southward migration is made farther offshore
(Risch et al. 2014).
Based on modeling for the western North Atlantic, higher densities
are expected to occur north of 35[deg] N; very low densities are
expected south of 35[deg] N (Mannocci et al. 2017; Palka et al. 2021).
Minke whales are common off the U.S. East Coast over continental shelf
waters during spring to fall (CETAP 1982; DoN 2008a,b; Hayes et al.
2022). Seasonal movements in the Northwest Atlantic are apparent, with
animals moving south and into offshore waters from late fall through
early spring (DoN 2008a,b; Hayes et al. 2022). Risch et al. (2014)
deployed acoustic detectors throughout the North Atlantic to detect
minke whale occurrence. They found that minke whales migrate north of
30[deg] N from March-April and migrate south from mid-October to early
November. During spring migration, animals migrate along the
continental shelf, whereas they migrate farther offshore during fall.
In the southeastern U.S., minke whales were commonly detected
during winter; at recorders situated at the shelf edge, detections were
from November through April, with no detections during the summer
(Risch et al. 2014; Kowarski et al. 2022). However, detections were
made during every season in deep, offshore waters (Kowarski et al.
2022). Based on a reduced number of acoustic detections during summer
off the southeastern U.S., Risch et al. (2014) suggested that most
minke whales likely occur in Canadian waters during the summer. Off the
coasts of Georgia and Florida, there are numerous sightings on the
shelf during winter (December-April), but there were no records for
summer, and very few during spring and fall (DoN 2008c). Summer surveys
by NEFSC and SEFSC found no sightings off the southeastern U.S. (Hayes
et al. 2022). There are no records in the OBIS database for the
proposed survey area (OBIS 2022).
Since January 2017, elevated minke whale mortalities have occurred
along the U.S. Atlantic coast from Maine through South Carolina, with a
total of 147 known strandings. This event has been declared a UME. Full
or partial necropsy examinations were conducted on more than 60 percent
of the whales. Preliminary findings in several of the whales have shown
evidence of human interactions or infectious disease, but these
findings are not consistent across all of the whales examined, so more
research is needed. More information is available at:
<a href="http://www.fisheries.noaa.gov/national/marine-life-distress/2017-2021-minke-whale-unusual-mortality-event-along-atlantic-coast">www.fisheries.noaa.gov/national/marine-life-distress/2017-2021-minke-whale-unusual-mortality-event-along-atlantic-coast</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. 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, 2019) recommended that marine mammals be divided into hearing
groups based on directly measured (behavioral or auditory evoked
potential techniques) or estimated hearing ranges (behavioral response
data, anatomical modeling, etc.). 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.
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).
[[Page 37397]]
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).
For more detail concerning these groups and associated frequency
ranges, please see NMFS (2018) for a review of available information.
Potential Effects of Specified Activities on Marine Mammals and Their
Habitat
This section provides a discussion of the ways in which 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 whether those
impacts are reasonably expected to, or reasonably likely to, adversely
affect the species or stock through effects on annual rates of
recruitment or survival.
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.,
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):
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;
Precipitation: Sound from rain and hail impacting the water surface
can become an important component of total
[[Page 37398]]
sound at frequencies above 500 Hz, and possibly down to 100 Hz during
quiet times;
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
Anthropogenic: Sources of anthropogenic 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 this 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. 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., NMFS, 2018; 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 \1\--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, if it
occurs at all, will occur almost exclusively in cases where a noise is
within an animal's hearing frequency range. We first describe specific
manifestations of acoustic effects before providing discussion specific
to the use of airgun arrays.
---------------------------------------------------------------------------
\1\ 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.
---------------------------------------------------------------------------
Richardson et al. (1995) described zones of increasing intensity of
effect that might be expected to occur, in relation to distance from a
source and assuming that the signal is within an animal's hearing
range. First is the area within which the acoustic signal would be
audible (potentially perceived) to the animal, but not strong enough to
elicit any overt behavioral or physiological response. The next zone
corresponds with the area where the signal is audible to the animal and
of sufficient intensity to elicit behavioral or physiological response.
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
[[Page 37399]]
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). Threshold shift can be
permanent (PTS), in which case the loss of hearing sensitivity is not
fully recoverable, or temporary (TTS), in which case the animal's
hearing threshold would recover over time (Southall et al., 2007).
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 typically 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 impulsive 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 3 captive
bottlenose dolphins before and after exposure to 10 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 was 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 is no direct data available on noise-induced
hearing loss for mysticetes.
Critical questions remain regarding the rate of TTS growth and
recovery after exposure to intermittent noise and the effects of single
and multiple pulses. Data at present are also insufficient to construct
generalized models for recovery and determine the time necessary to
treat subsequent exposures as independent events. More information is
needed on the relationship between auditory evoked potential and
behavioral measures of TTS for various stimuli. For summaries of data
on TTS in marine mammals or for further discussion of TTS onset
thresholds, please see Southall et al. (2007, 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
[[Page 37400]]
(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).
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 disruptions in
biologically significant activities (e.g., foraging) or they may be of
little biological significance. The impact of an alteration to dive
behavior resulting from an acoustic exposure depends on what the animal
is doing at the time of the exposure and the type and magnitude of the
response.
Disruption of feeding behavior can be difficult to correlate with
anthropogenic sound exposure, so it is usually inferred by observed
displacement from known foraging areas, the appearance of secondary
indicators (e.g., bubble nets or sediment plumes), or changes in dive
behavior. As for other types of behavioral response, the frequency,
duration, and temporal pattern of signal presentation, as well as
differences in species sensitivity, are likely contributing factors to
differences in response in any given circumstance (e.g., Croll et al.,
2001; Nowacek et al.; 2004; Madsen et al., 2006; Yazvenko et al.,
2007). A determination of whether foraging disruptions incur fitness
consequences would require information on or estimates of the energetic
requirements of the affected individuals and the relationship between
prey availability, foraging effort and success, and the life history
stage of the animal.
Visual tracking, passive acoustic monitoring (PAM), 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, or
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
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
[[Page 37401]]
production during production of aversive signals (Bowles et al., 1994).
Cerchio et al. (2014) used PAM 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 minutes sampled period) on singer number. The number of
singers significantly decreased with increasing received level of
noise, suggesting that humpback whale communication 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 cumulative sound exposure level
(SEL<INF>cum</INF>) of ~127 dB). Overall, these results suggest that
bowhead whales may adjust their vocal output in an effort to compensate
for noise before ceasing vocalization effort and ultimately deflecting
from the acoustic source (Blackwell et al., 2013, 2015). These studies
demonstrate that even low levels of noise received far from the source
can induce changes in vocalization and/or behavior for mysticetes.
Avoidance is the displacement of an individual from an area or
migration path as a result of the presence of 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 show 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. Avoidance of overlap between
disturbing noise and areas and/or times of particular importance for
sensitive species may be critical to avoiding population-level impacts
because (particularly for animals with high site fidelity) there may be
a strong motivation to remain in the area despite negative impacts.
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. Forney et al. (2017) specifically 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 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 5-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
[[Page 37402]]
lasting less than 1 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 arrays of large airguns
(considered to be 500 in\3\ or more in that study) 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, significant masking could disrupt
behavioral patterns, which in turn could affect fitness for survival
and reproduction. It is important to distinguish TTS and PTS, which
persist after the sound exposure, from masking, which occurs during the
sound exposure. Because masking (without resulting in TS) is not
associated with abnormal physiological function, it is not considered a
physiological effect, but rather a potential behavioral effect.
The frequency range of the potentially masking sound is important
in predicting 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 may be less 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
[[Page 37403]]
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 noise levels during
intervals between seismic 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 2,000 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 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.
Ship 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., Martins et al., 2016;
O'Brien et al., 2016; Tenessen and Parks 2016). Harp seals did not
increase their call frequencies in environments with increased low-
frequency sounds (Terhune and Bosker 2016). Holt et al. (2015) reported
that changes in vocal modifications can have increased energetic costs
for individual marine mammals. A negative correlation between the
presence of some cetacean species and the number of vessels in an area
has been demonstrated by several studies (e.g., Campana et al. 2015;
Culloch et al. 2016).
Baleen whales are thought to be more sensitive to sound at these
low frequencies than are toothed whales (e.g., MacGillivray et al.
2014), possibly causing localized avoidance of the proposed survey area
during seismic operations. Reactions of gray and humpback whales to
vessels have been studied, and there is limited information available
about the reactions of right whales and rorquals (fin, blue, and minke
whales). Reactions of humpback whales to boats are variable, ranging
from approach to avoidance (Payne 1978; Salden 1993). Baker et al.
(1982, 1983) and Baker and Herman (1989) found humpbacks often move
away when vessels are within several kilometers. Humpbacks seem less
likely to react overtly when actively feeding than when resting or
engaged in other activities (Krieger and Wing 1984, 1986). Increased
levels of ship noise have been shown to affect foraging by humpback
whales (Blair et al., 2016). Fin whale sightings in the western
Mediterranean were negatively correlated with the number of vessels in
the area (Campana et al. 2015). Minke whales and gray seals have shown
slight displacement in response to construction-related vessel traffic
(Anderwald et al., 2013).
Many odontocetes show considerable tolerance of vessel traffic,
although they sometimes react at long distances if confined by ice or
shallow water, if previously harassed by vessels, or 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.,
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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 is little 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).
Vessel Strike
Vessel collisions with marine mammals, or ship strikes, can result
in death or serious injury of the animal. Wounds resulting from vessel
strike may include massive trauma, hemorrhaging, broken bones, or
propeller lacerations (Knowlton and Kraus, 2001). An animal at the
surface may be struck directly by a vessel, a surfacing animal may hit
the bottom of a vessel, or an animal just below the surface may be cut
by a vessel's propeller. Superficial strikes may not kill or result in
the death of the animal. These interactions are typically associated
with large whales (e.g., fin whales), which are occasionally found
draped across the bulbous bow of large commercial ships upon arrival in
port. Although smaller cetaceans are more maneuverable in relation to
large vessels than are large whales, they may also be susceptible to
strike. The severity of injuries typically depends on the size and
speed of the vessel, with the probability of death or serious injury
increasing as vessel speed increases (Knowlton and Kraus, 2001; Laist
et al., 2001; Vanderlaan and Taggart, 2007; Conn and Silber, 2013).
Impact forces increase with speed, as does the probability of a strike
at a given distance (Silber et al., 2010; Gende et al., 2011).
Pace and Silber (2005) also found that the probability of death or
serious injury increased rapidly with increasing vessel speed.
Specifically, the predicted probability of serious injury or death
increased from 45 to 75 percent as vessel speed increased from 10 to 14
kn, and exceeded 90 percent at 17 kn. Higher speeds during collisions
result in greater force of impact, but higher speeds also appear to
increase the chance of severe injuries or death through increased
likelihood of collision by pulling whales toward the vessel (Clyne,
1999; Knowlton et al., 1995). In a separate study, Vanderlaan and
Taggart (2007) analyzed the probability of lethal mortality of large
whales at a given speed, showing that the greatest rate of change in
the probability of a lethal injury to a large whale as a function of
vessel speed occurs between 8.6 and 15 kn. The chances of a lethal
injury decline from approximately 80 percent at 15 kn to approximately
20 percent at 8.6 kn. At speeds below 11.8 kn, the chances of lethal
injury drop below 50 percent, while the probability asymptotically
increases toward one hundred percent above 15 kn.
The Langseth will travel at a speed of 5 kn while towing seismic
survey gear. At this speed, both the possibility of striking a marine
mammal and the possibility of a strike resulting in serious injury or
mortality are discountable. At average transit speed, the probability
of serious injury or mortality resulting from a strike is less than 50
percent. However, the likelihood of a strike actually happening is
again discountable. Vessel strikes, as analyzed in the studies cited
above, generally involve commercial shipping, which is much more common
in both space and time than is geophysical survey activity. Jensen and
Silber (2004) summarized vessel 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). No such incidents
were reported for geophysical survey vessels during that time period.
It is possible for vessel strikes to occur while traveling at slow
speeds. For example, a hydrographic survey vessel traveling at low
speed (5.5 kn) while conducting mapping surveys off the central
California coast struck and killed a blue whale in 2009. The State of
California determined that the whale had suddenly and unexpectedly
surfaced beneath the hull, with the result that the propeller severed
the whale's vertebrae, and that this was an unavoidable event. This
strike represents the only such incident in approximately 540,000 hours
of similar coastal mapping activity (p = 1.9 x 10<SUP>-6</SUP>; 95
percent confidence interval = 0-5.5 x 10<SUP>-6</SUP>; NMFS, 2013). In
addition, a research vessel reported a fatal strike in 2011 of a
dolphin in the Atlantic, demonstrating that it is possible for strikes
involving smaller cetaceans to occur. In that case, the incident report
indicated that an animal apparently was struck by the vessel's
propeller as it was intentionally swimming near the vessel. While
indicative of the type of unusual events that cannot be ruled out,
neither of these instances represents a circumstance that would be
considered reasonably foreseeable or that would be considered
preventable.
Although the likelihood of the vessel striking a marine mammal is
low, we propose a robust vessel strike avoidance protocol (see Proposed
Mitigation), which we believe eliminates any foreseeable risk of vessel
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 proposed 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, the possibility of vessel
strike is discountable and, further, 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 vessel 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
[[Page 37405]]
legal definition for a stranding under the MMPA is that a marine mammal
is dead and is on a beach or shore of the United States; or in waters
under the jurisdiction of the United States (including any navigable
waters); or a marine mammal is alive and is on a beach or shore of the
United States and is unable to return to the water; 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 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, vessel 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 military 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).
Military MFA sonar affects beaked whales differently than airguns
do because it produces energy at different frequencies than airguns.
Mid-frequency cetacean hearing is generically thought to be best
between 8.8 to 110 kHz, i.e., these cutoff values define the range
above and below which a species in the group is assumed to have
declining auditory sensitivity, until reaching frequencies that cannot
be heard (NMFS, 2018). However, beaked whale hearing is likely best
within a higher, narrower range (20-80 kHz, with best sensitivity
around 40 kHz), based on a few measurements of hearing in stranded
beaked whales (Cook et al., 2006; Finneran et al., 2009; Pacini et al.,
2011) and several studies of acoustic signals produced by beaked whales
(e.g., Frantzis et al., 2002; Johnson et al., 2004, 2006; Zimmer et
al., 2005). While precaution requires that the full range of audibility
be considered when assessing risks associated with noise exposure
(Southall et al., 2007, 2019), animals typically produce sound at
frequencies where they hear best. More recently, Southall et al. (2019)
suggested that certain species in the historical mid-frequency hearing
group (beaked whales, sperm whales, and killer whales) are likely more
sensitive to lower frequencies within the group's generalized hearing
range than are other species within the group, and state that the data
for beaked whales suggest sensitivity to approximately 5 kHz. However,
this information is consistent with the general conclusion that beaked
whales (and other mid-frequency cetaceans) are relatively insensitive
to the frequencies where most energy of an airgun signal is found.
Military MFA sonar is typically considered to operate in the frequency
range of approximately 3-14 kHz (D'Amico et al., 2009), i.e., outside
the range of likely best hearing for beaked whales but within or close
to the lower bounds, whereas most energy in an airgun signal is
radiated at much lower frequencies, below 500 Hz (Dragoset, 1990).
It is important to distinguish between energy (loudness, measured
in dB) and frequency (pitch, measured in Hz). In considering the
potential impacts of mid-frequency components of airgun noise (1-10
kHz, where beaked whales can be expected to hear) on marine mammal
hearing, one needs to account for the energy associated with these
higher frequencies and determine what energy is truly ``significant.''
Although there is mid-frequency energy associated with airgun noise (as
expected from a broadband source), airgun sound is predominantly below
1 kHz (Breitzke et al., 2008; Tashmukhambetov et al., 2008; Tolstoy et
al., 2009). As stated by Richardson et
[[Page 37406]]
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., MFA sonar) will likely be closer to
the whales (because attenuation limits the range of detection of mid-
frequencies) and moving faster (because it will be on faster-moving
vessels), any antipredator response would be more likely to be severe
(with greater perceived predation risk, an animal is more likely to
disregard the cost of the response; Frid and Dill, 2002). Indeed, when
analyzing movements of a beaked whale exposed to playback of killer
whale predation calls, Allen et al. (2014) found that the whale engaged
in a prolonged, directed avoidance response, suggesting a behavioral
reaction that could pose a risk factor for stranding. Overall, these
significant differences between sound from MFA sonar and the mid-
frequency sound component from airguns and the likelihood that MFA
sonar signals will be interpreted in error as a predator are critical
to understanding the likely risk of behaviorally-mediated injury due to
seismic surveys.
The available scientific literature also provides a useful contrast
between airgun noise and MFA sonar regarding the likely risk of
behaviorally-mediated injury. There is strong evidence for the
association of beaked whale stranding events with MFA sonar use, and
particularly detailed accounting of several events is available (e.g.,
a 2000 Bahamas stranding event for which 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 10 events were at minimum
spatially and temporally coincident with naval activity likely to have
included MFA sonar use and, despite incomplete knowledge of timing and
location of the stranding or the naval activity in some cases, there
was no evidence for an alternative cause of stranding. The U.S. Navy
has publicly stated agreement that five such events since 1996 were
associated in time and space with MFA sonar use, either by the U.S.
Navy alone or in joint training exercises with the North Atlantic
Treaty Organization. The U.S. Navy additionally noted that, as of 2017,
a 2014 beaked whale stranding event in Crete coincident with naval
exercises was under review and had not yet been determined to be linked
to sonar activities (U.S. Navy, 2017). Separately, the International
Council for the Exploration of the Sea reported in 2005 that,
worldwide, there have been about 50 known strandings, consisting mostly
of beaked whales, with a potential causal link to MFA sonar (ICES,
2005). In contrast, very few such associations have been made to
seismic surveys, despite widespread use of airguns as a geophysical
sound source in numerous locations around the world.
A more recent review of possible stranding associations with
seismic surveys (Castellote and Llorens, 2016) states plainly that,
``[s]peculation concerning possible links between seismic survey noise
and cetacean strandings is available for a dozen events but without
convincing causal evidence.'' The authors' ``exhaustive'' search of
available information found 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
[[Page 37407]]
survey. As described above, D'Amico et al. (2009) found that two events
were ranked ``1'' and 10 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: 1 stranding in Peru involving dolphins and porpoises
and a 2008 stranding in Madagascar. This latter ranking can only be
broadly 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 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
nautical miles (100,000 km) of previous NSF-funded seismic surveys when
observers were aboard (e.g., Smultea and Holst 2003; Haley and Koski
2004; Holst 2004; Smultea et al., 2004; Holst et al., 2005a; Haley and
Ireland 2006; SIO and NSF 2006b; Hauser et al., 2008; Holst and Smultea
2008). Although entanglement with the streamer is theoretically
possible, it has not been documented during tens of thousands of miles
of NSF-sponsored seismic cruises or, to our knowledge, during hundreds
of thousands of miles of industrial seismic cruises. There are a
relative few deployed devices, and no interaction between marine
mammals and any such device has been recorded during prior NSF surveys
using the devices. There are no meaningful entanglement risks posed by
the proposed survey, and entanglement risks are not discussed further
in this document.
Anticipated Effects on Marine Mammal Habitat
Physical Disturbance--Sources of seafloor disturbance related to
geophysical surveys that may impact marine mammal habitat include
placement of anchors, nodes, cables, sensors, or other equipment on or
in the seafloor for various activities. Equipment deployed on the
seafloor has the potential to cause direct physical damage and could
affect bottom-associated fish resources.
Placement of equipment, 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., 1992; Skalski et al., 1992;
Santulli et al., 1999; Paxton et al., 2017), though the bulk of studies
indicate no or slight reaction to noise (e.g., Miller and Cripps, 2013;
Dalen and Knutsen, 1987; Pena et al., 2013; Chapman and Hawkins, 1969;
Wardle et al., 2001; Sara et al., 2007; Jorgenson and Gyselman, 2009;
Blaxter et al., 1981; Cott et al., 2012; Boeger et al., 2006), and
that, most commonly, while there are likely to be impacts to fish as a
result of noise from nearby airguns, such effects will be temporary.
For example, investigators reported significant, short-term declines in
commercial fishing catch rate of gadid fishes during and for up to five
days after seismic survey operations, but the catch rate subsequently
returned to normal (Engas et al., 1996; Engas and Lokkeborg, 2002).
Other studies have reported similar findings (Hassel et al., 2004).
Skalski et al., (1992) also found a reduction in catch rates--for
rockfish (Sebastes spp.) in response to controlled airgun exposure--but
suggested that the mechanism underlying the decline was not dispersal
but rather decreased responsiveness to baited hooks associated with an
alarm behavioral response. A companion study showed that alarm and
startle responses were not sustained following the removal of the sound
source (Pearson et al., 1992). Therefore, Skalski et al. (1992)
suggested that the effects on fish abundance may be transitory,
primarily occurring during the sound exposure itself. In some cases,
effects on catch rates are variable within a study, which may be more
broadly representative of temporary displacement of fish in response to
airgun noise (i.e., catch rates may increase in some locations and
decrease in others) than any long-term damage to the fish themselves
(Streever et al., 2016).
Sound pressure levels 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
[[Page 37408]]
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. (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 3 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 recently described study produced results
inconsistent with those of McCauley et al. (2017). Researchers
conducted a field and laboratory study to assess if exposure to airgun
noise affects mortality, predator escape response, or gene expression
of the copepod Calanus finmarchicus (Fields et al., 2019). Immediate
mortality of copepods was significantly higher, relative to controls,
at distances of 5 m or less from the airguns. Mortality one week after
the airgun blast was significantly higher in the copepods placed 10 m
from the airgun but was not significantly different from the controls
at a distance of 20 m from the airgun. The increase in mortality,
relative to controls, did not exceed 30 percent at any distance from
the airgun. Moreover, the authors caution that even this higher
mortality in the immediate vicinity of the airguns may be more
pronounced than what would be observed in free-swimming animals due to
increased flow speed of fluid inside bags containing the experimental
animals. There were no sublethal effects on the escape performance or
the sensory threshold needed to initiate an escape response at any of
the distances from the airgun that were tested. Whereas McCauley et al.
(2017) reported an SEL of 156 dB at a range of 509-658 m, with
zooplankton mortality observed at that range, Fields et al. (2019)
reported an SEL of 186 dB at a range of 25 m, with no reported
mortality at that distance. Regardless, if we assume a worst-case
likelihood of severe impacts to zooplankton within approximately 1 km
of the acoustic source, the 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 recent review article concluded that, while laboratory results
provide scientific evidence for high-intensity and low-frequency sound-
induced physical trauma and other negative effects on some fish and
invertebrates, the sound exposure scenarios in some cases are not
realistic to those encountered by marine organisms during routine
seismic operations (Carroll et al., 2017). The review finds that there
has been no evidence of reduced catch or abundance following seismic
activities for invertebrates, and that there is conflicting evidence
for fish with catch observed to increase, decrease, or remain the same.
Further, where there is evidence for decreased catch rates in response
to airgun noise, these findings provide no information about the
underlying biological cause of catch rate reduction (Carroll et al.,
2017).
In summary, impacts of the specified activity on marine mammal prey
species will likely be limited to behavioral responses, the majority of
prey species
[[Page 37409]]
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
determinations.
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).
Anticipated takes would primarily be Level B harassment, as use of
the airgun arrays have the potential to result in disruption of
behavioral patterns for individual marine mammals. There is also some
potential for auditory injury (Level A harassment) to result for
species of certain hearing groups due to the size of the predicted
auditory injury zones for those groups. Auditory injury is less likely
to occur for mid-frequency species, due to their relative lack of
sensitivity to the frequencies at which the primary energy of an airgun
signal is found, as well as such species' general lower sensitivity to
auditory injury as compared to high-frequency cetaceans. As discussed
in further detail below, we do not expect auditory injury for mid-
frequency cetaceans. The proposed mitigation and monitoring measures
are expected to minimize the severity of such taking to the extent
practicable. No mortality is anticipated as a result of these
activities. Below we describe how the proposed take numbers are
estimated.
For acoustic impacts, 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 factors can contribute to a basic calculation to
provide an initial prediction of potential 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 estimates.
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--Though significantly driven by received level,
the onset of behavioral disturbance from
[[Page 37410]]
anthropogenic noise exposure is also informed to varying degrees by
other factors related to the source or exposure context (e.g.,
frequency, predictability, duty cycle, duration of the exposure,
signal-to-noise ratio, distance to the source), the environment (e.g.,
bathymetry, other noises in the area, predators in the area), and the
receiving animals (hearing, motivation, experience, demography, life
stage, depth) and can be difficult to predict (e.g., Southall et al.,
2007, 2021; Ellison et al., 2012). Based on what the available science
indicates and the practical need to use a threshold based on a metric
that is both predictable and measurable for most activities, NMFS
typically uses a generalized acoustic threshold based on received level
to estimate the onset of behavioral harassment. NMFS generally predicts
that marine mammals are likely to be behaviorally harassed in a manner
considered to be Level B harassment when exposed to underwater
anthropogenic noise above root-mean-squared pressure received levels
(RMS SPL) of 120 dB (referenced to 1 micropascal (re 1 [mu]Pa)) for
continuous (e.g., vibratory pile-driving, drilling) and above RMS SPL
160 dB re 1 [mu]Pa for non-explosive impulsive (e.g., seismic airguns)
or intermittent (e.g., scientific sonar) sources. Generally speaking,
Level B harassment take estimates based on these behavioral harassment
thresholds are expected to include any likely takes by TTS as, in most
cases, the likelihood of TTS occurs at distances from the source less
than those at which behavioral harassment is likely. TTS of a
sufficient degree can manifest as behavioral harassment, as reduced
hearing sensitivity and the potential reduced opportunities to detect
important signals (conspecific communication, predators, prey) may
result in changes in behavior patterns that would not otherwise occur.
L-DEO's proposed survey includes the use of impulsive seismic
sources (e.g., Bolt airguns), and therefore the 160 dB re 1 [mu]Pa is
applicable for analysis of Level B harassment.
Level A Harassment--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 survey includes the use of impulsive seismic sources (e.g.,
airguns).
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="http://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance">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 are used in estimating the area ensonified above the
acoustic thresholds, including source levels and transmission loss
coefficient.
When the NMFS Technical Guidance (2016a) was published, in
recognition of the fact that ensonified area/volume could be more
technically challenging to predict because of the duration component in
the new thresholds, we developed a user spreadsheet that includes tools
to help predict a simple isopleth that can be used in conjunction with
marine mammal density or occurrence to help predict takes. We note that
because of some of the assumptions included in the methods used for
these tools, we anticipate that isopleths produced are typically going
to be overestimates of some degree, which may result in some degree of
overestimate of Level A harassment take. However, these tools offer the
best way to predict appropriate isopleths when more sophisticated 3D
modeling methods are not available, and NMFS continues to develop ways
to quantitatively refine these tools, and will qualitatively address
the output where appropriate.
The proposed survey would entail the use of a 36-airgun array with
a total discharge volume of 6,600 in\3\ at a tow depth of 10-12 m. L-
DEO's model results are used to determine the 160 dB<INF>rms</INF>
radius for the 36-airgun array in water depth ranging from >100-5,200
m. Received sound levels have been predicted by L-DEO's model (Diebold
et al. 2010) as a function of distance from the 36-airgun array. Models
for the 36-airgun array used a 12-m tow depth. This modeling approach
uses ray tracing for the direct wave traveling from the array to the
receiver and its associated source ghost (reflection at the air-water
interface in the vicinity of the array), in a constant-velocity half-
space (infinite 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 (~1,600 m),
intermediate water depth on the slope (~600-1,100 m), and shallow water
(~50 m) in the Gulf of Mexico (Tolstoy et al. 2009; Diebold et al.
2010).
For deep and intermediate water cases, the field measurements
cannot be used readily to derive the harassment isopleths, as at those
sites the calibration hydrophone was located at a roughly constant
depth of 350-550 m, which may not intersect all the SPL isopleths at
their widest point from the sea surface down to the assumed
[[Page 37411]]
maximum relevant water depth (~2,000 m) for marine mammals. At short
ranges, where the direct arrivals dominate and the effects of seafloor
interactions are minimal, the data at the deep sites are suitable for
comparison with modeled levels at the depth of the calibration
hydrophone. At longer ranges, the comparison with the model--
constructed from the maximum SPL through the entire water column at
varying distances from the airgun array--is the most relevant.
In deep and intermediate water depths at short ranges, sound levels
for direct arrivals recorded by the calibration hydrophone and L-DEO
model results for the same array tow depth are in good alignment (see
Figures 12 and 14 in Diebold et al. 2010). Consequently, isopleths
falling within this domain can be predicted reliably by the L-DEO
model, although they may be imperfectly sampled by measurements
recorded at a single depth. At greater distances, the calibration data
show that seafloor-reflected and sub-seafloor-refracted arrivals
dominate, whereas the direct arrivals become weak and/or incoherent
(see Figures 11, 12, and 16 in Diebold et al. 2010). Aside from local
topography effects, the region around the critical distance is where
the observed levels rise closest to the model curve. However, the
observed sound levels are found to fall almost entirely below the model
curve. Thus, analysis of the Gulf of Mexico calibration measurements
demonstrates that although simple, the L-DEO model is a robust tool for
conservatively estimating isopleths.
The proposed survey would acquire data with the 36-airgun array at
a tow depth of 10-12 m. For deep water (>1,000 m), we use the deep-
water radii obtained from L-DEO model results down to a maximum water
depth of 2,000 m for the 36-airgun array. The radii for intermediate
water depths (100-1,000 m) are derived from the deep-water ones by
applying a correction factor (multiplication) of 1.5, such that
observed levels at very near offsets fall below the corrected
mitigation curve (see Figure 16 in Diebold et al. 2010).
L-DEO's modeling methodology is described in greater detail in L-
DEO's application. The estimated distances to the Level B harassment
isopleth for the proposed airgun configuration are shown in Table 4.
Table 4--Predicted Radial Distances From the R/V Langseth Seismic Source to Isopleth Corresponding to Level B
Harassment Threshold
----------------------------------------------------------------------------------------------------------------
Predicted
distances (in m)
Airgun configuration Tow depth (m) Water depth (m) to the Level B
harassment
threshold
----------------------------------------------------------------------------------------------------------------
4 strings, 36 airguns, 6,600 in\3\........................ 12 >1,000 \1\ 6,733
100-1,000 \2\ 10,100
----------------------------------------------------------------------------------------------------------------
\1\ Distance is 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.
Table 5 presents the modeled PTS isopleths for each cetacean
hearing group based on L-DEO modeling incorporated in the companion
user spreadsheet (NMFS 2018).
Table 5--Modeled Radial Distance to Isopleths Corresponding to Level A Harassment Thresholds
----------------------------------------------------------------------------------------------------------------
High
Low frequency Mid frequency frequency
----------------------------------------------------------------------------------------------------------------
MCS Surveys
----------------------------------------------------------------------------------------------------------------
PTS SELcum...................................................... 320.2 0 1
PTS Peak........................................................ 38.9 13.6 268.3
----------------------------------------------------------------------------------------------------------------
OBS Surveys
----------------------------------------------------------------------------------------------------------------
PTS SELcum...................................................... 80 0 0.3
PTS Peak........................................................ 38.9 13.6 268.3
----------------------------------------------------------------------------------------------------------------
The largest distance (in bold) of the dual criteria (SELcum or Peak) was used to estimate threshold distances
and potential takes by Level A harassment.
Predicted distances to Level A harassment isopleths, which vary
based on marine mammal hearing groups, were calculated based on
modeling performed by L-DEO using the Nucleus software program and the
NMFS user spreadsheet, described below. The acoustic thresholds for
impulsive sounds (e.g., airguns) contained in the NMFS Technical
Guidance were presented as dual metric acoustic thresholds using both
SEL<INF>cum</INF> and peak sound pressure metrics (NMFS 2016a). As dual
metrics, NMFS considers onset of PTS (Level A harassment) to have
occurred when either one of the two metrics is exceeded (i.e., metric
resulting in the largest isopleth). The SEL<INF>cum</INF> metric
considers both level and duration of exposure, as well as auditory
weighting functions by marine mammal hearing group. In recognition of
the fact that the requirement to calculate Level A harassment
ensonified areas could be more technically challenging to predict due
to the duration component and the use of weighting functions in the new
SEL<INF>cum</INF> thresholds, NMFS developed an optional user
spreadsheet that includes tools to help predict a simple isopleth that
can be used in conjunction with marine mammal density or occurrence
[[Page 37412]]
to facilitate the estimation of take numbers.
The SEL<INF>cum</INF> for the 36-airgun array is derived from
calculating the modified farfield signature. The farfield signature is
often used as a theoretical representation of the source level. To
compute the farfield signature, the source level is estimated at a
large distance (right) below the array (e.g., 9 km), and this level is
back projected mathematically to a notional distance of 1 m from the
array's geometrical center. However, it has been recognized that the
source level from the theoretical farfield signature is never
physically achieved at the source when the source is an array of
multiple airguns separated in space (Tolstoy et al., 2009). Near the
source (at short ranges, distances <1 km), the pulses of sound pressure
from each individual airgun in the source array do not stack
constructively as they do for the theoretical farfield signature. The
pulses from the different airguns spread out in time such that the
source levels observed or modeled are the result of the summation of
pulses from a few airguns, not the full array (Tolstoy et al., 2009).
At larger distances, away from the source array center, sound pressure
of all the airguns in the array stack coherently, but not within one
time sample, resulting in smaller source levels (a few dB) than the
source level derived from the 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 far-field signature
is not an appropriate measure of the sound source level for large
arrays. See L-DEO's application for further detail on acoustic
modeling.
Auditory injury is unlikely to occur for mid-frequency cetaceans,
given very small modeled zones of injury for those species (all
estimated zones less than 15 m for mid-frequency cetaceans), 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 two to three 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] TN07JN23.001
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] TN07JN23.002
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] TN07JN23.003
and calculate D directly given a particular frequency and known speed
of sound (here assumed to be 1,500 m 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 approximately 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 138.7-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 to be de minimis, even before the likely moderating
effects of aversion and/or other compensatory behaviors
[[Page 37413]]
(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
and do not propose to authorize any take by Level A harassment for
these species.
The Level A and Level B harassment estimates are based on a
consideration of the number of marine mammals that could be within the
area around the operating airgun array where received levels of sound
>=160 dB re 1 [mu]Pa rms are predicted to occur (see Table 1). The
estimated numbers are based on the densities (numbers per unit area) of
marine mammals expected to occur in the area in the absence of seismic
surveys. To the extent that marine mammals tend to move away from
seismic sources before the sound level reaches the criterion level and
tend not to approach an operating airgun array, these estimates likely
overestimate the numbers actually exposed to the specified level of
sound.
Marine Mammal Occurrence
In this section we provide information about the occurrence of
marine mammals, including density or other relevant information that
will inform the take calculations.
Habitat-based density models produced by the Duke University Marine
Geospatial Ecology Laboratory (Roberts et al., 2016; Roberts and
Halpin, 2022) represent the best available information regarding marine
mammal densities in the survey area. This density information
incorporates aerial and shipboard line-transect survey data from NMFS
and other organizations and incorporates data from 8 physiographic and
16 dynamic oceanographic and biological covariates, and controls for
the influence of sea state, group size, availability bias, and
perception bias on the probability of making a sighting. These density
models were originally developed for all cetacean taxa in the U.S.
Atlantic (Roberts et al., 2016). In subsequent years, certain models
have been updated based on additional data as well as certain
methodological improvements. More information is available online at
<a href="https://seamap.env.duke.edu/models/Duke/EC">https://seamap.env.duke.edu/models/Duke/EC</a>/. Marine mammal density
estimates in the survey area (animals/km\2\) were obtained using the
most recent model results for all taxa.
Monthly density grids (e.g., rasters) for each species were
overlaid with the Survey Area and values from all grid cells that
overlapped the Survey Area (plus a 40-km buffer) were averaged to
determine monthly mean density values for each species. Monthly mean
density values within the survey area were averaged for each of the two
water depth categories (intermediate and deep) for the months May to
October. The highest mean monthly density estimates for each species
were used to estimate take.
Take Estimation
Here we describe how the information provided above is synthesized
to produce a quantitative estimate of the take that is reasonably
likely to occur and proposed for authorization. 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 the predicted isopleth 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 harassment thresholds. The distance for the 160-
dB Level B harassment threshold and PTS (Level A harassment) thresholds
(based on L-DEO model results) was used to draw a buffer around the
area expected to be ensonified (i.e., the survey area). The ensonified
areas were then increased by 25 percent to account for potential
delays, which is the equivalent to adding 25 percent to the proposed
line km to be surveyed. The highest mean monthly density for each
species was then multiplied by the daily ensonified areas (increased as
described above), and then multiplied by the number of survey days (40)
to estimate potential takes (see Appendix B of L-DEO's application for
more information).
L-DEO generally assumed that their estimates of marine mammal
exposures above harassment thresholds 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, we have
added L-DEO's estimated exposures above Level A harassment thresholds
to their estimated exposures above the Level B harassment threshold to
produce a total number of incidents of take by Level B harassment that
is proposed for authorization. Estimated exposures and proposed take
numbers for authorization are shown in Table 6. As requested by L-DEO
with NMFS concurrence, when zero take was calculated we have authorized
one group size of take as a precaution since the species could
potentially occur in the survey area.
Table 6--Estimated Take Proposed for Authorization
--------------------------------------------------------------------------------------------------------------------------------------------------------
Estimated Take Proposed Authorized Take
Species Stock ---------------------------------------------------- Abundance \3\ Percent of
Level B Level A Level B Level A Stock
--------------------------------------------------------------------------------------------------------------------------------------------------------
North Atlantic right whale.............. Western North Atlantic.... 0 0 0 0 \4\ 338 n/a
Humpback whale.......................... Gulf of Maine............. 0 0 \1\ 2 0 \6\ 2,259 <0.1
Fin whale............................... Western North Atlantic.... 5 0 5 0 \5\ 3,587 0.1
Sei whale............................... Nova Scotia............... 28 2 28 2 \5\ 1,043 2.9
Minke whale............................. Canadian East Coast....... 20 1 20 1 \5\ 4,044 0.5
Blue whale.............................. Western North Atlantic.... 2 0 2 0 \6\ 33 6.1
Sperm whale............................. North Atlantic............ 706 3 709 0 \5\ 6,576 9.3
Kogia spp............................... .......................... 601 50 601 50 \6\ 7,980 8.2
Cuvier's beaked whale................... Western North Atlantic.... 365 1 366 0 \6\ 5,588 6.5
Mesoplodont beaked whales............... .......................... 154 1 155 0 \6\ 6,526 2.4
Pilot whales............................ .......................... 1,424 4 1,428 0 \6\23,905 6
Rough-toothed dolphin................... Western North Atlantic.... 301 1 302 0 \6\ 1,011 30
Bottlenose dolphin...................... Western North Atlantic 4,445 12 4,457 0 \5\ 68,739 6.5
Offshore.
Pantropical spotted dolphin............. Western North Atlantic.... 419 1 420 0 \6\ 1,403 30
Atlantic spotted dolphin................ Western North Atlantic.... 1,768 6 1,774 0 \5\39,352 4.5
Spinner dolphin......................... Western North Atlantic.... 149 0 149 0 \6\ 885 16.8
Clymene dolphin......................... Western North Atlantic.... 0 0 \2\ 182 0 \6\ 8,576 2.1
Striped dolphin......................... Western North Atlantic.... 0 0 \1\ 46 0 \6\ 54,707 <0.1
Fraser's dolphin........................ Western North Atlantic.... 226 1 227 0 \6\ 658 34.5
Risso's dolphin......................... Western North Atlantic.... 1,277 3 1,280 0 \5\ 24,260 5.3
Common dolphin.......................... Western North Atlantic.... 181 1 182 0 \5\ 144,036 0.1
[[Page 37414]]
Melon-headed whale...................... Western North Atlantic.... 212 1 213 0 \6\ 618 34.5
Pygmy killer whale...................... Western North Atlantic.... 20 0 20 0 \6\ 68 29.4
False killer whale...................... Western North Atlantic.... 4 0 \2\ 6 0 \6\ 139 4.3
Killer whale............................ Western North Atlantic.... 6 0 6 0 \6\ 73 8.2
Harbor porpoise......................... Gulf of Maine/Bay of Fundy 0 0 \1\ 3 0 \5\ 55,049 <0.1
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Proposed take increased to mean group size from AMAPPS (Palka et al., 2017 and 2021).
\2\ Proposed take increased to mean group size from OBIS (2023).
\3\ Modeled abundance (Roberts and Halpin 2022) used unless noted.
\4\ Abundance from draft 2022 U.S, Atlantic and Gulf of Mexico Marine Mammal SARs.
\5\ Averaged monthly (May-Oct) abundance.
\6\ Only single annual abundance given.
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, NMFS
considers 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), 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 and impact on
operations.
Vessel-Based Visual Mitigation Monitoring
Visual monitoring requires the use of trained observers (herein
referred to as visual protected species observers (PSO)) to scan the
ocean surface for the presence of marine mammals. The area to be
scanned visually includes primarily the shutdown zone (SZ), 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 SZ to be monitored for the presence of marine
mammals that may enter the SZ. During pre-start clearance monitoring
(i.e., before ramp-up begins), the buffer zone also acts as an
extension of the SZ 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 SZ, out to a radius of 1,000 m
from the edges of the airgun array (500-1,000 m). This 1,000-m zone (SZ
plus buffer) represents the pre-start clearance zone. Visual monitoring
of the SZ 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 SZ by alerting the visual observer and crew of marine
mammals that are outside of, but may approach and enter, the SZ.
L-DEO must use dedicated, trained, and 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 1 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 shutdown and buffer zones.
These zones shall be based upon the radial distance from the edges of
the acoustic source
[[Page 37415]]
(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 SZ) 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 1 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
Passive acoustic monitoring means the use of trained personnel
(sometimes referred to as 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 SZ 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 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 1 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 10 hours in
any 24-hour period.
Establishment of Shutdown and Pre-Start Clearance Zones
An SZ 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 SZ with a 500-m radius. The 500-m SZ
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 must be
clear of marine mammals prior to beginning ramp-up of the acoustic
source, and includes the SZ plus the buffer zone. Detections of marine
mammals within the pre-start clearance zone would prevent airgun
operations from beginning (i.e., ramp-up).
The 500-m SZ is intended to be precautionary in the sense that it
would be expected to contain sound exceeding the injury criteria for
all cetacean hearing groups, (based on the dual criteria of
SEL<INF>cum</INF> and peak SPL), while also providing a consistent,
reasonably observable zone within which PSOs would typically be able to
conduct effective observational effort. Additionally, a 500-m SZ is
expected to minimize the likelihood that marine mammals will be exposed
to levels likely to result in more severe behavioral responses.
Although significantly greater distances may be observed from an
elevated platform under good conditions, we believe that 500 m is
likely regularly attainable for PSOs using the naked eye during typical
conditions. The pre-start clearance zone simply represents the addition
of a buffer to the SZ, doubling the SZ size during pre-clearance.
An extended SZ of 1,500 m must be enforced for all beaked whales
and Kogia species. No buffer of this extended SZ is required, as NMFS
concludes that this extended SZ is sufficiently protective to mitigate
harassment to beaked whales and Kogia species.
Pre-Start Clearance and Ramp-Up
Ramp-up (sometimes referred to as ``soft start'') means the gradual
and systematic increase of emitted sound levels from an airgun array.
Ramp-up begins by first activating a single airgun of the smallest
volume, followed by doubling the number of active elements in stages
until the full complement of an array's airguns are active. Each stage
should be approximately the same duration, and the total duration
should not be less than approximately 20 minutes. The intent of pre-
start clearance observation (30 minutes) is to ensure no marine mammals
are observed within the pre-start clearance zone (or extended SZ, for
beaked whales and Kogia spp.) prior to the beginning of ramp-up. During
the pre-start clearance period is the only time observations of marine
mammals in the buffer zone would prevent operations (i.e., the
beginning of ramp-up). The intent of ramp-up is to warn marine mammals
of pending seismic survey operations and to allow sufficient time
[[Page 37416]]
for those animals to leave the immediate vicinity prior to the sound
source reaching full intensity. A ramp-up procedure, involving a step-
wise increase in the number of airguns firing and total array volume
until all operational airguns are activated and the full volume is
achieved, is required at all times as part of the activation of the
acoustic source. All operators must adhere to the following pre-start
clearance and ramp-up requirements:
<bullet> The operator must notify a designated PSO of the planned
start of ramp-up as agreed upon with the lead PSO; the notification
time should not be less than 60 minutes prior to the planned ramp-up in
order to allow the PSOs time to monitor the pre-start clearance zone
(and extended SZ) for 30 minutes prior to the initiation of ramp-up
(pre-start clearance);
<bullet> Ramp-ups shall be scheduled so as to minimize the time
spent with the source activated prior to reaching the designated run-
in;
<bullet> One of the PSOs conducting pre-start clearance
observations must be notified again immediately prior to initiating
ramp-up procedures and the operator must receive confirmation from the
PSO to proceed;
<bullet> Ramp-up may not be initiated if any marine mammal is
within the applicable shutdown or buffer zone. If a marine mammal is
observed within the pre-start clearance zone (or extended SZ, for
beaked whales and Kogia species) during the 30 minute pre-start
clearance period, ramp-up may not begin until the animal(s) has been
observed exiting the zones or until an additional time period has
elapsed with no further sightings (15 minutes for small odontocetes,
and 30 minutes for all mysticetes and all other odontocetes, including
sperm whales, beaked whales, and large delphinids, such as pilot
whales);
<bullet> Ra
[…truncated; see source link]Indexed from Federal Register on June 7, 2023.
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.