Notice2025-08672
Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to Narwhal, LLC Oil and Gas Exploration Activities in West Harrison Bay, 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
May 16, 2025
Issuing agencies
Commerce DepartmentNational Oceanic and Atmospheric Administration
Abstract
NMFS has received a request from Narwhal, LLC (Narwhal) for authorization to take marine mammals incidental to oil and gas exploration activities in west Harrison Bay, 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, one-year renewal that could be issued under certain circumstances and if all requirements are met, as described in Request for Public Comments at the end of this notice. NMFS will consider public comments prior to making any final decision on the issuance of the requested MMPA authorization and agency responses will be summarized in the final notice of our decision.
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[Federal Register Volume 90, Number 94 (Friday, May 16, 2025)]
[Notices]
[Pages 21182-21214]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2025-08672]
[[Page 21181]]
Vol. 90
Friday,
No. 94
May 16, 2025
Part III
Department of Commerce
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National Oceanic Atmospheric Administration
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Takes of Marine Mammals Incidental to Specified Activities; Taking
Marine Mammals Incidental to Narwhal, LLC Oil and Gas Exploration
Activities in West Harrison Bay, Alaska; Notice
Federal Register / Vol. 90 , No. 94 / Friday, May 16, 2025 /
Notices
[[Page 21182]]
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DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
[RTID 0648-XC940]
Takes of Marine Mammals Incidental to Specified Activities;
Taking Marine Mammals Incidental to Narwhal, LLC Oil and Gas
Exploration Activities in West Harrison Bay, 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 Narwhal, LLC (Narwhal) for
authorization to take marine mammals incidental to oil and gas
exploration activities in west Harrison Bay, 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, one-year renewal
that could be issued under certain circumstances and if all
requirements are met, as described in Request for Public Comments at
the end of this notice. NMFS will consider public comments prior to
making any final decision on the issuance of the requested MMPA
authorization and agency responses will be summarized in the final
notice of our decision.
DATES: Comments and information must be received no later than June 16,
2025.
ADDRESSES: Submit all electronic public comments via the Federal e-
Rulemaking Portal. Go to <a href="https://www.regulations.gov">https://www.regulations.gov</a> and enter NOAA-
NMFS-2025-0042 in the Search box. Click on the ``Comment'' icon,
complete the required fields, and enter or attach your comments.
Instructions: Comments sent by any other method, to any other
address or individual, or received after the end of the comment period,
may not be considered by NMFS. All comments received are a part of the
public records and will generally be posted for public viewing on
<a href="https://www.regulations.gov">https://www.regulations.gov</a> without change. All personal identifying
information (e.g., name, address), confidential business information,
or otherwise sensitive information submitted voluntarily by the sender
will be publicly accessible. NMFS will accept anonymous comments (enter
``N/A'' in the required fields if you wish to remain anonymous).
Attachments to electronic comments will be accepted in Microsoft Word,
Excel, or Adobe PDF file formats only.
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.
FOR FURTHER INFORMATION CONTACT: Craig Cockrell, 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 mitigation,
monitoring and reporting of the takings are set forth. The definitions
of all applicable MMPA statutory terms cited above are included in the
relevant sections below.
National Environmental Policy Act
To comply with the National Environmental Policy Act of 1969 (NEPA;
42 U.S.C. 4321 et seq.) and NOAA Administrative Order (NAO) 216-6A,
NMFS must review our proposed action (i.e., the issuance of an IHA)
with respect to potential impacts on the human environment.
Accordingly, NMFS is preparing an Environmental Assessment (EA) to
consider the environmental impacts associated with the issuance of the
proposed IHA. In accordance with the National Environmental Policy Act
of 1969 (NEPA; 42 U.S.C. 4321 et seq.) and NOAA policy and procedures
(NOAA Administrative Order 216-6A and its Companion Manual), NMFS has
prepared a draft environmental assessment analyzing the potential
impacts of NMFS' proposed action of issuance of an IHA. NMFS is seeking
public comment on the draft EA. The draft EA is 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> for a 30 day public comment period.
NMFS will consider all comments submitted in response to this notice
prior to concluding the NEPA process or making a final decision on the
IHA request.
Summary of Request
On October 25, 2022, NMFS received a request from Narwhal for an
IHA to take marine mammals incidental to oil and gas exploration
activities in and around west Harrison Bay, Alaska. After withdrawing
its original request, on November 1, 2024, Narwhal resubmitted its
application, which included a revised project schedule and minor
changes to its activity. The application was deemed adequate and
complete on January 27, 2025. Narwhal's request is for take of four
marine mammal species by Level B harassment only. Neither Narwhal nor
NMFS expect serious injury or mortality to result from the specified
activity, and therefore, an IHA is appropriate.
Description of Proposed Activity
Overview
Narwhal proposes to conduct shallow hazard geophysical surveys and
exploratory drilling operations, which includes construction and
operation of ice trails, roads, and pads, in west Harrison Bay, Alaska
to explore its oil and gas leases in the area. The activities would
occur between August 2025 and July 2026 and would occur primarily in
west Harrison Bay and the area between west Harrison Bay and Prudhoe
Bay, Alaska. Narwhal would also conduct mobilization and barge
transport activities out of Prudhoe Bay, Alaska. Shallow hazard
geophysical surveys (hereinafter, ``shallow water hazard surveys'')
would use airguns and
[[Page 21183]]
sparkers as acoustic sources and would introduce underwater sound that
may result in take by Level B harassment of marine mammals.
Construction and operation of sea ice trails around the Colville River
Delta may result in take by Level B harassment of ringed seals due to
the introduction of underwater sound. A number of other activities
would occur during the course of this project but are not expected to
result in take of marine mammals.
Dates and Duration
The proposed IHA would be effective for a period of one year, and
activities are anticipated to occur year-round. Work that may result in
the take of marine mammals is expected to take place between August and
September (shallow hazard surveys) and through December and March (ice
trail construction and operation). Figure 2-1 of Narwhal's IHA
application provides more detail regarding timing of project
activities. Please refer to Narwhal's application for additional
information about the timing of its various proposed activities.
Shallow hazard surveys at all six sites would take place over
approximately 12 days and would occur over a 12 hour period each day.
Offshore ice road and trail construction would occur over approximately
167 days and would occur as needed throughout a 24-hour period.
Several communities on the North Slope of Alaska engage in marine
mammal subsistence hunting activities at varying times and in varying
locations. These subsistence hunts are further described below in the
Potential Effects of Specified Activities on Subsistence Uses of Marine
Mammals section. The proposed activities would occur closest to the
marine subsistence use area used by the Native Village of Nuiqsut,
which typically occurs August 25th to September 15th or earlier if
whaling is complete.
Specific Geographic Region
Narwhal's proposed activities would primarily occur in west
Harrison Bay and between Oliktok Point and west Harrison Bay in the
Beaufort Sea, Alaska. Additionally, the activity would include transit
between west Harrison Bay and Prudhoe Bay, Alaska. All activities would
occur primarily in shallow waters of 3 meters (m) or less.
BILLING CODE 3510-22-P
[GRAPHIC] [TIFF OMITTED] TN16MY25.014
BILLING CODE 3510-22-C
Detailed Description of the Specified Activity
Narwhal is proposing to conduct a variety of activities in and
around Harrison Bay, Alaska in support of oil and gas exploration.
Shallow Water Hazard Surveys
Narwhal plans to conduct shallow hazard surveys beginning in August
2025 at up to six offshore locations to identify up to four sites for
exploratory drilling in winter 2026 (figure 1-5 of Narwal's
application). The shallow hazard surveys include use of a single airgun
as the primary acoustic source and would also use a sub-bottom profiler
(SBP), echosounder/fathometer, side scan sonar (SSS), and sparker.
Use of acoustic sources other than the sparker and airgun are not
reasonably expected to result in take of marine mammals and will not be
discussed further beyond the brief summaries provided below.
Non-parametric SBPs are used to provide high data density in sub-
bottom profiles that are typically required for
[[Page 21184]]
cable routes, very shallow water, and archaeological surveys.
Parametric SPBs are usually mounted on a pole, either over the side of
the vessel or through a moon pool in the bottom of the hull. The SBP
proposed by Narwhal will be pointed vertically from the water surface
into the water column along track lines spaced 600 m (1969 ft), 300 m
(984 ft), and 150 m (492 ft) apart. For the proposed project, the SBP
used would generate sound pulses at frequencies around 2 to 16 kHz.
Ruppel et al. (2022) recommend that towed SBPs, including the
Compressed High-Intensity Radar Pulse (CHIRP) SBP planned for use by
Narwhal, be considered de minimis with regard to their potential to
cause incidental take of marine mammals. The authors base this
conclusion largely on the low likelihood that marine mammals would
experience a received level exceeding 160 dB re 1 [micro]Pa (see
Background on Active Acoustic Sound Sources and Acoustic Terminology
Section) as a result of typical use of this class of acoustic sources.
NMFS has determined that this is appropriate here and, therefore,
considers use of SBPs by Narwhal as unlikely to result in incidental
take of marine mammals.
Narwhal anticipates collecting bathymetric data using a single-beam
echosounder due to the shallow water at each survey location.
Echosounders and fathometers are used to determine water depths and
general bottom topography. Echosounder and fathometer sonar systems
project sonar pulses in angled beams from a transducer mounted to a
ship's hull. The beams radiate out from the transducer in a fan-shaped
pattern orthogonally to the ship's direction. SSS are used for seabed
sediment classification purposes and to identify natural and man-made
acoustic targets on the seafloor. The sonar device emits conical or
fan-shaped pulses down toward the seafloor in multiple beams at a wide
angle, perpendicular to the path of the sensor through the water
column. The proposed echosounders, fathometers, and SSS have operating
frequencies >200 kHz which are outside the general hearing range of
marine mammals. Therefore, take is not expected to occur from use of
these sources.
Additionally, Narwhal may conduct vibracore sediment sampling to
obtain shallow cores of the seafloor sediment from the surface.
Sediment cores will be analyzed for load-bearing capacity, shear
strength, grain size, and other parameters to be determined. The
proposed mini vibracore sampler is a hand-held device with a 3-position
switch that allows immediate on/off controls. To collect samples, an
electric motor oscillates the core barrel into the sediment to extract
a sediment core. Generally, the sound source (driving mechanism)
operates for one to two minutes with the entire process requiring less
than 1 hour. Vibracoring would produce a very brief duration of
continuous non-impulsive sound. NMFS does not typically expect that
vibracoring or similar sources of continuous noise to result in
incidental take of marine mammals.
High-resolution three-dimensional (3D) seismic surveys are also
expected to be conducted at the four potential drilling sites using a
single 105 cubic inch (cu. in.; 1,721 cubic centimeter (cc)) towed
airgun and geophone sound receivers. Approximately 480 geophones will
be embedded in the seafloor by hand with a wood or aluminum planting
pole to a maximum depth of 2 m (6.56 ft) in a grid pattern. The grids
would be spaced at 50 m (164 ft) intervals along receiver lines as
shown in figure 1-7 of Narwhal's application. This pattern will be the
same in each of the four exploratory drilling locations. The airgun
would fire about once every 6 or 7 seconds while traveling at a speed
of approximately 2 m per second.
The airgun will be towed by the source vessel perpendicular to the
receiver lines, while a support vessel will deploy and retrieve the
geophones from the seafloor. Narwhal expects the survey for each site
to take approximately 2 days to survey over a 12 hour period each day.
In total to survey the six sites it is anticipated to take up to 30
days to complete the seismic surveys (including retrieving the
geophones; 12 days of airgun use). Use of the airgun is expected to
present the potential to cause incidental take of marine mammals.
Narwhal proposes to use a sparker during shallow hazard survey
activities. Use of the sparker has the potential to cause incidental
take of marine mammals. Sparkers are medium penetration impulsive
sources used to map deep subsurface stratigraphy (soils down to at
least 100 m (328 ft) below the seabed in sand and at least 125 m (410
ft) below the seabed in mixed sediments). Sparkers are typically towed
behind the vessel, and may be operated with different numbers of
electrode tips to allow tuning of the acoustic waveform for specific
applications. Narwhal plans to use the Applied Acoustics UHD Dura-Spark
or a similar system. The operation of the sparker is expected to result
in the incidental take of marine mammals.
Vessels used for the shallow water hazard surveys will be mobilized
from West Dock in Prudhoe Bay or from Oliktok Point. Periodic resupply,
logistics support, and personnel transfers for the surveys would occur
at Oliktok Point. Figures 1-1 and 1-5 of Narwhal's application show the
anticipated mobilization and resupply routes for the shallow water
hazard survey vessel(s). Narwhal estimates daily trips between Oliktok
Point and the west Harrison Bay work area will be required over a
period of 35 days during shallow water hazard survey. Bathymetry, side
scan sonar, and sub-bottom profiling will require one survey vessel and
one support vessel. The 3D seismic survey will require one vessel
equipped with a single airgun, one vessel responsible for deploying and
retrieving geophones on the seafloor, and one to two support vessels
for berthing crew and expediting. The non-3D seismic shallow hazard
survey work (bathymetry, sub-bottom profiler, side scan sonar, sparker)
will be conducted from a single vessel, with the possible inclusion of
one additional vessel for additional berth capacity, if necessary. The
berthing vessel may transit to Oliktok Point during the day if
necessary to pick up supplies or transport personnel. The operation of
these vessels are not expected to result in take of marine mammals.
Sea Ice Trail Construction and Operation
Sea ice trails would be used by Narwhal to support the transport of
light tracked vehicles and would largely consist of unimproved roads
once constructed. Narwhal would use snow machines and light-weight
tracked vehicles to mark the sea ice trail corridor as soon as it is
determined to be safe to access (i.e., as soon as there is stable
grounded sea ice along the shoreline at Oliktok Point). Narwhal will
install a small, 15-person camp on a 0.008 km\2\ (.004 mi\2\) pad
adjacent to Oliktok Point on the grounded sea ice (Oliktok Point camp).
This location will receive freight from the existing gravel road
infrastructure to be transferred to west Harrison Bay.
After completion of the Oliktok Point camp, the crew will construct
the first section of the sea ice trail southwesterly along the coast on
grounded ice to the Colville River Delta. The coastal sea ice trail may
be smoothed during all-terrain vehicle (ATV) passes with a drag (i.e.,
pulling a pipe or similar straight tool behind the ATV) during setting
of the trail and periodically thereafter. Narwhal would need to thicken
the ice in five or six channels in the Colville
[[Page 21185]]
River Delta to support any heavy equipment transport that may be
needed.
To thicken the ice, seawater will be pumped to the surface and
allowed to freeze in layers until at least 0.9 m of ice thickness has
been achieved to allow for heavy equipment to be moved down the trail.
Narwhal would manually install lightweight equipment such as
centrifugal pumps to pump water to the ice surface. These pumps would
be periodically repositioned along the route across the channel.
Heavier pumping/auger equipment, which would be self-driven from
Oliktok Point along the grounded sea ice trail, would be used to
complete thickening of the sea ice once the channel ice is thick enough
to support such equipment. Narwhal anticipates that thickening will
require mobilization of six pumping units, which will be mobilized to
west Harrison Bay upon completion of the ice trail route. Narwhal
anticipates that the thickening of the Delta channels would take up to
25 days, and that thickening would require six trips per day between
Oliktok Point and the western extent of the Delta for fuel resupply,
crew change, and technical support.
Critical habitat for ringed seals was designated on April 1, 2022
(87 FR 19232) and outlined three primary biological features of
suitable habitat, one of which is water depths greater than 3 m.
Whenever possible, sea ice trials will be constructed on grounded ice
to minimize the need for sea ice thickening and the potential to
encounter ringed seal habitat defined in NMFS (2022a). Only small
portions of sea ice trail are expected to be constructed in areas that
may be in waters less than 3 m in depth (i.e., the Colville River Delta
portion). Narwhal anticipates that it would construct a section of the
coastal sea ice trail (57.8 km; 35.9 mi) over a period of 12 days,
after thickening of the Colville River Delta channels. Construction of
this section of the sea ice trail would not require significant ice
construction work. Narwhal would complete construction with a two-
person crew and two ATVs to scout the remaining trail and set the
global positioning system (GPS) points along the trail, as the
construction generally consists of packing the trail with repeated ATV
passes to create a hard and relatively smooth surface to travel on.
Narwhal may also use a drag on initial passes to establish a smooth
surface. The two-person crew will return to Oliktok Point after
completing the trail to support mobilization of additional equipment to
the west Harrison Bay area.
Narwhal anticipates that total construction of the coastal sea ice
trail will occur over a period of 30 days and that the completed trail
would be 57.8 km long with an approximate average width of 340 m.
During exploratory drilling operations (described below) over an
86-day period, an estimated average of 10 ATV trips per day will
transit from Oliktok Point to the west Harrison Bay area for daily
resupply if supporting a two-rig program. For a one-rig program,
approximately five ATV trips per day are anticipated for daily support.
The ATVs will travel in groups of two or more for safety purposes
resulting in an average of two to four groups of ATVs transiting the
sea ice trail daily during this period. Each trip will likely take
approximately 6 hours (i.e., 12 hours roundtrip within a 24-hour
period).
Narwhal would transport, during mobilization phase, all necessary
equipment to the west Harrison Bay area via the coastal sea ice trail
utilizing various ATVs (e.g., rolligons or steiger tractors). Narwhal
will transport camp and ice construction equipment first, followed by
equipment and materials needed for exploratory drilling after ice pads
are complete. The ATVs will travel in groups of two or more for safety
reasons. Typically, one or two groups of ATVs will travel on the trail
on a daily basis. Narwhal anticipates approximately 410 ATV trips as
part of mobilization activities in January and early February 2026. If
Narwhal stages equipment and materials in advance (discussed above),
mobilization would require approximately 120 ATV trips on the coastal
sea ice trail rather than 210 trips.
During the construction and operation of the sea ice trail across
the Colville River Delta, NMFS expects that take could occur due to the
potential for open leads or cracks in the sea ice, which could provide
suitable habitat for ringed seals.
Project Demobilization
Narwhal would relocate all project equipment, materials, and
personnel from the west Harrison Bay operations area to Oliktok Point
after completion of drilling operations. This demobilization would
occur over up to 200 ATV trips via the coastal sea ice trail and would
be completed by the end of April or early May 2026. NMFS expects that
this activity may result in take due to disturbance caused by ATV
presences on the sea ice trail in the Coleville River Delta section.
Onshore, Offshore, and Freshwater Lake Surveys, Archaeological,
Historical and Cultural Resources Clearance Surveys and Thermistor
Install and Water Access Roads
Narwhal plans to conduct several activities onshore in the west
Harrison Bay area. Field archaeological surveys would be conducted in
the area immediately south of west Harrison Bay where onshore ice roads
would be constructed (see below) to access freshwater source lakes.
These surveys would occur in mid-to-late July 2026. Offshore
archaeological and historical surveys would also be conducted to assess
routes planned for the coastal sea ice trail, roads, and pads. Coastal
areas of the project with shallow water less than 1.8 m in depth are
inaccessible by the geophysical survey vessels. Narwhal plans to
conduct lake surveys to locate adequate freshwater supplies for its
activities during August 2025. Surveys will be conducted using
helicopters to visually inspect water sources from the air and a zodiac
type or other small vessel will be used to assess various
characteristics such as fish presence and water quality. Surveys would
occur over approximately 10 days and would include one daily flight to
the work area from Deadhorse, Alaska. Aerial surveys would be flown by
helicopter at an altitude of 457 m (1499 ft), unless such an altitude
is unsafe. Narwhal may land one to three times per day during the
onshore surveys. Narwhal anticipates that onshore surveys would occur
over approximately three days and the offshore and lake surveys to
occur over 10 days. Narwhal would also construct lake access roads and
may install thermistors along the tundra access routes from the sea ice
to selected source water lakes to monitor soil temperatures during
freeze up fall 2025.
These activities would occur over land or over extremely shallow
waters in West Harrison Bay, and therefore, are not anticipated to
harass marine mammals and are not discussed further.
Optional Staging on Kogru Airstrip and Barges
Narwhal may stage equipment in advance of winter activities to
reduce the total number of ATV trips and time required for mobilizing
project equipment via the coastal sea ice trail from Oliktok Point and
to enable faster start-up once sea ice conditions permit. Advance
equipment staging would occur during mid-August or September of 2025.
Narwhal identified two options for advance staging sites.
Option 1, Kogru Airstrip--Narwhal would use the existing gravel
Kogru
[[Page 21186]]
airstrip (see figure 1-10 of Narwhal's IHA application) and place a
series of interlocking tundra mats between the shoreline and the
airstrip to provide support for offloading materials from barges along
shore up to the existing Kogru airstrip. This scenario would require
water depth sufficient for barge activity in the nearshore vicinity of
the Kogru airstrip.
Option 2, Protected Location in West Harrison Bay--Narwhal would
tow up to six empty anchored barges from Tuktoyaktuk, Canada, and
anchor them in a protected location within west Harrison Bay. The
barges would be pushed into a sandy beach by tug and frozen in place
during fall 2025. Narwhal would use a temporary ramp to offload a
front-end loader onto the beach. The loader would then set 4 to 6
anchors on the beach to hold the barges fast to the shoreline. The
barges will be tied to each other in a rectangle arrangement to provide
a continuous staging surface for the placement of equipment and
materials.
Narwhal may also place two to four anchors in the water at the
open-water end of the barges. These anchors would be set by lowering
them into the water (estimate 1 m (3 ft) depth) from a barge with the
same loader, and then connecting the anchors to the moored barges.
Final locations for placement of anchors on the beach and in open water
will be subject to a mooring analysis that will ensure the barges are
not moved off location by wind and ice movement during breakup. Narwhal
identified protected locations for this option in the Kogru River, near
the Eskimo Islands and other western areas of Harrison Bay (see figure
1-12 in Narwhal's IHA application), generally in waters less than 1 m
deep. Narwhal does not anticipate needing a tug to hold the barge
against significant tides or currents, as the area selected for
advanced staging will be relatively calm and in shallow water.
Narwhal anticipates that transfer of equipment and materials for
advance staging would require a total of five barge trips from West
Dock/Prudhoe Bay or Oliktok Point. However, vessel transit is not
generally anticipated to result in take of marine mammals due to the
proposed routes in relatively shallow water and the slow speed of the
vessels. Given this, NMFS does not anticipate either option to result
in take of marine mammals due to the transport of barges for equipment
staging, and these activities are not discussed further.
Narwhal would employ a two-person caretaker crew that would remain
on site during the staging period mid-August through September 2025 to
monitor the equipment and fuel, patrol the area, and collect basic
ocean data. The crew would stay at a small skid camp located at the
advance staging location. Narwhal may repurpose the small skid camp as
a company office and sleeping facility at the drilling location during
drilling operations or it may be set as the safety stop at the
approximate halfway point of the coastal sea ice trail. Narwhal
anticipates one helicopter flight per week will provide support to the
caretaker crew. NMFS does not expect take to occur during these flights
given they would occur mostly over land and over 457 m in elevation as
specified in the Proposed Mitigation section.
The advance staging barges would be transported back to
Tuktoyaktuk, Canada in the latter half of July or early August 2026
when ice conditions permit barge transport.
Sea Ice Road Construction and Operation
Narwhal would construct local sea ice roads to support exploratory
drilling operations. Ice roads are designed to accommodate heavier
equipment, including standard vehicles such as pick-up trucks, SUVs,
buses and other trucks to be used to transport personnel and equipment
including the drilling rigs to the drill sites. Table 1-4 of Narwhal's
application summarizes the estimated lengths of each ice road and
timeframes for construction.
Narwhal also proposes that between January 20 and April 12, 2026,
it will take an estimated five ATV trips per day between Oliktok Point
and the west Harrison Bay operations base for resupply. The ATVs will
travel in groups of two or more for safety purposes resulting in an
average of one or two groups of ATVs transiting the sea ice trail daily
during this period. Each trip will likely take approximately six hours
(i.e., 12 hours roundtrip within a 24-hr period).
Narwhal would determine the final west Harrison Bay ice road routes
to exploratory drilling locations and onshore freshwater source lakes
using ongoing geological and geophysical analysis, the results of the
shallow hazard surveys, and the pre-clearance archaeological and
freshwater lake surveys.
Where the ice road route includes floating sections of sea ice,
Narwhal would thicken the ice using flooding techniques shown in figure
1-19 of Narwhal's application. Narwhal will thicken the road until the
ice is grounded or at least 1.5 m (5 ft) to 1.8 m (6 ft) thick. After
the ice road is sufficiently grounded or thickened to the prescribed
depth, Narwhal will place a freshwater cap on the ice road to provide a
harder and more durable surface for equipment. In a typical year,
natural sea ice growth in west Harrison Bay generally reaches a maximum
thickness of approximately 1.8 m by the end of April, which is
anticipated to be the maximum ice road thickness. Flooding and ice
buildup or maintenance activities may be conducted during non-daylight
hours.
Narwhal would need to smooth the sea ice road routes as well. On
grounded sea ice road sections that do not require flooding, Narwhal
would conduct smoothing using ATV techniques used on the coastal sea
ice trail or by using a motor grader. Ungrounded sea ice road sections
that did require flooding to thicken the road would generally be
smoothed out by the flooding process, though Narwhal may use a motor
grader when the road is near completion and can support heavier
equipment. Narwhal would use a bulldozer to breach any ice ridges
present on the ice road route, though ice ridges are not anticipated to
be a significant issue in west Harrison Bay, as the ice sheet is
generally very smooth over most of the area with ice ridging occurring
along the subsea feature of Pacific Shoal. Re-routing of sea ice roads
will be minimized whenever possible.
Narwhal anticipates that the maintained ice road width, including
taper areas and shoulders where blown snow may be placed, would be
approximately 49 m (161 ft). Vehicle trips on local ice roads in west
Harrison Bay would be concentrated between the base camp and the active
drilling and testing location(s). Narwhal anticipates 25 round trips
would occur on a daily basis between the rig and base camp for drilling
and an additional 20 round trips per day for testing (separate from
drilling; i.e., 45 total trips). Well testing operations on a given
well would be anticipated to last approximately 10 days.
The construction and operation of the sea ice roads is expected to
be conducted entirely on grounded sea ice which would not be suitable
habitat for ringed seals and therefore, NMFS does not expect take of
marine mammals to occur on ice roads. As stated above, the portion of
the sea ice trail that crosses the Colville River Delta is the only
portion where NMFS expects take of marine mammals to occur.
Ice Pad Construction for Drilling Operations
As described below in the Exploratory Drilling Operations section,
Narwhal
[[Page 21187]]
would conduct exploratory drilling operations at four sites that it
surveys. Therefore, it would construct four sea ice pads (one at each
drill site) using the same techniques described above for sea ice
roads. Narwhal would construct sea ice pads in shallow water (1 m or
less) using the flooding techniques if the ice is not already grounded.
Narwhal may also add snow or ice chips to water to freeze the material
in place. All ice pads will be grounded with additional ice above sea
level to protect against ice movement during a storm event with higher
seas. Narwhal would construct ice pads in deeper water (up to 2.5 m)
with spray ice techniques to build up the base level with sufficient
ice above sea level to ensure the ice pad will not be moved during a
storm surge event.
When the desired pad elevation has been achieved, Narwhal would
smooth the ice surface with a bulldozer and motor grader, and add a
freshwater cap to provide a durable work surface as is done for the ice
roads. Ice pad construction would occur concurrently with ice road
construction and would take approximately 2-3 weeks depending on water
depth and ambient temperatures. Ice pads will be constructed in
sequence. The finished diameter of an ice pad would be approximately
183 m (600 ft).
NMFS does not expect take of marine mammals to occur due to the
construction of ice pads since pads would only be constructed on
grounded sea ice.
Temporary Airstrip and Base Camp Construction and Use
Narwhal plans to construct a temporary airstrip on grounded sea ice
(23 m (75 ft) wide and up to 1,525 m (5,003 ft) long). The specific
location is generally anticipated to be close to the exploratory
drilling base camp (see figure 1-16 in Narwhal's IHA application). To
construct the airstrip, Narwhal would plow snow off the sea ice to
create a smooth surface for aircraft and install perimeter lighting for
visual flight operations. Narwhal may plow the strip as necessary with
a motor grader to remove snow, or use a snow blower if large drifts
occur. However, the airstrip will be sited to avoid drifted snow to the
extent possible. Narwhal may periodically spread fresh water on the
runway surface as needed to maintain a hard, smooth, and safe surface
for aircraft.
Aircraft would use the temporary airstrip between December 6, 2025
and May 5, 2026. Narwhal does not anticipate using helicopters after
the sea ice airstrip is established. During ice construction and
drilling, Narwhal anticipates that it would make approximately 68
flights using fixed wing aircraft.
NMFS does not anticipate that use of aircraft associated with this
project would result in take of marine mammals. Born et al. (1999)
analyzed ``escape responses'' (i.e., hauled out animals entering the
water) from an aircraft and a helicopter flying at an altitude of 150 m
(492 ft). The results of the study indicated that if the aircraft do
not approach the seals closer than 500 m (1,640 ft) at that altitude,
the risk of flushing the seals into the water can be greatly reduced.
While Bradford and Weller (2005) note that helicopter presence resulted
in flushing of most of the hauled out seals during observations, they
did not note specific distances of the helicopter at which flushing
occurred. Use of aircraft is not expected to result in take given the
proposed mitigation measures related to aircraft that reduce the
potential for take. See the Proposed Mitigation section of this
document for further detail.
Narwhal would assemble and start up the base camp where it will set
modules approximately 3.7 m (12 ft) wide by 18 m (59 ft) long side by
side with a front end loader. Narwhal has not determined the exact camp
location, but estimates that the footprint of the overall camp facility
would be 100 m (328 ft) by 50 m (164 ft). Narwhal may use additional
sea ice area around camp for staging equipment and materials, fuel
storage, and loading and receipt of freight. NMFS does not expect take
to occur during the construction of the base camp on sea ice since it
would be constructed on grounded ice.
Summer Cleanup
In early July 2026, after the snow has melted off the tundra,
Narwhal would use a helicopter to conduct cleanup of the coastal sea
ice route and freshwater access routes in the west Harrison Bay area.
Narwhal would collect and dispose of project debris that can be safely
retrieved. Narwhal would use one helicopter to complete this work over
a period of approximately 3 to 5 days, including possible weather
delays. These activities would require approximately 6 hours per day of
flight time with up to 25-40 landings per day.
The use of the helicopter is not expected to result in take.
However, this proposed IHA includes mitigation measures related to all
aircraft that further reduce any potential for take. See the Proposed
Mitigation section of this document for further detail.
Exploratory Drilling Operations
Upon completion of the sea ice roads and pads, Narwhal would
assemble the exploratory drilling rig on site over about 7 to 10 days.
Exploratory drilling is estimated to occur over 21 days per well
including moving between sites via sea ice road. Narwhal may conduct
flow testing on a well after the rig has been moved to the next well.
To conduct well testing, Narwhal would install a test tree on top
of a completed well to control flow from the well at the surface. Prior
to flowing fluids to the surface, Narwhal will perforate the well
casing downhole to allow formation fluids to flow into the well. Well
fluids would flow through the tree into a choke manifold and then to a
line heater and into a three-phase separator. High pressure piping will
connect all testing equipment. Separated gas will be measured and
flared with oil and water directed to separate tanks for measurement.
Produced liquids will either be reinjected back into the well after
testing is complete or backhauled to the Prudhoe Bay infrastructure for
disposal. Testing operations including rig up and rig down of the test
spread is anticipated to take 15 days. At the completion of testing
operations, the well will be plugged and abandoned in accordance with
Alaska Oil and Gas Conservation Commission regulations. Plugging and
abandonment will include pumping cement into the well to seal off the
casing perforations, any annuli, and a surface cement plug will be
installed in the upper 45 m of the wellbore. After cementing, the well
will be cut off at least five feet below the seafloor.
Exploratory drilling operations would be conducted 24 hours per
day. Narwhal anticipates that rig moves between wells would take 5 days
or less and would be done with conventional heavy haul trucks and
trailers. Each rig move is anticipated to require 60 truck trips from
one drilling location to the next. Narwhal anticipates that drilling
operations would occur over approximately 82 days, including time to
move the rig, for the entirety of the drilling operation. All drilled
exploration wells will be plugged and abandoned during the 2025/2026
winter season.
Drilling sounds are expected to transmit poorly from the drill rig
machinery through ice or soft substrate into the water (Richardson et
al. 1995). Recordings of underwater sounds during drilling operations
were recorded in late February and early March of 2001 and 2002 from
Northstar Island, an artificial gravel island located
[[Page 21188]]
approximately 125 km (77 mi) east of west Harrison Bay in water 11.9 m
(39 ft) deep. Underwater sound during drilling alone (i.e., without
other production noises from the island) were reported in Blackwell et
al. (2004a) as 114 dB re 1[mu]Pa at 250 m (820 ft) from the source
during ice-covered conditions. The lowest level of underwater sound
recorded during drilling alone was reported as 104 dB re 1[mu]Pa at 1
km, while background sound levels (measured at 95 dB re 1[mu]Pa) were
reached 2 to 4 km from the source (Blackwell et al. 2004a). None of
these underwater sounds exceeded the120-dB root mean square continuous
noise threshold criterion (see Background on Active Acoustic Sound
Sources and Acoustic Terminology section) at the reported distances
close to the island, and similar low-level underwater sounds are
expected during short-term (i.e., 25 non-continuous days) exploratory
drilling in west Harrison Bay.
Airborne drilling sounds are similarly not expected to exceed the
100 dB re 20 1[mu]Pa threshold criterion for pinnipeds (other than
harbor seals). In the early winter-spring of 2001 and 2002, the levels,
frequency characteristics, and range dependence of sounds and
vibrations during industrial activity (i.e., mainly drilling and
production) at Northstar were recorded (Blackwell et al. 2004a). The
``drilling'' category included only periods of time during which the
drill bit was boring through subsurface formations. Only recordings
when wind speed was <5 m/s were used to minimize contamination in the
data. The highest (80 dB re: 20 mPa) and lowest (44 dB re: 20 mPa)
broadband levels were recorded in 2002 at 220 m (722 ft) and 9.4 km (31
ft), respectively. NMFS concludes that neither airborne nor underwater
noise resulting from drilling operations is likely to exceed associated
threshold criteria. As a result, no take of marine mammals is
anticipated during exploratory drilling during winter in west Harrison
Bay and this activity is not discussed further.
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 1 lists all species or stocks for which take is likely from
the specified activities and proposed to be authorized 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. 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. Alaska SARs. All values presented in table 1 are the most
recent available at the time of publication, including from the draft
2024 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 1--Species \1\ Likely Impacted by the Specified Activities
--------------------------------------------------------------------------------------------------------------------------------------------------------
Annual
ESA/MMPA status; Stock abundance (CV, mortality/
Common name Scientific name Stock strategic (Y/N) Nmin, most recent PBR serious
\2\ abundance survey) \3\ injury (M/
SI) \4\
--------------------------------------------------------------------------------------------------------------------------------------------------------
Order Artiodactyla--Cetacea--Mysticeti (baleen whales)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Family Balaenidae:
Bowhead whale................... Balaena mysticetus..... Western Arctic......... E, D, Y 15,227 (0.165, 13,263, 133 57
2019).
--------------------------------------------------------------------------------------------------------------------------------------------------------
Order Carnivora--Pinnipedia
--------------------------------------------------------------------------------------------------------------------------------------------------------
Family Phocidae (earless seals):
Bearded Seal.................... Erignathus barbatus.... Beringia............... T, D, Y Unknown (UND) (UND, UND 6,709
UND, 2013).
Ringed Seal..................... Pusa hispida........... Arctic................. T, D, Y UND (UND, UND, 2013).. UND 6,459
Spotted Seal.................... Phoca largha........... Bering................. -, -, N 461,625 (N/A, 423,237, 25,394 5,254
2013).
--------------------------------------------------------------------------------------------------------------------------------------------------------
\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>).
\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' 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.
[[Page 21189]]
As indicated above, all four species, comprising four managed
stocks, in table 1 temporally and spatially co-occur with the specified
activities to the degree that take is reasonably likely to occur. While
gray whale (Eschrichtius robustus), beluga whale (Delphinapterus
leucas), and harbor porpoise (Phocoena phocoena) have been documented
in the Beaufort Sea, the temporal and/or spatial occurrence of these
species is such that take is not expected to occur, and they are not
discussed further beyond the explanation provided here. Gray whales and
harbor porpoises rarely occur east of Point Barrow, approximately 200
km west of the project area. Further, while beluga whales occasionally
occur in the Beaufort Sea, they are generally distributed at or beyond
the continental shelf break outside of the project area (Ireland et al.
2016).
In addition, the polar bear (Ursus maritimus) may be found in west
Harrison Bay. However, polar bear are managed by the U.S. Fish and
Wildlife Service and are not considered further in this document.
Bowhead Whale
Of the five stocks of bowhead whale, only the Western Arctic stock
occurs in U.S. waters. The Western Arctic stock of bowhead whales are
distributed seasonally in ice-covered waters of the Arctic and near-
Arctic, generally between 60 degrees and 75 degrees North latitude in
the Western Arctic Basin (Moore and Reeves 1993; Muto et al. 2018). The
majority of the stock migrates annually from wintering areas (December
to March) in the central and northwestern Bering Sea, north through the
Chukchi Sea in the spring (April through May) following offshore ice
leads around the coast of Alaska, and into the eastern Beaufort Sea
where they spend most of the summer (June through early to mid-
October). Most animals from the stock return to the Bering Sea in the
fall (September through December) where they overwinter (Braham et al.
1980; Moore and Reeves 1993; Citta et al. 2015; Muto et al. 2018).
The annual migration of the Western Arctic stock to and from the
summer feeding grounds in the Beaufort Sea has been monitored by the
Bureau of Ocean Energy Management (BOEM) (and predecessor agencies),
NMFS, and/or industry since 1982 (Treacy et al. 2006; Blackwell et al.
2007; Ireland et al. 2009; Reiser et al. 2011; Bisson et al. 2013;
Clarke et al. 2014). Survey data indicate that the fall migration off
northern Alaska occurs primarily over the continental shelf, generally
12-37 mi (19-60 km) offshore, in waters 11-60 m deep (Moore et al.
1989; Moore and Reeves 1993; Treacy 2002; Monnett and Treacy 2005;
Treacy et al. 2006). Waters less than 4.5 m deep are considered too
shallow to support these whales, and in three decades of aerial surveys
by BOEM Aerial Surveys of Arctic Marine Mammals (ASAMM), no bowhead
whale has been recorded in waters less than 5 m deep (Clarke and
Ferguson 2010).
In September 2020, Brower et al. (2022) reported an unusual
sighting of an aggregation of bowhead whales just east of Harrison Bay
(see figure 4-2 of Narwhal's application). Bowhead whales had not
typically been observed in this area since 1982, when similar aerial
surveys (now referred to as ASAMM) began (Brower et al. 2022). The
sighting data represented in figure 4-2 of Narwhal's application are
approximately 5 to 10 km west-northwest of Narwhal's proposed
activities that would occur during the open-water season. As described
in Brower et al. (2022), the aggregation of bowheads near Harrison Bay
was attributed to a large oceanographic front due to high freshwater
discharge from the Colville River (three and a half times the
historical mean), which can aggregate prey.
Hauser et al. (2008) reported results for bowhead whale surveys
near the Colville River Delta in August and September 2008, reporting
that most bowheads were observed between 25 and 30 km north of the
barrier islands offshore. In 2017, Quintillion Subsea Operations, LLC
monitored for marine mammals during installation of a fiber optics
cable more than 50 km offshore of Oliktok Point moving west to Point
Barrow and beyond (Green et al. 2018). In the fall of 2017, the project
recorded 17 groups of bowhead whales (25 individuals) during operations
offshore of Oliktok Point. Bowhead whale group size ranged from 1 to 5
with a mean of 1.47 (Green et al. 2018).
In September 2022 as part of a long term study, researchers tagged
11 bowhead whales with satellite transmitters to help determine how
decreasing sea ice, changing wind patterns, warmer water, and
increasing human activity are affecting bowhead whale behavior and
distribution (<a href="http://www.adfg.alaska.gov/index.cfm?adfg=marinemammalprogram.bowhead">http://www.adfg.alaska.gov/index.cfm?adfg=marinemammalprogram.bowhead</a>). This project began in 2006
and is a collaboration among the Alaska Department of Fish and Game
(ADF&G), the Alaska Eskimo Whaling Commission (AEWC), Whaling Captain's
Associations of Barrow, Kaktovik, Gambell, and Savoonga, the Aklavik
and Tuktoyaktuk Hunters and Trappers Committees, the North Slope
Borough (NSB), the Barrow Arctic Science Consortium, the Department of
Fisheries and Oceans Canada, and the Greenland Institute of Natural
Resources. Further analysis of the movement patterns showed that these
tagged animals from 2022 did not extend into Harrison Bay, Alaska.
Critical habitat has not been designated for the bowhead whale.
However, Clarke et al. (2023) identified several Biological Important
Areas (BIAs) for feeding and migration for both mature and juvenile
whales that directly overlap or occur close to the project area.
Bowhead feeding BIAs encompass much of the Arctic region from May
through December with the August, September, and October BIAs occurring
close to the proposed project area. These areas were delineated from
data collected during the ASAMM survey where both juvenile and adult
bowhead whales were observed feeding or milling (Clark et al. 2023).
Ferguson et al. (2023) found that correlations with Arctic krill
(Euphausia superba) and specifically ``krill traps'' created by wind
driven upwelling bringing prey from depth and concentrating it near
freshwater runoff drove much of the feeding aggregations. Migratory
BIAs also occur in the vicinity of the project area and overlap with
feeding BIAs from August through October. Migration routes were found
closely correlated with feeding areas and essentially contain the same
habitat type as described above (Clark et al. 2023). The reproductive
BIAs identified for bowhead whale all occur over 32 km (20 mi) offshore
from the project area and are not anticipated to be affected by
Narwhal's activities.
In summary, we expect that bowhead whales would occur within the
project area during the open water season. Much of the presence of
bowhead whales and their important habitat as described above would be
at the farthest extent of the project area during the open water
periods. NMFS expects that there is some potential for bowhead whales
to occur in the project area in the summer and fall and may experience
disturbance from the underwater noise produced during the operation of
the seismic airgun. NMFS would not expect bowheads to be present during
Narwhal's ice-cover activities.
Bearded Seal
The Alaska stock of bearded seals occur seasonally in the shallow
shelf waters of the Beaufort, Chukchi, and
[[Page 21190]]
Bering Seas (Cameron et al. 2010). A reliable population estimate for
the entire stock is not available. The actual number of ringed seals in
the U.S. portion of the Bering Sea is likely much higher (Young et al.
2023). Bearded seals are closely associated with ice and their
migration coincides with the sea ice retreat and advancement. During
winter, most bearded seals in Alaskan waters are found in the Bering
Sea as their movements are related to the advance and retreat of sea
ice (Kelly 1988). In the Chukchi and Beaufort seas, favorable
conditions for bearded seals are more limited, and they are less
abundant. From mid-April to June as the ice recedes, some of the
bearded seals that overwintered in the Bering Sea migrate northward
through the Bering Strait to the Chukchi and Beaufort seas. During the
summer, bearded seals are found near the fragmented margin of multi-
year ice that covers the continental shelf of the Chukchi Sea and in
nearshore areas of the central and western Beaufort Sea (Ireland et al.
2016).
Aerial surveys conducted in the Beaufort Sea indicated that bearded
seals preferred water depths between 25-75 m (82-246 ft) and areas of
open ice cover (Cameron et al. 2010). ASAMM commonly observe bearded
seals offshore in the Beaufort Sea; however, no sightings have been
observed in the west Harrison Bay. Based on bearded seal water depth
and ice coverage preferences, survey observations in the Prudhoe Bay
region, and the normal level of ongoing industrial activity in the
project area, only very small numbers of bearded seals are expected
near the project area.
Critical habitat for the bearded seal was designated in May 2022
and includes marine waters off the coast of Harrison Bay, Alaska (87 FR
19180; April 1, 2022). Essential features established by NMFS for
conservation of the bearded Beringia Distinct Population Segment (DPS)
and the U.S. portion of the Beringia stock include (1) Sea ice habitat
suitable for whelping and nursing, which is defined as areas with
waters 200 m or less in depth containing pack ice of at least 25
percent concentration and providing bearded seals access to those
waters from the ice; (2) Sea ice habitat suitable as a platform for
molting, which is defined as areas with waters 200 m or less in depth
containing pack ice of at least 15 percent concentration and providing
bearded seals access to those waters from the ice, and (3) Primary prey
resources to support bearded seals: Waters 200 m or less in depth
containing benthic organisms, including epifaunal and infaunal
invertebrates, and demersal fishes. Narwhal's proposed project would
not overlap with bearded seal critical habitat and therefore, not have
any potential effects to that habitat.
In summary, bearded seals may occur in the project area during the
open water season as the sea ice recedes in the Harrison Bay area. NMFS
expects that some individuals would inhabit the coastal areas of west
Harrison Bay and have the potential to be disturbed by seismic surveys.
Bearded seals could potentially occur in the project area during the
remainder of the year; however, given the shallow waters of west
Harrison Bay, NMFS expects bearded seals to mainly occur offshore in
pack ice during the ice covered periods.
Ringed Seal
Ringed seals are distributed in all seasonally ice-covered seas of
the Northern Hemisphere (Lang et al. 2021, Muto et al. 2020). Five
subspecies of ringed seals are currently recognized, with only the
Arctic stock occurring in U.S. waters of the Arctic Ocean and Bering
Sea (Rice and Society for Marine Mammalogy 1998). Although Conn et al.
(2014) calculated an abundance estimate of 171,418 using a subset of
aerial survey data collected in 2012 by Moreland et al. (2013) that
covered the entire ice-covered portions of the Bering Sea, this
estimate is considered to be low and was multiplied by a factor of two
(Young et al. 2023).
They are year-round residents of the Chukchi and Beaufort seas and
are generally the most encountered seal in the U.S. Arctic. While other
ice seals, such as spotted and bearded seals, may be present in the
Beaufort Sea during the open-water season, only ringed seals are
expected to be in the nearshore environment during the ice-covered
months and, therefore, are the only species expected to be affected by
Narwhal's activities, such as ice trail construction and operation,
during the ice covered season (see Detailed Description of Specified
Activities section).
Ringed seals are abundant in the winter and spring on shorefast and
pack ice in the northern Bering Sea, Norton Sound, Kotzebue Sound,
Chukchi Sea, and Beaufort Sea, where they utilize sea ice for pupping
and nursing as well as resting. Landfast ice has been shown to be the
best habitat for ringed seal pupping (Kelly 1988). Moulton et al.
(2002) found the highest concentrations of ringed seals on stable,
shorefast ice over water depths of about 10-20 m in late May and early
June; but waters less than 5 m deep are not preferred wintering areas
for ringed seals (Frost et al. 2004, Moulton et al. 2002). In the
summer months, they use sea ice as a platform for molting and resting,
although ringed seals can remain pelagic in productive foraging areas
for long periods of time. In the fall, ringed seals utilize sea ice as
a platform for resting, and rarely haul out in terrestrial habitats.
During the winter, ringed seals excavate and maintain breathing
holes in the ice and occupy lairs in accumulated snow (Smith and
Stirling 1975). Ringed seals give birth in lairs from mid-March through
April, nurse their pups in the lairs for 5 to 8 weeks, and mate in late
April and May (Smith 1973; Hammill et al. 1991; Lydersen and Hammill
1993; as cited in (Ireland et al. 2016)). Seal mothers continue to
forage throughout lactation and move young pups between a network of
four to six lairs (Ireland et al. 2016). Arctic ringed seals generally
prefer landfast ice along the shoreline for pupping. Frost et al.
(2004) conducted aerial surveys over the Beaufort Sea coast from
Utqia[gdot]vik to Kaktovik and determined that ringed seal density was
greatest in water depths between 16 and 115 ft (5 and 35 m), and in
relatively flat ice close to the fast ice edge. Aerial surveys
conducted in association with construction near the Northstar facility
found ringed seal annual densities ranged from 0.39 to 0.83 seals per
km\2\ (Moulton et al. 2005).
The ringed seal diet is composed predominantly of pelagic fish such
as cod (Crain et al. 2021) but also includes shrimp and planktonic
crustaceans; the relative importance of each type of prey depends on
local availability and season (Lowry et al. 1998, as cited in (Ireland
et al. 2016)). They have been shown to dive to depths of up to 46 m or
more while foraging. Ringed seals are hunted by killer whales and polar
bears. Spatial distributions and population fluctuations of ringed
seals and polar bears appear to be tightly correlated in some areas
(Stirling and [Oslash]ritsland 1995 as cited in (Ireland et al. 2016)).
Optimal overwintering areas for ringed seals in the Beaufort Sea
occur in waters between 10 and 35 m deep, preferably in the landfast
ice along the shoreline close to lead systems. In May 2022, two trained
wildlife-detection dogs were used to survey an area in Prudhoe Bay near
Northstar Island. A total of 61 ringed seal structures (47 breathing
holes and 14 lairs) were identified in an 88.2 km\2\ area resulting in
a density of 0.68 structures/km2. Lair density was higher in water
deeper than 5m; however, seal structures were found in all water depths
(Quakenbush et al.
[[Page 21191]]
2022). Ringed seal movements during winter and spring are typically
quite limited, especially where ice cover is extensive (Kelly et al.
2010a).
During spring (i.e., May and June in the Arctic), ringed seals
spend time basking on the ice. Based on a tagging study in the mid-
2000s between Pt. Barrow and Peard Bay along the Chukchi Sea coast,
tagged seals (n=43) spent an average of 3 percent (95 percent
Confidence Level (CL): 1-4 percent) of their time in lairs and an
average of 37 percent (95 percent CL: 32-41 percent) of their time
basking after the first emergence from the subnivean lair. Basking
duration (median) on the ice increased to nine hours before ice melt
during the course of the study (Kelly et al.2010a).
On April 1, 2022, NMFS designated critical habitat for the Arctic
subspecies of ringed seals (87 FR 19232). The critical habitat
designation covers areas of marine habitat in the Bering, Chukchi, and
Beaufort seas. During the designation, NMFS considered their primary
biological features: (1) snow covered sea ice suitable for subnivean
birth lair formation and maintenance defined as waters 3 m or more in-
depth containing area of shorefast ice or dense stable pack ice that
contain snow drifts at least 54 cm deep to maintain lairs; (2) sea ice
suitable for basking and molting defined as waters 3 m or more in depth
with 15 percent or higher concentrations of sea ice; and primary prey
resources to support ringed seals defined as small, schooling fish and
small crustaceans. Narwhal's proposed project would not overlap with
ringed seal critical habitat and therefore, not have any potential
effects to that habitat.
Ringed seals were the most common pinniped observed during marine
mammal monitoring for installation of an offshore fiber optic cable in
the Beaufort and Chukchi seas; 57 groups (77 individuals) were recorded
(Green et al. 2018). All but three of the seals were recorded during
operations offshore of Oliktok Point. Four of the ringed seals were
identified as juveniles. Figure 4-6 of Narwhal's application depicts
observations of ringed seals during summer and fall from industry-
sponsored vessels over the period 2006-2012, including detections in
eastern Harrison Bay and the area around Oliktok. NMFS expects that
ringed seals would be the most common pinniped observed during the
project during the open-water period and the only species during the
ice-covered months.
Spotted Seal
In U.S. waters, spotted seals from the Bering stock are distributed
along the continental shelf of the Bering, Chukchi, and Beaufort seas
(Muto et al. 2021). They are present in the Beaufort Sea from July
through late August (Ireland et al. 2016); they sometimes haul out on
land but also spend extended periods at sea and are rarely seen on the
pack ice. During the spring when pupping, breeding, and molting,
spotted seals are found along the southern edge of the sea ice in the
Okhotsk and Bering seas (Rugh et al. 1997). As the ice cover thickens
at the onset of winter, spotted seals leave the northern portions of
their range and move into the Bering Sea (Lowry et al. 1998; Von Duyke
et al. 2016; as cited in Ireland et al. (2016)).
Historically, the Colville and Sagavanirktok rivers deltas
supported up 600 spotted seals; however, by the late 1900s, fewer than
20 seals were been seen at either location (Johnson et al. 1999; as
cited in (Ireland et al. 2016)). Johnson et al. (1999) stated that
while specific surveys for spotted seals were not conducted in 1998,
known haulouts were checked opportunistically during aerial surveys for
other species. An estimated 16 seals were hauled out on a small island
in the East Channel off the mouth of the Kachemach River, on August 25,
1998. Four seals were observed hauled out at a consistently used site
at the southwest end of Anachlik Island on September 14, 1998. In 1997,
during eight aerial surveys, small groups of spotted seals were seen on
four occasions, hauled out on sand spits or in adjacent shoals in these
same two locations. Seals were not seen elsewhere on the delta, nor
were any seen on or around the Jones Islands or Pingok Island in 1997
(Johnson et al. 1999).
In 2014, visual and passive acoustic monitoring was undertaken from
August 25-September 30 in an approximately 30-km\2\ survey area between
the Spy Islands and Oliktok Point near Simpson Lagoon (i.e., near the
Colville River Delta) (Lomac-MacNair et al. 2018). An Inupiat hunter
also conducted vessel-based visual surveys for spotted seal haulout
sites in the area. A total of 90 marine mammals were observed during
visual surveys including 40 spotted seals, five ringed seals, 28 seals
identified as either spotted or ringed, two bearded seals, and two
beluga whales (Lomac-MacNair et al. 2018).
During oil exploration projects from 1996 to 2001, 12 spotted seals
were positively identified near a seismic source vessel during open-
water in the central Alaskan Beaufort Sea (Moulton and Lawson 2002; as
cited in (Moulton et al. 2005)). Bisson et al. (2013) recorded 38
sightings of spotted seals during 2012 operations in the Beaufort Sea,
and 46 spotted seal sightings were reported during barge operations
between West Dock and Cape Simpson (Green et al. 2007; as cited in
Ireland et al. (2016)). Most sightings occurred from WHB to Cape
Simpson, with only one sighting occurring offshore of the Colville
River Delta.
Sighting data indicate that spotted seals could be present in the
project area during the summer months; however, we do not expect
spotted seals to occur in the project area during the ice-covered
portion of the project activities. Since spotted seals are not listed
as threatened or endangered under the ESA, there is no designated
critical habitat. No BIAs have been designated for spotted seals.
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.). Generalized hearing ranges were
chosen based on the ~65 decibel (dB) threshold from composite
audiograms, previous analyses in NMFS (2018), and/or data from Southall
et al. (2007) and Southall et al. (2019). We note that the names of two
hearing groups and the generalized hearing ranges of all marine mammal
hearing groups have been recently updated (NMFS 2024) as reflected
below in table 2.
[[Page 21192]]
Table 2--Marine Mammal Hearing Groups
[NMFS, 2024]
------------------------------------------------------------------------
Hearing group Generalized hearing range *
------------------------------------------------------------------------
Low-frequency (LF) cetaceans (baleen 7 Hz to 36 kHz.
whales).
High-frequency (HF) cetaceans 150 Hz to 160 kHz.
(dolphins, toothed whales, beaked
whales, bottlenose whales).
Very High-frequency (VHF) cetaceans 200 Hz to 165 kHz.
(true porpoises, Kogia, river
dolphins, Cephalorhynchid,
Lagenorhynchus cruciger & L.
australis).
Phocid pinnipeds (PW) (underwater) 40 Hz to 90 kHz.
(true seals).
Otariid pinnipeds (OW) (underwater) 60 Hz to 68 kHz.
(sea lions and fur seals).
------------------------------------------------------------------------
* Represents the generalized hearing range for the entire group as a
composite (i.e., all species within the group), where individual
species' hearing ranges may not be as broad. Generalized hearing range
chosen based on ~65 dB threshold from composite audiogram, previous
analysis in NMFS 2018, and/or data from Southall et al. 2007; Southall
et al. 2019. Additionally, animals are able to detect very loud sounds
above and below that ``generalized'' hearing range.
The pinniped functional hearing group was modified from Southall et
al. (2007) on the basis of data indicating that phocid species have
consistently demonstrated an extended frequency range of hearing
compared to otariids, especially in the higher frequency range
(Hemil[auml] et al., 2006; Kastelein et al., 2009; Reichmuth and Holt,
2013).
For more detail concerning these groups and associated frequency
ranges, please see NMFS (2024) for a review of available information
(<a href="https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance-other-acoustic-tools">https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance-other-acoustic-tools</a>).
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 species or stock through effects on
annual rates of recruitment or survival.
Background on Active Acoustic Sound Sources and Acoustic Terminology
This section contains a brief technical background on sound, the
characteristics of certain sound types, and metrics used in this
proposal inasmuch as the information is relevant to the specified
activity and to the discussion of the effects of the specified activity
on marine mammals in this document. For general information on sound
and its interaction with the marine environment, please see Au and
Hastings (2008); Richardson et al. (1995); Urick (1983).
Sound travels in waves, the basic components of which are
frequency, wavelength, velocity, and amplitude. Frequency is the number
of pressure waves that pass by a reference point per unit of time and
is measured in hertz or cycles per second. Wavelength is the distance
between two peaks or corresponding points of a sound wave (length of
one cycle). Higher frequency sounds have shorter wavelengths than lower
frequency sounds, and typically attenuate (decrease) more rapidly,
except in certain cases in shallower water. Amplitude is the height of
the sound pressure wave or the ``loudness'' of a sound and is typically
described using the relative unit of the decibel. A sound pressure
level (SPL) in dB is described as the ratio between a measured pressure
and a reference pressure (for underwater sound, this is 1 microPascal
([mu]Pa)), and is a logarithmic unit that accounts for large variations
in amplitude. Therefore, a relatively small change in dB corresponds to
large changes in sound pressure. The source level (SL) represents the
SPL referenced at a distance of 1 m from the source (referenced to 1
[mu]Pa), while the received level is the SPL at the listener's position
(referenced to 1 [mu]Pa).
Sound exposure level (SEL; represented as dB re 1 [mu]Pa2-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. The per-pulse SEL is calculated over the time window
containing the entire pulse (i.e., 100 percent of the acoustic energy).
SEL is a cumulative metric; it can be accumulated over a single pulse,
or calculated over periods containing multiple pulses. Cumulative SEL
represents the total energy accumulated by a receiver over a defined
time window or during an event. Peak sound pressure (also referred to
as zero-to-peak sound pressure or 0-pk) is the maximum instantaneous
sound pressure measurable in the water at a specified distance from the
source and is represented in the same units as the rms sound pressure.
When underwater objects vibrate or activity occurs, sound-pressure
waves are created. These waves alternately compress and decompress the
water as the sound wave travels. Underwater sound waves radiate in a
manner similar to ripples on the surface of a pond and may be either
directed in a beam or beams or may radiate in all directions
(omnidirectional sources), as is the case for sound produced by the
shallow water hazard survey considered here. The compressions and
decompressions associated with sound waves are detected as changes in
pressure by aquatic life and man-made sound receptors such as
hydrophones.
Even in the absence of sound from the specified activity, the
underwater environment is typically loud due to ambient sound, which is
defined as environmental background sound levels lacking a single
source or point (Richardson et al., 1995). The sound level of a region
is defined by the total acoustical energy being generated by known and
unknown sources. These sources may include physical (e.g., wind and
waves, earthquakes, ice, atmospheric sound), biological (e.g., sounds
produced by marine mammals, fish, and invertebrates), and anthropogenic
(e.g., vessels, dredging, construction) sound. A number of sources
contribute to ambient sound, including wind and waves, which are a main
source of naturally occurring ambient sound for frequencies between 200
hertz (Hz) and 50 kilohertz (kHz) (Mitson, 1995). In general, ambient
sound levels tend to increase with increasing wind speed and wave
height. Precipitation can become an important
[[Page 21193]]
component of total sound at frequencies above 500 Hz, and possibly down
to 100 Hz during quiet times. Marine mammals can contribute
significantly to ambient sound levels, as can some fish and snapping
shrimp. The frequency band for biological contributions is from
approximately 12 Hz to over 100 kHz. Sources of ambient 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 ambient sound for frequencies between 20 and 300 Hz. In general,
the frequencies of anthropogenic sounds are below 1 kHz and, if higher
frequency sound levels are created, they attenuate rapidly.
The sum of the various natural and anthropogenic sound sources that
comprise ambient sound at any given location and time depends not only
on the source levels (as determined by current weather conditions and
levels of biological and human activity) but also on the ability of
sound to propagate through the environment. In turn, sound propagation
is dependent on the spatially and temporally varying properties of the
water column and sea floor, and is frequency-dependent. As a result of
the dependence on a large number of varying factors, ambient sound
levels can be expected to vary widely over both coarse and fine spatial
and temporal scales. Sound levels at a given frequency and location can
vary by 10-20 dB from day to day (Richardson et al., 1995). The result
is that, depending on the source type and its intensity, sound from the
specified activity may be a negligible addition to the local
environment or could form a distinctive signal that may affect marine
mammals. Details of source types are described in the following text.
Sounds are often considered to fall into one of two general types:
pulsed and non-pulsed (defined in the following). The distinction
between these two sound types is important because they have differing
potential to cause physical effects, particularly with regard to
hearing (e.g., Ward, 1997 in Southall et al., 2007). Please see
Southall et al. (2007) for an in-depth discussion of these concepts.
The distinction between these two sound types is not always obvious, as
certain signals share properties of both pulsed and non-pulsed sounds.
A signal near a source could be categorized as a pulse, but due to
propagation effects as it moves farther from the source, the signal
duration becomes longer (e.g., Greene and Richardson, 1988).
Pulsed sound sources (e.g., airguns, explosions, gunshots, sonic
booms, impact pile driving) produce signals that are brief (typically
considered to be less than one second), broadband, atonal transients
(ANSI, 1986, 2005; Harris, 1998; NIOSH, 1998; ISO, 2003) and occur
either as isolated events or repeated in some succession. Pulsed sounds
are all characterized by a relatively rapid rise from ambient pressure
to a maximal pressure value followed by a rapid decay period that may
include a period of diminishing, oscillating maximal and minimal
pressures, and generally have an increased capacity to induce physical
injury as compared with sounds that lack these features.
Non-pulsed sounds can be tonal, narrowband, or broadband, brief or
prolonged, and may be either continuous or intermittent (ANSI, 1995;
NIOSH, 1998). Some of these non-pulsed sounds can be transient signals
of short duration but without the essential properties of pulses (e.g.,
rapid rise time). Examples of non-pulsed sounds include those produced
by vessels, aircraft, machinery operations such as drilling or
dredging, vibratory pile driving, and active sonar systems. The
duration of such sounds, as received at a distance, can be greatly
extended in a highly reverberant environment.
Airgun arrays produce pulsed signals with energy in a frequency
range from about 10-2,000 Hz, with most energy radiated at frequencies
below 200 Hz. The amplitude of the acoustic wave emitted from the
source is equal in all directions (i.e., omnidirectional), but airgun
arrays do possess some directionality due to different phase delays
between guns in different directions. Airgun arrays are typically tuned
to maximize functionality for data acquisition purposes, meaning that
sound transmitted in horizontal directions and at higher frequencies is
minimized to the extent possible.
Potential Effects on Marine Mammals
The effects of sounds from airgun and sparker pulses may include
one or more of the following: tolerance, masking of natural sounds,
behavioral disturbance, and auditory injury (permanent) or temporary
hearing impairment or non-auditory effects (Richardson et al., 1995).
The effects of noise on marine mammals are highly variable, often
depending on species and contextual factors (based on Richardson et
al., 1995).
Tolerance: Numerous studies have shown that pulsed sounds from air
guns are often readily detectable in the water at distances of many
kilometers. Numerous studies have also shown that marine mammals at
distances more than a few kilometers from operating survey vessels
often show no apparent response. That is often true even in cases when
the pulsed sounds must be readily audible to the animals based on
measured received levels and the hearing sensitivity of that mammal
group. In general, pinnipeds and small odontocetes (toothed whales)
seem to be more tolerant of exposure to air gun pulses than baleen
whales. Although various toothed whales and, less frequently, pinnipeds
have been shown to react behaviorally to airgun pulses under some
conditions; at other times, mammals of both types have shown no overt
reactions. Weir (2008) observed marine mammal responses to seismic
pulses from a 24 airgun array firing a total volume of either 5,085
in\3\ or 3,147 in\3\ in Angolan waters between August 2004 and May
2005. Weir recorded a total of 207 sightings of humpback whales (n =
66), sperm whales (n = 124), and Atlantic spotted dolphins (n = 17) and
reported that there were no significant differences in encounter rates
(sightings/hr) for humpback and sperm whales according to the airgun
array's operational status (i.e., active versus silent).
Behavioral Disturbance: Marine mammals may behaviorally react to
sound when exposed to anthropogenic noise. These behavioral reactions
are often shown as: Changing durations of surfacing and dives, number
of blows per surfacing, or moving direction and/or speed; reduced/
increased vocal activities; changing/cessation of certain behavioral
activities (such as socializing or feeding); visible startle response
or aggressive behavior (such as tail/fluke slapping or jaw clapping);
avoidance of areas where noise sources are located; and/or flight
responses (e.g., pinnipeds flushing into water from haulouts or
rookeries).
The biological significance of many of these behavioral
disturbances is difficult to predict, especially if the detected
disturbances appear minor. However, the consequences of behavioral
modification have the potential to be biologically significant if the
change affects growth, survival, or reproduction. Examples of
behavioral modifications that could impact growth, survival or
reproduction include:
<bullet> Drastic changes in diving/surfacing/swimming patterns that
could lead to stranding;
<bullet> Habitat abandonment (temporary or permanent) due to loss
of desirable acoustic environment; and
[[Page 21194]]
<bullet> Disruption of feeding or social interaction resulting in
significant energetic costs, inhibited breeding, or cow-calf
separation.
The onset of behavioral disturbance from anthropogenic noise
depends on both external factors (characteristics of noise sources and
their paths) and the receiving animals (hearing, motivation,
experience, demography) and is also difficult to predict (Southall et
al., 2007).
Cerchio et al. (2014) used passive acoustic monitoring to document
the presence of singing humpback whales off the coast of northern
Angola and to opportunistically test for the effect of seismic survey
activity on the number of singing whales. Two recording units were
deployed between March and December 2008 in the offshore environment;
numbers of singers were counted every hour. Generalized Additive Mixed
Models were used to assess the effect of survey day (seasonality), hour
(diel variation), moon phase, and received levels of noise (measured
from a single pulse during each ten minute sampled period) on singer
number. The number of singers significantly decreased with increasing
received level of noise, suggesting that humpback whale communication
was disrupted to some extent by the survey activity.
Castellote et al. (2012) reported acoustic and behavioral changes
by fin whales in response to shipping and airgun noise. Acoustic
features of fin whale song notes recorded in the Mediterranean Sea and
northeast Atlantic Ocean were compared for areas with different
shipping noise levels and traffic intensities and during an airgun
survey. During the first 72 hours of the survey, a steady decrease in
song received levels and bearings to singers indicated that whales
moved away from the acoustic source and out of the study area. This
displacement persisted for a time period well beyond the 10-day
duration of airgun activity, providing evidence that fin whales may
avoid an area for an extended period in the presence of increased
noise. The authors hypothesize that fin whale acoustic communication is
modified to compensate for increased background noise and that a
sensitization process may play a role in the observed temporary
displacement.
Seismic pulses at average received levels of 131 dB re 1 [mu]Pa\2\-
s caused blue whales to increase call production (Di Iorio and Clark,
2010). In contrast, McDonald et al. (1995) tracked a blue whale with
seafloor seismometers and reported that it stopped vocalizing and
changed its travel direction at a range of 10 km from the acoustic
source vessel (estimated received level 143 dB pk-pk). Blackwell et al.
(2013) found that bowhead whale call rates dropped significantly at
onset of airgun use at sites with a median distance of 41-45 km from
the survey. Blackwell et al. (2015) expanded this analysis to show that
whales actually increased calling rates as soon as airgun signals were
detectable before ultimately decreasing calling rates at higher
received levels (i.e., 10-minute cumulative sound exposure level (cSEL)
of ~127 dB). Overall, these results suggest that bowhead whales may
adjust their vocal output in an effort to compensate for noise before
ceasing vocalization effort and ultimately deflecting from the acoustic
source (Blackwell et al., 2013, 2015). These studies demonstrate that
even low levels of noise received far from the source can induce
changes in vocalization and/or behavior for mysticetes.
Avoidance is the displacement of an individual from an area or
migration path as a result of the presence of a sound or other
stressors, and is one of the most obvious manifestations of disturbance
in marine mammals (Richardson et al., 1995). For example, gray whales
are known to change direction--deflecting from customary migratory
paths--in order to avoid noise from airgun surveys (Malme et al.,
1984). Humpback whales showed avoidance behavior in the presence of an
active airgun array during observational studies and controlled
exposure experiments in western Australia (McCauley et al., 2000a).
Avoidance may be short-term, with animals returning to the area once
the noise has ceased (e.g., Bowles et al., 1994; Goold, 1996; Stone et
al., 2000; Morton and Symonds, 2002; Gailey et al., 2007). Longer-term
displacement is possible, however, which may lead to changes in
abundance or distribution patterns of the affected species in the
affected region if habituation to the presence of the sound does not
occur (e.g., Bejder et al., 2006; Teilmann et al., 2006).
Stone (2015a) reported data from at-sea observations during 1,196
airgun surveys from 1994 to 2010. When large arrays of airguns
(considered to be 500 in\3\ or more) were firing, lateral displacement,
more localized avoidance, or other changes in behavior were evident for
most odontocetes. However, significant responses to large arrays were
found only for the minke whale and fin whale. Behavioral responses
observed included changes in swimming or surfacing behavior, with
indications that cetaceans remained near the water surface at these
times. Cetaceans were recorded as feeding less often when large arrays
were active. Behavioral observations of gray whales during an airgun
survey monitored whale movements and respirations pre-, during-, and
post-seismic survey (Gailey et al., 2016). Behavioral state and water
depth were the best `natural' predictors of whale movements and
respiration and, after considering natural variation, none of the
response variables were significantly associated with survey or vessel
sounds.
Pinnipeds are not likely to show a strong avoidance reaction to the
airgun sources proposed for use. Visual monitoring from seismic vessels
has shown only slight (if any) avoidance of airguns by pinnipeds and
only slight (if any) changes in behavior. Monitoring work in the
Alaskan Beaufort Sea during 1996-2001 provided considerable information
regarding the behavior of Arctic ice seals exposed to seismic pulses
(Harris et al., 2001; Moulton and Lawson, 2002). These seismic projects
usually involved arrays of 6 to 16 airguns with total volumes of 560 to
1,500 in\3\. The combined results suggest that some seals avoid the
immediate area around seismic vessels. In most survey years, ringed
seal sightings tended to be farther away from the seismic vessel when
the airguns were operating than when they were not (Moulton and Lawson,
2002). However, these avoidance movements were relatively small, on the
order of 100 m (328 ft) to a few hundreds of meters, and many seals
remained within 100-200 m (328-656 ft) of the trackline as the
operating airgun array passed by. Seal sighting rates at the water
surface were lower during airgun array operations than during no-airgun
periods in each survey year except 1997. Similarly, seals are often
very tolerant of pulsed sounds from seal-scaring devices (Mate and
Harvey, 1987; Jefferson and Curry, 1994; Richardson et al., 1995a).
However, initial telemetry work suggests that avoidance and other
behavioral reactions by two other species of seals to small airgun
sources may at times be stronger than evident to date from visual
studies of pinniped reactions to airguns (Thompson et al., 1998). Even
if reactions of the species occurring in the present study area are as
strong as those evident in the telemetry study, reactions are expected
to be confined to relatively small distances and durations, with no
long-term effects on pinniped individuals or populations.
Behavioral disturbance of marine mammals is the most likely
acoustic effect expected from Narwhal's single airgun and sparker
operation during the
[[Page 21195]]
shallow water hazard survey. As described above, the effects would be
temporary in nature and take during the seismic operation would likely
only result in Level B harassment of cetaceans and pinnipeds.
Masking: Masking is the obscuring of sounds of interest by other
sounds, often at similar frequencies. Marine mammals are highly
dependent on sound, and their ability to recognize sound signals amid
other noise is important in communication; predator and prey detection;
and, in the case of toothed whales, echolocation. Although some degree
of masking is inevitable when high levels of human-made broadband
sounds are introduced into the ocean, marine mammals have evolved
systems and behaviors that function to reduce the impacts of masking.
Structured signals, such as the echolocation click sequences of small,
toothed whales, may be readily detected even in the presence of strong
background noise because their frequency content and temporal features
usually differ strongly from those of the background noise (Au and
Moore 1988, 1990). The components of background noise that are similar
in frequency to the sound signal in question primarily determine the
degree of signal masking. Masking effects of underwater sounds from
Narwhal's proposed activities on marine mammal calls and other natural
sounds are anticipated to be limited. There is little concern regarding
masking from the airgun in this case due to the brief duration of these
pulses and relatively longer silence between airgun shots near the
sound source.
Auditory Injury and Permanent Threshold Shift (PTS)--NMFS defines
auditory injury as ``damage to the inner ear that can result in
destruction of tissue . . . which may or may not result in PTS'' (NMFS,
2024). 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, 2024). Available data from humans and other terrestrial
mammals indicate that a 40-dB TS approximates PTS onset (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 various ethical reasons, experiments involving anthropogenic
noise exposure at levels inducing PTS are not typically pursued or
authorized (NMFS, 2018).
Temporary Threshold Shift (TTS)--It's 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 cetacean TTS
measurements (Southall et al., 2007, 2019), a TTS of 6 dB is considered
the minimum TS clearly larger than any day-to-day or session-to-session
variation in a subject's normal hearing ability (Schlundt et al., 2000;
Finneran et al., 2000, 2002). As described in Finneran (2015), marine
mammal studies have shown the amount of TTS increases with cumulative
sound exposure level (SELcum) in an accelerating fashion. At low
exposures with lower SELcum, the amount of TTS is typically small and
the growth curves have shallow slopes. At exposures with higher SELcum,
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), 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 the Masking
section, above). 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 (Phoca vitulina), elephant seals (Mirounga
angustirostris), bearded seals and California sea lions (Zalophus
californianus) (Kastak et al., 2007; Kastelein et al., 2019b, 2019c,
2021, 2022a, 2022b; Reichmuth et al., 2019; Sills et al., 2020). TTS
was not observed in spotted and ringed seals exposed to single airgun
impulse sounds at levels 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 at low frequencies, well below the region of best sensitivity
for a species or hearing group, are less hazardous than those at higher
frequencies, 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
sound exposure level (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
[[Page 21196]]
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 (such as
impact pile driving pulses as received close to the source) are at
least 6 dB higher than the TTS threshold on a peak-pressure basis and
PTS cumulative sound exposure level thresholds are 15 to 20 dB higher
than TTS cumulative sound exposure level thresholds (Southall et al.,
2007, 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.
The single airgun and sparker source Narwhal proposes to use for
this project is a mobile source being towed by a vessel moving
approximately 2 m/second. Effects on marine mammals from the operation
of the sparker are expected to be similar to the operation of the
single airgun (e.g., impulsive noise). When considering the impacts to
marine mammals, the effects described above for airguns would be
expected with sparkers. Also, the water depth where these surveys are
expected to occur are shallow and animals are expected to only spend
brief periods, if any, in the ensonified area. Given the movement of
the sound source 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 PTS or TTS declines is unlikely.
Vessel Strike
Vessel collisions with marine mammals, or vessel strikes, can
result in death or serious injury of the animal. These interactions are
typically associated with large whales, which are less maneuverable
than are smaller cetaceans or pinnipeds in relation to large vessels.
The severity of injuries typically depends on the size and speed of the
vessel, with the probability of death or serious injury increasing as
vessel speed increases (Knowlton and Kraus, 2001; Laist et al., 2001;
Vanderlaan and Taggart, 2007; Conn and Silber, 2013). Impact forces
increase with speed, as does the probability of a strike at a given
distance (Silber et al., 2010; Gende et al., 2011). The chances of a
lethal injury decline from approximately 80 percent at 15 kn to
approximately 20 percent at 8.6 kn. At speeds below 11.8 kn, the
chances of lethal injury drop below 50 percent (Vanderlaan and Taggart,
2007).
Ship strikes generally involve commercial shipping, which is much
more common in both space and time than is geophysical survey activity
and barge transports which typically involves larger vessels moving at
faster speeds. Jensen and Silber (2004) summarized ship strikes of
large whales worldwide from 1975-2003 and found that most collisions
occurred in the open ocean and involved large vessels (e.g., commercial
shipping). Commercial fishing vessels were responsible for 3 percent of
recorded collisions, while no such incidents were reported for
geophysical survey vessels during that time period.
For vessels used in geophysical survey activities, vessel speed
while towing gear is typically only 4-5 knots. At these speeds, both
the possibility of striking a marine mammal and the possibility of a
strike resulting in serious injury or mortality are so low as to be
discountable. However, the likelihood of a strike actually happening is
low given the smaller size of these vessels, generally slower speeds,
and the coastal route vessels would take to the survey area. We
anticipate that vessel collisions involving seismic data acquisition
vessels towing gear, while not impossible, represent unlikely,
unpredictable events for which there are no preventive measures. Given
the required mitigation measures, the relatively slow speeds of vessels
towing gear, the presence of bridge crew watching for obstacles at all
times (including marine mammals), the presence of protected species
observers, and the small number of seismic survey cruises relative to
commercial ship traffic, we believe that the possibility of ship strike
is discountable and, further, that were a strike of a large whale to
occur, it would be unlikely to result in serious injury or mortality.
No incidental take resulting from ship strike is anticipated or
proposed for authorization, and this potential effect of the specified
activity will not be discussed further in the following analysis.
The potential effects of Narwhal's shallow hazards survey activity
are expected to be limited to Level B harassment consisting of
behavioral harassment and/or temporary auditory effects and, for
bowhead whales and three species pinnipeds only. No permanent auditory
effects for any species belonging to other hearing groups are expected.
Ice Trails
Ringed seals could be adversely affected by exposure to visual and
acoustic disturbances during ice trail construction and operation. The
majority of impacts are likely to occur from visual exposure by
machinery and vehicles used for ice roads and ice trails construction
and from human presence. The associated noise from the machinery and
vehicles could also cause pinniped behavioral modification and
temporary displacement within the vicinity of the action area if the
noise levels are high enough. These activities are not expected to
result in serious injury or mortality given the proposed mitigation
measures (see Proposed Mitigation section) for construction and
operation of the ice trails.
A series of reports from the Northstar development provide evidence
of ringed seal reactions to human activity during ice road construction
beginning in 1999. As summarized in Richardson and Williams (2000),
approximately 6.6 km\2\ (2.5 mi\2\) were surveyed for ringed seals
prior to initiation of ice road construction activities. Though much of
the ice was flat and not optimal for seal lairs, surveys were conducted
by biologists and Inupiat hunters who used avalanche probes to identify
potential breathing holes and lairs. No breathing holes or lairs were
documented during this survey. A follow-up survey for ringed seal
breathing holes and lairs was conducted in using trained dogs. The
follow-up survey did locate at least two, possibly three, open
breathing holes within the area previously surveyed.
[[Page 21197]]
The following year, a subsequent survey was undertaken using dog-
based searches which found numerous seal structures within about 1 km
(0.6 mi) of Northstar facilities before and after intensive
construction activities in early and late winter. This may indicate
that the survey method using avalanche probes and Inupiat hunters was
not effective or that ringed seals were unaffected by ice road/trail
construction to such extent that it prevented them from establishing
breathing holes in the project area (Richardson and Williams 2000).
During two replicate aerial surveys conducted in 1999, ringed seals
were observed within approximately 0.64 km (0.4 mi) of ice roads
(Richardson and Williams 2000). These six seals were not assumed to be
the only seals located within that 0.64 km (0.4 mi) area. Using seal
densities in similar water depths approximately 4 to 10 km (about 2 to
6.2 mi) from the ice roads, about 12 ringed seals would be expected to
occur within 0.64 km (0.4 mi), and 110 ringed seals within 4 km (2.5
mi), during 1999. Seal behavior within 0 to 0.64 km (0.4 mi) of the
road may have been affected in some subtle way; however, the
observation of seals within that area suggests that effects of the ice
roads were minor and localized. As summarized in Williams et al.
(2006), several factors influence the rate of abandonment of seal
lairs, making it challenging to attribute abandonment to any specific
factor. Of 181 seal structures located within 11 to 3,500 m of
Northstar during surveys conducted in 2001, 118 (65 percent) were still
actively used in late May (the end of ice road season).
The effect of underwater noise on ringed seals is dependent on the
ability of the seal to perceive or hear the sounds. Due to the overall
relatively low noise levels associated with the ice trails construction
and that most of these noises are airborne, it is highly unlikely seals
in the vicinity of the construction site would suffer hearing damages
(i.e., PTS or TTS). Temporary short-term changes in behavior or
avoidance of the affected area as a result of disturbance is the most
common response of marine mammals to increased noise levels (Richardson
et al. 1995). Nonetheless, some minor disturbance due to in-air or
underwater (ice-covered) conditions may occur as a result of ice trail
activities. The types of impacts to ringed seals exposed to low-level
noise may include masking and temporary displacement. Increased levels
of natural and artificial sounds can disrupt behavior by masking. The
masking of communication signals by anthropogenic noise may reduce the
communication space of animals (Clark et al. 2009). Factors other than
received sound level such as the activity state of animals exposed can
affect the probability of a behavioral response (Ellison et al. 2012).
Southall et al. (2007) assessed relevant studies, found
considerable variability among pinnipeds, and determined exposures
between approximately 90 and 140 dB generally do not induce strong
behavioral responses of pinnipeds in water, but an increasing
probability of avoidance and other behavioral effects exists in the 120
to 160 dB range. The use of the Ditchwitch to cut ice or from pumping
at Northstar did not exceed 120 dB at 100 m (328 ft) (Greene et al.
2008). Despite the potential exposure to such noise levels, it is
highly unlikely the disturbance would result in biologically
significant effects on the seals (individually or to the population) as
evident from Northstar research (Richardson and Williams 2000). In
addition, Kelly et al. (1986) report that some ringed seals temporarily
departed their lairs when sound sources were within 97 to 3,000 m (0.06
to 1.9 mi) but did return to their lairs later. Haul outs with and
without disturbance were not significantly different, and time spent in
the water versus hauled out was not significantly different.
Displacement of seals from ice trail construction is considered
unlikely but could occur. As described in Williams et al. (2006),
during three surveys conducted in November/December, March and May of
2001 during Northstar construction activities, 181 ringed seal
structures were located and 118 (65 percent) were still actively used
by late May 2001. Active ringed seal structures appeared to be evenly
distributed across the Northstar study area in relation to the
facility. The noise heard through snow and ice, and into the subnivean
lair or den location of the animal should be considerably weaker than
at source due to sound being attenuated in the ice and snow. In March
2002, sounds and vibrations from vehicles traveling along an ice road
along Flaxman Island (a barrier Island east of Prudhoe Bay) were
recorded in artificially constructed polar bear dens. Sounds were
attenuated strongly by the snow cover of the artificial dens; broadband
vehicle traffic noise was reduced by 30-42 dB. Due to attenuation of
noise through ice and snow, it is less likely that seals in lairs would
be exposed to levels exceeding 120 dB re 1 [mu]Pa underwater and that
such exposure would result in displacement.
In air noise associated with ice trail activities is not expected
to cause disturbance to ringed seals, as construction noise is not
likely to exceed 100 dB re 20 [mu]Pa at the source. During the winter
of 2000, background unweighted in air noise levels from various
machineries measured in the vicinity of Northstar ranged from 59 to 84
dB re 20 [mu]Pa, and this background noise level was related to wind
speed (Greene et al. 2008). Similar levels were reported during the
winter of 2001 and 2002 by Blackwell et al. (2004a, b) with minimum
background unweighted in air noise levels of 44 to 52 dB re 20 [mu]Pa
measured in ice-covered conditions with low wind up to 10 km (6 mi)
from Northstar in Prudhoe Bay. As a result of the expected low levels,
in air noise during Narwhal's construction and operation of the sea ice
trails is not expected to result in harassment of seals.
The probability that acoustic noise associated with ice trail
construction would result in masking any acoustic signals of ringed
seals during construction is very low. Ice trail construction
activities would be initiated prior to March 1st when animals begin
constructing dens prior to pupping and during pupping when seals are
minimally vocal in the dens to prevent predation (Ireland et. al.
2016). The probability that the noise producing activities associated
with Narwhal's proposed project would result in masking acoustic
signals important to the behavior and survival of marine mammal species
in the project area is low.
Potential Effects on Marine Mammal Habitat
Experimental studies have shown that sounds from non-explosive
survey devices, such as airguns, are generally not lethal to fish
(Sharp 2011). The characteristics of airgun sounds are such that the
zone of potential injury to fish and invertebrates would be limited to
a few meters from the source (Buchanan et al. 2004, Sharp 2011). Adult
fish near seismic operations are likely to avoid the immediate vicinity
of the sound source and thus avoid injury. Sound pulses at levels of
180 dB have been documented to cause noticeable changes in behavior
(Pearson et al. 1992). While underwater sounds from airgun survey
activities may reach these levels, the areas ensonified to 160 dB are
not expected to exceed 3,188 m from the source and would be temporary
(i.e., up to 12 hours per day over an intermittent period of 30 days).
The operation of the sparker would be expected to have similar
potential habitat effects as use of
[[Page 21198]]
the airgun, but over a smaller area. Underwater sound levels from
seismic activities in WHB are not expected to result in measurable
effects to prey fish species populations.
The proposed vibracoring would minimally and briefly impact
physical habitat features, such as substrates and/or water quality.
Vibracoring would be used to obtain shallow cores of the seafloor
sediment within the footprint of the winter exploratory drilling
location, the few samples collected would be expected to have only a
slight, temporary effect on benthic habitat. Vibracoring would occur
over a very short duration at each of the drilling site. Therefore,
impacts on habitat from proposed activities during open-water
activities would be limited to potential impacts on prey species of
bowhead whales and ice seals.
The construction and maintenance of ice trails is not expected to
cause significant impacts on habitat used by ringed seals or on their
food sources. Landfast ice near the shoreline is the best habitat for
ringed seal pupping (Kelly 1988), with water depth strongly dictating
whether ringed seals overwinter in a given area. Depths greater than
about 3 m (10 ft) are typically the minimum depth suitable for
successful lair construction (Miller et al. 1998, Link et al. 1999)
although more shallow areas with open leads or cracks can be attractive
to seals as described for the ice trail across the Colville River
Delta.
While ringed seals may be present in the proposed project areas
during winter, the number of seals is generally expected to be
relatively low during ice trail activities. Ice trail construction
would be a short-term activity expected to result in minor disruptions
to habitat. Ringed seals feed on fish and a variety of benthic species
including crabs and shrimp. There should be no impact on the
distribution of fish or zooplankton as a result of ice trail
construction within the proposed project areas. The trails melt each
year and do not affect water circulation, substrate, fish presence or
use of the area, or benthic populations.
Disturbance associated with construction, operation and maintenance
of ice trails is unlikely to have long-term effects on the availability
of sea ice habitat identified in the critical habitat features 1 and 2.
Disturbances due to ice trail construction and maintenance activities
are not expected to have any effect on critical habitat feature 3,
because these activities would not cause injury or mortality to fish
species, nor would it displace food resources of ringed seals.
NMFS does not expect impacts to marine mammal habitat, including
prey, from the proposed activities of Narwhal in west Harrison Bay.
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 both
NMFS' consideration of ``small numbers,'' and the negligible impact
determinations.
Harassment is the only type of take expected to result from these
activities. Except with respect to certain activities not pertinent
here, section 3(18) of the MMPA defines ``harassment'' as any act of
pursuit, torment, or annoyance, which (i) has the potential to injure a
marine mammal or marine mammal stock in the wild (Level A harassment);
or (ii) has the potential to disturb a marine mammal or marine mammal
stock in the wild by causing disruption of behavioral patterns,
including, but not limited to, migration, breathing, nursing, breeding,
feeding, or sheltering (Level B harassment).
Authorized takes would be by Level B harassment only, in the form
of disruption of behavioral patterns and/or TTS for individual marine
mammals resulting from exposure to noise resulting from use of airguns
and sparkers (i.e., geophysical survey) and the construction and
operation of ice trails. Based on the nature of the activity and the
anticipated effectiveness of the mitigation measures (i.e., shutdown
zones and ice trails specific measures) discussed in detail below in
the Proposed Mitigation section, Level A harassment (auditory injury)
is neither anticipated nor proposed to be authorized.
As described previously, no serious injury or mortality is
anticipated or proposed to be authorized for these activities. Below we
describe how the proposed take numbers are estimated.
For acoustic impacts, generally speaking, we estimate take by
considering: (1) acoustic thresholds above which NMFS believes the best
available science indicates marine mammals will be behaviorally
harassed or incur some degree of permanent hearing impairment; (2) the
area or volume of water that will be ensonified above these levels in a
day; (3) the density or occurrence of marine mammals within these
ensonified areas; and, (4) the number of days of activities. We note
that while these factors can contribute to a basic calculation to
provide an initial prediction of potential takes, additional
information that can qualitatively inform take estimates is also
sometimes available (e.g., previous monitoring results or average group
size). Below, we describe the factors considered here in more detail
and present the proposed take estimates.
Acoustic Thresholds
NMFS recommends the use of acoustic thresholds that identify the
received level of underwater sound above which exposed marine mammals
would be reasonably expected to be behaviorally harassed (equated to
Level B harassment) or to incur auditory injury 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., 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 recommends use of a
generalized acoustic threshold based on received level to estimate the
onset of behavioral harassment. NMFS generally predicts that marine
mammals are likely to be behaviorally harassed in a manner considered
to be Level B harassment when exposed to underwater anthropogenic noise
above root-mean-squared pressure received levels (RMS SPL) of 120 dB
(referenced to 1 micropascal (re 1 [mu]Pa)) for continuous (e.g.,
vibratory pile driving, drilling) and above RMS SPL 160 dB re 1 [mu]Pa
for non-explosive impulsive (e.g., seismic airguns) or intermittent
(e.g., scientific sonar) sources. Generally speaking, Level B
harassment take estimates based on these behavioral harassment
thresholds are expected to include any likely takes by TTS as, in most
cases, the likelihood of TTS occurs at distances from the source less
than those at which behavioral harassment is likely. TTS of a
sufficient degree can manifest as behavioral harassment, as reduced
hearing sensitivity and the potential reduced opportunities to detect
important signals (conspecific communication, predators, prey) may
result in changes in behavior patterns that would not otherwise occur.
[[Page 21199]]
Narwhal's proposed activities include the use of impulsive (single
airgun and sparker) sources, and therefore, the RMS SPL threshold of
160 dB re 1 [mu]Pa is applicable. Narwhal's proposed activities also
include the use of construction equipment while building ice trials,
which would produce continuous sounds, for which use of the RMS SPL
threshold of 120 dB re 1 [mu]Pa is applicable. However, as noted in the
Marine Mammal Effects section, that threshold is not expected to be met
for the construction equipment that will be used by Narwhal and, in
general, disturbance of seals due to ice trails activities may be
attributable broadly to a suite of potential sources of disturbance,
including acoustic or visual disturbance.
Level A harassment--NMFS' Updated Technical Guidance for Assessing
the Effects of Anthropogenic Sound on Marine Mammal Hearing (Version
3.0) (NMFS, 2024) identifies dual criteria to assess Auditory Injury
(AUD INJ) (Level A harassment) to five different underwater marine
mammal groups (based on hearing sensitivity) as a result of exposure to
noise from two different types of sources (impulsive or non-impulsive).
Narwhal's proposed activity includes the use of impulsive (i.e., single
airgun and sparker) sources, and no take of marine mammals is expected
to result from exposure to continuous noise produced by Narwhal's
activities (e.g., ice trail construction).
The 2024 Updated Technical Guidance criteria include both updated
thresholds and updated weighting functions for each hearing group. The
thresholds are provided in table 3. The references, analysis, and
methodology used in the development of the criteria are described in
NMFS' 2024 Updated Technical Guidance, which may be accessed at:
<a href="https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance-other-acoustic-tools">https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance-other-acoustic-tools</a>.
Table 3--Thresholds Identifying the Onset of Permanent Threshold Shift
----------------------------------------------------------------------------------------------------------------
AUD INJ Onset Thresholds * (Received Level)
Hearing group ------------------------------------------------------------------------
Impulsive Non-impulsive
----------------------------------------------------------------------------------------------------------------
Low-Frequency (LF) Cetaceans........... Cell 1: L0-pk,flat: 222 Cell 2: LE,LF,24h: 197 dB.
dB; LE,LF,24h: 183 dB.
High-Frequency (HF) Cetaceans.......... Cell 3: L0-pk,flat: 230 Cell 4: LE,HF,24h: 201 dB.
dB; LE,HF,24h: 193 dB.
Very High-Frequency (VHF) Cetaceans.... Cell 5: L0-pk,flat: 202 Cell 6: LE,VHF,24h: 181 dB.
dB; LE,VHF,24h: 159 dB.
Phocid Pinnipeds (PW) (Underwater)..... Cell 7: L0-pk.flat: 223 Cell 8: LE,PW,24h: 195 dB.
dB; LE,PW,24h: 183 dB.
Otariid Pinnipeds (OW) (Underwater).... Cell 9: L0-pk,flat: 230 Cell 10: LE,OW,24h: 199 dB.
dB; LE,OW,24h: 185 dB.
----------------------------------------------------------------------------------------------------------------
IN-AIR
----------------------------------------------------------------------------------------------------------------
Phocid Pinnipeds (PA).................. Cell 11: L0-pk.flat: 162 Cell 12: LE,PA,24h: 154 dB.
dB; LE,PA,24h: 140 dB.
Otariid Pinnipeds (OA)................. Cell 13: L0-pk,flat: 177 Cell 14: LE,OA,24h: 177 dB.
dB; LE,OA,24h: 163 dB.
----------------------------------------------------------------------------------------------------------------
* Dual metric thresholds for impulsive sounds: Use whichever results in the largest isopleth for calculating AUD
INJ onset. If a non-impulsive sound has the potential of exceeding the peak sound pressure level thresholds
associated with impulsive sounds, these thresholds are recommended for consideration.
Note: Peak sound pressure level (L0-pk) has a reference value of 1 [mu]Pa, and weighted cumulative sound
exposure level (LE,p) has a reference value of 1[mu]Pa\2\s. In this table, thresholds are abbreviated to be
more reflective of International Organization for Standardization standards (ISO 2017). The subscript ``flat''
is being included to indicate peak sound pressure are flat weighted or unweighted within the generalized
hearing range of marine mammals (i.e., 7 Hz to 165 kHz). The subscript associated with cumulative sound
exposure level thresholds indicates the designated marine mammal auditory weighting function (LF, HF, and VHF
cetaceans, and PW and OW pinnipeds) and that the recommended accumulation period is 24 hours. The weighted
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 thresholds will be exceeded.
Ensonified Area for the Single Airgun
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.
Sound propagation and the distances to the sound isopleths for
marine mammal hearing groups are defined by NMFS for Level A harassment
of marine mammals under the 2024 Technical Acoustic Guidance. To assess
the potential for exposure to underwater sounds that might exceed
relevant threshold criteria during seismic surveys, Narwhal conducted
noise modeling of the single 105 cu. in. (1,721 cc) airgun at a
proposed survey site to determine sound source levels that are shown in
table 4 based on Gundalf Designer software, which is a seismic source
modelling software package that may be used to estimate source levels
of active acoustic sources. The estimated distances discussed in this
section are used for estimating potential exposures to noise exceeding
relevant harassment criteria.
Table 4--Estimated Underwater Sound Source Levels for the Single Airgun
------------------------------------------------------------------------
Source
Source level type (measured at site 10) levels
------------------------------------------------------------------------
Peak sound pressure level (Pk SPL) (dB re 1 [mu]Pa @1 m)..... 231
Root-mean-square sound pressure level (rms SPL) (dB re 1 204
[mu]Pa @1 m with a 90%-energy pulse duration of 12.5
milliseconds)...............................................
Sound exposure level (SEL) (dB re [mu]Pa2[middot]s @1 m)..... 193
------------------------------------------------------------------------
Estimated Level A harassment zone distances were modeled for the
single 105-cu. in. (1,721 cc) airgun, which is an impulsive, mobile
source. Estimated distances to Level A harassment thresholds for
weighted SEL<INF>24hr</INF> are
[[Page 21200]]
presented here and in greater detail in Appendix B of the Narwhal
application. Shallow hazard surveys will be conducted one site at a
time. Each survey block is approximately 2,400 m (7,874 ft) by 2,400 m
in area. The airgun will fire every 12.5 m (41 ft) along a track line
(i.e., every 6 or 7 seconds traveling at a speed of 2 m/s). Therefore,
there will be an estimated 192 shots per track line. The area of
ensonification for the seismic survey was calculated by multiplying the
estimated distances (in km) to the harassment thresholds by the
distance of the seismic track line (in km) to be surveyed each day. A
single track line is approximately 2 km (1 mi) in length, which will
take approximately 20 minutes to shoot assuming a vessel speed of 2 m/
s. In a 24-hour period, assuming no delays, the survey team will be
able to collect data for approximately 10 km within a site over a
period of 12 hours.
Level A harassment zones were calculated using the source levels
modeled from the Gundalf software. A fluid parabolic equation modelling
algorithm (RAMGeo) was used to calculate the propagation of noise form
the airgun source. The noise source was assumed to be omnidirectional
and modelled as a point source. Only low frequency acoustic energy (<1
kHz e.g., single airgun) was modeled. Greater detail on the modeling
methods used by Narwhal are available in Section 6.2.3.1 and Appendix B
of Narwhal's application. Modeling results estimated Level A harassment
zone distances for LF cetaceans as 1,076 m (3,530 ft) and for phocids
as 322 m (1,056 ft) from the seismic source vessel while the airgun is
operating.
The following equation is used to estimate the ensonified area:
Mobile Ensonification Area (km2) Equation = Distance*(2*Threshold
Value/1000) + (Pi*(Threshold Value/1000)[caret]2)
Following the same process, with additional procedures described in
Appendix B of Narwhal's application to convert modeled SEL values to
RMS SPLs, Narwhal estimated the distance to the 160 dB re 1 [mu]Pa
Level B harassment threshold to be 3,188 m (10,459 ft). Narwhal then
used the mobile ensonification equation above to calculate the total
area of the Level B harassment, which resulted in an area of 337.98
km\2\ (210 mi\2\). It should be noted that since the study area is in
close proximity to shore, some sound is likely to be truncated by land
to a certain extent.
Ensonified Area for the Sparker
Using data from Crocker and Fratantonio (2016), NMFS estimated
source levels for the sparker to be 213 db RMS while operating at 1000
joules of energy across 240 active tips.
Take by Level A harassment is not expected during the use of the
sparker given the small injury zone sizes expected with the sparker use
and likelihood that marine mammals will avoid the sound source before
incurring auditory injury. Using the source levels above, NMFS
calculated the estimated distance to the 160 dB re 1 [mu]Pa Level B
harassment threshold to be 447 m (1,467 ft). NMFS then used the same
mobile ensonification equation to calculate the total area of the Level
B harassment zone which resulted in an area of 43.54 km\2\ (27 mi\2\).
Disturbance Area for the Ice Trails on the Colville River Delta
Ringed seals are the only marine mammal expected to be present in
the project area during winter activities. To estimate incidents of
disturbance that may constitute a take, the total area of potential
disturbance (i.e., ice trails) associated with construction and
maintenance of specific portions of the coastal sea ice trail are
included in the estimate. As noted in the Description of Marine Mammals
in the Area of Specified Activities section, ground sea ice (occurring
>3 m of water depth) is not considered suitable habitat for ringed
seals. The coastal sea ice trail will be on grounded ice; however, the
Colville River Delta is included in the take estimate to account for
the possibility that ringed seals may occur in that section of the
route given the potential for open leads or cracks in the sea ice,
which could provide habitat for ringed seals. For the offshore sea ice
trails/roads in west Harrison Bay, water depths at planned pad
locations are less than 3 m (average); therefore, the majority of ice
trails/roads in west Harrison Bay will be on grounded ice or limited
portions of floating ice in water depths between 1.6 m (5 ft) and 3 m
(10 ft) and not expected to provided suitable ringed seal habitat.
The width of the coastal sea ice trail across the Colville River
Delta is defined as 170 m (558 ft) on either side of the ice trail
centerline, or a total width of 340 m (1,115 ft). The total width (340
m or 0.34 km (.21 mi)) is then multiplied by the portion of the total
length of trail/roads transiting ringed seal habitat, as described
above. The linear distance of the coastal sea ice trail across the
Colville River Delta is 57.8 km (36 mi). To calculate the potential
exposure area, linear distance is multiplied by the total width (i.e.,
57.8 km * 0.34 km = 19.65 km\2\ (12.2 mi\2\). The calculated area of
disturbance (19.65 km\2\) is applied to activity associated with
Narwhal's construction, operation, and demobilization phases.
Marine Mammal Density Estimates
In this section, we provide information about the occurrence of
marine mammals, including density or other relevant information that
will inform the take calculations.
Narwhal and NMFS used a variety of data sources to estimate
appropriate marine mammal densities for evaluation of potential take
incidental to the proposed activities. Neither NMFS nor Narwhal relied
on data available from Ca[ntilde]adas et al. 2020 (Duke University
Arctic Study Area Models; see <a href="https://seamap.env.duke.edu/models/Duke/Arctic/">https://seamap.env.duke.edu/models/Duke/Arctic/</a>). For bowhead whales, more recent data (through 2021) is
available in the ASAMM dataset, opposed to the Arctic Study Area Models
where data through 2019 was used. For bearded seal, estimates of
density are available but, as noted in Ca[ntilde]adas et al. (2020),
there is a high degree of observer bias, which leads to uncertainty in
species identification and, therefore, uncertainty in model outputs and
resultant densities. Therefore, data from previous, site-specific
vessel surveys (Funk et al. 2010) provide the best estimates of species
proportions in Harrison Bay during the open water period. Neither
spotted seal nor ringed seal density estimates are available from
Ca[ntilde]adas et al. (2020).
Bowhead Whale
Bowhead whale sighting data from ASAMM aerial survey Block 3, which
includes Harrison Bay, for the period 2012-2021 were used to estimate
bowhead density near the project area. For reference, Harrison Bay is
approximately 250 km\2\ relative to the larger total area of ASAMM
survey Block 3. Harrison Bay also is not preferred habitat of bowhead
whales given the lack of observations from within the bay as noted
above in the Description of Marine Mammals in the Area of Specified
Activities Section. Therefore, the density estimates presented here
could be slightly higher than would be expected in the project area.
Densities were calculated by Narwhal using a two-step approach. First,
a sighting rate is calculated based on whales per km, then transect
length (km) is multiplied by the effective strip width of the transect
using the modeled effective strip width for bowhead whales observed
during aerial surveys
[[Page 21201]]
conducted from an Aero Commander airplane (1.15 km (CV = 0.08))
(Ferguson and Clarke 2013). Therefore, whales per km\2\ = whales per
km/(2*1.15 km). For survey Block 3, the average density estimate in
summer is 0.009 bowhead whales per km\2\ (table 5). The average fall
density was calculated at 0.017 bowhead whales per km\2\; however,
since the shallow water hazard survey work is proposed to be completed
in the summer, NMFS used the summer density for calculating take
estimates.
As noted in the Description of Marine Mammals in the Area of
Specified Activities section, we do not expect bowhead whales to be
present during Narwhal's winter or spring activities.
Table 5--Bowhead Whale Sighting Data From 2012 Through 2020 and Resulting Densities
--------------------------------------------------------------------------------------------------------------------------------------------------------
Bowhead whale
Survey year Survey time period On transect sightings on Bowhead whales Bowhead whales
distance (km) transect per km per km\2\
--------------------------------------------------------------------------------------------------------------------------------------------------------
2012 Summer.................................... Jul-Aug.......................... 1,742 1 0.001 0.004
2012 Fall...................................... Sep-Oct.......................... 1,388 26 0.019 0.083
2013 Summer.................................... Jul-Aug.......................... 950 8 0.009 0.0039
2013 Fall...................................... Sep-Oct.......................... 1,217 7 0.006 0.0026
2014 Summer.................................... Jul-Aug.......................... 1,290 0 0.000 0.000
2014 Fall...................................... Sep-Oct.......................... 1,927 1 0.001 0.0004
2015 Summer.................................... Jul-Aug.......................... 1,570 0 0.000 0.000
2015 Fall...................................... Sep-Oct.......................... 1,949 66 0.034 0.0148
2016 Summer.................................... Jul-Aug.......................... 1,845 259 0.141 0.0613
2016 Fall...................................... Sep-Oct.......................... 1,959 61 0.032 0.0139
2017 Summer.................................... Jul-Aug.......................... 2,188 6 0.003 0.0013
2017 Fall...................................... Sep-Oct.......................... 2,269 35 0.016 0.0070
2018 Summer.................................... Jul-Aug.......................... 2,049 7 0.004 0.0017
2018 Fall...................................... Sep-Oct.......................... 2,390 32 0.014 0.0061
2019 Summer.................................... Jul-Aug.......................... 2,822 7 0.003 0.0013
2019 Fall...................................... Sep-Oct.......................... 3,853 8 0.003 0.0013
2020 Fall...................................... Sep-Oct.......................... 654 32 0.049 0.0213
2021 Fall...................................... Sep-Oct.......................... 1,637 58 0.035 0.0154
-----------------
Summer Average............................. ................................. .............. ................ ................ 0.009
Fall Average............................... ................................. .............. ................ ................ 0.017
--------------------------------------------------------------------------------------------------------------------------------------------------------
Bearded and Spotted Seals
Spring aerial surveys conducted as part of industry monitoring for
the Northstar production facility provide limited sighting numbers of
bearded seals from 1999-2002 (Richardson and Williams, 2002 and 2003).
Given the lack of bearded seal data in Harrison Bay, NMFS reviewed
survey data from Funk et al. (2010). This information represents a
compilation of monitoring data gathered during vessel-based seismic
operations in the Beaufort Sea from 2006-2008. NMFS considers this the
best available data to derive a density estimate for bearded seals and
spotted seals (see below). This survey observed ringed seals, bearded
seals, spotted seals, ribbon seals, and some unidentified seals.
Narwhal proposed to base the percentage of seals present in the survey
area as a percentage of the total identified seals and multiplying that
percentage by the ringed seal summer/fall density. The density that
Narwhal proposed in their application was 0.03 bearded seals/km\2\.
NMFS expects that relying on this method to calculate the percentage of
bearded and spotted seals may result in underestimation of potential
seal occurrence.
Therefore, NMFS modified this approach and calculated the bearded
seal percentage as a proportion of the observed ringed seals in the
Funk et al. (2010) survey. NMFS took this approach because the bearded
seal density was being derived from the ringed seal summer/fall
density, and such does not utilize the best available scientific
information and likely underestimates the potential for bearded seal
take. Percentages calculated using NMFS method are found in table 6 and
differ from the Narwhal application. Based on this ratio NMFS expects
that the bearded seal density would be 21.3 percent of the summer/fall
ringed seal density (0.213 * 0.32 = 0.07 bearded seals/km\2\).
Similar to the method used for bearded seals, NMFS derived the
density of spotted seals by first determining the ratio of the number
spotted seals observed to the number of ringed seals observed from Funk
et al. (2010) (table 6). Based on this ratio, NMFS expects that the
spotted seal density would be 34.8 percent of the summer/fall ringed
seal density (0.348 * 0.32 = 0.11 spotted seals/km\2\).
Table 6--Bearded Seal and Spotted Seal Ratios Based on the Observed
Ringed Seals From Funk et al. (2010)
------------------------------------------------------------------------
Percentage of
Species ringed seal
------------------------------------------------------------------------
Bearded Seal............................................ 21.3
Spotted Seal............................................ 34.8
------------------------------------------------------------------------
Ringed Seal
Winter/Spring Density--Narwhal originally proposed in their
application the use of data from a number of on-ice surveys and aerial
surveys for ringed seal density estimates for on-ice periods. These
included site-specific surveys for ringed seals along the Beaufort Sea
coast that were conducted in association with industry activities in
the late 1980s and continued into the 2020s (Kelly et al. 1986; Frost
and Burns 1989; Frost and Lowry 1987; Richardson and Williams 2001,
2002, and 2004; Frost et al. 2004; Moulton et al. 2005; and Quakenbush
et al. 2022 and 2023). Several of these studies estimated approximate
seal densities by considering the detection by trained dogs of seal
structures such as breathing holes, haulout lairs, or pupping lairs.
Aerial surveys were also included in the density estimate that
[[Page 21202]]
was completed in the spring of the year. Narwhal proposed a ringed seal
density estimate for the winter/spring season of 0.49 seals/km\2\ (see
table 6-3 in Narwhal's application).
However, NMFS determined that a different approach to use of these
data for calculating the ringed seal density would be more appropriate,
as several of the papers used by Narwhal included inconsistent
correction factors for seal abundance (Quakenbush 2022 and 2023), some
of the data Narwhal proposed for use was approximately 40 years old,
and because NMFS assumed that aerial surveys provide a more accurate
density calculation than on-ice surveys given they are actual seal
counts rather than counts of potential seal structures. NMFS relied
only on spring aerial surveys conducted in 1997-2002 (Moulton et al.
2005) and 1996-1999 (Frost et al. 2004), which included a broad section
of the total survey area. Densities reported by Moulton et al. (2005)
were lower than those estimated by Frost et al. (2004) for that same
area: 0.43 vs. 0.73 seals/km\2\ in 1997, 0.39 vs. 0.64 seals/km\2\ in
1998, and 0.63 vs. 0.87 seals/km\2\ in 1999. Narwhal had noted that the
differences in density were mainly because of differences in ice
composition (fast ice vs. pack ice) between Frost et al. (2004) and
Moulton et al. (2005). Since these observed densities are for the same
area and years, NMFS does not believe the higher observed densities
reported by Frost et al. (2004) are due to differences in the
composition of sea ice surveyed between the two studies. Further, Frost
et al. (2004) noted that the two studies were similar in timing and
methods. For these reasons, NMFS calculated an average density (without
trimming to calculate the average density) of 0.63 seals/km\2\ using
these two data sources (table 7).
Table 7--Ringed Seal Aerial Survey Densities for Winter/Spring
------------------------------------------------------------------------
Observed
Source Year density
(seals/km\2\)
------------------------------------------------------------------------
Moulton et al. (2005)................... 1997 0.43
Moulton et al. (2005)................... 1998 0.39
Moulton et al. (2005)................... 1999 0.63
Moulton et al. (2005)................... 2000 0.47
Moulton et al. (2005)................... 2001 0.54
Moulton et al. (2005)................... 2002 0.83
Frost et al. (2004)..................... 1996 0.81
Frost et al. (2004)..................... 1997 0.73
Frost et al. (2004)..................... 1998 0.64
Frost et al. (2004)..................... 1999 0.87
-------------------------------
Average............................. .............. 0.63
------------------------------------------------------------------------
Summer/Fall Density--Hauser et al. (2008) summarized sighting data
from a 2008 seismic survey (inside and outside the barrier islands)
near Thetis Island north and east of the action area. Hauser et al.
(2008) found that most seal sightings were observed in waters seaward
of the barrier islands (~76 percent of 38 sightings). Sightings of
ringed seals in the shallow waters shoreward of the barrier islands
were substantially lower. Narwhal's action area is most similar to what
Hauser et al. (2008) defined as shallow waters. Hauser et al. (2008)
reported a seal density for all species combined of 0.11 seals/km\2\
for shallow waters during open-water conditions.
While this average seal density based on actual observations do not
reflect seals that may not have been visible to observers, several
publications acknowledge that during open-water months, ringed seals
are more abundant farther offshore (Harwood and Stirling 1992, Kelly et
al. 2010b, McLaren 1958, Von Duyke et al. 2020). For example, 1999
aerial surveys conducted over 8 days near Prudhoe Bay reported that the
density of seals visible near shore decreased compared to the density
offshore (Richardson and Williams 2000b). Narwhal estimated a summer
density for ringed seals by using a 50 percent conversion factor of the
winter/spring densities (table 8). NMFS agrees with this methodology
and estimated the summer/fall density to be 0.32 seals/km\2\ (i.e., 50
percent of 0.63 seals/km\2\ the winter/spring density).
Take Estimation
Here, we describe how the information provided above is synthesized
to produce a quantitative estimate of the take that is reasonably
likely to occur and proposed for authorization.
For all marine mammal species, NMFS does not expect or propose to
authorize take by Level A harassment during any activities. Narwhal
proposes to implement an 1,100 m (3,608 ft) shutdown zone for LF
cetaceans and a 350 m (1,148 ft) shutdown zone for phocids during the
operation of the single 105 cu. in. (1,721 cc) airgun. These zones are
larger than the respective Level A harassment zones and therefore,
would reduce the already low likelihood of take by Level A harassment.
Take by Level A harassment is unlikely because Narwhal would shutdown
the single airgun before a marine mammal would enter the Level A
harassment zone. Take by Level A harassment is also unlikely because
animals will avoid the area of active acoustic sources.
Summer/Fall Take Estimates--As described above, the estimated Level
B harassment area for the seismic airgun is 337.98 km\2\ and for the
sparker 43.54 km\2\. Given that the Level B harassment zone of 447 m
for the sparker, it is expected that Narwhal would implement a shutdown
zone of 500 m for bowhead whales and no take of bowhead whales would
occur during sparker use. Similar to the single airgun, Narwhal would
shutdown the sparker before a marine mammal would enter the Level A
harassment zone and therefore prevent take by Level A harassment. This
area was used to determine the number of take based on the densities of
marine mammals as described above multiplied by the number of days
(i.e., 12 days of seismic survey and sparker use) of activity. NMFS
expects the number of take for each species as outlined in table 8.
[[Page 21203]]
Table 8--Estimated Level B Harassment of Marine Mammals During Shallow Hazard Survey Activity
----------------------------------------------------------------------------------------------------------------
Ensonified Total take
Density area of the Ensonified area Days of estimate by
Species (animal/km\2\) airgun of the sparker activity Level B
(km\2\) (km\2\) harassment
----------------------------------------------------------------------------------------------------------------
Bowhead Whale................. 0.009 337.98 N/A for take 12 37
calculation.
Ringed Seal................... 0.320 337.98 43.54........... 12 1,465
Bearded Seal.................. 0.070 337.98 43.54........... 12 320
Spotted Seal.................. 0.110 337.98 43.54........... 12 504
----------------------------------------------------------------------------------------------------------------
Winter/Spring Take Estimate--NMFS estimated the take estimates
based on the total construction and operation area that would be
affected during the winter period. As discussed previously, the total
potential disturbance area of the Colville River Delta sea ice trail is
estimated to be 19.65 km. NMFS multiplied the area of the sea ice trail
with the winter/spring density of ringed seals for the construction,
operation, and demobilization activities to determine the total number
of potential takes by Level B harassment for ringed seals (table 9).
Table 9--Estimated Level B Harassment of Ringed Seals During Colville River Delta Coastal Sea Ice Trail
Activities
----------------------------------------------------------------------------------------------------------------
Total take
Area of Density Days of estimate by
Sea ice trail activity disturbance (animal/km\2\) activity Level B
(km\2\) harassment
----------------------------------------------------------------------------------------------------------------
Construction.................................... 19.65 0.63 25 300
Operation....................................... 19.65 0.63 40 480
Demobilization.................................. 19.65 0.63 22 264
---------------------------------------------------------------
Total....................................... .............. .............. .............. 1,044
----------------------------------------------------------------------------------------------------------------
The total number of take estimated for Narwhal's specified activity
is available in table 10.
Table 10--Summary of All Marine Mammal Exposures Requested by Species
--------------------------------------------------------------------------------------------------------------------------------------------------------
Total take by
Total take by Level B
Level B harassment Total take by Take as a
Species Stock harassment during ice Level B Population percentage of
during the trail harassment estimate the
shallow water construction population
hazard survey and operation
--------------------------------------------------------------------------------------------------------------------------------------------------------
Bowhead Whale............................. Western Artic............... 37 0 37 15,277 0.2
Ringed Seals.............................. Artic....................... 1,465 1,044 2,509 \a\ 342,836 0.7
Bearded Seals............................. Beringia.................... 320 0 320 \b\ 301,836 0.1
Spotted Seals............................. Bering...................... 504 0 504 461,625 0.1
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ Conn et al. (2014) calculated an abundance estimate of 171,418 using a subset of aerial survey data collected in 2012 by Moreland et al. (2013) that
covered the entire ice-covered portions of the Bering Sea. This estimate is consider to be low and was multiplied by a factor of two (Young et al.
2023).
\b\ Conn et al. (2014), using a sub-sample of the data collected from the U.S. portion of the Bering Sea in 2012, calculated an abundance estimate of
301,836 bearded seals (Young et al. 2023).
Potential Effects of Specified Activities on Subsistence Uses of Marine
Mammals
The availability of the affected marine mammal stocks or species
for subsistence uses may be impacted by this activity. The subsistence
uses that may be affected and the potential impacts of the activity on
those uses are described below. Measures included in this IHA to reduce
the impacts of the activity on subsistence uses are described in the
Proposed Mitigation section. Last, the information from this section
and the Proposed Mitigation section is analyzed to determine whether
the necessary findings may be made in the Unmitigable Adverse Impact
Analysis and Determination section.
The communities of Nuiqsut, Utqiagvik and Kaktovik engage in
subsistence harvests off the North Slope of Alaska. Alaska Native
communities have harvested bowhead whales for subsistence and cultural
purposes with oversight and quotas regulated by the International
Whaling Commission (IWC). The NSB Department of Wildlife Management has
been conducting bowhead whale subsistence harvest research since the
early 1980's to collect the data needed by the IWC to set harvest
quotas. Impacts to bowhead whales and ice seals would include limited,
temporary behavioral disturbances only. Level A harassment, serious
injury, or mortality of marine mammals is not anticipated from the
proposed activities, and the activities are not expected to have any
impacts on
[[Page 21204]]
reproductive or survival rates of any marine mammal species at any of
the locations where subsistence harvest is occurring.
These communities also engage in subsistence harvest of beluga and
gray whales. NMFS is not proposing to authorize take of these species
in this IHA (see Description of Marine Mammals in the Area of Specified
Activities section), and therefore, the specified activities are not
expected to affect the availability to access belugas and gray whales
for subsistence use. Additional information on subsistence harvest of
these species is included below. Most of the Beaufort Sea population of
beluga whales migrate from the Bering Sea into the Beaufort Sea in
April or May. The spring migration routes through ice leads are similar
to those of the bowhead whale. Fall migration through the western
Beaufort Sea is in September or October. Surveys of the fall
distribution strongly indicate that most belugas migrate offshore along
the pack ice front beyond the reach of subsistence harvesters. Beluga
whales are harvested opportunistically during the bowhead harvest and
throughout ice-free months. No beluga whale harvests were reported in
2006 survey interviews conducted by Stephen R. Braund & Associates
(SRBA) in any community (SRBA 2010). Beluga harvests were also not
reported in Nuiqsut and Kaktovik, although households did report using
beluga whale, likely through sharing from other communities (Brown et
al., 2016). Gray whale harvests were not reported by any of the
communities surveyed by ADF&G in any of the survey years.
Nuiqsut
The proposed oil and gas exploration activities would occur closest
to the marine subsistence use area used by the Native Village of
Nuiqsut. Nuiqsut is located on the west bank of the Nechelik Channel on
the lower Colville River, about 25 mi (40 km) from the Arctic Ocean and
approximately 150 mi (242 km) southeast of Utqiagvik. Nuiqsut
subsistence hunters utilize an extensive search area, across the
central Arctic Slope (Brown et al., 2016). Marine mammal hunting is
primarily concentrated in two areas: (1) Harrison Bay, between Atigaru
Point and Oliktok Point, including a northward extent of approximately
50 mi (80 km) beyond the Colville River Delta (Brown et al., 2016); and
(2) east of the Colville River Delta between Prudhoe and Foggy Island
bays, which includes an area of approximately 100 square mi surrounding
the Midway Islands, McClure Island and Cross Island (Brown et al.,
2016).
Ringed, spotted and bearded seals are also harvested by the
community of Nuiqsut. Seal hunting typically begins in April and May
with the onset of warmer temperatures. Many residents continue to hunt
seals after spring breakup as well (Brown et al., 2016). The most
important seal hunting area for Nuiqsut hunters is off the Colville
Delta, an area extending as far west as Fish Creek and as far east as
Pingok Island. Seal hunting search areas by Nuiqsut hunters also
include Harrison Bay, and a 30-mi (48-km) stretch northeast of Nuiqsut
between the Colville and Kuparuk rivers, near Simpson Lagoon and Jones
Islands (Brown et al., 2016). Cross Island is a productive area for
seals, but is too far from Nuiqsut to be used on a regular basis.
Nuiqsut residents commonly harvest ringed seal in the Beaufort Sea
during the summer months (SRBA 2010). There are a higher number of use
areas extending east and west of the Colville River delta. Residents
reported traveling as far as Cape Halkett to the west and Camden Bay to
the east in search of ringed seal. Survey respondents reported
traveling offshore up to 30 mi (48 km; SRBA 2010). Residents reported
hunting ringed seals throughout the late spring, summer, and early fall
with a higher number of use areas reported in June, July, and August
(SRBA 2010). In 2006, 12 people (36 percent of survey respondents)
indicated that they had recently hunted for ringed seals in Nuiqsut
(SRBA 2010).
Nuiqsut bearded seal hunting areas extend as far west as Cape
Halkett, as far east as Camden Bay, and offshore up to 40 mi (64 km).
In 2006, 12 people (69 percent of survey respondents) indicated that
they had recently hunted for bearded seals in Nuiqsut (SRBA 2010).
Nuiqsut hunters reported hunting bearded seal during the summer season
in open water as the seals are following the ice pack. Residents
reported hunting bearded seal between June and September, although a
small number of use areas were reportedly used in May and October (SRBA
2010). The number of reported bearded seal use areas peak in July and
August, when the majority of seals are available along the ice pack
(SRBA 2010).
Nuiqsut's bowhead whale hunt occurs in the fall at Cross Island, a
barrier island located approximately 90 mi (144 km) east of west
Harrison Bay. Nuiqsut whalers base their activities from Cross Island
(Galginaitis 2014), and the whaling search and the harvest areas
typically are concentrated north of the island. Hunting activities
between 1997 and 2006 occurred almost as far west as Thetis Island, as
far east as Barter Island (Kaktovik), and up to approximately 50 mi (80
km) offshore (SRBA 2010). Harvest locations in 1973-2011 and GPS tracks
of 2001-2020 whaling efforts are shown in figure 4-7 of Narwhal's
application.
Bowhead whales are harvested by Nuiqsut whalers during the fall
whaling season. Nuiqsut residents typically hunt bowhead whales in
September, although a small number of use areas were reported in August
and extending into October (SRBA 2010). While seismic operations would
occur during Nuiqsut whaling season, the proposed project area is at a
distance that would not affect whaling operations. The distance to
whaling grounds used by Nuiqsut residents is approximately 100 mi (155
km) east of the project area and further than expected acoustic effects
of the shallow hazard survey.
Nuiqsut subsistence hunting crews operating from Cross Island have
typically harvested three to four bowhead whales per year (Bacon et
al., 2009; Galginaitis 2014; Suydam et al. 2020). In 2014, the AEWC
allocated Nuiqsut a quota of four bowhead whales each year; however,
through transfers of quota from other communities, in 2015 Nuiqsut was
able to harvest five whales (Brown et al., 2016). In 2006, 10 people
(30 percent of survey respondents) in Nuiqsut indicated that they had
recently hunted for bowhead whales (SRBA 2010). In 2016, Nuiqsut
whaling crews harvested four bowhead whales (Suydam et al., 2017). In
2019, Nuiqsut whaling crews harvested three bowhead whales (Suydam et
al., 2020).
Narwhal plans to sign a Conflict Avoidance Agreement (CAA) with
Nuiqsut to reduce any impacts to Nuiqsut whaling season (see Proposed
Mitigation section). Narwhal has consulted with AEWC and NSB on
mitigation measures to limit impacts and has continued to provide
formal and informal project updates to these groups, as recently as
April 2025.
The proposed activities are not expected to impact marine mammals
in numbers or locations that would affect the availability for
subsistence harvest given the short-term, temporary, and localized
nature of seismic operations and ice trials construction, and the
proposed mitigation measures. Impacts to marine mammals would mostly
include limited, temporary behavioral disturbances of bowhead whales
and seals. Serious injury or mortality of marine mammals is not
anticipated from the proposed activities, and the activities are not
expected to have any
[[Page 21205]]
impacts on reproductive or survival rates of any marine mammal species.
In summary, impacts to subsistence hunting are not expected due to
the distance between Narwhal activities and primary seal hunting areas
and proposed mitigation for subsistence activities below during the
Nuiqsut bowhead whale hunt.
Utqiagvik
Utqiagvik (formerly known as Barrow) is the northernmost community
on the North Slope and the United States and is approximately 179.6 km
(111.6 mi) northwest of Harrison Bay. According to Brown et al. (2016),
71 percent of households reported using marine mammals as a resource.
Of the marine mammals harvested, bowhead whale made up the largest
composition of marine mammals harvested at 54 percent by weight while
bearded seals represented 30 percent, ringed seals 2 percent, and
beluga whale 2 percent of total marine mammal weight harvested (Brown
et al., 2016). Bowhead whale was reported as a resource used in 70
percent of households, bearded seal in 44 percent of households, ringed
seal in 19 percent of households, beluga whale in 15 percent of
households, and spotted seals in 5 percent.
The spring hunt of bowhead whales occurs while bowheads are making
their migration east toward the eastern Beaufort Sea. Crews begin to
camp on the ice in mid- to late-April and stay out on the edge of the
ice for about 2-6 weeks, depending on the condition of the ice (Brown
et al., 2016). During the fall bowhead migration west, crews travel on
open boat, making day trips from the community. During the summer
months of July and August, bearded seals and ringed seals are targeted
offshore near ice floes (Brown et al., 2016).
The community of Utqia[gdot]vik's subsistence activities occur
outside of the specified geographical region. We do not expect impacts
to Utqia[gdot]vik's subsistence activities, and they are not discussed
further beyond the explanation provided here. Impacts to marine mammals
from the planned oil and gas exploratory activities would mostly
include limited, temporary behavioral disturbances of seals.
Additionally, a small number of takes of bowhead whales, by Level B
harassment only, are predicted to occur in the vicinity of Narwhal's
activity. Even if some subset of taken individuals deflected farther
offshore near the project site, it is reasonable to predict that most
individuals would likely resume a more typical migration path by the
time they reach the Utqia[gdot]vik hunting area, and therefore,
significant impacts to the Utqia[gdot]vik hunt would be unlikely.
The planned activities and associated harassment of marine mammals
are not expected to impact marine mammals in numbers or locations
sufficient to render them unavailable for Utqia[gdot]vik subsistence
harvest given the short-term, temporary, and localized nature of survey
and ice trail construction and operation activities and the planned
mitigation measures. Additionally, no serious injury or mortality of
marine mammals is expected or proposed for authorization.
Kaktovik
Kaktovik is the easternmost village in the NSB. Kaktovik is located
on the north shore of Barter Island, situated between the Okpilak and
Jago rivers on the Beaufort Sea coast. Kaktovik's subsistence-harvest
areas are to the east of the project area and target marine mammal
species migrating eastward during spring and summer. This migration
occurs seaward of the project area and westward in the fall.
Kaktovik bowhead whale hunters reported traveling between Camden
Bay to the west and Nuvagapak Lagoon to the east (SRBA 2010). This
range does not include the project area impacted by the activities
analyzed for this proposed IHA. The small number of takes of bowhead
whales, by Level B harassment only, predicted to occur in the vicinity
of Narwhal's activity are not expected to have any impacts on the
fitness of any bowhead whales. Further, we do not expect Narwhal's
activities to deflect the bowhead whale migration offshore in the
Kaktovik hunting area, given the distance from the western extent of
the hunting area (Camden Bay) to Narwhal's proposed project area. Even
if some subset of taken individuals deflected farther offshore near the
project area, it is reasonable to predict that most individuals would
likely resume a more typical migration path by the time they reach the
Kaktovik hunting area during the eastbound migration, and during the
westbound migration, a bowhead exposed to project noise would have
already passed the hunting area prior to exposure. Significant impacts
to the Kaktovik hunt would be unlikely, and Kaktovik bowhead whale
hunting is not discussed further.
Ringed, spotted and bearded seals are harvested by the community of
Kaktovik. Residents hunt seals in rivers during ice-free months,
primarily July-August. Ringed seals are an important subsistence
resource for Alaska Natives living in communities along the Beaufort
Sea coast. Kaktovik hunters travel by boat to look for ringed seals on
floating ice (often while also hunting for bearded seal) or sometimes
along the ice edge by snow machine before break-up during the spring
(SRBA 2010). In 2006, 7 people (18 percent of survey respondents)
indicated that they had recently hunted for ringed seals in Kaktovik
(SRBA 2010). Residents reported looking for ringed seal, usually while
also searching for bearded seal, offshore between Prudhoe Bay to the
west and Demarcation Bay to the east (SRBA 2010). Ringed seal hunting
typically peaks between March and August but continues into September
(SRBA 2010). Although residents reported hunting ringed seals up to
approximately 30 mi (48 km) from shore, the most overlapping use areas
generally occur within a few miles from shore (SRBA 2010). Harvest of
ringed seals by Kaktovik hunters does not typically occur to the west
of Prudhoe Bay and therefore, is not expected to be affected by
Narwhal's proposed activities. Additionally, impacts to ringed seals
are expected to include temporary behavioral disturbances only. Level A
harassment, serious injury, or mortality of ringed seals is not
anticipated from the proposed activities, and the activities are not
expected to have any impacts on ringed seal reproductive or survival
rates, or to impact availability of ringed seals. Therefore, Narwhal's
proposed activities are not expected to impact Kaktovik ringed seal
harvests.
Kaktovik bearded seal hunting occurs along the coast as far west as
Prudhoe Bay and as far east as the United States/Canada border (SRBA
2010). Residents reported looking for bearded seal as far as
approximately 30 mi (48 km) from shore but generally hunt them closer
to shore, up to 5 mi (8 km; SRBA 2010). Between 1994 and 2003, 29
bearded seals were taken in Kaktovik. In 2006, 7 people (18 percent of
survey respondents) indicated that they had recently hunted for bearded
seals in Kaktovik (SRBA 2010). Bearded seal hunting activities, like
ringed seal, begin in March, peaking in July and August, and then
conclude in September (SRBA 2010). Kaktovik hunters harvested 126
pounds (57.15 kilograms) of spotted seals in 1992 (ADF&G Community
Subsistence Information System; retrieved and analyzed August 15,
2018). Spotted seals were not reported harvested in 2006 survey
interviews conducted in Nuiqsut (SRBA 2010).
The community of Kaktovik is approximately 200 (direct) mi (320 km)
from the proposed project in west Harrison Bay; subsistence activities
for these communities occur outside of the
[[Page 21206]]
project area and associated Level A and Level B harassment zones. The
proposed oil and gas exploration would occur in west Harrison Bay,
which is in an area that is not typically used for subsistence hunting
by residents of Kaktovik.
Because of the distance from Kaktovik, it is unlikely that the
planned activities would have any effects on the use of marine mammals
for subsistence by residents of Kaktovik. Further, the proposed
activities are not expected to impact marine mammals in numbers or
locations sufficient to render them unavailable for subsistence harvest
given the short-term, temporary, and localized nature of project
activities, and the proposed mitigation measures. Therefore, we do not
discuss Kaktovik's subsistence activities further.
Proposed Mitigation
In order to issue an IHA under section 101(a)(5)(D) of the MMPA,
NMFS must set forth the permissible methods of taking pursuant to the
activity, and other means of effecting the least practicable impact on
the species or stock and its habitat, paying particular attention to
rookeries, mating grounds, and areas of similar significance, and on
the availability of the species or stock for taking for certain
subsistence uses. NMFS regulations require applicants for incidental
take authorizations to include information about the availability and
feasibility (economic and technological) of equipment, methods, and
manner of conducting the activity or other means of effecting the least
practicable adverse impact upon the affected species or stocks, and
their habitat (50 CFR 216.104(a)(11)).
In evaluating how mitigation may or may not be appropriate to
ensure the least practicable adverse impact on species or stocks and
their habitat, as well as subsistence uses where applicable, NMFS
considers two primary factors:
(1) The manner in which, and the degree to which, the successful
implementation of the measure(s) is expected to reduce impacts to
marine mammals, marine mammal species or stocks, and their habitat, as
well as subsistence uses. This considers the nature of the potential
adverse impact being mitigated (likelihood, scope, range). It further
considers the likelihood that the measure will be effective if
implemented (probability of accomplishing the mitigating result if
implemented as planned), the likelihood of effective implementation
(probability implemented as planned), and;
(2) The practicability of the measures for applicant
implementation, which may consider such things as cost and impact on
operations.
Mitigation for Shallow Water Hazard Surveys
Vessels used during the surveys will not allow lines to remain in
the water unless both ends are under tension and affixed to vessels or
gear. No materials capable of becoming entangled around marine mammals
will be discarded into marine waters.
Vessel-Visual Based Mitigation Monitoring--Visual monitoring
requires the use of trained observers (herein referred to as visual
protected species observers (PSOs)) to scan the ocean surface visually
for the presence of marine mammals. PSOs shall establish and monitor a
pre-start clearance zone (shutdown zones in table 11) and, to the
extent practicable, a Level B harassment zone (table 11). These zones
shall be based upon the radial distance from the edges of the acoustic
source (rather than being based around the vessel itself). The shutdown
zones are based off the size of the Level A harassment zone with
slightly larger areas to ensure shutdown before the animal enters the
harassment zone. During pre-start clearance (i.e., before ramp-up
begins), the pre-start clearance zone is the area in which observations
of marine mammals within the zone would prevent airgun and sparker
operations from beginning (i.e., ramp-up). The pre-start clearance zone
would encompass the shutdown zones.
During survey operations (e.g., any day on which use of the
acoustic source is planned to occur, and whenever the acoustic source
is in the water, whether activated or not), a minimum of two PSOs
during the operation of the airgun and a minimum of one PSO during the
operation of the sparker must be on duty and conducting visual
observations at all times during daylight hours (i.e., from 30 minutes
prior to sunrise through 30 minutes following sunset). Visual
monitoring must begin no less than 15 minutes prior to use of the
acoustic source and must continue until 1 hour after use of the
acoustic source ceases or until 30 minutes past sunset. Visual PSO(s)
must coordinate to ensure 360 degree visual coverage around the vessel
from the most appropriate observation posts, and must conduct visual
observations using binoculars and the naked eye while free from
distractions and in a consistent, systematic, and diligent manner.
Any observations of marine mammals by crew members shall be relayed
to the PSO team. During good conditions (e.g., daylight hours, Beaufort
sea state (BSS) 3 or less), visual PSOs shall conduct observations when
the acoustic source is not operating for comparison of sightings rates
and behavior with and without use of the acoustic source and between
acquisition periods, to the maximum extent practicable.
Visual PSOs may be on watch for a maximum of 4 consecutive hours
followed by a break of at least 1 hour between watches and may conduct
a maximum of 12 hours of observation per 24-hour period.
Pre-Start Clearance and Ramp-Up--A ramp-up procedure, involving a
gradual increase in source level output, is not required for use of the
airgun but would be required at the start of the activation of the
sparker when technically feasible. Operators should ramp up sparker
source to half power for 5 minutes and then proceed to full power. A
15-minute pre-start clearance observation period must occur prior to
the start of ramp-up. The intent of pre-start clearance observation (15
minutes) is to ensure no marine mammals are within the shutdown zones
prior to the beginning of ramp-up. The intent of ramp-up is to warn
marine mammals of pending operations and to allow sufficient time for
those animals to leave the immediate vicinity. A 15 minute pre-start
clearance period is proposed for all species for this project due to
the quick succession of track lines and in general the shallow water of
the project area. All sound source operators must adhere to the
following pre-start clearance and ramp-up requirements:
<bullet> The operator must notify a designated PSO of the planned
start of ramp-up as agreed upon with the lead PSO; the notification
time should not be less than 60 minutes prior to the planned ramp-up in
order to allow the PSOs time to monitor the shutdown zones for 15
minutes prior to the initiation of ramp-up (pre-start clearance).
During this 15 minute pre-start clearance period, the entire applicable
shutdown zones must be visible, except as indicated in below.
<bullet> Source use shall be scheduled so as to minimize the time
spent with the source activated prior to the start of acquisition.
<bullet> A visual PSO conducting pre-start clearance observations
must be notified again immediately prior to initiating ramp-up
procedures and the operator must receive confirmation from the PSO to
proceed.
<bullet> Any PSO on duty has the authority to delay the start of
survey operations if a protected species is detected within the
applicable pre-start clearance zone.
[[Page 21207]]
<bullet> The operator must establish and maintain clear lines of
communication directly between PSOs on duty and crew controlling the
acoustic source to ensure that mitigation commands are conveyed swiftly
while allowing PSOs to maintain watch.
<bullet> Ramp-up may not be initiated if any marine mammal is
within the applicable shutdown zone. If a marine mammal is observed
within the applicable shutdown zone during the 15 minute pre-start
clearance period, ramp-up may not begin until the animal(s) has been
observed exiting the zones or until an additional time period has
elapsed with no further sightings (15 minutes for all marine mammals).
<bullet> PSOs must monitor the shutdown zones 15 minutes before and
during ramp-up, and ramp-up must cease and the source must be shut down
upon observation of a marine mammal within the applicable shutdown
zone.
<bullet> Ramp-up may occur at times of poor visibility, including
nighttime, if appropriate visual monitoring has occurred with no
detections of protected species in the 15 minutes prior to beginning
ramp-up.
<bullet> If the acoustic source is shut down for brief periods
(i.e., less than 30 minutes) for reasons other than implementation of
prescribed mitigation (e.g., mechanical difficulty), it may be
activated again without ramp-up if PSOs have maintained constant visual
observation and no detections of protected species have occurred within
the applicable shutdown zone. For any longer shutdown, pre-start
clearance observation and ramp-up are required.
Shutdown Procedures
Any PSO on duty will have the authority to call for shutdown of the
acoustic sources, as appropriate. The operator must also establish and
maintain clear lines of communication directly between PSOs on duty and
crew controlling the acoustic sources to ensure that shutdown commands
are conveyed swiftly while allowing PSOs to maintain watch. Narwhal
must implement shutdown if a marine mammal species for which take was
not authorized or a species for which authorization was granted but the
authorized takes have been met approaches the Level B harassment zone.
If the seismic activity is halted due to the presence of a marine
mammal, the activity may not resume until either the animal has
voluntarily exited and been visually confirmed beyond the shutdown zone
indicated in table 11, or 15 minutes have passed without re-detection
of any marine mammal.
Table 11--Shutdown Zones and Level B Harassment Zones for Each Activity
----------------------------------------------------------------------------------------------------------------
Shutdown zone radius (m) Level B
---------------------------------- harassment
Activity Low-frequency Phocid zone radius
cetaceans pinnipeds (m)
----------------------------------------------------------------------------------------------------------------
Single Airgun................................................. 1,100 350 3,188
Sparker....................................................... 500 N/A 447
----------------------------------------------------------------------------------------------------------------
Vessel Strike Avoidance
Crew and supply vessel personnel should use an appropriate
reference guide that includes identifying information on all marine
mammals and other marine aquatic protected species that may be
encountered. Vessel operators must comply with the below measures
except under extraordinary circumstances when the safety of the vessel
or crew is in doubt or the safety of life at sea is in question.
<bullet> Vessel operators and crews must maintain a vigilant watch
for all protected species and slow down, stop their vessel, or alter
course, as appropriate and regardless of vessel size, to avoid striking
any protected species. A single protected species at the surface may
indicate the presence of submerged animals in the vicinity of the
vessel; therefore, precautionary measures should always be exercised. A
visual observer aboard the vessel must monitor a vessel strike
avoidance zone around the vessel (species-specific distances detailed
below). Visual observers monitoring the vessel strike avoidance zone
may be third-party observers (i.e., PSOs) or crew members, but crew
members responsible for these duties must be provided sufficient
training to (1) distinguish protected species from other phenomena and
(2) broadly to identify a marine mammal as a whale, seal, or other
marine mammals.
<bullet> Vessel speed within west Harrison Bay must generally be
restricted to 15 knots (kn) or less, must be reduced to 5 kn if within
300 yds (274 m) of a whale and must be reduced to 10 kn or less when
weather conditions reduce visibility to 1.6 km or less;
<bullet> All vessels must maintain a minimum separation distance of
100 m from bowhead whales. If a bowhead whale is sighted within the
relevant separation distance, the vessel must steer a course away at 10
knots or less until the 100-m separation distance has been established.
<bullet> All vessels must, to the maximum extent practicable,
attempt to maintain a minimum separation distance of 100 yds (91 m)
from all other marine mammals, with an understanding that at times this
may not be possible (e.g., for animals that approach the vessel), and;
<bullet> When protected species are sighted while a vessel is
underway, the vessel shall take action as necessary to avoid violating
the relevant separation distance (e.g., attempt to remain parallel to
the animal's course, avoid excessive speed or abrupt changes in
direction until the animal has left the area, reduce speed and shift
the engine to neutral). This does not apply to any vessel towing gear
or any vessel that is navigationally constrained
Mitigation for the Sea Ice Trail Crossing the Colville River Delta
Unless otherwise noted, these measures apply to ringed seals and
the portion of the sea ice trail crossing the Colville River Delta.
Take is only expected for this section of trail because this is the
only suitable ringed seal habitat the ice trails will cross. These
mitigation measures are organized into the following categories: (1)
general mitigation measures (implemented throughout the ice trail
season, which occurs generally from December through May) and (2)
mitigation measures that begin after March 1st.
General Ice Trail Mitigation Measures
Ice trail mitigation measures are based on the following
assumptions: ice trail construction occurs from approximately December
1st to mid-February (or as soon as sea ice conditions allow safe access
and permit such activity); operations and maintenance generally occur
from approximately mid-January through mid- to late May. Ringed seals
[[Page 21208]]
begin to establish birth lairs in late March. Therefore, ice trail
construction should be initiated no later than March 1st (i.e.,
surface-disturbing activities such as clearing or packing of snow or
grading to be completed for the full spatial extent of the ice trails
prior to March 1st) to reduce the potential for disturbance to ringed
seal birth lairs/dens; and disturbance associated with construction
prior to March 1st may deter pregnant seals from establishing birth
lairs in the disturbed areas.
The following mitigation measures will be implemented throughout
the entire ice trail season, including during construction,
maintenance, active use, and decommissioning:
<bullet> Personnel shall not approach or interact with any
wildlife.
<bullet> Personnel must follow directions of Security and posted
signs when traveling the ice trail.
<bullet> Workers must notify appropriate personnel if a seal is
observed within 50 meters, or if a seal structure (i.e., breathing hole
or lair) is observed within 150 m, of the centerline of the ice trail.
<bullet> Workers must stay in the vehicle and continue traveling at
a constant speed if a seal is observed near the trail. Do not slow
down, stop, or exit the vehicle.
<bullet> Transport vehicles (passenger vehicles and trucks hauling
goods) will not stop within 50 m (164 ft) of observed seals or 150 m
(about 500 ft) of known seal lairs. Instead, they will continue
travelling at a constant speed.
<bullet> Ice trail speed limits will be 45 miles per hour (mph) or
less, based on environmental, road conditions, and ice trail longevity
considerations.
<bullet> Delineators will mark the roadway in a minimum of \1/4\-
mile increments on both sides of the portions of ice trails in west
Harrison Bay to delineate the path of vehicle travel and areas of
planned on-ice activities (e.g., emergency response exercises).
Delineators may also be used to mark the centerline of the roadway.
<bullet> Corners of rig mats, steel plates, and other materials
used to bridge sections of hazardous ice will be clearly marked or
mapped using GPS coordinates of the locations.
<bullet> Any seal structures (i.e., breathing holes and lairs)
observed will be avoided by a minimum of 150 meters (about 500 feet)
during ice testing and new trail construction and their locations will
be reported and physically marked.
<bullet> Personnel will be instructed that approaching or
interacting with seals is prohibited.
<bullet> If a seal is observed within 50 meters (164 feet) or if a
seal structure (i.e., breathing hole or lair) is detected within 150
meters (about 500 feet) of the centerline of an ice trail, the project
proponent's Environmental Specialist or Project Manager will be
informed of the observation, who will then carry out the notification
protocol and implement the procedures described in the General
Monitoring Measures for Ice Trails section (below). The following
procedures will also be followed:
[cir] The location of the seal or seal structure will be physically
marked (e.g., at its position along the axis of the ice trail) by
placing a readily visible marker (e.g., pole and flag) within 15 meters
(50 feet) of the edge of the ice trail, while maintaining a distance of
at least 15 meters (50 feet) from the seal/seal structure.
[cir] Construction, maintenance, or decommissioning work will not
occur within 50 meters (164 feet) of the seal, but may proceed as soon
as the seal, of its own accord, moves farther than 50 meters distance
away from the activities or has not been observed within that area for
at least 24 hours. Transport vehicles may continue their route within
the designated trail if they can do so without stopping.
[cir] During the period in which a seal structure is periodically
monitored as described in the General Monitoring Measures for Ice
Trails section (below), maintenance work will proceed in a manner that
minimizes impacts or disturbance to the area.
Ice Trail Mitigation Measures That Begin After March 1st
After March 1st and continuing until decommissioning of ice trails
is completed, on-ice activities can occur anywhere on sea ice where
water depth is less than 3 meters (10 feet) (i.e., habitat less
suitable for ringed seal lairs and breathing holes). However, after
March 1st on those sections of the ice trails where water depth is
greater than 3 meters (10 feet), all activities will occur within the
boundaries of the driving lane or shoulder area of the ice trail and
other previously disturbed areas (e.g., spill and emergency response
areas, snow push areas), as long as personnel safety is ensured.
<bullet> If safety concerns due to unstable ice trail conditions
warrant the creation of workaround route after March 1st, the route
will be surveyed for seal structures using a trained observer in a
tracked vehicle approximately 2 days prior to establishing the route,
weather permitting. Surveys must occur following improved weather
conditions before establishing the workaround route. The fo
[…truncated; see source link]Indexed from Federal Register on May 16, 2025.
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.