2024-22394. Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to the Army Corps of Engineers Baker Bay Pile Dike Repair Project

Table 1—Species Likely Impacted by the Specified Activities ¹

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—Infraorder Cetacea—Mysticeti (baleen whales)
Family Eschrichtiidae (baleen whale):
Gray Whale	Eschrichtius robustus	Eastern N Pacific	-, -, N	26,960 (0.05, 25,849, 2016)	801	131
Family Balaenopteridae (rorquals)
Humpback whale	Megaptera novaeangliae	Central America/Southern Mexico—CA/OR/WA	E, D, Y	1,494 (0.171, 1,284, 2021)	3.5	14.9
		Mainland Mexico—CA/OR/WA	T, D, Y	3,477 (0.101, 3,185, 2018)	43	22
Odontoceti (toothed whales, dolphins, and porpoises)
Family Delphinidae:
Killer whale	Orcinus orca	West Coast Transient	-, -, N	349 (N/A, 349, 2018)	3.5	0.4
Family Phocoenidae (porpoises):
Harbor porpoise	Phocoena phocoena	Northern OR/WA Coast	-, -, N	22,074 (0.391, 16,068, 2022)	161	3.2
Order Carnivora—Pinnipedia
Family Otariidae (eared seals and sea lions):
Steller sea lion	Eumetopias jubatus	Eastern DPS	-, -, N	36,308 (N/A, 36,308, 2022)	2,178	93.2
California sea lion	Zalophus californianus	U.S	-, -, N	257,606 (N/A, 233,515, 2014)	14,011	>321
Family Phocidae (earless seals):
Harbor seal	Phoca vitulina	OR/WA Coastal	-, -, N	UNK (UNK, UNK, 1999)	UND	10.6
Northern elephant seal	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.
2  Endangered Species Act (ESA) status: Endangered (E), Threatened (T)/MMPA status: Depleted (D). A dash (-) indicates that the species is not listed under the ESA or designated as depleted under the MMPA. Under the MMPA, a strategic stock is one for which the level of direct human-caused mortality exceeds PBR or which is determined to be declining and likely to be listed under the ESA within the foreseeable future. Any species or stock listed under the ESA is automatically designated under the MMPA as depleted and as a strategic stock.
3  NMFS marine mammal stock assessment reports online at: https://www.fisheries.noaa.gov/​national/​marine-mammal-protection/​marine-mammal-stock-assessment-reports-region. CV is coefficient of variation; N min is the minimum estimate of stock abundance. In some cases, CV is not applicable.
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.

A detailed description of the species likely to be affected by the Baker Bay pile dike 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 60385, 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 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 ( print page 79559) (behavioral response data, anatomical modeling, etc.). Subsequently, NMFS (2018) described generalized hearing ranges for these marine mammal hearing groups. Generalized hearing ranges were chosen based on the approximately 65-decibel (dB) threshold from the normalized composite audiograms, with the exception for lower limits for low-frequency cetaceans where the lower bound was deemed to be biologically implausible and the lower bound from Southall et al. (2007) retained. Marine mammal hearing groups and their associated hearing ranges are provided in table 2.

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).

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.

Potential Effects of Specified Activities on Marine Mammals and Their Habitat

The effects of underwater noise from the ACOE'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 60385, July 25, 2024) included a discussion of the effects of anthropogenic noise on marine mammals and the potential effects of underwater noise from the ACOE's construction 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 60385, July 25, 2024).

Estimated Take of Marine Mammals

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

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

Authorized takes will primarily be by Level B harassment, as use of the construction equipment ( i.e., pile driving) has the potential to result in disruption of behavioral patterns for individual marine mammals. There is also some potential for auditory injury (Level A harassment) of phocids because predicted auditory injury zones are larger than for other species. The 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 to be authorized for this activity. Below we describe how the 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 take estimates.

Acoustic Thresholds

NMFS recommends the use of acoustic thresholds that identify the received level of underwater sound above which exposed marine mammals would be reasonably expected to be behaviorally harassed (equated to Level B harassment) or to incur 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, 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- ( print page 79560) 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 will not otherwise occur.

The ACOE's construction includes the use of continuous (vibratory pile driving) and impulsive (impact pile driving) sources, and therefore the RMS SPL thresholds of 120 and 160 dB re 1 μPa are applicable.

Level A Harassment —NMFS' Technical Guidance for Assessing the Effects of Anthropogenic Sound on Marine Mammal Hearing (Version 2.0; Technical Guidance 2018) identifies dual criteria to assess auditory injury (Level A harassment) to 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 ACOE's construction includes the use of impulsive (impact pile driving) and non-impulsive (vibratory pile driving) sources.

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

Table 3—Thresholds Identifying the Onset of Permanent Threshold Shift

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

Ensonified Area

Here, we describe operational and environmental parameters of the activity that are used in estimating the area ensonified above the acoustic thresholds, including source levels and transmission loss 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 and vibratory pile driving and removal). The maximum (underwater) area ensonified above the thresholds for behavioral harassment referenced above is 20.72 km² (12.87 mi² ), and will consist of most of the mouth of the Columbia River immediately south of West Sand Island (See figure 1 in the proposed IHA 89 FR 60385, July 25, 2024). Additionally, vessel traffic in the project area may contribute to elevated background noise levels which may mask sounds produced by the project.

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

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

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

This formula neglects loss due to scattering and absorption, which is assumed to be zero here. The degree to which underwater sound propagates away from a sound source is dependent on a variety of factors, most notably the water bathymetry and presence or absence of reflective or absorptive conditions including in-water structures and sediments. Spherical spreading occurs in a perfectly unobstructed (free-field) environment not limited by depth or water surface, resulting in a 6-dB reduction in sound level for each doubling of distance from the source (20*log[range]). Cylindrical spreading occurs in an environment in which sound propagation is bounded by the water surface and sea bottom, resulting in a reduction of 3 dB in sound level for each doubling of distance from the source (10*log[range]). A practical spreading value of 15 is often used under conditions, such as the project site, where water increases with depth as the receiver moves away from the shoreline, resulting in an expected propagation environment that will lie between spherical and cylindrical spreading loss conditions. Practical spreading loss is assumed here.

The intensity of pile driving sounds is greatly influenced by factors such as the ( print page 79561) type of piles, hammers, and the physical environment in which the activity takes place. In order to calculate the distances to the Level A harassment and the Level B harassment sound thresholds for the methods and piles being used in this project, the applicant and NMFS used acoustic monitoring data from other locations to develop proxy source levels for the various pile types, sizes and methods. The project includes vibratory and impact pile installation of steel pipe and sheet piles and vibratory removal of steel sheet piles. Source levels for 24-in steel pipe piles are used as a proxy for all steel piles that may be placed for marker piles of the dike system, though smaller piles may be used during the construction. NMFS consulted multiple sources to determine valid proxy source levels for the impact installation of sheet piles, as indicated in table 4. This is the best available data for sheet pile source levels and is based on 24-in sheet piles used for a project in California. Source levels for each pile size and driving method are presented in table 4.

Table 4—Proxy Sound Source Levels for Pile Sizes and Driving Methods

Pile size	Method	Proxy source level (at 10 m)			Literature source
		dB RMS re 1µPa	dB SEL re 1µPa2 sec	dB peak re 1µPa
24-in	Vibratory	154	N/A	N/A	Navy 2015.
24-in sheet pile	Vibratory	160	N/A	N/A	Caltrans 2020.
24-in	Impact	189	178	203	Caltrans 2015.

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 impact or vibratory pile driving, 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 are reported below (table 5). The resulting estimated Level A harassment isopleths and the Level B harassment isopleths are reported in table 6.

Table 5—User Spreadsheet Inputs for Calculating Level A Harassment Isopleths

Pile size and installation method	Spreadsheet tab used	Weighting factor adjustment (kHz)	Number of strikes per pile	Number of piles per day	Activity duration (minutes)
24-in vibratory installation (MOF Option 2)	A.1 Vibratory pile driving	2.5	N/A	8	20
24-in vibratory removal (MOF Option 2)	A.1 Vibratory pile driving	2.5	N/A	16	5
24-in sheet pile vibratory installation (MOF Option 1)	A.1 Vibratory pile driving	2.5	N/A	25	15
24-in sheet pile vibratory removal (MOF Option 1)	A.1 Vibratory pile driving	2.5	N/A	60	3
24-in vibratory installation (Pile Markers)	A.1 Vibratory pile driving	2.5	N/A	8	15
24-in impact installation (Pile Markers)	E.1 Impact pile driving	2	225	5	N/A

Table 6—Calculated Level A and Level B Harassment Isopleths

Activity	Level A harassment zone (m)					Level B harassment zone (m)
	LF- cetaceans	MF- cetaceans	HF- cetaceans	Phocids	Otariids
24-in Steel Pipe Pile Vibratory Install (MOF Option 2)	4.5	0.4	6.6	2.7	0.2	1,847.8
24-in Steel Pipe Pile Vibratory Removal (MOF Option 2)	2.8	0.3	4.2	1.7	0.1
24-in sheet pile vibratory installation (MOF Option 1)	23.4	2.1	34.6	14.2	1.0	4,641.1
24-in sheet pile vibratory removal (MOF Option 1)	12.2	1.1	18	7.4	0.5
24-in vibratory installation (Pile Markers)	3.7	0.3	5.5	2.3	0.2	1,847.8
24-in impact installation (Pile Markers)	501.4	17.8	597.2	268.3	19.5	857.7

( print page 79562)

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 the take calculations. We describe how the information provided is synthesized to produce a quantitative estimate of the take that is reasonably likely to occur and authorized.

When available, peer-reviewed scientific publications were used to estimate marine mammal abundance in the project area. Data from monitoring reports from the previous Sand Island Test Pile Project was used to calculate take for several species. However, scientific surveys and resulting data, such as population estimates, densities, and other quantitative information, are lacking for some species. The ACOE also gathered qualitative information from discussions with knowledgeable local people that frequent the mouth of the Columbia River. Assumptions regarding the size of expected groups of different species, and the frequency of occurrence of those groups, were made by the ACOE on the basis of the aforementioned information and are described for each species below.

Since reliable densities are not available, the take numbers are based on the assumed occurrence of a given stock during the activity. The applicant used equation 1, below, to estimate take of killer whales and Steller sea lions, equation 2 to estimate take of humpback whale, harbor porpoise, California sea lions, and harbor seals, and neither equation for gray whale or Northern elephant seals. NMFS concurs with this method. The estimated take calculation for these/this species is explained in the relevant section below.

(1) Estimated Take = number of individuals in a group × groups per day × days of pile-related activity

(2) Estimated Take = total expected duration of the project (minutes) ÷ total duration of the Sand Island Test Pile Project × the total number of animals of a given species observed during the Sand Island Test Pile Project

Gray Whale

Historically gray whales have not frequented the mouth of the Columbia River. No gray whales were observed during monitoring activities of the Sand Island Test Pile Project (Hamer Environment L.P. 2020). In August of 2020, an ACOE biologist observed two gray whales traveling upriver from the project site. Given this recent sighting and the temporal overlap of the project and the most recent sighting, NMFS authorized two takes of gray whales by Level B harassment.

The largest Level A harassment zone for gray whales extends 513 m from the noise source (table 6). ACOE is planning to implement shutdown zones for low-frequency cetaceans that exceed the Level A harassment isopleth for all activities. Therefore, especially in combination with the already low occurrence of gray whales in the area, implementation of the shutdown zones is expected to eliminate the potential for take by Level A harassment of gray whale. Therefore, no take by Level A harassment is anticipated or authorized for humpback whales.

Humpback Whales

Humpback whales have occurred in the lower Columbia River near the project area in recent years. Feeding groups have been using the mouth of the Columbia River as a foraging ground, arriving as early as mid-June, and have been observed as late as mid-November with a peak of abundance coinciding with the peak abundance of forage fish in mid-summer (The Columbian 2019). During pile driving activities of the Sand Island Test Pile Project, seven animals were observed (Hamer Environment L.P. 2020). The ACOE estimated take of humpback whales using equation 2 above resulting in a take estimate of 16 takes by Level B harassment (2277 (pile driving minutes for this activity)/1037 (pile driving minutes for Sand Island Test Pile Project) × 7 observed animals). NMFS agrees with this approach and estimated take. As described above, NMFS anticipates that 42 percent of takes will occur to individuals of the Central America/Southern Mexico-CA/OR/WA stock and 58 percent of takes will occur to individuals of the Mainland Mexico-CA/OR/WA which will equate to seven and nine takes respectively.

The largest Level A harassment zone for humpback whales extends 513 m from the noise source (table 6). ACOE is planning to implement shutdown zones for low-frequency cetaceans that exceed the Level A harassment isopleth for all activities. Implementation of the shutdown zones is expected to eliminate the potential for take by Level A harassment of humpback whale. No take by Level A harassment is anticipated or authorized for humpback whales.

Killer Whale

Use of the mouth of the Columbia River is rare for killer whales, but in recent years pods of killer whales have been observed in and around the mouth of the Columbia River. During the recent monitoring of the Sand Island Test Pile Project, no killer whales were observed (Hamer Environment L.P. 2020). Aerial seabird marine mammal surveys observed 0 killer whales in January 2011, 0 in February 2012, and 10 in September 2012 within an approximately 1,500 km2 range near the Mouth of the Columbia River (Adams 2014). A pod of transient killer whales was detected near the Astoria Bridge in May of 2018 (Frankowicz 2018) and in 2022 (Tomlinson 2022). The ACOE estimated the average group sizes from these past observations was seven. Based on the rare occurrence of killer whales in the project area, ACOE expects that one group of seven killer whales may occur during the 12 days of construction in the Level B harassment zone. NMFS concurs and authorized seven takes of killer whale by Level B harassment.

The largest Level A harassment zone for killer whales extends 17.8 m from the noise source (table 6). ACOE is planning to implement shutdown zones for mid-frequency cetaceans that exceed the Level A harassment isopleth for all activities. Implementation of the shutdown zones is expected to eliminate the potential for take by Level A harassment of killer whale. No take by Level A harassment is anticipated or authorized for killer whales.

Harbor Porpoise

Harbor porpoises are regularly observed in the offshore waters near the mouth of the Columbia River and are known to occur there year-round. Porpoise abundance peaks when anchovy ( Engraulis mordax) abundance in the river and nearshore are highest, which is usually between April and August (Litz et al. 2008). Harbor porpoise tend to occur in groups of one to two individuals. During the recent monitoring of the Sand Island Test Pile Project, eight harbor porpoise were observed during construction activities (Hamer Environment L.P. 2020). Using equation 2 above, ACOE expects that 18 takes by Level B harassment will occur over the 12 days of pile driving (2277 (pile driving minutes for this activity)/1037 (pile driving minutes for Sand Island Test Pile Project) × 8 observed animals). NMFS agrees with this approach and authorized 18 takes by Level B harassment of harbor porpoise.

The largest Level A harassment zone for harbor porpoise extends 597 m from the noise source (table 6). ACOE is planning to implement shutdown zones for high-frequency cetaceans that exceed the Level A harassment isopleth for all activities, and it did not request take by ( print page 79563) Level A harassment of harbor porpoise. For some activities ( i.e., impact driving of 24-in piles), the shutdown zones extends farther than Protected Species Observers (PSO) may be able to reliably detect harbor porpoise. However, given the portion of the zone within which PSOs could reliably detect a harbor porpoise, the infrequency of harbor porpoise observations during the Sand Island Test Pile project monitoring, and harbor porpoise sensitivity to noise, no take by Level A harassment is anticipated or authorized for harbor porpoise.

Steller Sea Lion

Steller sea lion occurrence was estimated using Washington Department of Fish and Wildlife haulout survey data from the South Jetty at the mouth of the Columbia River from 2000 to 2014. During the recent monitoring of the Sand Island Test Pile Project no Steller sea lions were observed (Hamer Environment L.P. 2020). Given the close proximity of the haulout, NMFS expects that Steller sea lions could occur near the project site. Occurrence was estimated using the monthly haulout numbers for the months when work will be occurring during the project. In August, the average number of Steller sea lions hauled out at the jetty was 72, and in October, the average number of sea lions at the jetty was 77. In August, construction will occur over 7-days, and in October, construction will occur over 5 days. Given the daily occurrence rates and days of in-water construction, and using equation 1, the ACOE expects that 889 takes by Level B harassment will occur (daily occurrence (72 or 77) × days of activity), and NMFS authorized 889 takes by Level B harassment of Steller sea lion.

The largest Level A harassment zone for Steller sea lions extends 19.5 m from the noise source (table 6). ACOE is planning to implement shutdown zones for otariids that exceed the Level A harassment isopleth for all activities. Implementation of the shutdown zones is expected to eliminate the potential for take by Level A harassment of Steller sea lion. No take by Level A harassment is anticipated or authorized for Steller sea lion.

California Sea Lion

Similar to Steller sea lions, California sea lions use the South Jetty at the mouth of the Columbia River and make frequent trips inside the mouth of the river. Occurrence on the South Jetty peaks in summer and use in the fall and winter is more concentrated. During recent monitoring activities of the Sand Island Test Pile Project 59 animals were observed (Hamer Environment L.P. 2020). Using equation 2 above, ACOE expects that 144 takes by Level B harassment California sea lions will occur (2277 (pile driving minutes for this activity)/1037 (pile driving minutes for Sand Island Test Pile Project) × 59 observed animals), and NMFS authorized 144 takes by Level B harassment of California sea lion.

The largest Level A harassment zone for California sea lions extends 19.5 m from the noise source (table 6). ACOE is planning to implement shutdown zones for otariids that exceed the Level A harassment isopleth for all activities. Implementation of the shutdown zones is expected to eliminate the potential for take by Level A harassment of California sea lion. No take by Level A harassment is anticipated or authorized for California sea lion.

Harbor Seal

Harbor seals are the most abundant pinniped in Oregon and occur in the project are year-round. Large numbers of harbor seals move through the mouth of the Columbia River throughout the year and are expected to be present in the project area. During recent monitoring of the Sand Island Test Pile Project, a total of 309 harbor seals were observed during construction activities (Hamer Environment L.P. 2020). Take estimates were generated using equation 2 above and the Sand Island Pile Test Project monitoring results. ACOE expects that 679 takes by Level B harassment of harbor seals will occur during the project (2277 (pile driving minutes for this activity)/1037 (pile driving minutes for Sand Island Test Pile Project) × 309 observed animals), and NMFS authorized 679 takes by Level B harassment of harbor seal.

The Level A harassment zone for harbor seals during impact installation is 268 m (table 6). ACOE will implement a shutdown zone of 150 m given the difficulty of observing harbor seals at greater distances and practicability concerns regarding efficient work production rates that will be associated with a larger shutdown zone (see Mitigation section). During impact installation ACOE expects that two harbor seals could be present in the Level A harassment zone. Therefore, over the 3 days of impact pile driving, NMFS anticipates, and authorized, six takes by Level A harassment (two takes per day * 3 days = six takes by Level B harassment).

Northern Elephant Seal

Northern elephant seals occur infrequently in the mouth of the Columbia River. Recent sightings of elephant seals have occurred in the fall and spring upriver from the project site. Although, no Northern elephant seals were observed during the Sand Island Test Pile Project (Hamer Environment L.P. 2020). ACOE expects that two animals may be present in the Level B harassment zone during the 12-days of construction, and NMFS authorized two takes by Level B harassment of elephant seal.

The largest Level A harassment zone for Northern elephant seals extends 268 m from the noise source (table 6). ACOE is planning to implement shutdown zones for Northern elephant seal that exceed the Level A harassment isopleth for all activities. Implementation of the shutdown zones is expected to eliminate the potential for take by Level A harassment of Northern elephant seal. No take by Level A harassment is anticipated or authorized for Northern elephant seals.

Table 7—Authorized Take by Level A and Level B Harassment, by Species and Stock

Common name	Stock	Stock abundance a	Level A	Level B	Total take	Take as a percentage
Gray Whale	Eastern N Pacific	26,960	0	2	2	<1
Humpback Whale	Central America/Southern Mexico-CA/OR/WA	1,494	0	7	7	<1
	Mainland Mexico-CA/OR/WA	3,477	0	9	9	<1
Killer Whale	West Coast Transients	349	0	7	7	2
Harbor Porpoise	Northern OR/WA Coast	22,074	0	18	18	<1
Steller sea lion	Eastern	36,308	0	889	889	2.4
California Sea Lion	United States	257,074	0	144	144	<1
Harbor Seal	OR/WA Coastal	UKN	6	679	685	N/A
( print page 79564)
Northern Elephant Seal	CA Breeding	187,386	0	2	2	<1
a  Stock size is best estimate of population (Nbest) according to NMFS 2022 Final Stock Assessment Reports and where apporiate the draft NMFS 2022 Final Stock Assessment Reports was used to estimate Nbest.

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. 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, impact on operations.

ACOE is required to implement the following mitigation measures:

Implementation of Shutdown Zones —For all pile driving/removal activities, the ACOE will implement shutdowns within designated zones. The purpose of a shutdown zone is generally to define an area within which shutdown of activity will occur upon sighting of a marine mammal (or in anticipation of an animal entering the defined area). Implementation of shutdowns will be used to minimize the number and severity of takes from vibratory and impact pile driving and removal (table 8). For all pile driving/removal activities, a minimum 25-m shutdown zone will be established for pinnipeds and 50-m shutdown zone for cetaceans as outlined in the ACOE application for an IHA. For harbor seals, ACOE will implement a shutdown zone of 25 m given its concerns about potential frequent shutdowns that may occur with a larger shutdown zone in consideration of high occurrence of harbor seals in the project area. To minimize the potential of Level A harassment of harbor seals, NMFS recommended a shutdown zone of 150 m for harbor seals. ACOE concurred that this zone was practicable, and therefore, NMFS required a shutdown zone of 150 m for harbor seals. Shutdown zones for impact pile driving are based on the Level A harassment zones and therefore vary by marine mammal hearing group (table 8). The placement of PSOs during all pile driving activities (described in detail in the Monitoring and Reporting section) will ensure the full extent of shutdown zones are visible to PSOs.

Table 8—Shutdown Zones During Pile Installation and Removal

Activity	Pile size	Shutdown zones (m)
		LF cetaceans	MF cetaceans	HF cetaceans	Harbor seals	Northern elephant seal	Otariids
Vibratory Installation	24-in (pile markers)	50	50	50	25	25	25
Vibratory Installation and removal	24-in (MOF option 2)	50	50	50	25	25	25
Vibratory Installation and removal	24-in sheet pile (MOF option 1)	50	50	50	25	25	25
Impact Installation	24-in (pile markers)	510	50	600	150	270	25