2024-17470. Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to Weyerhaeuser Company for Their Log Export Dock Project on the Columbia River Near Longview, Washington

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 Carnivora—Pinnipedia
Family Otariidae (eared seals and sea lions)
California Sea Lion	Zalophus californianus	U.S	-, -, N	257,606 (N/A, 233,515, 2014)	14,011	>321
Steller Sea Lion	Eumetopias jubatus	Eastern	-, -, N	36,308 (N/A, 36,308, 2022) 5	2,178	93.2
Family Phocidae (earless seals):
Harbor Seal	Phoca vitulina	OR/WA Coastal	-, -, N	UNK (UNK, UNK, 1999)	UND	10.6
1  Information on the classification of marine mammal species can be found on the web page for The Society for Marine Mammalogy's Committee on Taxonomy ( https://marinemammalscience.org/​science-and-publications/​list-marine-mammal-species-subspecies; Committee on Taxonomy, 2022).
2  ESA status: Endangered (E), Threatened (T)/MMPA status: Depleted (D). A dash (-) indicates that the species is not listed under the ESA or designated as depleted under the MMPA. Under the MMPA, a strategic stock is one for which the level of direct human-caused mortality exceeds PBR or which is determined to be declining and likely to be listed under the ESA within the foreseeable future. Any species or stock listed under the ESA is automatically designated under the MMPA as depleted and as a strategic stock.
3  NMFS marine mammal SARs online at: https://www.fisheries.noaa.gov/​national/​marine-mammal-protection/​marine-mammal-stock-assessment-reports-region. CV is coefficient of variation; N min is the minimum estimate of stock abundance. 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 mortality and serious injury (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 best estimate of counts, which have not been corrected for animals at sea during abundance surveys. Estimates provided are for the U.S. only.

As indicated above, all three species (with three managed stocks) in table 2 temporally and spatially 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 Weyerhaeuser'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 48579, June 7, 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.). 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 in hertz (Hz) and kilohertz (kHz) *
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 spp., river dolphins, Cephalorhynchids, 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 the ~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). This division between phocid and otariid pinnipeds is now reflected in the updated hearing groups proposed in Southall et al. (2019).

For more detail concerning these groups and associated frequency ranges, 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 Weyerhaeuser's pile driving activities have the potential to result in behavioral harassment of marine mammals in the vicinity of the project area. The notice of the proposed IHA (FR 48579, June 7, 2024) included a discussion of the effects of anthropogenic noise on marine mammals and the potential effects of underwater noise from Weyerhaeuser's pile driving activities on marine mammals and their habitat. That information and analysis is incorporated by reference into this final IHA determination and is not repeated here; please refer to the notice of the proposed IHA (FR 48579, June 7, 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 acoustic source ( 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) to result, primarily for phocids because predicted auditory injury zones are larger than for otariids. Auditory injury is unlikely to occur for otariids. The proposed 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. Here we describe how the information provided above is synthesized to produce a quantitative estimate of the take that is reasonably likely to occur and is authorized.

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 permeant 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-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.

Weyerhaeuser's activity 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 1μPa 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). Weyerhaeuser's activity 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 PTS

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 (ANSI) 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 proposed project. Pile driving generates underwater noise that can potentially result in disturbance to marine mammals in the project area. The maximum (underwater) area ensonified is determined by the topography of the Columbia River, including intersecting land masses that will reduce the overall area of potential impact. Additionally, vessel traffic, including the other half of the dock (berth B) remaining operational during construction, 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; 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.

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 × log₁₀ [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 × log₁₀ [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 would 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 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, NMFS used acoustic monitoring data from other locations to develop proxy source levels for the various pile types, sizes and methods (table 4). Generally, we choose source levels from similar pile types from locations ( e.g., geology, bathymetry) similar to the project.

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

Pile type and size	Peak SPL (re 1 μPa)	RMS SPL (re 1 μPa)	SEL (re 1 μPa2 -s )	Source
Vibratory pile installation and removal
16-in timber pile		162		Caltrans, 2020.
12-in steel pipe		158		Laughlin, 2012.
12-in steel H-pile		152		Laughlin, 2019.
16-in steel pipe 1		161		Navy, 2015.
24-in temporary steel pipe		161		Navy, 2015.
30-in steel pipe		163		Anchor, QEA, 2021; Greenbush, 2019; Denes et al., 2016, table 72.
Impact pile installation
30-in steel pipe 2	210 (205)	190 (185)	177 (177)	Caltrans, 2020.
1  For the purposes of this analysis, the underwater sound source level for removal of existing 16-in steel piles ( i.e., 161 dB RMS per Navy, 2015) has been used for the removal of approximately 36 16-in steel pipe piles and 20 fender piles (14- or 16-in steel pipe piles).
2  Values in parentheses indicate the calculated proxy source value minus 5 dB of assumed attenuation from the unconfined bubble curtain.

For this project, two hammers, including any combination of vibratory and impact hammers, may operate simultaneously. As noted earlier, the estimated ensonified area reflects the worst-case scenario (both hammers installing 30-in steel pipe piles) for the project. However, the most likely scenario is the removal of a 16-in timber pile at the same time as installing a 30-in steel pipe pile. The calculated proxy source levels for the different potential concurrent pile driving scenarios are shown in table 5.

Two Impact Hammers

For simultaneous impact driving of two 30-in steel pipe piles (the most conservative scenario), the number of strikes per pile was doubled to estimate total sound exposure during simultaneous installation. While the likelihood of impact pile driving strikes completely overlapping in time is rare due to the intermittent nature and short duration of strikes, NMFS conservatively estimates that up to 20 percent of strikes may overlap completely in time. Therefore, to calculate Level B isopleths for simultaneous impact pile driving, dB addition (if the difference between the two sound source levels is between 0 and 1 dB, 3 dB are added to the higher sound source level) was used to calculate the combined sound source level of 188 dB RMS that was used in this analysis.

One Impact Hammer, One Vibratory Hammer

To calculate Level B isopleths for one impact and one vibratory hammer operating simultaneously, sources were treated as though they were non-overlapping and the isopleth associated with the individual source which results in the largest Level B harassment isopleth was conservatively used for both sources to account for periods of overlapping activities.

Two Vibratory Hammers

To calculate Level B isopleths for two simultaneous vibratory hammers, the NMFS acoustic threshold calculator was used with modified inputs to account for accumulation, weighting, and source overlap in space and time. Using the rules of dB addition if the difference between the two sound source levels is between 0 and 1 dB, 3 dB are added to the higher sound source level), the combined sound source level for the simultaneous vibratory installation of two 30-in steel piles is 166 dB RMS.

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, like 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, and the resulting estimated isopleths, are reported in table 6, below.

To calculate Level A isopleths for two impact hammers operating simultaneously, the NMFS User Spreadsheet calculator was used with modified inputs to account for the total estimated number of strikes for all piles. For simultaneous impact driving of two 30-in steel pipe piles (the most conservative scenario), the number of strikes per pile was doubled to estimate total sound exposure during simultaneous installation, and the number of piles per day was reduced to one. The source level for two simultaneous impact hammers was not adjusted because for identical sources the accumulation of energy depends only on the total number of strikes, whether or not they overlap fully in time. Therefore, the source level used for two simultaneous impact hammers was 172 dB single-strike sound exposure level (SEL_ss).

To calculate Level A isopleths of one impact hammer and one vibratory hammer operating simultaneously, sources were treated as though they were non-overlapping and the isopleth associated with the individual source which resulted in the largest Level A isopleth was conservatively used for both sources to account for periods of overlapping activities.

To calculate Level A isopleths of two vibratory hammers operating simultaneously, the NMFS acoustic threshold calculator was used with modified inputs to account for accumulation, weighting, and source overlap in space and time. Using the rules of dB addition (NMFS, 2024; if the difference between the two sound source levels is between 0 and 1 dB, 3 dB are added to the higher sound source level), the combined sound source level for the simultaneous vibratory installation of two 30-in steel piles is 166 dB RMS.

Table 5—Calculated Proxy Sound Source Levels for Potential Concurrent Pile Driving Scenarios

Scenario	Pile type and proxy	Calculated proxy sound source level
Two impact hammers	Impact install of 30-in steel pipe pile (172 dB SEL, 185 dB RMS) AND impact install of 30-in steel pipe pile (172 dB SEL, 185 dB RMS)	172 dB SEL for Level A. 188 dB RMS for Level B
One impact hammer, one vibratory hammer	Impact install of 30-in steel pipe pile (172 dB SEL, 185 dB RMS) AND vibratory install of 30-in steel pipe pile (163 dB RMS)	172 dB SEL for Level A. 163 dB RMS for Level B
Two vibratory hammers	Vibratory install of 30-in steel pipe pile (163 dB RMS) AND vibratory install of 30-in steel pipe pile (163 dB RMS)	166 dB RMS.

Table 6—NMFS User Spreadsheet Inputs

Pile size and type	Spreadsheet tab used	Weighting factor adjustment (kHz)	Number of piles per day	Duration to drive a single pile (min)	Number of strikes per pile
Vibratory pile driving and removal
16-in timber pile	A.1. Vibratory pile driving	2.5	8	60	NA
12-in steel pipe	A.1. Vibratory pile driving	2.5	8	60	NA
12-in steel H-pile	A.1. Vibratory pile driving	2.5	8	60	NA
16-in steel pipe	A.1 Vibratory pile driving	2.5	8	60	NA
24-in temporary steel pipe	A.1 Vibratory pile driving	2.5	8	60	NA
30-in steel pipe	A.1. Vibratory pile driving	2.5	8	60	NA
Impact pile driving
30-in steel pipe	E.1. Impact pile driving	2	8	NA	1000
Concurrent pile driving  1
Impact install of 30-in steel pipe pile AND impact install of 30-in steel pipe pile	E.1. Impact pile driving	2	1	NA	8000
Impact install of 30-in steel pipe pile AND vibratory install of 30-in steel pipe pile	E.1. Impact pile driving	2	1	NA	8000
Vibratory install of 30-in steel pipe pile AND vibratory install of 30-in steel pipe pile	A.1. Vibratory pile driving	2.5	1	480	NA
1  Number of strikes is no longer per pile, it is the total number of strikes per day. The number of piles per day has been reduced to one.

Table 7—Calculated Levels A and B Harassment Isopleths

Pile size and type	Level A harassment zone (m/km2 )		Level B harassment zone (m/km2 )
	Phocid	Otariid
Vibratory pile driving and removal
16-in timber pile	20/0.000693	2/0.000012	6,310/8.25
12-in steel pipe	11/0.000226	1/0.000003	3,415/5.14
12-in steel H-pile	5/0.000055	1/0.000003	1,585/2.46
16-in steel pipe	17/0.000509	2/0.000012	5,412/7.47
24-in temporary steel pipe
30-in steel pipe	23/0.000906	2/0.000012	7,356a  b /8.96
Impact pile driving
30-in steel pipe	395/0.25181	29/0.001393	464/0.35
Concurrent pile driving
Impact install of 30-in steel pipe pile AND impact install of 30-in steel pipe pile	395/0.25181	29/0.001393	736/0.89
Impact install of 30-in steel pipe pile AND vibratory install of 30-in steel pipe pile			7,356a  b /8.96
Vibratory install of 30-in steel pipe pile AND vibratory install of 30-in steel pipe pile	36/2,153	3/0.000023	11,660 b /10.52
a  The Level B harassment thresholds for the vibratory installation of a single 30-in steel pile are equivalent to the potential simultaneous installation of up to two 30-inch steel piles using one impact hammer and one vibratory hammer operating concurrently. As noted previously, Levels A and B harassment thresholds for simultaneous pile driving were analyzed based on interim guidance provided by NMFS (2024).
b  The Level B harassment thresholds reported above were calculated using the practical spreading loss model, although the extent of actual sound propagation will be limited to the areas identified in figure 6-3 of Weyerhaeuser's application due to the shape and configuration of the Columbia River in the vicinity.

Marine Mammal Occurrence and Take Estimation

In this section, we provide information about the occurrence of marine mammals that will inform the take calculations, and describe how the information provided is synthesized to produce a quantitative estimate of the take that is reasonably likely to occur and authorized. Daily occurrence data cones from USACE compiled weekly monitoring reports collected at the Bonneville Dam (river mile (RM) 146) from 2020 through 2021 (van der Leeuw and Tidwell, 2022). As pinnipeds would need to swim past the proposed project site to reach the dam, the number of animals observed at Bonneville Dam may be slightly lower than what would be observed at the project site. The take calculations for this project are:

Incidental take estimate = (number of days during work window × estimated number of animals per day) + (number of days outside work window × estimated number of animals per day).

California Sea Lion

The numbers of California sea lions observed at Bonneville Dam have been in decline in recent years and ranged from 149 in 2016 to a total of 24 in 2021 (van der Leeuw and Tidwell, 2022). During the spring period from January 1 to May 6, 2020, daily counts averaged 0.9 animals ± 3.3 standard deviation, with a high of seven individuals (Tidwell et al., 2020). During spring 2021, California sea lions were present from late March through late May, but in relatively low numbers, with most days having five or fewer present (van der Leeuw and Tidwell, 2022). It is difficult to estimate the number of California sea lions that could potentially occur in the Level B harassment zone during the fall in-water work window from these data, because the numbers at Bonneville Dam reflect a strong seasonal presence in spring. A conservative estimate of three California sea lions per day during the in-water work window and five California sea lions per day outside the in-water work window was used. Therefore, using the equation given above, the estimated number of takes by Level B harassment for California sea lions would be 510.

The largest Level A harassment zone for California sea lions extends 29 m from the sound source (table 7) during impact pile driving. All construction work would be shut down prior to a California sea lion entering the Level A harassment zone specific to the in-water activity underway at the time. In consideration of the small Level A harassment isopleth and proposed shutdown requirements, no take by Level A harassment is anticipated or authorized for California sea lions.

Steller Sea Lion

Steller sea lions have been observed in varying numbers at Bonneville Dam throughout much of the year, with a peak in April and May (Tidwell et al., 2020; van der Leeuw and Tidwell, 2022). Reports from a 2-year period observed daily counts of 12 to 20 Steller sea lions during the fall survey period (Tidwell et al., 2020, Tidwell and van der Leeuw, 2021), and up to 27 Steller sea lions per day in the spring (van der Leeuw and Tidwell, 2022). A conservative estimate of 20 Steller sea lions per day during the in-water work window and 27 Steller sea lions per day outside the in-water work window was used. Therefore, using the equation given above, the estimated number of takes by Level B harassment for Steller sea lions would be 3,210.

The largest Level A harassment zone for Steller sea lions extends 29 m from the sound source (table 7) during impact pile driving. All construction work would be shut down prior to a Steller sea lion entering the Level A harassment zone specific to the in-water activity underway at the time. In consideration of the small Level A harassment isopleth and proposed shutdown requirements, no take by Level A harassment is anticipated or authorized for Steller sea lions.

Harbor Seal

Harbor seals are rarely observed at Bonneville Dam, but have been recorded in low numbers over the past 10 years. A recent IHA issued for the Port of Kalama Manufacturing and Marine Export Facility (85 FR 76527), which is located near the proposed project site, used a conservative estimate based on anecdotal information of harbor seals residing near the mouths of the Cowlitz and Kalama Rivers and estimated that there could be up to 10 present on any given day of pile driving (NMFS, 2017; 81 FR 15064, March 21, 2016). Therefore, using the equation given above, the calculated estimate of take by Level B harassment for harbor seals would be 1,500.

The largest Level A harassment zone for harbor seals extends 395 m from the sound source (table 7) during impact pile driving. The Port of Kalama project estimated that one harbor seal per day could be present in the Level A harassment zone for each day of impact pile driving. Given that the largest Level A isopleth extends approximately half the width of the river (810 m), the calculated estimated take by Level A harassment for harbor seals would be 58 (1 seal on 48.5% of the 120 impact pile driving days).

Table 8—Estimated Take by Levels A and B Harassment

Common name	Stock	Stock abundance	Level A harassment	Level B harassment	Total authorized take	Authorized take as a percentage of stock
California sea lion	U.S. Stock	257,606	0	510	510	0.2
Steller sea lion	Eastern DPS	36,308	0	3,210	3,210	8.8
Harbor seal	OR/WA coastal stock	24,732	58	1,500	1,558	6.3

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.

The mitigation measures described in the following paragraphs will apply to the Weyerhaeuser in-water construction activities.

Shutdown and Monitoring Zones

Weyerhaeuser must establish shutdown zones and Level B harassment monitoring 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 animal (or in anticipation of an animal entering the defined area). Shutdown zones are based on the largest Level A harassment zone for each pile size/type and driving method, and behavioral monitoring zones are meant to encompass Level B harassment zones for each pile size/type and driving method, as shown in table 9. A minimum shutdown zone of 10 m will be required for all in-water construction activities to avoid physical interaction with marine mammals. Shutdown zones for each activity type are shown in table 9.

Prior to pile driving, Protected Species Observers (PSOs) will survey the shutdown zones and surrounding areas for at least 30 minutes before pile driving activities start. If marine mammals are found within the shutdown zone, pile driving will be delayed until the animal has moved out of the shutdown zone, either verified by an observer or by waiting until 15 minutes has elapsed without a sighting. If a marine mammal approaches or enters the shutdown zone during pile driving, the activity will be halted. Pile driving may resume after the animal has moved out of and is moving away from the shutdown zone or after at least 15 minutes has passed since the last observation of the animal.

All marine mammals will be monitored in the Level B harassment to the extent of visibility for the on-duty PSOs. If a marine mammal for which take is authorized enters the Level B harassment zone, in-water activities will continue and PSOs will document the animal's presence within the estimated harassment zone.

If a species for which authorization has not been granted, or for which the authorized takes are met, is observed approaching or within the Level B harassment zone, pile driving activities will be shut down immediately. Activities will not resume until the animal has been confirmed to have left the area or 15 minutes has elapsed with no sighting of the animal.

Table 9—Shutdown and Level B Monitoring Zones by Activity

Method	Pile size and type	Minimum shutdown zone (m)		Harassment monitoring zone (m)
		Phocid	Otariid
Vibratory	16-in timber pile removal	20	10	6,310
	12-in steel pipe pile removal	15	10	3,415
	12-in steel H-pile removal	10	10	1,585
	16-in steel pipe removal	20	10	5,412
	24-in steel pipe pile (temporary) installation and removal	20	10	5,412
	30-in steel pipe pile installation	25	10	7,356
Impact	30-in steel pipe pile installation	200	30	464
Concurrent pile driving	Two impact hammers	200	30	736
	One impact hammer and one vibratory hammer	200	30	7,356
	Two vibratory hammers	40	10	11,660