2024-21287. Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to Washington State Department of Transportation's Seattle Slip 3 Vehicle Transfer Span Project in Washington State

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
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
Minke whale	Balaenoptera acutorostrata	CA/OR/WA	-, -, N	915 (0.792, 509, 2018)	4.1	0.19
Odontoceti (toothed whales, dolphins, and porpoises)
Family Delphinidae:
Killer whale 5	Orcinus orca	West Coast Transient	-, -, N	349 (N/A, 349, 2018)	3.5	0.4
Bottlenose dolphin	Tursiops truncatus	CA/OR/WA offshore	-, -, N	3,477 (0.696, 2,048, 2018)	19.70	≥0.82
Long beaked common dolphin	Delphinus capensis	CA	-, -, N	83,379 (0.216, 69,636, 2018)	668	≥29.7
Pacific white-sided Dolphin	Lagenorhynchus obliquidens	CA/OR/WA	-, -, N	34,999 (0.222, 29,090, 2018)	279	7
Family Phocoenidae (porpoises):
Dall's porpoise	Phocoenoides dalli	CA/OR/WA	-, -, N	16,498 (0.61, 10,286, 2018)	99	≥0.66
Harbor porpoise	Phocoena phocoena	Washington Inland Waters	-, -, N	11,233 (0.37, 8,308, 2015)	66	≥7.2
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 6	Eumetopias jubatus	Eastern	-, -, N	36,308 (N/A, 36,308, 2022)	2,178	93.2
Family Phocidae (earless seals):
Harbor seal	Phoca vitulina	Washington Northern Inland Waters	-, -, N	16,451 (0.07, 15,462, 2019)	928	40
Northern elephant seal 7	Mirounga angustirostris	CA Breeding	-, -, N	187,386 (N/A, 85,369, 2013)	5,122	13.7
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 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; Nmin is the minimum estimate of stock abundance.
4  These values, found in NMFS's SARs, represent annual levels of human-caused mortality plus serious injury from all sources combined ( e.g., commercial fisheries, ship strike). Annual M/SI often cannot be determined precisely and is in some cases presented as a minimum value or range. A CV associated with estimated mortality due to commercial fisheries is presented in some cases.
5  Nest is based upon count of individuals identified from photo-ID catalogs in analysis of a subset of data from 1958-2018.
6  Nest is best estimate of counts, which have not been corrected for animals at sea during abundance surveys. Estimates provided are for the U.S. only.
7  There is uncertainty in available population estimates due to limited surveys, limited reproductive data, and uncertainty in stock relationships and harvest statistics.

As indicated above, all 12 species in table 1 spatially and temporally co-occur with the activity to the degree that take is reasonably likely to occur. A detailed description of the species likely to be affected by WSDOT's 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 61064, July 30, 2024); since that time, we are not aware of any changes in the status of these species and stocks; therefore, detailed descriptions are not provided here. Please refer to that Federal Register notice for these descriptions. Please also refer to NMFS' website ( https://www.fisheries.noaa.gov/​find-species) for generalized species accounts.

Marine Mammal Hearing

Hearing is the most important sensory modality for marine mammals underwater, and exposure to anthropogenic sound can have deleterious effects. To appropriately assess the potential effects of exposure to sound, it is necessary to understand the frequency ranges marine mammals are able to hear. Not all marine mammal species have equal hearing capabilities ( e.g., Richardson et al., 1995; Wartzok and Ketten, 1999; Au and Hastings, 2008). To reflect this, Southall et al. (2007, 2019) recommended that marine mammals be divided into hearing groups based on directly measured (behavioral or auditory evoked potential techniques) or estimated hearing ranges (behavioral response data, anatomical modeling, etc.). 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.

The pinniped functional hearing group was modified from Southall et al. (2007) on the basis of data indicating that phocid species have consistently demonstrated an extended frequency range of hearing compared to otariids, especially in the higher frequency range (Hemilä et al., 2006; Kastelein et al., 2009; Reichmuth et al., 2013).

For more detail concerning these groups and associated frequency ranges, please see NMFS (2018) for a review of available information. ( print page 76807)

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).

Potential Effects of Specified Activities on Marine Mammals and Their Habitat

The effects of underwater noise from WSDOT's construction activities have the potential to result in behavioral harassment of marine mammals in the vicinity of the project area. The notice of proposed IHA (89 FR 61064, July 30, 2024) included a discussion of the effects of anthropogenic noise on marine mammals and the potential effects of underwater noise from WSDOT's construction activity 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 61064, July 30, 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” and the negligible impact determinations.

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

Authorized takes may occur by Level B harassment only, in the form behavioral reactions and temporary threshold shift (TTS) for individual marine mammals resulting from exposure to noise from impact and vibratory pile driving and removal. Based on the nature of the activity and the anticipated effectiveness of the mitigation measures ( i.e., shutdown zones at the Level A harassment area) discussed in detail below in the Mitigation section, Level A harassment is neither anticipated nor authorized.

As described previously, no serious injury or mortality is anticipated or authorized for this activity. Below we describe how the information provided above is synthesized to produce a quantitative estimate of the take that is reasonably like to occur and is authorized.

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 numbers.

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 permanent threshold shift (PTS) of some degree (equated to Level A harassment). Acoustic thresholds used in the analysis were discussed in detail in the notice of proposed IHA (89 FR 61064, July 30, 2024) and not repeated here. Please see that notice for additional detail.

Ensonified Area

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

The sound field in the project area is the existing background noise plus additional construction noise from the construction project. Marine mammals are expected to be affected by sound generated from the impact and vibratory pile driving components of this project.

In order to calculate distances to the Level A harassment and Level B harassment thresholds for the methods and piles used in the project, NMFS used acoustic monitoring data from previous pile driving at WSDOTs Bainbridge Island Ferry Terminal Project (vibratory removal of 12-inch H-piles), Phase 2 of Colman Dock construction for the Seattle Multimodal Project (impact installation of 24-inch steel piles), and the Ebey Slough Bridge Replacement Project (72-inch steel piles). Each of the projects listed above occurred within the Puget Sound and provided the most suitable source levels due to similar physical habitat characteristics, pile sizes, and pile driving or removal methods (table 3).

Source levels from the Bainbridge Terminal Ferry Project and the Ebey Slough Bridge Replacement Project were used as proxies for the vibratory removal of 14-inch steel H-piles and the vibratory installation of 24, 30, and 78-inch steel pipe piles for the project because source levels for identical pile sizes were unavailable. Results from the vibratory installation of 72-inch piles at the Ebey Slough Bridge Replacement Project showed that source levels ranged between 148 to 166 dB re 1 µPa at 10 m, therefore 174 dB re 1 µPa at 10 m, as proposed for use by WSDOT, was used as a conservative source level estimate for the vibratory installation of 24, 30, and 78-in steel pipe piles (WSDOT 2011). The source level for 14-inch H-piles was assumed to be ( print page 76808) equivalent to the vibratory removal of 12-inch H-piles at the Bainbridge Island Ferry Terminal where the unweighted RMS SPL source level was 153 dB re 1 µPa at 10 m (Laughlin 2019). Bubble curtains would be employed for impact installation of 24-inch steel piles but zero dB of effective attenuation is assumed because a bubble curtain was used at Phase 2 of Colman Dock construction for the Seattle Multimodal Project, thus source levels would be the same.

Table 3—Seattle Slip 3 Vehicle Transfer Span Proxy Sound Source Levels for Pile Sizes and Driving Methods

Pile type and size (in)	Method	Source level at 10 m (dB re 1 µPA)	Reference
14-inch steel H-piles	Vibratory Removal	153 dB rms	Laughlin (2019).
24-inch steel pipe piles	Vibratory installation and removal	174 dB rms	WSDOT (2011).
24-inch steel pipe piles	Impact installation	166 SEL, 176 dB rms, 194 dB peak	Greenbusch Group (2019).
30-inch steel sheet piles	Vibratory installation	174 dB rms	WSDOT (2011).
78-inch steel pipe piles	Vibratory installation	174 dB rms	WSDOT (2011).

Level B Harassment Zones

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

TL = B * Log10 (R1/R2)

Where:

TL = transmission loss in dB

B = transmission loss coefficient; 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. 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 WSDOTs activities in the absence of specific modelling. The estimated Level B harassment zones for the WSDOTs activities are shown in tables 4 and 5.

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 Technical Guidance that can be used to relatively simply predict an isopleth distance for use in conjunction with marine mammal density or occurrence to help predict potential takes. We note that because of some of the assumptions included in the methods underlying this optional tool, we anticipate that the resulting isopleth estimates are typically 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 installation and removal, the optional User Spreadsheet tool predicts the distance at which, if a marine mammal remained at that distance for the duration of the activity, it would be expected to incur PTS. Inputs used in the optional User Spreadsheet tool ( e.g., number of piles per day, during and/or strikes per pile) are presented in table 1 of the proposed IHA Federal Register notice (89 FR 61064; July 30, 2024), and the resulting estimated isopleths and ensonified areas are reported in tables 4 and 5 below.

Table 4—Level A and Level B Harassment Zones

Pile size and type	Pile driving method	Level A harassment zone (m)					Level B harassment zone (m)
		LF cetaceans	MF cetaceans	HF cetaceans	Phocids	Otarids
14-inch steel	Vibratory removal	3.2	0.3	4.7	1.9	0.1	1,585
24-inch steel	Vibratory installation and removal	65.8	5.8	97.3	40.0	2.8	a  15,410
24-inch steel	Impact installation	75.9	2.7	90.4	40.6	3.0	736
30-inch steel	Vibratory installation	50.2	4.5	74.3	30.5	2.1	a  15,410
78-in steel	Vibratory installation	50.2	4.5	74.3	30.5	2.1	a  15,410
a  Land is reached at a maximum of 15,410 km/9.6 miles.

Table 5—Level A and Level B Ensonified Areas

Pile size and type	Pile driving method	Level A ensonified area (m2 )					Level B harassment zone (m)
		LF cetaceans	MF cetaceans	HF cetaceans	Phocids	Otarids
14-inch steel	Vibratory removal	8.0	0.07	17.4	2.8	0.007	3,247,392
24-inch steel	Vibratory installation and removal	4,524.5	5.7	6,418	1,294.6	7.07	75,844,286
24-inch steel	Impact installation	75.9	2.7	90.4	40.6	3.0	861,188
30-inch steel	Vibratory installation	1,979.2	15.9	4,336	730.6	3.5	75,844,286
78-inch steel	Vibratory Installation	1,979.2	15.9	4,336	730.6	3.5	75,844,286

( print page 76809)

Marine Mammal Occurrence and Take Estimation

In this section we provide information about the occurrence of marine mammals, including density or other relevant information which will inform take incidental to WSDOTs pile driving activities for the Seattle Slip 3 VTS Replacement Project. Throughout this section the pile installation or removal will be referred to as “pile driving” unless specified otherwise. From 2017 through 2021 WSDOT monitored for marine mammals in Elliott Bay for the Seattle Multimodal Project. During this time, marine mammal monitoring occurred for 377 days. Since the Seattle Multimodal Project occurred in Elliott Bay, WSDOT considered this marine mammal monitoring data to be the most comprehensive and relevant for estimating take for the Seattle Slip 3 VTS Replacement Project. Therefore, this data compiled all of these monitoring results and calculated total sightings, average sightings per day, and maximum sightings per day for all species of marine mammals that were observed (table 6). WSDOT used their best professional judgement and used this data to estimate take by multiplying maximum sighting per day by 19, which is the maximum number of in-water working days WSDOT estimates it would take to complete the project in a total worst case scenario.

NMFS has carefully evaluated these methods and concludes that it is an accurate and appropriate method for estimating take for WSDOTs activities for this project.

Table 6—Marine Mammals Sighted at the Seattle Multimodal Project

Species	Total individuals sighted a	Average individuals sighted/day (377 days) a	Maximum individuals sighted in one-day a	Take requested
Harbor seal	2,271	6.0	32	Yes.
Northern elephant seal	1	0.003	1	Yes.
California sea ion	3,669	9.7	29	Yes.
Steller sea ion	112	0.3	10	Yes.
Unidentified pinniped	121	N/A	N/A	N/A.
Killer whale Southern resident	170	0.5	26	No.
Killer whale transient	79	0.2	20	Yes.
Gray whale	5	0.01	2	Yes.
Humpback whale	8	0.02	1	No.
Minke whale	3	0.008	1	Yes.
Unidentified large whale	2	N/A	1	N/A.
Unidentified small whale	10	N/A	N/A	N/A.
Harbor porpoise	655	1.7	72	Yes.
Dall's porpoise	8	0.02	5	Yes.
Common bottlenose dolphin	6	0.02	2	Yes.
Pacific white-sided dolphin	2	0.005	2	Yes.
Long-beaked common dolphin	0	N/A	0	Yes.
Unidentified dolphin/porpoise	46	N/A	6	N/A.
a  WSDOT 2022.

Gray Whale —Although gray whales are common on the southern ends of Whidbey and Camano Islands in the Puget Sound February through May, they are rarely sighted in the construction area (Calambokidis et. al. 2024). During the Seattle multimodal project only five gray whales were detected over 377 days of monitoring with a maximum of two individuals observed on a single day (WSDOT 2022). WSDOT estimated that up to 2 gray whales could be taken per day for the 19 days of construction, for a total of 38 takes by Level B harassment.

Since Seattle Slip 3 VTS Replacement Project construction would occur from August through mid-February, gray whales occurrence is expected to be relatively low. In this context, and given that gray whales are highly conspicuous, we have a high degree of confidence that WSDOT can successfully implement shutdowns as necessary to avoid any potential Level A harassment of gray whales. WSDOT must also monitor the Orca Network and the Whale Report Alert System (WRAS) daily in order to maintain awareness of regional whale occurrence and movements ( see Mitigation and Monitoring and Reporting sections below). Therefore, take of gray whales by Level A harassment is not anticipated or authorized.

Minke Whale —Minke whales are uncommon during fall and winter months in the Puget Sound but are rarely sighted in the construction area (Calambokidis and Baird 1994). During the Seattle Multimodal Project only three minke whale detections occurred over 377 days of monitoring with a maximum of one detection on a single day (WSDOT 2022). WSDOT estimated that up to 1 minke whale could be taken per day for the 19 days of construction, for a total of 19 takes by Level B harassment.

Since the Seattle Slip 3 VTS Replacement Project construction would occur from August through mid-February, minke whale occurrence is expected to be relatively low. In these circumstances, and given that minke whales are highly conspicuous, we have a high degree of confidence that WSDOT can successfully implement shutdowns as necessary to avoid any potential Level A harassment of minke whales. WSDOT must also monitor the Orca Network and the WRAS daily in order to maintain awareness of regional whale occurrence and movements ( see Mitigation and Monitoring and Reporting sections below). Therefore, take of minke whales by Level A harassment is not anticipated or authorized.

Transient Killer Whale —Transient killer whales are common in in the Puget Sound in all months and a total of 79 transient killer whale detections occurred over 377 days of monitoring for the Seattle Multimodal Project with a maximum of 20 detections in a single day (Orca Network 2021, WSDOT 2022). WSDOT estimated that up to 20 incidents of take for transient killer whales could occur per day for 19 days of construction, for a total of 380 takes by Level B Harassment. Transient killer whales are common in the Puget Sound and are highly conspicuous. ( print page 76810)

The largest Level A harassment zone for mid-frequency cetaceans for all construction for the Seattle Slip 3 VTS Replacement Project is less than 6 m. It is highly unlikely that any cetacean would enter within 6 m of active pile driving, and no take by Level A harassment for any mid-frequency cetacean is expected to occur. WSDOT must also monitor the Orca Network and the WRAS daily in order to maintain awareness of regional whale occurrence and movements (see Mitigation and Monitoring and Reporting sections below). Therefore, take of transient killer whales by Level A harassment is not anticipated or authorized.

Bottlenose Dolphin —Bottlenose dolphins are considered to be rare in the Puget Sound but they were detected by the Cascadia Research Collective and reported via the Orca Network in 2017 (Cascadia Research Collective, 2017). They were also detected on six occasions with a maximum of two detections on a single day during the Seattle Multimodal Project (WSDOT 2022). WSDOT estimated that up to 2 bottlenose dolphins could be taken per day for the 19 days of construction, for a total of 38 takes by Level B harassment.

The largest Level A harassment zone for mid-frequency cetaceans for all construction of the Seattle Slip 3 VTS Replacement Project is less than 6 m. It is highly unlikely that any cetacean would enter within 6 m of active pile driving, and no take by Level A harassment for any mid-frequency cetacean is expected to occur. WSDOT must also monitor the Orca Network and the WRAS daily in order to maintain awareness of regional whale occurrence and movements (see Mitigation and Monitoring and Reporting sections below). Therefore, take of bottlenose dolphins by Level A harassment is not anticipated or authorized.

Long-Beaked Common Dolphin —No confirmed detections of long-beaked common dolphins occurred during the Seattle Multimodal Project but six unidentified delphinids were observed (WSDOT 2022). WSDOT assumed that up to two of these unidentified delphinids could have been long-beaked common dolphins. Therefore, WSDOT estimated that up to 2 long-beaked common dolphins could be taken per day for the 19 days of construction, for a total of 38 takes by Level B harassment.

The largest Level A harassment zone for mid-frequency cetaceans for all construction of the Seattle Slip 3 VTS Replacement Project is less than 6 m. It is highly unlikely that any cetacean would enter within 6 m of active pile driving, and no take by Level A harassment for any mid-frequency cetacean is expected to occur. WSDOT must also monitor the Orca Network and the WRAS daily in order to maintain awareness of regional whale occurrence and movements (see Mitigation and Monitoring and Reporting sections below). Therefore, take of long-beaked common dolphins by Level A harassment is not anticipated or authorized.

Pacific White-Sided Dolphin —Pacific white-sided dolphins are rare in the Puget Sound but have been observed in San Juan Channel (Orca Network 2012). Two Pacific white sided dolphins were also observed during the Seattle Multimodal Project (WSDOT 2022). WSDOT estimated that up to 2 Pacific white-sided dolphins could be taken per day for the 19 days of construction, for a total of 38 takes by Level B harassment.

The largest Level A harassment zone for mid-frequency cetaceans for all construction of the Seattle Slip 3 VTS Replacement Project is less than 6 m. It is highly unlikely that any cetacean would enter within 6 m of active pile driving, and no take by Level A harassment for any mid-frequency cetacean is expected to occur. WSDOT must also monitor the Orca Network and the WRAS daily in order to maintain awareness of regional whale occurrence and movements ( see Mitigation and Monitoring and Reporting sections below). Therefore, take of Pacific white-sided dolphins by Level A harassment is not anticipated or authorized.

Dall's Porpoise —Dall's porpoises are considered rare within the project area. WSDOT recorded only eight detections over 377 days of monitoring during the Seattle Multimodal Project (WSDOT 2022). WSDOT estimated that up to 5 Dall's porpoises could be taken per day for the 19 days of construction, for a total of 95 takes by Level B harassment.

The largest Level A harassment zone for high-frequency cetaceans for all construction of the Seattle Slip 3 VTS Replacement Project is less than 100 m. Due to the relatively short duration of construction for the Seattle Slip 3 VTS Replacement Project and infrequent detections of Dall's porpoises, WSDOT estimated that no Dall's porpoises would be likely to enter the Level A harassment zone. Take by Level A harassment of Dall's porpoises is not anticipated or authorized.

Harbor Porpoise —From 2017 through 2022, WSDOT recorded 655 detections of harbor porpoises with a maximum of 72 detections on a single day (WSDOT 2022). WSDOT estimated that up to 72 instances of take for harbor porpoises could occur per day for the 19 days of construction, for a total of 1,368 takes by Level B harassment.

The largest Level A harassment zone for high-frequency cetaceans is under 100 m. Although harbor porpoises are relatively common in the Puget Sound, we assume that WSDOT would be able to cease construction if harbor porpoises entered the Level A harassment zone before sufficient duration of exposure for PTS to occur. Take by Level A harassment is not anticipated or authorized.

California Sea Lion —California sea lions are relatively common throughout the Puget Sound. During the Seattle Multimodal Project a maximum of 29 sea lions were detected on a single day with a total of 3,669 sightings over the 377 days of monitoring (WSDOT 2022). WSDOT estimated that 32 California sea lions would enter the Level B harassment zone for each of the 19 days of construction, for a total of 551 takes by Level B harassment.

The largest Level A harassment zone for Otariids for all construction of the Seattle Slip 3 VTS Replacement Project is less than 3 m. It is highly unlikely that any Otariids would enter within 3 m of active pile driving, and no take by Level A harassment for any mid-frequency cetacean is expected to occur. Therefore, take of California sea lions by Level A harassment is not anticipated or authorized.

Steller Sea Lion —Monitoring during the Seattle Multimodal Project recorded 112 detections of Steller sea lions over 377 days of monitoring, which is less than 1 detection per day. However, a maximum of 10 detections were recorded in a single day. Therefore, WSDOT estimated that 10 Steller sea lions would enter the Level B harassment zone each day for the 19 days of construction of the project, for a total of 190 takes by Level B harassment.

The largest Level A harassment zone for Otariids for all construction of the Seattle Slip 3 VTS Replacement Project is less than 3 m. It is highly unlikely that any Otariids would enter within 3 m of active pile driving, and no take by Level A harassment for any mid-frequency cetacean is expected to occur. Therefore, take of steller sea lions by Level A harassment is not anticipated or authorized.

Harbor Seal —Harbor seals are common in the project area. During the Seattle Multimodal Project WSDOT recorded an average of 6 harbor seal detections per day and a maximum of ( print page 76811) 32 in a single day (WSDOT 2022). WSDOT estimated that a maximum of 32 harbor seals will enter the Level B harassment zones for each of the 19 days of construction, for a total of 608 takes by Level B harassment.

The largest Level A harassment zone for high-frequency phocids is under 41 m. Although harbor seals are relatively common in the Puget Sound, we assume that WSDOT would be able to cease construction if harbor seals entered the Level A harassment zone before sufficient duration of exposure for PTS to occur. Take by Level A harassment is not anticipated or authorized.

Northern Elephant Seal —Although northern elephant seals are rare in the Puget Sound, one individual was detected during the Seattle Multimodal Project. Since northern elephant seals are rare in the construction area, WSDOT estimated that a maximum of one elephant seal would enter the Level B harassment zone per day for each of the 19 days of construction. A total of 19 takes by Level B harassment is estimated for northern elephant seals for construction associated with the Seattle Slip 3 VTS Replacement Project.

Similar to harbor seals, the largest harassment zone is less than 41 m for all construction activities. Given the anticipated rarity of occurrence for elephant seals, WSDOT does not expect northern elephant seals to enter Level A harassment zones without being detected prior to shutdown. Construction will cease if a northern elephant seal is observed entering Level A harassment zone. Therefore, no take by Level A harassment of northern elephant seals is anticipated or authorized.

Table 7—Estimated Take of Marine Mammal by Level B Harassment for 19 Days of In-Water Construction

Species	Maximum sightings/day a	Total takes by Level B harassment	Percent of stock
Phocids:
Harbor seal	32	608	5.51
Northern elephant seal	1	19	0.02
Otariids:
California sea lion	29	551	0.24
Steller sea lion	10	190	0.23
Cetaceans:
Killer whale transient	20	380	110
Gray whale	2	38	0.15
Minke whale	1	19	3.7
Harbor porpoise	72	1,368	16.5
Dall's porpoise	5	95	0.37
Common bottlenose dolphin	2	38	3.0
Pacific white-sided dolphin	2	38	0.13
Long-beaked common dolphin	5	38	0.05
a  WSDOT 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 (latter not applicable for this action). NMFS regulations require applicants for incidental take authorizations to include information about the availability and feasibility (economic and technological) of equipment, methods, and manner of conducting the activity or other means of effecting the least practicable adverse impact upon the affected species or stocks, and their habitat (50 CFR 216.104(a)(11)).

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

(1) The manner in which, and the degree to which, the successful implementation of the measure(s) is expected to reduce impacts to marine mammals, marine mammal species or stocks, and their habitat. 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.

Shutdown Zones

Prior to the start of any in-water construction, WSDOT must establish shutdown zones for all planned activities. Shutdown zones are pre-defined areas within which construction will be halted upon sightings of a marine mammal or in anticipation of a marine mammal entering the established shutdown zones. Pile-driving will not re-commence until all marine mammals are assumed to have cleared these established shutdown zones.

WSDOT must establish shutdown zones for Southern Resident killer whales (SRKWs) and humpback whales (HWs) at the Level B harassment zone for the vibratory removal of 14-in piles at 1,600 m and at 750 m for impact driving 24-in piles (table 4 and table 8). These shutdown zones are the Level B harassment zone rounded up to the nearest 50 m for each pile size and driving method. Shutdown zones for the remaining pile-driving for SRKWs and HWs will be established at 15,410 m, which is equivalent to the maximum Level B harassment area before it reaches land.

The largest Level A harassment zone for the vibratory removal of 14-in piles is 3.2 m for all cetaceans and pinnipeds. However, WSDOT will implement a shutdown zone at 50 m for removal of 14-in piles. The shutdown zones for the ( print page 76812) remaining pile-driving activities will be established at 100 m for all hearing groups of cetaceans (except SRKWs and HWs, as discussed above) and 50 m for all pinnipeds. The largest Level A harassment zone amongst all hearing groups of cetaceans would be 97.3 m for the remaining pile-driving (table 4). The largest Level A harassment zone amongst pinnipeds will be 40.6 m for the remaining pile driving (table 4). With WSDOTs established shutdown zones, all incidental take will be prevented for SRKWs and HWs and only take by Level B harassment is authorized to occur for the remaining species of cetaceans and pinnipeds.

WSDOT will also establish shutdown zones for all other species of marine mammals for which take has not been authorized or for which incidental take has been authorized but the number of authorized takes has already been met. Those zones will be equivalent to Level B harassment zones provided for each activity in table 4.

In addition to the shutdown zones mentioned above, WSDOT proposes to implement shutdown measures for SRKWs and HWs. If SRKWs or HWs are observed within or approaching established shutdown zones (see table 8), WSDOT will shut down pile driving equipment to avoid take of these species. If a killer whale approaches a Level B harassment zone, and it is unknown if it is a SRKW or a Transient killer whale, WSDOT would assume it is a SRKW and implement shutdown measures. Pile driving would only resume if the killer whale could be confirmed as a Transient killer whale.

Table 8—Shutdown Zones for All Pile-Driving Activities for the Seattle Slip 3 VTS Replacement Project

Pile size and type	Pile driving method	Shutdown zones (m)					SRKW and HW shutdown zones (m)
		LF cetaceans	MF cetaceans	HF cetaceans	Phocids	Otarids
14-in steel	Vibratory removal	50	50	50	50	50	1,600
24-in steel	Vibratory installation and removal	100	100	100	50	50	* 15,410
24-in steel	Impact installation	100	100	100	50	50	750
30-in steel	Vibratory installation	100	100	100	50	50	* 15,410
78-in steel	Vibratory Installation	100	100	100	50	50	* 15,410
* 15,410 m is the maximum distance sound can travel before reaching land.