Notice2024-16112
Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to Hilcorp Alaska, LLC Production Drilling Support in Cook Inlet, Alaska
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
July 24, 2024
Issuing agencies
Commerce DepartmentNational Oceanic and Atmospheric Administration
Abstract
NMFS has received a request from Hilcorp Alaska, LLC (Hilcorp) for authorization to take marine mammals incidental to production drilling support activities in Cook Inlet, Alaska. 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 89, Number 142 (Wednesday, July 24, 2024)]
[Notices]
[Pages 60164-60202]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2024-16112]
[[Page 60163]]
Vol. 89
Wednesday,
No. 142
July 24, 2024
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 Hilcorp Alaska, LLC Production Drilling
Support in Cook Inlet, Alaska; Notice
Federal Register / Vol. 89 , No. 142 / Wednesday, July 24, 2024 /
Notices
[[Page 60164]]
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DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
[RTID 0648-XD960]
Takes of Marine Mammals Incidental to Specified Activities;
Taking Marine Mammals Incidental to Hilcorp Alaska, LLC Production
Drilling Support in Cook Inlet, Alaska
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 Hilcorp Alaska, LLC (Hilcorp)
for authorization to take marine mammals incidental to production
drilling support activities in Cook Inlet, Alaska. 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 August
23, 2024.
ADDRESSES: Comments should be addressed to Jolie Harrison, Chief,
Permits and Conservation Division, Office of Protected Resources,
National Marine Fisheries Service and should be submitted via email to
<a href="/cdn-cgi/l/email-protection#0a435e5a247e7379656424676565786f4a64656b6b246d657c"><span class="__cf_email__" data-cfemail="2d64797d0359545e4243034042425f486d43424c4c034a425b">[email protected]</span></a>. Electronic copies of the application and
supporting documents, as well as a list of the references cited in this
document, may be obtained online at: <a href="https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-oil-and-gas">https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-oil-and-gas</a>. In case of problems accessing these documents, please call the
contact listed below.
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="https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-oil-and-gas">https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-oil-and-gas</a> without change. All personal
identifying information (e.g., name, address) voluntarily submitted by
the commenter may be publicly accessible. Do not submit confidential
business information or otherwise sensitive or protected information.
FOR FURTHER INFORMATION CONTACT: Reny Tyson Moore, Office of Protected
Resources, NMFS, (301) 427-8401.
SUPPLEMENTARY INFORMATION:
Background
The MMPA prohibits the ``take'' of marine mammals, with certain
exceptions. Sections 101(a)(5)(A) and (D) of the MMPA (16 U.S.C. 1361
et seq.) direct the Secretary of Commerce (as delegated to NMFS) to
allow, upon request, the incidental, but not intentional, taking of
small numbers of marine mammals by U.S. citizens who engage in a
specified activity (other than commercial fishing) within a specified
geographical region if certain findings are made and either regulations
are proposed or, if the taking is limited to harassment, a notice of a
proposed 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 monitoring and
reporting of the takings. The definitions of all applicable MMPA
statutory terms cited above are included in the relevant sections
below.
National Environmental Policy Act
To comply with the National Environmental Policy Act of 1969 (NEPA;
42 U.S.C. 4321 et seq.) and NOAA Administrative Order (NAO) 216-6A,
NMFS must review our proposed action (i.e., the issuance of an IHA)
with respect to potential impacts on the human environment.
Accordingly, NMFS is preparing an Environmental Assessment (EA) to
consider the environmental impacts associated with the issuance of the
proposed IHA. NMFS' draft EA will be made available at <a href="https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-oil-and-gas">https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-oil-and-gas</a> at the time of publication of this
notice. We will review all comments submitted in response to this
notice prior to concluding our NEPA process or making a final decision
on the IHA request.
Summary of Request
On August 2, 2023, NMFS received a request from Hilcorp for an IHA
to take marine mammals incidental to production drilling support
activities in Cook Inlet, Alaska. Following NMFS' review of the
application, Hilcorp submitted revised versions on September 29, 2023,
December 27, 2023, February 29, 2024, and April 8, 2024. The
application was deemed adequate and complete on April 12, 2024.
Hilcorp's request is for take of 12 species of marine mammals, by Level
B harassment. Neither Hilcorp nor NMFS expect serious injury or
mortality to result from this activity and, therefore, an IHA is
appropriate.
NMFS previously issued an IHA to Hilcorp for similar work (87 FR
62364, October 1, 2022). Hilcorp complied with all the requirements
(e.g., mitigation, monitoring, and reporting) of the previous IHA, and
information regarding their monitoring results may be found in the
Potential Effects of Specified Activities on Marine Mammals and their
Habitat section of this notice.
Description of Proposed Activity
Overview
Hilcorp plans to use three tug boats to tow and hold, and up to
four tug boats to position, a jack-up rig to support production
drilling at existing platforms in middle Cook Inlet and Trading Bay,
Alaska, on 6 non-consecutive days between September 14, 2024, and
September 13, 2025. Noise produced by tugs under load with a jack-up
rig may result in take, by Level B harassment, of twelve marine mammal
species.
Dates and Duration
The IHA would be effective from September 14, 2024, through
September 13, 2025. As noted above, Hilcorp proposes to conduct the
jack-up rig towing, holding, and positioning activities on 6 non-
consecutive days
[[Page 60165]]
during the authorization period. Hilcorp would only conduct tug towing
rig activities at night if necessary to accommodate a favorable tide.
Specific Geographic Region
Hilcorp's proposed activities would take place in middle Cook Inlet
and Trading Bay, Alaska, extending north from Rig Tenders Dock on the
eastern side of Cook Inlet near Nikiski to an area approximately 32
kilometers (km) south of Point Possession, west to the Tyonek platform
in middle Cook Inlet, south to the Dolly Varden platform in Trading
Bay, and across Cook Inlet to the Rig Tenders Dock. For the purposes of
this project, lower Cook Inlet refers to waters south of the East and
West Forelands; middle Cook Inlet refers to waters north of the East
and West Forelands and south of Threemile River on the west and Point
Possession on the east; Trading Bay refers to waters from approximately
the Granite Point Tank Farm on the north to the West Foreland on the
south; and upper Cook Inlet refers to waters north and east of Beluga
River on the west and Point Possession on the east. A map of the
specific area in which Hilcorp plans to operate is provided in figure 1
below.
BILLING CODE 3510-22-P
[[Page 60166]]
[GRAPHIC] [TIFF OMITTED] TN24JY24.000
BILLING CODE 3510-22-C
Detailed Description of the Specified Activity
Hilcorp proposes to conduct production drilling activities from
existing platforms in middle Cook Inlet and Trading Bay between
September 14, 2024, and September 13, 2025, during which period there
would be a need for an estimated six days of tug activity. For the
preceding months (September 2023 to September 2024), Hilcorp is
operating under an existing IHA (See 87 FR 62364, October 14, 2022). In
2024, the Spartan 151 jack-up rig (or an equivalent rig) will be
mobilized for production drilling from the Rig Tenders Dock in Nikiski
and towed to an existing platform under the aforementioned 2023-2024
IHA. Tug activities associated with the current IHA request would
include one demobilization effort of a jack-up rig (Spartan 151 or
equivalent rig) from an existing platform to Rig Tenders Dock in
Nikiski, one jack-up rig relocation between existing
[[Page 60167]]
platforms, and one remobilization effort of the jack-up rig from Rig
Tenders Dock in Nikiski to middle Cook Inlet. A jack-up rig is a type
of mobile offshore drill unit used in offshore oil and gas drilling
activities. It is comprised of a buoyant mobile platform or hull with
moveable legs that are adjusted to raise and lower the hull over the
surface of the water. Three tugs are needed to safely and effectively
tow the jack-up rig during moves and to hold it into the correct
position where it can be temporarily secured to the seafloor. A fourth
tug may be needed to assist with the positioning of the jack-up rig on
location.
Development drilling activities occur from existing platforms
within Cook Inlet through either well slots or existing wellbores in
existing platform legs, and no well construction occurs during
production drilling. All Hilcorp platforms have potential for
development drilling activities. Drilling activities from platforms
within Cook Inlet are accomplished by using conventional drilling
equipment from a variety of rig configurations.
Some platforms in Cook Inlet have permanent drilling rigs installed
that operate using power provided by the platform power generation
systems; other platforms do not have drill rigs, and the use of a
mobile drill rig is required. Mobile offshore drill rigs may be powered
by the platform power generation system (if compatible with the
platform power generation system) or may self-generate power with the
use of diesel-powered generators.
While traveling with the jack-up rig during the proposed moves, the
most common configuration is two tugs positioned side by side
(approximately 30 to 60 m apart), pulling from the front of the jack-up
rig, and one tug approximately 200 m behind the front tugs positioned
behind the jack-up rig, applying tension on the line as needed for
steering and straightening. While positioning the jack-up rig on a
platform, the tugs may be fanned out around the jack-up rig to provide
the finer control of movement necessary to safely position the jack-up
rig on the platform.
Upon arrival and readiness to position the rig adjacent to a
platform, a fourth tug would be on standby to provide assistance. The
fourth tug would not be expected to extend assistance beyond one hour.
The horsepower of each of the tugs used during the proposed activities
may range between 4,000 and 8,000. Specifications of the tugs
anticipated for use are provided in table 1 below. If these specific
tugs are not available, the tugs contracted would be of similar size
and power to those listed in table 1.
Table 1--Description of Tugs (or Similar) Used for Towing, Holding, and Positioning the Jack-Up Rig
----------------------------------------------------------------------------------------------------------------
Vessel Activity Length (m) Width (m) Gross tonnage
----------------------------------------------------------------------------------------------------------------
Bering Wind........................ Towing, holding, and 22 10 144
positioning the jack-up
rig.
Stellar Wind....................... Towing, holding, and 32 11 160
positioning the jack-up
rig.
Glacial Wind....................... Towing, holding, and 37 11 196
positioning the jack-up
rig.
Dr. Hank Kaplan.................... Standby tug used only for 23 11 196
positioning the jack-up
rig, if needed.
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Note: m = meters.
The amount of time the tugs are under load transiting, holding, and
positioning the jack-up rig in Cook Inlet would be tide-dependent. The
amount of operational effort (i.e., power output) the tugs use for
transiting would depend on whether the tugs are towing with or against
the tide and could vary across a tidal cycle as the current increases
or decreases in speed over time. Hilcorp would make every effort to
transit with the tide (which requires lower power output) and minimize
transit against the tide (which requires higher power output).
A high slack tide would be preferred to position the jack-up rig on
an existing platform or well site. The relatively slow current and calm
conditions at a slack tide would enable the tugs to perform the fine
movements necessary to safely position the jack-up rig within several
feet of the platform. Additionally, positioning and securing the jack-
up rig at high slack tide rather than low slack tide would allow for
the legs to be pinned down (jack the legs down onto the sea floor) at
an adequate height to ensure that the hull of the jack-up rig remains
above the water level of the subsequent incoming high tide. Because 12
hours elapse between each high slack tide, tugs are generally under
load for those 12 hours, even if the towed distance is small, as high
slack tides are preferred to both attach and detach the jack-up rig
from the tugs. Once the tugs are on location with the jack-up rig at
high slack tide (12 hours from the previous departure), there is a 1 to
2-hour window when the tide is slow enough for the tugs to initiate
positioning the jack-up rig and pin the legs to the seafloor on
location. The tugs are estimated to be under load, generally at half-
power conditions or less, for up to 14 hours from the time of departure
through the initial positioning attempt of the jack-up rig. One
additional tug may engage during positioning activities to assist with
fine movements necessary to place the jack-up rig. The fourth tug is
estimated to engage with the three tugs during a positioning attempt
for up to 1 hour at half power.
If the first positioning attempt takes longer than anticipated, the
increasing current speed would prevent the tugs from safely positioning
the jack-up rig on location. If the first positioning attempt is not
successful, the jack-up rig would be pinned down at a nearby location
and the tugs would be released from the jack-up rig and no longer under
load. The tugs would remain nearby, generally floating with the
current. Approximately an hour before the next high slack tide, the
tugs would re-attach to the jack-up rig and reattempt positioning over
a period of 2 to 3 hours. Positioning activities would generally be at
half power. If a second attempt is needed, the tugs would be under load
holding or positioning the jack-up rig on a second day for up to 5
hours. Typically, the jack-up rig can be successfully positioned over
the platform in one or two attempts.
During a location-to-location transport (e.g., platform-to-
platform), the tugs would transport the jack-up rig traveling with the
tide in nearly all circumstances except in situations that threaten the
safety of humans and/or infrastructure integrity. In a north-to-south
transit, the tugs would tow the jack-up rig with the outgoing tide and
would typically arrive at their next location to position the jack-up
rig on the low slack tide, requiring half power or a lower power output
during the transport. In a south-to-north transit, Hilcorp would prefer
to pull the jack-up rig from the platform on
[[Page 60168]]
a low slack tide to begin transiting north following the incoming tide.
This would maximize their control over the jack-up rig and would
require half power or a lower power output. There may be a situation
wherein the tugs pulling the jack-up rig begin transiting with the tide
to their next location, miss the tide window to safely set the jack-up
rig on the platform or pin it nearby, and so have to transport the
jack-up rig against the tide to a safe harbor. Tugs may also need to
transport the jack-up rig against the tide if large pieces of ice or
extreme wind events threaten the stability of the jack-up rig on the
platform. All tug towing, holding, or positioning would be done in a
manner implementing best management practices to preserve water
quality, and no work would occur around creek mouths or river systems
leading to prey abundance reductions.
Although the variability in power output from the tugs can range
from an estimated 20 percent to 90 percent throughout the hours under
load with the jack-up rig, as described above, the majority of the
hours (spent transiting, holding, and positioning) occur at half power
or less. See the Estimated Take of Marine Mammals section of this
proposed notice of issuance for more detail on assumptions related to
power output.
Proposed mitigation, monitoring, and reporting measures are
described in detail later in this document (please see Proposed
Mitigation and Proposed Monitoring and Reporting).
Description of Marine Mammals in the Area of Specified Activities
Sections 3 and 4 of the application summarize available information
regarding status and trends, distribution and habitat preferences, and
behavior and life history of the potentially affected species. NMFS
fully considered all of this information, and we refer the reader to
these descriptions, instead of reprinting the information. Additional
information regarding population trends and threats may be found in
NMFS' Stock Assessment Reports (SARs; <a href="https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments">https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments</a>) and
more general information about these species (e.g., physical and
behavioral descriptions) may be found on NMFS' website (<a href="https://www.fisheries.noaa.gov/find-species">https://www.fisheries.noaa.gov/find-species</a>).
Table 2 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 anticipated or proposed
to be authorized here, 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 managed stocks in this region are assessed in
NMFS' U.S. 2022 SARs. All values presented in table 2 are the most
recent available at the time of publication (including from the draft
2023 SARs) and are available online at: <a href="https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments">https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments</a>.
Table 2--Species \1\ Likely Impacted by the Specified Activities
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ESA/MMPA status; Stock abundance (CV,
Common name Scientific name Stock Strategic (Y/N) Nmin, most recent PBR Annual M/
\2\ abundance survey) \3\ SI \4\
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Order Artiodactyla--Cetacea--Mysticeti (baleen whales)
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Family Eschrichtiidae:
Gray Whale...................... Eschrichtius robustus.. Eastern N Pacific...... -, -, N 26,960 (0.05, 25,849, 801 131
2016).
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Family Balaenidae
Family Balaenopteridae (rorquals):
Fin Whale....................... Balaenoptera physalus.. Northeast Pacific...... E, D, Y UND \5\ (UND, UND, UND 0.6
2013).
Humpback Whale.................. Megaptera novaeangliae. Hawai'i................ -, -, N 11,278 (0.56, 7,265, 127 27.09
2020).
Mexico-North Pacific... T, D, Y N/A\6\ (N/A, N/A, UND 0.57
2006).
Western North Pacific.. E, D, Y 1,084 (0.088, 1,007, 3.4 5.82
2006).
Minke Whale..................... Balaenoptera Alaska................. -, -, N N/A \7\ (N/A, N/A, N/ UND 0
acutorostrata. A).
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Odontoceti (toothed whales, dolphins, and porpoises)
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Family Delphinidae:
Killer Whale.................... Orcinus orca........... Eastern North Pacific -, -, N 1,920 (N/A, 1,920, 19 1.3
Alaska Resident. 2019).
Eastern North Pacific -, -, N 587 (N/A, 587, 2012).. 5.9 0.8
Gulf of Alaska,
Aleutian Islands and
Bering Sea Transient.
Pacific White-Sided Dolphin..... Lagenorhynchus North Pacific.......... -, -, N 26,880 (N/A, N/A, UND 0
obliquidens. 1990).
Family Monodontidae (white whales):
Beluga Whale.................... Delphinapterus leucas.. Cook Inlet............. E, D, Y 279 \8\ (0.061, 267, 0.53 0
2018).
Family Phocoenidae (porpoises):
[[Page 60169]]
Dall's Porpoise................. Phocoenoides dalli..... Alaska................. -, -, N UND \9\ (UND, UND, UND 37
2015).
Harbor Porpoise................. Phocoena phocoena...... Gulf of Alaska......... -, -, Y 31,046 (0.21, N/A, UND 72
1998).
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Order Carnivora--Pinnipedia
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Family Otariidae (eared seals and
sea lions):
CA Sea Lion..................... Zalophus californianus. U.S.................... -, -, N 257,606 (N/A, 233,515, 14,011 >321
2014).
Steller Sea Lion................ Eumetopias jubatus..... Western................ E, D, Y 49,837 \10\ (N/A, 299 267
49,837, 2020).
Family Phocidae (earless seals):
Harbor Seal..................... Phoca vitulina......... Cook Inlet/Shelikof -, -, N 28,411 (N/A, 26,907, 807 107
Strait. 2018).
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\1\ Information on the classification of marine mammal species can be found on the web page for The Society for Marine Mammalogy's Committee on Taxonomy
(<a href="https://marinemammalscience.org/science-and-publications/list-marine-mammal-species-subspecies/">https://marinemammalscience.org/science-and-publications/list-marine-mammal-species-subspecies/</a>; Committee on Taxonomy (2022)).
\2\ Endangered Species Act (ESA) status: Endangered (E), Threatened (T)/MMPA status: Depleted (D). A dash (-) indicates that the species is not listed
under the ESA or designated as depleted under the MMPA. Under the MMPA, a strategic stock is one for which the level of direct human-caused mortality
exceeds PBR or which is determined to be declining and likely to be listed under the ESA within the foreseeable future. Any species or stock listed
under the ESA is automatically designated under the MMPA as depleted and as a strategic stock.
\3\ 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.
\4\ These values, found in NMFS's SARs, represent annual levels of human-caused mortality plus serious injury from all sources combined (e.g.,
commercial fisheries, ship strike). Annual M/SI often cannot be determined precisely and is in some cases presented as a minimum value or range. A CV
associated with estimated mortality due to commercial fisheries is presented in some cases.
\5\ The best available abundance estimate for this stock is not considered representative of the entire stock as surveys were limited to a small portion
of the stock's range. Based upon this estimate and the Nmin, the PBR value is likely negatively biased for the entire stock.
\6\ Abundance estimates are based upon data collected more than 8 years ago and, therefore, current estimates are considered unknown.
\7\ Reliable population estimates are not available for this stock. Please see Friday et al. (2013) and Zerbini et al. (2006) for additional information
on numbers of minke whales in Alaska.
\8\ On June 15, 2023, NMFS released an updated abundance estimate for endangered CIBWs in Alaska (Goetz et al., 2023). Data collected during NOAA
Fisheries' 2022 aerial survey suggest that the whale population is stable or may be increasing slightly. Scientists estimated that the population size
is between 290 and 386, with a median best estimate of 331. In accordance with the MMPA, this population estimate will be incorporated into the CIBW
SAR, which will be reviewed by an independent panel of experts, the Alaska Scientific Review Group. After this review, the SAR will be made available
as a draft for public review before being finalized.
\9\ The best available abundance estimate is likely an underestimate for the entire stock because it is based upon a survey that covered only a small
portion of the stock's range.
\10\ Nest is best estimate of counts, which have not been corrected for animals at sea during abundance surveys.
As indicated above, all 12 species (with 15 managed stocks) in
table 2 temporally and spatially co-occur with the activity to the
degree that take is reasonably likely to occur. In addition, the
northern sea otter may be found in Cook Inlet, Alaska. However,
northern sea otters are managed by the U.S. Fish and Wildlife Service
and are not considered further in this document.
Gray Whale
The stock structure for gray whales in the Pacific has been studied
for a number of years and remains uncertain as of the most recent
(2022) Pacific SARs (Carretta et al., 2023). Gray whale population
structure is not determined by simple geography and may be in flux due
to evolving migratory dynamics (Carretta et al., 2023). Currently, the
SARs delineate a western North Pacific (WNP) gray whale stock and an
eastern North Pacific (ENP) stock based on genetic differentiation
(Carretta et al., 2023). WNP gray whales are not known to feed in or
travel to upper Cook Inlet (Conant and Lohe, 2023; Weller et al.,
2023). Therefore, we assume that gray whales near the project area are
members of the ENP stock.
An Unusual Mortality Event (UME) for gray whales along the West
Coast and in Alaska occurred from December 17, 2018 through November 9,
2023. During that time, 146 gray whales stranded off the coast of
Alaska. The investigative team concluded that the preliminary cause of
the UME was localized ecosystem changes in the whale's Subarctic and
Arctic feeding areas that led to changes in food, malnutrition,
decreased birth rates, and increased mortality (see <a href="https://www.fisheries.noaa.gov/national/marine-life-distress/2019-2023-gray-whale-unusual-mortality-event-along-west-coast-and">https://www.fisheries.noaa.gov/national/marine-life-distress/2019-2023-gray-whale-unusual-mortality-event-along-west-coast-and</a> for more
information).
Gray whales are infrequent visitors to Cook Inlet, but may be
seasonally present during spring and fall in the lower inlet (Bureau of
Ocean Energy Management (BOEM), 2021). Migrating gray whales pass
through the lower inlet during their spring and fall migrations to and
from their primary summer feeding areas in the Bering, Chukchi, and
Beaufort seas (Swartz, 2018; Silber et al., 2021; BOEM, 2021). Several
surveys and monitoring programs have sighted gray whales in lower Cook
Inlet (Shelden et al., 2013; Owl Ridge, 2014; Lomac-MacNair et al.,
2013, 2014; Kendall et al., 2015, as cited in Weston and SLR, 2022).
Gray whales are occasionally seen in mid- and upper Cook Inlet, Alaska,
but they are not common. During NMFS aerial surveys conducted in June
1994, 2000, 2001, 2005, and 2009 gray whales were observed in Cook
Inlet near Port Graham and Elizabeth Island as well as near Kamishak
Bay, with one gray whale observed as far north as the Beluga River
(Shelden et al., 2013). Gray whales were also observed offshore of Cape
Starichkof in 2013 by marine mammal observers monitoring Buccaneer's
Cosmopolitan drilling project (Owl Ridge, 2014) and in middle Cook
Inlet in 2014 during the 2014 Apache 2D seismic survey (Lomac-MacNair
et al., 2015). Several projects performed in Cook Inlet in recent years
reported no observations of gray whales. These project activities
included the SAExploration seismic survey in 2015 (Kendall and Cornick,
2015), the 2018 Cook Inlet Pipeline (CIPL) Extension Project
(Sitkiewicz et al., 2018), the 2019 Hilcorp seismic survey in lower
Cook Inlet (Fairweather Science, 2020),
[[Page 60170]]
and Hilcorp's 2023 aerial and rig-based monitoring efforts.
In 2020, a young male gray whale was stranded in the Twentymile
River near Girdwood for over a week before swimming back into Turnagain
Arm. The whale did not survive and was found dead in west Cook Inlet
later that month (NMFS, 2020). One gray whale was sighted in Knik Arm
near the Port of Alaska (POA) in Anchorage in upper Cook Inlet in May
of 2020 during observations conducted during construction of the
Petroleum and Cement Terminal project (61N Environmental, 2021). The
sighting occurred less than a week before the reports of the gray whale
stranding in the Twentymile River and was likely the same animal. In
2021, one small gray whale was sighted in Knik Arm near Ship Creek,
south of the POA (61N Environmental, 2022a). Although some sightings
have been documented in the middle and upper Inlet, the gray whale
range typically only extends into the lower Cook Inlet region.
Humpback Whale
The 2022 NMFS Alaska and Pacific SARs described a revised stock
structure for humpback whales which modifies the previous designated
stocks to align more closely with the ESA-designated Distinct
Population Segments (DPSs) (Carretta et al., 2023; Young et al., 2023).
Specifically, the three previous North Pacific humpback whale stocks
(Central and Western North Pacific stocks and a CA/OR/WA stock) were
replaced by five stocks, largely corresponding with the ESA-designated
DPSs. These include Western North Pacific and Hawaii stocks and a
Central America/Southern Mexico-California (CA)/Oregon (OR)/Washington
(WA) stock (which corresponds with the Central America DPS). The
remaining two stocks, corresponding with the Mexico DPS, are the
Mainland Mexico-CA/OR/WA and Mexico-North Pacific stocks (Carretta et
al., 2023; Young et al., 2023). The former stock is expected to occur
along the west coast from California to southern British Columbia,
while the latter stock may occur across the Pacific, from northern
British Columbia through the Gulf of Alaska and Aleutian Islands/Bering
Sea region to Russia.
The Hawaii stock consists of one demographically independent
population (DIP) (Hawaii--Southeast Alaska/Northern British Columbia
DIP) and the Hawaii--North Pacific unit, which may or may not be
composed of multiple DIPs (Wade et al., 2021). The DIP and unit are
managed as a single stock at this time, due to the lack of data
available to separately assess them and lack of compelling conservation
benefit to managing them separately (NMFS 2019, 2022c, 2023a). The DIP
is delineated based on two strong lines of evidence: genetics and
movement data (Wade et al., 2021). Whales in the Hawaii--Southeast
Alaska/Northern British Columbia DIP winter off Hawaii and largely
summer in Southeast Alaska and Northern British Columbia (Wade et al.,
2021). The group of whales that migrate from Russia, western Alaska
(Bering Sea and Aleutian Islands), and central Alaska (Gulf of Alaska
excluding Southeast Alaska) to Hawaii have been delineated as the
Hawaii--North Pacific unit (Wade et al., 2021). There are a small
number of whales that migrate between Hawaii and southern British
Columbia/Washington, but current data and analyses do not provide a
clear understanding of which unit these whales belong to (Wade et al.,
2021; Carretta et al., 2023; Young et al., 2023).
The Mexico--North Pacific stock is likely composed of multiple
DIPs, based on movement data (Martien et al., 2021, Wade, 2021, Wade et
al., 2021). However, because currently available data and analyses are
not sufficient to delineate or assess DIPs within the unit, it was
designated as a single stock (NMFS, 2019, 2022d, 2023a). Whales in this
stock winter off Mexico and the Revillagigedo Archipelago and summer
primarily in Alaska waters (Martien et al., 2021; Carretta et al.,
2023; Young et al., 2023).
The Western North Pacific stock consists of two units--the
Philippines/Okinawa--North Pacific unit and the Marianas/Ogasawara--
North Pacific unit. The units are managed as a single stock at this
time, due to a lack of data available to separately assess them (NMFS,
2019, 2022d, 2023a). Recognition of these units is based on movements
and genetic data (Oleson et al., 2022). Whales in the Philippines/
Okinawa--North Pacific unit winter near the Philippines and in the
Ryukyu Archipelago and migrate to summer feeding areas primarily off
the Russian mainland (Oleson et al., 2022). Whales that winter off the
Mariana Archipelago, Ogasawara, and other areas not yet identified and
then migrate to summer feeding areas off the Commander Islands, and to
the Bering Sea and Aleutian Islands comprise the Marianas/Ogasawara--
North Pacific unit.
The most comprehensive photo-identification data available suggest
that approximately 89 percent of all humpback whales in the Gulf of
Alaska are from the Hawaii stock, 11 percent are from the Mexico stock,
and less than 1 percent are from the Western North Pacific stock (Wade,
2021). Individuals from different stocks are known to intermix in
feeding grounds. There is no designated critical habitat for humpback
whales in or near the Project area (86 FR 21082, April 21, 2021), nor
does the project overlap with any known biologically important areas.
Humpback whales are encountered regularly in lower Cook Inlet and
occasionally in mid-Cook Inlet; sightings are rare in upper Cook Inlet.
Eighty-three groups containing an estimated 187 humpbacks were sighted
during the Cook Inlet beluga whale aerial surveys conducted by NMFS
from 1994 to 2012 (Shelden et al., 2013). Surveys conducted north of
the forelands have documented small numbers in middle Cook Inlet.
During the 2014 Apache seismic surveys in Cook Inlet, five groups (six
individuals) were reported, with three groups north of the forelands on
the east side of the inlet (Lomac-MacNair et al., 2014). In 2015,
during the construction of the Furie Operating Alaska, LLC (Furie)
platform and pipeline, four groups of humpback whales were documented.
Another group of 6 to 10 unidentified whales, thought to be either
humpback or gray whales, was sighted approximately 15 km northeast of
the Julius R. Platform. Large cetaceans were visible near the project
(i.e., whales or blows were visible) for 2 hours out of the 1,275 hours
of observation conducted (Jacobs, 2015). During SAExploration's 2015
seismic program, three humpback whales were observed in Cook Inlet,
including two near the Forelands and one in lower Cook Inlet (Kendall
et al., 2015 as cited in Weston and SLR, 2022). Hilcorp did not record
any sightings of humpback whales from their aerial or rig-based
monitoring efforts in 2023 (Horsley and Larson, 2023).
Minke Whale
Two stocks of minke whales occur within U.S. waters: Alaska and
California/Oregon/Washington (Muto et al., 2022). The Alaskan stock of
minke whales is considered migratory, as they are speculated to migrate
seasonally from the Bering and Chukchi Seas in fall to areas of the
central North Pacific Ocean (Delarue et al., 2013). Although they are
likely migratory in Alaska, minke whales have been observed off Cape
Starichkof and Anchor Point year-round (Muto et al., 2017).
Minke whales are most abundant in the Gulf of Alaska during summer
and occupy localized feeding areas (Zerbini et al., 2006). During the
NMFS annual and semiannual surveys of Cook Inlet, minke whales were
observed near
[[Page 60171]]
Anchor Point in 1998, 1999, 2006, and 2021 (Shelden et al., 2013,
2015b, 2017, 2022; Shelden and Wade, 2019) and near Ninilchik and the
middle of lower Cook Inlet in 2021 (Shelden et al., 2022). Minkes were
sighted southeast of Kalgin Island and near Homer during Apache's 2014
survey (Lomac-MacNair et al., 2014), and one was observed near Tuxedni
Bay in 2015 (Kendall et al., 2015, as cited in Weston and SLR, 2022).
During Hilcorp's seismic survey in lower Cook Inlet in the fall of
2019, eight minke whales were observed (Fairweather Science, 2020). In
2018, no minke whales were observed during observations conducted for
the CIPL project near Tyonek (Sitkiewicz et al., 2018). Minke whales
were also not recorded during Hilcorp's aerial or rig-based monitoring
efforts in 2023 (Horsley and Larson, 2023).
Fin Whale
In U.S. Pacific waters, fin whales are seasonally found in the Gulf
of Alaska, and Bering Sea and as far north as the northern Chukchi Sea
(Muto et al., 2021). Several surveys have been conducted to assess the
distribution and habitat preferences of fin whales within parts of
their range in the North Pacific. In coastal waters of the Aleutians
and the Alaska Peninsula, they were found primarily from the Kenai
Peninsula to the Shumagin Islands, with a higher abundance near the
Semidi Islands and Kodiak Island (Zerbini et al., 2006). An
opportunistic survey in the Gulf of Alaska revealed that fin whales
were concentrated west of Kodiak Island, in Shelikof Strait, and in the
southern Cook Inlet region, with smaller numbers observed over the
shelf east of Kodiak to Prince William Sound (Alaska Fisheries Science
Center [AFSC], 2003). Muto et al. (2021) reported visual sightings and
acoustic detections in the northeastern Chukchi Sea have been
increasing, suggesting that the stock may be re-occupying habitat used
prior to large-scale commercial whaling. Delarue et al. (2013) also
detected fin whale calls in the northeastern Chukchi Sea from July
through October in a 3-year acoustic study.
Fin whales' range extends into lower Cook Inlet; however, their
sightings are infrequent, and they are mostly spotted near the inlet's
entrance. Fin whales are usually observed as individuals traveling
alone, although they are sometimes observed in small groups. Rarely,
large groups of 50 to 300 fin whales can travel together during
migrations (NMFS, 2010). Fin whales in Cook Inlet have only been
observed as individuals or in small groups. From 2000 to 2022, 10
sightings of 26 estimated individual fin whales in lower Cook Inlet
were observed during NMFS aerial surveys (Shelden et al., 2013, 2015b,
2017, 2022; Shelden and Wade, 2019). No fin whales were observed during
the 2018 Harvest's CIPL Extension Project Acoustic Monitoring Program
in middle Cook Inlet (Sitkiewicz et al., 2018). In September and
October 2019, Castellote et al. (2020) detected fin whales acoustically
in lower Cook Inlet during three-dimensional (3D) seismic surveys,
which coincided with the Hilcorp lower Cook Inlet seismic survey.
During this period, 8 sightings of 23 individual fin whales were
reported, indicating the offshore waters of lower Cook Inlet may be
more heavily used than previously believed, especially during the fall
season (Fairweather Science, 2020). Hilcorp did not record any
sightings of fin whales from their aerial or rig-based monitoring
efforts in 2023 (Horsley and Larson, 2023).
Beluga Whale
Five stocks of beluga whales are recognized in Alaska: the Beaufort
Sea stock, eastern Chukchi Sea stock, eastern Bering Sea stock, Bristol
Bay stock, and Cook Inlet stock (Young et al., 2023). The Cook Inlet
stock is geographically and genetically isolated from the other stocks
(O'Corry-Crowe et al., 1997; Laidre et al., 2000) and resides year-
round in Cook Inlet (Laidre et al., 2000; Castellote et al., 2020).
Only the Cook Inlet stock inhabits the proposed project area. Cook
Inlet beluga whales (CIBWs) were designated as depleted under the MMPA
in 2000 (65 FR 34950, May 31, 2000), and as a DPS and listed as
endangered under the ESA in October 2008 (73 FR 62919, October 10,
2008) when the species failed to recover following a moratorium on
subsistence harvest. Between 2008 and 2018, CIBWs experienced a decline
of about 2.3 percent per year (Wade et al., 2019). The decline
overlapped with the northeast Pacific marine heatwave that occurred
from 2014 to 2016 in the Gulf of Alaska, significantly impacting the
marine ecosystem (Suryan et al., 2021, as cited in Goetz et al., 2023).
In June 2023, NMFS released an updated abundance estimate for CIBWs
in Alaska that incorporates aerial survey data from June 2021 and 2022
and accounted for visibility bias (Goetz et al., 2023). This report
estimated that CIBW abundance is between 290 and 386, with a median
best estimate of 331. Goetz et al. (2023) also present an analysis of
population trends for the most recent 10-year period (2012-2022). The
addition of data from the 2021 and 2022 survey years in the analysis
resulted in a 65.1 percent probability that the CIBW population is now
increasing at 0.9 percent per year (95 percent prediction interval of -
3 to 5.7 percent). This increase drops slightly to 0.2 percent per year
(95 percent prediction interval of -1.8 to 2.6 percent) with a 60
percent probability that the CIBW population is increasing more than 1
percent per year when data from 2021, which had limited survey coverage
due to poor weather, are excluded from the analysis. Median group size
estimates in 2021 and 2022 were 34 and 15, respectively (Goetz et al.,
2023). For management purposes, NMFS has determined that the carrying
capacity of Cook Inlet is 1,300 CIBWs (65 FR 34590, May 31, 2000) based
on historical CIBW abundance estimated by Calkins (1989).
Threats that have the potential to impact this stock and its
habitat include the following: changes in prey availability due to
natural environmental variability, ocean acidification, and commercial
fisheries; climatic changes affecting habitat; predation by killer
whales; contaminants; noise; ship strikes; waste management; urban
runoff; construction projects; and physical habitat modifications that
may occur as Cook Inlet becomes increasingly urbanized (Moore et al.,
2000; Hobbs et al., 2015; NMFS, 2016b). Another source of CIBW
mortality in Cook Inlet is predation by transient-type (mammal-eating)
killer whales (NMFS, 2016b; Shelden et al., 2003). No human-caused
mortality or serious injury of CIBWs through interactions with
commercial, recreational, and subsistence fisheries, takes by
subsistence hunters, and or human-caused events (e.g., entanglement in
marine debris, ship strikes) has been recently documented and
harvesting of CIBWs has not occurred since 2008 (NMFS, 2008b).
Recovery Plan. In 2010, a Recovery Team, consisting of a Science
Panel and Stakeholder Panel, began meeting to develop a Recovery Plan
for the CIBW. The Final Recovery Plan was published in the Federal
Register on January 5, 2017 (82 FR 1325). In September 2022, NMFS
completed the ESA 5-year review for the CIBW DPS and determined that
the CIBW DPS should remain listed as endangered (NMFS, 2022d).
In its Recovery Plan (82 FR 1325, January 5, 2017), NMFS identified
several potential threats to CIBWs, including: (1) high concern:
catastrophic events (e.g., natural disasters, spills, mass strandings),
cumulative effects of multiple stressors, and noise; (2) medium
concern: disease agents (e.g., pathogens, parasites, and harmful algal
[[Page 60172]]
blooms), habitat loss or degradation, reduction in prey, and
unauthorized take; and (3) low concern: pollution, predation, and
subsistence harvest. The recovery plan did not treat climate change as
a distinct threat but rather as a consideration in the threats of high
and medium concern. Other potential threats most likely to result in
direct human-caused mortality or serious injury of this stock include
vessel strikes.
Critical Habitat. On April 11, 2011, NMFS designated two areas of
critical habitat for CIBW (76 FR 20179). The designation includes 7,800
square kilometers (km\2\) of marine and estuarine habitat within Cook
Inlet, encompassing approximately 1,909 km\2\ in Area 1 and 5,891 km\2\
in Area 2 (see figure 1 in 76 FR 20179). Area 1 of the CIBW critical
habitat encompasses all marine waters of Cook Inlet north of a line
connecting Point Possession (lat. 61.04[deg] N, long. 150.37[deg] W)
and the mouth of Three Mile Creek (lat. 61.08.55[deg] N, long.
151.04.40[deg] W), including waters of the Susitna, Little Susitna, and
Chickaloon Rivers below mean higher high water (MHHW). From spring
through fall, Area 1 critical habitat has the highest concentration of
CIBWs due to its important foraging and calving habitat. Critical
Habitat Area 2 encompasses some of the fall and winter feeding grounds
in middle Cook Inlet. This area has a lower concentration of CIBWs in
spring and summer but is used by CIBWs in fall and winter. More
information on CIBW critical habitat can be found at <a href="https://www.fisheries.noaa.gov/action/critical-habitat-cook-inlet-beluga-whale">https://www.fisheries.noaa.gov/action/critical-habitat-cook-inlet-beluga-whale</a>.
The designation identified the following Primary Constituent
Elements, essential features important to the conservation of the CIBW:
(1) Intertidal and subtidal waters of Cook Inlet with depths of
less than 9 m mean lower-low water (MLLW) and within 8 km of high- and
medium-flow anadromous fish streams;
(2) Primary prey species, including four of the five species of
Pacific salmon (chum (Oncorhynchus keta), sockeye (Oncorhynchus nerka),
Chinook (Oncorhynchus tshawytscha), and coho (Oncorhynchus kisutch)),
Pacific eulachon (Thaleichthys pacificus), Pacific cod (Gadus
macrocephalus), walleye Pollock (Gadus chalcogrammus), saffron cod
(Eleginus gracilis), and yellowfin sole (Limanda aspera);
(3) The absence of toxins or other agents of a type or amount
harmful to CIBWs;
(4) Unrestricted passage within or between the critical habitat
areas; and
(5) The absence of in-water noise at levels resulting in the
abandonment of habitat by CIBWs.
Biologically Important Areas. Wild et al. (2023) delineated a Small
and Resident Population Biologically Important Area (BIA) in Cook Inlet
that is active year-round and overlaps Hilcorp's proposed project area.
The authors assigned the BIA an importance score of 2, an intensity
score of 2, a data support score of 3, and a boundary certainty score
of 2 (scores range from 1 to 3, with a higher score representing an
area of more concentrated or focused use and higher confidence in the
data supporting the BIA; Harrison et al., 2023). These scores indicate
that the BIA is of moderate importance and intensity, the authors have
high confidence that the population is small and resident and in the
abundance and range estimates of the population, and the boundary
certainty is medium (see Harrison et al. (2023) for additional
information about the scoring process used to identify BIAs). The
boundary of the CIBW BIA is consistent with NMFS' critical habitat
designation (Wild et al., 2023).
Ecology. Generally, female beluga whales reach sexual maturity at 9
to 12 years old, while males reach maturity later (O'Corry-Crowe,
2009); however, this can vary between populations. For example, in
Greenland, males in a population of beluga whales were found to reach
sexual maturity at 6 to 7 years of age and females at 4 to 7 years
(Heide-Joregensen and Teilmann, 1994). Suydam (2009) estimated that 50
percent of females were sexually mature at age 8.25 and the average age
at first birth was 8.27 years for belugas sampled near Point Lay.
Mating behavior in beluga whales typically occurs between February and
June, peaking in March (Burns and Seaman, 1986; Suydam, 2009). In the
Chukchi Sea, the gestation period of beluga whales was determined to be
14.9 months, with a calving interval of 2 to 3 years and a pregnancy
rate of 0.41, declining after 25 years of age (Suydam, 2009). Calves
are born between mid-June and mid-July and typically remain with the
mother for up to 2 years of age (Suydam, 2009).
CIBWs feed on a wide variety of prey species, particularly those
that are seasonally abundant. From late spring through summer, most
CIBW stomachs sampled contained salmon, which corresponded to the
timing of fish runs in the area. Anadromous smolt and adult fish
aggregate at river mouths and adjacent intertidal mudflats (Calkins,
1989). All five Pacific salmon species (i.e., Chinook, pink
(Oncorhynchus gorbuscha), coho, sockeye, and chum) spawn in rivers
throughout Cook Inlet (Moulton, 1997; Moore et al., 2000). Overall,
Pacific salmon represent the highest percent frequency of occurrence of
prey species in CIBW stomachs. This suggests that their spring feeding
in upper Cook Inlet, principally on fat-rich fish such as salmon and
eulachon, is important to the energetics of these animals (NMFS,
2016b).
The nutritional quality of Chinook salmon in particular is
unparalleled, with an energy content four times greater than that of a
Coho salmon. It is suggested the decline of the Chinook salmon
population has left a nutritional void in the diet of the CIBWs that no
other prey species can fill in terms of quality or quantity (Norman et
al., 2020, 2022).
In fall, as anadromous fish runs begin to decline, CIBWs return to
consume fish species (cod and bottom fish) found in nearshore bays and
estuaries. Stomach samples from CIBWs are not available for winter
(December through March), although dive data from CIBWs tagged with
satellite transmitters suggest that they feed in deeper waters during
winter (Hobbs et al., 2005), possibly on such prey species as flatfish,
cod, sculpin, and pollock.
Distribution in Cook Inlet. The CIBW stock remains within Cook
Inlet throughout the year, showing only small seasonal shifts in
distribution (Goetz et al., 2012a; Lammers et al., 2013; Castellotte et
al., 2015; Shelden et al., 2015a, 2018; Lowry et al., 2019). The
ecological range of CIBWs has contracted significantly since the 1970s.
From late spring to fall, nearly the entire population is now found in
the upper inlet north of the forelands, with a range reduced to
approximately 39 percent of the size documented in the late 1970s
(Goetz et al., 2023). The recent annual and semiannual aerial surveys
(since 2008) found that approximately 83 percent of the population
inhabits the area between the Beluga River and Little Susitna River
during the survey period, typically conducted in early June. Some
aerial survey counts were performed in August, September, and October,
finding minor differences in the numbers of belugas in the upper inlet
compared to June, reinforcing the importance of the upper inlet habitat
area (Young et al., 2023).
During spring and summer, CIBWs generally aggregate near the warmer
waters of river mouths along the northern shores of middle and upper
Cook Inlet where prey availability is high and predator occurrence is
low (Moore et al., 2000; Shelden and Wade, 2019; McGuire et al., 2020).
In particular, CIBW groups are seen in the
[[Page 60173]]
Susitna River Delta, the Beluga River and along the shore to the Little
Susitna River, Knik Arm, and along the shores of Chickaloon Bay. Small
groups were recorded farther south in Kachemak Bay, Redoubt Bay (Big
River), and Trading Bay (McArthur River) prior to 1996, but rarely
thereafter. Since the mid-1990s, most CIBWs (96 to 100 percent)
aggregate in shallow areas near river mouths in upper Cook Inlet, and
they are only occasionally sighted in the central or southern portions
of Cook Inlet during summer (Hobbs et al., 2008). Almost the entire
population can be found in northern Cook Inlet from late spring through
the summer and into the fall (Muto et al., 2020), shifting into deeper
waters in middle Cook Inlet in winter (Hobbs et al., 2008).
Data from tagged whales (14 tags deployed July 2000 through March
2003) show that CIBWs use upper Cook Inlet intensively between summer
and late autumn (Hobbs et al., 2005). CIBWs tagged with satellite
transmitters continue to use Knik Arm, Turnagain Arm, and Chickaloon
Bay as late as October, but some range into lower Cook Inlet to
Chinitna Bay, Tuxedni Bay, and Trading Bay (McArthur River) in fall
(Hobbs et al., 2005, 2012). From September through November, CIBWs move
between Knik Arm, Turnagain Arm, and Chickaloon Bay (Hobbs et al.,
2005; Goetz et al., 2012b). By December, CIBWs are distributed
throughout the upper to mid-inlet. From January into March, they move
as far south as Kalgin Island and slightly beyond in central offshore
waters. CIBWs make occasional excursions into Knik Arm and Turnagain
Arm in February and March in spite of ice cover (Hobbs et al., 2005).
Although tagged CIBWs move widely around Cook Inlet throughout the
year, there is no indication of seasonal migration in and out of Cook
Inlet (Hobbs et al., 2005). Data from NMFS aerial surveys,
opportunistic sighting reports, and corrected satellite-tagged CIBWs
confirm that they are more widely dispersed throughout Cook Inlet
during winter (November-April), with animals found between Kalgin
Island and Point Possession. Generally fewer observations of CIBWs are
reported from the Anchorage and Knik Arm area from November through
April (76 FR 20179, April 11, 2011; Rugh et al., 2000, 2004). Later in
winter (January into March), belugas were sighted near Kalgin Island
and in deeper waters offshore. However, even when ice cover exceeds 90
percent in February and March, belugas travel into Knik Arm and
Turnagain Arm (Hobbs et al., 2005).
The NMFS Marine Mammal Lab has conducted long-term passive acoustic
monitoring demonstrating seasonal shifts in CIBW concentrations
throughout Cook Inlet. Castellote et al. (2015) conducted long-term
acoustic monitoring at 13 locations throughout Cook Inlet between 2008
and 2015: North Eagle Bay, Eagle River Mouth, South Eagle Bay, Six
Mile, Point MacKenzie, Cairn Point, Fire Island, Little Susitna, Beluga
River, Trading Bay, Kenai River, Tuxedni Bay, and Homer Spit; the
former 6 stations being located within Knik Arm. In general, the
observed seasonal distribution is in accordance with descriptions based
on aerial surveys and satellite telemetry: CIBW detections are higher
in the upper inlet during summer, peaking at Little Susitna, Beluga
River, and Eagle Bay, followed by fewer detections at those locations
during winter. Higher detections in winter at Trading Bay, Kenai River,
and Tuxedni Bay suggest a broader CIBW distribution in the lower inlet
during winter.
Goetz et al. (2012b) modeled habitat preferences using NMFS' 1994-
2008 June abundance survey data. In large areas, such as the Susitna
Delta (Beluga to Little Susitna Rivers) and Knik Arm, there was a high
probability that CIBWs were in larger groups. CIBW presence and
acoustic foraging behavior also increased closer to rivers with Chinook
salmon runs, such as the Susitna River (e.g., Castellote et al., 2021).
Movement has been correlated with the peak discharge of seven major
rivers emptying into Cook Inlet. Boat-based surveys from 2005 to the
present (McGuire and Stephens, 2017) and results from passive acoustic
monitoring across the entire inlet (Castellote et al., 2015) also
support seasonal patterns observed with other methods. Based on long-
term passive acoustic monitoring, foraging behavior was more prevalent
during summer, particularly at upper inlet rivers, than during winter.
The foraging index was highest at Little Susitna, with a peak in July-
August and a secondary peak in May, followed by Beluga River and then
Eagle Bay; monthly variation in the foraging index indicates CIBWs
shift their foraging behavior among these three locations from April
through September. The location of the towing routes are areas of
predicted low density in the summer months.
CIBWs are believed to mostly calve in the summer, and breed between
late spring and early summer (NMFS, 2016b), primarily in upper Cook
Inlet. The only known observed occurrence of calving occurred on July
20, 2015, in the Susitna Delta area (T. McGuire, personal
communication, March 27, 2017). The first neonates encountered during
each field season from 2005 through 2015 were always seen in the
Susitna River Delta in July. The photographic identification team's
documentation of the dates of the first neonate of each year indicate
that calving begins in mid-late July/early August, generally coinciding
with the observed timing of annual maximum group size. Probable mating
behavior of CIBWs was observed in April and May of 2014, in Trading
Bay. Young CIBWs are nursed for 2 years and may continue to associate
with their mothers for a considerable time thereafter (Colbeck et al.,
2013). Important calving grounds are thought to be located near the
river mouths of upper Cook Inlet.9
During Apache's seismic test program in 2011 along the west coast
of Redoubt Bay, lower Cook Inlet, a total of 33 CIBWs were sighted
during the survey (Lomac-MacNair et al., 2013). During Apache's 2012
seismic program in mid-inlet, a total of 151 groups consisting of an
estimated 1,463 CIBWs were observed (note individuals were likely
observed more than once) (Lomac-MacNair et al., 2014). During
SAExploration's 2015 seismic program, a total of eight groups of 33
estimated individual CIBWs were visually observed during this time
period and there were two acoustic detections of CIBWs (Kendall et al.,
2015). During Harvest Alaska's recent CIPL project on the west side of
Cook Inlet in between Ladd Landing and Tyonek Platform, a total of 143
CIBW groups (814 individuals) were observed almost daily from May 31 to
July 11, even though observations spanned from May 9 through September
15 (Sitkiewicz et al., 2018). There were two CIBW carcasses observed by
the project vessels in the 2019 Hilcorp lower Cook Inlet seismic survey
in the fall which were reported to the NMFS Marine Mammal Stranding
Network (Fairweather Science, 2020). Both carcasses were moderately
decomposed when they were sighted by the Protected Species Observers
(PSO). Daily aerial surveys specifically for CIBWs were flown over the
lower Cook Inlet region, but no beluga whales were observed. In 2023,
Hilcorp recorded 21 groups of more than 125 beluga whales during aerial
surveys in middle Cook Inlet, and an additional 21 opportunistic groups
which included approximately 81 CIBWs (Horsley and Larson, 2023).
Hilcorp did not record any sightings of CIBWs from their rig-based
monitoring efforts (Horsley and Larson, 2023)
Killer Whale
Along the west coast of North America, seasonal and year-round
occurrence of killer whales has been
[[Page 60174]]
noted along the entire Alaska coast (Braham and Dahlheim, 1982), in
British Columbia and Washington inland waterways (Bigg et al., 1990),
and along the outer coasts of Washington, Oregon, and California (Green
et al., 1992; Barlow 1995, 1997; Forney et al., 1995). Killer whales
from these areas have been labeled as ``resident,'' ``transient,'' and
``offshore'' type killer whales (Bigg et al., 1990; Ford et al., 2000;
Dahlheim et al., 2008) based on aspects of morphology, ecology,
genetics, and behavior (Ford and Fisher, 1982; Baird and Stacey, 1988;
Baird et al., 1992; Hoelzel et al., 1998, 2002; Barrett-Lennard, 2000;
Dahlheim et al., 2008). Based on data regarding association patterns,
acoustics, movements, and genetic differences, eight killer whale
stocks are now recognized within the U.S. Pacific, two of which have
the potential to be found in the proposed project area: the Eastern
North Pacific Alaska Resident stock and the Gulf of Alaska, Aleutian
Islands, and the Bering Sea Transient stock. Both stocks occur in lower
Cook Inlet, but rarely in middle and upper Cook Inlet (Shelden et al.,
2013). While stocks overlap the same geographic area, they maintain
social and reproductive isolation and feed on different prey species.
Resident killer whales are primarily fish-eaters, while transients
primarily hunt and consume marine mammals, such as harbor seals, Dall's
porpoises, harbor porpoises, beluga whales and sea lions. Killer whales
are not harvested for subsistence in Alaska. Potential threats most
likely to result in direct human-caused mortality or serious injury of
killer whales in this region include oil spills, vessel strikes, and
interactions with fisheries.
Killer whales have been sighted near Homer and Port Graham in lower
Cook Inlet (Shelden et al., 2003, 2022; Rugh et al., 2005). Resident
killer whales from pods often sighted near Kenai Fjords and Prince
William Sound have been occasionally photographed in lower Cook Inlet
(Shelden et al., 2003). The availability of salmon influences when
resident killer whales are more likely to be sighted in Cook Inlet.
Killer whales were observed in the Kachemak and English Bay three times
during aerial surveys conducted between 1993 and 2004 (Rugh et al.,
2005). Passive acoustic monitoring efforts throughout Cook Inlet
documented killer whales at the Beluga River, Kenai River, and Homer
Spit, although they were not encountered within Knik Arm (Castellote et
al., 2016). These detections were likely resident killer whales.
Transient killer whales likely have not been acoustically detected due
to their propensity to move quietly through waters to track prey
(Small, 2010; Lammers et al., 2013). Transient killer whales were
increasingly reported to feed on belugas in the middle and upper Cook
Inlet in the 1990s.
During the 2015 SAExploration seismic program near the North
Foreland, two killer whales were observed (Kendall et al., 2015, as
cited in Weston and SLR, 2022). Killer whales were observed in lower
Cook Inlet in 1994, 1997, 2001, 2005, 2010, 2012, and 2022 during the
NMFS aerial surveys (Shelden et al., 2013, 2022). Eleven killer whale
strandings have been reported in Turnagain Arm: 6 in May 1991 and 5 in
August 1993. During the Hilcorp lower Cook Inlet seismic survey in the
fall of 2019, 21 killer whales were documented (Fairweather Science,
2020). Throughout 4 months of observation in 2018 during the CIPL
project in middle Cook Inlet, no killer whales were observed
(Sitkiewicz et al., 2018). In September 2021, two killer whales were
documented in Knik Arm in upper Cook Inlet, near the POA (61N
Environmental, 2022a). Hilcorp did not record any sightings of killer
whales from their aerial or rig-based monitoring efforts in 2023
(Horsley and Larson, 2023).
Pacific White-Sided Dolphin
The Pacific white-sided dolphin is divided into three stocks within
U.S. waters. The North Pacific stock includes the coast of Alaska,
including the project area. Pacific white-sided dolphins are common in
the Gulf of Alaska's pelagic waters and Alaska's nearshore areas,
British Columbia, and Washington (Ferrero and Walker, 1996, as cited in
Muto et al., 2022). They do not typically occur in Cook Inlet, but in
2019, Castellote et al. (2020) documented short durations of Pacific
white-sided dolphin presence using passive acoustic recorders near
Iniskin Bay (6 minutes) and at an offshore mooring located
approximately midway between Port Graham and Iniskin Bay (51 minutes).
Detections of vocalizations typically lasted on the order of minutes,
suggesting the animals did not remain in the area and/or continue
vocalizing for extended durations. Visual monitoring conducted during
the same period by marine mammal observers on seismic vessels near the
offshore recorder did not detect any Pacific white-sided dolphins
(Fairweather Science, 2020). These observational data, combined with
anecdotal information, indicate that there is a small potential for
Pacific white-sided dolphins to occur in the Project area. On May 7,
2014, Apache Alaska observed three Pacific white-sided dolphins during
an aerial survey near Kenai. This is one of the only recorded visual
observations of Pacific white-sided dolphins in Cook Inlet; they have
not been reported in groups as large as those estimated in other parts
of Alaska (Muto et al., 2022).
Harbor Porpoise
In the eastern North Pacific Ocean, harbor porpoise range from
Point Barrow, along the Alaska coast, and down the west coast of North
America to Point Conception, California. The 2022 Alaska SARs describe
a revised stock structure for harbor porpoises (Young et al., 2023).
Previously, NMFS had designated three stocks of harbor porpoises: the
Bering Sea stock, the Gulf of Alaska stock, and the Southeast Alaska
stock (Muto et al., 2022; Zerbini et al., 2022). The 2022 Alaska SARs
splits the Southeast Alaska stock into three separate stocks, resulting
in five separate stocks in Alaskan waters for this species. This update
better aligns harbor porpoise stock structure with genetics, trends in
abundance, and information regarding discontinuous distribution trends
(Young et al., 2023). Harbor porpoises found in Cook Inlet are assumed
to be members of the Gulf of Alaska stock (Young et al., 2023).
Harbor porpoises occur most frequently in waters less than 100 m
deep (Hobbs and Waite, 2010) and are common in nearshore areas of the
Gulf of Alaska, Shelikof Strait, and lower Cook Inlet (Dahlheim et al.,
2000). Harbor porpoises are often observed in lower Cook Inlet in
Kachemak Bay and from Cape Douglas to the West Foreland (Rugh et al.,
2005). They can be opportunistic foragers but consume primarily
schooling forage fish (Bowen and Siniff, 1999). Given their shallow
water distribution, harbor porpoise are vulnerable to physical
modifications of nearshore habitats resulting from urban and industrial
development (including waste management and nonpoint source runoff) and
activities such as construction of docks and other over-water
structures, filling of shallow areas, dredging, and noise
(Linnenschmidt et al., 2013). Subsistence users have not reported any
harvest from the Gulf of Alaska harbor porpoise stock since the early
1900s (Shelden et al., 2014). Calving occurs from May to August;
however, this can vary by region. Harbor porpoises are often found
traveling alone, or in small groups of less than 10 individuals
(Schmale, 2008).
Harbor porpoises occur throughout Cook Inlet, with passive acoustic
detections being more prevalent in
[[Page 60175]]
lower Cook Inlet. Although harbor porpoises have been frequently
observed during aerial surveys in Cook Inlet (Shelden et al., 2014),
most sightings are of single animals and are concentrated at Chinitna
and Tuxedni bays on the west side of lower Cook Inlet (Rugh et al.,
2005), with smaller numbers observed in upper Cook Inlet between April
and October. The occurrence of larger numbers of porpoise in the lower
Cook Inlet may be driven by greater availability of preferred prey and
possibly less competition with CIBWs, as CIBWs move into upper inlet
waters to forage on Pacific salmon during the summer months (Shelden et
al., 2014).
An increase in harbor porpoise sightings in upper Cook Inlet was
observed over recent decades (e.g., 61N Environmental, 2021, 2022a;
Shelden et al., 2014). Small numbers of harbor porpoises have been
consistently reported in upper Cook Inlet between April and October
(Prevel-Ramos et al., 2008). The overall increase in the number of
harbor porpoise sightings in upper Cook Inlet is unknown, although it
may be an artifact of increased studies and marine mammal monitoring
programs in upper Cook Inlet. It is also possible that the contraction
in the CIBW's range has opened up previously occupied CIBW range to
harbor porpoises (Shelden et al., 2014).
During Apache's 2012 seismic program in middle Cook Inlet, 137
groups of harbor porpoises comprising 190 individuals were documented
between May and August (Lomac-MacNair et al., 2013). In June 2012,
Shelden et al. (2015b) documented 65 groups of 129 individual harbor
porpoises during an aerial survey, none of which were in upper Cook
Inlet. Kendall et al. (2015, as cited in Weston and SLR, 2022)
documented 52 groups comprising 65 individuals north of the Forelands
during SAExploration's 2015 seismic survey. Shelden et al. (2017, 2019,
and 2022) also conducted aerial surveys in June and July over Cook
Inlet in 2016, 2018, 2021, and 2022 and recorded 65 individuals.
Observations occurred in middle and lower Cook Inlet with a majority in
Kachemak Bay. There were two sightings of three harbor porpoises
observed during the 2019 Hilcorp lower Cook Inlet seismic survey in the
fall (Fairweather Science, 2020). A total of 29 groups (44 individuals)
were observed north of the Forelands from May to September during the
CIPL Extension Project (Sitkiewicz et al., 2018). During jack-up rig
moves in 2021, a PSO observed two individual harbor porpoises in middle
Cook Inlet: one in July and one in October. Four monitoring events were
conducted at the POA in Anchorage between April 2020 and August 2022,
during which 42 groups of harbor porpoises comprising 50 individual
porpoises were documented over 285 days of observation (61N
Environmental 2021, 2022a, 2022b, and 2022c). One harbor porpoise was
observed during Hilcorp's boat-based monitoring efforts in June 2023
(Horsley and Larson, 2023).
Dall's Porpoise
Dall's porpoises are found throughout the North Pacific, from
southern Japan to southern California north to the Bering Sea. All
Dall's porpoises in Alaska are of the Alaska stock. This species can be
found in offshore, inshore, and nearshore habitat. The Dall's porpoise
range in Alaska includes lower Cook Inlet, but very few sightings have
been reported in upper Cook Inlet. Observations have been documented
near Kachemak Bay and Anchor Point (Owl Ridge, 2014; BOEM, 2015).
Shelden et al. (2013) and Rugh et al. (2005) collated data from aerial
surveys conducted between 1994 and 2012 and documented 9 sightings of
25 individuals in the lower Cook Inlet during June and/or July 1997,
1999, and 2000. No Dall's porpoise were observed on subsequent surveys
in June and/or July 2014, 2016, 2018, 2021, and 2022 (Shelden et al.,
2015b, 2017, and 2022; Shelden and Wade, 2019). During Apache's 2014
seismic survey, two groups of three Dall's porpoises were observed in
Upper and middle Cook Inlet (Lomac-MacNair et al., 2014). In August
2015, one Dall's porpoise was reported in the mid-inlet north of
Nikiski in middle Cook Inlet during SAExploration's seismic program
(Kendall et al., 2015 as cited in Weston and SLR, 2022). During aerial
surveys in Cook Inlet, they were observed in Iniskin Bay, Barren
Island, Elizabeth Island, and Kamishak Bay (Shelden et al., 2013). No
Dall's porpoises were observed during the 2018 CIPL Extension Project
Acoustic Monitoring Program in middle Cook Inlet (Sitkiewicz et al.,
2018); however, 30 individuals in 10 groups were sighted during a lower
Cook Inlet seismic project in the fall 2019 (Fairweather Science,
2020). Hilcorp recorded three sightings of Dall's porpoises in 2021 and
one sighting of a Dall's porpoise in 2023 from their rig-based
monitoring efforts in the project area (Korsmo et al., 2022; Horsley
and Larson, 2023). This higher number of sightings suggests Dall's
porpoise may use portions of middle Cook Inlet in greater numbers than
previously expected but would still be considered infrequent in middle
and upper Cook Inlet.
Steller Sea Lion
Two DPSs of Steller sea lion occur in Alaska: the western DPS and
the eastern DPS. The western DPS includes animals that occur west of
Cape Suckling, Alaska, and therefore includes individuals within the
Project area. The western DPS was listed under the ESA as threatened in
1990 (55 FR 49204, November 26, 1990), and its continued population
decline resulted in a change in listing status to endangered in 1997
(62 FR 24345, May 5, 1997). Since 2000, studies indicate that the
population east of Samalga Pass (i.e., east of the Aleutian Islands)
has increased and is potentially stable (Young et al., 2023).
There is uncertainty regarding threats currently impeding the
recovery of Steller sea lions, particularly in the Aleutian Islands.
Many factors have been suggested as causes of the steep decline in
abundance of western Steller sea lions observed in the 1980s, including
competitive effects of fishing, environmental change, disease,
contaminants, killer whale predation, incidental take, and illegal and
legal shooting (Atkinson et al., 2008; NMFS, 2008a). A number of
management actions have been implemented since 1990 to promote the
recovery of the Western U.S. stock of Steller sea lions, including 5.6-
km (3-nautical mile) no-entry zones around rookeries, prohibition of
shooting at or near sea lions, and regulation of fisheries for sea lion
prey species (e.g., walleye pollock, Pacific cod, and Atka mackerel
(Pleurogrammus monopterygius)) (Sinclair et al., 2013; Tollit et al.,
2017). Additionally, potentially deleterious events, such as harmful
algal blooms (Lefebvre et al., 2016) and disease transmission across
the Arctic (VanWormer et al., 2019) that have been associated with
warming waters, could lead to potentially negative population-level
impacts on Steller sea lions.
NMFS designated critical habitat for Steller sea lions on August
27, 1993 (58 FR 45269), including portions of the southern reaches of
lower Cook Inlet. The critical habitat designation for the Western DPS
of was determined to include a 37-km (20-nautical mile) buffer around
all major haul-outs and rookeries, and associated terrestrial,
atmospheric, and aquatic zones, plus three large offshore foraging
areas, none of which occurs in the project area. There is no designated
critical habitat for Steller sea lions in the mid- or upper inlet, nor
are there any known BIAs for Steller sea lions within the project area.
Rookeries and haul out sites in lower
[[Page 60176]]
Cook Inlet include those near the mouth of the inlet, which are
approximately 56 km or more south of the closest action area.
Steller sea lions are opportunistic predators, feeding primarily on
a wide variety of seasonally abundant fishes and cephalopods, including
Pacific herring (Clupea pallasi), walleye pollock, capelin (Mallotus
villosus), Pacific sand lance (Ammodytes hexapterus), Pacific cod,
salmon (Oncorhynchus spp.), and squid (Teuthida spp.); (Jefferson et
al., 2008; Wynne et al., 2011). Steller sea lions do not generally eat
every day, but tend to forage every 1-2 days and return to haulouts to
rest between foraging trips (Merrick and Loughlin, 1997; Rehberg et
al., 2009). Steller sea lions feed largely on walleye pollock, salmon,
and arrowtooth flounder during the summer, and walleye pollock and
Pacific cod during the winter (Sinclair and Zeppelin, 2002).
Most Steller sea lions in Cook Inlet occur south of Anchor Point on
the east side of lower Cook Inlet, with concentrations near haulout
sites at Shaw Island and Elizabeth Island and by Chinitna Bay and
Iniskin Bay on the west side (Rugh et al., 2005). Steller sea lions are
rarely seen in upper Cook Inlet (Nemeth et al., 2007). About 3,600 sea
lions use haulout sites in the lower Cook Inlet area (Sweeney et al.,
2017), with additional individuals venturing into the area to forage.
Several surveys and monitoring programs have documented Steller sea
lions throughout Cook Inlet, including in upper Cook Inlet in 2012
(Lomac-MacNair et al., 2013), near Cape Starichkof in 2013 (Owl Ridge,
2014), in middle and lower Cook Inlet in 2015 (Kendall et al., 2015, as
cited in Weston and SLR, 2022), in middle Cook Inlet in 2018
(Sitkiewicz et al., 2018), in lower Cook Inlet in 2019 (Fairweather
Science, 2020), and near the POA in Anchorage in 2020, 2021, and 2022
(61N Environmental, 2021, 2022a, 2022b, and 2022c). During NMFS Cook
Inlet beluga whale aerial surveys from 2000 to 2016, 39 sightings of
769 estimated individual Steller sea lions in lower Cook Inlet were
recorded (Shelden et al., 2017). Sightings of large congregations of
Steller sea lions during NMFS aerial surveys occurred outside the
specific geographic region, on land in the mouth of Cook Inlet (e.g.,
Elizabeth and Shaw Islands). In 2012, during Apache's 3D Seismic
surveys, three sightings of approximately four individuals in upper
Cook Inlet were recorded (Lomac-MacNair et al., 2013). PSOs associated
with Buccaneer's drilling project off Cape Starichkof observed seven
Steller sea lions in summer 2013 (Owl Ridge, 2014), and another four
Steller sea lions were observed in 2015 in Cook Inlet during
SAExploration's 3D Seismic Program. Of the three 2015 sightings, one
sighting occurred between the West and East Forelands, one occurred
near Nikiski, and one occurred northeast of the North Foreland in the
center of Cook Inlet (Kendall and Cornick, 2015). Five sightings of
five Steller sea lions were recorded during Hilcorp's lower Cook Inlet
seismic survey in the fall of 2019 (Fairweather Science, 2020).
Additionally, one sighting of two individuals occurred during the CIPL
Extension Project in 2018 in middle Cook Inlet (Sitkiewicz et al.,
2018). At the end of July 2022, while conducting a waterfowl survey an
estimated 25 Steller sea lions were observed hauled-out at low tide in
the Lewis River, on the west side of Cook Inlet. (K. Lindberg, personal
communication, August 15, 2022). Steller sea lions have also been
reported near the POA in Anchorage in 2020, 2021, and 2022 (61N 2021,
2022a, 2022b, and 2022c). Hilcorp did not record any sightings of
Steller sea lions from their aerial or rig-based monitoring efforts in
2023 (Horsley and Larson, 2023).
Harbor Seal
Harbor seals inhabit waters all along the western coast of the
United States, British Columbia, and north through Alaska waters to the
Pribilof Islands and Cape Newenham. NMFS currently identifies 12 stocks
of harbor seals in Alaska based largely on genetic structure (Young et
al., 2023). Harbor seals in the proposed project area are members of
the Cook Inlet/Shelikof stock, which ranges from the southwest tip of
Unimak Island east along the southern coast of the Alaska Peninsula to
Elizabeth Island off the southwest tip of the Kenai Peninsula,
including Cook Inlet, Knik Arm, and Turnagain Arm. Distribution of the
Cook Inlet/Shelikof stock extends from Unimak Island, in the Aleutian
Islands archipelago, north through all of upper and lower Cook Inlet
(Young et al., 2023).
Harbor seals inhabit the coastal and estuarine waters of Cook Inlet
and are observed in both upper and lower Cook Inlet throughout most of
the year (Boveng et al., 2012; Shelden et al., 2013). High-density
areas include Kachemak Bay, Iniskin Bay, Iliamna Bay, Kamishak Bay,
Cape Douglas, and Shelikof Strait. Up to a few hundred seals seasonally
occur in middle and upper Cook Inlet (Rugh et al. 2005), with the
highest concentrations found near the Susitna River and other
tributaries within upper Cook Inlet during eulachon and salmon runs
(Nemeth et al., 2007; Boveng et al., 2012), but most remain south of
the forelands (Boveng et al., 2012).
Harbor seals haul out on rocks, reefs, beaches, and drifting
glacial ice (Young et al., 2023). Their movements are influenced by
tides, weather, season, food availability, and reproduction, as well as
individual sex and age class (Lowry et al., 2001; Small et al., 2003;
Boveng et al., 2012). The results of past and recent satellite tagging
studies in Southeast Alaska, Prince William Sound, Kodiak Island, and
Cook Inlet are also consistent with the conclusion that harbor seals
are non-migratory (Lowry et al., 2001; Small et al., 2003; Boveng et
al., 2012). However, some long-distance movements of tagged animals in
Alaska have been recorded (Pitcher and McAllister, 1981; Lowry et al.,
2001; Small et al., 2003; Womble, 2012; Womble and Gende, 2013). Strong
fidelity of individuals for haulout sites during the breeding season
has been documented in several populations (H[auml]rk[ouml]nen and
Harding, 2001), including in Cook Inlet (Pitcher and McAllister, 1981;
Small et al., 2005; Boveng et al., 2012; Womble, 2012; Womble and
Gende, 2013). Harbor seals usually give birth to a single pup between
May and mid-July; birthing locations are dispersed over several haulout
sites and not confined to major rookeries (Klinkhart et al., 2008).
More than 200 haulout sites are documented in lower Cook Inlet
(Montgomery et al., 2007) and 18 in middle and upper Cook Inlet (London
et al., 2015). Of the 18 in middle and upper Cook Inlet, nine are
considered ``key haulout'' locations where aggregations of 50 or more
harbor seals have been documented. Seven key haulouts are in the
Susitna River delta, and two are near the Chickaloon River.
Recent research on satellite-tagged harbor seals observed several
movement patterns within Cook Inlet (Boveng et al., 2012), including a
strong seasonal pattern of more coastal and restricted spatial use
during the spring and summer (breeding, pupping, molting) and more
wide-ranging movements within and outside of Cook Inlet during the
winter months, with some seals ranging as far as Shumagin Islands.
During summer months, movements and distribution were mostly confined
to the west side of Cook Inlet and Kachemak Bay, and seals captured in
lower Cook Inlet generally exhibited site fidelity by remaining south
of the Forelands in lower Cook Inlet after release (Boveng et al.,
2012). In the fall, a portion of the harbor seals appeared to move out
of Cook Inlet and into Shelikof Strait, northern Kodiak Island, and
[[Page 60177]]
coastal habitats of the Alaska Peninsula. The western coast of Cook
Inlet had higher usage by harbor seals than eastern coast habitats, and
seals captured in lower Cook Inlet generally exhibited site fidelity by
remaining south of the Forelands in lower Cook Inlet after release
(south of Nikiski; Boveng et al., 2012).
Harbor seals have been sighted in Cook Inlet during every year of
the aerial surveys conducted by NMFS and during all recent mitigation
and monitoring programs in lower, middle, and upper Cook Inlet (61N
Environmental, 2021, 2022a, 2022b, and 2022c; Fairweather Science,
2020; Kendall et al., 2015 as cited in Weston and SLR, 2022; Lomac-
MacNair et al., 2013, 2014; Sitkiewicz et al., 2018). In addition,
Hilcorp recorded one sighting of a harbor seal in 2021 and three
sightings of harbor seals in 2023 from their aerial and rig-based
monitoring efforts in the project area (Korsmo et al. 2022; Horsley and
Larson, 2023).
California Sea Lion
California sea lions live along the Pacific coastline spanning an
area from central Mexico to Southeast Alaska and typically breed on
islands located in southern California, western Baja California, and
the Gulf of California (Carretta et al., 2020). Five genetically
distinct geographic populations are known to exist: Pacific Temperate,
Pacific Subtropical, Southern Gulf of California, Central Gulf of
California, and Northern Gulf of California (Schramm et al., 2009).
Few observations of California sea lions have been reported in
Alaska and most observations have been limited to solitary individuals,
typically males that are known to migrate long distances. Occasionally,
California sea lions can be found in small groups of two or more and
are usually associated with Steller sea lions at their haul outs and
rookeries (Maniscalco et al., 2004). The few California sea lions
observed in Alaska typically do not travel further north than Southeast
Alaska. They are often associated with Steller sea lion haulouts and
rookeries (Maniscalco et al., 2004). Sightings in Cook Inlet are rare,
with two documented during the Apache 2012 seismic survey (Lomac-
MacNair et al., 2013) and anecdotal sightings in Kachemak Bay. None
were sighted during the 2019 Hilcorp lower Cook Inlet seismic survey
(Fairweather Science, 2020), the CIPL project in 2018 (Sitkiewicz et
al., 2018), or the 2023 Hilcorp aerial or rig-based monitoring efforts
(Horsley and Larson, 2023).
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.). Subsequently, NMFS (2018) described
generalized hearing ranges for these marine mammal hearing groups.
Generalized hearing ranges were chosen based on the approximately 65
decibel (dB) threshold from the normalized composite audiograms, with
the exception for lower limits for low-frequency cetaceans where the
lower bound was deemed to be biologically implausible and the lower
bound from Southall et al. (2007) retained. Marine mammal hearing
groups and their associated hearing ranges are provided in table 3.
Specific to this action, gray whales, fin whales, minke whales, and
humpback whales are considered low-frequency (LF) cetaceans, beluga
whales, pacific white-sided dolphins, and killer whales are considered
mid-frequency (MF) cetaceans, harbor porpoises and Dall's porpoises are
considered high-frequency (HF) cetaceans, Steller sea lions and
California sea lions are otariid pinnipeds (OW), and harbor seals are
phocid pinnipeds (PW).
Table 3--Marine Mammal Hearing Groups
[NMFS, 2018]
------------------------------------------------------------------------
Hearing group Generalized hearing range *
------------------------------------------------------------------------
Low-frequency (LF) cetaceans (baleen 7 Hz to 35 kHz.
whales).
Mid-frequency (MF) cetaceans (dolphins, 150 Hz to 160 kHz.
toothed whales, beaked whales, bottlenose
whales).
High-frequency (HF) cetaceans (true 275 Hz to 160 kHz.
porpoises, Kogia, river dolphins,
Cephalorhynchid, Lagenorhynchus cruciger &
L. australis).
Phocid pinnipeds (PW) (underwater) (true 50 Hz to 86 kHz.
seals).
Otariid pinnipeds (OW) (underwater) (sea 60 Hz to 39 kHz.
lions and fur seals).
------------------------------------------------------------------------
* Represents the generalized hearing range for the entire group as a
composite (i.e., all species within the group), where individual
species' hearing ranges are typically not as broad. Generalized
hearing range chosen based on ~65 dB threshold from normalized
composite audiogram, with the exception for lower limits for LF
cetaceans (Southall et al., 2007) and PW pinniped (approximation).
The pinniped functional hearing group was modified from Southall et
al. (2007) on the basis of data indicating that phocid species have
consistently demonstrated an extended frequency range of hearing
compared to otariids, especially in the higher frequency range
(Hemil[auml] et al., 2006; Kastelein et al., 2009; Reichmuth and Holt,
2013). This division between phocid and otariid pinnipeds is now
reflected in the updated hearing groups proposed in Southall et al.
(2019).
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 of Marine Mammals 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 of Marine Mammals 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
[[Page 60178]]
species or stock through effects on annual rates of recruitment or
survival.
Effects on marine mammals during the specified activity are
expected to potentially occur from three to four tugs towing, holding,
and or positioning a jack-up rig. Underwater noise from Hilcorp's
proposed activities have the potential to result in Level B harassment
of marine mammals in the action area.
Background on Sound
This section contains a brief technical background on sound, on the
characteristics of certain sound types, and on metrics used 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.
For general information on sound and its interaction with the marine
environment, please see: Erbe and Thomas (2022); Au and Hastings
(2008); Richardson et al. (1995); Urick (1983); as well as the
Discovery of Sound in the Sea website at <a href="https://dosits.org/">https://dosits.org/</a>.
Sound is a vibration that travels as an acoustic wave through a
medium such as a gas, liquid or solid. Sound waves alternately compress
and decompress the medium as the wave travels. In water, sound waves
radiate in a manner similar to ripples on the surface of a pond and may
be either directed in a beam (narrow beam or directional sources) or
sound may radiate in all directions (omnidirectional sources), as is
the case for sound produced by tugs under load with a jack-up rig
considered here. The compressions and decompressions associated with
sound waves are detected as changes in pressure by marine mammals and
human-made sound receptors such as hydrophones.
Sound travels more efficiently in water than almost any other form
of energy, making the use of sound as a primary sensory modality ideal
for inhabitants of the aquatic environment. In seawater, sound travels
at roughly 1,500 meters per second (m/s). In air, sound waves travel
much more slowly at about 340 m/s. However, the speed of sound in water
can vary by a small amount based on characteristics of the transmission
medium such as temperature and salinity.
The basic characteristics of a sound wave 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 with
distance, except in certain cases in shallower water. The amplitude of
a sound pressure wave is related to the subjective ``loudness'' of a
sound and is typically expressed in dB, which are a relative unit of
measurement that is used to express the ratio of one value of a power
or pressure to another. A sound pressure level (SPL) in dB is described
as the ratio between a measured pressure and a reference pressure, 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. For example, a 10-dB increase is a 10-fold increase
in acoustic power. A 20-dB increase is then a 100-fold increase in
power and a 30-dB increase is a 1000-fold increase in power. However, a
10-fold increase in acoustic power does not mean that the sound is
perceived as being 10 times louder. The dB is a relative unit comparing
two pressures; therefore, a reference pressure must always be
indicated. For underwater sound, this is 1 microPascal ([mu]Pa). For
in-air sound, the reference pressure is 20 microPascal ([mu]Pa). The
amplitude of a sound can be presented in various ways; however, NMFS
typically considers three metrics: sound exposure level (SEL), root-
mean-square (RMS) SPL, and peak SPL (defined below). The source level
represents the SPL referenced at a standard distance from the source,
typically 1 m (Richardson et al., 1995; American National Standards
Institute (ANSI), 2013), while the received level is the SPL at the
receiver's position. For tugging activities, the SPL is typically
referenced at 1 m.
SEL (represented as dB referenced to 1 micropascal squared second
(re 1 [mu]Pa\2\-s)) represents the total energy in a stated frequency
band over a stated time interval or event, and considers both intensity
and duration of exposure. SEL can also be a cumulative metric; it can
be accumulated over a single pulse (i.e., during activities such as
impact pile driving) or calculated over periods containing multiple
pulses (SEL<INF>cum</INF>). Cumulative SEL (SEL<INF>cum</INF>)
represents the total energy accumulated by a receiver over a defined
time window or during an event. The SEL metric is useful because it
allows sound exposures of different durations to be related to one
another in terms of total acoustic energy. The duration of a sound
event and the number of pulses, however, should be specified as there
is no accepted standard duration over which the summation of energy is
measured.
RMS SPL is equal to 10 times the logarithm (base 10) of the ratio
of the mean-square sound pressure to the specified reference value, and
given in units of dB (International Organization for Standardization
(ISO), 2017). RMS is calculated by squaring all of the sound
amplitudes, averaging the squares, and then taking the square root of
the average (Urick, 1983). RMS 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 SPL. For impulsive sounds, RMS is
calculated by the portion of the waveform containing 90 percent of the
sound energy from the impulsive event (Madsen, 2005).
Peak SPL (also referred to as zero-to-peak sound pressure or 0-pk)
is the maximum instantaneous sound pressure measurable in the water,
which can arise from a positive or negative sound pressure, during a
specified time, for a specific frequency range at a specified distance
from the source, and is represented in the same units as the RMS sound
pressure (ISO, 2017). Along with SEL, this metric is used in evaluating
the potential for permanent threshold shift (PTS) and temporary
threshold shift (TTS) associated with impulsive sound sources.
Sounds are also characterized by their temporal components.
Continuous sounds are those whose sound pressure level remains above
that of the ambient or background sound with negligibly small
fluctuations in level (ANSI, 2005) while intermittent sounds are
defined as sounds with interrupted levels of low or no sound (National
Institute for Occupational Safety and Health (NIOSH), 1998). A key
distinction between continuous and intermittent sound sources is that
intermittent sounds have a more regular (predictable) pattern of bursts
of sounds and silent periods (i.e., duty cycle), which continuous
sounds do not. Tugs under load are considered sources of continuous
sound.
Sounds may be either impulsive or non-impulsive (defined below).
The distinction between these two sound types is important because they
have differing potential to cause physical effects, particularly with
regard to noise-induced hearing loss (e.g., Ward, 1997 in Southall et
al., 2007). Please see
[[Page 60179]]
NMFS (2018) and Southall et al. (2007, 2019) for an in-depth discussion
of these concepts.
Impulsive sound sources (e.g., explosions, gunshots, sonic booms,
seismic airgun shots, impact pile driving) produce signals that are
brief (typically considered to be less than 1 second), broadband,
atonal transients (ANSI, 1986, 2005; NIOSH, 1998) and occur either as
isolated events or repeated in some succession. Impulsive 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. Impulsive
sounds are intermittent in nature. The duration of such sounds, as
received at a distance, can be greatly extended in a highly reverberant
environment.
Non-impulsive 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-impulsive sounds can be transient
signals of short duration but without the essential properties of
impulses (e.g., rapid rise time). Examples of non-impulsive sounds
include those produced by vessels (including tugs under load),
aircraft, machinery operations such as drilling or dredging, vibratory
pile driving, and active sonar systems.
Even in the absence of sound from the specified activity, the
underwater environment is characterized by sounds from both natural and
anthropogenic sound sources. Ambient sound is defined as a composite of
naturally-occurring (i.e., non-anthropogenic) sound from many sources
both near and far (ANSI, 1995). Background sound is similar, but
includes all sounds, including anthropogenic sounds, minus the sound
produced by the proposed activities (NMFS, 2012, 2016a). 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 background and ambient sound,
including wind and waves, which are a main source of naturally
occurring ambient sound for frequencies between 200 Hz and 50 kilohertz
(kHz) (Mitson, 1995). In general, background and ambient sound levels
tend to increase with increasing wind speed and wave height.
Precipitation can become an important component of total sound at
frequencies above 500 Hz, and possibly down to 100 Hz during quiet
times. Marine mammals can contribute significantly to background and
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. Sources of background sound related to human activity
include transportation (surface vessels), dredging and construction,
oil and gas drilling and production, geophysical surveys, sonar, and
explosions. Vessel noise typically dominates the total background sound
for frequencies between 20 and 300 Hz. In general, the frequencies of
many anthropogenic sounds, particularly those produced by construction
activities, are below 1 kHz (Richardson et al., 1995). When sounds at
frequencies greater than 1 kHz are produced, they generally attenuate
relatively rapidly (Richardson et al., 1995), particularly above 20 kHz
due to propagation losses and absorption (Urick, 1983).
Transmission loss (TL) defines the degree to which underwater sound
has spread in space and lost energy after having moved through the
environment and reached a receiver. It is defined as the reduction in a
specified level between two specified points that are within an
underwater acoustic field (ISO, 2017). Careful consideration of
transmission loss and appropriate propagation modeling is a crucial
step in determining the impacts of underwater sound, as it helps to
define the ranges (isopleths) to which impacts are expected and depends
significantly on local environmental parameters such as seabed type,
water depth (bathymetry), and the local speed of sound. Geometric
spreading laws are powerful tools which provide a simple means of
estimating TL, based on the shape of the sound wave front in the water
column. For a sound source that is equally loud in all directions and
in deep water, the sound field takes the form of a sphere, as the sound
extends in every direction uniformly. In this case, the intensity of
the sound is spread across the surface of the sphere, and thus we can
relate intensity loss to the square of the range (as area = 4*pi*r\2\).
When expressing logarithmically in dB as TL, we find that TL =
20*Log<INF>10</INF>(range), this situation is known as spherical
spreading. In shallow water, the sea surface and seafloor will bound
the shape of the sound, leading to a more cylindrical shape, as the top
and bottom of the sphere is truncated by the largely reflective
boundaries. This situation is termed cylindrical spreading, and is
given by TL = 10*Log<INF>10</INF>(range) (Urick, 1983). An intermediate
scenario may be defined by the equation TL =
15*Log<INF>10</INF>(range), and is referred to as practical spreading.
Though these geometric spreading laws do not capture many often
important details (scattering, absorption, etc.), they offer a
reasonable and simple approximation of how sound decreases in intensity
as it is transmitted. Cook Inlet is a particularly complex acoustic
environment with strong currents, large tides, variable sea floor and
generally changing conditions.
The sum of the various natural and anthropogenic sound sources at
any given location and time depends not only on the source levels, but
also on the propagation of sound through the environment. Sound
propagation is dependent on the spatially and temporally varying
properties of the water column and sea floor, and is frequency-
dependent. As a result of the dependence on a large number of varying
factors, background and 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 to 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 specified activity may
be a negligible addition to the local environment or could form a
distinctive signal that may affect marine mammals.
Description of Sound Sources for the Specified Activities
In-water activities associated with the project that have the
potential to incidentally take marine mammals through exposure to sound
would be tugs towing, holding, and positioning the jack-up rig. Unlike
discrete noise sources with known potential to harass marine mammals
(e.g., pile driving, seismic surveys), both the noise sources and
impacts from the tugs towing the jack-up rig are less well documented.
Sound energy associated with the specified activity is produced by
vessel propeller cavitation. Bow thrusters would be occasionally used
for a short duration (20 to 30 seconds) to either push or pull a vessel
in or away from a dock or platform. Other sound sources include onboard
diesel generators and sound from the main engine, but both are
subordinate to the thruster and main
[[Page 60180]]
propeller blade rate harmonics (Gray and Greeley, 1980). The various
scenarios that may occur during this project include tugs in a
stationary mode positioning the drill rig and pulling the jack-up rig
at nearly full power against strong tides. Our assessments of the
likelihood for harassment of marine mammals incidental to Hilcorp's tug
activities specified here are conservative in light of the general
Level B harassment exposure thresholds, the fact that NMFS is still in
the process of developing analyses of the impact that non-quantitative
contextual factors have on the likelihood of Level B harassment
occurring, and the nature and duration of the particular tug activities
analyzed here.
Acoustic Impacts
The introduction of anthropogenic noise into the aquatic
environment from tugs under load is the primary means by which marine
mammals may be harassed from Hilcorp's specified activity. In general,
animals exposed to natural or anthropogenic sound may experience
physical and psychological effects, ranging in magnitude from none to
severe (Southall et al., 2007, 2019). Exposure to anthropogenic noise
has the potential to result in auditory threshold shifts and behavioral
reactions (e.g., avoidance, temporary cessation of foraging and
vocalizing, changes in dive behavior). It can also lead to non-
observable physiological responses, such as an increase in stress
hormones. Additional noise in a marine mammal's habitat can mask
acoustic cues used by marine mammals to carry out daily functions, such
as communication and predator and prey detection. The effects of noise
on marine mammals are dependent on several factors, including but not
limited to sound type (e.g., impulsive vs. non-impulsive), the species,
age and sex class (e.g., adult male vs. mom with calf), duration of
exposure, the distance between the vessel and the animal, received
levels, behavior at time of exposure, and previous history with
exposure (Wartzok et al., 2004; Southall et al., 2007). Here we discuss
physical auditory effects (threshold shifts) followed by behavioral
effects and potential impacts on habitat.
NMFS defines a noise-induced threshold shift (TS) as a change,
usually an increase, in the threshold of audibility at a specified
frequency or portion of an individual's hearing range above a
previously established reference level (NMFS, 2018). The amount of
threshold shift is customarily expressed in dB. A TS can be permanent
or temporary. As described in NMFS (2018) there are numerous factors to
consider when examining the consequence of TS, including but not
limited to the signal temporal pattern (e.g., impulsive or non-
impulsive), likelihood an individual would be exposed for a long enough
duration or to a high enough level to induce a TS, the magnitude of the
TS, time to recovery (seconds to minutes or hours to days), the
frequency range of the exposure (i.e., spectral content), the hearing
frequency range of the exposed species relative to the signal's
frequency spectrum (i.e., how animal uses sound within the frequency
band of the signal; e.g., Kastelein et al., 2014), and the overlap
between the animal and the source (e.g., spatial, temporal, and
spectral).
Permanent Threshold Shift (PTS). NMFS defines PTS as a permanent,
irreversible increase in the threshold of audibility at a specified
frequency or portion of an individual's hearing range above a
previously established reference level (NMFS, 2018). PTS does not
generally affect more than a limited frequency range, and an animal
that has incurred PTS has incurred some level of hearing loss at the
relevant frequencies; typically animals with PTS are not functionally
deaf (Au and Hastings, 2008; Finneran, 2016). Available data from
humans and other terrestrial mammals indicate that a 40-dB threshold
shift approximates PTS onset (see Ward et al., 1958, 1959; Ward 1960;
Kryter et al., 1966; Miller, 1974; Ahroon et al., 1996; Henderson et
al., 2008). PTS levels for marine mammals are estimates, as with the
exception of a single study unintentionally inducing PTS in a harbor
seal (Kastak et al., 2008), there are no empirical data measuring PTS
in marine mammals largely due to the fact that, for ethical reasons,
experiments involving anthropogenic noise exposure at levels inducing
PTS are not typically pursued or authorized (NMFS, 2018).
Temporary Threshold Shift (TTS). TTS is a temporary, reversible
increase in the threshold of audibility at a specified frequency or
portion of an individual's hearing range above a previously established
reference level (NMFS, 2018). Based on data from marine mammal TTS
measurements (see Southall et al., 2007, 2019), a TTS of 6 dB is
considered the minimum threshold shift clearly larger than any day-to-
day or session-to-session variation in a subject's normal hearing
ability (Finneran et al., 2000, 2002; Schlundt et al., 2000). As
described in Finneran (2015), marine mammal studies have shown the
amount of TTS increases with SEL<INF>cum</INF> in an accelerating
fashion: at low exposures with lower SEL<INF>cum</INF>, the amount of
TTS is typically small and the growth curves have shallow slopes. At
exposures with higher SEL<INF>cum</INF>, the growth curves become
steeper and approach linear relationships with the noise SEL.
Depending on the degree (elevation of threshold in dB), duration
(i.e., recovery time), and frequency range of TTS, and the context in
which it is experienced, TTS can have effects on marine mammals ranging
from discountable to serious (similar to those discussed in auditory
masking, below). For example, a marine mammal may be able to readily
compensate for a brief, relatively small amount of TTS in a non-
critical frequency range that takes place during a time when the animal
is traveling through the open ocean, 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. We note that reduced hearing sensitivity as
a simple function of aging has been observed in marine mammals, as well
as humans and other taxa (Southall et al., 2007), so we can infer that
strategies exist for coping with this condition to some degree, though
likely not without cost.
Many studies have examined noise-induced hearing loss in marine
mammals (see Finneran (2015) and Southall et al. (2019) for summaries).
TTS is the mildest form of hearing impairment that can occur during
exposure to sound (Kryter, 2013). 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. For
cetaceans, published data on the onset of TTS are limited to captive
bottlenose dolphin (Tursiops truncatus), beluga whale, harbor porpoise,
and Yangtze finless porpoise (Neophocoena asiaeorientalis) (Southall et
al., 2019). For pinnipeds in water, measurements of TTS are limited to
harbor seals, elephant seals (Mirounga angustirostris), bearded seals
(Erignathus barbatus) and California sea lions (Kastak et al., 1999,
2007; Kastelein et al., 2019b, 2019c, 2021, 2022a, 2022b; Reichmuth et
al., 2019; Sills et al., 2020). TTS was not observed in spotted (Phoca
largha) and ringed (Pusa hispida) seals exposed to single airgun
impulse sounds at levels
[[Page 60181]]
matching previous predictions of TTS onset (Reichmuth et al., 2016).
These studies examine hearing thresholds measured in marine mammals
before and after exposure to intense or long-duration sound exposures.
The difference between the pre-exposure and post-exposure thresholds
can be used to determine the amount of threshold shift at various post-
exposure times.
The amount and onset of TTS depends on the exposure frequency.
Sounds below the region of best sensitivity for a species or hearing
group are less hazardous than those near the region of best sensitivity
(Finneran and Schlundt, 2013). At low frequencies, onset-TTS exposure
levels are higher compared to those in the region of best sensitivity
(i.e., a low frequency noise would need to be louder to cause TTS onset
when TTS exposure level is higher), as shown for harbor porpoises and
harbor seals (Kastelein et al., 2019a, 2019c). Note that in general,
harbor seals and harbor porpoises have a lower TTS onset than other
measured pinniped or cetacean species (Finneran, 2015). In addition,
TTS can accumulate across multiple exposures, but the resulting TTS
will be less than the TTS from a single, continuous exposure with the
same SEL (Mooney et al., 2009; Finneran et al., 2010; Kastelein et al.,
2014, 2015). This means that TTS predictions based on the total,
cumulative SEL will overestimate the amount of TTS from intermittent
exposures, such as sonars and impulsive sources. Nachtigall et al.
(2018) describe measurements of hearing sensitivity of multiple
odontocete species (bottlenose dolphin, harbor porpoise, beluga, and
false killer whale (Pseudorca crassidens)) when a relatively loud sound
was preceded by a warning sound. These captive animals were shown to
reduce hearing sensitivity when warned of an impending intense sound.
Based on these experimental observations of captive animals, the
authors suggest that wild animals may dampen their hearing during
prolonged exposures or if conditioned to anticipate intense sounds.
Another study showed that echolocating animals (including odontocetes)
might have anatomical specializations that might allow for conditioned
hearing reduction and filtering of low-frequency ambient noise,
including increased stiffness and control of middle ear structures and
placement of inner ear structures (Ketten et al., 2021). Data available
on noise-induced hearing loss for mysticetes are currently lacking
(NMFS, 2018). Additionally, the existing marine mammal TTS data come
from a limited number of individuals within these species.
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 decibels above that inducing mild TTS (e.g., a 40-dB threshold
shift approximates PTS onset (Kryter et al., 1966; Miller, 1974), while
a 6-dB threshold shift approximates TTS onset (Southall et al., 2007,
2019). Based on data from terrestrial mammals, a precautionary
assumption is that the PTS thresholds for impulsive sounds 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,
2019). 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. Given the nature of tugging, a transient
activity, and the fact that many marine mammals are likely moving
through the project areas and not remaining for extended periods of
time, the potential for threshold shift is low.
Non-acoustic Stressors. HiIlcorp's proposed activities on marine
mammals could also involve non-acoustic stressors. Potential non-
acoustic stressors could result from the physical presence of the
equipment (e.g., tug configuration) and personnel; however, given there
are no known pinniped haul-out sites in the vicinity of the project
site, visual and other non-acoustic stressors would be limited, and any
impacts to marine mammals are expected to primarily be acoustic in
nature.
Behavioral Harassment. Exposure to noise also has the potential to
behaviorally disturb marine mammals to a level that rises to the
definition of Level B harassment under the MMPA. 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 may include changing durations of surfacing and
dives, changing direction and/or speed; reducing/increasing vocal
activities; changing/cessation of certain behavioral activities (such
as socializing or feeding); eliciting a visible startle response or
aggressive behavior (such as tail/fin slapping or jaw clapping); and
avoidance of areas where sound sources are located (Erbe et al., 2019).
In addition, pinnipeds may increase their haul out time, possibly to
avoid in-water disturbance (Thorson and Reyff, 2006).
Behavioral responses to sound are highly variable and context-
specific and any reactions depend on numerous intrinsic and extrinsic
factors (e.g., species, state of maturity, experience, current
activity, reproductive state, auditory sensitivity, time of day), as
well as the interplay between factors (e.g., Richardson et al., 1995;
Wartzok et al., 2004; Southall et al., 2007, 2019; Weilgart, 2007;
Archer et al., 2010; Erbe et al. 2019). 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). 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;
Wartzok et al., 2004; National Research Council (NRC), 2005). In
general, pinnipeds seem more tolerant of, or at least habituate more
quickly to, potentially disturbing underwater sound than do cetaceans,
and generally seem to be less responsive to exposure to industrial
sound than most cetaceans. Please see appendices B and C of Southall et
al. (2007) and Gomez et al. (2016) for reviews 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., 2004). 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.
[[Page 60182]]
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 (e.g., Erbe et al. 2019). 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. 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; Costa et al., 2003; Ng and Leung, 2003; Nowacek et
al., 2004; Goldbogen et al., 2013a, 2013b, Blair et al., 2016).
Variations in dive behavior may reflect interruptions in biologically
significant activities (e.g., foraging) or they may be of little
biological significance. The impact of an alteration to dive behavior
resulting from an acoustic exposure depends on what the animal is doing
at the time of the exposure and the type and magnitude of the response.
Disruption of feeding behavior from anthropogenic sound exposure 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. Acoustic and movement bio-logging
tools also have been used in some cases to infer responses to
anthropogenic noise. For example, Blair et al. (2016) reported
significant effects on humpback whale foraging behavior in Stellwagen
Bank in response to ship noise including slower descent rates, and
fewer side-rolling events per dive with increasing ship nose. In
addition, Wisniewska et al. (2018) reported that tagged harbor
porpoises demonstrated fewer prey capture attempts when encountering
occasional high-noise levels resulting from vessel noise as well as
more vigorous fluking, interrupted foraging, and cessation of
echolocation signals observed in response to some high-noise vessel
passes. 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).
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).
Avoidance is the displacement of an individual from an area or
migration path as a result of the presence of a sound or other
stressors, and is one of the most obvious manifestations of disturbance
in marine mammals (Richardson et al., 1995). For example, gray whales
are known to change direction--deflecting from customary migratory
paths--in order to avoid noise from seismic surveys (Malme et al.,
1984). Harbor porpoises, Atlantic white-sided dolphins (Lagenorhynchus
actusus), and minke whales have demonstrated avoidance in response to
vessels during line transect surveys (Palka and Hammond, 2001). In
addition, beluga whales in the St. Lawrence Estuary in Canada have been
reported to increase levels of avoidance with increased boat presence
by way of increased dive durations and swim speeds, decreased surfacing
intervals, and by bunching together into groups (Blane and Jaakson,
1994). 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., Blackwell et al., 2004; Bejder et al., 2006; Teilmann
et al., 2006).
A flight response is a dramatic change in normal movement to a
directed and rapid movement away from the perceived location of a sound
source. The flight response differs from other avoidance responses in
the intensity of the response (e.g., directed movement, rate of
travel). Relatively little information on flight responses of marine
mammals to anthropogenic signals exist, although observations of flight
responses to the presence of predators have occurred (Connor and
Heithaus, 1996; Bowers et al., 2018). 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 (England et al., 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 fishes 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 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
[[Page 60183]]
substantive (i.e., meaningful) 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.
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., Selye, 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
sufficient 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. In
addition, Lemos et al. (2022) observed a correlation between higher
levels of fecal glucocorticoid metabolite concentrations (indicative of
a stress response) and vessel traffic in gray 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, 2005), however
distress is an unlikely result of this project based on observations of
marine mammals during previous, similar construction projects.
Norman (2011) reviewed environmental and anthropogenic stressors
for CIBWs. Lyamin et al. (2011) determined that the heart rate of a
beluga whale increases in response to noise, depending on the frequency
and intensity. Acceleration of heart rate in the beluga whale is the
first component of the ``acoustic startle response.'' Romano et al.
(2004) demonstrated that captive beluga whales exposed to high-level
impulsive sounds (i.e., seismic airgun and/or single pure tones up to
201 dB RMS) resembling sonar pings showed increased stress hormone
levels of norepinephrine, epinephrine, and dopamine when TTS was
reached. Thomas et al. (1990) exposed beluga whales to playbacks of an
oil-drilling platform in operation (``Sedco 708,'' 40 Hz-20 kHz; source
level 153 dB). Ambient SPL at ambient conditions in the pool before
playbacks was 106 dB and 134 to 137 dB RMS during playbacks at the
monitoring hydrophone across the pool. All cell and platelet counts and
21 different blood chemicals, including epinephrine and norepinephrine,
were within normal limits throughout baseline and playback periods, and
stress response hormone levels did not increase immediately after
playbacks. The difference between the Romano et al. (2004) and Thomas
et al. (1990) studies could be the differences in the type of sound
(seismic airgun and/or tone versus oil drilling), the intensity and
duration of the sound, the individual's response, and the surrounding
circumstances of the individual's environment. The sounds in the Thomas
et al. (1990) study would be more similar to those anticipated by
Hilcorp's tugs under load with a jack-up rig; therefore, no more than
short-term, low-hormone stress responses, if any, of CIBWs or other
marine mammals are expected as a result of exposure to noise during
tugs under load with a jack-up rig during Hilcorp's planned activities.
Auditory Masking. Since many marine mammals rely on sound to find
prey, moderate social interactions, and facilitate mating (Tyack,
2008), noise from anthropogenic sound sources can interfere with these
functions, but only if the noise spectrum overlaps with the hearing
sensitivity of the receiving marine mammal (Southall et al., 2007;
Clark et al., 2009; Hatch et al., 2012). Chronic exposure to excessive,
though not high-intensity, noise could cause masking at particular
frequencies for marine mammals that utilize sound for vital biological
functions (Clark et al., 2009). Acoustic masking is when other noises
such as from human sources interfere 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). Therefore, under certain
circumstances, marine mammals whose acoustical sensors or environment
are being severely masked could also be impaired from maximizing their
performance fitness for survival and reproduction. 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 (Hotchkin and
Parks, 2013).
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
[[Page 60184]]
response. For example, in the presence of potentially masking signals,
humpback whales and killer whales have been observed to increase the
length of their songs (Miller et al., 2000; Fristrup et al., 2003) or
vocalizations (Foote et al., 2004), respectively, while North Atlantic
right whales (Eubalaena glacialis) 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).
Fin whales have also been documented lowering the bandwidth, peak
frequency, and center frequency of their vocalizations under increased
levels of background noise from large vessels (Castellote et al. 2012).
Other alterations to communication signals have also been observed. For
example, gray whales, in response to playback experiments exposing them
to vessel noise, have been observed increasing their vocalization rate
and producing louder signals at times of increased outboard engine
noise (Dahlheim and Castellote, 2016). Alternatively, in some cases,
animals may cease sound production during production of aversive
signals (Bowles et al., 1994; Wisniewska et al., 2018).
Under certain circumstances, marine mammals experiencing
significant masking could also be impaired from maximizing their
performance fitness in survival and reproduction. Therefore, when the
coincident (masking) sound is human-made, it may be considered
harassment when disrupting or altering critical behaviors. It is
important to distinguish TTS and PTS, which persist after the sound
exposure, from masking, which occurs during the sound exposure. Because
masking (without resulting in TS) is not associated with abnormal
physiological function, it is not considered a physiological effect,
but rather a potential behavioral effect (though not necessarily one
that would be associated with harassment).
The frequency range of the potentially masking sound is important
in determining any potential behavioral impacts. For example, low-
frequency signals may have less effect on high-frequency echolocation
sounds produced by odontocetes but are more likely to affect detection
of mysticete communication calls and other potentially important
natural sounds such as those produced by surf and some prey species.
The masking of communication signals by anthropogenic noise may be
considered as a reduction in the communication space of animals (e.g.,
Clark et al., 2009) and may result in energetic or other costs as
animals change their vocalization behavior (e.g., Miller et al., 2000;
Foote et al., 2004; Parks et al., 2007; Di Iorio and Clark, 2010; Holt
et al., 2009). Masking can be reduced in situations where the signal
and noise come from different directions (Richardson et al., 1995),
through amplitude modulation of the signal, or through other
compensatory behaviors (Hotchkin and Parks, 2013).
Marine mammals at or near the proposed project site may be exposed
to anthropogenic noise which may be a source of masking. Vocalization
changes may result from a need to compete with an increase in
background noise and include increasing the source level, modifying the
frequency, increasing the call repetition rate of vocalizations, or
ceasing to vocalize in the presence of increased noise (Hotchkin and
Parks, 2013). For example, in response to vessel noise, CIBWs may shift
the frequency of their echolocation clicks and communication signals,
reduce their overall calling rates, and or increase the emission of
certain call signals to prevent masking by anthropogenic noise (Lesage
et al. 1999; Tyack, 2000; Eickmeier and Vallarta, 2022).
Masking occurs in the frequency band that the animals utilize, and
is more likely to occur in the presence of broadband, relatively
continuous noise sources such as tugging. Since noises generated from
tugs towing and positioning are mostly concentrated at low frequency
ranges, with a small concentration in high frequencies as well, these
activities likely have less effect on mid-frequency echolocation sounds
by odontocetes (toothed whales) such as CIBWs. However, lower frequency
noises are more likely to affect detection of communication calls and
other potentially important natural sounds such as surf and prey noise.
Low-frequency noise may also affect communication signals when they
occur near the frequency band for noise and thus reduce the
communication space of animals (e.g., Clark et al., 2009) and cause
increased stress levels (e.g., Holt et al., 2009). Unlike TS, masking,
which can occur over large temporal and spatial scales, can potentially
affect the species at population, community, or even ecosystem levels,
in addition to individual levels. Masking affects both senders and
receivers of the signals, and at higher levels for longer durations,
could have long-term chronic effects on marine mammal species and
populations. However, the noise generated by the tugs will not be
concentrated in one location or for more than 5 hours per positioning
attempt, and up to two positioning attempts at the same site. Thus,
while Hilcorp's activities may mask some acoustic signals that are
relevant to the daily behavior of marine mammals, the short-term
duration and limited areas affected make it very unlikely that the
fitness of individual marine mammals would be impacted.
In consideration of the range of potential effects (PTS to
behavioral disturbance), we consider the potential exposure scenarios
and context in which species would be exposed to tugs under load with a
jack-up rig during Hilcorp's planned activities. CIBWs may be present
in low numbers during the work; therefore, some individuals may be
reasonably expected to be exposed to elevated sound levels However,
CIBWs are expected to be transiting through the area, given this work
is proposed primarily in middle Cook Inlet (as described in the
Description of Marine Mammals in the Area of Specified Activities
section), thereby limiting exposure duration, as CIBWs in the area are
expected to be headed to or from the concentrated foraging areas
farther north near the Beluga River, Susitna Delta, and Knik and
Turnigan Arms. Similarly, humpback whales, fin whales, minke whales,
gray whales, killer whales, California sea lion, and Steller sea lions
are not expected to remain in the area of the tugs. Dall's porpoise,
harbor porpoise, and harbor seal have been sighted with more regularity
than many other species during oil and gas activities in Cook Inlet but
due to the transitory nature of these species, they are unlikely to
remain close to a tug under load for the full duration of the noise-
producing activity. In fact, during Hilcorp's jack-up rig-based
monitoring efforts in 2023, only one Dall's porpoise, two harbor seals,
and one harbor porpoise were observed across four different sightings,
and observations only lasted 1 to 5 minutes (Horsley and Larson, 2023).
Because of this and the relatively low-level sources, the likelihood of
PTS and TTS over the course of the tug activities is discountable.
Harbor seals may linger or haul-out in the area but they are not known
to do so in any large number or for extended periods of time (there are
no known major haul-outs or rookeries coinciding with the anticipated
transit routes). Here we find there is small potential for TTS over the
course of tug activities but again, PTS is not likely due to the nature
of tugging. Potential for PTS and TTS due to pile driving is discussed
further in the Estimated Take section.
Given most marine mammals are likely transiting through the area,
exposure is expected to be brief but the
[[Page 60185]]
actual presence of the tug and jack-up rig may result in animals
shifting pathways around the work site (e.g., avoidance), increasing
speed or dive times, changing their group formations, or altering their
acoustic signals. The likelihood of no more than a short-term,
localized disturbance response is supported by data from Hilcorp's
previous jack-up rig-based monitoring efforts in 2023, which reported
no observable reactions to the towing activities outside of two harbor
seals diving. Further other data indicate CIBWs and other marine
mammals regularly pass by industrialized areas such as the POA (61N
Environmental, 2021, 2022a, 2022b, 2022c; Easley-Appleyard and Leonard,
2022); therefore, we do not expect abandonment of their transiting
route or other disruptions of their behavioral patterns. We also
anticipate some animals may respond with such mild reactions to the
project that the response would not be detectable. For example, during
low levels of tug power output (e.g., while tugs may be operating at
low power because of favorable conditions), the animals may be able to
hear the work but any resulting reactions, if any, are not expected to
rise to the level of take.
While in some cases marine mammals have exhibited little to no
obviously detectable response to certain common or routine
industrialized activity (Cornick et al., 2011; Horley and Larson,
2023), it is possible some animals may at times be exposed to received
levels of sound above the Level B harassment threshold. This potential
exposure in combination with the nature of the tug and jack-up rig
configuration (e.g., difficult to maneuver, potential need to operate
at night) means it is possible that take by Level B harassment could
occur over the total estimated period of activities; therefore, NMFS in
response to Hilcorp's IHA application proposes to authorize take by
Level B harassment from Hilcorp's use of tugs towing a jack-up rig for
both positioning and straight-line tug activities.
Potential Effects on Marine Mammal Habitat
Hilcorp's proposed activities could have localized, temporary
impacts on marine mammal habitat, including prey, by increasing in-
water sound pressure levels. Increased noise levels may affect acoustic
habitat and adversely affect marine mammal prey in the vicinity of the
project areas (see discussion below). Elevated levels of underwater
noise would ensonify the project areas where both fishes and mammals
occur and could affect foraging success. Additionally, marine mammals
may avoid the area during rig towing, holding, and or positioning;
however, displacement due to noise is expected to be temporary and is
not expected to result in long-term effects to the individuals or
populations.
The total area likely impacted by Hilcorp's activities is
relatively small compared to the available habitat in Cook Inlet.
Avoidance by potential prey (i.e., fish) of the immediate area due to
increased noise is possible. The duration of fish and marine mammal
avoidance of this area after tugging stops is unknown, but a rapid
return to normal recruitment, distribution, and behavior is
anticipated. Any behavioral avoidance by fish or marine mammals of the
disturbed area would still leave significantly large areas of fish and
marine mammal foraging habitat in the nearby vicinity. Increased
turbidity near the seafloor is not anticipated
Potential Effects on Prey. Sound may affect marine mammals through
impacts on the abundance, behavior, or distribution of prey species
(e.g., crustaceans, cephalopods, fishes, zooplankton). Marine mammal
prey varies by species, season, and location and, for some, is not well
documented. Studies regarding the effects of noise on known marine
mammal prey are described here.
Fishes utilize the soundscape and components of sound in their
environment to perform important functions such as foraging, predator
avoidance, mating, and spawning (e.g., Zelick et al., 1999; Fay, 2009).
Depending on their hearing anatomy and peripheral sensory structures,
which vary among species, fishes hear sounds using pressure and
particle motion sensitivity capabilities and detect the motion of
surrounding water (Fay et al., 2008). The potential effects of noise on
fishes depends on the overlapping frequency range, distance from the
sound source, water depth of exposure, and species-specific hearing
sensitivity, anatomy, and physiology. Reactions also depend on the
physiological state of the fish, past exposures, motivation (e.g.,
feeding, spawning, migration), and other environmental factors.
Fish react to sounds that are especially strong and/or intermittent
low-frequency sounds, and behavioral responses such as flight or
avoidance are the most likely effects. Short duration, sharp sounds can
cause overt or subtle changes in fish behavior and local distribution.
SPLs of sufficient strength have been known to cause injury to fishes
and fish mortality (summarized in Popper et al., 2014). However, in
most fish species, hair cells in the ear continuously regenerate and
loss of auditory function likely is restored when damaged cells are
replaced with new cells. Halvorsen et al. (2012) showed that a TTS of 4
to 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. Injury caused by barotrauma can range
from slight to severe and can cause death, and is most likely for fish
with swim bladders.
Fish have been observed to react when engine and propeller sounds
exceed a certain level (Olsen et al., 1983; Ona, 1988; Ona and Godo,
1990). Avoidance reactions have been observed in fish, including cod
and herring, when vessel sound levels were 110 to 130 dB re 1 [mu]Pa
rms (Nakken, 1992; Olsen, 1979; Ona and Godo, 1990; Ona and Toresen,
1988). Vessel sound source levels in the audible range for fish are
typically 150 to 170 dB re 1 [mu]Pa per Hz (Richardson et al., 1995).
The tugs used during the specified activity could be expected to
produce levels in this range when in transit. Based upon the reports in
the literature and the predicted sound levels from these vessels, some
temporary avoidance by fish in the immediate area may occur. Overall,
no more than negligible impacts on fish are expected as a result of the
specified activity.
Zooplankton is a food source for several marine mammal species, as
well as a food source for fish that are then preyed upon by marine
mammals. Population effects on zooplankton could have indirect effects
on marine mammals. Data are limited on the effects of underwater sound
on zooplankton species, particularly sound from ship traffic and
construction (Erbe et al., 2019). Popper and Hastings (2009) reviewed
information on the effects of human-generated sound and concluded that
no substantive data are available on whether the sound levels from pile
driving, seismic activity, or any human-made sound would have
physiological effects on invertebrates. Any such effects would be
limited to the area very near (1 to 5 m) the sound source and would
result in no population effects because of the relatively small area
affected at any one time and the reproductive strategy of most
zooplankton species (short generation, high fecundity, and very high
natural mortality). No adverse impact on zooplankton populations is
expected to occur from the specified activity due in part to large
reproductive capacities and naturally high levels of predation and
mortality of these populations. Any
[[Page 60186]]
mortalities or impacts that might occur would be negligible.
In summary, given the relatively small areas being affected, as
well as the temporary and mostly transitory nature of the tugging, any
adverse effects from Hilcorp's activities on any prey habitat or prey
populations are expected to be minor and temporary. The most likely
impact to fishes at the project site would be temporary avoidance of
the area. Any behavioral avoidance by fish of the disturbed area would
still leave significantly large areas of fish and marine mammal
foraging habitat in the nearby vicinity. Thus, we preliminarily
conclude that impacts of the specified activities 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 of Marine Mammals
This section provides an estimate of the number of incidental takes
proposed for authorization through the IHA, which will inform NMFS'
consideration of ``small numbers,'' the negligible impact
determinations, and impacts on subsistence uses.
Harassment is the only type of take expected to result from these
activities. Except with respect to certain activities not pertinent
here, section 3(18) of the MMPA defines ``harassment'' as any act of
pursuit, torment, or annoyance, which (i) has the potential to injure a
marine mammal or marine mammal stock in the wild (Level A harassment);
or (ii) has the potential to disturb a marine mammal or marine mammal
stock in the wild by causing disruption of behavioral patterns,
including, but not limited to, migration, breathing, nursing, breeding,
feeding, or sheltering (Level B harassment).
Authorized takes would be by Level B harassment only, in the form
of behavioral reactions and or TTS for individual marine mammals
resulting from exposure to Hilcorp's acoustic sources (i.e., tugs
towing, holding, and positioning). Based on the nature of the activity,
Level A harassment is neither anticipated nor proposed to be
authorized.
As described previously, no serious injury or mortality is
anticipated or proposed to be authorized for this activity. 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 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., Richardson et al., 1995; 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 (i.e., Level B harassment). NMFS
generally predicts that marine mammals are likely to be behaviorally
disturbed 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., tugging, 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 thresholds are expected to include any likely takes by
TTS as, in most cases, the likelihood of TTS occurs at distances from
the source smaller 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.
Hilcorp's proposed activity includes the use of continuous sources
(tugs towing, holding, and positioning a jack-up rig), and therefore
the RMS SPL threshold of 120 is applicable.
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). Hilcorp's
proposed activity includes the use of non-impulsive sources (i.e., tugs
towing, holding, and positioning a jack-up rig).
These thresholds are provided in table 4 below. The references,
analysis, and methodology used in the development of the thresholds are
described in NMFS' 2018 Technical Guidance, which may be accessed at:
<a href="https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance">https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance</a>.
Table 4--Thresholds Identifying the Onset of Permanent Threshold Shift
----------------------------------------------------------------------------------------------------------------
PTS onset acoustic thresholds * (received level)
Hearing group ------------------------------------------------------------------------
Impulsive Non-impulsive
----------------------------------------------------------------------------------------------------------------
Low-Frequency (LF) Cetaceans........... Cell 1: Lpk,flat: 219 dB; Cell 2: LE,LF,24h: 199 dB.
LE,LF,24h: 183 dB.
[[Page 60187]]
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.
The sound field in the project area is the existing background
noise plus additional noise resulting from tugs under load with a jack-
up rig. Marine mammals are expected to be affected via sound generated
by the primary components of the project (i.e., tugs towing, holding,
and positioning a jack-up rig). Calculation of the area ensonified by
the proposed action is dependent on the background sound levels at the
project site, the source levels of the proposed activities, and the
estimated transmission loss coefficients for the proposed activities at
the site. These factors are addressed below.
Sound Source Levels of Proposed Activities. The project includes 3
to 4 tugs under load with a jack-up rig. Hilcorp conducted a literature
review of underwater sound emissions of tugs under various loading
efforts. The sound source levels for tugs of various horsepower (2,000
to 8,200) under load can range from approximately 164 dB RMS to 202 dB
RMS. This range largely relates to the level of operational effort,
with full power output and higher speeds generating more propeller
cavitation and hence greater sound source levels than lower power
output and lower speeds. Tugs under tow produce higher source levels
than tugs transiting with no load because of the higher power output
necessary to pull the load. The amount of power the tugs expend while
operating is the best predictor of relative sound source level. Several
factors would determine the duration that the tugboats are towing the
jack-up rig, including the origin and destination of the towing route
(e.g., Rig Tenders Dock, an existing platform) and the tidal
conditions. The power output would be variable and influenced by the
prevailing wind direction and velocity, the current velocity, and the
tidal stage. To the extent feasible, transport would be timed with the
tide to minimize towing duration and power output.
Hilcorp's literature review identified no existing data on sound
source levels of tugs towing jack-up rigs. Accordingly, for this
analysis, Hilcorp considered data from tug-under-load activities,
including berthing and towing activities. Austin and Warner (2013)
measured 167 dB RMS for tug towing barge activity in Cook Inlet.
Blackwell and Greene (2002) reported berthing activities in the POA
with a source level of 179 dB RMS. Laurinolli et al. (2005) measured a
source level of 200 dB RMS for anchor towing activities by a tugboat in
the Strait of Juan de Fuca, WA. The Roberts Bank Terminal 2 study
(2014) repeated measurements of the same tug operating under different
speeds and loading conditions. Broadband measurements from this study
ranged from approximately 162 dB RMS up to 200 dB RMS.
The rig manager for Hilcorp, who is experienced with towing jack-up
rigs in Cook Inlet, described operational conditions wherein the tugs
generally operate at half power or less for the majority of the time
they are under load (pers. Comm., Durham, 2021). Transits with the tide
(lower power output) are preferred for safety reasons, and effort is
made to reduce or eliminate traveling against the tide (higher power
output). The Roberts Bank Terminal 2 study (2014) allowed for a
comparison of source levels from the same vessel (Seaspan Resolution
tug) at half power versus full power. Seaspan Resolution's half-power
(i.e., 50 percent) berthing scenario had a sound source level of 180 dB
RMS. In addition, the Roberts Bank Terminal 2 Study (2014) reported a
mean tug source level of 179.3 dB RMS from 650 tug transits under
varying load and speed conditions.
The 50 percent (or less) power output scenario occurs during the
vast majority of tug towing jack-up rig activity, as described in the
Detailed Description of the Specific Activity section. Therefore, based
on Hilcorp's literature review, a source level of 180 dB RMS was found
to be an appropriate proxy source level for a single tug under load
based on the Roberts Bank Terminal 2 study. If all three tugs were
operating simultaneously at 180 dB RMS, the overall source emission
levels would be expected to increase by approximately 5 dB when
logarithmically adding the sources (i.e., to 185 dB RMS). To further
support this level as an appropriate proxy, a sound source verification
(SSV) study performed by JASCO Applied Sciences (JASCO) in Cook Inlet
in October 2021 (Lawrence et al., 2022) measured the sound source level
from three tugs pulling a jack-up rig in Cook Inlet at various power
outputs. Lawrence et al. (2022) reported a source level of 167.3 dB RMS
for the 20 percent-power scenario and a source level of 205.9 dB RMS
for the 85 percent-power scenario. Assuming a linear scaling of tug
power, a source level of 185 dB RMS was calculated as a single point
source level for three tugs operating at 50 percent power output.
Because the 2021 Cook Inlet SSV measurements by JASCO represent the
most recent best available data, and because multiple tugs may be
operating simultaneously, the analyses presented below use a mean tug
sound source level scenario of 185 dB RMS to calculate the Level B
harassment estimates for three tugs operating at 50
[[Page 60188]]
percent power output. In practice, the load condition of the three tugs
is unlikely to be identical at all times, so sound emissions would be
dominated by the single tug in the group that is working hardest at any
point in time.
Further modeling was done to account for one additional tug working
for one hour at 50 percent power during jack-up rig positioning, a
stationary activity. This is equivalent in terms of acoustic energy to
three tugs operating at 180.0 dB RMS (each of them) for 4 hours, joined
by a fourth tug for 1 hour, increasing the source level to 186.0 dB RMS
only during the 1-hour period (the logarithmic sum of four tugs working
together at 180.0 dB RMS). An SEL of 185.1 dB was used to account for
the cumulative sound exposure when calculating Level A harassment by
adding a 4th tug operating at 50 percent power for 20 percent of the 5-
hour period. This is equivalent in terms of acoustic energy to 3 tugs
operating at 185.0 dB for 4 hours, joined by a fourth tug for 1 hour,
increasing the source level to 186.0 dB only during the 1-hour period.
The use of the 20 percent duty cycle was a computational requirement
and, although equal in terms of overall energy and determination of
impacts, should not be confused with the actual instantaneous SPL (see
section 6.2.1.1 of Hilcorp's application for additional computational
details).
In summary, Hilcorp has proposed to use a source level of 185.0 dB
RMS to calculate the stationary Level B harassment isopleth where three
tugs were under load for 4 hours with a 50 percent power output and a
source level of 186.0 dB RMS to calculate the stationary Level B
harassment isopleth where four tugs were under load for 1 hour with a
50 percent power output. Further, Hilcorp has proposed to use a source
level of 185.1 dB SEL to calculate the stationary Level A harassment
isopleths where three tugs were underload for 4 hours and then one tug
joined for 1 additional hour. Lastly, Hilcorp proposed to use the 185.0
dB RMS level to model the mobile Level A harassment isopleths for three
tugs under load with a 50 percent power output. NMFS concurs that
Hilcorp's proposed source levels are appropriate.
Underwater Sound Propagation Modeling. Hilcorp contracted SLR
Consulting to model the extent of the Level A and Level B harassment
isopleths for tugs under load with a jack-up rig during their proposed
activities. Cook Inlet is a particularly complex acoustic environment
with strong currents, large tides, variable sea floor and generally
changing conditions. Accordingly, Hilcorp applied a more detailed
propagation model than the ``practical spreading loss'' approach that
uses a factor of 15. The objective of a more detailed propagation
calculation is to improve the representation of the influence of some
environmental variables, in particular, by accounting for bathymetry
and specific sound source locations and frequency-dependent propagation
effects.
Modeling was conducted using the dBSea software package. The fluid
parabolic equation modeling algorithm was used with 5 Pad[eacute] terms
to calculate the TL between the source and the receiver at low
frequencies (\1/3\-octave bands, 31.5 Hz up to 1 kHz). For higher
frequencies (1 kHz up to 8 kHz) the ray tracing model was used with
1,000 reflections for each ray. Sound sources were assumed to be
omnidirectional and modeled as points. The received sound levels for
the project were calculated as follows: (1) One-third octave source
spectral levels were obtained via reference spectral curves with
subsequent corrections based on their corresponding overall source
levels; (2) TL was modeled at one-third octave band central frequencies
along 100 radial paths at regular increments around each source
location, out to the maximum range of the bathymetry data set or until
constrained by land; (3) The bathymetry variation of the vertical plane
along each modeling path was obtained via interpolation of the
bathymetry dataset which has 83 m grid resolution; (4) The one-third
octave source levels and transmission loss were combined to obtain the
received levels as a function of range, depth, and frequency; and (5)
The overall received levels were calculated at a 1-m depth resolution
along each propagation path by summing all frequency band spectral
levels.
Model Inputs. Bathymetry data used in the model was collected from
the NOAA National Centers for Environmental Information (AFSC, 2019).
Using NOAA's temperature and salinity data, sound speed profiles were
computed for depths from 0 to 100 m for May, July, and October to
capture the range of possible sound speed depending on the time of year
Hilcorp's work could be conducted. These sound speed profiles were
compiled using the Mackenzie Equation (1981) and are presented in table
8 of Hilcorp's application (available at <a href="https://www.fisheries.noaa.gov/action/incidental-take-authorization-hilcorp-alaska-llc-oil-and-gas-activities-cook-inlet-alaska-0">https://www.fisheries.noaa.gov/action/incidental-take-authorization-hilcorp-alaska-llc-oil-and-gas-activities-cook-inlet-alaska-0</a>). Geoacoustic
parameters were also incorporated into the model. The parameters were
based on substrate type and their relation to depth. These parameters
are presented in table 9 of Hilcorp's application (available at <a href="https://www.fisheries.noaa.gov/action/incidental-take-authorization-hilcorp-alaska-llc-oil-and-gas-activities-cook-inlet-alaska-0">https://www.fisheries.noaa.gov/action/incidental-take-authorization-hilcorp-alaska-llc-oil-and-gas-activities-cook-inlet-alaska-0</a>).
Detailed broadband sound transmission loss modeling in dBSea used
the source level of 185 dB RMS calculated in one-third octave band
levels (31.5 Hz to 64,000 Hz) for frequency dependent solutions. The
frequencies associated with tug sound sources occur within the hearing
range of marine mammals in Cook Inlet. Received levels for each hearing
marine mammal group based on one-third octave auditory weighting
functions were also calculated and integrated into the modeling
scenarios of dBSea. For modeling the distances to relevant PTS
thresholds, a weighting factor adjustment was not used; instead, the
data on the spectrum associated with their source was used and
incorporated the full auditory weighting function for each marine
mammal hearing group.
The tugs towing the jack-up rig represent a mobile sound source,
and tugs holding and positioning the jack-up rig on a platform are more
akin to a stationary sound source. In addition, three tugs would be
used for towing (mobile) and holding and positioning (stationary) and
up to four tugs could be used for positioning (stationary).
Consequently, sound TL modeling was undertaken for the various
stationary and mobile scenarios for three and four tugs to generate
Level A and Level B harassment threshold distances.
For acoustic modeling purposes of the stationary Level A harassment
thresholds, two locations representative of where tugs will be
stationary while they position the jack-up rig were selected in middle
Cook Inlet near the Tyonek platform and in lower Trading Bay where the
production platforms are located. To account for the mobile scenarios,
the acoustic model generated Levels A and Level B harassment distances
along a representative route from the Rig Tenders dock in Nikiski to
the Tyonek platform, the northernmost platform in Cook Inlet
(representing middle Cook Inlet), as well as from the Tyonek Platform
to the Dolly Varden platform in lower Trading Bay, then from the Dolly
Varden platform back to the Rig Tenders Dock in Nikiski. Note that this
route is representative of a typical route the tugs may take; the
specific route is not yet known, as the order in which platforms will
be drilled with the jack-up rig is not yet known. These results were
used to calculate Level A and Level B harassment exposure estimates
from mobile tugs
[[Page 60189]]
towing a jack-up rig. The Level B harassment results were also used to
calculate Level B harassment exposure estimates from stationary tugs
holding or positioning a jack-up rig, as the mobile route encompassed
the stationary modeling points. The locations represent a range of
water depths from 18 to 77 m found throughout the project area.
For mobile Level B harassment and stationary Level B harassment
with three tugs, the average distance to the 120 dB RMS threshold was
based on the assessment of 100 radials at 25 locations across seasons
(May, July, and October) and represents the average Level B harassment
zone for each season and location (table 5). The result is a mobile and
stationary Level B harassment zone of 3,850 m when three tugs are used
(table 5). For stationary Level B harassment with four tugs, the
average distance to the 120 dB RMS threshold was based on 100 radials
at two locations, one in Trading Bay and one in middle Cook Inlet,
across seasons (May, July, and October) and represents the average
Level B harassment zone for each season and location. The result is a
stationary Level B harassment zone of 4,453 m when four tugs are in use
(table 6). NMFS concurs that 3,850 m and 4,453 m are appropriate
estimates for the extent of the Level B harassment zones for Hilcorp's
towing, holding, and positioning activities when using three and four
tugs, respectively.
Table 5--Average Distances to the Level B Harassment Threshold (120 dB) for Three Tugs Towing (Mobile) and
Holding and Positioning for 4 Hours (Stationary)
----------------------------------------------------------------------------------------------------------------
Average distance to 120 dB threshold (m) Season
------------------------------------------------ average
Location distance to
May July October threshold (m)
----------------------------------------------------------------------------------------------------------------
M1.............................................. 4,215 3,911 4,352 4,159
M2.............................................. 3,946 3,841 4,350 4,046
M3.............................................. 4,156 3,971 4,458 4,195
M4.............................................. 4,040 3,844 4,364 4,083
M5.............................................. 4,053 3,676 4,304 4,011
M6.............................................. 3,716 3,445 3,554 3,572
M7.............................................. 2,947 2,753 2,898 2,866
M8.............................................. 3,270 3,008 3,247 3,175
M9.............................................. 3,567 3,359 3,727 3,551
M10............................................. 3,600 3,487 3,691 3,593
M11............................................. 3,746 3,579 4,214 3,846
M12............................................. 3,815 3,600 3,995 3,803
M13............................................. 4,010 3,831 4,338 4,060
M14............................................. 3,837 3,647 4,217 3,900
M15............................................. 3,966 3,798 4,455 4,073
M16............................................. 3,873 3,676 4,504 4,018
M18............................................. 5,562 3,893 4,626 4,694
M20............................................. 5,044 3,692 4,320 4,352
M22............................................. 4,717 3,553 4,067 4,112
M24............................................. 4,456 3,384 4,182 4,007
M25............................................. 3,842 3,686 4,218 3,915
M26............................................. 3,690 3,400 3,801 3,630
M27............................................. 3,707 3,497 3,711 3,638
M28............................................. 3,546 3,271 3,480 3,432
M29............................................. 3,618 3,279 3,646 3,514
---------------------------------------------------------------
Average..................................... 3,958 3,563 4,029 3,850
----------------------------------------------------------------------------------------------------------------
Table 6--Average Distances to the Level B Harassment Threshold (120 dB) for Four Tugs Positioning (Stationary)
for 1 Hour
----------------------------------------------------------------------------------------------------------------
Average distance to Level B harassment Season
threshold (m) average
Location ------------------------------------------------ distance to
May July October threshold (m)
----------------------------------------------------------------------------------------------------------------
Trading Bay..................................... 4,610 3,850 4,810 4,423
Middle CI....................................... 4,820 4,130 4,500 4,483
---------------------------------------------------------------
Average..................................... 4,715 3,990 4,655 4,453
----------------------------------------------------------------------------------------------------------------
The average Level A harassment distances for the stationary, four
tug scenario were calculated assuming a SEL of 185.1 dB for a 5-hour
exposure duration (table 7). For the mobile, three tug scenario, the
average Level A harassment distances were calculated assuming a SEL of
185.0 dB with an 18-second exposure period (table 8). This 18-second
exposure was derived using the standard TL equation (Source Level-TL =
Received Level) for determining threshold distance (R [m]), where TL =
15Log10. In this case, the equation was 185.0 dB-15Log10 = 173 dB.
Solving for threshold distance (R) yields a distance of approximately 6
m, which was then used as the preliminary
[[Page 60190]]
ensonified radius to determine the duration of time it would take for
the ensonified area of the sound source traveling at a speed of 2.06 m/
s (4 knots) to pass a marine mammal. The duration (twice the radius
divided by speed of the source) that the ensonified area of a single
tug would take to pass a marine mammal under these conditions is 6
seconds. An 18-second exposure was used in the model to reflect the
time it would take for three ensonified areas (from three consecutive
individual tugs) to pass a single point that represents a marine mammal
(6 seconds + 6 seconds + 6 seconds = 18 seconds).
Table 7--Average Distances to the Level A Harassment Thresholds for Four Stationary Tugs Under Load With a Jack-Up Rig for 5 Hours
--------------------------------------------------------------------------------------------------------------------------------------------------------
Average distance (m) to Level A harassment threshold by functional hearing
group
Location Season -------------------------------------------------------------------------------
LF MF HF PW OW \1\
--------------------------------------------------------------------------------------------------------------------------------------------------------
Trading Bay............................... May......................... 107 77 792 64 ..............
Trading Bay............................... July........................ 132 80 758 66 ..............
Trading Bay............................... October..................... 105 75 784 79 ..............
Middle Cook Inlet......................... May......................... 86 85 712 78 ..............
Middle Cook Inlet......................... July........................ 95 89 718 80 ..............
Middle Cook Inlet......................... October..................... 82 86 730 80 ..............
Average................................... ............................ 102 82 749 75 0
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ The Level A harassment distances are smaller than the footprint of the tugs.
Table 8--Average Distances to the Level A Harassment Thresholds for Three Mobile Tugs Under Load
With a Jack-Up Rig Assuming a 18-Second Exposure Duration
--------------------------------------------------------------------------------------------------------------------------------------------------------
Average distance (m) to Level A threshold by functional hearing group
Location Season -------------------------------------------------------------------------------
LF \1\ MF \1\ HF PW \1\ OW \1\
--------------------------------------------------------------------------------------------------------------------------------------------------------
M2........................................ May......................... .............. .............. 10 .............. ..............
M2........................................ July........................ .............. .............. 5 .............. ..............
M2........................................ October..................... .............. .............. 10 .............. ..............
M11....................................... May......................... .............. .............. 10 .............. ..............
M11....................................... July........................ .............. .............. 5 .............. ..............
M11....................................... October..................... .............. .............. 10 .............. ..............
M22....................................... May......................... .............. .............. 10 .............. ..............
M22....................................... July........................ .............. .............. 5 .............. ..............
M22....................................... October..................... .............. .............. 10 .............. ..............
-------------------------------------------------------------------------------------------------------------
Average............................... ............................ 0 0 8 0 0
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ The Level A harassment distances are smaller than the footprint of the tugs.
Tugs are anticipated to be towing the jack-up rig between platforms
and considered a mobile sound source for 6 hours in a single day per
jack-up rig move. Tugs are anticipated to be towing the jack-up rig and
considered a mobile source during demobilization and mobilization to/
from Rig Tenders Dock in Nikiski for 9 hours. One jack-up rig move
between platforms is planned during the IHA period. Tugs are
anticipated to be holding or positioning the jack-up rig at the
platforms or Rig Tenders Dock during demobilization and mobilization
and are considered a stationary sound source for 5 hours in the first
day and 5 hours in the second day if a second attempt to pin the jack-
up rig is required. A second attempt was built into the exposure
estimate for each pinning event; three total pinning events are
anticipated during the IHA period for production drilling.
The ensonified area for a location-to-location transport for
production drilling represents a rig move between two production
platforms in middle Cook Inlet and/or Trading Bay and includes 6 mobile
hours over an average distance of 16.77 km in a single day and 5
stationary hours on the first day and 5 stationary hours on a second
day. The 5 stationary hours are further broken into 4 hours with three
tugs under load and 1 hour with four tugs under load. One location-to-
location jack-up rig move is planned for the IHA period.
The ensonified area for production drilling demobilization and
mobilization represents a rig move from a production platform in middle
Cook Inlet to Rig Tenders Dock in Nikiski and reverse for mobilization
and includes 9 mobile hours over a distance of up to 64.34 km in a
single day and 5 stationary hours on the first day and 5 stationary
hours on a second day, which are further broken into the same three
tugs working for 4 hours and four tugs working for 1 hour as mentioned
above. A summary of the estimated Level A and Level B harassment
distances and areas for the various tugging scenarios if provided in
table 9.
[[Page 60191]]
Table 9--Average Distances and Areas to the Estimated Level A and Bevel B Harassment Thresholds for the Various
Tugging Scenarios
----------------------------------------------------------------------------------------------------------------
Level A harassment distance (m)/area (km\2\) Level B
----------------------------------------------------------------- harassment
Activity distance (m)/area
LF MF HF PW OW (km\2\)
----------------------------------------------------------------------------------------------------------------
Demobilization/Mobilization
----------------------------------------------------------------------------------------------------------------
3 Tugs Towing a Jack-Up Rig-- \1\ \1\ 8/1.07 \1\ \1\ 3,850/541.96
Mobile.....................
3 Tugs Towing a Jack-Up Rig-- 102/0.03 82/0.02 749/1.76 75/0.02 \1\ 3,850/46.56
Stationary for up to 4
hours......................
4 Tugs Towing a Jack-Up Rig-- 102/0.03 82/0.02 749/1.76 75/0.02 \1\ 4,453/62.30
Stationary for up to 1 hour
----------------------------------------------------------------------------------------------------------------
Location-to-Location
----------------------------------------------------------------------------------------------------------------
3 Tugs Towing a Jack-Up Rig-- \1\ \1\ 8/0.28 \1\ \1\ 3,850/175.6
Mobile.....................
3 Tugs Towing a Jack-Up Rig-- 102/0.03 82/0.02 749/1.76 75/0.02 \1\ 3,850/46.56
Stationary for up to 4
hours......................
4 Tugs Towing a Jack-Up Rig-- 102/0.03 82/0.02 749/1.76 75/0.02 \1\ 4,453/62.30
Stationary for up to 1 hour
----------------------------------------------------------------------------------------------------------------
\1\ The Level A harassment distances are smaller than the footprint of the tugs.
Marine Mammal Occurrence
In this section we provide information about the occurrence of
marine mammals, including density or other relevant informa
[…truncated; see source link]Indexed from Federal Register on July 24, 2024.
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.