2024-26069. Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to the Lower Columbia River Dredged Material Management Plan, Oregon and Washington

Table 1—Pile Spacing Assumptions for Timber and Steel Pipe Piles

Pile dike segment	Pile spacing for 12-in timber (ft)	Pile spacing for 24-in steel pipe (ft)
Shore to 1/3 point of structure	1.5	3
1/3 point to 1/2 point of structure	2.5	5
1/2 point to 3/4 point of structure	4	8

For planning purposes and the calculations included in this LOA, it is assumed that one-third of the piles will be timber and two-thirds will be steel. Timber piles will most likely be installed in areas of shallow water with loose/soft to medium dense foundation. Steel piles will most likely be installed in deep water or in dense/hard foundations. This is a conservative assumption to ensure sufficient numbers of steel piles and associated effects are accounted for should hard foundations be more prevalent. Prior contractors have also expressed difficulties securing timber piles over the last 3-5 years. Thus, this assumption also accounts for potential supply chain issues affecting the availability of timber pilings. For a structure with a total length of L, the formulas for computing the number of piles are as follows:

• Timber piles number of piles = 0.351 × L
• Steel piles number of piles = 0.176 × L

The total length of proposed structures is approximately 13,050 ft. However, excluding W-35.6-IW-D (only marker piles) and the 2 sites beyond the scope of this LOA (W-24.9-IW-S and O-26.7-IW-S) the total length for estimating the number of piles is 8,796 ft (table 2). Pile driving at the 2 out-of-scope locations is tentatively planned for 2032/2033 and 2033/2034, beyond the effective period of these proposed regulations. The assumed length of timber pile structures to be installed under this LOA is 2,932 ft ( i.e., one-third of the total length) and the assumed length of steel pile structures is 5,864 ft ( i.e., two-thirds of the total length). Using the equations above, the anticipated total number of timber piles will be 1,029 and the total number of steel piles will be 1,032 plus 6 additional marker piles for site W-35.6-IW-D. These total numbers of piles are for the 5 placement sites that will require pile driving under this LOA (see table 2).

Table 2—Location and Properties of Proposed Pile Structures at Confined Aquatic Placement Sites

System name	Structures in system	Length of structure (ft)	Width of structure (ft)	Material	Anticipated LOA year(s)
O-23.5-BN-ADD2	4	1,544	50-100	Piles and enrockment	Year 1.
W-35.6-IW-D	2	1,555	100	Enrockment and 6 marker piles	Year 2.
O-23.5-BN-ADD1	5	2,119	50-100	Piles and enrockment	Year 3.
O-27.3-BN	3	1,906	50-100	Piles and enrockment	Year 4.
O-31.4-BN	3	3,227	50-100	Piles and enrockment	Year 5.

( print page 89547)

Note that the lower parts of the piles will be surrounded by enrockment (also referred to as stone or riprap). The thickness of the enrockment will be about one-third of the water depth in terms of low water. The volume of enrockment will depend on the elevation profile of the riverbed along the structure alignment. NMFS, however, has determined that enrockment installation is not likely to result in harassment under the MMPA.

Table 3 shows the locations, number and types of piles, as well as pile driving workdays anticipated to be required for the DMMP project spanning roughly 13 RM. These structures will support new confined aquatic placement sites in the LCR.

Table 3—In-Water Work, Pile Installation, and Workday Assumptions

In-water work location 1	Timber piles	Steel pipe piles	Total piles	Anticipated pile driving workdays 2
LOA YR-1 (Nov. 2027-Feb. 2028)
Enrockment placement and pile installation to construct 4 structures at Site O-23.5-BN-ADD2	181	181	362	25
LOA YR-2 (Nov. 2028-Feb. 2029)
Construction of 2 new structures at Site W-35.6-IW-D using enrockment and marker piles only	NA	6	6	1
LOA YR-3 (Nov. 2029-Feb. 2030)
Enrockment placement and pile installation to construct 5 structures at Site O-23.5-BN-ADD1	248	249	497	34
LOA YR-4 (Nov. 2030-Feb. 2031)
Enrockment placement and pile installation to construct 3 structures at Site O-27.3-BN	223	224	447	30
LOA YR-5 (Nov. 2031-Feb. 2032)
Enrockment placement and pile installation to construct 3 structures at Site O-31.4-BN	377	379	756	51
Total	1,029	1,038	2,068	141
1  Reference system name that denotes the side of the channel ( i.e., O for Oregon; W for Washington), river mile, type of placement ( i.e., BN for beach nourishment; IW-S for in-water shallow; IW-D for in-water deeper than 20 ft).
2  Though up to 20 piles will be installed in a day, we estimate the total number of workdays based on an average of 15 piles being installed per day to account for potential delays due to equipment, weather, and other unforeseen circumstances.

Proposed mitigation, monitoring, and reporting measures are described in detail later in this document (see Proposed Mitigation and Proposed Monitoring and Reporting).

Description of Marine Mammals in the Area of Specified Activities

Sections 3 and 4 of the Application summarize available information regarding status and trends, distribution and habitat preferences, and behavior and life history of the potentially affected species. NMFS fully considered all of this information, and we refer the reader to these descriptions, instead of reprinting the information. Additional information regarding population trends and threats may be found in NMFS' Stock Assessment Reports (SARs) (see https://www.fisheries.noaa.gov/​national/​marine-mammal-protection/​marine-mammal-stock-assessments) and more general information about these species ( e.g., physical and behavioral descriptions) may be found on NMFS' website at: https://www.fisheries.noaa.gov/​find-species.

Table 4 lists all species or stocks for which take is expected and proposed to be authorized for this activity and summarizes information related to the population or stock, including regulatory status under the MMPA and the Endangered Species Act (ESA) and potential biological removal (PBR), where known. PBR is defined by the MMPA as the maximum number of animals, not including natural mortalities, that may be removed from a marine mammal stock while allowing that stock to reach or maintain its optimum sustainable population (as described in NMFS' SARs). While no serious injury or mortality is anticipated or proposed to be authorized here, PBR and annual serious injury and mortality from anthropogenic sources are included here as gross indicators of the status of the species or stocks and other threats.

Marine mammal abundance estimates presented in this document represent the total number of individuals that make up a given stock or the total number estimated within a particular study or survey area. NMFS' stock abundance estimates for most species represent the total estimate of individuals within the geographic area, if known, that comprises that stock. For some species, this geographic area may extend beyond U.S. waters. All managed stocks in this region are assessed in NMFS' U.S. Pacific and Alaska SARs. All values presented in table 4 are the most recent available at the time of publication (including from the draft 2023 SARs) and are available online at: https://www.fisheries.noaa.gov/​national/​marine-mammal-protection/​marine-mammal-stock-assessments. ( print page 89548)

Table 4 — 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, Nmin, 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 5 (N/A, 36,308, 2022)	2,178	93.2
Family Phocidae (earless seals):
	Harbor Seal
Phoca vitulina	OR/WA Coastal	-, -, N	24,731 6 (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 at: https://marinemammalscience.org/​science-and-publications/​list-marine-mammal-species-subspecies.
2  ESA status: Endangered (E), Threatened (T)/MMPA status: Depleted (D). A dash (-) indicates that the species is not listed under the ESA or designated as depleted under the MMPA. Under the MMPA, a strategic stock is one for which the level of direct human-caused mortality exceeds PBR or which is determined to be declining and likely to be listed under the ESA within the foreseeable future. Any species or stock listed under the ESA is automatically designated under the MMPA as depleted and as a strategic stock.
3  NMFS marine mammal SARs online at: https://www.fisheries.noaa.gov/​national/​marine-mammal-protection/​marine-mammal-stock-assessment-reports-region. CV is coefficient of variation; Nmin 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.
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.
6  There is no current estimate of abundance available for this stock. Value presented is the most recent available and based on 1999 data.

As indicated above, all 3 species (with 3 managed stocks) in table 4 temporally and spatially co-occur with the activity to the degree that take is reasonably likely to occur.

California Sea Lion

California sea lions are the most frequently sighted sea lion found in Washington waters and use haulout sites along the outer coast, the Strait of Juan de Fuca, and in the Puget Sound. The U.S. stock of California sea lions breeds on islands off the southern California coast. They are commonly found in Oregon haul-out sites from September to May and during this period, adult and subadult males have been observed in bays, estuaries, and offshore rocks along the Oregon coast. In fact, a few males have reported in Oregon waters throughout the year (Mate 1973). The population breeds in the California Channel Islands and most females and young pups remain in that region year-around (Mate, 1973; Oregon Department of Fish and Wildlife (ODFW), 2023). California sea lions may occur in the project vicinity and often use that same haulout sites as Steller sea lions (ODFW, 2023, see figure 4-2 in the Application).

Steller Sea Lion

Steller sea lions that occur in the LCR, including the project vicinity, are members of the eastern Distinct Population Segment (DPS), ranging from Southeast Alaska to central California, including Washington (Jeffries et al., 2000; Scordino, 2006; NMFS, 2013). Steller sea lions have been detected in the LCR and may occur in the vicinity of the project. All sea lions detected in the LCR are male and the nearest sea lion haulout sites are in Astoria and upriver near Rainier, Washington (USACE, 2024, see figure 4-2 in the Application). However, Steller sea lions will likely transit the Project Area during winter, depending on the timing of the eulachon spawning run which can attract large numbers of sea lions.

Harbor Seal

Harbor seals are the most common widely-distributed marine mammal found in Washington marine waters and are frequently observed in the nearshore marine environment. They can commonly be found on offshore rocks and islands, along shores, and on exposed flats in the estuary (Harvey, 1987). Note that the Oregon/Washington Coastal Stock was most recently estimated at 24,732 harbor seals in 1999 and more recent abundance data is not available. There is no current estimate of abundance for this stock (Carretta et al., 2022).

Harbor seals in this population are typically non-migratory and reside year-round in the LCR, and generally remain in the same area throughout the year for breeding and feeding. Harbor seals in the LCR do exhibit some seasonal movement upriver, including into or through the Project Area of ensonification, to follow winter and spring runs of Pacific eulachon ( Thaleichthys pacificus) and out-migrating juvenile salmon ( Oncorhynchus spp.), and they are observed regularly in portions of the LCR including the Project Area. Within the LCR, they tend to congregate to feed at the mouths of tributary rivers, including the Cowlitz and Kalama rivers (RMs 68 and 73, respectively). There are several known haul-out sites within 5 of the stretch of river ( i.e., RM 23 to RM 36) proposed for new pile driving (see figure 4-1 in the Application) and highest utilization of these lower river sights has typically been observed in May/June (Wright and Riemer, 2023).

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, 2024) 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 ( print page 89549) lower bound from Southall et al. (2007) retained.

On May 3, 2024, NMFS published and solicited public comment on its draft Updated Technical Guidance (89 FR 36762), which includes updated hearing ranges and names for the marine mammal hearing groups and is intended to replace the 2018 Technical Guidance once finalized. The public comment period ended on June 17th, 2024. Because NMFS may finalize the Guidance prior to taking a final agency action on this proposed rulemaking, we considered both the 2018 and 2024 Technical Guidance in our effects and estimated take analysis below. Marine mammal hearing groups and their associated hearing ranges from NMFS (2018) and NMFS (2024) are provided in tables 5 and 6. In the draft Updated Technical Guidance, mid-frequency cetaceans have been re-classified as high-frequency cetaceans, and high-frequency cetaceans have been updated to very-high-frequency (VHF) cetaceans. Additionally, the draft Updated Technical Guidance includes in-air data for phocid (PA) and otariid (OA) pinnipeds.

Table 5—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).

Table 6—Marine Mammal Hearing Groups

[NMFS, 2024]

Hearing group	Generalized hearing range *
Low-frequency (LF) cetaceans (baleen whales)	7 Hz to 36 kHz.
High-frequency (HF) cetaceans (dolphins, toothed whales, beaked whales, bottlenose whales)	150 Hz to 160 kHz.
Very High-frequency (VHF) cetaceans (true porpoises, Kogia, river dolphins, Cephalorhynchid, Lagenorhynchus cruciger & L. australis)	200 Hz to 165 kHz.
Phocid pinnipeds (PW) (underwater) (true seals)	40 Hz to 90 kHz.
Otariid pinnipeds (OW) (underwater) (sea lions and fur seals)	60 Hz to 68 kHz.
* Represents the generalized hearing range for the entire group as a composite ( i.e., all species within the group), where individual species' hearing ranges may not be as broad. Generalized hearing range chosen based on ~65 dB threshold from composite audiogram, previous analysis in NMFS 2018, and/or data from Southall et al. (2007); Southall et al. (2019). Additionally, animals are able to detect very loud sounds above and below that “generalized” hearing range.

For more detail concerning these groups and associated frequency ranges, please see NMFS (2018, 2024) for a review of available information.

Potential Effects of Specified Activities on Marine Mammals and Their Habitat

This section provides a discussion of the ways in which components of the specified activity may impact marine mammals and their habitat. The Estimated Take of Marine Mammals section later in this document includes a quantitative analysis of the number of individuals that are expected to be taken by this activity. The Negligible Impact Analysis and Determination section considers the content of this section, the Estimated Take of Marine Mammals section, and the Proposed Mitigation section, to draw conclusions regarding the likely impacts of these activities on the reproductive success or survivorship of individuals and whether those impacts are reasonably expected to, or reasonably likely to, adversely affect the species or stock through effects on annual rates of recruitment or survival.

Description of Sound Sources

The marine soundscape is comprised of both ambient and anthropogenic sounds. Ambient sound is defined as the all-encompassing sound in a given place and is usually a composite of sound from many sources both near and far. The sound level of an area is defined by the total acoustical energy being generated by known and unknown sources. These sources may include physical ( e.g., waves, wind, precipitation, earthquakes, ice, atmospheric sound), biological ( e.g., sounds produced by marine mammals, fish, and invertebrates), and anthropogenic sound ( e.g., vessels, dredging, aircraft, construction).

The sum of the various natural and anthropogenic sound sources at any given location and time—which comprise “ambient” or “background” sound—depends not only on the source levels (as determined by current weather conditions and levels of biological and shipping activity) but also on the ability of sound to propagate through the environment. In turn, sound propagation is dependent on the spatially and temporally varying properties of the water column and sea floor and is frequency-dependent. As a result of the dependence on a large number of varying factors, ambient sound levels can be expected to vary widely over both coarse and fine spatial and temporal scales. Sound levels at a given frequency and location can vary by 10 to 20 dB from day to day (Richardson et al., 1995). The result is that, depending on the source type and its intensity, sound from the specified activity may be a negligible addition to the local environment or could form a distinctive signal that may affect marine mammals. ( print page 89550)

In-water construction activities associated with the project would include vibratory pile removal, and impact and vibratory pile driving. The sounds produced by these activities fall into 1 of 2 general sound types: impulsive and non-impulsive. Impulsive sounds ( e.g., explosions, gunshots, sonic booms, impact pile driving) are typically transient, brief (less than 1 second), broadband, and consist of high peak sound pressure with rapid rise time and rapid decay (American National Standards Institute (ANSI), 1986; National Institute for Occupational Safety and Health (NIOSH), 1998; ANSI, 2005; NMFS, 2018). Non-impulsive sounds ( e.g., aircraft, machinery operations such as drilling or dredging, vibratory pile driving, and active sonar systems) can be broadband, narrowband or tonal, brief or prolonged (continuous or intermittent), and typically do not have the high peak sound pressure with raid rise/decay time that impulsive sounds do (ANSI, 1995; NIOSH, 1998; NMFS, 2018). The distinction between these two sound types is important because they have differing potential to cause physical effects, particularly with regard to hearing ( e.g., Ward, 1997 in Southall et al., 2007).

Impact hammers operate by repeatedly dropping a heavy piston onto a pile to drive the pile into the substrate. Sound generated by impact hammers is characterized by rapid rise times and high peak levels, a potentially injurious combination (Hastings and Popper, 2005). Vibratory hammers install piles by vibrating them and allowing the weight of the hammer to push them into the sediment. The vibrations produced also cause liquefaction of the substrate surrounding the pile, enabling the pile to be extracted or driven into the ground more easily. Vibratory hammers produce significantly less sound than impact hammers. Peak sound pressure levels (SPLs) may be 180 dB or greater but are generally 10 to 20 dB lower than SPLs generated during impact pile driving of the same-sized pile (Oestman et al., 2009). Rise time is slower, reducing the probability and severity of injury, and sound energy is distributed over a greater amount of time (Nedwell and Edwards, 2002; Carlson et al., 2005).

The likely or possible impacts of the USACE's proposed activity on marine mammals could involve both non-acoustic and acoustic stressors. Potential non-acoustic stressors could result from the physical presence of the equipment and personnel; however, any impacts to marine mammals are expected to be primarily acoustic in nature. Acoustic stressors include effects of heavy equipment operation during pile installation and removal.

Acoustic Impacts

The introduction of anthropogenic noise into the aquatic environment from pile driving is the primary means by which marine mammals may be harassed from the proposed activity. In general, animals exposed to natural or anthropogenic sound may experience physical and psychological effects, ranging in magnitude from none to severe (Southall et al., 2007). In general, exposure to pile driving noise has the potential to result in an auditory threshold shift (TS) and behavioral reactions ( e.g., avoidance, temporary cessation of foraging and vocalizing, changes in dive behavior). Exposure to anthropogenic noise can also lead to non-observable physiological responses, such as an increase in stress hormones. Additional noise in a marine mammal's habitat can mask acoustic cues used by marine mammals to carry out daily functions such as communication and predator and prey detection. The effects of pile driving noise on marine mammals are dependent on several factors, including, but not limited to, sound type ( e.g., impulsive vs. non-impulsive), the species, age and sex class ( e.g., adult male vs. mom with calf), duration of exposure, the distance between the pile and the animal, received levels, behavior at time of exposure, and previous history with exposure (Wartzok et al., 2004; Southall et al., 2007). Here we discuss physical auditory effects (TS) followed by behavioral effects and potential impacts on habitat.

NMFS defines a noise-induced TS as a change, usually an increase, in the threshold of audibility at a specified frequency or portion of an individual's hearing range above a previously established reference level (NMFS, 2018, 2024). The amount of TS is customarily expressed in dB. A TS can be permanent or temporary. As described in NMFS (2018, 2024), there are numerous factors to consider when examining the consequence of TS, including, but not limited to, the signal temporal pattern ( e.g., impulsive or non-impulsive), likelihood an individual would be exposed for a long enough duration or to a high enough level to induce a TS, the magnitude of the TS, time to recovery (seconds to minutes or hours to days), the frequency range of the exposure ( i.e., spectral content), the hearing frequency range of the exposed species relative to the signal's frequency spectrum ( i.e., how an animal uses sound within the frequency band of the signal; e.g., Kastelein et al., 2014), and the overlap between the animal and the source ( e.g., spatial, temporal, and spectral).

Auditory Injury and Permanent Threshold Shift (PTS) —NMFS defines auditory injury as “damage to the inner ear that can result in destruction of tissue . . . which may or may not result in PTS” (NMFS, 2024). NMFS defines PTS as a permanent, irreversible increase in the threshold of audibility at a specified frequency or portion of an individual's hearing range above a previously established reference level (NMFS, 2024). PTS does not generally affect more than a limited frequency range, and an animal that has incurred PTS has incurred some level of hearing loss at the relevant frequencies; typically, animals with PTS are not functionally deaf (Au and Hastings, 2008; Finneran, 2016). Available data from humans and other terrestrial mammals indicate that a 40-dB threshold shift approximates PTS onset (see Ward et al., 1958, 1959, 1960; Kryter et al., 1966; Miller, 1974; Ahroon et al., 1996; Henderson et al., 2008). PTS levels for marine mammals are estimates, as with the exception of a single study unintentionally inducing PTS in a harbor seal (Kastak et al., 2008), there are no empirical data measuring PTS in marine mammals largely due to the fact that, for various ethical reasons, experiments involving anthropogenic noise exposure at levels inducing PTS are not typically pursued or authorized (NMFS, 2018).

Temporary Threshold Shift (TTS) —TTS is a temporary, reversible increase in the threshold of audibility at a specified frequency or portion of an individual's hearing range above a previously established reference level (NMFS, 2018). Based on data from cetacean TTS measurements (Southall et al., 2007, 2019), a TTS of 6 dB is considered the minimum TS clearly larger than any day-to-day or session-to-session variation in a subject's normal hearing ability (Schlundt et al., 2000; Finneran et al., 2000, 2002). As described in Finneran (2015), marine mammal studies have shown the amount of TTS increases with cumulative sound exposure level (SEL_cum) in an accelerating fashion: At low exposures with lower SEL_cum, the amount of TTS is typically small and the growth curves have shallow slopes. At exposures with higher SEL_cum, the growth curves become steeper and approach linear relationships with the noise SEL.

Depending on the degree (elevation of threshold in dB), duration ( i.e., recovery time), and frequency range of TTS, and ( print page 89551) the context in which it is experienced, TTS can have effects on marine mammals ranging from discountable to serious (similar to those discussed in auditory masking, below). For example, a marine mammal may be able to readily compensate for a brief, relatively small amount of TTS in a non-critical frequency range that takes place during a time when the animal is traveling through the open ocean, where ambient noise is lower and there are not as many competing sounds present. Alternatively, a larger amount and longer duration of TTS sustained during a time when communication is critical for successful mother/calf interactions could have more serious impacts. We note that reduced hearing sensitivity as a simple function of aging has been observed in marine mammals, as well as humans and other taxa (Southall et al., 2007), so we can infer that strategies exist for coping with this condition to some degree, though likely not without cost.

Many studies have examined noise-induced hearing loss in marine mammals (see Finneran (2015) and Southall et al. (2019) for summaries). TTS is the mildest form of hearing impairment that can occur during exposure to sound (Kryter, 2013). While experiencing TTS, the hearing threshold rises, and a sound must be at a higher level in order to be heard. In terrestrial and marine mammals, TTS can last from minutes or hours to days (in cases of strong TTS). In many cases, hearing sensitivity recovers rapidly after exposure to the sound ends. For pinnipeds in water, measurements of TTS are limited to harbor seals, elephant seals ( Mirounga angustirostris), bearded seals ( Erignathus barbatus) and California sea lions (Kastak et al., 1999, 2007; Kastelein et al., 2019b, 2019c, 2021, 2022a, 2022b; Reichmuth et al., 2019; Sills et al., 2020). These studies examined hearing thresholds measured in marine mammals before and after exposure to intense or long-duration sound exposures. The difference between the pre-exposure and post-exposure thresholds can be used to determine the amount of TS at various post-exposure times.

The amount and onset of TTS depends on the exposure frequency. Sounds at low frequencies, well below the region of best sensitivity for a species or hearing group, are less hazardous than those at higher frequencies, near the region of best sensitivity (Finneran and Schlundt, 2013). At low frequencies, onset-TTS exposure levels are higher compared to those in the region of best sensitivity ( i.e., a low frequency noise would need to be louder to cause TTS onset when TTS exposure level is higher), as shown for harbor porpoises and harbor seals (Kastelein et al., 2019a, 2019c). Note that in general, harbor seals have a lower TTS onset than other measured pinniped species (Finneran, 2015). In addition, TTS can accumulate across multiple exposures, but the resulting TTS will be less than the TTS from a single, continuous exposure with the same SEL (Mooney et al., 2009; Finneran et al., 2010; Kastelein et al., 2014, 2015). This means that TTS predictions based on the total, SEL_cum will overestimate the amount of TTS from intermittent exposures, such as sonars and impulsive sources. Nachtigall et al. (2018) describes measurements of hearing sensitivity of multiple odontocete species ( i.e., bottlenose dolphin, harbor porpoise, beluga, and false killer whale ( Pseudorca crassidens)) when a relatively loud sound was preceded by a warning sound. These captive animals were shown to reduce hearing sensitivity when warned of an impending intense sound. Based on these experimental observations of captive animals, the authors suggest that wild animals may dampen their hearing during prolonged exposures or if conditioned to anticipate intense sounds. Additionally, the existing marine mammal TTS data come from a limited number of individuals within these species.

Relationships between TTS and PTS thresholds have not been studied in marine mammals, but such relationships are assumed to be similar to those in humans and other terrestrial mammals. PTS typically occurs at exposure levels at least several dBs above that inducing mild TTS ( e.g., a 40-dB TS approximates PTS onset (Kryter et al., 1966; Miller, 1974), while a 6-dB TS approximates TTS onset (Southall et al., 2007, 2019). Based on data from terrestrial mammals, a precautionary assumption is that the PTS thresholds for impulsive sounds (such as impact pile driving pulses as received close to the source) are at least 6 dB higher than the TTS threshold on a peak-pressure basis and PTS SEL_cum thresholds are 15 to 20 dB higher than TTS SEL_cum thresholds (Southall et al., 2007, 2019). Given the higher level of sound or longer exposure duration necessary to cause PTS as compared with TTS, it is considerably less likely that PTS could occur.

Installing piles for this project requires either impact pile driving or vibratory pile driving. For this project, these activities would not occur at the same time, and there would be pauses in activities producing the sound during each day. Given these pauses, and that many marine mammals are likely moving through the ensonified area and not remaining for extended periods of time, the potential for TS declines.

Behavioral Harassment —Exposure to noise from pile driving and removal also has the potential to behaviorally disturb marine mammals. Available studies show wide variation in response to underwater sound; therefore, it is difficult to predict specifically how any given sound in a particular instance might affect marine mammals perceiving the signal. If a marine mammal does react briefly to an underwater sound by changing its behavior or moving a small distance, the impacts of the change are unlikely to be significant to the individual, let alone the stock or population. However, if a sound source displaces marine mammals from an important feeding or breeding area for a prolonged period, impacts on individuals and populations could be significant ( e.g., Lusseau and Bejder, 2007; Weilgart, 2007; National Research Council (NRC), 2005).

Disturbance may result in changing durations of surfacing and dives, number of blows per surfacing, or moving direction and/or speed; reduced/increased vocal activities; changing/cessation of certain behavioral activities ( e.g., socializing or feeding); visible startle response or aggressive behavior ( e.g., tail/fluke slapping or jaw clapping); or avoidance of areas where sound sources are located. Pinnipeds may increase their haul out time, possibly to avoid in-water disturbance (Thorson and Reyff, 2006).

Behavioral responses to sound are highly variable and context-specific and any reactions depend on numerous intrinsic and extrinsic factors ( e.g., species, state of maturity, experience, current activity, reproductive state, auditory sensitivity, time of day), as well as the interplay between factors ( e.g., Richardson et al., 1995; Wartzok et al., 2003; Southall et al., 2007; Weilgart, 2007; Archer et al., 2010). Behavioral reactions can vary not only among individuals but also within an individual, depending on previous experience with a sound source, context, and numerous other factors (Ellison et al., 2012), and can vary depending on characteristics associated with the sound source ( e.g., whether it is moving or stationary, number of sources, distance from the source). In general, pinnipeds seem more tolerant of, or at least habituate more quickly to, potentially disturbing underwater sound than do cetaceans, and generally seem to be less responsive to exposure to ( print page 89552) industrial sound than most cetaceans. Please see appendices B-C of Southall et al. (2007) and Gomez et al. (2016) for a review of studies involving marine mammal behavioral responses to sound.

Disruption of feeding behavior can be difficult to correlate with anthropogenic sound exposure, so it is usually inferred by observed displacement from known foraging areas, the appearance of secondary indicators ( e.g., bubble nets or sediment plumes), or changes in dive behavior. As for other types of behavioral response, the frequency, duration, and temporal pattern of signal presentation, as well as differences in species sensitivity, are likely contributing factors to differences in response in any given circumstance ( e.g., Croll et al., 2001; Nowacek et al., 2004; Madsen et al., 2006; Yazvenko et al., 2007). A determination of whether foraging disruptions incur fitness consequences would require information on or estimates of the energetic requirements of the affected individuals and the relationship between prey availability, foraging effort and success, and the life history stage of the animal.

Stress Responses —An animal's perception of a threat may be sufficient to trigger stress responses consisting of some combination of behavioral responses, autonomic nervous system responses, neuroendocrine responses, or immune responses ( e.g., Seyle, 1950; Moberg, 2000). In many cases, an animal's first and sometimes most economical (in terms of energetic costs) response is behavioral avoidance of the potential stressor. Autonomic nervous system responses to stress typically involve changes in heart rate, blood pressure, and gastrointestinal activity. These responses have a relatively short duration and may or may not have a significant long-term effect on an animal's fitness.

Neuroendocrine stress responses often involve the hypothalamus-pituitary-adrenal system. Virtually all neuroendocrine functions that are affected by stress—including immune competence, reproduction, metabolism, and behavior—are regulated by pituitary hormones. Stress-induced changes in the secretion of pituitary hormones have been implicated in failed reproduction, altered metabolism, reduced immune competence, and behavioral disturbance ( e.g., Moberg, 1987; Blecha, 2000). Increases in the circulation of glucocorticoids are also equated with stress (Romano et al., 2004).

The primary distinction between stress (which is adaptive and does not normally place an animal at risk) and “distress” is the cost of the response. During a stress response, an animal uses glycogen stores that can be quickly replenished once the stress is alleviated. In such circumstances, the cost of the stress response would not pose serious fitness consequences. However, when an animal does not have sufficient energy reserves to satisfy the energetic costs of a stress response, energy resources must be diverted from other functions. This state of distress will last until the animal replenishes its energetic reserves sufficient to restore normal function.

Relationships between these physiological mechanisms, animal behavior, and the costs of stress responses are well studied through controlled experiments and for both laboratory and free-ranging animals ( e.g., Holberton et al., 1996; Hood et al., 1998; Jessop et al., 2003; Krausman et al., 2004; Lankford et al., 2005). Stress responses due to exposure to anthropogenic sounds or other stressors and their effects on marine mammals have also been reviewed (Fair and Becker, 2000; Romano et al., 2002b) and, more rarely, studied in wild populations ( e.g., Romano et al., 2002a). For example, Rolland et al. (2012) found that noise reduction from reduced ship traffic in the Bay of Fundy was associated with decreased stress in North Atlantic right whales. These and other studies lead to a reasonable expectation that some marine mammals will experience physiological stress responses upon exposure to acoustic stressors and that it is possible that some of these would be classified as “distress.” In addition, any animal experiencing TTS would likely also experience stress responses (NRC, 2003), however distress is an unlikely result of this project based on observations of marine mammals during previous, similar projects in the area.

Masking —Sound can disrupt behavior through masking, or interfering with, an animal's ability to detect, recognize, or discriminate between acoustic signals of interest ( e.g., those used for intraspecific communication and social interactions, prey detection, predator avoidance, navigation) (Richardson et al., 1995). Masking occurs when the receipt of a sound is interfered with by another coincident sound at similar frequencies and at similar or higher intensity and may occur whether the sound is natural ( e.g., snapping shrimp, wind, waves, precipitation) or anthropogenic ( e.g., pile driving, shipping, sonar, seismic exploration) in origin. The ability of a noise source to mask biologically important sounds depends on the characteristics of both the noise source and the signal of interest ( e.g., signal-to-noise ratio, temporal variability, direction), in relation to each other and to an animal's hearing abilities ( e.g., sensitivity, frequency range, critical ratios, frequency discrimination, directional discrimination, age or TTS hearing loss), and existing ambient noise and propagation conditions. Masking of natural sounds can result when human activities produce high levels of background sound at frequencies important to marine mammals. Conversely, if the background level of underwater sound is high ( e.g., on a day with strong wind and high waves), an anthropogenic sound source would not be detectable as far away as would be possible under quieter conditions and would itself be masked.

Airborne Acoustic Effects —Although pinnipeds are known to haul out regularly on manmade objects, we believe that incidents of take resulting solely from airborne sound are unlikely because there are no known haulouts within the immediate project vicinity on the LCR. There is a possibility that an animal could surface in-water, but with head out, within the area in which airborne sound exceeds relevant thresholds and thereby be exposed to levels of airborne sound that we associate with harassment, but any such occurrence would likely be accounted for in our estimation of incidental take from underwater sound. Therefore, authorization of incidental take resulting from airborne sound for pinnipeds is not warranted, and airborne sound is not discussed further here.

Marine Mammal Habitat Effects

The USACE's construction activities could have localized, temporary impacts on marine mammal habitat by increasing in-water SPLs and slightly decreasing water quality. No net habitat loss is expected, as the dock will be reconstructed within its original footprint. Construction activities are localized and would likely have temporary impacts on marine mammal habitat through increases in underwater sounds. Increased noise levels may affect acoustic habitat (see masking discussion above) and adversely affect marine mammal prey in the vicinity of the Project Area (see discussion below). During pile driving activities, elevated levels of underwater noise would ensonify the Project Area where both fishes and marine mammals may occur and could affect foraging success. Additionally, marine mammals may avoid the area during construction; however, displacement due to noise is expected to be temporary and is not ( print page 89553) expected to result in long-term effects to the individuals or populations.

Temporary and localized reduction in water quality would occur because of in-water construction activities as well. Most of this effect would occur during the installation and removal of piles when bottom sediments are disturbed. The installation of piles would disturb bottom sediments and may cause a temporary increase in suspended sediment in the Project Area. In general, turbidity associated with pile installation is localized to about 25-ft (7.6-m) radius around the pile (Everitt et al., 1980). Pinnipeds are not expected to be close enough to the pile driving areas to experience effects of turbidity and could avoid localized areas of turbidity. Therefore, we expect the impact from increased turbidity levels to be discountable to marine mammals and do not discuss it further.

In-Water Construction Effects on Potential Foraging Habitat

The proposed activities would not result in permanent impacts to habitats used directly by marine mammals. The total riverbed area affected by pile installation and removal is a very small area compared to the vast foraging area available to marine mammals in the LCR and Washington's outer coast and contains no habitat areas of particular importance. Pile installation may have impacts on benthic invertebrate species primarily associated with disturbance of sediments that may cover or displace some invertebrates. The impacts would be temporary and highly localized, and no habitat would be permanently displaced by construction. Therefore, it is not expected to have impacts on foraging opportunities for marine mammals.

It is possible that avoidance by potential prey ( i.e., fish) in the immediate area may occur due to temporary loss of this foraging habitat. The duration of fish avoidance of this area after pile driving stops is unknown, but we anticipate a rapid return to normal recruitment, distribution and behavior. Any behavioral avoidance by fish of the disturbed area would still leave large areas of fish and marine mammal foraging habitat in the nearby vicinity in the in the Project Area and LCR.

Effects on Potential Prey

Sound may affect marine mammals through impacts on the abundance, behavior, or distribution of prey species ( i.e., fish). Marine mammal prey varies by species, season, and location. Here, we describe studies regarding the effects of noise on known marine mammal prey.

Fish utilize the soundscape and components of sound in their environment to perform important functions such as foraging, predator avoidance, mating, and spawning ( e.g., Zelick et al., 1999; Fay, 2009). Depending on their hearing anatomy and peripheral sensory structures, which vary among species, fish hear sounds using pressure and particle motion sensitivity capabilities and detect the motion of surrounding water (Fay et al., 2008). The potential effects of noise on fish depends on the overlapping frequency range, distance from the sound source, water depth of exposure, and species-specific hearing sensitivity, anatomy, and physiology. Key impacts to fish may include behavioral responses, hearing damage, barotrauma ( i.e., pressure-related injuries), and mortality.

Fish react to sounds which are especially strong and/or intermittent low-frequency sounds, and behavioral responses, such as flight or avoidance are the most likely effects. Short duration, sharp sounds can cause overt or subtle changes in fish behavior and local distribution. The reaction of fish to noise depends on the physiological state of the fish, past exposures, motivation ( e.g., feeding, spawning, migration), and other environmental factors. Hastings and Popper (2005) identified several studies that suggest fish may relocate to avoid certain areas of sound energy. Additional studies have documented effects of pile driving on fish, although several are based on studies in support of large, multiyear bridge construction projects ( e.g., Scholik and Yan, 2001, 2002; Popper and Hastings, 2009). Several studies have demonstrated that impulse sounds might affect the distribution and behavior of some fishes, potentially impacting foraging opportunities or increasing energetic costs ( e.g., Fewtrell and McCauley, 2012; Pearson et al., 1992; Skalski et al., 1992; Santulli et al., 1999; Paxton et al., 2017). However, some studies have shown no or slight reaction to impulse sounds ( e.g., Pena et al., 2013; Wardle et al., 2001; Jorgenson and Gyselman, 2009; Cott et al., 2012).

SPLs of sufficient strength have been known to cause injury to fish and fish mortality (summarized in Popper et al., 2014). However, in most fish species, hair cells in the ear continuously regenerate and loss of auditory function likely is restored when damaged cells are replaced with new cells. Halvorsen et al. (2012b) showed that a TTS of 4 to 6 dB was recoverable within 24 hours for one species. Impacts would be most severe when the individual fish is close to the source and when the duration of exposure is long. Injury caused by barotrauma can range from slight to severe and can cause death and is most likely for fish with swim bladders. Barotrauma injuries have been documented during controlled exposure to impact pile driving (Halvorsen et al., 2012a; Casper et al., 2013, 2017).

Fish populations in the proposed Project Area that serve as marine mammal prey could be temporarily affected by noise from pile installation and removal. The frequency range in which fishes generally perceive underwater sounds is 50 to 2,000 Hertz (Hz), with peak sensitivities below 800 Hz (Popper and Hastings, 2009). Fish behavior or distribution may change, especially with strong and/or intermittent sounds that could harm fishes. High underwater SPLs have been documented to alter behavior, cause hearing loss, and injure or kill individual fish by causing serious internal injury (Hastings and Popper, 2005).

The greatest potential impact to fishes during construction would occur during impact pile driving. However, the duration of impact pile driving would be limited to the final stage of installation (“proofing”) after the pile has been driven as close as practicable to the design depth with a vibratory driver. In-water construction activities would only occur during daylight hours, allowing fish to forage and transit the Project Area in the evening. Vibratory pile driving could elicit behavioral reactions from fishes such as temporary avoidance of the area but is unlikely to cause injuries to fishes or have persistent effects on local fish populations. Additionally, all pile installation would occur only during the USACE's and United States Fish and Wildlife Service designated in-water work window to minimize potential exposure of ESA-listed fish species migrating through the project site to noise from impact pile driving. Construction also would have minimal permanent and temporary impacts on benthic invertebrate species, a marine mammal prey source.

The area impacted by the project is relatively small compared to the available habitat in the remainder of the LCR, and there are no areas of particular importance that would be impacted by this project. Any behavioral avoidance by fish of the disturbed area would still leave significantly large areas of fish and marine mammal foraging habitat in the nearby vicinity. As described in the preceding, the potential for the USACE's construction to affect the availability of ( print page 89554) prey to marine mammals or to meaningfully impact the quality of physical or acoustic habitat is considered to be insignificant.

Estimated Take of Marine Mammals

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

Harassment, defined previously in the Purpose and Need for Regulatory Action section, is the only type of take expected to result from these activities.

Authorized takes would 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 proposed to be authorized for this activity. We describe how the proposed take numbers are estimated below.

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 proposed take estimates.

Acoustic Thresholds

NMFS recommends the use of acoustic thresholds that identify the received level of underwater sound above which exposed marine mammals would be reasonably expected to be behaviorally harassed (equated to Level B harassment) or to incur PTS of some degree (equated to Level A harassment).

Level B Harassment —Though significantly driven by received level, the onset of behavioral disturbance from anthropogenic noise exposure is also informed to varying degrees by other factors related to the source or exposure context ( e.g., frequency, predictability, duty cycle, duration of the exposure, signal-to-noise ratio, distance to the source), the environment ( e.g., bathymetry, other noises in the area, predators in the area), and the receiving animals (hearing, motivation, experience, demography, life stage, depth) and can be difficult to predict ( e.g., 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 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 ( e.g., conspecific communication, predators, prey) may result in changes in behavior patterns that would not otherwise occur.

The USACE's proposed 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 1 μPa are applicable.

Level A Harassment —NMFS' Technical Guidance for Assessing the Effects of Anthropogenic Sound on Marine Mammal Hearing (Version 2.0; NMFS, 2018) and the draft Updated Technical Guidance (NMFS, 2024) identify 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). This proposed rule estimates Level A harassment using the existing Technical Guidance (NMFS, 2018) as well as the draft Updated Technical Guidance (NMFS, 2024) because at the time of the final agency decision on this request for incidental take, it's possible NMFS may have made a final agency decision on the draft Guidance.

These thresholds are provided in tables 7 and 8 below. The references, analysis, and methodology used in the development of the thresholds are described in NMFS' 2018 Technical Guidance and NMFS' 2024 draft Updated Technical Guidance, both of which may be accessed at: https://www.fisheries.noaa.gov/​national/​marine-mammal-protection/​marine-mammal-acoustic-technical-guidance.

The USACE's proposed activity includes the use of impulsive (impact pile driving) and non-impulsive (vibratory driving) sources.

Table 7—NMFS' 2018 Thresholds Identifying the Onset of Permanent Threshold Shift (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.
( print page 89555)
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 SPL thresholds associated with impulsive sounds, these thresholds should also be considered.
Note: Peak sound pressure ( Lpk ) has a reference value of 1 µPa, and SEL cum 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 NMFS' 2018 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 SEL cum 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 SEL cum 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.

Table 8—NMFS' 2024 Thresholds Identifying the Onset of Auditory Injury (AUD INJ)

Hearing group	AUD INJ acoustic thresholds * (received level)
	Impulsive	Non-impulsive
Underwater
Low-Frequency (LF) Cetaceans	Cell 1: Lp, 0-pk,flat : 222 dB; LE, p, LF,24h : 183 dB	Cell 2: LE, p, LF,24h : 197 dB.
High-Frequency (HF) Cetaceans	Cell 3: Lp, 0-pk,flat : 230 dB; LE,p, HF,24h : 193 dB	Cell 4: LE, p, HF,24h : 201 dB.
Very High-Frequency (VHF) Cetaceans	Cell 5: Lp, 0-pk,flat : 202 dB; LE,p,VHF,24h : 159 dB	Cell 6: LE, p, VHF,24h : 181 dB.
Phocid Pinnipeds (PW) (Underwater)	Cell 7: Lp, 0-pk.flat : 223 dB; LE,p,PW,24h : 183 dB	Cell 8: LE, p, PW,24h : 195 dB.
Otariid Pinnipeds (OW) (Underwater)	Cell 9: Lp, 0-pk,flat : 230 dB; LE,p,OW,24h : 185 dB	Cell 10: LE, p, OW,24h : 199 dB.
In-Air
Phocid Pinnipeds (PA) (In-Air)	Cell 11: L p, 0-pk.flat : 162 dB; LE,p,PA,24h : 140 dB	Cell 12: LE, p, PA,24h : 154 dB.
Otariid Pinnipeds (OA) (In-Air)	Cell 13: L p, 0-pk,flat : 177 dB; LE,p,OA,24h : 163 dB	Cell 14: LE, p, OA,24h : 177 dB.
* Dual metric acoustic thresholds for impulsive sounds: Use whichever results in the largest isopleth for calculating AUD INJ 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 NMFS' 2018 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

This section describes the operational and environmental parameters of the activity that are used in estimating the area ensonified above the acoustic thresholds, including source levels and transmission loss ( TL) coefficient.

The sound field in the Project Area is the existing background noise plus additional construction noise from the 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 LCR, including intersecting land masses that will reduce the overall area of potential impact. Additionally, vessel traffic in the LCR during construction may contribute to elevated background noise levels, which may mask sounds produced by the project.

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

( print page 89556)

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 9). Generally, we choose source levels from similar pile types from locations ( e.g., geology, bathymetry) similar to the project.

Table 9—Proxy Sound Source Levels for Pile Sizes and Driving Methods

Pile type	Sound pressure level (single strike)
24-in Steel Pipe 1 Vibratory (unattenuated)		159 dB RMS
24-in Steel Pipe 1  3 Impact (attenuated)	198 dB PEAK	185 dB RMS	171 dB SEL .
12-in Timber 2 Vibratory (unattenuated)		162 dB RMS
12-in Timber 2  3 Impact (attenuated)	175 dB PEAK	165 dB RMS	155 dB SEL .
1  Reference levels based on the Sand Island Test Piles project in the Columbia River (Robert Miner Dynamic Testing 2021). While the original study tested various pile tips for driving through existing enrockment, the DMMP will not use pile tips so we referenced sound levels solely for piles excluding tips during vibratory driving. For impact driving, all piles in the Sand Island study included tips so we used the average SPLs across all piles as a conservative estimate.
2  All timber pile assumptions are based on Caltrans (2020).
3  We assume bubble curtains will be employed for all piles installed with an impact hammer under this LOA, thus, SPLs in this table reflect reference noise estimates reduced by 5 dB.

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, the optional User Spreadsheet tool offers the best way to estimate isopleth distances when more sophisticated modeling methods are not available or practical. For stationary sources such as pile driving, 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 10 below. The calculated Level A and Level B harassment isopleths are shown in table 11 and table 12.

Table 10—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
24-in steel pile (Vibratory)	A.1) Vibratory pile driving	2.5	20	25	NA
12-in Timber (Vibratory)	A.1) Vibratory pile driving	2.5	20	25	NA
Impact pile driving
24-in steel pile (Impact attenuated)	E.1) Impact pile driving	2	20	NA	45
12-in Timber (Impact attenuated)	E.1) Impact pile driving	2	20	NA	45

Table 11—Calculated Distance of Level A (Based on NMFS' 2018 Technical Guidance) and Level B Harassment by Pile Type and Pile Driving Method

Pile size and type	Level A harassment (m)		Level B harassment (m)
	Phocid	Otariid
Vibratory pile driving
24-in steel pile	12.63	0.9	3,981.1
12-in timber pile	19.9	1.4	6,309.6
Impact pile driving
24-in steel pile	79.0	5.7	464.2
12-in timber pile	6.8	0.5	21.5

( print page 89557)

Table 12—Calculated Distance of Level A (Based on NMFS' Proposed 2024 Update to the 2018 Technical Guidance) and Level B Harassment by Pile Type and Pile Driving Method

Pile size and type	Level A harassment (m)		Level B harassment (m)
	Phocid	Otariid
Vibratory pile driving
24-in steel pile	35.9	12.1	3,981.1
12-in timber pile	56.9	19.1	6,309.6
Impact pile driving
24-in steel pile	130.6	48.7	464.2
12-in timber pile	11.2	4.2	21.5

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 and describe how the information provided is synthesized to produce a quantitative estimate of the take that is reasonably likely to occur and proposed for authorization. The USACE referenced data provided by the Oregon Department of Fish and Wildlife (ODFW) and the Washington Department of Fish and Wildlife (WDFW) to support assumptions regarding marine mammal occurrence in the Project Area. The ODFW conducts periodic counts of pinnipeds at haul out sites along the Oregon coast and in the LCR. The WDFW has collected recent anecdotal evidence of pinniped abundance at haul out sites in the LCR near the confluence of the Cowlitz River at RM 67.5. While the confluence of the two rivers is located approximately 31.5 river miles upstream from the Project Area, it is the closest site that features data on pinniped activity. The USACE used the proximal count estimates from ODFW and WDFW to estimate the number of harbor seals, Steller sea lions, and California sea lions that could transit or occupy the Project Area during proposed pile driving in winter ( i.e., November through February). For sea lions, the USACE estimated the maximum number of animals likely to be encountered in a single day based on the maximum number of animals detected at haul out sites within 5- of proposed pile driving, as well as the closest haul out sites upstream or downstream. For harbor seals, the USACE estimated the harbor seal density using the approximate span of river where they have been observed at haul out sites.

Harbor Seal

The most recent harbor seal aerial surveys were conducted by ODFW during the 2021 summer pupping season. The average, maximum daily count of harbor seals counted across all haulout sites in the project vicinity in May and June was 837 (pups and non-pups combined) (USACE, 2024). After applying the Huber et al. (2001) correction factor of 1.53, used to account for likely imperfect detection during surveys, the adjusted number of harbor seals that may have been present during the 2021 surveys was 1,281 individuals. However, that estimate is not necessarily representative of the number of harbor seals that may be present in winter.

Jeffries et al. (1984) synthesized survey data collected by the state of Washington to document pinniped abundance and distribution in the LCR between 1980 and 1983. Table 13 summarizes the harbor seal count by month detected over that roughly 3-year study period (Jeffries et al., 1984). The USACE used this data to calculate the average, maximum total count observed across all haulout sites in the project vicinity to estimate the proportion of animals present from November through February relative to counts observed from May to June. The average harbor seal count observed between November and February was approximately 618 animals, whereas the average count for May and June was roughly 464. The count of harbor seals in winter was 1.33 times the number counted in May and June. To account for this seasonality, the most recent estimate of 1,281 harbor seals in the project vicinity during the pupping season, based on ODFW counts, could equate to a maximum of 1,706 harbor seals in the project vicinity each day in winter. While the USACE and NMFS acknowledge that the seasonal correction factor is based on data that is over 40 years old, all recent surveys have focused solely on the summer pupping season and there is no winter data corresponding to those counts. Therefore, the USACE, with NMFS' concurrence, relied on available data from a historic study that included counts for multiple seasons in the same year.

The USACE assumed the maximum winter abundance of 1,706 individuals and an even distribution of animals throughout the span of river between the river mouth and the upstream end of Tenasillahe Island (figure 6-21 in the Application). The hatched area in the figure is roughly 377 square kilometers (km² ) which yielded an approximate daily harbor seal density of 5 individuals per km² in the Project Area. The calculated take by Level A harassment is likely an overestimate because the likelihood of a harbor seal coming within a specified Level A harassment isopleth of the pile and remaining long enough to experience PTS during the brief period of potential impact driving that could be needed to reach the last ~5 ft of embedment depth is fairly low. In addition, the USACE utilized the Level A harassment isopleth area of the longest pile dike at each site, when in actuality, some sites have shorter structures, and a pile dike is composed of multiple individual piles with much smaller noise isopleths. ( print page 89558)

Table 13—Maximum Monthly Counts of Harbor Seals Detected During Low-Tide Aerial Surveys at Haulout Locations in the Lower Columbia River Estuary Between 1980 and 1983

[Adapted from Jeffries et al., 1984]

Month	South Jetty	Baker Bay	Desdemona Sands	Taylor Sands	Grays Bay	Miller Sands	Green Island	N of Woody Island	Total
January	0	0	566	444	1	381	0	72	1,464
February	0	NS	NS	NS	NS	* 200	NS	55	255
March	1	0	* 650	548	0	82	0	3	1,284
April	0	* 20	884	260	* 20	137	0	18	1,339
May	0	1	568	4	4	0	16	0	593
June	1	0	273	22	11	1	* 26	* 0	334
July	0	0	525	21	10	0	38	0	594
August	3	7	378	0	0	32	35	0	455
September	4	11	563	7	12	0	26	0	623
October	0	* 25	223	59	0	6	0	0	313
November	NS	NS	* 230	NS	NS	NS	NS	NS	230
December	0	0	301	174	0	46	0	0	521
NS = Not Surveyed.
* Count based on visual estimate from airplane, boat, or jetty.

For harbor seals only, take by Level A and Level B harassment was calculated based on the following equations, which were performed for Level A and Level B harassment and for steel and timber piles:

Harassment = Harbor seal density * ensonified area * pile driving workdays

The estimated isopleth areas associated with the longest pile dike at each site are presented in table 14. These inputs were used in the equation above to estimate the number of harbor seals possible within those isopleths each day (table 15) and then calculate the overall level of take based on the number of workdays projected in each year (table 16). The number of takes requested by Level A and Level B harassment by the USACE for Year 1 through Year 5 are shown in table 16. NMFS concurs with this assessment and is proposing to authorize harbor seal take according to the totals contained in table 16.

Table 14—Pile Dike Lengths (m) and Corresponding Level A and Level B Harassment Areas (km² )

Site	Pile dike length (m)	Phocids level A (km2 ) 24-in Steel Impact	All Marine Mammals level B (km2 ) 24-in steel impact	All Marine Mammals level B (km2 ) 24-in steel vibratory	All Marine Mammals level B (km2 ) 12-in timber vibratory
O-23.5-BN-ADD1	22.40	0.213	0.74	37.29	81.45
O-23.5-BN-ADD2	25.00	0.180	0.58	18.06	30.79
O-27.3-BN	27.86	0.162	0.68	13.52	22.97
O-31.4-BN	31.46	0.293	1.05	17.97	26.33
O-35.6-IW-D	35.41	0.135	0.63	10.70	16.51

Table 15—Estimated Harbor Seals in Level A and Level B Harassment Zones per Day

Site	Installation timeframe	HS * in Level A isopleth area 24-in steel impact	HS in Level B isopleth area 24-in steel impact	HS in Level B isopleth area 24-in steel vibratory	HS in Level B isopleth area 12-in timber vibratory
O-23.5-BN- ADD1	LOA YR-3	2	4	187	408
O-23.5-BN- ADD2	LOA YR-1	1	3	91	154
O-27.3-BN	LOA YR-4	1	4	68	115
O-31.4-BN	LOA YR-5	2	6	90	132
O-35.6-IW-D	LOA YR-2	1	4	54	83

Table 16—Calculated Level A and Level B Harassment Take for Harbor Seals During Pile Driving Activities Each Year

	Site	Steel pile driving workdays	Timber pile driving workdays	Level A (steel piles)	Level B (steel piles)	Level B (timber piles)
YR-1	O-23.5-BN-ADD2	13	12	26	2,405	4,896
YR-2	O-35.6-IW-D	1	0	1	90	0
YR-3	O-23.5-BN-ADD1	17	17	17	1,139	1,955
YR-4	O-27.3-BN	15	15	30	1,320	1,980
YR-5	O-31.4-BN	26	25	26	1,378	2,075

( print page 89559)

California and Steller Sea Lions

Take estimates for California and Steller sea lions were based on assumed daily abundances in the Project Area rather than the estimated densities. The ODFW counted sea lions during recent aerial surveys of three key haulout locations in the LCR. All sea lions detected in winter are non-pup males and average counts of both California and Steller sea lions observed during surveys between 2019 and 2022 are shown in table 17. The haulout at East Mooring Basin (EMB) is just south of the Project Area and likely downstream of pile driving harassment isopleths. The USACE used the average counts observed at EMB (RM 15 from there) as a proxy for sea lions that may be present during pile driving and used the average across all winter months as a proxy for the number of sea lions in the Project Area since that haulout is closer to the Project Area (RM 23 to RM 36) compared to the Rainer (RM 67) and Coffin Rock (RM 72) locations. Based on counts of sea lions at the EMB site (table 17), the USACE estimated 182 California sea lions and 3 Steller sea lions by Level B harassment per day in the project vicinity. Level A harassment is not likely since the Level A harassment zones for otariids are smaller than the shutdown zone proposed (15-20 m) for all pile driving scenarios as shown in table 12, and no such take is proposed for authorization.

Table 17—Average Counts of California and Steller Sea Lions Detected at Haulout Locations Depicted in Figure 4-2 During ODFW Winter Aerial Surveys, 2019-2022

[USACE, 2024]

Haulout site	Month	Average of CSL	Average of SSL
East Mooring Basin (EMB)	November	128	0
	December	234	3
	January	166	4
	February	197	5

Take estimates for California and Steller sea lions were calculated based on the equation below and number of workdays shown in table 18:

Level B exposure = N animals/day * total driving days

There could be 25 total days of noise exposure from pile driving during year 1 (YR-1); 34 days in YR-3; 30 days in YR-4, and up to 51 days in YR-5.

Table 18—Proposed Take by Level B Harassment for California and Steller Sea Lions Likely To Be in the Project Vicinity

	Total pile driving Workdays	Level B harassment CSL	Level B harassment SSL
YR-1	25	4,550	75
YR-2	1	182	3
YR-3	34	6,188	102
YR-4	30	5,460	90
YR-5	51	9,282	153

The annual and total number of takes of marine mammal species requested by the USACE and proposed for authorization by NMFS are shown in table 19. ( print page 89560)

Table 19—Proposed Takes by Level A Harassment and Level B Harassment Annually Over 5 Years 

Species	Stock	Yr 1		Yr 2		Yr 3		Yr 4		Yr 5		5-Yr total
		Level A	Level B	Level A	Level B	Level A	Level B	Level A	Level B	Level A	Level B	Level A	Level B
Harbor Seal	OR/WA Coastal	26	7,301	1	90	17	3,094	30	3,300	26	3,453	87	17,238
California sea lion	U.S		4,550		182		6,188		5,460		9,282		25,662
Steller sea lion	Eastern		75		3		102		90		153		423

( print page 89561)

To inform both the negligible impact analysis and the small numbers determination, NMFS assesses the maximum number of takes of marine mammals that could occur within any given year during the effective LOA period. In this calculation, the maximum estimated number of Level A harassment takes in any one year is summed with the maximum estimated number of Level B harassment takes in any 1 year for each species to yield the highest number of estimated take that could occur in any year (table 20). Table 20 also depicts the number of takes proposed relative to the abundance of each stock.

Table 20—Maximum Number of Proposed Takes (by Level A Harassment and Level B Harassment) That Could Occur in Any One Year of the Project Relative to Stock Population Size

Species	NMFS stock abundance	Maximum Level A harassment	Maximum Level B harassment	Maximum annual take 1	Total percent stock taken based on maximum annual take
Harbor seal	2  24,732	30	7,301	7,331	29.6
California sea lion	257,606		9,282	9,282	3.6
Steller sea lion	36,308		153	153	<0.01
1  Calculations of the maximum annual take are based on the maximum requested Level A harassment take in any one year + the total requested Level B harassment take in any one year.
2  The Oregon/Washington Coastal Stock was most recently estimated at 24,732 harbor seals in 1999 and more recent abundance data is not available (Carretta et al., 2022).

Proposed Mitigation

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 2 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 ( e.g., likelihood, scope, range). It further considers the likelihood that the measure will be effective if implemented ( i.e., probability of accomplishing the mitigating result if implemented as planned), the likelihood of effective implementation ( i.e., probability implemented as planned); and

2. The practicability of the measures for applicant implementation, which may consider such things as cost, impact on operations.

The mitigation measures described in the following sections would apply to the USACE in-water construction activities.

Proposed Shutdown and Monitoring Zones

In most impact and pile driving scenarios, the proposed shutdown zones exceed the calculated Level A isopleths; an exception occurs during impact pile driving of 24-in steel piles for phocids ( e.g. harbor seals) when the calculated Level A harassment isopleth (130.6 m) exceeds the proposed shutdown zone of 50 m. There was concern that the potential for seals to enter into a shutdown zone of 130 m would result in frequent delays and could impede the project's schedule. Therefore, the shutdown zone will be established at 50 m for phocid pinnipeds during impact driving of 24-in steel piles.

Table 21—Proposed Shutdown Zone and Level B Monitoring Zones by Activity

Pile size and type	Shutdown zone (m)		Level B harassment (m)
	Phocid	Otariid
Vibratory pile driving
24-in steel pile	50	15	3,981.1
12-in timber pile	60	20	6,309.6
Impact pile driving
24-in steel pile	50	50	464.2
12-in timber pile	15	15	21.5