2024-30455. Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to U.S. Coast Guard Fast Response Cutter Homeporting in Seward and Sitka, Alaska

Table 1—Marine Mammal Species ¹ Likely Impacted by the Specified Activities

Common name	Scientific name	Stock	ESA/MMPA status; strategic (Y/N) 2	Stock abundance (CV, N min , most recent abundance survey) 3	PBR	Annual M/SI 4
Family Eschrichtiidae
Gray Whale	Eschrichtius robustus	Eastern North Pacific	-, -, N	26,960 (0.05, 25,849, 2016)	801	131
Family Balaenopteridae (rorquals)
Fin Whale	Balaenoptera physalus	Northeast Pacific	E, D, Y	UND (UND, UND, 2013)	UND	0.6
Humpback Whale	Megaptera novaeangliae	Hawai'i	-, -, N	11,278 (0.56, 7,265, 2020)	127	27.09
Humpback Whale	Megaptera novaeangliae	Mexico-North Pacific	T, D, Y	N/A (N/A, N/A, 2006)	UND	0.57
Minke Whale 5	Balaenoptera acutorostrata	Alaska	-, -, N	N/A (N/A, N/A, N/A)	UND	0
Family Delphinidae
Killer Whale	Orcinus orca	Eastern North Pacific Alaska Resident	-, -, N	1,920 (N/A, 1,920, 2019)	19	1.3
Killer Whale	Orcinus orca	Eastern North Pacific Gulf of Alaska, Aleutian Islands and Bering Sea Transient	-, -, N	587 (N/A, 587, 2012)	5.9	0.8
Killer Whale	Orcinus orca	Eastern Northern Pacific Northern Resident	-, -, N	302 (N/A, 302, 2018)	2.2	0.2
Killer Whale	Orcinus orca	West Coast Transient	-, -, N	349 (N/A, 349, 2018)	3.5	0.4
Pacific White-Sided Dolphin	Lagenorhynchus obliquidens	North Pacific	-, -, N	26,880 (N/A, N/A, 1990)	UND	0
Family Phocoenidae (porpoises)
Dall's Porpoise 6	Phocoenoides dalli	Alaska	-, -, N	UND (UND, UND, 2015)	UND	37
Harbor Porpoise	Phocoena phocoena	Gulf of Alaska	-, -, Y	31,046 (0.21, N/A, 1998)	UND	72
Harbor Porpoise 7	Phocoena phocoena	Yakutat/Southeast Alaska Offshore Waters	-, -, N	N/A (N/A, N/A, 1997)	UND	22.2
Family Otariidae (eared seals and sea lions)
Northern Fur Seal	Callorhinus ursinus	Eastern Pacific	-, D, Y	626,618 (0.2, 530, 376, 2019)	11,403	373
Steller Sea Lion	Eumetopias jubatus	Western	E, D, Y	49,837 (N/A, 49,837, 2022)	299	267
Steller Sea Lion	Eumetopias jubatus	Eastern	-, -, N	36,308 (N/A, 36,308, 2022)	2,178	93.2
Family Phocidae (earless seals)
Harbor Seal	Phoca vitulina	Prince William Sound	-, -, N	44,756 (N/A, 41,776, 2015)	1,253	413
Harbor Seal	Phoca vitulina	Sitka/Chatham Strait	-, -, N	13,289 (N/A, 11,883, 2015)	356	77
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/​).
2  ESA status: Endangered (E), Threatened (T)/MMPA status: Depleted (D). A dash (-) indicates that the species is not listed under the ESA or designated as depleted under the MMPA. Under the MMPA, a strategic stock is one for which the level of direct human-caused mortality exceeds PBR or which is determined to be declining and likely to be listed under the ESA within the foreseeable future. Any species or stock listed under the ESA is automatically designated under the MMPA as depleted and as a strategic stock.
3  NMFS marine mammal SARs online at: https://www.fisheries.noaa.gov/​national/​marine-mammal-protection/​marine-mammal-stock-assessment-reports-region. CV is coefficient of variation; N min is the minimum estimate of stock abundance.
4  These values, found in NMFS's SARs, represent annual levels of human-caused mortality plus serious injury from all sources combined ( e.g., commercial fisheries, vessel 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  No population estimates have been made for the number of minke whales in the entire North Pacific. Some information is available on the numbers of minke whales in some areas of Alaska, but in the 2009, 2013, and 2015 offshore surveys, so few minke whales were seen during the surveys that a population estimate for the species in this area could not be determined (Rone et al., 2017). Therefore, this information is N/A (not available).
6  Previous abundance estimates covering the entire stock's range are no longer considered reliable and the current estimates presented in the SARs and reported here only cover a portion of the stock's range. Therefore, the calculated N min and PBR is based on the 2015 survey of only a small portion of the stock's range. PBR is considered to be biased low since it is based on the whole stock whereas the estimate of mortality and serious injury is for the entire stock's range.
7  Abundance estimates assumed that detection probability on the trackline was perfect; work is underway on a corrected estimate. Additionally, preliminary data results based on environmental DNA analysis show genetic differentiation between harbor porpoise in the northern and southern regions on the inland waters of southeast Alaska. Geographic delineation is not yet known. Data to evaluate population structure for harbor porpoise in Southeast Alaska have been collected and are currently being analyzed. Should the analysis identify different population structure than is currently reflected in the Alaska SARs, NMFS will consider how to best revise stock designations in the future.

As indicated above, all 11 species (with 18 managed stocks) in table 1 temporally and spatially co-occur with the activities to the degree that take is reasonably likely to occur at either location. All species that could potentially occur in the project areas are included in section 4 and tables 3-1 and 3-2 of the USCG's IHA application.

A detailed description of the species likely to be affected by the USCG project, including brief introductions to the species and relevant stocks as well as available information regarding population trends and threats, and information regarding local occurrence, were provided in the Federal Register notice for the proposed IHA (89 FR 60359, July 25, 2024); since that time, we are not aware of any changes in the status of these species and stocks; therefore, detailed descriptions are not provided here. Please refer to that Federal Register notice for these descriptions. Please also refer to NMFS' website ( https://www.fisheries.noaa.gov/​find-species) for generalized species accounts.

Marine Mammal Hearing

Hearing is the most important sensory modality for marine mammals underwater, and exposure to anthropogenic sound can have deleterious effects. To appropriately assess the potential effects of exposure ( print page 104093) 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 auditory or auditory evoked potential techniques) or estimated hearing ranges (behavioral response data, anatomical modeling, etc.). NMFS (2018) described generalized hearing ranges for these marine mammal hearing groups and, in 2024, updated the hearing group terminology (NMFS, 2024). Generalized hearing ranges were chosen based on the approximately 65-decibel (dB) threshold from the composite audiograms, previous analysis in NMFS (2018), and/or data from Southall et al. (2007) and Southall et al. (2019). Marine mammal hearing groups and their associated hearing ranges based on the Updated Technical Guidance are provided in table 2.

Table 2—Marine Mammal Hearing Groups

[NMFS, 2024]

Hearing group ^	Generalized hearing range *
Low-frequency (LF) cetaceans (baleen whales)	7 Hz to 36 ** kHz.
High-frequency (HF) cetaceans (dolphins, toothed whales, beaked whales, bottlenose whales)	150 Hz to 160 kHz.
Very High-frequency (VHF) cetaceans (true porpoises, Kogia, river dolphins, cephalorhynchid, Lagenorhynchus cruciger & L. australis)	200 Hz to 165 kHz.
Phocid pinnipeds (PW) (underwater) (true seals)	40 Hz to 90 kHz.
Otariid pinnipeds (OW) (underwater) (sea lions and fur seals)	60 Hz to 68 kHz.
^ Southall et al. (2019) indicates that as more data become available there may be separate hearing group designations for Very Low-Frequency cetaceans (blue, fin, right, and bowhead whales) and Mid-Frequency cetaceans (sperm, killer, and beaked whales). However, at this point, all baleen whales are part of the LF cetacean hearing group, and sperm, killer, and beaked whales are part of the HF cetacean hearing group. Additionally, recent data indicates that as more data become available for Monachinae seals, separate hearing group designations may be appropriate for the two phocid subfamilies (Ruscher et al., 2021; Sills et al., 2021).
* 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 the ~65-dB threshold from composite audiogram, previous analysis in NMFS (2018), and/or data from Southall et al. (2007) and Southall et al. (2019). Additionally, animals are able to detect very loud sounds above and below that “generalized” hearing range.
** NMFS is aware that the National Marine Mammal Foundation successfully collected preliminary hearing data on two minke whales during their third field season (2023) in Norway. These data have implications for not only the generalized hearing range for low-frequency cetaceans but also on their weighting function. However, at this time, no official results have been published. Furthermore, a fourth field season (2024) has concluded, where more data were collected. Thus, it is premature for us to propose any changes to our current Updated Technical Guidance. However, mysticete hearing data is identified as a special circumstance that could merit reevaluating the acoustic criteria in this document. Therefore, we anticipate that once the data from both field seasons are published, it will likely necessitate updating this document ( i.e., likely after the data gathered in the summer 2024 field season and associated analysis are published).

For more detail concerning these groups and associated frequency ranges, please see NMFS (2024) for a review of available information.

Potential Effects of Specified Activities on Marine Mammals and Their Habitat

The effects of underwater noise from the USCG's construction activities have the potential to result in harassment of marine mammals in the vicinity of the project areas. The notice of proposed IHA (89 FR 60359, July 25, 2024) included a discussion of the effects of anthropogenic noise on marine mammals and the potential effects of underwater noise from the USCG's construction 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 60359, July 25, 2024).

Estimated Take of Marine Mammals

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

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

Authorized takes would primarily be by Level B harassment, as use of the acoustic sources ( i.e., vibratory and impact pile driving, DTH) has the potential to result in disruption of behavioral patterns for individual marine mammals. There is also some potential for AUD INJ (Level A harassment) to result, primarily for high-frequency species and phocids, because predicted AUD INJ zones are large and these species could enter the Level A harassment zones and remain undetected for a sufficient duration to incur AUD INJ due to their small size and inconspicuous nature. Although AUD INJ could occur for low-frequency species due to large predicted AUD INJ zones associated with DTH, due to their large size, conspicuous nature, and planned mitigation ( i.e., large shutdown zones, boat-based protected species observers (PSOs)), it is assumed that all low-frequency species would be visually detected and, therefore, taking by Level A harassment would be eliminated. The planned mitigation and monitoring measures are expected to minimize the severity of the taking to the extent practicable.

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

For acoustic impacts, generally speaking, we estimate take by considering: (1) acoustic thresholds above which NMFS believes the best available science indicates marine mammals will be behaviorally harassed or incur some degree of permanent hearing impairment; (2) the area or volume of water that will be ensonified above these levels in a day; (3) the density or occurrence of marine mammals within these ensonified areas; and (4) the number of days of activities. We note that while these factors can contribute to a basic calculation to provide an initial prediction of potential takes, additional information that can qualitatively inform take estimates is also sometimes available ( e.g., previous monitoring results or average group size). Below, we describe the factors considered here in more detail and present the authorized take estimates. ( print page 104094)

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 AUD INJ (which includes, but is not limited to, permanent threshold shift (PTS)) of some degree (equated to Level A harassment).

Level B Harassment —Though significantly driven by received level, the onset of behavioral disturbance from anthropogenic noise exposure is also informed to varying degrees by other factors related to the source or exposure context ( e.g., frequency, predictability, duty cycle, duration of the exposure, signal-to-noise ratio, distance to the source), the environment ( e.g., bathymetry, other noises in the area, predators in the area), and the receiving animals (hearing, motivation, experience, demography, life stage, depth) and can be difficult to predict ( e.g., Southall et al., 2007; Southall et al., 2021; Ellison et al., 2012). Based on what the available science indicates and the practical need to use a threshold based on a metric that is both predictable and measurable for most activities, NMFS typically uses a generalized acoustic threshold based on received level to estimate the onset of behavioral harassment. NMFS generally predicts that marine mammals are likely to be behaviorally harassed in a manner considered to be Level B harassment when exposed to underwater anthropogenic noise above root-mean-squared pressure received levels (RMS SPL) of 120 dB (referenced to 1 microPascal (re 1 μPa)) for continuous ( e.g., vibratory pile driving, drilling) and above RMS SPL 160 dB re 1 μPa for non-explosive impulsive ( e.g., seismic airguns) or intermittent ( e.g., scientific sonar) sources. Generally speaking, Level B harassment take estimates based on these behavioral harassment thresholds are expected to include any likely takes by temporary threshold shift (TTS) as, in most cases, the likelihood of TTS occurs at distances from the source less than those at which behavioral harassment is likely. TTS of a sufficient degree can manifest as behavioral harassment, as reduced hearing sensitivity and the potential reduced opportunities to detect important signals (conspecific communication, predators, prey) may result in changes in behavior patterns that would not otherwise occur.

The USCG's planned activity includes the use of continuous (vibratory and DTH) and impulsive (impact driving and DTH) sources, and therefore the 120 and 160 dB re 1 μPa (RMS) thresholds, respectively, are applicable.

Level A harassment —NMFS' 2024 Updated Technical Guidance (NMFS, 2024) identifies dual criteria to assess AUD INJ (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). The USCG's planned activity includes the use of impulsive (impact driving and DTH) and non-impulsive (vibratory and DTH) sources.

These criteria are provided in table 3 below. The references, analysis, and methodology used in the development of the thresholds are described in the 2024 Updated Technical Guidance, which may be accessed at: https://www.fisheries.noaa.gov/​national/​marine-mammal-protection/​marine-mammal-acoustic-technical-guidance-other-acoustic-tools.

Table 3—Summary of Marine Mammal AUD INJ Onset Criteria

[NMFS, 2024]

Hearing group	AUD INJ onset criteria * (received level)
	Impulsive	Non-impulsive
Low-Frequency (LF) Cetaceans	Cell 1: Lp, 0-pk,flat : 222 dB; LE,p, LF,24h : 183 dB	Cell 2: LE,p, LF,24h : 197 dB.
High-Frequency (HF) Cetaceans	Cell 3: Lp, 0-pk,flat : 230 dB; LE,p, HF,24h : 193 dB	Cell 4: LE,p, HF,24h : 201 dB.
Very High-Frequency (VHF) Cetaceans	Cell 5: Lp, 0-pk,flat : 202 dB; LE,p, VHF,24h : 159 dB	Cell 6: LE,p, VHF,24h : 181 dB.
Phocid Pinnipeds (PW) (Underwater)	Cell 7: Lp, 0-pk,flat : 223 dB; LE,p, PW,24h : 183 dB	Cell 8: LE,p, PW,24h : 195 dB.
Otariid Pinnipeds (OW) (Underwater)	Cell 9: Lp ,0-pk,flat : 230 dB; LE,p, OW,24h : 185 dB	Cell 10: LE,p, OW,24h : 199 dB.
* Dual metric criteria for impulsive sounds: Use whichever criteria results in the larger isopleth for calculating AUD INJ onset. If a non-impulsive sound has the potential of exceeding the peak sound pressure level criteria associated with impulsive sounds, the PK SPL criteria are recommended for consideration for non-impulsive sources.
Note: Peak sound pressure level ( Lp, 0-pk ) has a reference value of 1 μPa (underwater) and 20 μPa (in air), and weighted cumulative sound exposure level ( LE,p ) has a reference value of 1μPa2 s (underwater) and 20 μPa2 s (in air). In this table, criteria are abbreviated to be more reflective of International Organization for Standardization standards (ISO, 2017; ISO, 2020). The subscript “flat” is being included to indicate peak sound pressure are flat weighted or unweighted within the generalized hearing range of marine mammals underwater ( i.e., 7 Hz to 165 kHz) or in air ( i.e., 42 Hz to 52 kHz). The subscript associated with cumulative sound exposure level criteria indicates the designated marine mammal auditory weighting function (LF, HF, and VHF cetaceans, and PW and OW pinnipeds) and that the recommended accumulation period is 24 hours. The weighted cumulative sound exposure level criteria 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 criteria 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 construction noise from the project. Marine mammals are expected to be affected via sound generated by the primary components of the project ( i.e., impact pile driving, vibratory pile driving, vibratory pile removal, and DTH).

In order to calculate distances to the Level A harassment and Level B harassment thresholds for the methods and piles planned for this project, NMFS used acoustic monitoring data from other locations to develop source levels for the various pile types, sizes, and methods (tables 4-7).

NMFS recommends treating DTH systems as both impulsive and continuous, non-impulsive sound source types simultaneously. Thus, impulsive thresholds are used to evaluate Level A harassment, and continuous thresholds are used to evaluate Level B harassment. With regards to DTH mono-hammers, NMFS ( print page 104095) recommends proxy levels for Level A harassment based on available data regarding DTH systems of similar sized piles and holes (Denes et al., 2019; Guan and Miner, 2020; Heyvaert and Reyff, 2021; Reyff, 2020; Reyff and Heyvaert, 2019).

Table 4—Observed Non-Impulsive Sound Levels and Durations for In-Water Activities Likely To Occur at Moorings Seward

In-water activity	Pile size and type	RMS SPL (dB re 1 μPa) at 10 m	Average duration per pile (seconds)	Piles per day
Vibratory Pile Extraction a	14-inch steel guide pile	160	1,800	5
Vibratory Pile Settling a	30-inch concrete guide pile	163	600	2
Rock socket drill b (non-impulsive component)	30-inch concrete guide pile	174	c  10,800	2
Note: Abbreviations: dB re 1 μPa = decibels referenced to a pressure of 1 microPascal, m = meters.
a  NMFS, 2024.
b  NMFS, 2022.
c  Rock socket drilling is a DTH activity with multiple strikes per second. DTH activities produce sounds that simultaneously contain both non-impulsive and impulsive components.

Table 5—Observed Impulsive Sound Levels and Durations for Pile Installation Activities Likely To Occur at Moorings Seward

Installation method	Pile size and type	Peak (dB re 1 μPa) at 10 m	RMS (dB re 1 μPa) at 10 m	SEL single-strike (dB re 1 μPa2 s) at 10 m	Strikes per day	Maximum strikes per pile	Piles per day
Rock socket drill a	30-inch concrete guide pile	194	174	164	c  216,000	108,000	2
Impact hammer proofing b	30-inch concrete guide pile	198	186	173	10	5	2
Note: Abbreviations: dB re 1 μPa = decibels referenced to a pressure of 1 microPascal, m = meters.
a  NMFS, 2022.
b  NMFS, 2024.
c  Rock socket drilling is a DTH activity with multiple strikes per second. DTH activities produce sounds that simultaneously contain both non-impulsive and impulsive components.

Table 6—Observed Non-Impulsive Sound Levels and Durations for In-Water Activities Likely To Occur at Moorings Sitka

In-water activity	Pile size and type	RMS SPL (dB re 1 μPa) at 10 m	Average duration per pile (seconds)	Piles per day
Vibratory Pile Extraction a	12-inch timber piles	162	1,800	5
Vibratory Pile Settling b	30-inch concrete guide and structure pile	163	600	2
Rock socket drill c (non-impulsive component)	30-inch concrete guide and structure pile	174	10,800	2
Note: Abbreviations: dB re 1 μPa = decibels referenced to a pressure of 1 microPascal, m = meters.
a  NMFS, 2024.
b  NMFS, 2022.
c  Rock socket drilling is a DTH activity with multiple strikes per second. DTH activities produce sounds that simultaneously contain both non-impulsive and impulsive components.

Table 7—Observed Impulsive Sound Levels and Durations for Pile Installation Activities Likely To Occur at Moorings Sitka

Installation method	Pile size and type	Peak (re 1 μPa) at 10 m	RMS (dB re 1 μPa) at 10 m	SEL single-strike (dB re 1 μPa2 s) at 10 m	Strikes per day	Maximum strikes per pile	Piles per day
Impact drive a	13-inch plastic fender pile	177	153	NA	200	100	2
Impact drive a	14-inch timber guide pile	180	170	160	320	160	2
Rock socket drill b	30-inch concrete guide pile	194	174	164	d  216,000	108,000	2
Impact hammer proofing c	30-inch concrete guide pile	198	186	173	10	5	2
Note: Abbreviations: dB re 1 μPa = decibels referenced to a pressure of 1 microPascal, m = meters.
a  Caltrans, 2020.
b  NMFS, 2022.
c  NMFS, 2024.
d  Rock socket drilling is a DTH activity with multiple strikes per second. DTH activities produce sounds that simultaneously contain both non-impulsive and impulsive components.

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

TL = B × log₁₀ ( R₁ / R₂),

Where:

( print page 104096)

TL = transmission loss in dB

B = transmission loss coefficient; for practical spreading equals 15

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

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

The recommended TL coefficient for most nearshore environments is the practical spreading value of 15 (-4.5 dB per doubling of distance). This value results in an expected propagation environment that would lie between spherical and cylindrical spreading loss conditions, which is the most appropriate assumption for the USCG's planned activities. This analysis uses practical spreading loss, a standard assumption regarding sound propagation for similar environments, to estimate transmission of sound through water. The Level B harassment zones and approximate amount of area ensonified for the planned underwater activities are shown in tables 8 and 9.

Level A Harassment Zones —The ensonified area associated with Level A harassment is more technically challenging to predict due to the need to account for a duration component. Therefore, NMFS developed an optional User Spreadsheet tool to accompany the Updated Technical Guidance that can be used to relatively simply predict an isopleth distance for use in conjunction with marine mammal density or occurrence to help predict potential takes. A weighting adjustment factor of 2.5 or 2, a standard default value for vibratory pile driving and removal or impact driving and DTH respectively, was used to calculate Level A harassment areas. We note that because of some of the assumptions included in the methods underlying this optional tool, we anticipate that the resulting isopleth estimates are typically going to be overestimates of some degree, which may result in an overestimate of potential take by Level A harassment. However, this optional tool offers the best way to estimate isopleth distances when more sophisticated modeling methods are not available or practical. For stationary sources such as pile driving and DTH, the optional Updated User Spreadsheet tool predicts the distance at which, if a marine mammal remained at that distance for the duration of the activity, it would be expected to incur AUD INJ. Inputs used in the optional Updated User Spreadsheet tool ( e.g., number of piles per day, duration and/or strikes per pile) are presented in tables 4-7, and the resulting estimated isopleths and total ensonified areas are reported below in tables 8 and 9.

Table 8—Projected Distances to Level A Harassment Isopleths Using 2018 and 2024 Technical Guidance and Level B Harassment Isopleths by Marine Mammal Hearing Group at Moorings Seward

Activity	Distance to level A for LF	Distance to level A for HF	Distance to level A for VHF	Distance to level A for PW	Distance to level A for OW	Level B Distance (m)	Total ensonified area (km2 )
Vibratory pile extraction	10.8 m ( 14.6 m)	1 m ( 5.6 m)	16 m ( 11.9 m)	6.6 m ( 18.8 m)	0.5 m ( 6.3 m)	4,641.6	1.94
DTH (Impulsive component) concrete	1,945.5 ( 1,938.5 m)	69.2 ( 247.3 m)	2,317.4 ( 2,999.8 m)	1,041.2 ( 1,722.1 m)	75.8 ( 641.9 m)	39,810.7	* 2.26
Vibratory settling concrete	4.5 m ( 6 m)	0.4 m ( 2.3 m)	6.6 m ( 4.9 m)	2.7 m ( 7.8 m)	0.2 m ( 2.6 m)	7,356.4	* 2.26
Impact driver proofing concrete	10 m	0.4 m ( 1.3 m)	11.9 m ( 15.4 m)	5.3 m ( 8.8 m)	0.4 m ( 3.3 m)	541.2	0.11
Note 1: Abbreviations: LF = low-frequency cetaceans, HF = high-frequency cetaceans, VHF = very high-frequency cetaceans, PW = phocid pinnipeds in water, OW = otariid pinnipeds in water.
Note 2: Isopleths based on NMFS (2018) are shown above updated isopleths from NMFS (2024), which are italicized in parentheses below the original isopleths.
* Total harassment areas are the same despite having varying radii because the maximum distance intersects with the other side of Resurrection Bay near Seward resulting in the same areal extent.

Table 9—Projected Distances to Level A Harassment Isopleths Using 2018 and 2024 Technical Guidance and Level B Harassment Isopleths by Marine Mammal Hearing Group at Moorings Sitka

Activity	Distance to level A for LF	Distance to level A for HF	Distance to level A for VHF	Distance to level A for PW	Distance to level A for OW	Level B distance (m)	Total ensonified area (km2 )
Vibratory pile extraction	14.7 m ( 19.8 m)	1.3 m ( 7.6 m)	21.7 m ( 16.2 m)	6.9 m ( 25.5 m)	0.6 m ( 8.6 m)	6,309.6 m	4.17
Impact drive plastic	13.6 m ( 13.5 m)	0.5 m ( 1.7 m)	16.2 m ( 21 m)	7.3 m ( 12 m)	0.5 m ( 4.5 m)	3.4 m	0
Impact drive timber	13.7 m ( 13.6 m)	0.5 m ( 1.7 m)	16.3 m ( 21.1 m)	7.3 m ( 12.1 m)	0.5 m ( 4.5 m)	46.4 m	0.01
DTH (Impulsive component)	1,945.5 m ( 1,938.5 m)	69.2 m ( 247.3 m)	2,317.4 m ( 2,999.8 m)	1,041.2 m ( 1,722.1 m)	75.8 m ( 641.9 m)	39,810.7 m	6.31
Vibratory settling concrete	4.5 m ( 6 m)	0.4 m ( 2.3 m)	6.6 m ( 4.9 m)	2.7 m ( 7.8 m)	0.2 m ( 2.6 m)	7,356.4 m	4.89
Impact driver proofing concrete	10 m	0.4 m ( 1.3 m)	11.9 m ( 15.4 m)	5.3 m ( 8.8 m)	0.4 m ( 3.3 m)	541.2 m	0.33
Note 1: Abbreviations: LF = low-frequency cetaceans, HF = high-frequency cetaceans, VHF = very high-frequency cetaceans, PW = phocid pinnipeds in water, OW = otariid pinnipeds in water.
Note 2: Isopleths based on NMFS (2018) are shown with updated isopleths from NMFS (2024) are italicized in parentheses.

Marine Mammal Occurrence

In this section we provide information about the occurrence of marine mammals, including density or other relevant information which informed the take calculations. Available information regarding marine mammal occurrence and density in the project areas includes monitoring data, prior ( print page 104097) incidental take authorizations, and ESA consultations on previous projects. When local density information was not available, data aggregated in the Navy's Marine Mammal Species Density Database (Navy, 2019; Navy, 2020) for the Northwest or Gulf of Alaska Testing and Training areas or nearby proxies from the monitoring data were used. Daily occurrence probability of each marine mammal species is based on consultation with previous monitoring reports, local researchers and marine professionals. Occurrence probability estimates at Moorings Sitka are based on conservative density approximations for each species and factor in historic data of occurrence, seasonality, and group size in Sitka Sound and Sitka Channel. A summary of occurrence is shown in table 10. Group size is based on the best available published research for these species and their presence in the project areas.

Table 10—Estimated Species Occurrence or Density Values

Species	Stock	Moorings Seward	Moorings Sitka
Steller sea lion  a b	Western	2 individuals/day	2 groups of 2 individuals/day of either stock
Steller sea lion  a b	Eastern	0	2 groups of 2 individuals/day of either stock
Northern fur seal	Eastern Pacific	0	1 individual/month
Harbor seal	Prince William Sound	48.95 individuals/day	0
Harbor seal a	Sitka/Chatham Strait	0	2 groups of 2.1 individuals/day
Killer whale	Alaska Resident	1 group of 7 individuals/week of either stock	1 group of 6.6 individuals/week of any stock
Killer whale	Gulf of Alaska, Aleutian Islands, and Bering Sea Transient	1 group of 7 individuals/week of either stock	1 group of 6.6 individuals/week of any stock
Killer whale	Northern Resident	0	1 group of 6.6 individuals/week of any stock
Killer whale	West Coast Transient	0	1 group of 6.6 individuals/week of any stock
Pacific white-sided dolphin	North Pacific	3 individuals/day	0
Harbor porpoise	Gulf of Alaska	0.4547 individuals/km2	0
Harbor porpoise	Yakutat/Southeast Alaska Offshore Waters	0	1 group of 5 individuals/week
Dall's porpoise	Alaska	0.25 individuals/day	0.121 individuals/km2
Sperm whale	North Pacific	0	0.002 individuals/km2
Humpback whale c	Hawai'i	1 individual/day of either stock	1 group of 3.4 individuals/week of either stock
Humpback whale c	Mexico-North Pacific	1 individual/day of either stock	1 group of 3.4 individuals/week of either stock
Gray whale	Eastern North Pacific	0.0155 individuals/km2	1 group of 3.5 individuals/2 weeks
Fin whale	Northeast Pacific	0.068 individuals/km2	0.0001 individuals/km2
Minke whale	Alaska	0.006 individuals/km2	1 group of 3.5 individuals/2 weeks
Note: Occurrence value presented as individuals per unit time; density value presented as individuals per square kilometer.
a  Likelihood of one group per day in the Level A harassment zone and likelihood of two groups per day in the Level B harassment zone.
b  Steller sea lion stock attribution is 100 percent Western DPS at Moorings Seward; 97.8 percent Eastern DPS and 2.2 percent Western DPS at Moorings Sitka.
c  Humpback whale stock attribution is 89 percent Hawai'i and 11 percent Mexico-North Pacific at Moorings Seward; 98 percent Hawai'i and 2 percent Mexico-North Pacific at Moorings Sitka.

Gray whale —Members of the ENP stock have a small chance to occur at the northern end of Resurrection Bay near Moorings Seward, with an estimated density of 0.0155 individuals/km² .

During 190 hours of observation from 1994 to 2002 from Sitka's Whale Park, only three gray whales were observed (Straley et al., 2017). However, Straley and Wild (unpublished data) note that since 2014, the number of gray whale sightings in Sitka Sound has increased to an estimated 150-200 individuals in 2021 and 2022. Based on this and recent monitoring data collected near Sitka, the estimated occurrence of gray whales at Moorings Sitka is one group of 3.5 individuals every 2 weeks.

Fin whale —Fin whales have the potential to occur at both Moorings Seward and Moorings Sitka. Based on survey data, fin whales in the vicinity of Moorings Seward are anticipated to occur at a density of 0.068/km² and fin whales in the vicinity of Moorings Sitka are anticipated to occur at a density of 0.0001/km² .

Humpback whale —Humpback whales found in the project areas are predominantly members of the Hawai'i DPS (89 percent at Moorings Seward, 98 percent probability at Moorings Sitka), which is not listed under the ESA. However, based on a comprehensive photo-identification study, members of the Mexico DPS, which is listed as threatened, have a small potential to occur in all project locations (11 percent at Moorings Seward, 2 percent at Moorings Sitka) (Wade, 2016), and it is estimated that one individual per day of either stock may occur at Moorings Seward while one group of 3.5 individuals per 2 weeks of either stock may occur at Moorings Sitka.

Minke whale —Minke whales are generally found in shallow, coastal waters within 200 m (656 ft) of shore (Zerbini et al., 2006). Dedicated surveys for cetaceans in southeast Alaska found that minke whales were scattered throughout inland waters from Glacier Bay and Icy Strait to Clarence Strait, with small concentrations near the entrance of Glacier Bay. Surveys took place in spring, summer, and fall, and minke whales were present in low numbers in all seasons and years (Dahlheim et al., 2009). Additionally, minke whales were observed during the Biorka Island Dock Replacement Project at the mouth of Sitka Sound (Turnagain Marine Construction, 2018). Minke whale density at Moorings Seward is estimated as 0.006 individuals/km² while estimated occurrence at Moorings Sitka is one group of 3.5 individuals every 2 weeks. ( print page 104098)

Killer whale —Killer whales occur along the entire coast of Alaska (Braham and Dahlheim, 1982) and four stocks may be present in the project areas as follows: (1) Alaska Resident stock—both locations; (2) Gulf of Alaska, Aleutian Islands, and Bering Sea Transient stock—both locations; (3) Northern Resident—Sitka only; and (4) West Coast Transient stock—Sitka only.

The Alaska Resident stock occurs from southeast Alaska to the Aleutian Islands and Bering Sea. The Gulf of Alaska, Aleutian Islands, and Bering Sea Transient stock occurs from the northern British Columbia coast to the Aleutian Islands and Bering Sea. The Northern Resident stock occurs from Washington north through part of southeast Alaska. The West Coast Transient stock occurs from California north through southeast Alaska (Muto et al., 2020). One group of seven individuals per week from either the Alaska Resident stock or the Gulf of Alaska, Aleutian Islands, and Bering Sea Transient stock are estimated to occur at Moorings Seward. One group of 6.6 individuals per week from any of the four stocks are estimated to occur at Moorings Sitka.

Pacific white-sided dolphin —Pacific white-sided dolphins are anticipated to occur in the vicinity of Moorings Seward only. Previous construction monitoring reported by NOAA as an appropriate proxy for Moorings Seward is three individuals per day. During 8 years of surveys near Sitka, Straley et al. (2017) only documented seven Pacific white-sided dolphins, therefore, we do not reasonably expect the species to occur in the vicinity of Moorings Sitka.

Dall's porpoise —Dall's porpoise are anticipated to occur in the vicinity of both locations. At Moorings Seward, the expected occurrence rate is approximately 0.25 animals per day, and the average group size throughout Alaskan waters is estimated to be between 2 and 12 individuals. We therefore estimate that approximately one group of up to six individuals could occur over 22 non-consecutive days of in-water work. At Moorings Sitka, the estimated density of Dall's porpoise is 0.121 individuals/km² .

Harbor porpoise —Only the Yakutat/Southeast Alaska Offshore Waters stock and the Gulf of Alaska stock are expected to be encountered in the project areas. The Gulf of Alaska stock range includes Moorings Seward while the Yakutat/Southeast Alaska Offshore Waters stock's range includes Moorings Sitka. The estimated density of harbor porpoises at Moorings Seward is 0.4547/km² and the estimated occurrence at Moorings Sitka is one group of five individuals every week.

Northern fur seal —Northern fur seals are not expected near Moorings Seward and one individual per month is estimated to occur at Moorings Sitka.

Steller sea lion —Only the Western stock of Steller sea lion is expected to occur at Moorings Seward with an estimated occurrence of two individuals per day. Both the Western and Eastern stocks may occur at Moorings Sitka, which is located in the Central Outer Coast population mixing zone delineated by Hastings et al. (2020). Based on these data, 2.2 percent of Steller sea lions near Sitka are expected to be from the Western stock while 97.8 percent are expected to be from the Eastern stock (Hastings et al., 2020), and it is estimated that two groups of two individuals per day may occur at Moorings Sitka in the Level A harassment zone.

Harbor seal —There are 12 stocks of harbor seals in Alaska, 2 of which occur in the project areas: (1) the Prince William Sound stock ranges from Elizabeth Island off the southwest tip of the Kenai Peninsula to Cape Fairweather, including Moorings Seward; and (2) the Sitka/Chatham Strait stock ranges from Cape Bingham south to Cape Ommaney, extending inland to Table Bay on the west side of Kuiu Island and north through Chatham Strait to Cube Point off the west coast of Admiralty Island, and as far east as Cape Bendel on the northeast tip of Kupreanof Island, which includes Moorings Sitka. Daily occurrence of harbor seals at Moorings Sitka is estimated as 48.95 individuals/day and at Moorings Sitka 2 groups of 2.1 individuals/day are estimated based on previous monitoring in the vicinity, with a likelihood of 2 groups per day in the Level A harassment zone.

Take Estimation

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

Neither the applicant nor NMFS have fine-scale data to quantitatively assess the number of animals in the relatively small predicted Level A harassment zones at either location. Therefore, we assumed that, for cryptic species ( e.g., Steller sea lion, Pacific white-sided dolphin (Moorings Seward only), harbor seal, harbor porpoise), up to 25 percent of the animals that entered the Level B harassment zone could enter the Level A harassment zone undetected, potentially accumulating sound exposure that rises to the level of Level A harassment.

For species with observational data, the following equation was used to estimate take by Level B harassment, where daily occurrence is measured as individuals per day:

Estimated take = (daily occurrence × number of days)−Level A harassment takes

For species with observational data, the following equation was used to estimate take by Level A harassment, where daily occurrence is multiplied by the number of days of work, which is then multiplied by 25 percent:

Estimated take = (daily occurrence × number of days) × 25 percent

For species with density data, the following equation was used to estimate take by Level B harassment, where ensonified area is measured as km² :

Estimated take = (species density × daily ensonified Level B harassment area × number of days)—Level A harassment takes

For species with density data, the following equation was used to estimate take by Level A harassment, where species density is multiplied by the daily ensonified Level A harassment area multiplied by the number of days of work:

Estimated take = species density × daily ensonified Level A harassment area × number of days

Table 11 summarizes the amount of take authorized by both Level A and Level B harassment, as well as the percentage of each stock expected to be taken, at Moorings Seward.

Table 11—Authorized Take of Marine Mammals by Level A and Level B Harassment at Moorings Seward

Species	Stock	Level A	Level B	Total	SAR abundance	Percentage of population
Steller sea lion	Western	10	34	44	49,837	0.09
Harbor seal	Prince William Sound	245	833	1078	44,756	2.41
Killer whale *	Alaska Resident	0	21	21	1,920	1.09
( print page 104099)
Killer whale *	Eastern North Pacific Gulf of Alaska, Aleutian Islands and Bering Sea Transient	0	7	7	587	1.19
Pacific white-sided dolphin	North Pacific	15	51	66	26,880	0.25
Harbor porpoise	Gulf of Alaska	8	15	23	31,046	0.07
Dall's porpoise	Alaska	1	5	6	UND	UND
Humpback whale	Hawai'i	0	20	20	11,278	0.18
Humpback whale	Mexico-North Pacific	0	2	2	N/A	N/A
Gray whale	Eastern North Pacific	0	1	1	26,960	0
Fin whale	Northeast Pacific	0	3	3	UND	UND
Note: Humpback whale stock attribution: 89 percent Hawai'i and 11 percent Mexico-North Pacific.
* Percent of stock impacted for killer whales was estimated assuming each stock is taken in proportion to its population size at each location from the total take. At Moorings Seward, the Alaska Resident and Gulf of Alaska stocks are the only stocks present. Of these, the Alaska Resident stock represents approximately 76 percent of the available animals, while the Gulf of Alaska stock represents approximately 23 percent. Takes were then calculated for each site based on the proportional representation of available stocks, so for Moorings Seward, this results in 21 Level B harassment takes of the Alaska Resident stock of killer whale and 7 Level B harassment takes of the Gulf of Alaska stock of killer whale. Total takes for each stock are shown as a percentage of the stock size.

Table 12 summarizes amount of take authorized by both Level A and Level B harassment, as well as the percentage of each stock expected to be taken, at Moorings Sitka.

Table 12—Authorized Take of Marine Mammals by Level A and Level B Harassment at Moorings Sitka

Species	Stock	Level A	Level B	Total	SAR abundance	Percentage of population
Steller sea lion	Western	2	6	8	49,837	0.02
Steller sea lion	Eastern	82	270	352	36,308	0.97
Northern fur seal	Eastern Pacific	0	3	3	626,618	0
Harbor seal	Sitka/Chatham Strait	88	272	360	13,289	2.71
Killer whale *	Alaska Resident	0	55	55	1,920	2.86
Killer whale *	Eastern North Pacific Gulf of Alaska, Aleutian Islands and Bering Sea Transient	0	17	17	587	2.90
Killer whale *	Northern Resident	0	8	8	302	2.65
Killer whale *	West Coast Transient	0	10	10	349	2.87
Harbor porpoise	Yakutat/Southeast Alaska Offshore Waters	15	20	35	N/A	N/A
Dall's porpoise	Alaska	24	42	66	UND	UND
Humpback whale	Hawai'i	0	43	43	11,278	0.38
Humpback whale	Mexico-North Pacific	0	1	1	N/A	N/A
Gray whale	Eastern North Pacific	0	22	22	26,960	0.08
Minke whale	Alaska	0	22	22	N/A	N/A
Note: Steller sea lion stock attribution: 97.8 percent Eastern DPS and 2.2 percent Western DPS at Moorings Sitka. Humpback whale stock attribution: 98 percent Hawai'i and 2 percent Mexico-North Pacific.
* Percent of stock impacted for killer whales was estimated assuming each stock is taken in proportion to its population size at each location from the total take. At Moorings Sitka, the Alaska Resident, Gulf of Alaska, Northern Resident, and West Coast Transient stocks are expected, and the Alaska Resident stock represents approximately 60 percent of the available animals, the Gulf of Alaska stock represents approximately 19 percent, the Northern Resident stock represents approximately 10 percent, and the West Coast Transient represents approximately 11 percent. Takes were then calculated based on the proportional representation of available stocks, which results in 55 Level B harassment takes of the Alaska Resident stock, 17 Level B harassment takes of the Gulf of Alaska stock, 8 Level B harassment takes of the Northern Resident stock, and 10 Level B harassment takes of the West Coast Transient stock. Total takes for each stock are shown as a percentage of the stock size.

Mitigation

In order to issue an IHA under section 101(a)(5)(D) of the MMPA, NMFS must set forth the permissible methods of taking pursuant to the activity, and other means of effecting the least practicable impact on the species or stock and its habitat, paying particular attention to rookeries, mating grounds, and areas of similar significance, and on the availability of the species or stock for taking for certain subsistence uses. NMFS regulations require applicants for incidental take authorizations to include information about the availability and feasibility (economic and technological) of equipment, methods, and manner of conducting the activity or other means of effecting the least practicable adverse impact upon the affected species or stocks, and their habitat (50 CFR 216.104(a)(11)).

In evaluating how mitigation may or may not be appropriate to ensure the least practicable adverse impact on species or stocks and their habitat, as well as subsistence uses where applicable, NMFS considers two primary factors:

(1) The manner in which, and the degree to which, the successful implementation of the measure(s) is expected to reduce impacts to marine ( print page 104100) 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.

For each IHA, the USCG must:

• Ensure that construction supervisors and crews, the monitoring team, and relevant USCG staff are trained prior to the start of all pile driving and DTH activity, so that responsibilities, communication procedures, monitoring protocols, and operational procedures are clearly understood. New personnel joining during the project must be trained prior to commencing work;
• Employ one to five PSOs and establish monitoring locations as described in the application and the IHA. The USCG must monitor the project area to the maximum extent possible based on the required number of PSOs, required monitoring locations, and environmental conditions. For all pile driving and removal at least one PSO must be used. The PSO will be stationed as close to the activity as possible;
• The placement of the PSOs during all pile driving and removal and DTH activities will ensure that the entire shutdown zone is visible during pile installation;
• Monitoring must take place from 30 minutes prior to initiation of pile driving or DTH activity (i.e., pre-activity monitoring) through 30 minutes post-activity of pile driving or DTH activity;
• Pre-activity monitoring must be conducted during periods of visibility sufficient for the lead PSO to determine that the shutdown zones indicated in table 13 are clear of marine mammals. Pile driving and DTH may commence following 30 minutes of observation when the determination is made that the shutdown zones are clear of marine mammals;
• The USCG must use soft start techniques when impact pile driving. Soft start requires contractors to provide an initial set of three strikes at reduced energy, followed by a 30-second waiting period, then two subsequent reduced-energy strike sets. A soft start must be implemented at the start of each day's impact pile driving and at any time following cessation of impact pile driving for a period of 30 minutes or longer; and
• If a marine mammal is observed entering or within the shutdown zones indicated in table 13, pile driving and DTH must be delayed or halted. If pile driving is delayed or halted due to the presence of a marine mammal, the activity may not commence or resume until either the animal has voluntarily exited and been visually confirmed beyond the shutdown zone (table 13) or 15 minutes have passed without re-detection of the animal.

As proposed by the applicant, in-water activities will take place only between civil dawn and civil dusk (generally 30 minutes after sunrise and up to 45 minutes before sunset), and work may not begin without sufficient daylight to conduct pre-activity monitoring, and may extend up to 3 hours past sunset, as needed to either completely remove an in-process pile or to embed a new pile far enough to safely leave piles in place until work can resume the next day; during conditions with a Beaufort Sea State of four or less; and when the entire shutdown zones are visible.

Protected Species Observers

The placement of PSOs during all pile driving activities (described in Monitoring and Reporting) will ensure that the entire shutdown zone is visible. Should environmental conditions deteriorate such that the entire shutdown zone will not be visible ( e.g., fog, heavy rain), pile driving will be delayed until the PSO is confident marine mammals within the shutdown zone could be detected.

PSOs will monitor the full shutdown zones and the Level B harassment zones to the extent practicable. Monitoring zones provide utility for observing by establishing monitoring protocols for areas adjacent to the shutdown zones. Monitoring zones enable observers to be aware of and communicate the presence of marine mammals in the project areas outside the shutdown zones and thus prepare for a potential cessation of activity should the animal enter the shutdown zone.

Pre- and Post-Activity Monitoring

Monitoring must take place from 30 minutes prior to initiation of pile driving activities ( i.e., pre-clearance monitoring) through 30 minutes post-completion of pile driving. Prior to the start of daily in-water construction activity, or whenever a break in pile driving of 30 minutes or longer occurs, PSOs will observe the shutdown and monitoring zones for a period of 30 minutes. The shutdown zone will be considered cleared when a marine mammal has not been observed within the zone for a 30-minute period. If a marine mammal is observed within the shutdown zones listed in table 9, pile driving activity will be delayed or halted. If work ceases for more than 30 minutes, the pre-activity monitoring of the shutdown zones will commence. A determination that the shutdown zone is clear must be made during a period of good visibility ( i.e., the entire shutdown zone and surrounding waters must be visible to the naked eye).

Soft-Start Procedures for Impact Driving

Soft-start procedures provide additional protection to marine mammals by providing warning and/or giving marine mammals a chance to leave the area prior to the hammer operating at full capacity. If impact pile driving is necessary to achieve required tip elevation, the USCG is required to provide an initial set of three strikes from the hammer at reduced energy, followed by a 30-second waiting period, then two subsequent reduced-energy strike sets. Soft-start must be implemented at the start of each day's impact pile driving and at any time following cessation of impact pile driving for a period of 30 minutes or longer.

Shutdown Zones

The USCG must establish shutdown zones for all pile driving activities. The purpose of a shutdown zone is generally to define an area within which shutdown of the activity would occur upon sighting of a marine mammal (or in anticipation of an animal entering the defined area). Shutdown zones are based upon the Level A harassment thresholds for each pile size/type and driving method where applicable, as shown in table 13. During all in-water piling activities, the USCG plans to implement a minimum 30-m shutdown zone, larger than NMFS' typical requirement of a minimum 10-m shutdown zone, with the addition of larger zones during DTH. These distances exceed the estimated Level A harassment isopleths described in tables 8 and 9. Adherence to this expanded shutdown zone will reduce the potential for the take of marine mammals by Level A harassment but, due to the large zone sizes and small, inconspicuous nature of five species (Steller sea lion, Pacific white-sided dolphin (Moorings Seward only), harbor seal, harbor porpoise, Dall's porpoise), the potential for Level A harassment cannot be completely avoided. If a marine ( print page 104101) mammal is observed entering, or detected within, a shutdown zone during pile driving activity, the activity must be stopped until there is visual confirmation that the animal has left the zone or the animal is not sighted for a period of 15 minutes. Shutdown zones for each activity type are shown in table 13.

All marine mammals would be monitored in the Level B harassment zones and throughout the area as far as visual monitoring can take place. If a marine mammal enters the Level B harassment zone, in-water activities will continue and PSOs will document the animal's presence within the estimated harassment zone.

Table 13—Shutdown Zones and Harassment Zones

Activity	Shutdown zone (m) for LF	Shutdown zone (m) for HF	Shutdown zone (m) for VHF	Shutdown zone (m) for PW	Shutdown zone (m) for OW	Level B harassment zone (m) at Seward	Level B harassment zone (m) at Sitka
Vibratory pile extraction	30	30	30	30	30	4,645	6,310
Impact drive plastic pile	30	30	30	30	30	N/A	5
Impact drive timber pile	30	30	30	30	30	N/A	50
DTH (Impulsive component) concrete pile	1,955	85	2,325	1,050	85	39,815	39,815
Vibratory concrete pile settling	30	30	30	30	30	7,360	7,360
Impact drive concrete pile proofing	30	30	30	30	30	545	545
Note: Level A (AUD INJ onset) harassment will only potentially result from DTH rock socket drilling activities that will generate underwater noise in exceedance of Level A harassment thresholds for all marine mammal hearing groups beyond the 30-m shutdown zone that will be implemented for all in-water activities. Therefore, larger shutdown zones will be implemented during DTH activities and at least two additional PSOs will be assigned to a captained vessel at one or more monitoring locations that provide full views of the shutdown zones and as much of the monitoring zones as possible.