2024-21469. Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to Furie Operating Alaska, LLC Natural Gas Activities in Cook Inlet, Alaska

Table 1—Species ¹ Likely Impacted by the Specified Activities

Common name	Scientific name	Stock	ESA/MMPA status; strategic (Y/N) 2	Stock abundance (CV, N min , most recent abundance survey) 3	PBR	Annual M/SI 4
Order Artiodactyla—Cetacea—Mysticeti (baleen whales)
Family Eschrichtiidae:
Gray whale	Eschrichtius robustus	Eastern N Pacific	-, -, N	26,960 (0.05, 25,849, 2016)	801	131
Family Balaenidae:
Family Balaenopteridae (rorquals):
Fin whale	Balaenoptera physalus	Northeast Pacific	E, D, Y	UND 5 (UND, UND, 2013)	UND	0.6
Humpback whale	Megaptera novaeangliae	Hawai'i	-, -, N	11,278 (0.56, 7,265, 2020)	127	27.09
Humpback whale	Megaptera novaeangliae	Mexico-North Pacific	T, D, Y	N/A 6 (N/A, N/A, 2006)	UND	0.57
Humpback whale	Megaptera novaeangliae	Western North Pacific	E, D, Y	1,084 7 (0.088, 1,007, 2006)	3.4	5.82
Minke whale	Balaenoptera acutorostrata	AK	-, -, N	N/A 8 (N/A, N/A, N/A)	UND	0
Odontoceti (toothed whales, dolphins, and porpoises)
Family Delphinidae:
Killer whale	Orcinus orca	Eastern North Pacific Alaska Resident	-, -, N	1,920 (N/A, 1,920, 2019)	19	1.3
Killer whale	Orcinus orca	Eastern North Pacific Gulf of Alaska, Aleutian Islands and Bering Sea Transient	-, -, N	587 (N/A, 587, 2012)	5.9	0.8
Pacific white-sided dolphin	Lagenorhynchus obliquidens	N Pacific	-, -, N	26,880 (N/A, N/A, 1990)	UND	0
Family Monodontidae (white whales):
Beluga whale	Delphinapterus leucas	Cook Inlet	E, D, Y	279 9 (0.061, 267, 2018)	0.53	0
Family Phocoenidae (porpoises):
Dall's porpoise	Phocoenoides dalli	AK	-, -, N	UND 10 (UND, UND, 2015)	UND	37
Harbor porpoise	Phocoena phocoena	Gulf of Alaska	-, -, Y	31,046 (0.21, N/A, 1998)	UND	72
Order Carnivora—Pinnipedia
Family Otariidae (eared seals and sea lions):
CA sea lion	Zalophus californianus	U.S.	-, -, N	257,606 (N/A, 233,515, 2014)	14,011	>321
Steller wea lion	Eumetopias jubatus	Western	E, D, Y	49,837 11 (N/A, 49,837, 2022)	299	267
Family Phocidae (earless seals):
( print page 77844)
Harbor seal	Phoca vitulina	Cook Inlet/Shelikof Strait	-, -, N	28,411 (N/A, 26,907, 2018)	807	107
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 ( https://marinemammalscience.org/​science-and-publications/​list-marine-mammal-species-subspecies/​; Committee on Taxonomy (2022)).
2  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 SARs online at: https://www.fisheries.noaa.gov/​national/​marine-mammal-protection/​marine-mammal-stock-assessment-reports-region. CV is coefficient of variation; N min is the minimum estimate of stock abundance.
4  These values, found in NMFS's SARs, represent annual levels of human-caused mortality plus serious injury from all sources combined ( e.g., commercial fisheries, ship strike). Annual M/SI often cannot be determined precisely and is in some cases presented as a minimum value or range. A CV associated with estimated mortality due to commercial fisheries is presented in some cases.
5  The best available abundance estimate for this stock is not considered representative of the entire stock as surveys were limited to a small portion of the stock's range. Based upon this estimate and the N min , the PBR value is likely negatively biased for the entire stock.
6  Abundance estimates are based upon data collected more than 8 years ago and, therefore, current estimates are considered unknown.
7  The best estimates of abundance for the stock (1,084) and the portion of the stock migrating to summering areas in U.S. waters (127) were derived from a reanalysis of the 2004-2006 SPLASH data (Wade 2021). Although these data are more than fifteen years old, the estimates are still considered valid minimum population estimates.
8  Reliable population estimates are not available for this stock. Please see Friday et al. (2013) and Zerbini et al. (2006) for additional information on numbers of minke whales in Alaska.
9  On June 15, 2023, NMFS released an updated abundance estimate for endangered Cook Inlet beluga whales in Alaska (Goetz et al. 2023). Data collected during NOAA Fisheries' 2022 aerial survey suggest that the whale population is stable or may be increasing slightly. Scientists estimated that the population size is between 290 and 386, with a median best estimate of 331. In accordance with the MMPA, this population estimate will be incorporated into the Cook Inlet beluga whale SAR, which will be reviewed by an independent panel of experts, the Alaska Scientific Review Group. After this review, the SAR will be made available as a draft for public review before being finalized.
10  The best available abundance estimate is likely an underestimate for the entire stock because it is based upon a survey that covered only a small portion of the stock's range.
11  Nest is best estimate of counts, which have not been corrected for animals at sea during abundance surveys.

As indicated above, all 12 species (with 15 number managed stocks) in table 3 temporally and spatially co-occur with the activity to the degree that take could occur. In addition, the northern sea otter may be found in Cook Inlet, Alaska. However, northern sea otters are managed by the U.S. Fish and Wildlife Service and are not considered further in this document.

A detailed description of the species likely to be affected by Furie's activities, including a brief introduction to the affected stock as well as available information regarding population trends and threats, and information regarding local occurrence, were provided in the Federal Register notice of the proposed IHA (89 FR 51102; June 14, 2024). Since that time, we are not aware of any changes in the status of these species and stocks; therefore, detailed descriptions are not provided here. Please refer to that Federal Register notice for these descriptions. Please also refer to NMFS' website ( https://www.fisheries.noaa.gov/​find-species) for generalized species accounts.

Marine Mammal Hearing

Hearing is the most important sensory modality for marine mammals underwater, and exposure to anthropogenic sound can have deleterious effects. To appropriately assess the potential effects of exposure to sound, it is necessary to understand the frequency ranges marine mammals are able to hear. Not all marine mammal species have equal hearing capabilities ( e.g., Richardson et al. 1995; Wartzok and Ketten, 1999; Au and Hastings, 2008). To reflect this, Southall et al. (2007, 2019) recommended that marine mammals be divided into hearing groups based on directly measured (behavioral or auditory evoked potential techniques) or estimated hearing ranges (behavioral response data, anatomical modeling, etc.). Note that no direct measurements of hearing ability have been successfully completed for mysticetes ( i.e., low-frequency cetaceans). Subsequently, NMFS (2018) described generalized hearing ranges for these marine mammal hearing groups. Generalized hearing ranges were chosen based on the approximately 65 dB threshold from the normalized composite audiograms, with the exception for lower limits for low-frequency cetaceans where the lower bound was deemed to be biologically implausible and the lower bound from Southall et al. (2007) retained. Marine mammal hearing groups and their associated hearing ranges are provided in table 2.

Table 2—Marine Mammal Hearing Groups (NMFS, 2018)

Hearing group	Generalized hearing range *
Low-frequency (LF) cetaceans (baleen whales)	7 Hz to 35 kHz.
Mid-frequency (MF) cetaceans (dolphins, toothed whales, beaked whales, bottlenose whales)	150 Hz to 160 kHz.
High-frequency (HF) cetaceans (true porpoises, Kogia, river dolphins, Cephalorhynchid, Lagenorhynchus cruciger & L. australis)	275 Hz to 160 kHz.
Phocid pinnipeds (PW) (underwater) (true seals)	50 Hz to 86 kHz.
Otariid pinnipeds (OW) (underwater) (sea lions and fur seals)	60 Hz to 39 kHz.
* Represents the generalized hearing range for the entire group as a composite ( i.e., all species within the group), where individual species' hearing ranges are typically not as broad. Generalized hearing range chosen based on ~65 dB threshold from normalized composite audiogram, with the exception for lower limits for LF cetaceans (Southall et al. 2007) and PW pinniped (approximation).

( print page 77845)

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 (Hemilä et al. 2006; Kastelein et al. 2009; Reichmuth et al. 2013). This division between phocid and otariid pinnipeds is now reflected in the updated hearing groups proposed in Southall et al. (2019).

For more detail concerning these groups and associated frequency ranges, please see NMFS (2018) for a review of available information.

Potential Effects of Specified Activities on Marine Mammals and Their Habitat

The effects of underwater noise from Furie's activities have the potential to result in behavioral harassment of marine mammals in the vicinity of the project area. The notice of proposed IHA (89 FR 51102; June 14, 2024) included a discussion of the effects of anthropogenic noise on marine mammals and the potential effects of underwater noise from rig tugging and pile driving on marine mammals and their habitat. That information and analysis is referenced in this final IHA determination and is not repeated here; please refer to the notice of proposed IHA (89 FR 51102; June 14, 2024).

Estimated Take of Marine Mammals

This section provides an estimate of the number of incidental takes authorized through the IHAs, which will inform NMFS' consideration of “small numbers,” the negligible impact determinations, and impacts on subsistence uses.

Harassment is the only type of take expected to result from these activities. Except with respect to certain activities not pertinent here, section 3(18) of the MMPA defines “harassment” as any act of pursuit, torment, or annoyance, which (i) has the potential to injure a marine mammal or marine mammal stock in the wild (Level A harassment); or (ii) has the potential to disturb a marine mammal or marine mammal stock in the wild by causing disruption of behavioral patterns, including, but not limited to, migration, breathing, nursing, breeding, feeding, or sheltering (Level B harassment).

Authorized take will primarily be by Level B harassment, as use of the acoustic sources ( i.e., pile driving and tug towing and positioning) may result in disruption of behavioral patterns of individual marine mammals. We note here that given the slow, predictable, and generally straight path of tug towing and positioning, the likelihood of a resulting disruption of marine mammal behavioral patterns that would qualify as harassment is considered relatively low; however, at the request of the applicant, we have quantified the potential take from this activity, analyzed the impacts, and authorized take. There is also some potential for auditory injury (Level A harassment) to result to phocids because of species occurrence and because predicted auditory injury zones are larger than for mid-frequency and otariid species. Auditory injury is unlikely to occur for low-frequency, mid-frequency, high-frequency, or otariid species. The required mitigation and monitoring measures are expected to minimize the severity of the taking to the extent practicable.

As described previously, no serious injury or mortality is anticipated or authorized for this activity. Below we describe how the take numbers are estimated.

To determine whether Level B harassment is expected to result from acoustic exposure, NMFS considers both the received levels a marine mammal is expected to be exposed to as compared to the relevant NMFS Level B harassment thresholds, as well as contextual factors that can impact whether a marine mammal's behavioral patterns are likely to be disrupted ( e.g., bearing and distance, predictability of source movement, whether habituation in a noisier/busy area is likely); specifically, whether any contextual factors would be expected to reduce the likelihood of behavioral disturbance even when a marine mammal is exposed above the Level B harassment threshold. Where the take of marine mammals is considered likely or is requested by the applicant, 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 take estimates.

Acoustic Thresholds

NMFS recommends the use of acoustic thresholds that identify the received level of underwater sound above which exposed marine mammals would be reasonably expected to be behaviorally harassed (equated to Level B harassment) or to incur PTS of some degree (equated to Level A harassment).

Level B Harassment —Though significantly driven by received level, the onset of behavioral disturbance from anthropogenic noise exposure is also informed to varying degrees by other factors related to the source or exposure context ( e.g., frequency, predictability, duty cycle, duration of the exposure, signal-to-noise ratio, distance to the source), the environment ( e.g., bathymetry, other noises in the area, predators in the area), and the receiving animals (hearing, motivation, experience, demography, life stage, depth) and can be difficult to predict ( e.g., Southall et al. 2007, 2021, Ellison et al. 2012). Based on what the available science indicates and the practical need to use a threshold based on a metric that is both predictable and measurable for most activities, NMFS typically uses a generalized acoustic threshold based on received level to support the estimation of the onset of Level B harassment and to quantify likely Level B harassment. Acknowledging the consideration of contextual factors noted above, NMFS generally predicts that marine mammals are likely to be affected 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 re 1 μPa for continuous ( e.g., vibratory pile driving, drilling) and above RMS SPL 160 dB re 1 μPa for non-explosive impulsive ( e.g., seismic airguns) or intermittent ( e.g., scientific sonar) sources. Generally speaking, Level B harassment take estimates based on these thresholds are expected to include any likely takes by temporary threshold shift (TTS) as, in most cases, the likelihood of TTS occurs at distances from the source smaller than those at which onset of Level B harassment is likely. TTS of a sufficient degree can manifest as Level B harassment, as reduced hearing sensitivity and the potential reduced opportunities to detect important signals (conspecific communication, predators, prey) may result in disruptions in behavior patterns that would not otherwise occur.

Furie's planned activity includes the use of continuous (tugs towing rig) and impulsive (impact pile driving) sources, and therefore the RMS SPL thresholds ( print page 77846) of 120 and 160 dB re 1 μPa are applicable.

Level A harassment —NMFS' Technical Guidance for Assessing the Effects of Anthropogenic Sound on Marine Mammal Hearing (Version 2.0) (Technical Guidance, 2018) identifies dual criteria to assess auditory injury (Level A harassment) to 5 different marine mammal groups (based on hearing sensitivity) as a result of exposure to noise from two different types of sources (impulsive or non-impulsive). Furie's planned activity includes the use of impulsive (impact pile driving) and non-impulsive (tugs towing and positioning rig) sources.

These thresholds are provided in the table below. The references, analysis, and methodology used in the development of the thresholds are described in NMFS' 2018 Technical Guidance, which may be accessed at: https://www.fisheries.noaa.gov/​national/​marine-mammal-protection/​marine-mammal-acoustic-technical-guidance.

Table 3—Thresholds Identifying the Onset of Permanent Threshold Shift

Hearing group	PTS onset acoustic thresholds * (received level)
	Impulsive	Non-impulsive
Low-Frequency (LF) Cetaceans	Cell 1:Lpk,flat : 219 dB; LE,LF,24h : 183 dB	Cell 2:LE,LF,24h : 199 dB.
Mid-Frequency (MF) Cetaceans	Cell 3:Lpk,flat : 230 dB; LE,MF,24h : 185 dB	Cell 4:LE,MF,24h: 198 dB.
High-Frequency (HF) Cetaceans	Cell 5:Lpk,flat : 202 dB; LE,HF,24h : 155 dB	Cell 6:LE,HF,24h : 173 dB.
Phocid Pinnipeds (PW) (Underwater)	Cell 7:Lpk,flat : 218 dB; LE,PW,24h : 185 dB	Cell 8:LE,PW,24h : 201 dB.
Otariid Pinnipeds (OW) (Underwater)	Cell 9:Lpk,flat : 232 dB; LE,OW,24h : 203 dB	Cell 10:LE,OW,24h : 219 dB.
* Dual metric acoustic thresholds for impulsive sounds: Use whichever results in the largest isopleth for calculating PTS onset. If a non-impulsive sound has the potential of exceeding the peak sound pressure level thresholds associated with impulsive sounds, these thresholds should also be considered.
Note: Peak sound pressure ( Lpk ) has a reference value of 1 µPa, and cumulative sound exposure level ( LE ) has a reference value of 1µPa2 s. In this table, thresholds are abbreviated to reflect American National Standards Institute standards (ANSI 2013). However, peak sound pressure is defined by ANSI as incorporating frequency weighting, which is not the intent for this Technical Guidance. Hence, the subscript “flat” is being included to indicate peak sound pressure should be flat weighted or unweighted within the generalized hearing range. The subscript associated with cumulative sound exposure level thresholds indicates the designated marine mammal auditory weighting function (LF, MF, and HF cetaceans, and PW and OW pinnipeds) and that the recommended accumulation period is 24 hours. The cumulative sound exposure level thresholds could be exceeded in a multitude of ways ( i.e., varying exposure levels and durations, duty cycle). When possible, it is valuable for action proponents to indicate the conditions under which these acoustic thresholds will be exceeded.

Ensonified Area

Here, we describe operational and environmental parameters of the activity that are used in estimating the area ensonified above the acoustic thresholds, including source levels and transmission loss (TL) coefficient.

The sound field in the project area is the existing background noise plus additional noise from the planned project. Marine mammals are expected to be affected via sound generated by the primary components of the project ( i.e., pile driving and tug towing and positioning). The calculated distance to the farthest Level B harassment isopleth is approximately 4,483 m (2.8 miles (mi)).

The project includes impact installation of up to two conductor pipe piles (ranging in potential size from 20-in to 36-in) in each year. The monopod leg of the JRP will encase the well slot, which will encase the conductor pipes; therefore, some attenuation is expected during conductor pipe pile installation. However, water-filled isolation casings (such as the well slot and caisson at the JRP) are expected to provide limited sound attenuation (Caltrans 2015). Due to the well slot's reflective surfaces and the monopod leg's caisson inside the JRP, some attenuation of the impact noise is expected before reaching the open water. However, lacking project-specific empirical data for a 20-in to 36-in conductor installed within a well slot located within a monopod leg, the unaltered sound source levels (SSLs) from U.S. Navy (2015) are used to calculate Level A harassment and Level B harassment isopleths.

For tug activities, as described in 87 FR 27597 (May 9, 2022), Hilcorp conducted a literature review of available source level data for tugs under load in varying power output scenarios. Table 4 below provides values of measured source levels for tugs varying from 2,000 to 8,200 horsepower. For the purposes of this table, berthing activities could include tugs either pushing or pulling a load. The SSLs appear correlated to speed and power output, with full power output and higher speeds generating more propeller cavitation and greater SSLs than lower power output and lower speeds. Additional tug source levels are available from the literature but they are not specific to tugs under load but rather measured values for tugs during activities such as transiting, docking, and anchor pulling. For a summary of these additional tug values, see table 7 in Hilcorp's 2022 IHA application, available at https://www.fisheries.noaa.gov/​action/​incidental-take-authorization-hilcorp-alaska-llc-oil-and-gas-activities-cook-inlet-alaska-0.

Table 4—Literature Values of Measured Tug Source Levels

Vessel	Vessel length (m)	Speed (knots)	Activity	Source level @1 m (re: 1 µPa)	Horsepower	Reference
Eagle	32	9.6	Towing barge	173	6,770	Bassett et al. 2012.
Valor	30	8.4	Towing barge	168	2,400
Lela Joy	24	4.9	Towing barge	172	2,000
Pacific Eagle	28	8.2	Towing barge	165	2,000
Shannon	30	9.3	Towing barge	171	2,000
James T Quigg	30	7.9	Towing barge	167	2,000
( print page 77847)
Island Scout	30	5.8	Towing barge	174	4,800
Chief	34	11.4	Towing barge	174	8,200
Lauren Foss	45	N/A	Berthing barge	167	8,200	Austin et al. 2013.
Seaspan Resolution	30	N/A	Berthing at half power	180	6,000	Roberts Bank Terminal 2 Technical Report 2014.
Seaspan Resolution	30	N/A	Berthing at full power	200	6,000

The Roberts Bank Terminal 2 Technical Report (2014), although not in Cook Inlet, includes repeated measurements of the same tug operating under different speeds and loads. This allows for a comparison of source levels from the same vessel at half power versus full power, which is an important distinction for Furie's activities, as a small fraction of the total time spent by tugs under load will be at greater than 50 percent power. The Seaspan Resolution's half-power berthing scenario has a sound source level of 180 dB re 1 μPa at 1 m. In addition, the Roberts Bank Report (2014) analyzed 650 tug transits under varying load and speed conditions and reported mean tug source levels of 179.3 dB re 1 μPa at 1 m; the 25th percentile was 179.0 dB re 1 μPa at 1 m, and 5th percentile source levels were 184.9 dB re 1 μPa at 1 m.

Based solely on the literature review, a source level of 180 dB for a single tug under load would be appropriate. However, Furie's use of a three tug configuration would increase the literature source level to approximately 185 dB at 1 m (Lawrence et al. 2022, as cited in Weston and SLR 2022).

As described in the Detailed Description of the Specific Activity section of the notice of proposed IHA (89 FR 51102, June 14, 2024), based on in situ measurements of Hilcorp's tug and a review of the available literature of tugs under load described above, NMFS finds that a source level of 185 dB re 1 µPa is appropriate for Furie's 3 tug configuration for towing the rig.

As described above in the Detailed Description of the Specific Activity section, Furie may need to use four tugs to position the rig at the JRP. The SPL_RMS of 185 dB for three tugs at 50 percent power implies each tug individually has a source level of 180.2 dB SPL_rms because the addition of 3 equal-intensity sound signals adds 4.8 dB to the sound level of a single source (Engineering Toolbox 2023). Each doubling of sound intensity adds 3 dB to the baseline (Engineering Toolbox 2023), and 4 tugs represents two doublings of a single source. Therefore, adding 6 dB to the 180.2 dB baseline results in an expected SSL of 186.2 dB rms SPL for the use of 4 tugs. Source levels for each activity are presented in table 5.

Table 5—SSLs for Project Activities

Sound source	SSL
	SEL	SPL RMS
3 tugs at 50 percent power		185 dB at 1 m.
4 tugs at 50 percent power		186.2 dB at 1 m.
Conductor pipe pile (20-in to 36-in, impact)	184 dB at 10 m	193 dB at 10 m.

Several factors will determine the duration that the tugboats are towing the Enterprise 151, including the origin and destination of the towing route ( e.g., Rig Tenders Dock, the JRP, one of Hilcorp's platforms) and the tidal conditions. The power output will be variable and influenced by the prevailing wind direction and velocity, the current velocity, and the tidal stage. To the extent feasible, transport will be timed with the tide to minimize towing duration and power output.

TL is the decrease in acoustic intensity as an acoustic pressure wave propagates out from a source. TL parameters vary with frequency, temperature, sea conditions, current, source and receiver depth, water depth, water chemistry, and bottom composition and topography. The general formula for underwater

TL is:

TL = B * Log10 (R1/R2),

where

TL = transmission loss in dB

B = transmission loss coefficient

R1 = the distance of the modeled SPL from the driven pile, and

R2 = the distance from the driven pile of the initial measurement

Absent site-specific acoustical monitoring with differing measured TL, a practical spreading value of 15 is used as the TL coefficient in the above formula. Site-specific TL data for pile driving with relevant parallel characteristics are not available; therefore, the default coefficient of 15 is used to determine the distances to the Level A harassment and Level B harassment thresholds for conductor pile driving.

For its tugging activities, Hilcorp contracted SLR Consulting to model the extent of the 120-dB isopleth as well as the extent of the Level A harassment isopleth for their planned tugging using three tugs. Rather than applying practical spreading loss, SLR Consulting created a more detailed propagation loss model in an effort to improve the accuracy of the results by considering the influence of environmental variables ( e.g., bathymetry) at Hilcorp's specific well sites. Modeling was conducted using dBSea software. The fluid parabolic equation modeling algorithm was used with 5 Padé terms (see page 57 in Hilcorp's application, available at https://www.fisheries.noaa.gov/​action/​incidental-take-authorization-hilcorp-alaska-llc-oil-and-gas-activities-cook-inlet-alaska-0, for more detail) to calculate the TL between the source and the receiver at low frequencies ( 1/3 -octave bands, 31.5 Hertz (Hz) up to 1 kilohertz (kHz)). For higher frequencies (1 kHz up to 8 kHz) the ray tracing ( print page 77848) model was used with 1,000 reflections for each ray. Sound sources were assumed to be omnidirectional and modeled as points. The received sound levels for the project were calculated as follows: (1) One-third octave source spectral levels were obtained via reference spectral curves with subsequent corrections based on their corresponding overall source levels; (2) TL was modeled at one-third octave band central frequencies along 100 radial paths at regular increments around each source location, out to the maximum range of the bathymetry data set or until constrained by land; (3) The bathymetry variation of the vertical plane along each modeling path was obtained via interpolation of the bathymetry dataset which has 83 m grid resolution; (4) The one-third octave source levels and TL were combined to obtain the received levels as a function of range, depth, and frequency; and (5) The overall received levels were calculated at a 1 m depth resolution along each propagation path by summing all frequency band spectral levels.

Bathymetry data used in the model was collected from the NOAA National Centers for Environmental Information (AFSC 2019). Using NOAA's temperature and salinity data, sound speed profiles were computed for depths from 0 to 100 m for May, July, and October to capture the range of possible sound speed depending on the time of year Hilcorp's work could be conducted. These sound speed profiles were compiled using the Mackenzie Equation (1981) and are presented in table 8 of Hilcorp's application (available at https://www.fisheries.noaa.gov/​action/​incidental-take-authorization-hilcorp-alaska-llc-oil-and-gas-activities-cook-inlet-alaska-0). Geoacoustic parameters were also incorporated into the model. The parameters were based on substrate type and their relation to depth. These parameters are presented in table 9 of Hilcorp's application (available at https://www.fisheries.noaa.gov/​action/​incidental-take-authorization-hilcorp-alaska-llc-oil-and-gas-activities-cook-inlet-alaska-0).

Detailed broadband sound TL modeling in dBSea used the source level of 185 dB re 1 μPa at 1 m calculated in one-third octave band levels (31.5 Hz to 64,000 Hz) for frequency dependent solutions. The frequencies associated with tug sound sources occur within the hearing range of marine mammals in Cook Inlet. Received levels for each hearing marine mammal group based on one-third octave auditory weighting functions were also calculated and integrated into the modeling scenarios of dBSea. For modeling the distances to relevant PTS thresholds, a weighting factor adjustment was not used; instead, the data on the spectrum associated with their source was used and incorporated the full auditory weighting function for each marine mammal hearing group.

Furie plans to use the tugs towing the rig for two functions, rig positioning and towing. The activity was divided into two parts (stationary and mobile) and two approaches were taken for modeling the relevant isopleths.

SLR's model, described above, calculated the 120-dB isopleth propagating from three tugs towing a jack-up rig at 25 locations between Hilcorp platforms and well sites and the Rig Tenders Dock in Nikiski, Alaska. The average 120-dB isopleth across all locations and seasons was determined to be 3,850 m (Weston and SLR 2022). Given that Furie is conducting the same three tug activity as Hilcorp, also in middle Cook Inlet, Furie estimates, and NMFS concurs, that 3,850 m is also an appropriate estimate of its Level B harassment zone for tugging using three tugs. Similarly, Hilcorp modeled Level A harassment zones for each hearing group; Furie proposed using these Level A harassment zones for its towing and positioning activities using three tugs, and NMFS concurs. These zones are included in table 8.

As described in the Description of Proposed Activity section of the notice of the proposed IHA (89 FR 51102; June 14, 2024), when positioning the rig, Furie may use four tugs for up to 1 hour. Hilcorp did not model a 120-dB zone accounting for the use of four tugs. Furie estimated the Level B harassment zones for tugging and positioning with four tugs using a sound source level of 186.2 dB and a TL of 18.129.

NMFS estimated the Level A harassment zones from the use of four tugs using its User Spreadsheet and the Level A harassment zones modeled by Hilcorp for the use of three tugs. First, NMFS calculated the Level A harassment zones for the three tug scenario using the User Spreadsheet (sound source level of 185 dB, 5 hours of sound production, and a propagation loss coefficient of 18.129). Next, NMFS calculated the Level A harassment zones for the “combined scenario” (use of three tugs for 5 hours and four tugs for 1 hour, combined). NMFS then calculated the ratio between the three tug scenario and the combined scenario. For all hearing groups the combined scenario Level A harassment isopleths are 13.8 percent larger than the three tug scenario. Rather than using the Level A harassment isopleths for the combined scenario that were calculated using the User Spreadsheet, NMFS applied a 13.8 percent increase to the three tug Level A harassment isopleths modeled by Hilcorp, given that those isopleths are more conservative than the isopleths NMFS calculated using the User Spreadsheet. The Level A harassment isopleths that Furie will implement are included in table 8.

The 120-dB isopleth from the use of four tugs is 4,483 m, as described in Furie's application and included in table 6, calculated using a sound source level of 186.2 dB SPL. NMFS concurs and estimates a 120-dB zone of 4,483 m for the purpose of predicting the number of potential takes by Level B harassment from tugging and positioning using four tugs (Table 8).

Table 6—User Spreadsheet Inputs (Source Levels Provided in Table 5)

Source	Number of strikes per pile	Number of piles per day	Transmission loss coefficient
Conductor pipe pile, Day 1 (70 percent installation)	6,100	0.7	15
Conductor pipe pile, Day 2 (30 percent installation)		0.3

( print page 77849)

Table 7—Level A Harassment Isopleths Calculated Using NMFS' User Spreadsheet, and Used To Determine the Ratio Between the Three Tug Scenario and Three and Four Tugs Combined Scenario

Scenario	Level A harassment isopleth (m)
	Low-frequency cetaceans	Mid-frequency cetaceans	High- frequency cetaceans	Phocid pinnipeds	Otariid pinnipeds
Three Tug Scenario Level A harassment Isopleth	17.2	9.7	178.9	9.1	0.9
Combined Scenario Level A harassment Isopleth	19.6	11.0	203.6	10.3	1.0

The ensonified area associated with Level A harassment is more technically challenging to predict due to the need to account for a duration component. Therefore, NMFS developed an optional User Spreadsheet tool to accompany the Technical Guidance that can be used to relatively simply predict an isopleth distance for use in conjunction with marine mammal density or occurrence to help predict potential takes. We note that because of some of the assumptions included in the methods underlying this optional tool, we anticipate that the resulting isopleth estimates are typically overestimates of some degree, which may result in an overestimate of potential take by Level A harassment. However, this optional tool offers the best way to estimate isopleth distances when more sophisticated modeling methods are not available or practical. For stationary sources such as conductor pipe pile driving and rig positioning, the optional User Spreadsheet tool predicts the distance at which, if a marine mammal remained at that distance for the duration of the activity, it would be expected to incur PTS. For mobile sources such as tugging, the optional User Spreadsheet tool predicts the closest distance at which a stationary animal would not be expected to incur PTS if the sound source traveled by the stationary animal in a straight line at a constant speed. Inputs used in the optional User Spreadsheet tool, and the resulting estimated isopleths, are reported below.

Table 8—Level A Harassment and Level B Harassment Isopleths From Tugging and Impact Pile Driving

Sound source	Level A harassment isopleths (m)					Level B harassment isopleths (m)
	LF	MF	HF	PW	OW
Conductor pipe pile, 70 percent installation	3,064	109	3,650	1,640	119	1,585
Conductor pipe pile, 30 percent installation	1,742	62	2,075	932	68
Tugging/Positioning, 3 Tugs 1	95	78	679	69	0	3,850
Tugging/Positioning, 4 Tugs 2	108	89	773	79	1	4,483
1  These zones are results from Hilcorp's modeling.
2  For otariids, Hilcorp's model estimated a Level A harassment zone of 0 during tugging/positioning with three tugs. Therefore, for four tugs, NMFS applied the Level A harassment zone calculating with the User Spreadsheet.

Marine Mammal Occurrence

In this section we provide information about the occurrence of marine mammals, including density or other relevant information which will inform the take calculations.

Densities for marine mammals in Cook Inlet were derived from NMFS' Marine Mammal Laboratory (MML) aerial surveys, typically flown in June, from 2000 to 2018 (Rugh et al. 2005; Shelden et al. 2013, 2015, 2017, 2019). While the surveys are concentrated for a few days in June annually, which may skew densities for seasonally present species, they are still the best available long-term dataset of marine mammal sightings available in Cook Inlet. (Note that while more recent surveys have been conducted and published (Shelden et al. 2022; Goetz et al. 2023), the surveyed area was not included in either report, therefore they were not used to calculate density). Density was calculated by summing the total number of animals observed and dividing the number sighted by the area surveyed. The total number of animals observed accounts for both lower and upper Cook Inlet. There are no density estimates available for California sea lions and Pacific white-sided dolphins in Cook Inlet, as they are so infrequently sighted. Densities are presented in table 9.

Table 9—Marine Mammal Densities

Species	Density (individuals/km2 )
Humpback whale	0.00177
Minke whale	0.000009
Gray whale	0.000075
Fin whale	0.000311
Killer whale	0.000601
Beluga (Trading Bay)	0.004453-0.015053
Beluga (North Cook Inlet)	0.001664
Dall's porpoise	0.000154
Harbor porpoise	0.004386
Pacific white-sided dolphin	0
( print page 77850)
Harbor seal	0.241401
Steller sea lion	0.007609
California sea lion	0

For the beluga whale density, Furie, and subsequently NMFS, used the Goetz et al. (2012) habitat-based model. This model is derived from sightings and incorporates depth soundings, coastal substrate type, environmental sensitivity index, anthropogenic disturbance, and anadromous fish streams to predict densities throughout Cook Inlet. The output of this model is a beluga density map of Cook Inlet, which predicts spatially explicit density estimates for Cook Inlet belugas. Using the resulting grid densities, average densities were calculated for two regions applicable to Furie's operations. The densities applicable to the area of activity ( i.e., the North Cook Inlet Unit density for middle Cook Inlet activities and the Trading Bay density for activities in Trading Bay) are provided in table 9 and were carried forward to the take estimates. Likewise, when a range is given, the higher end of the range was conservatively used to calculate take estimates ( i.e., Trading Bay in the Goetz model has a range of 0.004453 to 0.015053; 0.015053 was used for the take estimates).

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 is authorized in each IHA.

Year 1 IHA

As described above, Furie plans to conduct rig towing and positioning and may install up to two conductor piles using an impact hammer in year 1. To quantify potential take by Level B harassment from tugging, acknowledging that there are contextual factors that make take less likely to result from this activity, for each species, Furie summed the estimated take for towing the rig at the beginning of the season, positioning the rig, and towing the rig at the end of the season. To estimate take for towing the rig (beginning and end of season), Furie multiplied the area of the Level B harassment zone (316.1 square kilometers (km² ); inclusive of the full potential tug path of 35 km) by the species density (table 9). To estimate take for positioning the rig, Furie multiplied the maximum area of the Level B harassment zone (63.1 km² , 4 tugs) by the species density (table 9), by the number of potential positioning attempts (2 attempts). NMFS concurs that this method for estimating take from tugging activities is appropriate.

To estimate take by Level B harassment from installation of conductor piles, Furie multiplied the Level B harassment zone (7.98 km² ) by the species density (table 9) by the estimated number of days that conductor pile installation would occur (4 days, 2 per pile). The Level B harassment zone used in the calculation conservatively assumes 70 percent installation of a conductor pile on a given day, and therefore, on 2 of the 4 days that conductor piles would be installed, the Level B harassment zone would likely be smaller. NMFS concurs that this method for estimating take from pile driving activities is appropriate.

NMFS summed the estimated take by Level B harassment from tugging and pile driving activities for each species. For species where the total calculated take by Level B harassment is less than the estimated group size for that species, NMFS rounded up the authorized take by Level B harassment to the anticipated group size. Authorized take during year 1 activities is included in table 10.

Based on the analysis described above, NMFS does did not authorize take by Level A harassment related to Furie's tugging activity. For mobile tugging activity, the distances to the PTS thresholds for high frequency cetaceans (the only hearing group for which modeling results in a Level A harassment zone greater than 0 m) are smaller than the overall size of the tug and rig configuration, making it unlikely a cetacean would remain close enough to the tug engines for a long enough duration to incur PTS. For stationary positioning of the rig, the PTS isopleths are up to 679 m for high frequency cetaceans, but calculated with the assumption that an animal would remain within several hundred meters of the rig for the full 5 hours of noise-producing activity which is unlikely. Therefore, take by Level A harassment due to stationary or mobile tugging is neither anticipated nor authorized.

For conductor pile installation, NMFS anticipates take by Level A harassment for harbor seal only. For all other species, calculated take by Level A harassment takes is less than one. Considering that along with the low likelihood that an individual of these species would enter and remain within the Level A harassment zone for long enough to incur PTS, particularly in consideration of implementation of required shutdown zones, Furie did not request, nor did NMFS authorize, take by Level A harassment. For harbor seal, NMFS authorized 3 takes by Level A harassment, conservatively rounded up from 2.7 Level A harassment takes calculated.

Table 10—Authorized Take by Level B Harassment, by Species, Activity, and in Total, Year ¹

Species	Rig tow, 3 tugs		Rig positioning, 4 tugs		Conductor pile installation		Total year 1 estimated take by Level B harassment	Authorized take by Level B harassment
	Ensonified area (km2 ) 1	Calculated take by Level B harassment 2	Ensonified area (km2 )	Calculated take by Level B harassment 3	Ensonified area (km2 )	Calculated take by Level B harassment 4
Humpback whale	316.1	1.2	63.1	0.2	7.89	0.06	1.5	3
Minke whale		0.006		0.001		0.0003	0.007	3
Gray whale		0.04		0.009		0.002	0.05	3
Fin whale		0.2		0.04		0.01	0.3	2
Killer whale		0.4		0.08		0.02	0.5	10
Beluga (Trading Bay)		0.5		0.2		0.05	0.8	11
Beluga (NCI)		4.8		NA		NA	4.8
( print page 77851)
Dall's porpoise		0.1		0.01		0.005	0.1	6
Harbor porpoise		2.8		0.3		0.1	3.2	12
Pacific white-sided dolphin		0.000		0.000		0.000	0.000	3
Harbor seal		152.6		15.2		7.6	175.4	176
Steller sea lion		4.8		0.5		0.2	5.5	6
California sea lion		0.000		0.000		0.000	0.000	2
1 This zone assumes a 35 km towing distance (the farthest potential distance that Furie may need to tow the rig).
2 Level B harassment zone area × density × 2 (towing at beginning and end of season), with the exception of Cook Inlet beluga whale. For Cook Inlet beluga whale, Furie used the Trading Bay density for the initial rig tow since the density is predicted to be higher there than in the North Cook Inlet Lease Unit (located offshore in middle Cook Inlet), and Furie may tug the rig though that area. Furie used the NCI density to estimate take for the end of season tow. NMFS concurs and has used these two separate densities in its analysis.
3 Level B harassment zone (63.1 km2 ) × species density (table 9) × number of potential positioning attempts (2).
4 Level B harassment zone (7.89 km2 ) × species density (table 9) × estimated number of days that conductor pile installation will occur (4).

Explanations for species for which the authorized take is greater than calculated take are included below.

Several recent surveys and monitoring programs have documented groups of humpback whales ranging up to 14 whales in size. During the annual survey, Shelden et al. (2022) recorded a group of three humpback whales west of Kachemak Bay in June of 2022. Past annual aerial surveys have documented groups up to 12 in number (Shelden et al. 2013, 2015, 2016, 2019). During Hilcorp's lower Cook Inlet seismic survey, group size ranged from 1 to 14 (Fairweather Science 2020). During monitoring of the Harvest Alaska Cross Inlet Pipeline (CIPL) project (the closest to Furie's Action Area), two sightings of three humpbacks were reported. During construction of the JRP in 2015, a group of 6 to 10 unidentified whales, thought to be either gray whales or humpbacks, was observed approximately 15 km northeast of the platform (Jacobs 2015). There were two sightings of three humpback whales observed near Ladd Landing north of the Forelands during the Harvest Alaska CIPL project (Sitkiewicz et al. 2018). Furie requested, and NMFS authorized, three takes of humpback whale by Level B harassment in year 1. This estimate accounts for the potential of take of a group of two animals and a solitary animal.

Groups of up to three minke whales have been recorded in recent years, including one group of three southeast of Kalgin Island (Lomac-MacNair et al. 2014). Other recent surveys in Cook Inlet typically have documented minkes traveling alone (Shelden et al. 2013, 2015, 2017; Kendall et al. 2015, as cited in Weston and SLR 2022; Fairweather Science 2020). As the occurrence of minke whales is expected to be less in middle Cook Inlet than lower Cook Inlet and considering the observed group sizes, Furie requested, and NMFS authorized, 3 takes of minke whale by Level B harassment in year 1 to account for the potential of take of a group of 3 minke whales.

During Apache's 2012 seismic program, nine gray whales were observed in June and July (Lomac-MacNair et al. 2013). During Apache's seismic program in 2014, one gray whale was observed (Lomac-MacNair et al. 2014). During construction of the JRP in 2015, 1 gray whale was documented approximately 5 km from the platform, and a group of 6 to 10 unidentified whales, thought to be either gray whales or humpbacks, was observed approximately 15 km northeast of the platform (Jacobs 2015). During SAExploration's seismic survey in 2015, the 2018 CIPL project, and Hilcorp's 2019 seismic survey, no gray whales were observed (Kendall et al. 2015; Sitkiewicz et al. 2018; Fairweather Science, 2020). None were observed during the 2018 CIPL project in middle Cook Inlet (Sitkiewicz et al. 2018). In 2020 and 2021, one gray whale was reported in each season at the POA (61N 2021, 2022a). The documented occasional presence of gray whales near and north of the project area suggests that gray whale density may be seasonally higher than the relatively low density suggested by the aerial surveys. Considering the project area is in middle Cook Inlet where sightings of gray whales are less common, Furie requested, and NMFS authorized, take of 3 gray whales in year 1.

During seismic surveys conducted in 2019 by Hilcorp in the lower Cook Inlet, fin whales were recorded in groups ranging in size from 1 to 15 individuals (Fairweather, 2020). During the NMFS aerial surveys in Cook Inlet from 2000 to 2018, 10 sightings of 26 estimated individual fin whales in lower Cook Inlet were observed (Shelden et al. 2013, 2015, 2016, 2019). Furie requested, and NMFS authorized, take of 1 group of 2 fin whales (the lower end of the range of common group sizes) in year 1.

Killer whales are typically sighted in pods of a few animals to 20 or more (NOAA, 2022a). During seismic surveys conducted in 2019 by Hilcorp in the lower Cook Inlet, 21 killer whales were observed, either as single individuals or in groups ranging in size from 2 to 5 individuals (Fairweather, 2020). Furie requested 10 takes by Level B harassment in year 1 to account for 2 groups of 5 animals. NMFS concurs and authorized 10 takes by Level B harassment of killer whale.

The 2018 MML aerial survey (Shelden and Wade 2019) estimated a median group size of approximately 11 beluga whales, although group sizes were highly variable (2 to 147 whales) as was the case in previous survey years (Boyd et al. 2019). Over 3 seasons of monitoring at the POA, 61N reported groups of up to 53 belugas, with a median group size of 3 and a mean group size of 4.4 (61N 2021, 2022a, 2022b, and 2022c). Additionally, vessel-based surveys in 2019 observed beluga whale groups in the Susitna River Delta (roughly 24 km (15 miles) north of the Tyonek Platform) that ranged from 5 to 200 animals (McGuire et al. 2022). The very large groups seen in the Susitna River Delta are not expected in Trading Bay or offshore areas near the JRP or the towing route for the Enterprise 151. However, smaller groups ( i.e., around the median group size) could be traveling through to access the Susitna River Delta and other nearby coastal locations, particularly in the shoulder seasons when belugas are more likely to occur in middle Cook Inlet. Few if any takes of beluga whale are anticipated during impact installation of the conductor piles. Therefore, Furie requested, and NMFS authorized, 11 ( print page 77852) takes by Level B harassment of beluga whale in year 1.

Dall's porpoises typically occur in groups averaging between 2 and 12 individuals (NOAA, 2024b). During seismic surveys conducted in 2019 by Hilcorp in the lower Cook Inlet, Dall's porpoises were observed in groups ranging in size from two to seven individuals (Fairweather, 2020). The 2012 Apache survey recorded two groups of three individual Dall's porpoises (Lomac-MacNair, 2014). Because occurrence of Dall's porpoise is anticipated to be less in middle Cook Inlet than lower Cook Inlet, the smaller end of documented group sizes (three individuals) is used. NMFS authorized six takes (two groups of three animals) by Level B harassment of Dall's porpoise in year 1.

Shelden et al. (2014) compiled historical sightings of harbor porpoises from lower to upper Cook Inlet that spanned from a few animals to 92 individuals. The 2018 CIPL project that occurred just north of the Action Area in Cook Inlet reported 29 sightings of 44 individuals (Sitkiewicz et al. 2018). While the duration of days that the tugs are towing a jack-up rig will be less than the CIPL project, given the increase in sightings of harbor porpoise in recent years, the sighting of harbor porpoise during Hilcorp's rig move in June 2022, and the inability to shut down the tugs, Furie requested, and NMFS authorized, 12 takes by Level B harassment of harbor porpoise. This accounts for two potential groups of six animals.

Calculated take of Pacific white-sided dolphin was zero because the estimated density is zero. However, in 2014, during Apache's seismic survey program, three Pacific white-sided dolphins were reported (Lomac-MacNair et al. 2014). They are considered rare in most of Cook Inlet, including in the lower entrance, but their presence was documented in Iniskin Bay and mid-inlet through passive acoustic recorders in 2019 (Castellote et al. 2020). Furie conservatively requested three takes based on the potential that a group similar in size to that encountered in 2014 could occur within the Level B harassment zone during project activities. NMFS concurs and has authorized three takes of Pacific white-sided dolphin by Level B harassment.

Calculated take of California sea lions was zero because the assumed density in Cook Inlet is zero. Any potential sightings would likely be of lone, out of habitat individuals. Two solitary individuals were seen during the 2012 Apache seismic survey in Cook Inlet (Lomac-MacNair et al. 2013). Furie requested two takes based on the potential that two lone animals could be sighted over a year of work, as was seen during Apache's year of work. NMFS concurs and has authorized two takes of California sea lion by Level B harassment.

Year 2 IHA

Given that Furie intends to conduct the same activities in year 2 as in year 1, authorized take by Level A harassment and Level B harassment for year 2 is the same as that authorized for year 1 (table 10).

Table 11—Authorized Take as a Percentage of Stock Abundance

Species	Stock	Abundance (Nbest)	Year 1		Year 2
			Total take (Level A and Level B harassment)	Take as a percentage of stock abundance	Total take (Level A and Level B harassment)	Take as a percentage of stock abundance
Humpback whale	Hawaii (Hawaii DPS)	11,278	3	<1	3	<1
	Mexico—North Pacific (Mexico DPS)	1  N/A		N/A		N/A
	Western North Pacific	1,084		<1		<1
Minke whale	Alaska	2  N/A	3	N/A	3	N/A
Gray whale	Eastern Pacific	26,960	3	<1	3	<1
Fin whale	Northeast Pacific	3  UND	2	N/A	2	N/A
Killer whale	Eastern North Pacific Alaska Resident	1,920	10	<1	10	<1
	Eastern North Pacific Gulf of Alaska, Aleutian Islands, and Bering Sea Transient	587		<1		<1
Beluga	Cook Inlet	4  279	11	3.9	11	3.9
Dall's porpoise	Alaska	5  UND	6	N/A	6	N/A
Harbor porpoise	Gulf of Alaska	31,046	12	<1	12	<1
Pacific white-sided dolphin	North Pacific	26,880	3	<1	3	<1
Harbor seal	Cook Inlet/Shelikof	28,411	179	<1	179	<1
Steller sea lion	Western U.S	6  49,932	6	<1	6	<1
California sea lion	U.S	257,606	2	<1	2	<1
1 Abundance estimates are based upon data collected more than 8 years ago and, therefore, current estimates are considered unknown.
2 Reliable population estimates are not available for this stock. Please see Friday et al. (2013) and Zerbini et al. (2006) for additional information on numbers of minke whales in Alaska.
3 The best available abundance estimate for this stock is not considered representative of the entire stock as surveys were limited to a small portion of the stock's range.
4 On June 15, 2023, NMFS released an updated abundance estimate for endangered Cook Inlet beluga whales in Alaska (Goetz et al. 2023). Data collected during NOAA Fisheries' 2022 aerial survey suggest that the whale population is stable or may be increasing slightly. Scientists estimated that the population size is between 290 and 386, with a median best estimate of 331. In accordance with the MMPA, this population estimate will be incorporated into the Cook Inlet beluga whale SAR, which will be reviewed by an independent panel of experts, the Alaska Scientific Review Group. After this review, the SAR will be made available as a draft for public review before being finalized. When the number of instances of takes is compared to this median abundance, the percent of the stock for which take is authorized is 3.3 percent.
5 The best available abundance estimate is likely an underestimate for the entire stock because it is based upon a survey that covered only a small portion of the stock's range.
6 Nest is best estimate of counts, which have not been corrected for animals at sea during abundance surveys.

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 ( print page 77853) 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.

In addition to the measures described in detail below, Furie will conduct briefings between conductor pipe installation supervisors, vessel captains and crew, and the marine mammal monitoring team before the start of all in-water work and when new personnel join the work to explain responsibilities, communication procedures, marine mammal monitoring protocol, and operational procedures.

Mitigation for Rig Tugging/Positioning

NMFS anticipates that there is a discountable potential for marine mammals to incur PTS from the tugging and positioning, as source levels are relatively low, non-impulsive, and animals would have to remain at very close distances for multiple hours to accumulate acoustic energy at levels that could damage hearing. Therefore, we do not believe there is reasonable potential for Level A harassment from rig tugging or positioning. However, Furie will implement a number of mitigation measures designed to reduce the potential for and severity of Level B harassment, and minimize the acoustic footprint of the project.

Protected Species Observers

Furie will station PSOs at the highest possible vantage point on either the rig or on one of the tugs.

Pre-Clearance and Post-Activity Monitoring

The tugs towing a rig are not able to shut down while transiting or positioning the rig. Furie will maneuver the tugs towing the rig such that they maintain a consistent speed (approximately 4 knots or less [7 km/hr]) and avoid multiple changes of speed and direction to make the course of the vessels as predictable as possible to marine mammals in the surrounding environment, characteristics that are expected to be associated with a lower likelihood of disturbance.

During tugging activities, Furie will implement a clearance zone of 1,500 m around the rig for all marine mammals other than Cook Inlet beluga whales. This clearance zone was determined to be appropriate as it is approximately twice as large as largest Level A harassment zone (table 10) and is a reasonable distance within which cryptic species ( e.g., porpoises, pinnipeds) could be observed. For Cook Inlet beluga whales, Furie will implement a clearance zone that extends as far as PSOs can feasibly observe for Cook Inlet beluga whales. Prior to commencing new activities during daylight hours or if there is a 30-minute lapse in operational activities, the PSOs will monitor the clearance zone for marine mammals for 30 minutes ( i.e., pre-clearance monitoring). (Note, transitioning from towing to positioning without shutting down is not considered commencing a new operational activity.) If no marine mammals are observed within the relevant clearance zone during this pre-clearance monitoring period, tugging activities may commence. If a non-beluga marine mammal(s) is observed within the relevant clearance zone during the pre-clearance monitoring period, tugging activities will be delayed, unless the delay interferes with the safety of working conditions. Operations will not commence until the PSO(s) observe that: (1) the non-beluga marine mammal(s) is outside of and on a path away from the clearance zone, or (2) for non-ESA-listed species, 15 minutes have elapsed without observing the marine mammal, or for ESA-listed species, 30 minutes have elapsed without observing the marine mammal. If a beluga whale is observed within the relevant clearance zone during those 30 minutes, operations may not commence until the beluga whale(s) is no longer detected at any range and 30 minutes have elapsed without any observations of beluga whales. PSOs must also conduct monitoring for marine mammals through 30 minutes post-completion of any tugging activity each day, and after each stoppage of 30 minutes or greater.

During nighttime hours or low/no-light conditions, night-vision devices (NVDs) shown to be effective at detecting marine mammals in low-light conditions ( e.g., Portable Visual Search-7 model, or similar) will be provided to PSOs to aid in their monitoring of marine mammals. Every effort will be made to observe that the relevant clearance zone is free of marine mammals by using night-vision devices and or the naked eye, however it may not always be possible to see and clear the entire clearance zones prior to nighttime transport. Prior to commencing new operational activities during nighttime hours, or if there is a 30-minute lapse in operational activities in low/no-light conditions, the PSOs must observe the extent visible while using night vision devices for 30 minutes ( i.e., pre-clearance monitoring). If no marine mammals are observed during this pre-clearance period, tugging activities may commence. If a marine mammal(s) is observed within the pre-clearance monitoring period, tugging activities will be delayed, unless the delay interferes with the safety of working conditions. Operations will not commence until the PSO(s) observe that: (1) the animal(s) is outside of the observable area; or (2) for non-ESA-listed species, 15 minutes have elapsed without observing the marine mammal, or for ESA-listed species, 30 minutes have elapsed without observing the marine mammal. Once the PSOs have determined one of those conditions are met, operations may commence.

Should a marine mammal be observed during towing or positioning of the rig, the PSOs will monitor and carefully record any reactions observed until the towing or positioning has concluded. PSOs will also collect behavioral information on marine mammals sighted during monitoring efforts.

Nighttime Work

Furie will conduct tug towing operations with the tide, resulting in a low power output from the tugs towing the rig, unless human safety or equipment integrity is at risk. Due to the nature of tidal cycles in Cook Inlet, it is possible the most favorable tide for the towing operation will occur during nighttime hours. Furie will only operate the tug towing activities at night if necessary to accommodate a favorable tide. Prior to commencing operational activities during nighttime hours or low/no-light conditions, Furie must implement the pre-clearance measures described above. ( print page 77854)

Susitna Delta

The Tyonek platform is within the Susitna Delta Exclusion Zone identified in Hilcorp's IHAs (87 FR 62364, October 14, 2022). If Hilcorp conducts work at the Tyonek platform, it will maintain operatorship and control of the Enterprise 151 until the tow is underway with lines taut and the Enterprise 151 is under tug power. Once the tow is underway, Furie representatives will take over operatorship of the Enterprise 151.

Out of concern for potential disturbance to Cook Inlet beluga whales in sensitive and essential habitat, Furie would maintain a distance of 2.4 km from the mean lower-low water (MLLW) line of the Susitna River Delta (Beluga River to the Little Susitna River) between April 15 and November 15. The dates of applicability of this exclusion zone have been expanded based on new available science, including visual surveys and acoustic studies, which indicate that substantial numbers of Cook Inlet beluga whales continue to occur in the Susitna Delta area through at least mid-November (M. Castellote, pers. comm., T. McGuire, pers. comm.).

Mitigation for Conductor Pile Installation

Furie must implement the following measures for impact driving of conductor piles.

Shutdown Zones

The purpose of a shutdown zone is generally to define an area within which shutdown of the activity will occur upon sighting of a marine mammal (or in anticipation of an animal entering the defined area). Construction supervisors and crews, PSOs, and relevant Furie staff must avoid direct physical interaction with marine mammals during construction activity. If a marine mammal comes within 10 m of such activity, operations must cease and vessels must reduce speed to the minimum level required to maintain steerage and safe working conditions, as necessary to avoid direct physical interaction. Further, Furie must implement shutdown zones as described in table 12. Furie states that if a shutdown or delay occurs, impact installation of the conductor pipe will not commence or resume until the animal has voluntarily left and been visually confirmed to be 100 m beyond the shutdown zone and on a trajectory away from the zone, or 30 minutes have passed without subsequent detections. If Cook Inlet beluga whales are observed within or approaching the Level B harassment zone for conductor pipe installation, impact installation of the conductor pipe will be delayed or halted until the beluga(s) have voluntarily left and been visually confirmed to be 100 m beyond the Level B harassment zone and on a trajectory away from the zone, or 30 minutes have passed without subsequent detections.

Table 12—Shutdown Zones for Conductor Pipe Pile Driving

Hearing group	Shutdown zone (m)
Low-frequency Cetaceans	2,000
Mid-frequency Cetaceans	110
High-frequency Cetaceans	400
Phocids	400
Otariids	120