2024-22293. Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to Hilcorp Alaska, LLC Production Drilling Support in Cook Inlet, Alaska

Table 1—Species ¹ With Estimated Take From 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
		Mexico-North Pacific	T, D, Y	N/A ⁶ (N/A, N/A, 2006)	UND	0.57
		Western North Pacific	E, D, Y	1,084 (0.088, 1,007, 2006)	3.4	5.82
Minke Whale	Balaenoptera acutorostrata	Alaska	-, -, N	N/A ⁷ (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
		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	North 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 ⁸ (0.061, 267, 2018)	0.53	0
Family Phocoenidae (porpoises):
Dall's Porpoise	Phocoenoides dalli	Alaska	-, -, N	UND ⁹ (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 Sea Lion	Eumetopias jubatus	Western	E, D, Y	49,837 ¹⁰ (N/A, 49,837, 2020)	299	267
Family Phocidae (earless seals):
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 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: 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 Reliable population estimates are not available for this stock. Please see Friday et al. (2013) and Zerbini et al. (2006) for additional information on numbers of minke whales in Alaska.
⁸ On June 15, 2023, NMFS released an updated abundance estimate for endangered Cook Inlet beluga whales (CIBWs) in Alaska (Goetz et al., 2023). Data collected during NOAA Fisheries' 2022 aerial survey suggest that the whale population is stable or may be increasing slightly. Scientists estimated that the population size is between 290 and 386, with a median best estimate of 331. In accordance with the MMPA, this population estimate will be incorporated into the CIBW SAR, which will be reviewed by an independent panel of experts, the Alaska Scientific Review Group. After this review, the SAR will be made available as a draft for public review before being finalized.
⁹ The best available abundance estimate is likely an underestimate for the entire stock because it is based upon a survey that covered only a small portion of the stock's range.
¹⁰ Nest is best estimate of counts, which have not been corrected for animals at sea during abundance surveys.

As indicated above, all 12 species (with 15 managed stocks) in table 1 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 Hilcorp's tugging 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 60164, July 24, 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 ( print page 79540) underwater, and exposure to anthropogenic sound can have deleterious effects. To appropriately assess the potential effects of exposure to sound, it is necessary to understand the frequency ranges marine mammals are able to hear. Not all marine mammal species have equal hearing capabilities ( e.g., Richardson et al., 1995; Wartzok and Ketten, 1999; Au and Hastings, 2008). To reflect this, Southall et al. (2007, 2019) recommended that marine mammals be divided into hearing groups based on directly measured (behavioral or auditory evoked potential techniques) or estimated hearing ranges (behavioral response data, anatomical modeling, etc.). Subsequently, NMFS (2018) described generalized hearing ranges for these marine mammal hearing groups. Generalized hearing ranges were chosen based on the approximately 65 decibel (dB) threshold from the normalized composite audiograms, with the exception for lower limits for low-frequency cetaceans where the lower bound was deemed to be biologically implausible and the lower bound from Southall et al. (2007) retained. Marine mammal hearing groups and their associated hearing ranges are provided in table 2. Specific to this action, gray whales, fin whales, minke whales, and humpback whales are considered low-frequency (LF) cetaceans, beluga whales, pacific white-sided dolphins, and killer whales are considered mid-frequency (MF) cetaceans, harbor porpoises and Dall's porpoises are considered high-frequency (HF) cetaceans, Steller sea lions and California sea lions are otariid pinnipeds (OW), and harbor seals are phocid pinnipeds (PW).

Table 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).

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 Hilcorp's tugging activities have the potential to result in harassment of marine mammals in the vicinity of the project area. The notice of proposed IHA (89 FR 60164, July 24, 2024) included a discussion of the effects of anthropogenic noise on marine mammals and the potential effects of underwater noise from tugging activities 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 60164, July 24, 2024).

Estimated Take of Marine Mammals

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

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

Authorized takes will be by Level B harassment only, as use of the acoustic sources ( i.e., tugging activities) 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, holding, 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. The required mitigation and monitoring measures are expected to minimize the potential for take and, if take were to occur, the severity of the taking to the extent practicable. Based on the nature of the activity ( e.g., the very small area ensonified above the Level A harassment threshold), Level A harassment is neither anticipated nor authorized.

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 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 multiple 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 lower 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 (absent relevant contextual factors) or incur some degree of permanent hearing impairment where relevant; (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 ( print page 79541) 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., Richardson et al., 1995; Southall et al. 2007, 2021, Ellison et al. 2012). Based on what the available science indicates and the practical need to use a threshold based on a metric that is both predictable and measurable for most activities, NMFS typically uses a generalized acoustic threshold based on received level to 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 behaviorally disturbed in a manner considered to be Level B harassment when exposed to underwater anthropogenic noise above root-mean-squared pressure received levels (root mean square [RMS] sound pressure level [SPL]) of 120 dB (referenced to 1 micropascal (re 1 μPa)) for continuous sources ( e.g., tugging, 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 TTS as, in most cases, the likelihood of TTS occurs at distances from the source smaller than those at which behavioral harassment is likely. TTS of a sufficient degree can manifest as behavioral harassment, as reduced hearing sensitivity and the potential reduced opportunities to detect important signals (conspecific communication, predators, prey) may result in changes in behavior patterns that would not otherwise occur.

Hilcorp's planned activity includes the use of continuous sources (tugging activities), and therefore the RMS SPL threshold of 120 dB is applicable.

Level A harassment —NMFS' Technical Guidance for Assessing the Effects of Anthropogenic Sound on Marine Mammal Hearing (Version 2.0) (Technical Guidance, 2018) identifies dual criteria to assess auditory injury (Level A harassment) to five different marine mammal groups (based on hearing sensitivity) as a result of exposure to noise from two different types of sources (impulsive or non-impulsive). Hilcorp's planned activity includes the use of non-impulsive sources ( i.e., tugging activities).

The thresholds identifying the onset of PTS are provided in table 3 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. Take by Level A harassment is considered unlikely for this action because of the small estimated Level A harassment zones resulting from tugs under load with a jack-up rig ( i.e., <1 m) (as described below), the mobile nature of both the activity itself and marine mammals in the project area, and the required mitigation and monitoring program (see the Mitigation and Monitoring sections of this notice).

Table 3—Thresholds Identifying the Onset of PTS
Hearing group	PTS onset acoustic thresholds * (received level)
Hearing group	Impulsive	Non-impulsive
Low-Frequency (LF) Cetaceans	Cell 1:L_pk,flat : 219 dB; L_E,LF,24h : 183 dB	Cell 2:L_E,LF,24h : 199 dB.
Mid-Frequency (MF) Cetaceans	Cell 3:L_pk,flat : 230 dB; L_E,MF,24h : 185 dB	Cell 4:L_E,MF,24h : 198 dB.
High-Frequency (HF) Cetaceans	Cell 5:L_pk,flat : 202 dB; L_E,HF,24h : 155 dB	Cell 6:L_E,HF,24h : 173 dB.
Phocid Pinnipeds (PW) (Underwater)	Cell 7:L_pk,flat : 218 dB; L_E,PW,24h : 185 dB	Cell 8:L_E,PW,24h : 201 dB.
Otariid Pinnipeds (OW) (Underwater)	Cell 9:L_pk,flat : 232 dB; L_E,OW,24h : 203 dB	Cell 10:L_E,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 ( L_pk ) has a reference value of 1 µPa, and cumulative sound exposure level ( L_E ) 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 resulting from the planned project. Marine mammals are expected to be affected via sound generated by the primary components of the project ( i.e., tugging activities). Calculation of the area ensonified by the planned action is dependent on the background sound levels at the project ( print page 79542) site, the source levels of the planned activities, and the estimated TL coefficients for the planned activities at the site. These factors are addressed below.

Sound Source Levels of Tugging Activities. The project includes three to four tugs under load with a jack-up rig. Hilcorp conducted a literature review of underwater sound emissions of tugs under various loading efforts. The sound source levels for tugs of various horsepower (2,000 to 8,200) under load can range from approximately 164 dB RMS to 202 dB RMS. This range largely relates to the level of operational effort, with full power output and higher speeds generating more propeller cavitation and hence greater sound source levels than lower power output and lower speeds. Tugs under tow produce higher source levels than tugs transiting with no load because of the higher power output necessary to pull the load. The amount of power the tugs expend while operating is the best predictor of relative sound source level. Several factors will determine the duration that the tugboats are towing the jack-up rig, including the origin and destination of the towing route ( e.g., Rig Tenders Dock, an existing platform) and the tidal conditions. The power output will be variable and influenced by the prevailing wind direction and velocity, the current velocity, and the tidal stage. Unless human safety or equipment integrity are at risk, transport will be timed with the tide to minimize towing duration and power output.

Hilcorp's literature review identified no existing data on sound source levels of tugs towing jack-up rigs. Accordingly, for this analysis, Hilcorp considered data from tug-under-load activities, including berthing and towing activities. Austin and Warner (2013) measured 167 dB RMS for tug towing barge activity in Cook Inlet. Blackwell and Greene (2002) reported berthing activities in the POA with a source level of 179 dB RMS. Laurinolli et al. (2005) measured a source level of 200 dB RMS for anchor towing activities by a tugboat in the Strait of Juan de Fuca, WA. The Roberts Bank Terminal 2 study (2014) repeated measurements of the same tug operating under different speeds and loading conditions. Broadband measurements from this study ranged from approximately 162 dB RMS up to 200 dB RMS.

The rig manager for Hilcorp, who is experienced with towing jack-up rigs in Cook Inlet, described operational conditions wherein the tugs generally operate at half power or less for the majority of the time they are under load (pers. Comm., Durham, 2021). Transits with the tide (lower power output) are preferred for safety reasons, and effort is made to reduce or eliminate traveling against the tide (higher power output). The Roberts Bank Terminal 2 study (2014) allowed for a comparison of source levels from the same vessel (Seaspan Resolution tug) at half power versus full power. Seaspan Resolution's half-power ( i.e., 50 percent) berthing scenario had a sound source level of 180 dB RMS. In addition, the Roberts Bank Terminal 2 Study (2014) reported a mean tug source level of 179.3 dB RMS from 650 tug transits under varying load and speed conditions.

The 50 percent (or less) power output scenario will occur during the vast majority of tug towing jack-up rig activity. Therefore, based on Hilcorp's literature review, a source level of 180 dB RMS was found to be an appropriate proxy source level for a single tug under load based on the Roberts Bank Terminal 2 study. If all three tugs were operating simultaneously at 180 dB RMS, the overall source emission levels will be expected to increase by approximately 5 dB when logarithmically adding the sources ( i.e., to 185 dB RMS). To further support this level as an appropriate proxy, a sound source verification (SSV) study performed by JASCO Applied Sciences (JASCO) in Cook Inlet in October 2021 (Lawrence et al., 2022) measured the sound source level from three tugs pulling a jack-up rig in Cook Inlet at various power outputs. Lawrence et al. (2022) reported a source level of 167.3 dB RMS for the 20 percent-power scenario and a source level of 205.9 dB RMS for the 85 percent-power scenario. Assuming a linear scaling of tug power, a source level of 185 dB RMS was calculated as a single point source level for three tugs operating at 50 percent power output. Because the 2021 Cook Inlet SSV measurements by JASCO represent the most recent best available data, and because multiple tugs may be operating simultaneously, the analyses presented below use a mean tug sound source level scenario of 185 dB RMS to calculate the 120-dB isopleths for three tugs operating at 50 percent power output. In practice, the load condition of the three tugs is unlikely to be identical at all times, so sound emissions will be dominated by the single tug in the group that is working hardest at any point in time.

Further modeling was done to account for one additional tug working for 1 hour at 50 percent power during jack-up rig positioning, a stationary activity. This is equivalent in terms of acoustic energy to three tugs operating at 180.0 dB RMS (each of them) for 4 hours, joined by a fourth tug for 1 hour, increasing the source level to 186.0 dB RMS only during the 1-hour period (the logarithmic sum of four tugs working together at 180.0 dB RMS). A sound exposure level (SEL) of 185.1 dB was used to account for the cumulative sound exposure when calculating Level A harassment by adding a 4th tug operating at 50 percent power for 20 percent of the 5-hour period. This is equivalent in terms of acoustic energy to three tugs operating at 185.0 dB for 4 hours, joined by a fourth tug for 1 hour, increasing the source level to 186.0 dB only during the 1-hour period. The use of the 20 percent duty cycle was a computational requirement and, although equal in terms of overall energy and determination of impacts, should not be confused with the actual instantaneous SPL (see section 6.2.1.1 of Hilcorp's application for additional computational details).

In summary, Hilcorp proposed to use a source level of 185.0 dB RMS to calculate the stationary 120-dB isopleth where three tugs were under load for 4 hours with a 50 percent power output and a source level of 186.0 dB RMS to calculate the stationary 120-dB isopleth where four tugs were under load for 1 hour with a 50 percent power output. Further, Hilcorp proposed to use a source level of 185.1 dB SEL to calculate the stationary Level A harassment isopleths where three tugs were underload for 4 hours and then one tug joined for 1 additional hour. Lastly, Hilcorp proposed to use the 185.0 dB RMS level to model the mobile Level A harassment isopleths for three tugs under load with a 50 percent power output. NMFS concurs that Hilcorp's proposed source levels are appropriate.

Underwater Sound Propagation Modeling. Hilcorp contracted SLR Consulting to model the extent of the harassment isopleths for tugs under load with a jack-up rig during their planned activities. Cook Inlet is a particularly complex acoustic environment with strong currents, large tides, variable sea floor and generally changing conditions. Accordingly, Hilcorp applied a more detailed propagation model than the “practical spreading loss” approach that uses a factor of 15. The objective of a more detailed propagation calculation is to improve the representation of the influence of some environmental variables, in particular by accounting for bathymetry and specific sound source locations and frequency-dependent propagation effects.

Modeling was conducted using the dBSea software package. The fluid parabolic equation modeling algorithm was used with 5 Padé terms to calculate ( print page 79543) the TL between the source and the receiver at low frequencies (1/3-octave bands, 31.5 Hz up to 1 kHz). For higher frequencies (1 kHz up to 8 kHz) the ray tracing model was used with 1,000 reflections for each ray. Sound sources were assumed to be omnidirectional and modeled as points. The received sound levels for the project were calculated as follows: (1) One-third octave source spectral levels were obtained via reference spectral curves with subsequent corrections based on their corresponding overall source levels; (2) TL was modeled at one-third octave band central frequencies along 100 radial paths at regular increments around each source location, out to the maximum range of the bathymetry data set or until constrained by land; (3) The bathymetry variation of the vertical plane along each modeling path was obtained via interpolation of the bathymetry dataset which has 83 m grid resolution; (4) The one-third octave source levels and transmission loss were combined to obtain the received levels as a function of range, depth, and frequency; and (5) The overall received levels were calculated at a 1-m depth resolution along each propagation path by summing all frequency band spectral levels.

Model Inputs. Bathymetry data used in the model was collected from the NOAA National Centers for Environmental Information (AFSC, 2019). Using NOAA's temperature and salinity data, sound speed profiles were computed for depths from 0 to 100 m for May, July, and October to capture the range of possible sound speed depending on the time of year Hilcorp's work could be conducted. These sound speed profiles were compiled using the Mackenzie Equation (1981) and are presented in table 8 of Hilcorp's application (available at 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 transmission loss modeling in dBSea used the source level of 185 dB RMS calculated in one-third octave band levels (31.5 Hz to 64,000 Hz) for frequency dependent solutions. The frequencies associated with tug sound sources occur within the hearing range of marine mammals in Cook Inlet. Received levels for each hearing marine mammal group based on one-third octave auditory weighting functions were also calculated and integrated into the modeling scenarios of dBSea. For modeling the distances to relevant PTS thresholds, a weighting factor adjustment was not used; instead, the data on the spectrum associated with their source was used and incorporated the full auditory weighting function for each marine mammal hearing group.

The tugs towing the jack-up rig represent a mobile sound source, while tugs holding and positioning the jack-up rig on a platform are more akin to a stationary sound source. In addition, three tugs will be used for towing (mobile) and holding and positioning (stationary) and up to four tugs could be used for positioning (stationary). Consequently, sound TL modeling was undertaken for the various stationary and mobile scenarios for three and four tugs to generate the distances to the 120-dB (relevant Level B) and Level A harassment isopleths.

For acoustic modeling of the stationary Level A harassment isopleths, two locations representative of where tugs will be stationary while they position the jack-up rig were selected in middle Cook Inlet near the Tyonek platform and in lower Trading Bay where the production platforms are located. To account for the mobile scenarios, the acoustic model calculated the Level A harassment isopleths along a representative route from the Rig Tenders dock in Nikiski to the Tyonek platform, the northernmost platform in Cook Inlet (representing middle Cook Inlet), as well as from the Tyonek Platform to the Dolly Varden platform in lower Trading Bay, then from the Dolly Varden platform back to the Rig Tenders Dock in Nikiski. Note that this route is representative of a typical route the tugs may take; the specific route is not yet known, as the order in which platforms will be drilled with the jack-up rig is not yet known. The locations represent a range of water depths from 18 to 77 m found throughout the project area.

For mobile Level B harassment and stationary Level B harassment with three tugs, the average distance to the 120 dB RMS threshold was based on the assessment of 100 radials at 25 locations across seasons (May, July, and October) and represented the average 120-dB isopleth for each season and location (table 4). The result is a mobile and stationary 120-dB isopleth of 3,850 m when three tugs are used (table 4). For four stationary tugs, the average distance to the 120 dB threshold was based on 100 radials at two locations, one in Trading Bay and one in middle Cook Inlet, across seasons (May, July, and October) and represents the average 120-dB isopleth for each season and location. The result is a stationary 120-dB isopleth of 4,453 m when four tugs are in use (table 5). NMFS concurs that 3,850 m and 4,453 m are appropriate estimates for the extent of the 120-dB isopleths for Hilcorp's towing, holding, and positioning activities when using three and four tugs, respectively, for the purpose of predicting the number of potential takes by Level B harassment.

Table 4—Average Distances to the 120- d B Threshold for Three Tugs Towing (Mobile) and Holding and Positioning for 4 Hours (Stationary)
Location	Average distance to 120-dB threshold (m)			Season average distance to 120-dB threshold (m)
Location	May	July	October	Season average distance to 120-dB threshold (m)
M1	4,215	3,911	4,352	4,159
M2	3,946	3,841	4,350	4,046
M3	4,156	3,971	4,458	4,195
M4	4,040	3,844	4,364	4,083
M5	4,053	3,676	4,304	4,011
M6	3,716	3,445	3,554	3,572
M7	2,947	2,753	2,898	2,866
M8	3,270	3,008	3,247	3,175
( print page 79544)
M9	3,567	3,359	3,727	3,551
M10	3,600	3,487	3,691	3,593
M11	3,746	3,579	4,214	3,846
M12	3,815	3,600	3,995	3,803
M13	4,010	3,831	4,338	4,060
M14	3,837	3,647	4,217	3,900
M15	3,966	3,798	4,455	4,073
M16	3,873	3,676	4,504	4,018
M18	5,562	3,893	4,626	4,694
M20	5,044	3,692	4,320	4,352
M22	4,717	3,553	4,067	4,112
M24	4,456	3,384	4,182	4,007
M25	3,842	3,686	4,218	3,915
M26	3,690	3,400	3,801	3,630
M27	3,707	3,497	3,711	3,638
M28	3,546	3,271	3,480	3,432
M29	3,618	3,279	3,646	3,514
Average	3,958	3,563	4,029	3,850

Table 5—Average Distances to the 120- d B Threshold for Four Tugs Positioning (Stationary) for 1 Hour
Location	Average distance to 120-dB threshold (m)			Season average distance to 120-dB threshold (m)
Location	May	July	October	Season average distance to 120-dB threshold (m)
Trading Bay	4,610	3,850	4,810	4,423
Middle CI	4,820	4,130	4,500	4,483
Average	4,715	3,990	4,655	4,453

The average Level A harassment distances for the stationary, four tug scenario were calculated assuming a SEL of 185.1 dB for a 5-hour exposure duration (table 6). For the mobile, three tug scenario, the average Level A harassment distances were calculated assuming a SEL of 185.0 dB with an 18-second exposure period (table 7). This 18-second exposure was derived using the standard TL equation (Source Level−TL = Received Level) for determining threshold distance (R [m]), where TL = 15Log10. In this case, the equation was 185.0 dB−15Log10 = 173 dB. Solving for threshold distance (R) yields a distance of approximately 6 m, which was then used as the preliminary ensonified radius to determine the duration of time it would take for the ensonified area of the sound source traveling at a speed of 2.06 m/s (4 knots) to pass a marine mammal. The duration (twice the radius divided by speed of the source) that the ensonified area of a single tug would take to pass a marine mammal under these conditions is 6 seconds. An 18-second exposure was used in the model to reflect the time it would take for three ensonified areas (from three consecutive individual tugs) to pass a single point that represents a marine mammal (6 seconds + 6 seconds + 6 seconds = 18 seconds).

Table 6—Average Distances to the Level A Harassment Thresholds for Four Stationary Tugs Under Load With a Jack-Up Rig for 5 Hours
Location	Season	Average distance (m) to Level A harassment threshold by functional hearing group
Location	Season	LF	MF	HF	PW	OW ¹
Trading Bay	May	107	77	792	64
Trading Bay	July	132	80	758	66
Trading Bay	October	105	75	784	79
Middle Cook Inlet	May	86	85	712	78
Middle Cook Inlet	July	95	89	718	80
Middle Cook Inlet	October	82	86	730	80
( print page 79545)
Average		102	82	749	75	0
¹ The Level A harassment distances are smaller than the footprint of the tugs.

Table 7—Average Distances to the Level A Harassment Thresholds for Three Mobile Tugs Under Load With a Jack-Up Rig Assuming an 18-Second Exposure Duration
Location	Season	Average distance (m) to Level A threshold by functional hearing group
Location	Season	LF ¹	MF ¹	HF	PW ¹	OW ¹
M2	May			10
M2	July			5
M2	October			10
M11	May			10
M11	July			5
M11	October			10
M22	May			10
M22	July			5
M22	October			10
Average		0	0	8	0	0
¹ The Level A harassment distances are smaller than the footprint of the tugs.

Tugs are anticipated to be towing the jack-up rig between platforms and considered a mobile sound source for 6 hours in a single day per jack-up rig move. Tugs are anticipated to be towing the jack-up rig and considered a mobile source during demobilization and mobilization to/from Rig Tenders Dock in Nikiski for 9 hours. One jack-up rig move between platforms is planned during the IHA period. Tugs are anticipated to be holding or positioning the jack-up rig at the platforms or Rig Tenders Dock during demobilization and mobilization and are considered a stationary sound source for 5 hours in the first day and 5 hours in the second day if a second attempt to pin the jack-up rig is required due to the first pinning event being unsuccessful. A second attempt was built into the exposure estimate for each pinning event; three total pinning events are anticipated during the IHA period for production drilling.

The ensonified area for a location-to-location transport for production drilling represents a rig move between two production platforms in middle Cook Inlet and/or Trading Bay and includes 6 mobile hours over an average distance of 16.77 km in a single day and 5 stationary hours on the first day and 5 stationary hours on a second day. The 5 stationary hours are further broken into 4 hours with three tugs under load and 1 hour with four tugs under load. One location-to-location jack-up rig move is planned for the IHA period.

The ensonified area for production drilling demobilization and mobilization represents a rig move from a production platform in middle Cook Inlet to Rig Tenders Dock in Nikiski and reverse for mobilization and includes 9 mobile hours over a distance of up to 64.34 km in a single day and 5 stationary hours on the first day and 5 stationary hours on a second day, which are further broken into the same three tugs working for 4 hours and four tugs working for 1 hour as mentioned above. A summary of the estimated Level A and Level B harassment distances and areas for the various tugging scenarios is provided in table 8.

Table 8—Average Distances and Areas to the Estimated Level A and Level B Harassment Thresholds for the Various Tugging Scenarios
Activity	Level A harassment distance (m)/area (km² )					Level B harassment distance (m)/area (km² )
Activity	LF	MF	HF	PW	OW	Level B harassment distance (m)/area (km² )
Demobilization/Mobilization
3 Tugs Towing a Jack-Up Rig—Mobile	(¹ )	(¹ )	8/1.07	(¹ )	(¹ )	3,850/541.96
3 Tugs Towing a Jack-Up Rig—Stationary for up to 4 hours	102/0.03	82/0.02	749/1.76	75/0.02	(¹ )	3,850/46.56
4 Tugs Towing a Jack-Up Rig—Stationary for up to 1 hour	102/0.03	82/0.02	749/1.76	75/0.02	(¹ )	4,453/62.30
Location-to-Location
3 Tugs Towing a Jack-Up Rig—Mobile	(¹ )	(¹ )	8/0.28	(¹ )	(¹ )	3,850/175.6
3 Tugs Towing a Jack-Up Rig—Stationary for up to 4 hours	102/0.03	82/0.02	749/1.76	75/0.02	(¹ )	3,850/46.56
4 Tugs Towing a Jack-Up Rig—Stationary for up to 1 hour	102/0.03	82/0.02	749/1.76	75/0.02	(¹ )	4,453/62.30
¹ The Level A harassment distances are smaller than the footprint of the tugs.

( print page 79546)

Marine Mammal Occurrence

In this section we provide information about the occurrence of marine mammals, including density or other relevant information that informed 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 2022 (Rugh et al., 2005; Shelden et al., 2013, 2015b, 2017, 2019, 2022; Goetz, et al. 2023). While the surveys are concentrated for a few days in summer annually, which may skew densities for seasonally present species, they represent the best available long-term dataset of marine mammal sightings available in Cook Inlet. Densities were calculated by summing the total number of animals observed during the MML surveys and dividing the number sighted by the approximate area of Cook Inlet. For CIBWs, several correction factors were applied to the density estimates to address perception, availability, and proximity bias; correction factors were not applied to the non-CIBW density estimates. For CIBWs, densities were derived for the entirety of Cook Inlet as well as for middle and lower Cook Inlet; for non-CIBW marine mammals densities account 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 were so infrequently sighted. Average densities across survey years are presented in table 9.

Table 9—Average Densities of Marine Mammal Species in Cook Inlet ¹
Species	Density (individuals per km² )
Humpback whale	0.00185
Minke whale	0.00003
Gray whale	0.00007
Fin whale	0.00028
Killer whale	0.00061
Beluga whale (Entire Cook Inlet)	0.07166
Beluga whale (Middle Cook Inlet)	0.00658
Beluga whale (Lower Cook Inlet)	0.00003
Beluga whale (North Cook Inlet) ²	0.00166
Beluga whale (Lower Cook Inlet) ²	0.00000
Beluga whale (Trading Bay) ²	0.01505
Dall's porpoise	0.00014
Harbor porpoise	0.00380
Pacific white-sided dolphin	³ N/A
Harbor seal	0.26819
Steller sea lion	0.00669
California sea lion	³ N/A
¹ Density estimates are derived from MML surveys unless otherwise identified.
² Density estimates are derived from the Goetz et al. (2012a) habitat-based model.
³ Density estimates are not available in Cook Inlet for this species.

CIBW densities estimated from the MML surveys across regions are low, however, there is a known effect of seasonality on their distribution. Thus, densities derived directly from these summer surveys might underestimate the density of CIBWs in lower Cook Inlet at other ice-free times of the year. Therefore, additional CIBW densities were considered as a comparison of available data. The other mechanism for arriving at CIBW density considered here is the Goetz et al. (2012a) 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 density map of Cook Inlet, which predicts spatially explicit density estimates for CIBW. Using the resulting grid densities, average densities were calculated for two regions applicable to Hilcorp's operations (table 9). 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 above and were carried forward to the exposure estimates as they were deemed to likely be the most representative estimates available. Likewise, when a range is given, the higher end of the range was used out of caution to calculate exposure estimates ( i.e., Trading Bay in the Goetz model has a range of 0.004453 to 0.015053; 0.015053 was used for the exposure estimates).

Take Estimation

Here we describe how the information provided above was synthesized to produce a quantitative estimate of the take that could occur and is authorized.

As described above, Hilcorp's tugging activity considers a total of three rig moves across 6 days (one 2-day location-to-location jack-up rig move, one 2-day demobilization effort, and one 2-day mobilization effort). For the location-to-location move, Hilcorp assumed 6 hours of mobile (towing) and 5 hours of stationary (holding and positioning) activities on the first day, and 5 hours of the stationary activity (4 hours with three tugs and 1 hour with four tugs) on the second day to account for two positioning attempts (across 2 days). For the demobilization and mobilization efforts, Hilcorp assumed 9 hours of mobile and 5 hours of stationary (4 hours with three tugs and 1 hour with four tugs) activities on the first day, and 5 hours of stationary (4 hours with three tugs and 1 hour with four tugs) activities on the second day (across 2 days for each effort, for a total of 4 days of tugs under load with a jack-up rigs).

Potential take by Level A harassment was quantified by multiplying the ensonified Level A harassment areas per tugging activity scenario for each functional hearing group (table 8) by the estimated marine mammal densities (table 9) to get an estimate of exposures per day. This value was then multiplied by the number of days per move and the number of moves of that type of activity scenario. The estimated exposures by activity scenario were then summed to result in a number of exposures for all tugging activities. Based on this ( print page 79547) analysis, only Dall's porpoise, harbor porpoise, and harbor seals had potential estimated take by Level A harassment that was greater than zero: 0.001, 0.018, and 0.006, respectively. For mobile tugging, the distances to the PTS thresholds for HF cetaceans and phocids are smaller than the overall size of the tug and rig configuration ( i.e., 8 m and 0 m, respectively), making it unlikely an animal will remain close enough to the tug engines to incur PTS. For stationary positioning of the jack up rig, the PTS isopleths for both the 3-tug and 4-tug scenarios are up to 749 m for HF cetaceans and up to 102 m for all other species, but calculated on the assumption that an animal would remain within several hundred meters of the jack-up rig for the full 5 hours of noise-producing activity. Given the location of the activity is not in an area known to be essential habitat for any marine mammal species with extreme site fidelity over the course of 2 days, in addition to the low exposure estimates for take by Level A harassment ( i.e., ≤0.18 for all species), the mobile nature of marine mammals, and the general tendencies of most marine mammals to avoid loud noises, the occurrence of PTS is unlikely and thus not authorized for any species.

The ensonified Level B harassment areas calculated per activity scenario (three tug stationary, four tug stationary, and three tug mobile for the location-to-location move and the demobilization and mobilization efforts) for a single day (see table 8) were multiplied by marine mammal densities to estimate takes by Level B harassment per day, acknowledging that there are contextual factors that make take less likely to result from this activity. This was then multiplied by the number of days per move and the number of moves of that type of activity scenario to arrive at the number of estimated exposures above 120 dB per activity type. These exposures by activity scenario were then summed to result in a number of exposures for all Hilcorp's tugging activities during the IHA period (table 10). As exposure estimates were calculated based on specific potential rig moves or well locations, the density value for CIBWs that was carried through the estimate was the higher density value for that particular location (table 9; i.e., 0.00658 for locations in middle Cook Inlet and 0.01505 for locations in Trading Bay). There are no estimated exposures based on this method of calculation for California sea lions and Pacific white-sided dolphins because the assumed density of these species in the project area is 0.00 animals per km² . Table 10 also indicates the number of takes, by Level B harassment, authorized. For species where the total calculated exposures above the Level B harassment threshold is less than the estimated group size for that species, NMFS adjusted the take authorized up to the anticipated group size. Explanations for species for which take authorized is greater than the calculated take are included below.

Table 10—Calculated Exposures and Total Authorized Take by Level B Harassment, by Species and Stock, for Hilcorp's Tugging Activities
Scenario	Location-to-location			Demobilization/mobilization			Total calculated Level B harassment exposures	Total authorized take by Level B harassment
Scenario	3 Mobile tugs	3 Stationary tugs	4 Stationary tugs	3 Mobile tugs	3 Stationary tugs	4 Stationary tugs	Total calculated Level B harassment exposures	Total authorized take by Level B harassment
Level B Harassment Area (km² )	175.67	46.56	62.30	541.96	46.56	62.30
Species	Calculated Exposures above the Level B Harassment threshold
Humpback whale	0.324	0.029	0.010	2.001	0.057	0.019	2.440	3
Minke whale	0.005	0.000	0.000	0.031	0.001	0.000	0.037	3
Gray whale	0.012	0.001	0.000	0.072	0.002	0.001	0.088	3
Fin whale	0.048	0.004	0.001	0.299	0.009	0.003	0.364	2
Killer whale	0.108	0.009	0.003	0.663	0.019	0.006	0.808	10
Beluga whale	1.900	0.168	0.056	7.133	0.204	0.068	9.529	15
Dall's porpoise	0.024	0.002	0.001	0.148	0.004	0.001	0.180	6
Harbor porpoise	0.667	0.059	0.020	4.117	0.118	0.039	5.020	12
Pacific white-sided dolphin	0.000	0.000	0.000	0.000	0.000	0.000	0.000	3
Harbor seal	47.112	4.163	1.392	290.699	8.325	2.785	354.476	355
Steller sea lion	1.175	0.104	0.035	7.253	0.208	0.069	8.844	9
California sea lion	0.000	0.000	0.000	0.000	0.000	0.000	0.000	2

During annual aerial surveys conducted in Cook Inlet from 2000 to 2016, humpback group sizes ranged from 1 to 12 individuals, with most groups comprised of 1 to 3 individuals (Shelden et al., 2013). Three humpback whales were observed in Cook Inlet during SAExploration's seismic study in 2015: two near the Forelands and one in Kachemak Bay (Kendall and Cornick, 2015). In total, 14 sightings of 38 humpback whales (ranging in group size from 1 to 14) were recorded in the 2019 Hilcorp lower Cook Inlet seismic survey in the fall (Fairweather Science, 2020). Two sightings totaling three individual humpback whales were recorded near Ladd Landing north of the Forelands on the recent Harvest Alaska CIPL Extension Project (Sitkiewicz et al., 2018). Based on documented observations from the CIPL Extension Project, which is the data closest to the specific geographic region, NMFS has authorized, three takes by Level B harassment for humpback whales, which is slightly greater than the calculated exposures using the methods described above (0.2440 takes by Level B harassment, table 10).

Minke whales usually travel in groups of two to three individuals (NMFS, 2023b). During Cook Inlet-wide aerial surveys conducted from 1993 to 2004, minke whales were encountered three times (1998, 1999, and 2006), all were observed off Anchor Point (Shelden et al., 2013, 2015b, and 2017). Several minke whales were recorded off Cape Starichkof in early summer 2013 during exploratory drilling (Owl Ridge, 2014), suggesting this location is regularly used by minke whales year-round. During Apache's 2014 survey, a total of two minke whale groups (three individuals) were observed. One sighting occurred southeast of Kalgin Island while the other sighting occurred near Homer (Lomac-MacNair et al., 2014). SAExploration noted one minke whale near Tuxedni Bay in 2015 (Kendall and Cornick, 2015). Eight sightings of eight minke whales were recorded in the 2019 Hilcorp lower Cook Inlet seismic survey ( print page 79548) (Fairweather Science, 2020). Based on these observations of group size and consistency of sightings in Cook Inlet, NMFS has authorized three takes by Level B harassment for minke whales (table 10). This is higher than the exposure estimate ( i.e., 0.037, table 10) to allow for the potential occurrence of a group, or several individuals, during the project period.

During Apache's 2012 seismic program, nine sightings of a total of nine gray whales were observed in June and July (Lomac-MacNair et al., 2013). In 2014, one gray whale was observed during Apache's seismic program (Lomac-MacNair et al., 2014) and in 2015, no gray whales were observed during SAExploration's seismic survey (Kendall and Cornick, 2015). No gray whales were observed during the 2018 CIPL Extension Project (Sitkiewicz et al., 2018) or during the 2019 Hilcorp seismic survey in lower Cook Inlet (Fairweather Science, 2020). The greatest densities of gray whales in Cook Inlet occur from November through January and March through May; the former are southbound, the latter are northbound (Ferguson et al., 2015). Based on this information, NMFS has authorized three takes by Level B harassment for gray whales. This is higher than the exposure estimate ( i.e., 0.088, table 10) to allow for the potential occurrence of a group, or several individuals, particularly during the fall shoulder season during the higher density periods mentioned above.

Fin whales most often travel alone, although they are sometimes seen in groups of two to seven individuals. During migration they may be in groups of 50 to 300 individuals (NMFS, 2010). During the NMFS aerial surveys in Cook Inlet from 2000 to 2018, 10 sightings of 26 estimated individual fin whales were recorded in lower Cook Inlet (Shelden et al., 2013, 2015b, and 2017; Shelden and Wade, 2019). Wild et al. (2023) identified areas south of the mouth of Cook Inlet as a fin whale feeding BIA from June to September with an importance score of 1 and an intensity score of 1 (see Harrison et al. 2023 for more details regarding BIA scoring). As such, the potential for fin whales to occupy waters adjacent to the BIA during that time period and near the specified area may be higher. Acoustic detections of fin whales were recorded during passive acoustic monitoring in the fall of 2019 (Castellote et al., 2020) Additionally, during seismic surveys conducted in 2019 by Hilcorp in lower Cook Inlet, 8 sightings of 23 fin whales were recorded in groups ranging in size from 1 to 15 individuals (Fairweather Science, 2020). The higher number of sightings in a single year relative to the multi-year NMFS aerial surveys flown earlier in season each year suggests fin whales may be present in greater numbers in the fall. Given the possible presence of fin whales in the project area, NMFS has authorized two takes by Level B harassment for fin whales during Hilcorp's planned activities.

Killer whale pods typically consist of a few to 20 or more animals (NMFS, 2023c). During seismic surveys conducted in 2019 by Hilcorp in lower Cook Inlet, 21 killer whales were observed. Although also observed as single individuals, killer whales were recorded during this survey in groups ranging in size from two to five individuals (Fairweather Science, 2020). One killer whale group of two individuals was observed during the 2015 SAExploration seismic program near the North Foreland (Kendall and Cornick, 2015). Based on recent documented sightings, observed group sizes, and the established presence of killer whales in Cook Inlet, NMFS has authorized 10 takes by Level B harassment for killer whales. This will account for two sightings with a group size of five individuals, which represents the upper end of recorded group size in recent surveys conducted in Cook Inlet.

The total calculated exposures for CIBW was calculated to be 9.529 individuals based on recorded densities and estimated durations that tugs will be under load with a jack-up rig (table 10). The 2018 MML aerial survey (Shelden and Wade, 2019) reported a median beluga group size estimate of approximately 11 whales, although estimated group sizes were highly variable (ranging from 2 to 147 whales) as was the case in previous survey years (Boyd et al., 2019). The median group size during 2021 and 2022 MML aerial surveys was 34 and 15, respectively, with variability between 1 and 174 between the years (Goetz et al., 2023). Additionally, vessel-based surveys in 2019 found CIBW groups in the Susitna River Delta (roughly 24 km north of the Tyonek Platform) that ranged from 5 to 200 animals (McGuire et al., 2022). Based on these observations, NMFS increased the estimated take calculated above and has authorized 15 takes by Level B harassment for CIBWs to account for 1 group of 15 individuals, the lower end of the 2022 median group size, or 2 observations of smaller-sized groups. While large groups of CIBWs have been seen in the Susitna River Delta region, they are not expected near Hilcorp's specified activity because groups of this size have not been observed or documented outside river deltas in upper Cook Inlet; however, smaller groups ( i.e., around the 2022 median group size) could be traveling through to access the Susitna River Delta and other nearby coastal locations.

Dall's porpoises are usually found in groups averaging between 2 and 12 individuals (NMFS, 2023d). During seismic surveys conducted in 2019 by Hilcorp in lower Cook Inlet, Dall's porpoises were recorded in groups ranging from two to seven individuals (Fairweather Science, 2020). The 2012 Apache survey recorded two groups of three individual Dall's porpoises (Lomac-MacNair et al., 2014). NMFS has authorized six takes by Level B harassment for Dall's porpoises. This is greater than the estimated exposure estimate for this species (0.180, table 10), but will allow for at least one group at the higher end of documented group size or a combination of small groups plus individuals.

Harbor porpoises are most often seen in groups of two to three (NMFS, 2023e); however, based on observations during project-based marine mammal monitoring, they can also occur in larger group sizes. 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 Extension Project that occurred in middle Cook Inlet reported 29 sightings of 44 individuals (Sitkiewicz et al., 2018). NMFS has authorized 12 takes by Level B harassment for harbor porpoises to allow for multiple group sightings during the specified activity. These authorized takes are greater than the exposure estimate calculated (5.020, table 10) but will account for the possibility of a couple sightings of small groups of harbor porpoises during Hilcorp's 6 days of tugging activity.

Recent data specific to Pacific white-sided dolphins within Cook Inlet are lacking, and the calculated exposure estimate is zero based on the paucity of sightings of this species in this region (table 10). However, Pacific-white sided dolphins have been observed in Cook Inlet. During an aerial survey in May 2014, Apache observed three Pacific white-sided dolphins near Kenai. No large groups of Pacific white-sided dolphins have been reported within Cook Inlet, although acoustic detections of several Pacific white-sided dolphins were recorded near Iniskin Bay during Hilcorp's 3D seismic survey in 2020. Prior to this, only one other survey in the last 20 years noted the presence of Pacific white-sided dolphins (three animals) within Cook Inlet. As a result of the dearth of current data on this species, an accurate density for Pacific ( print page 79549) white-sided dolphins in the specific project region has not been generated. However, based on the possibility of this species in the project area, NMFS has authorized three takes by Level B harassment for Pacific white-sided dolphins, the maximum number of Pacific white-sided dolphins that have been recorded in the somewhat recent past are present in Cook Inlet. This is consistent with NMFS' IHA for Hilcorp's previous tugging activities (87 FR 62364, October 14, 2022).

Harbor seals are often solitary in water but can haul out in groups of a few to thousands (Alaska Department of Fish and Game (ADF&G), 2022). Given their presence in the study region, NMFS has authorized 355 takes by Level B harassment for harbor seals, which is commensurate with the calculated exposure estimate based on harbor seal densities and Hilcorp's estimated durations for tugging activities (table 10).

Steller sea lions tend to forage individually or in small groups (Fiscus and Baines, 1966) but have been documented feeding in larger groups when schooling fish were present (Gende et al., 2001). Steller sea lions have been observed during marine mammal surveys conducted in Cook Inlet. In 2012, during Apache's 3D Seismic survey, three sightings of approximately four individuals in upper Cook Inlet were reported (Lomac-MacNair et al., 2013). Marine mammal observers associated with Buccaneer's drilling project off Cape Starichkof observed seven Steller sea lions during the summer of 2013 (Owl Ridge, 2014). During SAExploration's 3D Seismic Program in 2015, four Steller sea lions were observed in Cook Inlet. One sighting occurred between the West and East Forelands, one occurred near Nikiski, and one occurred northeast of the North Foreland in the center of Cook Inlet (Kendall and Cornick, 2015). During NMFS CIWB aerial surveys from 2000 to 2016, 39 sightings of 769 estimated individual Steller sea lions in lower Cook Inlet were reported (Shelden et al., 2017). During a waterfowl survey in upper Cook Inlet, an observer documented an estimated 25 Steller sea lions hauled out at low tide in the Lewis River on the west side of Cook Inlet (K. Lindberg, pers. comm., August 15, 2022). Hilcorp reported one sighting of two Steller sea lions while conducting pipeline work in upper Cook Inlet (Sitkiewicz et al., 2018). Commensurate with exposure estimates shown in table 10, NMFS has authorized nine takes by Level B harassment for Steller sea lions.

While California sea lions are uncommon in the specific geographic region, two were seen during the 2012 Apache seismic survey in Cook Inlet (Lomac-MacNair et al., 2013). California sea lions in Alaska are typically alone but may be seen in small groups usually associated with Steller sea lions at their haulouts and rookeries (Maniscalco et al., 2004). Despite the estimated exposure estimate being zero due to the lack of sightings during aerial surveys, NMFS has authorized two takes by Level B harassment for California sea lions to account for the potential to see up to two animals over the course of the season. This is consistent with NMFS authorization for Hilcorp's previous tugging activities (87 FR 62364, October 14, 2022).

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 ITAs 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.

There is a discountable potential for marine mammals to incur PTS from the project, 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 and we are not authorizing it. Hilcorp will implement a number of mitigation and related monitoring measures designed to reduce the potential for and severity of Level B harassment and further reduce the already insignificant potential for Level A harassment.

The tugs towing a jack-up rig are not able to shut down while transiting, holding, or positioning the rig. Hilcorp will maneuver the tugs towing the jack-up rig such that they maintain a consistent speed (approximately 4 knots [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.

Hilcorp will use two NMFS-approved PSOs to observe and implement clearance zone procedures as described below ( i.e., pre-clearance monitoring). If a 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. The pre-clearance zones include a distance of 1.5 km for non-CIBWs and any distance for CIBWs (note: transitioning from towing to positioning without shutting down will not be considered commencing a new operational activity). The 1.5 km clearance zone is consistent with previous authorizations for tugging activities (87 FR 62364, October 14, 2022), and was determined to be appropriate as it is approximately twice as large as the largest Level A harassment zone (table 9) and is a reasonable distance within which cryptic species ( e.g., porpoises, pinnipeds) could be observed. The larger clearance zone for CIBWs is a new measure aimed to further minimize any potential impacts from tugs under load with a jack-up rig on this species.

During daylight hours, for 30 minutes prior to commencing new operational activities, or if there is a 30-minute lapse in operational activities, two PSOs will observe and implement clearance zones procedures as described below ( i.e., pre-clearance monitoring); Note: transitioning from towing to positioning ( print page 79550) without shutting down will not be considered commencing a new operational activity. If no marine mammals are observed within the relevant clearance zones described above during this 30 minute pre-clearance monitoring period, tugging activities may commence. If a CIBW(s) is observed at any distance during those 30 minutes, operations may not commence until the PSO(s) confirm that the CIBW(s) or any other CIBW(s) has not been observed for 30 minutes, unless the delay interferes with the safety of working conditions. If a non-CIBW marine mammal(s) is observed within the relevant clearance zone ( i.e., 1.5 km) during the 30 minute pre-clearance monitoring period, tugging activities will not commence until the PSO(s) observe that the non-CIBW animal(s) is outside of and on a path away from the clearance zone, or 30 minutes have elapsed without observing the non-CIBW marine mammal.

During nighttime hours or low/no-light conditions, 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 two PSOs will observe and implement clearance zone procedures as described below while using NVDs ( i.e., pre-clearance monitoring). If a marine mammal(s) is observed during the 30 minute pre-clearance monitoring period, operations may not commence until the PSO(s) observe that one of the following conditions is met, unless the delay interferes with the safely of working conditions: (1) the animal(s) is outside of the observable area; or (2) 30 minutes have elapsed without observing the marine mammal. If no marine mammals are observed during the 30 minute pre-clearance monitoring period, tugs may commence towing, positioning, or holding the jack-up rig.

Hilcorp will operate with the tide, resulting in a low power output from the tugs towing the jack-up rig, unless human safety or equipment integrity are at risk. Due to the nature of tidal cycles in Cook Inlet, it is possible that the most favorable tide for the towing operation will occur during nighttime hours. Hilcorp will only operate the tugs towing the jack-up rigs at night if the nighttime operations result in a lower power output from the tugs by operating with a favorable tide.

Out of concern for potential disturbance to CIBWs in sensitive and essential habitat, Hilcorp will 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 area have been expanded based on new available science, including visual surveys and acoustic studies, which indicate that substantial numbers of CIBWs continue to occur in the Susitna Delta area through at least mid-November (M. Castellote, pers. comm., T. McGuire, pers. comm.). In addition, Hilcorp will coordinate with local Tribes as described in its Stakeholder Engagement Plan (see appendix C in Hilcorp's application), notify the communities of any changes in the operation, and take action to avoid or mitigate impacts to subsistence harvests.

For transportation of a jack-up rig to or from the Tyonek platform, in addition to the two PSOs stationed on the rig during towing, one additional PSO will be stationed on the Tyonek platform to monitor for marine mammals. The PSO will be on-watch for at least 1 hour before tugs are expected to arrive (scheduled to approach the estimated 120-dB isopleth).

Based on our evaluation of our proposed measures and consideration of public comments, NMFS has determined that the required mitigation and related monitoring measures (see below for additional descriptions) provide the means of effecting the least practicable 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 such species or stock for subsistence uses.

Monitoring and Reporting

In order to issue an IHA for an activity, section 101(a)(5)(D) of the MMPA states that NMFS must set forth requirements pertaining to the monitoring and reporting of such taking. The MMPA implementing regulations at 50 CFR 216.104(a)(13) indicate that requests for authorizations must include the suggested means of accomplishing the necessary monitoring and reporting that will result in increased knowledge of the species and of the level of taking or impacts on populations of marine mammals that are expected to be present while conducting the activities. Effective reporting is critical both to compliance as well as ensuring that the most value is obtained from the required monitoring.

Monitoring and reporting requirements prescribed by NMFS should contribute to improved understanding of one or more of the following:

Occurrence of marine mammal species or stocks in the area in which take is anticipated (e.g., presence, abundance, distribution, density);
Nature, scope, or context of likely marine mammal exposure to potential stressors/impacts (individual or cumulative, acute or chronic), through better understanding of: (1) action or environment (e.g., source characterization, propagation, ambient noise); (2) affected species ( e.g., life history, dive patterns); (3) co-occurrence of marine mammal species with the activity; or (4) biological or behavioral context of exposure ( e.g., age, calving or feeding areas);
Individual marine mammal responses (behavioral or physiological) to acoustic stressors (acute, chronic, or cumulative), other stressors, or cumulative impacts from multiple stressors;
How anticipated responses to stressors impact either: (1) long-term fitness and survival of individual marine mammals; or (2) populations, species, or stocks;
Effects on marine mammal habitat (e.g., marine mammal prey species, acoustic habitat, or other important physical components of marine mammal habitat); and,
Mitigation and monitoring effectiveness.

Hilcorp will abide by all monitoring and reporting measures contained within the IHA and their Marine Mammal Monitoring and Mitigation Plan (see appendix D of Hilcorp's application). A summary of those measures and additional requirements from NMFS is provided below.

Hilcorp must monitor the project area once tugging activities are underway to the maximum distance possible based on the required number of PSOs, required monitoring locations, and environmental conditions. PSOs must also conduct monitoring for marine mammals during the pre-clearance monitoring periods, through 30 minutes post-completion of any tugging activity each day, and after each stoppage of 30 minutes or greater.

A minimum of two NMFS-approved PSOs must be stationed on the tug or jack-up rig for monitoring purposes for the entirety of jack-up rig towing, ( print page 79551) holding, and positioning operations and pre-clearance monitoring. PSOs must be independent of the activity contractor (for example, employed by a subcontractor) and have no other assigned tasks during monitoring periods. At least one PSO must have prior experience performing the duties of a PSO during an activity pursuant to a NMFS-issued ITA or Letter of Concurrence. Other PSOs may substitute other relevant experience (including relevant Alaska Native traditional knowledge), education (degree in biological science or related field), or training for prior experience performing the duties of a PSO.

PSOs must also have the following additional qualifications:

(a) The ability to conduct field observations and collect data according to assigned protocols;

(b) Experience or training in the field identification of marine mammals, including the identification of behaviors;

(c) Sufficient training, orientation, or experience with the tugging operation to provide for personal safety during observations;

(d) Sufficient writing skills to record required information including but not limited to the number and species of marine mammals observed; dates and times when tugs were under load with the jack-up rig; dates, times, and reason for implementation of mitigation (or why mitigation was not implemented when required); and marine mammal behavior; and

(e) The ability to communicate orally, by radio or in person, with project personnel to provide real-time information on marine mammals observed in the area as necessary.

PSOs must be positioned aboard the tug or the jack-up-rig at the best practical vantage points that are determined to be safe, ideally an elevated stable platform from which a single PSO would have an unobstructed 360-degree view of the water or a total 360-degree view between all PSOs on-watch. Generally, one PSO will be on the port side and one PSO will be on the starboard side. Additionally, when towing the jack-up rig to the Tyonek platform, an additional PSO must be stationed on the Tyonek platform 1 hour before tugs are expected to arrive ( i.e., scheduled to approach the estimated 120-dB isopleth) to monitor for marine mammals. PSOs may use a combination of equipment to scan the monitoring area and to verify the required monitoring distance from the project site, including the naked eye, 7 by 50 binoculars, and NMFS approved NVDs for low light and nighttime operations. PSOs must be in communication with all vessel captains via VHF radio and/or cell phones at all times and alert vessel captains to all marine mammal sightings relative to the vessel location.

Hilcorp must submit interim monthly reports for all months in which tugging activities occur. Monthly reports will be due 14 days after the conclusion of each calendar month, and must include a summary of marine mammal species and behavioral observations, delays, and tugging activities completed ( i.e., tugs towing, holding, or positioning the jack-up rig). They also must include an assessment of the amount of tugging remaining to be completed, in addition to the number of CIBWs observed within estimated harassment zones to date.

A draft final summary marine mammal monitoring report must be submitted to NMFS within 90 days after the completion of the tug towing jack-up rig activities for the year or 60 calendar days prior to the requested issuance of any subsequent IHA for similar activity at the same location, whichever comes first. The draft summary report must include an overall description of all work completed, a narrative regarding marine mammal sightings, and associated marine mammal observation data sheets (data must be submitted electronically in a format that can be queried such as a spreadsheet or database). Specifically, the summary report must include:

Date and time that monitored activity begins or ends;
Activities occurring during each observation period, including (a) the type of activity (towing, holding, positioning), (b) the total duration of each type of activity, (c) the number of attempts required for positioning, (d) when nighttime operations were required, and (e) whether towing against the tide was required;
PSO locations during marine mammal monitoring;
Environmental conditions during monitoring periods (at the beginning and end of the PSO shift and whenever conditions change significantly), including Beaufort sea state, tidal state, and any other relevant weather conditions including cloud cover, fog, sun glare, overall visibility to the horizon, and estimated observable distance;
Upon observation of a marine mammal, the following information:

○ Name of PSO who sighted the animal(s) and PSO location and activity at time of sighting;

○ Time of sighting;

○ Identification of the animal(s) ( e.g., genus/species, lowest possible taxonomic level, or unidentified), PSO confidence in identification, and the composition of the group if there is a mix of species;

○ Distance and location of each observed marine mammal relative to the tug boats for each sighting;

○ Estimated number of animals (min/max/best estimate);

○ Estimated number of animals by cohort (adults, juveniles, neonates, group composition, etc.);

○ Animal's closest point of approach and estimated time spent within the harassment zone;

○ Description of any marine mammal behavioral observations ( e.g., observed behaviors such as feeding or traveling), including an assessment of behavioral responses thought to have resulted from the activity ( e.g., no response or changes in behavioral state such as ceasing feeding, changing direction, flushing, or breaching);

Number of marine mammals detected within the harassment zones, by species; and
Detailed information about implementation of any mitigation (e.g., delays), a description of specific actions that ensued, and resulting changes in behavior of the animal(s), if any.

If no comments are received from NMFS within 30 days, the draft summary report will constitute the final report. If comments are received, a final report addressing NMFS comments must be submitted within 30 days after receipt of comments.

In the event that personnel involved in Hilcorp's tugging activities discover an injured or dead marine mammal, Hilcorp must report the incident to the Office of Protected Resources, NMFS ( PR.ITP.MonitoringReports@noaa.gov, itp.tyson.moore@noaa.gov), and to the Alaska Regional Stranding Coordinator as soon as feasible. If the death or injury was clearly caused by the specified activity, Hilcorp must immediately cease the specified activities until NMFS is able to review the circumstances of the incident and determine what, if any, additional measures are appropriate to ensure compliance with the IHA. Hilcorp must not resume their activities until notified by NMFS. The report must include the following information:

Time, date, and location (latitude and longitude) of the first discovery (and updated location information if known and applicable);
Species identification (if known) or description of the animal(s) involved;
Condition of the animal(s) (including carcass condition if the animal is dead); ( print page 79552)
Observed behaviors of the animal(s), if alive;
If available, photographs or video footage of the animal(s); and
General circumstances under which the animal was discovered.

Negligible Impact Analysis and Determination

NMFS has defined negligible impact as an impact resulting from the specified activity that cannot be reasonably expected to, and is not reasonably likely to, adversely affect the species or stock through effects on annual rates of recruitment or survival (50 CFR 216.103). A negligible impact finding is based on the lack of likely adverse effects on annual rates of recruitment or survival ( i.e., population-level effects). An estimate of the number of takes alone is not enough information on which to base an impact determination. In addition to considering estimates of the number of marine mammals that might be “taken” through harassment, NMFS considers other factors, such as the likely nature of any impacts or responses ( e.g., intensity, duration), the context of any impacts or responses ( e.g., critical reproductive time or location, foraging impacts affecting energetics), as well as effects on habitat, and the likely effectiveness of the mitigation. We also assess the number, intensity, and context of estimated takes by evaluating this information relative to population status. Consistent with the 1989 preamble for NMFS' implementing regulations (54 FR 40338, September 29, 1989), the impacts from other past and ongoing anthropogenic activities are incorporated into this analysis via their impacts on the baseline ( e.g., as reflected in the regulatory status of the species, population size and growth rate where known, ongoing sources of human-caused mortality, or ambient noise levels).

To avoid repetition, the discussion of our analysis applies to all the species listed in table 10, except CIBWs, given that many of the anticipated effects of this project on different marine mammal stocks are expected to be relatively similar in nature. For CIBWs, there are potentially meaningful differences in anticipated responses to activities, impact of expected take on the population, or impacts on habitat; therefore, we provide a separate independent detailed analysis for CIBWs following the analysis for other species for which we authorize take.

NMFS has identified several key factors to assess whether potential impacts associated with a specified activity should be considered negligible. These include (but are not limited to) the type and magnitude of taking, the amount and importance of the available habitat for the species or stock that is affected, the duration of the anticipated effect on the individuals, and the status of the species or stock. The potential effects of the specified activity on humpback whales, minke whales, gray whales, fin whales, killer whales, Dall's porpoises, harbor porpoises, Pacific white-sided dolphins, Steller sea lions, harbor seals, and California sea lions are discussed below. These factors also apply to CIBWs; however, an additional analysis for CIBWs is provided in a separate sub-section below.

Tugs under load with the jack-up rig, as outlined previously, have the potential to disturb or displace marine mammals, and the number of authorized takes that could potentially result from Hilcorp's activities have been identified above in the Estimated Take section. Hilcorp's planned activities and associated impacts will occur within a limited, confined area of the affected species or stocks' range over a total of 6 days between September 24, 2024, and September 23, 2025. The intensity and duration of take by Level B harassment will be minimized through use of mitigation measures described herein. In addition, NMFS does not anticipate that serious injury or mortality will occur as a result of Hilcorp's planned activity given the nature of the activity, even in the absence of required mitigation.

Exposures to elevated sound levels produced during tugs under load with the jack-up rig may cause behavioral disturbance of some individuals within the vicinity of the sound source. Behavioral responses of marine mammals to tugs under load with the jack-up rig are expected to be mild, short term, and temporary. Effects on individuals that are taken by Level B harassment, as enumerated in the Estimated Take of Marine Mammals section, on the basis of reports in the literature as well as monitoring from other similar activities conducted by Hilcorp (Horsley and Larson, 2023), will likely be limited to behavioral response such as increased swimming speeds, changing in directions of travel and diving and surfacing behaviors, increased respiration rates, or decreased foraging (if such activity were occurring) (Ridgway et al., 1997; Nowacek et al., 2007; Thorson and Reyff, 2006; Kendall and Cornick, 2015; Goldbogen et al., 2013b; Blair et al., 2016; Wisniewska et al., 2018; Piwetz et al., 2021). Marine mammals within the 120-dB isopleths may not present any visual cues they are disturbed by activities, or they could become alert, avoid the area, leave the area, or have other mild responses that are not observable such as increased stress levels ( e.g., Rolland et al. 2012; Bejder et al., 2006; Rako et al., 2013; Pirotta et al., 2015; Pérez-Jorge et al., 2016). They may also exhibit increased vocalization rates ( e.g., Dahlheim, 1987; Dahlheim and Castellote, 2016), louder vocalizations ( e.g., Frankel and Gabriele, 2017; Fournet et al., 2018), alterations in the spectral features of vocalizations ( e.g., Castellote et al., 2012), or a cessation of communication signals ( e.g., Tsujii et al., 2018). However, as described in the Potential Effects of Specified Activities on Marine Mammals and Their Habitat section of the Federal Register notice of the proposed IHA (89 FR 60164, July 24, 2024), marine mammals observed near Hilcorp's planned activities have shown little to no observable reactions to tugs under load with a jack-up rig (Horsley and Larson, 2023).

Tugs towing, holding, and positioning a jack-up rig are slow-moving as compared to typical recreational and commercial vessel traffic. Assuming an animal is stationary, exposure from the moving tug configuration (which comprises most of the tug activity being considered) will be on the order of minutes in any particular location. The slow, predictable, and generally straight path of this activity is expected to further lessen the likelihood that sound exposures at the expected levels will result in the harassment of marine mammals, though the potential takes based on straight calculations have nonetheless been considered in the analysis. Also, this slow transit along a predictable path is planned in an area of routine vessel traffic where many large vessels move in slow straight-line paths, and some individuals are expected to be habituated to these sorts of sounds. While it is possible that animals may swim around the project area, avoiding closer approaches to the boats, we do not expect them to abandon any intended path. Further, most animals present in the region will likely be transiting through the area; therefore, any potential exposure is expected to be brief. Based on the characteristics of the sound source and the other activities regularly encountered in the area, it is unlikely Hilcorp's planned activities will be of a duration or intensity expected to result in impacts on reproduction or survival.

Further, most of the species present in the region will only be present temporarily based on seasonal patterns or during transit between other habitats. These temporarily present species will be exposed to even shorter periods of ( print page 79553) noise-generating activity, further decreasing the impacts. Most likely, individual animals will simply move away from the sound source and be temporarily displaced from the area. Takes also have the potential to occur during important feeding times. However, the project area represents a small portion of available foraging habitat and impacts on marine mammal feeding for all species should be minimal.

We anticipate that any potential reactions and behavioral changes are expected to subside quickly when the exposures cease and, therefore, we do not expect long-term adverse consequences from Hilcorp's planned activities for individuals of any species. The intensity of Level B harassment events will be minimized through use of mitigation measures described herein, which were not quantitatively factored into the take estimates. Hilcorp will use PSOs to monitor for marine mammals before commencing any tugging activity, which will minimize the potential for marine mammals to be present within the 120-dB isopleth when tugs are under load, further reducing the likely amount of any potential Level B harassment. Further, given the absence of any major rookeries or areas of known biological significance for marine mammals ( e.g., foraging hot spots) within the estimated harassment zones (other than critical habitat and a BIA for CIBWs as described below), we predict that potential takes by Level B harassment will have an inconsequential short-term effect on individuals and will not result in population-level impacts.

Theoretically, repeated, sequential exposure to elevated noise from tugs under load with a jack-up rig over a long duration could result in more severe impacts to individuals that could affect individual fitness or reproductive success (via sustained or repeated disruption of important behaviors such as feeding, resting, traveling, and socializing; Southall et al., 2007). Alternatively, marine mammals exposed to repetitious sounds may become habituated, desensitized, or tolerant after initial exposure to these sounds (reviewed by Richardson et al., 1995; Southall et al., 2007). Cook Inlet is a regional hub of marine transportation and is used by various classes of vessels, including containerships, bulk cargo freighters, tankers, commercial and sport-fishing vessels, and recreational vessels. Off-shore vessels, tug vessels, and tour boats represent 86 percent of the total operating days for vessels in Cook Inlet (BOEM, 2016). Given that marine mammals still frequent and use Cook Inlet despite being exposed to anthropogenic sounds such as those produced by tug boats and other vessels across many years, and that it is unlikely that any individual would be exposed to repeated, sequential exposures or repetitious sounds from Hilcop's activities, no impacts to the reproduction or survival of any marine mammal individuals from the additional noise produced by tugs under load with a jack-up rig are anticipated. The absence of any pinniped haul outs or other known home-ranges in the planned action area further decreases the likelihood of any more severe energetic impacts that might affect reproduction or survival.

Hilcorp's planned activities are also not expected to have significant adverse effects on any marine mammal habitat as no physical impacts to habitat are anticipated to result from the specified activities and any impacts to marine mammal habitat ( i.e., elevated sound levels) will be temporary. In addition to being temporary and short in overall duration, the acoustic footprint of the planned activity is small relative to the overall distribution of the animals in the area and their use of the area. Additionally, the habitat within the estimated acoustic footprint is not known to be heavily used by marine mammals.

Impacts to marine mammal prey species are also expected to be minor and temporary and to have, at most, short-term effects on foraging of individual marine mammals, and likely no effect on the populations of marine mammals as a whole. Overall, as described above, the area anticipated to be impacted by Hilcorp's planned activities is very small compared to the available surrounding habitat and does not include habitat of particular importance to marine mammals. The most likely impact to prey will be temporary behavioral avoidance of the immediate area. When tugs are under load with the jack-up rig, it is expected that some fish will temporarily leave the area of disturbance ( e.g., Nakken, 1992; Olsen, 1979; Ona and Godo, 1990; Ona and Toresen, 1988), thus impacting marine mammals' foraging opportunities in a limited portion of their foraging range. But, because of the relatively small area of the habitat that may be affected, and lack of any foraging habitat of particular importance, the impacts to marine mammal habitat are not expected to cause significant or long-term negative consequences.

Finally, Hilcorp will minimize potential exposure of marine mammals to elevated noise levels by delaying tugging activities if CIBWs are observed at any distance or if non-CIBW marine mammals are observed within 1.5 km during the pre-clearance monitoring period. Hilcorp will also implement vessel maneuvering measures to reduce the likelihood of disturbing marine mammals during any periods when marine mammals may be present near the vessels. Lastly, Hilcorp will also reduce the impact of their activity by conducting tugging operations with favorable tides whenever feasible.

In summary and as described above, the following factors (with additional analyses for CIBWs included below) primarily support our determinations that the impacts resulting from the activities described for this IHA are not expected to affect any individual marine mammal's fitness for survival or reproduction, and thus is not expected to adversely affect the species or stocks through effects on annual rates of recruitment or survival:

No takes by mortality, serious injury, or Level A harassment are anticipated or authorized;
Exposure, and resulting impacts, will likely be brief given the short duration of the specified activity and the transiting behavior of marine mammals in the action area;
Marine mammal densities are low in the project area; therefore, there will not be substantial numbers of marine mammals exposed to the noise from the project compared to the affected population sizes;
Take will not occur in places and/or times where take is more likely to accrue to impacts on reproduction or survival, such as within ESA-designated or proposed critical habitat, BIAs (other than for CIBWs as described below), or other habitats critical to recruitment or survival (e.g., rookery);
The project area represents a very small portion of the available foraging area for all potentially impacted marine mammal species;
Take will only occur within middle Cook Inlet and Trading Bay—a limited, confined area of any given stock's home range;
Monitoring reports from previous projects where tugs were under load with a jack-up rig in Cook Inlet have documented little to no observable effect on individuals of the same species impacted by the specified activities;
The required mitigation is expected to be effective in reducing the effects of the specified activity by minimizing the numbers of marine mammals exposed to sound and the intensity of the exposures; and
The intensity of anticipated takes by Level B harassment is low for all stocks consisting of, at worst, temporary ( print page 79554) modifications in behavior, and will not be of a duration or intensity expected to result in impacts on reproduction or survival.

Cook Inlet Beluga Whales. For CIBWs, we further discuss our negligible impact findings in addition to the findings discussed above for all species in the context of potential impacts to this endangered stock based on our evaluation of the take authorized (table 10).

All tugging activities will be done in a manner implementing best management practices to preserve water quality, and no work will occur around creek mouths or river systems leading to prey abundance reductions. In addition, no physical structures will restrict passage, though impacts to the acoustic habitat are relevant and discussed here. While the specified activity will occur within CIBW Critical Habitat Area 2, and the CIBW small and resident BIA (see the Description of Marine Mammals in the Area of Specified Activities section in the notice for the proposed IHA; 89 FR 60164, July 24, 2024), monitoring data from Hilcorp's activities suggest that the presence of tugs under load with a jack-up rig do not discourage CIBWs from transiting throughout Cook Inlet and between critical habitat areas and that the whales do not abandon critical habitat areas (Horsley and Larson, 2023). In addition, large numbers of CIBWs have continued to use Cook Inlet and pass through the area, likely traveling to critical foraging grounds found in upper Cook Inlet, while noise-producing anthropogenic activities, including vessel use, have taken place during the past two decades ( e.g., Shelden et al., 2013, 2015b, 2017, 2022; Shelden and Wade, 2019; Geotz et al., 2023). These findings are not surprising as food is a strong motivation for marine mammals. As described in Forney et al. (2017), animals typically favor particular areas because of their importance for survival ( e.g., feeding or breeding), and leaving may have significant costs to fitness (reduced foraging success, increased predation risk, increased exposure to other anthropogenic threats). Consequently, animals may be highly motivated to maintain foraging behavior in historical foraging areas despite negative impacts ( e.g., Rolland et al., 2012).

Generation of sound may result in avoidance behaviors that will be limited in time and space relative to the larger availability of important habitat areas in Cook Inlet; however, the area ensonified by sound from the specified activity is anticipated to be small compared to the overall available critical habitat for CIBWs to feed and travel. Therefore, the specified activity will not create a barrier to movement through or within important areas. We anticipate that disturbance to CIBWs will manifest in the same manner as other marine mammals described above ( i.e., increased swimming speeds, changes in the direction of travel and dive behaviors, increased respiration rates, decreased foraging (if such activity were occurring), or alterations to communication signals). We do not believe exposure to elevated noise levels during transit past tugging activity will have adverse effects on individuals' fitness for reproduction or survival.

Although data demonstrate that CIBWs are not abandoning the planned project area during anthropogenic activities, results of an expert elicitation (EE) at a 2016 workshop, which predicted the impacts of noise on CIBW survival and reproduction given a specific amount of lost foraging opportunities, helped to inform our assessment of impacts on this stock. The 2016 EE workshop used conceptual models of an interim population consequences of disturbance (PCoD) for marine mammals (NRC, 2005; New et al., 2014; Tollit et al., 2016) to help in understanding how noise-related stressors might affect vital rates (survival, birth rate and growth) for CIBW (King et al., 2015). NMFS (2016b) suggests that the main direct effects of noise on CIBWs are likely to be through masking of vocalizations used for communication and prey location and habitat degradation. The 2016 workshop on CIBWs was specifically designed to provide regulators with a tool to help understand whether chronic and acute anthropogenic noise from various sources and projects are likely to be limiting recovery of the CIBW population. The full report can be found at https://www.smruconsulting.com/publications/ with a summary of the expert elicitation portion of the workshop below.

For each of the noise effect mechanisms chosen for the EE, the experts provided a set of parameters and values that determined the forms of a relationship between the number of days of disturbance a female CIBW experiences in a particular period and the effect of that disturbance on her energy reserves. Examples included the number of days of disturbance during the period April, May, and June that would be predicted to reduce the energy reserves of a pregnant CIBW to such a level that she is certain to terminate the pregnancy or abandon the calf soon after birth, the number of days of disturbance in the period April-September required to reduce the energy reserves of a lactating CIBW to a level where she is certain to abandon her calf, and the number of days of disturbance where a female fails to gain sufficient energy by the end of summer to maintain herself and her calf during the subsequent winter. Overall, median values ranged from 16 to 69 days of disturbance depending on the question. However, for this elicitation, a “day of disturbance” was defined as any day on which an animal loses the ability to forage for at least one tidal cycle ( i.e., it forgoes 50-100 percent of its energy intake on that day). The day of disturbance considered in the context of the report is notably more severe than any Level B harassment expected to result from these activities, which as described is expected to be comprised predominantly of temporary modifications in the behavior of individual CIBWs ( e.g., faster swim speeds, longer dives, decreased sighting durations, alterations in communication). Also, NMFS has authorized 15 instances of take, with the instances representing disturbance events within a day—this means that either 15 different individual CIBWs are disturbed on no more than 1 day each, or some lesser number of individuals may be disturbed on more than 1 day, but with the product of individuals and days not exceeding 15. Given the overall authorized take, and the short duration of the specified activities ( i.e., 6 days), it is unlikely that any one CIBW will be disturbed on more than a couple of days. Lastly, even if a CIBW was exposed every day of Hilcorp's planned activities, these activities are only planned for 6 days, and thus do not fall into the expected range of days of disturbance expected to elicit an effect on energy reserves as determined by the experts as described above ( i.e., 16 to 19 days). Further, Hilcorp will implement mitigation measures specific to CIBWs whereby they will not begin tugging activities should a CIBW be observed at any distance. While Level B harassment (behavioral disturbance) is authorized, this measure, along with other mitigation measures described herein, will limit the severity of the effects of that Level B harassment to behavioral changes such as increased swim speeds, changes in diving and surfacing behaviors, and alterations to communication signals, not the loss of foraging capabilities. Finally, take by mortality, serious injury, or Level A harassment of CIBWs is not anticipated or authorized.

In summary and as described above, the additional following factors primarily support our determination ( print page 79555) that the impacts resulting from this activity are not expected to adversely affect the CIBWs through effects on annual rates of recruitment or survival:

The area of exposure will be limited to habitat primarily used for transiting, and not areas known to be of particular importance for feeding or reproduction;
The activities are not expected to result in CIBWs abandoning critical habitat nor are they expected to restrict passage of CIBWs within or between critical habitat areas; and
Any disturbance to CIBWs is expected to be limited to temporary modifications in behavior, and will not be of a duration or intensity expected to result in impacts on reproduction or survival.

Based on the analysis contained herein of the likely effects of the specified activity on marine mammals and their habitat, and taking into consideration the implementation of the required monitoring and mitigation measures, NMFS finds that the total marine mammal take from the planned specified activity will have a negligible impact on all affected marine mammal species or stocks.

Small Numbers

As noted previously, only take of small numbers of marine mammals may be authorized under section 101(a)(5)(D) of the MMPA for specified activities other than military readiness activities. The MMPA does not define small numbers and so, in practice, where estimated numbers are available, NMFS compares the number of individuals taken to the most appropriate estimation of abundance of the relevant species or stock in our determination of whether an authorization is limited to small numbers of marine mammals. When the predicted number of individuals to be taken is fewer than one-third of the species or stock abundance, the take is considered to be of small numbers (see 86 FR 5322, January 19, 2021). Additionally, other qualitative factors may be considered in the analysis, such as the temporal or spatial scale of the activities.

For all stocks whose abundance estimate is known, the amount of authorized taking is less than one-third of the best available population abundance estimate (in fact it is less than 2 percent for all stocks, except for CIBWs whose authorized take is for up to 5.38 percent of the stock; see table 11). The numbers of animals authorized to be taken are small relative to the relevant species or stock abundances even if each estimated take occurred to a new individual.

Table 11—Authorized Take as a Percentage of Stock Abundance
Species	Total amount of take authorized	Stock	Abundance (Nbest ¹ )	Percent of stock
Humpback whale	3	Hawaii (Hawaii DPS)	11,278	0.03
		Mexico-North Pacific (Mexico DPS)	¹ N/A	N/A
		Western North Pacific	1,084	0.28
Minke whale	3	Alaska	² N/A	N/A
Gray whale	3	Eastern Pacific	26,960	0.01
Fin whale	2	Northeast Pacific	³ UND	N/A
Killer whale	10	Eastern North Pacific Alaska Resident	1,920	0.52
		Eastern North Pacific Gulf of Alaska, Aleutian Islands, and Bering Sea Transient	587	1.7
Beluga whale	15	Cook Inlet	⁴ 279	5.38
Dall's porpoise	6	Alaska	⁵ UND	N/A
Harbor porpoise	12	Gulf of Alaska	31,046	0.04
Pacific white-sided dolphin	3	North Pacific	26,880	0.01
Harbor seal	365	Cook Inlet/Shelikof	28,411	1.29
Steller sea lion	9	Western U.S	⁶ 49,932	0.02
California sea lion	2	U.S	257,606	<0.01
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 CIBWs in Alaska (Goetz et al., 2023). Data collected during NOAA Fisheries' 2022 aerial survey suggest that the whale population is stable or may be increasing slightly. Scientists estimated that the population size is between 290 and 386, with a median best estimate of 331. In accordance with the MMPA, this population estimate will be incorporated into the CIBW SAR, which will be reviewed by an independent panel of experts, the Alaska Scientific Review Group. After this review, the SAR will be made available as a draft for public review before being finalized. When the number of instances of takes is compared to this median abundance, the percent of the stock authorized is 4.53 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 the best estimate of counts, which have not been corrected for Steller sea lions at sea during abundance surveys.

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Document Information

Effective Date:: 9/24/2024
Published:: 09/30/2024
Department:: National Oceanic and Atmospheric Administration
Entry Type:: Notice
Action:: Notice; issuance of an incidental harassment authorization.
Document Number:: 2024-22293
Dates:: This authorization is effective from September 24, 2024 through September 23, 2025.
Pages:: 79529-79557 (29 pages)
Docket Numbers:: RTID 0648-XE199
PDF File:: 2024-22293.pdf