The procedures to be used for the proposed survey would be similar to those used during previous seismic surveys and would use conventional seismic methodology. The survey would involve one source vessel, R/V Sally Ride, which is owned by the U.S. Navy and operated by SIO. During the low-energy 2D MCS seismic reflection survey Sally Ride would tow two GI airguns with a total discharge volume of 90 in 3 . The two inline airguns would be spaced 2 m apart. The receiving system would consist of a 1 km long solid-state hydrophone streamer. As the airguns are towed along the survey lines, the hydrophone streamer would transfer the data to the on-board processing system. Approximately 444 km of seismic data acquisition are planned. The survey would take place in water depths ranging from approximately 2,000 m to 3,500 m.

In addition to the operations of the airguns, the ocean floor would be mapped continuously with Kongsberg EM124 (12 kilohertz (kHz)) and Kongsberg EM712 (40-100 kHz) multibeam echosounders, and a Kongsberg BSP29 sub-bottom profiler (SBP). All planned geophysical data acquisition would be conducted by SIO with on-board assistance by scientists who have proposed the studies. The vessel would be self-contained, and the crew would live aboard the vessel. A Teledyne RDI Ocean Surveyor ADCP or Teledyne RDI 300 kHz Workhorse II Mariner surveyor acoustic Doppler current profiler (ADCP) would be used to measure water current velocities. Take of marine mammals is not expected to occur incidental to the use of multibeam echosounder, SBP, ADCP, operations whether or not the airguns are operating simultaneously with the other sources. Given their characteristics ( e.g., narrow downward-directed beam), marine mammals would experience no more than one or two brief ping exposures, if any exposure were to occur. NMFS does not expect that the use of these sources is likely to cause take of marine mammals.

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

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; 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 ( https://www.fisheries.noaa.gov/find-species).

Table 1 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 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 (M/SI) 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 1 are the most recent abundance estimates available at the time of publication (including from the draft 2024 SARs) and are available online at: https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments.

As indicated above, all 24 species (with 26 managed stocks) in table 1 temporally and spatially co-occur with the activity to the degree that take is reasonably likely to occur. All species that could potentially occur in the proposed survey areas are included in table 2 of the IHA application.

Some species could potentially occur in the proposed survey area but are not likely to be encountered due to the rarity of their occurrence in conjunction with the brief survey duration. These species include North Pacific right whale ( Eubalaena japonica ), short-finned pilot whale ( Globicephala macrorhynchus ), bottlenose dolphin ( Tursiops truncates ), false killer whale ( Pseudorca crassidens ), and striped dolphin ( Stenella coeruleoalba ). Therefore they are not discussed further beyond the explanation provided below.

Based on the very low abundance of North Pacific right whale, its rarity off the coasts of Washington and Oregon in recent decades, and the likelihood that animals would be feeding in the Bering Sea and Gulf of Alaska at the time of the survey, it is unlikely that a North Pacific right whale would be encountered in the proposed survey area during the period of operations.

Although zero estimated Level B harassment exposures were calculated for short-finned pilot whales, bottlenose dolphins, false killer whales, and striped dolphins, SIO requested authorization for the incidental harassment of these species. However, all these species have rare historical occurrence in the project area, and short-finned pilot whales prefer warmer tropical waters, bottlenose dolphins tend to stay in coastal waters in lower latitudes, and false killer whales are rarely observed north of Baja, California. The likelihood that SIO would encounter these species in the proposed survey area is discountable and NMFS is not proposing to authorize take of these species.

In addition to what is included in sections 3 and 4 of the IHA application, and NMFS' website, further detail informing the regional occurrence for select species of particular or unique vulnerability ( i.e., information regarding ESA listed or MMPA depleted species) is provided below.

Based on modeling of the dynamic topography of the region, blue whales could occur in relatively high densities off Oregon during summer and fall (Pardo et al., 2015: Hazen et al., 2017). Recent phenology analysis of marine mammal sightings revealed a peak of blue whale density over the Oregon continental shelf in September, and their sighting rates in the region have increased over the past three decades as a response to environmental changes influencing prey availability shifting their range northward (Derville et al., 2022). Densities along the U.S. west coast, including Oregon, were predicted to be highest in shelf waters, with lower densities in deeper offshore areas (Becker et al., 2012; Calambokidis et al., 2015). Blue whales have been detected acoustically off Oregon (McDonald et al., 1995; Stafford et al., 1998; Von Saunder and Barlow 1999).

Long-term passive acoustic monitoring of three shelf, slope, and canyon sites off Washington found the highest number of call detections on the slope and the lowest at the canyon site (Rice et al., 2021). Call rates were highest during fall and winter, but vocalizations were detected at all sites throughout the year (Rice et al., 2021).

One sighting (four animals) was made during the June-July 2021 Lamont-Doherty Earth Observatory (L-DEO) Cascadia survey (RPS 2022a), but no sightings were made during L-DEO's August 2022 Cascadia survey (RPS 2023), or LDEO's April 2022 Cascadia survey (RPS 2022b).

Although rare, blue whales could be encountered in the survey area.

Information about the seasonal distribution of fin whales in the North Pacific has been obtained from the detection of fin whale calls by bottom-mounted, offshore hydrophone arrays along the U.S. Pacific coast, in the central North Pacific, and in the western Aleutian Islands (Moore et al., 1998, 2006; Watkins et al., 2000a,b; Stafford et al., 2007, 2009). Fin whale calls are recorded in the North Pacific year-round ( e.g., Moore et al., 2006; Stafford et al., 2007, 2009; Edwards et al., 2015). In the central North Pacific, the Gulf of Alaska, and Aleutian Islands, call rates peak during fall and winter (Moore et al., 1998, 2006; Watkins et al., 2000a,b; Stafford et al., 2009).

Fin whales are routinely sighted during surveys off Oregon and Washington (Barlow and Forney 2007; Barlow 2010, 2016; Adams et al., 2014; Calambokidis et al., 2015; Edwards et al., 2015), including in coastal as well as offshore waters. They have also been detected acoustically in those waters during June-August (Edwards et al., 2015).

During long-term passive acoustic monitoring at three sites (shelf, slope, canyon) off northwestern Washington during 2004-2013, the highest number of call detections were recorded at the canyon site; most detections were made during fall and winter, but calls were detected throughout the year at all three sites (Rice et al., 2021). Fin whales are likely to be encountered in the proposed survey area.

Four fin whale sightings (eight individuals) were made during the August 2022 L-DEO Cascadia Survey (RPS 2023). Seventeen sightings (33 animals) were made during the June-July 2021 L-DEO Cascadia survey (RPS 2022a), and 1 sighting (3 animals) was made during the April 2022 L-DEO survey off Oregon (RPS 2022b).

Fin whale could be encountered in the survey area.

The humpback whale is the most common species of large cetacean reported off the coasts of Oregon and Washington from May-November (Calambokidis et al., 2000, 2004; Henry et al., 2020). The highest numbers have been reported off Oregon during May and June and off Washington during July-September (Calambokidis et al., 2000; Calambokidis and Barlow 2004). Based on data from 2016-2021, Derville et al., (2022) reported that the peak in humpback occurrence on the shelf of Oregon occurs during August. Humpbacks occur primarily over the continental shelf and slope during the summer, with few reported in offshore pelagic waters (Calambokidis and Barlow 2004, 2015; Becker et al., 2012; Barlow 2016; Derville et al., 2022).

During long-term (2004-2013) passive acoustic monitoring at three sites on the shelf, slope, and a canyon off northwestern Washington, the highest number of call detections were recorded at the canyon site and lowest at the slope site (Rice et al., 2021). Most detections occurred during fall and winter, but calls were also detected at all sites during August and September (Rice et al., 2021). Similarly, monitoring with acoustic recorders deployed at different locations off Washington during 2008-2013 showed that call rates were highest during fall and winter (Emmons et al., 2020).

Seven sightings (11 individuals) were reported during the L-DEO Cascadia survey in August 2022 (RPS 2023). Eighty-three sightings totaling 210 humpbacks were made during the June-July 2021 L-DEO Cascadia Subduction Zone seismic survey off the coast of the Pacific Northwest (including Washington, Oregon, and southern British Columbia (B.C)) (RPS 2022a), and 11 sightings of 24 animals were made during the April 2022 L-DEO survey off Oregon (RPS 2022b).

Humpback whale could be encountered in the survey area.

The 2022 Alaska and Pacific SARs described a revised stock structure for humpback whales, which modifies the previous stocks designated under the MMPA to align more closely with the ESA-designated distinct population segments (DPSs) (Caretta et al., 2023; Young et al., 2023). Specifically, the three previous North Pacific humpback whale stocks (the CA/OR/WA stock and the Central and Western North Pacific stocks) were replaced by five stocks, largely corresponding with the ESA-designated DPSs. These include Western North Pacific and Hawaii stocks and a Central America/Southern Mexico-CA/OR/WA stock (which corresponds with the Central America DPS). The remaining two stocks, corresponding to the Mexico DPS, are the Mainland Mexico-CA/OR/WA and Mexico-North Pacific stocks (Caretta et al.; Young et al., 2023). The former stock is expected to occur along the west coast from California to southern British Columbia, while the latter stock may occur across the Pacific, from northern British Columbia through the Gulf of Alaska and Aleutian Islands/Bering Sea region to Russia.

Within the project area, three humpback whale stocks may occur: The Central America/Southern Mexico—CA-OR-WA stock, which corresponds with the Central America DPS (found all along the west coast, but most common off California and Oregon; the Central America DPS is listed as endangered under the ESA); the Mainland Mexico—CA-OR-WA stock, which corresponds with the Mexico DPS (found all along the west coast; the Mexico DPS is listed as threatened under the ESA), and the Hawaii stock, which corresponds with the Hawaii DPS (found predominately off Washington and southern British Columbia; the Hawaii DPS is not listed under the ESA). According to Wade (2021), the probability that whales encountered in Oregon and California waters are from a given DPS are as follows: Central America DPS (42 percent); Mexico DPS (58 percent); Hawaii DPS (0 percent). The probability that humpback whales encountered in Washington and British Columbia waters are as follows: Central America DPS (6 percent); Mexico DPS (25 percent); Hawaii DPS (69 percent). Wade (2021) notes that the majority of humpback whales that may be found off of Washington are likely moving north of the United States border and feeding primarily off of southern British Columbia.

Sei whales are rare in the waters off Oregon and Washington (Brueggeman et al., 1990; Barlow 1994, 1997). Less than 20 confirmed sightings were reported in that region during extensive surveys during 1991-2018 (Hill and Barlow 1992; Carretta and Forney 1993; Mangels and Gerrodette 1994; Von Saunder and Barlow 1999; Barlow 2003, 2010, 2014; Forney 2007; Carretta et al., 2024).

A total of two sightings (four individuals) were reported during L-DEO Cascadia Survey (RPS 2023). No sei whales were sighted during the June-July 2021 L-DEO Cascadia survey (RPS 2022a), or the April 2022 L-DEO survey off Oregon (RPS 2022b.

Sei whales could be encountered during the proposed survey, although this species is considered rare in these waters.

Sperm whales are distributed widely across the North Pacific (Rice 1989). Sperm whales were sighted during surveys off Oregon in October 2011 and off Washington in June 2011 (Adams et al., 2014). Carretta et al. (2024) also reported numerous sperm whale sightings off Oregon and Washington during shipboard surveys. Sperm whales were detected acoustically in waters off Oregon and Washington in August 2016 during the NMFS Southwest Fisheries Science Center (SWFSC) Passive Acoustics Survey of Cetacean Abundance Levels (PASCAL) study using drifting acoustic recorders (Keating et al., 2018). Oleson et al. (2009) noted a significant diel pattern in the occurrence of sperm whale clicks at offshore and inshore monitoring locations off Washington, whereby clicks were more commonly heard during the day at the offshore site and at night at the inshore location, suggesting possible diel movements up and down the slope in search of prey. During long-term passive acoustic monitoring of three sites on the shelf, slope, and at a canyon off Washington during 2004-2013, sperm whale clicks were detected year-round with the highest number of call detections at the slope site (Rice et al., 2021). Similarly, monitoring at acoustic recorders deployed at different locations off Washington during 2008-2013 showed clicks were detected year-round (Emmons et al., 2020).

There were no sightings of sperm whale reported during L-DEO Cascadia Survey conducted in August 2022 (RPS 2023), the L-DEO Cascadia Survey conducted in June-July 2021 (RPS 2022a), or the L-DEO survey conducted in April 2022 (RPS 2022b). However, sperm whales could be encountered in the proposed survey area.

While at sea, Guadalupe fur seal is solitary but typically gathers in the hundreds to thousands at breeding sites. During the summer breeding season, most adults occur at rookeries in Mexico (Norris 2020; Carretta et al., 2021). Following the breeding season, adult males tend to move northward to forage. Several rehabilitated Guadalupe fur seals that were satellite tagged and released in central California traveled as far north as B.C. (Norris 2020). Guadalupe fur seals could be encountered during the proposed seismic surveys, but most animals are likely to occur at their breeding sites farther south at the time of the surveys.

There were no sightings of Guadalupe fur seal reported during L-DEO Cascadia Survey conducted in August 2022 (RPS 2023), the L-DEO Cascadia Survey conducted in June-July 2021 (RPS 2022a), or the L-DEO survey conducted in April 2022 (RPS 2022b). Guadalupe fur seal could be encountered in the survey area.

The northern fur seal breeding season spans from about May through November, with adult males usually coming ashore in May-August (though sometimes be present until November) and adult females coming ashore from June-November (Young et al. 2024). When not on rookery islands in the Bering seal, Russia, and southern and central California, northern fur seals are primarily pelagic (Young et al., 2024), spending 7-8 months feeding at sea after reproduction (Roppel 1984), typically in areas of upwelling along the continental slopes and over seamounts (Gentry 1981).

Males usually migrate only as far south as the Gulf of Alaska (Kajimura 1984). Ream et al. (2005) showed that migrating females moved over the continental shelf as they migrated southeasterly. Instead of following depth contours, their travel corresponded with movements of the Alaska Gyre and the North Pacific Current (Ream et al. 2005). Pups from the California stock also migrate to Washington, Oregon, and northern California after weaning (Lea et al., 2009).

Tagged adult northern fur seals were tracked from the Pribilof Islands to the waters off Washington/Oregon/California, with recorded movement throughout the proposed survey area (Pelland et al., 2014). Tracked adult male fur seals that were tagged on St. Paul Island in the Bering Sea in October 2009, wintered in the Bering Sea or northern North Pacific Ocean; females migrated to the Gulf of Alaska and the California Current, including off the west coasts of Haida Gwaii and Vancouver Island (Sterling et al., 2014). Some individuals reach California by December, after which time numbers increase off the west coast of North America (Ford 2014). The peak density shift over the course of the winter and spring, with peak densities occurring in California in February, April off Oregon and Washington, and May off B.C. and Southeast Alaska (Ford 2014).

Bonnell et al. (1992) noted the presence of northern fur seals year-round off Oregon/Washington, with the greatest numbers (87 percent) occurring in January-May. Northern fur seals were seen as far out from the coast as 185 km, and numbers increased with distance from land; they were 5-6 times more abundant in offshore waters than over the shelf or slope (Bonnell et al., 1992). The highest densities were seen in the Columbia River plume (~46° N) and in deep offshore waters (>2,000 m) off central and southern Oregon (Bonnell et al., 1992). The waters off Washington are a known foraging area for adult females, and concentrations of fur seals were also reported to occur near Cape Blanco, Oregon, at ~42.8° N (Pelland et al. 2014). While zero northern fur seals were reported during L-DEO's Cascadia survey conducted in August 2022 (RPS 2023), three northern fur seals were seen during the 2021 L-DEO Cascadia survey (RPS 2022a), and five were seen during the April 2022 L-DEO survey off Oregon (RPS 2022b). Northern fur seals could be observed in the proposed survey area, in particular females and juveniles. However, adult females are generally ashore from June through November (during the planned survey period).

Hearing is the most important sensory modality for marine mammals underwater, and exposure to anthropogenic sound can have deleterious effects. To appropriately assess the potential effects of exposure to sound, it is necessary to understand the frequency ranges marine mammals are able to hear. Not all marine mammal species have equal hearing capabilities ( e.g., Richardson et al., 1995; Wartzok and Ketten, 1999; Au and Hastings, 2008). To reflect this, Southall et al. (2007, 2019) recommended that marine mammals be divided into hearing groups based on directly measured (behavioral or auditory evoked potential techniques) or estimated hearing ranges (behavioral response data, anatomical modeling, etc. ). Generalized hearing ranges were chosen based on the ~65 decibel (dB) threshold from composite audiograms, previous analyses in NMFS (2018), and/or data from Southall et al. (2007) and Southall et al. (2019). We note that the names of two hearing groups and the generalized hearing ranges of all marine mammal hearing groups have been recently updated (NMFS 2024) as reflected below in table 2.

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

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.

This section contains a brief technical background on sound, the characteristics of certain sound types, and on metrics used in this proposal inasmuch as the information is relevant to the specified activity and to a discussion of the potential effects of the specified activity on marine mammals found later in this document.

Sound travels in waves, the basic components of which are frequency, wavelength, velocity, and amplitude. Frequency is the number of pressure waves that pass by a reference point per unit of time and is measured in hertz (Hz) or cycles per second. Wavelength is the distance between two peaks or corresponding points of a sound wave (length of one cycle). Higher frequency sounds have shorter wavelengths than lower frequency sounds, and typically attenuate (decrease) more rapidly, except in certain cases in shallower water. Amplitude is the height of the sound pressure wave or the “loudness” of a sound and is typically described using the relative unit of the dB. A sound pressure level (SPL) in dB is described as the ratio between a measured pressure and a reference pressure (for underwater sound, this is 1 microPascal (μPa)) and is a logarithmic unit that accounts for large variations in amplitude; therefore, a relatively small change in dB corresponds to large changes in sound pressure. The source level (SL) represents the SPL referenced at a distance of 1 m from the source (referenced to 1 μPa) while the received level is the SPL at the listener's position (referenced to 1 μPa).

Root mean square (RMS) is the quadratic mean sound pressure over the duration of an impulse. Root mean square is calculated by squaring all of the sound amplitudes, averaging the squares, and then taking the square root of the average (Urick, 1983). Root mean square accounts for both positive and negative values; squaring the pressures makes all values positive so that they may be accounted for in the summation of pressure levels (Hastings and Popper, 2005). This measurement is often used in the context of discussing behavioral effects, in part because behavioral effects, which often result from auditory cues, may be better expressed through averaged units than by peak pressures.

Sound exposure level (SEL; represented as dB re 1 μPa 2 -s) represents the total energy contained within a pulse and considers both intensity and duration of exposure. Peak sound pressure (also referred to as zero-to-peak sound pressure or 0-p) is the maximum instantaneous sound pressure measurable in the water at a specified distance from the source and is represented in the same units as the RMS sound pressure. Another common metric is peak-to-peak sound pressure (pk-pk), which is the algebraic difference between the peak positive and peak negative sound pressures. Peak-to-peak pressure is typically approximately 6 dB higher than peak pressure (Southall et al., 2007).

When underwater objects vibrate or activity occurs, sound-pressure waves are created. These waves alternately compress and decompress the water as the sound wave travels. Underwater sound waves radiate in a manner similar to ripples on the surface of a pond and may be either directed in a beam or beams or may radiate in all directions (omnidirectional sources), as is the case for pulses produced by the airguns considered here. The compressions and decompressions associated with sound waves are detected as changes in pressure by aquatic life and man-made sound receptors such as hydrophones.

Even in the absence of sound from the specified activity, the underwater environment is typically loud due to ambient sound. Ambient sound is defined as environmental background sound levels lacking a single source or point (Richardson et al., 1995), and the sound level of a region is defined by the total acoustical energy being generated by known and unknown sources. These sources may include physical ( e.g., wind and waves, earthquakes, ice, atmospheric sound), biological ( e.g., sounds produced by marine mammals, fish, and invertebrates), and anthropogenic ( e.g., vessels, dredging, construction) sound. A number of sources contribute to ambient sound, including the following (Richardson et al., 1995):

Wind and waves —The complex interactions between wind and water surface, including processes such as breaking waves and wave-induced bubble oscillations and cavitation, are a main source of naturally occurring ambient sound for frequencies between 200 Hz and 50 kHz (Mitson, 1995). In general, ambient sound levels tend to increase with increasing wind speed and wave height. Surf sound becomes important near shore, with measurements collected at a distance of 8.5 km from shore showing an increase of 10 dB in the 100 to 700 Hz band during heavy surf conditions;

Precipitation —Sound from rain and hail impacting the water surface can become an important component of total sound at frequencies above 500 Hz, and possibly down to 100 Hz during quiet times;

Biological —Marine mammals can contribute significantly to ambient sound levels, as can some fish and snapping shrimp. The frequency band for biological contributions is from approximately 12 Hz to over 100 kHz; and

Anthropogenic —Sources of ambient sound related to human activity include transportation (surface vessels), dredging and construction, oil and gas drilling and production, seismic surveys, sonar, explosions, and ocean acoustic studies. Vessel noise typically dominates the total ambient sound for frequencies between 20 and 300 Hz. In general, the frequencies of anthropogenic sounds are below 1 kHz and, if higher frequency sound levels are created, they attenuate rapidly. Sound from identifiable anthropogenic sources other than the activity of interest ( e.g., a passing vessel) is sometimes termed background sound, as opposed to ambient sound.

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 human 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 this 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 10-20 dB from day to day (Richardson et al., 1995). The result is that, depending on the source type and its intensity, sound from a given activity may be a negligible addition to the local environment or could form a distinctive signal that may affect marine mammals. Details of source types are described in the following text.

Sounds are often considered to fall into one of two general types: Pulsed and non-pulsed. 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., NMFS, 2018; Ward, 1997 in Southall et al., 2007). Please see Southall et al. (2007) for an in-depth discussion of these concepts.

Pulsed sound sources ( e.g., airguns, explosions, gunshots, sonic booms, impact pile driving) produce signals that are brief (typically considered to be less than one second), broadband, atonal transients (American National Standards Institute (ANSI), 1986, 2005; Harris, 1998; National Institute for Occupational Health and Safety (NIOSH), 1998; International Organization for Standardization (ISO), 2003) and occur either as isolated events or repeated in some succession. Pulsed sounds are all characterized by a relatively rapid rise from ambient pressure to a maximal pressure value followed by a rapid decay period that may include a period of diminishing, oscillating maximal and minimal pressures, and generally have an increased capacity to induce physical injury as compared with sounds that lack these features.

Non-pulsed sounds can be tonal, narrowband, or broadband, brief or prolonged, and may be either continuous or non-continuous (ANSI, 1995; NIOSH, 1998). Some of these non-pulsed sounds can be transient signals of short duration but without the essential properties of pulses ( e.g., rapid rise time). Examples of non-pulsed sounds include those produced by vessels, aircraft, machinery operations such as drilling or dredging, vibratory pile driving, and active sonar systems (such as those used by the U.S. Navy). The duration of such sounds, as received at a distance, can be greatly extended in a highly reverberant environment.

Airgun arrays produce pulsed signals with energy in a frequency range from about 10-2,000 Hz, with most energy radiated at frequencies below 200 Hz. The amplitude of the acoustic wave emitted from the source is equal in all directions ( i.e., omnidirectional), but airgun arrays do possess some directionality due to different phase delays between guns in different directions. Airgun arrays are typically tuned to maximize functionality for data acquisition purposes, meaning that sound transmitted in horizontal directions and at higher frequencies is minimized to the extent possible.

Here, we discuss the effects of active acoustic sources on marine mammals.

Potential Effects of Underwater Sound   1 —Anthropogenic sounds cover a broad range of frequencies and sound levels and can have a range of highly variable impacts on marine life, from none or minor to potentially severe responses, depending on received levels, duration of exposure, behavioral context, and various other factors. The potential effects of underwater sound from active acoustic sources can potentially result in one or more of the following: Temporary or permanent hearing impairment; non-auditory physical or physiological effects; behavioral disturbance; stress; and masking (Richardson et al., 1995; Gordon et al., 2004; Nowacek et al., 2007; Southall et al., 2007; Götz et al., 2009). The degree of effect is intrinsically related to the signal characteristics, received level, distance from the source, and duration of the sound exposure. In general, sudden, high level sounds can cause hearing loss, as can longer exposures to lower level sounds. Temporary or permanent loss of hearing, if it occurs at all, will occur almost exclusively in cases where a noise is within an animal's hearing frequency range. We first describe specific manifestations of acoustic effects before providing discussion specific to the use of airgun arrays.

Richardson et al. (1995) described zones of increasing intensity of effect that might be expected to occur, in relation to distance from a source and assuming that the signal is within an animal's hearing range. First is the area within which the acoustic signal would be audible (potentially perceived) to the animal, but not strong enough to elicit any overt behavioral or physiological response. The next zone corresponds with the area where the signal is audible to the animal and of sufficient intensity to elicit behavioral or physiological response. Third is a zone within which, for signals of high intensity, the received level is sufficient to potentially cause discomfort or tissue damage to auditory or other systems. Overlaying these zones to a certain extent is the area within which masking ( i.e., when a sound interferes with or masks the ability of an animal to detect a signal of interest that is above the absolute hearing threshold) may occur; the masking zone may be highly variable in size.

We describe the more severe effects of certain non-auditory physical or physiological effects only briefly as we do not expect that use of airgun arrays are reasonably likely to result in such effects (see below for further discussion). Potential effects from impulsive sound sources can range in severity from effects such as behavioral disturbance or tactile perception to physical discomfort, slight injury of the internal organs and the auditory system, or mortality (Yelverton et al., 1973). Non-auditory physiological effects or injuries that theoretically might occur in marine mammals exposed to high level underwater sound or as a secondary effect of extreme behavioral reactions ( e.g., change in dive profile as a result of an avoidance reaction) caused by exposure to sound include neurological effects, bubble formation, resonance effects, and other types of organ or tissue damage (Cox et al., 2006; Southall et al., 2007; Zimmer and Tyack, 2007; Tal et al., 2015). The survey activities considered here do not involve the use of devices such as explosives or mid-frequency tactical sonar that are associated with these types of effects.

Marine mammals, like all mammals, develop increased hearing thresholds over time due to age-related degeneration of auditory pathways and sensory cells of the inner ear. This natural, age-related hearing loss is contrasted by noise-induced hearing loss (Møller, 2012). Marine mammals exposed to high-intensity sound or to lower-intensity sound for prolonged periods can experience a noise-induced hearing threshold shift (TS), which NMFS defines 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 as a result of noise exposure (NMFS, 2018, 2024). The amount of TS is customarily expressed in dB. Noise-induced hearing TS can be temporary (TTS) or permanent (PTS), and higher-level sound exposures are more likely to cause PTS or other auditory injury (AUD INJ). 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 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).

NMFS (2024) defines AUD INJ as damage to the inner ear that can result in destruction of tissue, such as the loss of cochlear neuron synapses or auditory neuropathy (Houser, 2021; Finneran, 2024). AUD INJ may or may not result in a PTS. PTS is subsequently defined 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 some level of hearing loss at the relevant frequencies; typically animals with PTS or other AUD INJ are not functionally deaf (Au and Hastings, 2008; Finneran, 2016). For marine mammals, AUD INJ is considered to be possible when sound exposures are sufficient to produce 40 dB of TTS measured after exposure (Southall et al. 2007, 1019). AUD INJ levels for marine mammals are estimates, as with the exception of a single study unintentionally inducing PTS in a harbor seal ( Phoca vitulina ) (Reichmuth et al. 2019), there are no empirical data measuring AUD INJ in marine mammals largely due to the fact that, for various ethical reasons, experiments involving anthropogenic noise exposure at levels inducing AUD INJ are not typically pursued or authorized (NMFS, 2024).

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, 2024) that represents primarily tissue fatigue (Henderson et al., 2008), and is not considered an AUD INJ. Based on data from marine mammal TTS measurements (see Southall et al., 2007, 2019), a TTS of 6 dB is considered the minimum threshold shift clearly larger than any day-to-day or session-to-session variation in a subject's normal hearing ability (Finneran et al., 2000, 2002; Schlundt et al., 2000). While experiencing TTS, the hearing threshold rises, and a sound must be at a higher level in order to be heard (Finneran 2015).

In terrestrial and marine mammals, TTS can last from minutes or hours to days ( i.e., there is recovery back to baseline/pre-exposure levels), can occur within a specific frequency range ( i.e., an animal might only have a temporary loss of hearing sensitivity within a limited frequency band of its auditory range), and can be of varying amounts ( e.g., an animal's hearing sensitivity might be reduced by only 6 dB or reduced by 30 dB). In many cases, hearing sensitivity recovers rapidly after exposure to the sound ends. While there are data on sound levels and durations necessary to elicit mild TTS for marine mammals, recovery is complicated to predict and dependent on multiple factors. Depending on the degree (elevation of threshold in dB), duration ( i.e., recovery time), and frequency range of TTS, and the context in which it is experienced, TTS can have effects on marine mammals ranging from discountable to serious. 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 occurs during a time 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 time when communication is critical for successful mother/calf interactions could have more serious impacts.

Finneran et al. (2015) measured hearing thresholds in 3 captive bottlenose dolphins before and after exposure to 10 pulses produced by a seismic airgun in order to study TTS induced after exposure to multiple pulses. Exposures began at relatively low levels and gradually increased over a period of several months, with the highest exposures at peak SPLs from 196 to 210 dB and cumulative (unweighted) SELs from 193-195 dB. No substantial TTS was observed. In addition, behavioral reactions were observed that indicated that animals can learn behaviors that effectively mitigate noise exposures (although exposure patterns must be learned, which is less likely in wild animals than for the captive animals considered in this study). The authors note that the failure to induce more significant auditory effects was likely due to the intermittent nature of exposure, the relatively low peak pressure produced by the acoustic source, and the low-frequency energy in airgun pulses as compared with the frequency range of best sensitivity for dolphins and other high-frequency cetaceans.

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 and harbor porpoises have a lower TTS onset than other measured pinniped or cetacean species (Finneran, 2015).

Critical questions remain regarding the rate of TTS growth and recovery after exposure to intermittent noise and the effects of single and multiple pulses. Data at present are also insufficient to construct generalized models for recovery and determine the time necessary to treat subsequent exposures as independent events. More information is needed on the relationship between auditory evoked potential and behavioral measures of TTS for various stimuli. For summaries of data on TTS in marine mammals or for further discussion of TTS onset thresholds, please see Southall et al. (2007, 2019), Finneran and Jenkins (2012), Finneran (2015), and NMFS (2018).

Behavioral Effects —Behavioral disturbance may include a variety of effects, including subtle changes in behavior ( e.g., minor or brief avoidance of an area or changes in vocalizations), more conspicuous changes in similar behavioral activities, and more sustained and/or potentially severe reactions, such as displacement from or abandonment of high-quality habitat. 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, 2019; 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). Please see appendices B-C of Southall et al. (2007) for a review of studies involving marine mammal behavioral responses to sound.

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). There are broad categories of potential response, which we describe in greater detail here, that include alteration of dive behavior, alteration of foraging behavior, effects to breathing, interference with or alteration of vocalization, avoidance, and flight.

Changes in dive behavior can vary widely, and may consist of increased or decreased dive times and surface intervals as well as changes in the rates of ascent and descent during a dive ( e.g., Frankel and Clark, 2000; Ng and Leung, 2003; Nowacek et al., 2004; Goldbogen et al., 2013a,b). Variations in dive behavior may reflect disruptions in biologically significant activities ( e.g., foraging) or they may be of little biological significance. The impact of an alteration to dive behavior resulting from an acoustic exposure depends on what the animal is doing at the time of the exposure and the type and magnitude of the response.

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., 2007a,b). A determination of whether foraging disruptions affect 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.

Visual tracking, passive acoustic monitoring (PAM), and movement recording tags were used to quantify sperm whale behavior prior to, during, and following exposure to airgun arrays at received levels in the range 140-160 dB at distances of 7-13 km, following a phase-in of sound intensity and full array exposures at 1-13 km (Madsen et al., 2006; Miller et al., 2009). Sperm whales did not exhibit horizontal avoidance behavior at the surface. However, foraging behavior may have been affected. The sperm whales exhibited 19 percent less vocal, or buzz, rate during full exposure relative to post exposure, and the whale that was approached most closely had an extended resting period and did not resume foraging until the airguns had ceased firing. The remaining whales continued to execute foraging dives throughout exposure; however, swimming movements during foraging dives were 6 percent lower during exposure than control periods (Miller et al., 2009). These data raise concerns that seismic surveys may impact foraging behavior in sperm whales, although more data are required to understand whether the differences were due to exposure or natural variation in sperm whale behavior (Miller et al., 2009).

Changes in respiration naturally vary with different behaviors and alterations to breathing rate as a function of acoustic exposure can be expected to co-occur with other behavioral reactions, such as a flight response or an alteration in diving. However, respiration rates in and of themselves may be representative of annoyance or an acute stress response. Various studies have shown that respiration rates may either be unaffected or could increase, depending on the species and signal characteristics, again highlighting the importance in understanding species differences in the tolerance of underwater noise when determining the potential for impacts resulting from anthropogenic sound exposure ( e.g., Kastelein et al., 2001, 2005, 2006; Gailey et al., 2007, 2016).

Marine mammals vocalize for different purposes and across multiple modes, such as whistling, echolocation click production, calling, and singing. Changes in vocalization behavior in response to anthropogenic noise can occur for any of these modes and may result from a need to compete with an increase in background noise or may reflect increased vigilance or a startle response. For example, in the presence of potentially masking signals, humpback whales and killer whales have been observed to increase the length of their songs or amplitude of calls (Miller et al., 2000; Fristrup et al., 2003; Foote et al., 2004; Holt et al., 2012), while right whales have been observed to shift the frequency content of their calls upward while reducing the rate of calling in areas of increased anthropogenic noise (Parks et al., 2007). In some cases, animals may cease sound production during production of aversive signals (Bowles et al., 1994).

Cerchio et al. (2014) found that the number of humpback whales singing off the coast of northern Angola decreased with increasing received level of noise, suggesting that humpback whale communication was disrupted to some extent by the survey activity. Castellote et al. (2012) reported that fin whales moved away from the acoustic source and out of the study area, and this displacement persisted for a time period well beyond the 10-day duration of seismic airgun activity, providing evidence that fin whales may avoid an area for an extended period in the presence of increased noise. The authors hypothesize that fin whale acoustic communication is modified to compensate for increased background noise and that a sensitization process may play a role in the observed temporary displacement.

Seismic pulses at average received levels of 131 dB re 1 μPa 2 -s caused blue whales to increase call production (Di Iorio and Clark, 2010). In contrast, McDonald et al. (1995) tracked a blue whale with seafloor seismometers and reported that it stopped vocalizing and changed its travel direction at a range of 10 km from the acoustic source vessel (estimated received level 143 dB pk-pk). Blackwell et al., (2015) suggested that bowhead whales may adjust their vocal output in an effort to compensate for noise before ceasing vocalization effort and ultimately deflecting from the acoustic source. These studies demonstrate that even low levels of noise received far from the source can induce changes in vocalization and/or behavior for mysticetes.

Habituation can occur when an animal's response to a stimulus wanes with repeated exposure, usually in the absence of unpleasant associated events (Wartzok et al., 2003). Animals are most likely to habituate to sounds that are predictable and unvarying. It is important to note that habituation is appropriately considered as a “progressive reduction in response to stimuli that are perceived as neither aversive nor beneficial,” rather than as, more generally, moderation in response to human disturbance (Bejder et al., 2009).

The opposite process is sensitization, when an unpleasant experience leads to subsequent responses, often in the form of avoidance, at a lower level of exposure. As noted, behavioral state may affect the type of response. For example, animals that are resting may show greater behavioral change in response to disturbing sound levels than animals that are highly motivated to remain in an area for feeding (Richardson et al., 1995; NRC, 2003; Wartzok et al., 2003). Controlled experiments with captive marine mammals have shown pronounced behavioral reactions, including avoidance of loud sound sources (Ridgway et al., 1997). Observed responses of wild marine mammals to loud pulsed sound sources (typically seismic airguns or acoustic harassment devices) have been varied but often consist of avoidance behavior or other behavioral changes suggesting discomfort (Morton and Symonds, 2002; see also Richardson et al., 1995; Nowacek et al., 2007). Gray whales are known to change direction—deflecting from customary migratory paths—in order to avoid noise from seismic surveys (Malme et al., 1984). Humpback whales show avoidance behavior in the presence of an active seismic array during observational studies and controlled exposure experiments in western Australia (McCauley et al., 2000). Avoidance may be short-term, with animals returning to the area once the noise has ceased ( e.g., Bowles et al., 1994; Goold, 1996; Stone et al., 2000; Morton and Symonds, 2002; Gailey et al., 2007). Longer-term displacement is possible, however, which may lead to changes in abundance or distribution patterns of the affected species in the affected region if habituation to the presence of the sound does not occur ( e.g., Bejder et al., 2006; Teilmann et al., 2006). However, many delphinids approach acoustic source vessels with no apparent discomfort or obvious behavioral change ( e.g., Barkaszi et al., 2012, Barkaszi and Kelly, 2019).

Forney et al. (2017) detail the potential effects of noise on marine mammal populations with high site fidelity, including displacement and auditory masking, noting that a lack of observed response does not imply absence of fitness costs and that apparent tolerance of disturbance may have population-level impacts that are less obvious and difficult to document. Avoidance of overlap between disturbing noise and areas and/or times of particular importance for sensitive species may be critical to avoiding population-level impacts because (particularly for animals with high site fidelity) there may be a strong motivation to remain in the area despite negative impacts. Forney et al. (2017) state that, for these animals, remaining in a disturbed area may reflect a lack of alternatives rather than a lack of effects.

A flight response is a dramatic change in normal movement to a directed and rapid movement away from the perceived location of a sound source. The flight response differs from other avoidance responses in the intensity of the response ( e.g., directed movement, rate of travel). Relatively little information on flight responses of marine mammals to anthropogenic signals exist, although observations of flight responses to the presence of predators have occurred (Connor and Heithaus, 1996). The result of a flight response could range from brief, temporary exertion and displacement from the area where the signal provokes flight to, in extreme cases, marine mammal strandings (Evans and England, 2001). However, it should be noted that response to a perceived predator does not necessarily invoke flight (Ford and Reeves, 2008), and whether individuals are solitary or in groups may influence the response.

Behavioral disturbance can also impact marine mammals in more subtle ways. Increased vigilance may result in costs related to diversion of focus and attention ( i.e., when a response consists of increased vigilance, it may come at the cost of decreased attention to other critical behaviors such as foraging or resting). These effects have generally not been demonstrated for marine mammals, but studies involving fish and terrestrial animals have shown that increased vigilance may substantially reduce feeding rates ( e.g., Beauchamp and Livoreil, 1997; Fritz et al., 2002; Purser and Radford, 2011). In addition, chronic disturbance can cause population declines through reduction of fitness ( e.g., decline in body condition) and subsequent reduction in reproductive success, survival, or both ( e.g., Harrington and Veitch, 1992; Daan et al., 1996; Bradshaw et al., 1998). However, Ridgway et al. (2006) reported that increased vigilance in bottlenose dolphins exposed to sound over a 5-day period did not cause any sleep deprivation or stress effects.

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 sufficiently 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).

Auditory 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; Erbe et al., 2016). 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., 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.

Under certain circumstances, significant masking could disrupt behavioral patterns, which in turn could affect fitness for survival and reproduction. It is important to distinguish TTS and PTS, which persist after the sound exposure, from masking, which occurs during the sound exposure. Because masking (without resulting in a TS) is not associated with abnormal physiological function, it is not considered a physiological effect, but rather a potential behavioral effect.

The frequency range of the potentially masking sound is important in predicting any potential behavioral impacts. For example, low-frequency signals may have less effect on high-frequency echolocation sounds produced by odontocetes but are more likely to affect detection of mysticete communication calls and other potentially important natural sounds such as those produced by surf and some prey species. The masking of communication signals by anthropogenic noise may be considered as a reduction in the communication space of animals ( e.g., Clark et al., 2009) and may result in energetic or other costs as animals change their vocalization behavior ( e.g., Miller et al., 2000; Foote et al., 2004; Parks et al., 2007; Di Iorio and Clark, 2010; Holt et al., 2009). Masking may be less in situations where the signal and noise come from different directions (Richardson et al., 1995), through amplitude modulation of the signal, or through other compensatory behaviors (Houser and Moore, 2014). Masking can be tested directly in captive species ( e.g., Erbe, 2008), but in wild populations it must be either modeled or inferred from evidence of masking compensation. There are few studies addressing real-world masking sounds likely to be experienced by marine mammals in the wild ( e.g., Branstetter et al., 2013).

Masking affects both senders and receivers of acoustic signals and can potentially have long-term chronic effects on marine mammals at the population level as well as at the individual level. Low-frequency ambient sound levels have increased by as much as 20 dB (more than three times in terms of SPL) in the world's ocean from pre-industrial periods, with most of the increase from distant commercial shipping (Hildebrand, 2009). All anthropogenic sound sources, but especially chronic and lower-frequency signals ( e.g., from vessel traffic), contribute to elevated ambient sound levels, thus intensifying masking.

Masking effects of pulsed sounds (even from large arrays of airguns) on marine mammal calls and other natural sounds are expected to be limited, although there are few specific data on this. Because of the intermittent nature and low duty cycle of seismic pulses, animals can emit and receive sounds in the relatively quiet intervals between pulses. However, in exceptional situations, reverberation occurs for much or all of the interval between pulses ( e.g., Simard et al. 2005; Clark and Gagnon, 2006), which could mask calls. Situations with prolonged strong reverberation are infrequent. However, it is common for reverberation to cause some lesser degree of elevation of the background level between airgun pulses ( e.g., Gedamke, 2011; Guerra et al., 2011, 2016; Klinck et al., 2012; Guan et al., 2015), and this weaker reverberation presumably reduces the detection range of calls and other natural sounds to some degree. Guerra et al. (2016) reported that ambient noise levels between seismic pulses were elevated as a result of reverberation at ranges of 50 km from the seismic source. Based on measurements in deep water of the Southern Ocean, Gedamke (2011) estimated that the slight elevation of background noise levels during intervals between seismic pulses reduced blue and fin whale communication space by as much as 36-51 percent when a seismic survey was operating 450-2,800 km away. Wittekind et al. (2016) reported that airgun sounds could reduce the communication range of blue and fin whales 2,000 km from the seismic source. Nieukirk et al. (2012) and Blackwell et al. (2013) noted the potential for masking effects from seismic surveys on large whales.

Some baleen and toothed whales are known to continue calling in the presence of seismic pulses, and their calls usually can be heard between the pulses ( e.g., Nieukirk et al. 2012; Thode et al. 2012; Sciacca et al. 2016). Cerchio et al. (2014) suggested that the breeding display of humpback whales off Angola could be disrupted by seismic sounds, as singing activity declined with increasing received levels. In addition, some cetaceans are known to change their calling rates, shift their peak frequencies, or otherwise modify their vocal behavior in response to airgun sounds ( e.g., Di Iorio and Clark 2010; Castellote et al. 2012; Blackwell et al. 2013, 2015). The hearing systems of baleen whales are more sensitive to low-frequency sounds than are the ears of the small odontocetes that have been studied directly ( e.g., MacGillivray et al., 2014). The sounds important to small odontocetes are predominantly at much higher frequencies than are the dominant components of airgun sounds, thus limiting the potential for masking. In general, masking effects of seismic pulses are expected to be minor, given the normally intermittent nature of seismic pulses.

Vessel noise from the Sally Ride could affect marine animals in the proposed survey areas. Houghton et al. (2015) proposed that vessel speed is the most important predictor of received noise levels, and Putland et al. (2017) also reported reduced sound levels with decreased vessel speed. However, some energy is also produced at higher frequencies (Hermannsen et al., 2014); low levels of high-frequency sound from vessels has been shown to elicit responses in harbor porpoise (Dyndo et al., 2015).

Vessel noise, through masking, can reduce the effective communication distance of a marine mammal if the frequency of the sound source is close to that used by the animal, and if the sound is present for a significant fraction of time ( e.g., Richardson et al. 1995; Clark et al., 2009; Jensen et al., 2009; Gervaise et al., 2012; Hatch et al., 2012; Rice et al., 2014; Dunlop 2015; Jones et al., 2017; Putland et al., 2017). In addition to the frequency and duration of the masking sound, the strength, temporal pattern, and location of the introduced sound also play a role in the extent of the masking (Branstetter et al., 2013, 2016; Finneran and Branstetter 2013; Sills et al., 2017). Branstetter et al. (2013) reported that time-domain metrics are also important in describing and predicting masking.

Baleen whales are thought to be more sensitive to sound at these low frequencies than are toothed whales ( e.g., MacGillivray et al. 2014), possibly causing localized avoidance of the proposed survey area during seismic operations. Many odontocetes show considerable tolerance of vessel traffic, although they sometimes react at long distances if confined by ice or shallow water, if previously harassed by vessels, or have had little or no recent exposure to vessels (Richardson et al. 1995). Pirotta et al. (2015) noted that the physical presence of vessels, not just ship noise, disturbed the foraging activity of bottlenose dolphins. There is little data on the behavioral reactions of beaked whales to vessel noise, though they seem to avoid approaching vessels ( e.g., Würsig et al., 1998) or dive for an extended period when approached by a vessel ( e.g., Kasuya, 1986).

In summary, project vessel sounds would not be at levels expected to cause anything more than possible localized and temporary behavioral changes in marine mammals, and would not be expected to result in significant negative effects on individuals or at the population level. In addition, in all oceans of the world, large vessel traffic is currently so prevalent that it is commonly considered a usual source of ambient sound (NSF-USGS, 2011).

Vessel collisions with marine mammals, or vessel strikes, can result in death or serious injury of the animal. Wounds resulting from vessel strike may include massive trauma, hemorrhaging, broken bones, or propeller lacerations (Knowlton and Kraus, 2001). An animal at the surface may be struck directly by a vessel, a surfacing animal may hit the bottom of a vessel, or an animal just below the surface may be cut by a vessel's propeller. Superficial strikes may not kill or result in the death of the animal. These interactions are typically associated with large whales ( e.g., fin whales), which are occasionally found draped across the bulbous bow of large commercial vessels upon arrival in port. Although smaller cetaceans are more maneuverable in relation to large vessels than are large whales, they may also be susceptible to strike. The severity of injuries typically depends on the size and speed of the vessel, with the probability of death or serious injury increasing as vessel speed increases (Knowlton and Kraus, 2001; Laist et al., 2001; Vanderlaan and Taggart, 2007; Conn and Silber, 2013). Impact forces increase with speed, as does the probability of a strike at a given distance (Silber et al., 2010; Gende et al., 2011).

Pace and Silber (2005) also found that the probability of death or serious injury increased rapidly with increasing vessel speed. Specifically, the predicted probability of serious injury or death increased from 45 to 75 percent as vessel speed increased from 10 to 14 knots (kn, 26 kilometer per hour (kph)), and exceeded 90 percent at 17 kn (31 kph). Higher speeds during collisions result in greater force of impact, but higher speeds also appear to increase the chance of severe injuries or death through increased likelihood of collision by pulling whales toward the vessel (Clyne, 1999; Knowlton et al., 1995). In a separate study, Vanderlaan and Taggart (2007) analyzed the probability of lethal mortality of large whales at a given speed, showing that the greatest rate of change in the probability of a lethal injury to a large whale as a function of vessel speed occurs between 8.6 and 15 kn (28 kph). The chances of a lethal injury decline from approximately 80 percent at 15 kn (28 kph) to approximately 20 percent at 8.6 kn (16 kph). At speeds below 11.8 kn (22 kph), the chances of lethal injury drop below 50 percent, while the probability asymptotically increases toward 100 percent above 15 kn (28 kph).

The Sally Ride will travel at a speed of 5 kn (9 kph) while towing seismic survey gear. At this speed, both the possibility of striking a marine mammal and the possibility of a strike resulting in serious injury or mortality are discountable. At average transit speed, the probability of serious injury or mortality resulting from a strike is less than 50 percent. However, the likelihood of a strike actually happening is again discountable. Vessel strikes, as analyzed in the studies cited above, generally involve commercial shipping, which is much more common in both space and time than is geophysical survey activity. Jensen and Silber (2004) summarized vessel strikes of large whales worldwide from 1975-2003 and found that most collisions occurred in the open ocean and involved large vessels ( e.g., commercial shipping). No such incidents were reported for geophysical survey vessels during that time period.

It is possible for vessel strikes to occur while traveling at slow speeds. For example, a hydrographic survey vessel traveling at low speed (5.5 kn (10 kph)) while conducting mapping surveys off the central California coast struck and killed a blue whale in 2009. The State of California determined that the whale had suddenly and unexpectedly surfaced beneath the hull, with the result that the propeller severed the whale's vertebrae, and that this was an unavoidable event. This strike represents the only such incident in approximately 540,000 hours of similar coastal mapping activity ( p = 1.9 × 10 −6 ; 95 percent confidence interval = 0-5.5 × 10−6 ; NMFS, 2013). In addition, a research vessel reported a fatal strike in 2011 of a dolphin in the Atlantic, demonstrating that it is possible for strikes involving smaller cetaceans to occur. In that case, the incident report indicated that an animal apparently was struck by the vessel's propeller as it was intentionally swimming near the vessel. While indicative of the type of unusual events that cannot be ruled out, neither of these instances represents a circumstance that would be considered reasonably foreseeable or that would be considered preventable.

Although the likelihood of the vessel striking a marine mammal is low, we propose a robust vessel strike avoidance protocol (see Proposed Mitigation), which we believe eliminates any foreseeable risk of vessel strike during transit. We anticipate that vessel collisions involving a seismic data acquisition vessel towing gear, while not impossible, represent unlikely, unpredictable events for which there are no preventive measures. Given the proposed mitigation measures, the relatively slow speed of the vessel towing gear, the presence of bridge crew watching for obstacles at all times (including marine mammals), and the presence of marine mammal observers, the possibility of vessel strike is discountable and, further, were a strike of a large whale to occur, it would be unlikely to result in serious injury or mortality. No incidental take resulting from vessel strike is anticipated, and this potential effect of the specified activity will not be discussed further in the following analysis.

Stranding —Marine mammals strand for a variety of reasons, such as infectious agents, biotoxicosis, starvation, fishery interaction, vessel strike, unusual oceanographic or weather events, sound exposure, or combinations of these stressors sustained concurrently or in series, though numerous studies suggest that the physiology, behavior, habitat relationships, age, or condition of cetaceans may cause them to strand or might predispose them to strand when exposed to another phenomenon. These suggestions are consistent with the conclusions of numerous other studies that have demonstrated that combinations of dissimilar stressors commonly combine to kill an animal or dramatically reduce its fitness, even though one exposure without the other does not produce the same result (Chroussos, 2000; Creel, 2005; DeVries et al., 2003; Fair and Becker, 2000; Foley et al., 2003; Moberg, 2000; Relyea, 2005a; 2005b, Romero, 2004; Sih et al., 2004).

There is no conclusive evidence that exposure to airgun noise results in behaviorally-mediated forms of injury. Behaviorally-mediated injury ( i.e., mass stranding events) has been primarily associated with beaked whales exposed to mid-frequency active (MFA) sonar. MFA sonar operates at higher frequencies and emits longer pulses than airguns (D'Amico et al., 2009, Dragoset, 1990).

One should therefore not expect the same reaction to airgun noise as to these other sources, especially low-energy airgun noise. The potential for stranding to occur as a result of this survey is so unlikely as to be discountable.

Entanglement —Entanglements occur when marine mammals become wrapped around cables, lines, nets, or other objects suspended in the water column. During seismic operations, numerous cables, lines, and other objects primarily associated with the airgun array and hydrophone streamers will be towed behind the Sally Ride near the water's surface. However, we are not aware of any cases of entanglement of marine mammals in seismic survey equipment. Although entanglement with the streamer is theoretically possible, it has not been documented during tens of thousands of miles of NSF-sponsored seismic cruises or, to our knowledge, during hundreds of thousands of miles of industrial seismic cruises. There are relatively few deployed devices, and no interaction between marine mammals and any such device has been recorded during prior NSF surveys using the devices. There are no meaningful entanglement risks posed by the proposed survey, and entanglement risks are not discussed further in this document.

Effects to Prey —Marine mammal prey varies by species, season, and location and, for some, is not well documented. 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. However, the reaction of fish to airguns depends on the physiological state of the fish, past exposures, motivation ( e.g., feeding, spawning, migration), and other environmental factors. Several studies have demonstrated that airgun 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), though the bulk of studies indicate no or slight reaction to noise ( e.g., Miller and Cripps, 2013; Dalen and Knutsen, 1987; Peña et al., 2013; Chapman and Hawkins, 1969; Wardle et al., 2001; Jorgenson and Gyselman, 2009; Cott et al., 2012; Boeger et al., 2006), and that, most commonly, while there are likely to be impacts to fish as a result of noise from nearby airguns, such effects will be temporary. For example, investigators reported significant, short-term declines in commercial fishing catch rate of gadid fishes during and for up to 5 days after seismic survey operations, but the catch rate subsequently returned to normal (Engås et al., 1996; Engås and Lokkeborg, 2002). Other studies have reported similar findings (Hassel et al., 2004).

Skalski et al., (1992) also found a reduction in catch rates—for rockfish ( Sebastes spp.) in response to controlled airgun exposure—but suggested that the mechanism underlying the decline was not dispersal but rather decreased responsiveness to baited hooks associated with an alarm behavioral response. A companion study showed that alarm and startle responses were not sustained following the removal of the sound source (Pearson et al., 1992). Therefore, Skalski et al. (1992) suggested that the effects on fish abundance may be transitory, primarily occurring during the sound exposure itself. In some cases, effects on catch rates are variable within a study, which may be more broadly representative of temporary displacement of fish in response to airgun noise ( i.e., catch rates may increase in some locations and decrease in others) than any long-term damage to the fish themselves (Streever et al., 2016).

SPLs of sufficient strength have been known to cause injury to fish and fish mortality and, in some studies, fish auditory systems have been damaged by airgun noise (McCauley et al., 2003; Popper et al., 2005; Song et al., 2008). 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. (2012) showed that a TTS of 4-6 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; both of which are conditions unlikely to occur for this survey that is necessarily transient in any given location and likely result in brief, infrequent noise exposure to prey species in any given area. For this survey, the sound source is constantly moving, and most fish would likely avoid the sound source prior to receiving sound of sufficient intensity to cause physiological or anatomical damage. In addition, ramp-up may allow certain fish species the opportunity to move further away from the sound source.

A comprehensive review (Carroll et al., 2017) found that results are mixed as to the effects of airgun noise on the prey of marine mammals. While some studies suggest a change in prey distribution and/or a reduction in prey abundance following the use of seismic airguns, others suggest no effects or even positive effects in prey abundance. As one specific example, Paxton et al. (2017), which describes findings related to the effects of a 2014 seismic survey on a reef off of North Carolina, showed a 78 percent decrease in observed nighttime abundance for certain species. It is important to note that the evening hours during which the decline in fish habitat use was recorded (via video recording) occurred on the same day that the seismic survey passed, and no subsequent data is presented to support an inference that the response was long-lasting. Additionally, given that the finding is based on video images, the lack of recorded fish presence does not support a conclusion that the fish actually moved away from the site or suffered any serious impairment. In summary, this particular study corroborates prior studies indicating that a startle response or short-term displacement should be expected.

Available data suggest that cephalopods are capable of sensing the particle motion of sounds and detect low frequencies up to 1-1.5 kHz, depending on the species, and so are likely to detect airgun noise (Kaifu et al., 2008; Hu et al., 2009; Mooney et al., 2010; Samson et al., 2014). Auditory injuries (lesions occurring on the statocyst sensory hair cells) have been reported upon controlled exposure to low-frequency sounds, suggesting that cephalopods are particularly sensitive to low-frequency sound (André et al., 2011; Solé et al., 2013). Behavioral responses, such as inking and jetting, have also been reported upon exposure to low-frequency sound (McCauley et al., 2000b; Samson et al., 2014). Similar to fish, however, the transient nature of the survey leads to an expectation that effects will be largely limited to behavioral reactions and would occur as a result of brief, infrequent exposures.

With regard to potential impacts on zooplankton, McCauley et al. (2017) found that exposure to airgun noise resulted in significant depletion for more than half the taxa present and that there were two to three times more dead zooplankton after airgun exposure compared with controls for all taxa, within 1 km of the airguns. However, the authors also stated that in order to have significant impacts on r-selected species ( i.e., those with high growth rates and that produce many offspring) such as plankton, the spatial or temporal scale of impact must be large in comparison with the ecosystem concerned, and it is possible that the findings reflect avoidance by zooplankton rather than mortality (McCauley et al., 2017). In addition, the results of this study are inconsistent with a large body of research that generally finds limited spatial and temporal impacts to zooplankton as a result of exposure to airgun noise ( e.g., Dalen and Knutsen, 1987; Payne, 2004; Stanley et al., 2011). Most prior research on this topic, which has focused on relatively small spatial scales, has showed minimal effects ( e.g., Kostyuchenko, 1973; Booman et al., 1996; Sætre and Ona, 1996; Pearson et al., 1994; Bolle et al., 2012).

A modeling exercise was conducted as a follow-up to the McCauley et al. (2017) study (as recommended by McCauley et al. ), in order to assess the potential for impacts on ocean ecosystem dynamics and zooplankton population dynamics (Richardson et al., 2017). Richardson et al. (2017) found that for copepods with a short life cycle in a high-energy environment, a full-scale airgun survey would impact copepod abundance up to 3 days following the end of the survey, suggesting that effects such as those found by McCauley et al. (2017) would not be expected to be detectable downstream of the survey areas, either spatially or temporally.

Notably, a more recently described study produced results inconsistent with those of McCauley et al. (2017). Researchers conducted a field and laboratory study to assess if exposure to airgun noise affects mortality, predator escape response, or gene expression of the copepod Calanus finmarchicus (Fields et al., 2019). Immediate mortality of copepods was significantly higher, relative to controls, at distances of 5 m or less from the airguns. Mortality 1 week after the airgun blast was significantly higher in the copepods placed 10 m from the airgun but was not significantly different from the controls at a distance of 20 m from the airgun. The increase in mortality, relative to controls, did not exceed 30 percent at any distance from the airgun. Moreover, the authors caution that even this higher mortality in the immediate vicinity of the airguns may be more pronounced than what would be observed in free-swimming animals due to increased flow speed of fluid inside bags containing the experimental animals. There were no sublethal effects on the escape performance or the sensory threshold needed to initiate an escape response at any of the distances from the airgun that were tested. Whereas McCauley et al. (2017) reported an SEL of 156 dB at a range of 509-658 m, with zooplankton mortality observed at that range, Fields et al. (2019) reported an SEL of 186 dB at a range of 25 m, with no reported mortality at that distance. Regardless, if we assume a worst-case likelihood of severe impacts to zooplankton within approximately 1 km of the acoustic source, the brief time to regeneration of the potentially affected zooplankton populations does not lead us to expect any meaningful follow-on effects to the prey base for marine mammals.

A review article concluded that, while laboratory results provide scientific evidence for high-intensity and low-frequency sound-induced physical trauma and other negative effects on some fish and invertebrates, the sound exposure scenarios in some cases are not realistic to those encountered by marine organisms during routine seismic operations (Carroll et al., 2017). The review finds that there has been no evidence of reduced catch or abundance following seismic activities for invertebrates, and that there is conflicting evidence for fish with catch observed to increase, decrease, or remain the same. Further, where there is evidence for decreased catch rates in response to airgun noise, these findings provide no information about the underlying biological cause of catch rate reduction (Carroll et al., 2017).

In summary, impacts of the specified activity on marine mammal prey species will likely generally be limited to behavioral responses, the majority of prey species will be capable of moving out of the area during the survey, a rapid return to normal recruitment, distribution, and behavior for prey species is anticipated, and, overall, impacts to prey species will be minor and temporary. Prey species exposed to sound might move away from the sound source, experience TTS, experience masking of biologically relevant sounds, or show no obvious direct effects. Mortality from decompression injuries is possible in close proximity to a sound, but only limited data on mortality in response to airgun noise exposure are available (Hawkins et al., 2015). The most likely impacts for most prey species in the survey area would be temporary avoidance of the area. The proposed survey would move through an area relatively quickly, limiting exposure to multiple impulsive sounds. In all cases, sound levels would return to ambient once the survey moves out of the area or ends and the noise source is shut down and, when exposure to sound ends, behavioral and/or physiological responses are expected to end relatively quickly (McCauley et al., 2000). The duration of fish avoidance of a given area after survey effort stops is unknown, but a rapid return to normal recruitment, distribution, and behavior is anticipated. While the potential for disruption of spawning aggregations or schools of important prey species can be meaningful on a local scale, the mobile and temporary nature of this survey and the likelihood of temporary avoidance behavior suggest that impacts would be minor.

Acoustic Habitat —Acoustic habitat is the soundscape—which encompasses all of the sound present in a particular location and time, as a whole—when considered from the perspective of the animals experiencing it. Animals produce sound for, or listen for sounds produced by, conspecifics (communication during feeding, mating, and other social activities), other animals (finding prey or avoiding predators), and the physical environment (finding suitable habitats, navigating). Together, sounds made by animals and the geophysical environment ( e.g., produced by earthquakes, lightning, wind, rain, waves) make up the natural contributions to the total acoustics of a place. These acoustic conditions, termed acoustic habitat, are one attribute of an animal's total habitat.

Soundscapes are also defined by, and acoustic habitat influenced by, the total contribution of anthropogenic sound. This may include incidental emissions from sources such as vessel traffic, or may be intentionally introduced to the marine environment for data acquisition purposes (as in the use of airgun arrays). Anthropogenic noise varies widely in its frequency content, duration, and loudness and these characteristics greatly influence the potential habitat-mediated effects to marine mammals (please see also the previous discussion on masking under Acoustic Effects ), which may range from local effects for brief periods of time to chronic effects over large areas and for long durations. Depending on the extent of effects to habitat, animals may alter their communications signals (thereby potentially expending additional energy) or miss acoustic cues (either conspecific or adventitious). For more detail on these concepts see, e.g., Pijanowski et al., 2011; Francis and Barber, 2013; Lillis et al., 2014.

Problems arising from a failure to detect cues are more likely to occur when noise stimuli are chronic and overlap with biologically relevant cues used for communication, orientation, and predator/prey detection (Francis and Barber, 2013). Although the signals emitted by seismic airgun arrays are generally low frequency, they would also likely be of short duration and transient in any given area due to the nature of these surveys. As described previously, exploratory surveys such as these cover a large area but would be transient rather than focused in a given location over time and therefore would not be considered chronic in any given location.

Based on the information discussed herein, we conclude that impacts of the specified activity are not likely to have more than short-term adverse effects on any prey habitat or populations of prey species. Further, any impacts to marine mammal habitat are not expected to result in significant or long-term consequences for individual marine mammals, or to contribute to adverse impacts on their populations.

This section provides an estimate of the number of incidental takes proposed for authorization 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 would be by Level B harassment only, in the form of behavioral reactions and/or TTS for individual marine mammals resulting from exposure to noise from the use of seismic airguns. Based on the nature of the activity and the anticipated effectiveness of the mitigation measures ( i.e., shutdown) discussed in detail below in the Proposed Mitigation section, Level A harassment is neither anticipated nor proposed to be authorized.

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

For acoustic impacts, generally speaking, we estimate take by considering: (1) acoustic criteria above which NMFS believes the best available science indicates marine mammals will likely be behaviorally harassed or incur some degree of AUD INJ; (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.

NMFS recommends the use of acoustic criteria that identify the received level of underwater sound above which exposed marine mammals would be reasonably expected to be behaviorally harassed (equated to Level B harassment) or to incur AUD INJ of some degree (equated to Level A harassment). We note that the criteria for AUD INJ, as well as the names of two hearing groups, have been recently updated (NMFS 2024) as reflected below in the Level A harassment section.

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 (conspecific communication, predators, prey) may result in changes in behavior patterns that would not otherwise occur.

SIO's proposed activity includes the use of impulsive seismic sources ( i.e., airguns), and therefore the RMS SPL thresholds of 160 dB re 1 μPa is applicable.

Level A harassment —NMFS' Updated Technical Guidance for Assessing the Effects of Anthropogenic Sound on Marine Mammal Hearing (Version 3.0) (Updated Technical Guidance, 2024) identifies dual criteria to assess AUD INJ (Level A harassment) to five different underwater marine mammal groups (based on hearing sensitivity) as a result of exposure to noise from two different types of sources (impulsive or non-impulsive). SIO's proposed activity includes the use of impulsive sources ( i.e., airguns).

The 2024 Updated Technical Guidance criteria include both updated thresholds and updated weighting functions for each hearing group. The thresholds are provided in the table below. The references, analysis, and methodology used in the development of the criteria are described in NMFS' 2024 Updated Technical Guidance, which may be accessed at: https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance-other-acoustic-tools.

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 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 2024 Updated Technical Guidance that can be used to relatively simply predict an isopleth distance for use in conjunction with marine mammal density or occurrence to help predict potential takes. 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.

The proposed survey would entail the use of a cluster of two GI airguns with a total discharge volume of 90 in 3 (1,475 cc) at a tow depth of 4 m. L-DEO model results are used to determine the 160 dB RMS radius for the airgun source down to a maximum depth of 2,000 m. Received sound levels have been predicted by L-DEO's model (Diebold et al. 2010) as a function of distance from the airguns. This modeling approach uses ray tracing for the direct wave traveling from the airguns to the receiver and its associated source ghost (reflection at the air-water interface in the vicinity of the airguns), in a constant-velocity half-space (infinite homogeneous ocean layer, unbounded by a seafloor). In addition, propagation measurements of pulses from the 36-airgun array at a tow depth of 6 m have been reported in deep water (~1,600 m), intermediate water depth on the slope (~600-1,100 m), and shallow water (~50 m) in the Gulf of America (previously Gulf of Mexico) (Tolstoy et al. 2009; Diebold et al. 2010).

For deep and intermediate water cases, the field measurements cannot be used readily to derive the harassment isopleths, as at those sites the calibration hydrophone was located at a roughly constant depth of 350-550 m, which may not intersect all the SPL isopleths at their widest point from the sea surface down to the assumed maximum relevant water depth (~2000 m) for marine mammals. At short ranges, where the direct arrivals dominate and the effects of seafloor interactions are minimal, the data at the deep sites are suitable for comparison with modeled levels at the depth of the calibration hydrophone. At longer ranges, the comparison with the model—constructed from the maximum SPL through the entire water column at varying distances from the airgun array—is the most relevant.

In deep and intermediate water depths at short ranges, sound levels for direct arrivals recorded by the calibration hydrophone and L-DEO model results for the same array tow depth are in good alignment (see figures 12 and 14 in Diebold et al. 2010). Consequently, isopleths falling within this domain can be predicted reliably by the L-DEO model, although they may be imperfectly sampled by measurements recorded at a single depth. At greater distances, the calibration data show that seafloor-reflected and sub-seafloor-refracted arrivals dominate, whereas the direct arrivals become weak and/or incoherent (see figures 11, 12, and 16 in Diebold et al. 2010). Aside from local topography effects, the region around the critical distance is where the observed levels rise closest to the model curve. However, the observed sound levels are found to fall almost entirely below the model curve. Thus, analysis of the Gulf of America calibration measurements demonstrates that although simple, the L-DEO model is a robust tool for conservatively estimating isopleths.

The proposed low-energy survey would acquire data with two GI airguns at a tow depth of 4 m. For deep water (>1,000 m), we use the deep-water radii obtained from the L-DEO model results down to a maximum water depth of 2,000 m for the airguns.

L-DEO's modeling methodology is described in greater detail in SIO's application. The estimated distances to the Level B harassment isopleth for the proposed airgun configuration are shown in table 4.

Table 5 presents the modeled Level A harassment isopleths for each marine mammal hearing group based on L-DEO modeling incorporated in the companion user spreadsheet, for the low-energy surveys with the shortest shot interval ( i.e. greatest potential to cause injury based on accumulated sound energy) (NMFS 2018, 2024).

Predicted distances to Level A harassment isopleths, which vary based on marine mammal hearing groups, were calculated based on modeling performed by L-DEO using the Nucleus software program and the NMFS user spreadsheet, described below. The acoustic thresholds for impulsive sounds contained in the NMFS Technical Guidance were presented as dual metric acoustic thresholds using both SEL cum and peak sound pressure metrics (NMFS, 2016). As dual metrics, NMFS considers onset of PTS (Level A harassment) to have occurred when either one of the two metrics is exceeded ( i.e., metric resulting in the largest isopleth). The SEL cum metric considers both level and duration of exposure, as well as auditory weighting functions by marine mammal hearing group.

The SEL cum for the two GI airguns is derived from calculating the modified farfield signature. The farfield signature is often used as a theoretical representation of the source level. To compute the farfield signature, the source level is estimated at a large distance (right) below the airguns ( e.g., 9 km), and this level is back projected mathematically to a notional distance of 1 m from the geometrical center of the two airguns. However, it has been recognized that the source level from the theoretical farfield signature is never physically achieved at the source when the source is an array of multiple airguns separated in space (Tolstoy et al., 2009). Near the source (at short ranges, distances <1 km), the pulses of sound pressure from each individual airgun in the source array do not stack constructively as they do for the theoretical farfield signature. The pulses from the different airguns spread out in time such that the source levels observed or modeled are the result of the summation of pulses from a few airguns, not the full array (Tolstoy et al., 2009). At larger distances, away from the source, sound pressure of the two airguns stack coherently, but not within one time sample, resulting in smaller source levels (a few dB) than the source level derived from the farfield signature. Because the farfield signature does not take into account the large array effect near the source and is calculated as a point source, the farfield signature is not an appropriate measure of the sound source level for large arrays. See SIO's application for further detail on acoustic modeling.

In consideration of the received sound levels in the near-field as described above, we expect the potential for Level A harassment of any species to be de minimis, even before the likely moderating effects of aversion and/or other compensatory behaviors ( e.g., Nachtigall et al., 2018) are considered. We do not anticipate that auditory injury or Level A harassment is a likely outcome for any species and do not propose to authorize any take by Level A harassment for any species, given the very small modeled zones of injury for those species (estimated zones are less than 38 m for all species), in context of distributed source dynamics.

The Level B harassment estimates are based on a consideration of the number of marine mammals that could be within the area around the operating airguns where received levels of sound ≥160 dB re 1 μPa RMS are predicted to occur. The estimated numbers are based on the densities (numbers per unit area) of marine mammals expected to occur in the area in the absence of seismic surveys. To the extent that marine mammals tend to move away from seismic sources before the sound level reaches the criterion level and tend not to approach an operating airgun array, these estimates likely overestimate the numbers actually exposed to the specified level of sound.

In this section we provide information about the occurrence of marine mammals, including density or other relevant information which will inform the take calculations.

Ship surveys for cetaceans in slope and offshore waters of Oregon and Washington were conducted by NMFS/SWFSC in 1991, 1993, 1996, 2001, 2005, 2008, 2014, and 2018 and synthesized by Becker et al. (2020). These surveys were conducted up to ~556 km from shore typically from July to November, but included the months of June and December in 2018 (Becker et al. 2020). These data were used by SWFSC to develop spatial models of cetacean densities for the California Current Ecosystem (CCE). Although Becker et al. (2020) did not include updated densities for sperm or small beaked whales, these models were provided to SIO by Elizabeth Becker via pers. comm. in January 2025 (see application). The density models for cetaceans in the CCE were available in the form 10 x 10 km grid cells in Geographic Information System layers. There were 215 grid cells that overlapped with the survey area and an “all touched” method, in which any cell that overlapped any amount of the survey area was included in the calculations. The densities in the grid cells that overlap the proposed survey area were averaged to calculate densities for each species.

For species for which densities were not available from Becker et al. (2020), SIO used annual densities developed from the U.S. Navy Northwest Training and Testing Study Area (DON 2019).

Except California sea lion, SIO initially used the highest densities for spring, summer, or fall from DON (2019). Following discussion with NMFS, SIO updated the abundance estimates informing the density values by projecting the population growth based on information in the SARs, and then updated the density values accordingly. However, since the draft 2024 SAR includes up-to-date revisions to population estimates for Guadalupe fur seal, northern elephant seal, and northern fur seal (California stock), those population estimates did not require population growth corrections.

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 proposed for authorization.

In order to estimate the number of marine mammals predicted to be exposed to sound levels that would result in Level B harassment, radial distances from the airguns to the predicted isopleth corresponding to the Level A and Level B harassment thresholds are calculated, as described above. Those radial distances are then used to calculate the area(s) around the airguns predicted to be ensonified to sound levels that exceed the harassment thresholds. The distance for the 160-dB Level B harassment threshold (based on SIO model results) was used to draw a buffer around the area expected to be ensonified ( i.e., the survey area). The ensonified areas were then increased by 25 percent to account for potential delays, which is the equivalent to adding 25 percent to the proposed line km to be surveyed. The density for each species in table 6 were then multiplied by the daily ensonified areas expected to be ensonified (increased as described above), and then multiplied by the number of survey days (2) to estimate the potential takes (see appendix B of SIO's application).

SIO assumed that their estimates of marine mammal exposures above harassment thresholds equate to take and requested authorization of those takes. Those estimates in turn form the basis for our proposed take authorization numbers. Estimated exposures and proposed take numbers for authorization are shown in table 7.

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 requirements described in the following were proposed by SIO in its adequate and complete application or are the result of subsequent coordination between NMFS and SIO. SIO has agreed that all of the mitigation measures are practicable. NMFS has fully reviewed the specified activities and the mitigation measures included in the application to determine if the mitigation measures would result in the least practicable adverse impact on marine mammals and their habitat, as required by the MMPA, and has determined the proposed measures are appropriate. NMFS describes these below as proposed mitigation requirements, and has included them in the proposed IHA.

Visual monitoring requires the use of trained observers (herein referred to as visual protected species observers (PSOs)) to scan the ocean surface for the presence of marine mammals. The area to be scanned visually includes primarily the shutdown zone (SZ), within which observation of certain marine mammals requires shutdown of the acoustic source, a buffer zone, and to the extent possible depending on conditions, the surrounding waters. The buffer zone means an area beyond the SZ to be monitored for the presence of marine mammals that may enter the SZ. During pre-start clearance monitoring ( i.e., before ramp-up begins), the buffer zone also acts as an extension of the SZ in that observations of marine mammals within the buffer zone would also prevent airgun operations from beginning ( i.e., ramp-up). The buffer zone encompasses the area at and below the sea surface from the edge of the 0-100 m SZ, out to a radius of 200 m from the edges of the airguns (100-200 m). This 200-m zone (SZ plus buffer zone) represents the pre-start clearance zone. Visual monitoring of the SZ and adjacent waters (buffer plus surrounding waters) is intended to establish and, when visual conditions allow, maintain zones around the sound source that are clear of marine mammals, thereby reducing or eliminating the potential for injury and minimizing the potential for more severe behavioral reactions for animals occurring closer to the vessel. Visual monitoring of the buffer zone is intended to (1) provide additional protection to marine mammals that may be in the vicinity of the vessel during pre-start clearance, and (2) during airgun use, aid in establishing and maintaining the SZ by alerting the visual observer and crew of marine mammals that are outside of, but may approach and enter, the SZ.

During survey operations ( e.g., any day on which use of the airguns are planned to occur and whenever the airguns are in the water, whether activated or not), a minimum of two visual PSOs must be on duty and conducting visual observations at all times during daylight hours ( i.e., from 30 minutes prior to sunrise through 30 minutes following sunset). SIO also plans to employ two PSOs to conduct visual monitoring 30 minutes before and during ramp-ups. Visual monitoring of the pre-start clearance zone ( i.e., the shutdown zone and the buffer zone) must begin no less than 30 minutes prior to ramp-up and monitoring must continue until 1 hour after use of the airguns ceases or until 30 minutes past sunset. Visual PSOs shall coordinate to ensure 360° visual coverage around the vessel from the most appropriate observation posts and shall conduct visual observations using binoculars and the naked eye while free from distractions and in a consistent, systematic, and diligent manner.

PSOs shall establish and monitor the SZ and buffer zone. These zones shall be based upon the radial distance from the edges of the airguns (rather than being based on the center of the array or around the vessel itself). During use of the airguns ( i.e., anytime airguns are active, including ramp-up), detections of marine mammals within the buffer zone (but outside the SZ) shall be communicated to the operator to prepare for the potential shutdown of the airguns. Any observations of marine mammals by crew members shall be relayed to the PSO team. During good conditions ( e.g., daylight hours; Beaufort sea state (BSS) 3 or less), visual PSOs shall conduct observations when the airguns are not operating for comparison of sighting rates and behavior with and without use of the airguns and between acquisition periods, to the maximum extent practicable.

Visual PSOs may be on watch for a maximum of 4 consecutive hours followed by a break of at least 1 hour between watches and may conduct a maximum of 12 hours of observation per 24-hour period.

A SZ is a defined area within which occurrence of a marine mammal triggers mitigation action intended to reduce the potential for certain outcomes ( e.g., auditory injury, disruption of critical behaviors). The PSOs would establish a minimum SZ with a 100-m radius. The 100-m SZ would be based on radial distance from the edge of the airguns (rather than being based on the center of the airguns or around the vessel itself). With certain exceptions (described below), if a marine mammal appears within or enters this zone, the airguns would be shut down.

The pre-start clearance zone is defined as the area that must be clear of marine mammals prior to beginning ramp-up of the airguns and includes the SZ plus the buffer zone. Detections of marine mammals within the pre-start clearance zone would prevent airgun operations from beginning ( i.e., ramp-up).

The 100-m SZ is intended to be precautionary in the sense that it would be expected to contain sound exceeding the injury criteria for all cetacean hearing groups, (based on the dual criteria of SEL cum and peak SPL), while also providing a consistent, reasonably observable zone within which PSOs would typically be able to conduct effective observational effort. Additionally, a 100-m SZ is expected to minimize the likelihood that marine mammals will be exposed to levels likely to result in more severe behavioral responses. Although significantly greater distances may be observed from an elevated platform under good conditions, we expect that 100 m is likely regularly attainable for PSOs using the naked eye during typical conditions. The pre-start clearance zone simply represents the addition of a buffer to the SZ, doubling the SZ size during pre-clearance.

An extended SZ of 500 m must be implemented for all beaked whales, a large whale with a calf, and groups of six or more large whales. No buffer of this extended SZ is required, as NMFS concludes that this extended SZ is sufficiently protective to mitigate harassment to these groups.

Ramp-up (sometimes referred to as “soft start”) means the gradual and systematic increase of emitted sound levels from an airgun array. The intent of pre-start clearance observation (30 minutes) is to ensure no marine mammals are observed within the pre-start clearance zone (or extended SZ, for beaked whales, a large whale with a calf, and groups of six or more large whales) prior to the beginning of ramp-up. During the pre-start clearance period is the only time observations of marine mammals in the buffer zone would prevent operations ( i.e., the beginning of ramp-up). The intent of the ramp-up is to warn marine mammals of pending seismic survey operations and to allow sufficient time for those animals to leave the immediate vicinity prior to the sound source reaching full intensity. A ramp-up procedure, involving a stepwise increase in the number of airguns firing and total volume until all operational airguns are activated and the full volume is achieved, is required at all times as part of the activation of the airguns. All operators must adhere to the following pre-start clearance and ramp-up requirements:

• The operator must notify a designated PSO of the planned start of ramp-up as agreed upon with the lead PSO; the notification time should not be less than 60 minutes prior to the planned ramp-up in order to allow the PSOs time to monitor the pre-start clearance zone (and extended SZ) for 30 minutes prior to the initiation of ramp-up (pre-start clearance);

• Ramp-ups shall be scheduled so as to minimize the time spent with the source activated prior to reaching the designated run-in;

• One of the PSOs conducting pre-start clearance observations must be notified again immediately prior to initiating ramp-up procedures and the operator must receive confirmation from the PSO to proceed;

• Ramp-up may not be initiated if any marine mammal is within the applicable shutdown or buffer zone. If a marine mammal is observed within the pre-start clearance zone (or extended SZ, for beaked whales, a large whale with a calf, and groups of six or more large whales) during the 30 minute pre-start clearance period, ramp-up may not begin until the animal(s) has been observed exiting the zones or until an additional time period has elapsed with no further sightings (15 minutes for small odontocetes and pinnipeds, and 30 minutes for all mysticetes and all other odontocetes, including sperm whales, kogia, beaked whales, and large delphinids, such as Risso's dolphins);

• Ramp-up must begin by activating one GI airgun followed by the second, with each stage lasting no less than 5 minutes. The operator must provide information to the PSO documenting that appropriate procedures were followed;

• PSOs must monitor the pre-start clearance zone and extended SZ during ramp-up, and ramp-up must cease and the source must be shut down upon detection of a marine mammal within the applicable zone. Once ramp-up has begun, detections of marine mammals within the buffer zone do not require shutdown, but such observation shall be communicated to the operator to prepare for the potential shutdown;

• Ramp-up may occur at times of poor visibility if appropriate monitoring has occurred with no observations in the 30 minutes prior to beginning ramp-up. No monitoring is required as a prerequisite to nighttime ramp-up.

• If the airguns are shut down for brief periods ( i.e., less than 30 minutes) for reasons other than implementation of prescribed mitigation ( e.g., mechanical difficulty), it may be activated again without ramp-up if PSOs have maintained constant visual observation and no visual observations of marine mammals have occurred within the pre-start clearance zone (or extended SZ, where applicable). For any longer shutdown, pre-start clearance observation and ramp-up are required; and

• Testing of the airguns involving all elements requires ramp-up. Testing limited to individual source elements or strings does not require ramp-up but does require pre-start clearance of 30 minutes.

The shutdown of an airgun array requires the immediate de-activation of all individual airgun elements of the array. Any PSO on duty will have the authority to call for shutdown of the airgun array if a marine mammal is detected within the applicable SZ. The operator must also establish and maintain clear lines of communication directly between PSOs on duty and crew controlling the airguns to ensure that shutdown commands are conveyed swiftly while allowing PSOs to maintain watch. When the airguns are active ( i.e., anytime one or more airguns is active, including during ramp-up) and a marine mammal appears within or enters the applicable SZ the airguns will be shut down. When shutdown is called for by a PSO, the airguns will be immediately deactivated and any dispute resolved only following deactivation.

Following a shutdown, airgun activity would not resume until the marine mammal has cleared the SZ. The animal would be considered to have cleared the SZ if it is visually observed to have departed the SZ ( i.e., animal is not required to fully exit the buffer zone where applicable), or it has not been seen within the SZ for 15 minutes for small odontocetes and pinnipeds or 30 minutes for all mysticetes and all other odontocetes, including sperm whales, kogia, beaked whales, and large delphinids, such as Risso's dolphin.

The shutdown requirement is waived for specific genera of small dolphins if an individual is detected within the SZ. The small dolphin group is intended to encompass those members of the Family Delphinidae most likely to voluntarily approach the source vessel for purposes of interacting with the vessel and/or airguns ( e.g., bow riding). This exception to the shutdown requirement applies solely to the specific genera of small dolphins ( Lagenorhynchus, Lissodelphis, and Delphinus ).

We include this small dolphin exception because shutdown requirements for these species under all circumstances represent practicability concerns without likely commensurate benefits for the animals in question. Small dolphins are generally the most commonly observed marine mammals in the specific geographic region and would typically be the only marine mammals likely to intentionally approach the vessel. As described above, auditory injury is extremely unlikely to occur for high-frequency cetaceans ( e.g., delphinids), as this group is relatively insensitive to sound produced at the predominant frequencies in an airgun pulse while also having a relatively high threshold for the onset of auditory injury ( i.e., permanent threshold shift).

A large body of anecdotal evidence indicates that small dolphins commonly approach vessels and/or towed arrays during active sound production for purposes of bow riding with no apparent effect observed ( e.g., Barkaszi et al., 2012; Barkaszi and Kelly, 2019). The potential for increased shutdowns resulting from such a measure would require the Sally Ride to revisit the missed track line to reacquire data, resulting in an overall increase in the total sound energy input to the marine environment and an increase in the total duration over which the survey is active in a given area. Although other high-frequency hearing specialists ( e.g., large delphinids) are no more likely to incur auditory injury than are small dolphins, they are much less likely to approach vessels. Therefore, retaining a shutdown requirement for large delphinids would not have similar impacts in terms of either practicability for the applicant or corollary increase in sound energy output and time on the water. We do anticipate some benefit for a shutdown requirement for large delphinids in that it simplifies somewhat the total range of decision-making for PSOs and may preclude any potential for physiological effects other than to the auditory system as well as some more severe behavioral reactions for any such animals in close proximity to the Sally Ride.

Visual PSOs shall use best professional judgment in making the decision to call for a shutdown if there is uncertainty regarding identification ( i.e., whether the observed marine mammal(s) belongs to one of the delphinid genera for which shutdown is waived or one of the species with a larger SZ).

SIO must implement shutdown if a marine mammal species for which take was not authorized or a species for which authorization was granted but the authorized takes have been met approaches the Level B harassment zones. SIO must also implement shutdown if any large whale (defined as a sperm whale or any baleen whale species) with a calf (defined as an animal less than two-thirds the body size of an adult observed to be in close association with an adult) and/or an aggregation of six or more large whales are observed at any distance.

Vessel personnel should use an appropriate reference guide that includes identifying information on all marine mammals that may be encountered. Vessel operators must comply with the below measures except under extraordinary circumstances when the safety of the vessel or crew is in doubt or the safety of life at sea is in question. These requirements do not apply in any case where compliance would create an imminent and serious threat to a person or vessel or to the extent that a vessel is restricted in its ability to maneuver and, because of the restriction, cannot comply.

Vessel operators and crews must maintain a vigilant watch for all marine mammals and slow down, stop their vessel, or alter course, as appropriate and regardless of vessel size, to avoid striking any marine mammal. A single marine mammal at the surface may indicate the presence of submerged animals in the vicinity of the vessel; therefore, precautionary measures should always be exercised. A visual observer aboard the vessel must monitor a vessel strike avoidance zone around the vessel (separation distances stated below). Visual observers monitoring the vessel strike avoidance zone may be third-party observers ( i.e., PSOs) or crew members, but crew members responsible for these duties must be provided sufficient training to (1) distinguish marine mammals from other phenomena and (2) broadly to identify a marine mammal as a large whale (defined in this context as sperm whales or baleen whales), or other marine mammals.

Vessel speeds must be reduced to 10 kn (18.5 kph) or less when mother/calf pairs, pods, or large assemblages of cetaceans are observed near a vessel. All vessels must maintain a minimum separation distance of 100 m from sperm whales and all mystecites. All vessels must, to the maximum extent practicable, attempt to maintain a minimum separation distance of 50 m from all other marine mammals, with an understanding that at times this may not be possible ( e.g., for animals that approach the vessel).

When marine mammals are sighted while a vessel is underway, the vessel shall take action as necessary to avoid violating the relevant separation distance ( e.g., attempt to remain parallel to the animal's course, avoid excessive speed or abrupt changes in direction until the animal has left the area). If marine mammals are sighted within the relevant separation distance, the vessel must reduce speed and shift the engine to neutral, not engaging the engines until animals are clear of the area. This does not apply to any vessel towing gear or any vessel that is navigationally constrained.

NMFS conducted an independent evaluation of the applicant's proposed measures, and has preliminarily determined that the proposed mitigation measures provide the means of effecting the least practicable impact on the affected species or stocks and their habitat, paying particular attention to rookeries, mating grounds, and areas of similar significance.

In order to issue an IHA for an activity, section 101(a)(5)(D) of the MMPA states that NMFS must set forth requirements pertaining to the monitoring and reporting of such taking. The MMPA implementing regulations at 50 CFR 216.104(a)(13) indicate that requests for authorizations must include the suggested means of accomplishing the necessary monitoring and reporting that will result in increased knowledge of the species and of the level of taking or impacts on populations of marine mammals that are expected to be present while conducting the activities. Effective reporting is critical both to compliance as well as ensuring that the most value is obtained from the required monitoring.

Monitoring and reporting requirements prescribed by NMFS should contribute to improved understanding of one or more of the following:

• Occurrence of marine mammal species or stocks in the area in which take is anticipated ( e.g., presence, abundance, distribution, density);

• Nature, scope, or context of likely marine mammal exposure to potential stressors/impacts (individual or cumulative, acute or chronic), through better understanding of: (1) action or environment ( e.g., source characterization, propagation, ambient noise); (2) affected species ( e.g., life history, dive patterns); (3) co-occurrence of marine mammal species with the activity; or (4) biological or behavioral context of exposure ( e.g., age, calving or feeding areas);

• Individual marine mammal responses (behavioral or physiological) to acoustic stressors (acute, chronic, or cumulative), other stressors, or cumulative impacts from multiple stressors;

• How anticipated responses to stressors impact either: (1) long-term fitness and survival of individual marine mammals; or (2) populations, species, or stocks;

• Effects on marine mammal habitat ( e.g., marine mammal prey species, acoustic habitat, or other important physical components of marine mammal habitat); and,

• Mitigation and monitoring effectiveness.

The monitoring and reporting requirements described in the following were proposed by SIO in its adequate and complete application or are the result of subsequent coordination between NMFS and SIO. SIO has agreed that all of the monitoring and reporting measures are practicable. NMFS describes those below as proposed requirements, and has included them in the proposed IHA.

As described above, PSO observations would take place during daytime airgun operations. Two visual PSOs would be on duty at all times during daytime hours. The operator will work with the selected third-party observer provider to ensure PSOs have all equipment (including backup equipment) needed to adequately perform necessary tasks, including accurate determination of distance and bearing to observed marine mammals. SIO must use dedicated, trained, and NMFS-approved PSOs. At least one visual PSO aboard the vessel must have a minimum of 90 days at-sea experience working in those roles, respectively, with no more than 18 months elapsed since the conclusion of the at-sea experience. One visual PSO with such experience shall be designated as the lead for the entire protected species observation team. The lead PSO shall serve as primary point of contact for the vessel operator and ensure all PSO requirements per the IHA are met. To the maximum extent practicable, the experienced PSOs should be scheduled to be on duty with those PSOs with appropriate training but who have not yet gained relevant experience. The PSOs must have no tasks other than to conduct observational effort, record observational data, and communicate with and instruct relevant vessel crew with regard to the presence of marine mammals and mitigation requirements. PSO resumes shall be provided to NMFS for approval. Monitoring shall be conducted in accordance with the following requirements:

• PSOs shall be independent, dedicated, trained visual PSOs and must be employed by a third-party observer provider;

• PSOs shall have no tasks other than to conduct visual observational effort, collect data, and communicate with and instruct relevant vessel crew with regard to the presence of protected species and mitigation requirements (including brief alerts regarding maritime hazards); and

• PSOs shall have successfully completed an approved PSO training course appropriate for their designated task (visual).

• NMFS must review and approve PSO resumes accompanied by a relevant training course information packet that includes the name and qualifications ( i.e., experience, training completed, or educational background) of the instructor(s), the course outline or syllabus, and course reference material as well as a document stating successful completion of the course;

• PSOs must successfully complete relevant training, including completion of all required coursework and passing (80 percent or greater) a written and/or oral examination developed for the training program;

• PSOs must have successfully attained a bachelor's degree with a major in one of the natural sciences; and

• The educational requirements may be waived if the PSO has acquired the relevant skills through alternate experience. Requests for such a waiver shall be submitted to NMFS and must include written justification. Requests shall be granted or denied (with justification) by NMFS within 1 week of receipt of submitted information. Alternate experience that may be considered includes, but is not limited to (1) secondary education and/or experience comparable to PSO duties; (2) previous work experience conducting academic, commercial, or government-sponsored protected species surveys; or (3) previous work experience as a PSO; the PSO should demonstrate good standing and consistently good performance of PSO duties.

• For data collection purposes, PSOs shall use standardized electronic data collection forms. PSOs shall record detailed information about any implementation of mitigation requirements, including the distance of animals to the airguns and description of specific actions that ensued, the behavior of the animal(s), any observed changes in behavior before and after implementation of mitigation, and if shutdown was implemented, the length of time before any subsequent ramp-up of the airgun array. If required mitigation was not implemented, PSOs should record a description of the circumstances. At a minimum, the following information must be recorded:

○ Vessel name, vessel size and type, maximum speed capability of vessel;

○ Dates (MM/DD/YYYY) of departures and returns to port with port name;

○ PSO names and affiliations, PSO ID (initials or other identifier);

○ Date (MM/DD/YYYY) and participants of PSO briefings;

○ Visual monitoring equipment used (description);

○ PSO location on vessel and height (meters) of observation location above water surface;

○ Watch status (description);

○ Dates (MM/DD/YYYY) and times (Greenwich Mean Time (GMC)/Coordinated Universal Time (UTC)) of survey on/off effort and times (GMC/UTC) corresponding with PSO on/off effort;

○ Vessel location (decimal degrees) when survey effort began and ended and vessel location at beginning and end of visual PSO duty shifts;

○ Vessel location (decimal degrees) at 30-second intervals if obtainable from data collection software, otherwise at practical regular interval;

○ Vessel heading (compass heading) and speed (knots) at beginning and end of visual PSO duty shifts and upon any change;

○ Water depth (meters) (if obtainable from data collection software);

○ Environmental conditions while on visual survey (at beginning and end of PSO shift and whenever conditions changed significantly), including BSS and any other relevant weather conditions including cloud cover, fog, sun glare, and overall visibility to the horizon;

○ Factors that may have contributed to impaired observations during each PSO shift change or as needed as environmental conditions changed (description) ( e.g., vessel traffic, equipment malfunctions); and

○ Vessel/Survey activity information (and changes thereof) (description), such as airgun power output while in operation, number and volume of airguns operating, tow depth of the airguns, and any other notes of significance ( i.e., pre-start clearance, ramp-up, shutdown, testing, shooting, ramp-up completion, end of operations, streamers, etc. ).

• Upon visual observation of any marine mammals, the following information must be recorded:

○ Sighting ID (numeric);

○ Watch status (sighting made by PSO on/off effort, opportunistic, crew, alternate vessel/platform);

○ Location of PSO/observer (description);

○ Vessel activity at the time of the sighting ( e.g., deploying, recovering, testing, shooting, data acquisition, other);

○ PSO who sighted the animal/ID;

○ Time/date of sighting (GMT/UTC, MM/DD/YYYY);

○ Initial detection method (description);

○ Sighting cue (description);

○ Vessel location at time of sighting (decimal degrees);

○ Water depth (meters);

○ Direction of vessel's travel (compass direction);

○ Speed (knots) of the vessel from which the observation was made;

○ Direction of animal's travel relative to the vessel (description, compass heading);

○ Bearing to sighting (degrees);

○ Identification of the animal ( e.g., genus/species, lowest possible taxonomic level, or unidentified) and the composition of the group if there is a mix of species;

○ Species reliability (an indicator of confidence in identification) (1 = unsure/possible, 2 = probable, 3 = definite/sure, 9 = unknown/not recorded);

○ Estimated distance to the animal (meters) and method of estimating distance;

○ Estimated number of animals (high/low/best) (numeric);

○ Estimated number of animals by cohort (adults, yearlings, juveniles, calves, group composition, etc. );

○ Description (as many distinguishing features as possible of each individual seen, including length, shape, color, pattern, scars or markings, shape and size of dorsal fin, shape of head, and blow characteristics);

○ Detailed behavior observations ( e.g., number of blows/breaths, number of surfaces, breaching, spyhopping, diving, feeding, traveling; as explicit and detailed as possible; note any observed changes in behavior);

○ Animal's closest point of approach (meters) and/or closest distance from any of the airguns;

○ Description of any actions implemented in response to the sighting ( e.g., delays, shutdown, ramp-up) and time and location of the action.

○ Photos (Yes/No);

○ Photo Frame Numbers (List of numbers); and

○ Conditions at time of sighting (Visibility; Beaufort Sea State).

SIO shall submit a draft comprehensive report on all activities and monitoring results within 90 days of the completion of the survey or expiration of the IHA, whichever comes sooner. The report must describe all activities conducted and sightings of marine mammals, must provide full documentation of methods, results, and interpretation pertaining to all monitoring, and must summarize the dates and locations of survey operations and all marine mammal sightings (dates, times, locations, activities, associated survey activities). The draft report shall also include geo-referenced time-stamped vessel tracklines for all time periods during which airguns were operating. Tracklines should include points recording any change in airgun status ( e.g., when the sources began operating, when they were turned off, or when they changed operational status such as from two airguns to single gun or vice versa). Geographic Information System files shall be provided in Environmental Systems Research Institute shapefile format and include the UTC date and time, latitude in decimal degrees, and longitude in decimal degrees. All coordinates shall be referenced to the WGS84 geographic coordinate system. In addition to the report, all raw observational data shall be made available. The report must summarize data collected as described above in Proposed Monitoring and Reporting. A final report must be submitted within 30 days following resolution of any comments on the draft report.

Discovery of injured or dead marine mammals —In the event that personnel involved in the survey activities discover an injured or dead marine mammal, SIO shall report the incident to the Office of Protected Resources (OPR) as soon as feasible. The report must include the following information:

• Time, date, and location (latitude/longitude) of the first discovery (and updated location information if known and applicable);

• Species identification (if known) or description of the animal(s) involved;

• Condition of the animal(s) (including carcass condition if the animal is dead);

• Observed behaviors of the animal(s), if alive;

• If available, photographs or video footage of the animal(s); and

• General circumstances under which the animal was discovered.

Vessel strike —In the event of a strike of a marine mammal by any vessel involved in the activities covered by the authorization, SIO shall report the incident to OPR as soon as feasible. The report must include the following information:

• Time, date, and location (latitude/longitude) of the incident;

• Vessel's speed during and leading up to the incident;

• Vessel's course/heading and what operations were being conducted (if applicable);

• Status of all sound sources in use;

• Description of avoidance measures/requirements that were in place at the time of the strike and what additional measure were taken, if any, to avoid strike;

• Environmental conditions ( e.g., wind speed and direction, BSS, cloud cover, visibility) immediately preceding the strike;

• Species identification (if known) or description of the animal(s) involved;

• Estimated size and length of the animal that was struck;

• Description of the behavior of the marine mammal immediately preceding and following the strike;

• If available, description of the presence and behavior of any other marine mammals present immediately preceding the strike;

• Estimated fate of the animal ( e.g., dead, injured but alive, injured and moving, blood or tissue observed in the water, status unknown, disappeared); and

• To the extent practicable, photographs or video footage of the animal(s).

NMFS has defined negligible impact as an impact resulting from the specified activity that cannot be reasonably expected to, and is not reasonably likely to, adversely affect the species or stock through effects on annual rates of recruitment or survival (50 CFR 216.103). A negligible impact finding is based on the lack of likely adverse effects on annual rates of recruitment or survival ( i.e., population-level effects). An estimate of the number of takes alone is not enough information on which to base an impact determination. In addition to considering estimates of the number of marine mammals that might be “taken” through harassment, NMFS considers other factors, such as the likely nature of any impacts or responses ( e.g., intensity, duration), the context of any impacts or responses ( e.g., critical reproductive time or location, foraging impacts affecting energetics), as well as effects on habitat, and the likely effectiveness of the mitigation. We also assess the number, intensity, and context of estimated takes by evaluating this information relative to population status. Consistent with the 1989 preamble for NMFS' implementing regulations (54 FR 40338, September 29, 1989), the impacts from other past and ongoing anthropogenic activities are incorporated into this analysis via their impacts on the baseline ( e.g., as reflected in the regulatory status of the species, population size and growth rate where known, ongoing sources of human-caused mortality, or ambient noise levels).

To avoid repetition, the discussion of our analysis applies to all species listed in table 1, given that the anticipated effects of this activity on these different marine mammal stocks are expected to be similar. There is little information about the nature or severity of the impacts, or the size, status, or structure of any of these species or stocks that would lead to a different analysis for this activity.

NMFS does not anticipate that serious injury or mortality would occur as a result of SIO's planned survey, even in the absence of mitigation, and no serious injury or mortality is proposed to be authorized. As discussed in the Potential Effects of Specified Activities on Marine Mammals and their Habitat section above, non-auditory physical effects and vessel strike are not expected to occur. NMFS expects that all potential take would be in the form of Level B behavioral harassment in the form of temporary avoidance of the area or decreased foraging (if such activity was occurring), responses that are considered to be of low severity, and with no lasting biological consequences ( e.g., Southall et al., 2007, 2021). These low-level impacts of behavioral harassment are not likely to impact the overall fitness of any individual or lead to population level effects of any species. As described above, Level A harassment is not expected to occur given the estimated small size of the Level A harassment zones.

In addition, the maximum expected Level B harassment zone around the survey vessel is 505 m. Therefore, the ensonified area surrounding the vessel is relatively small compared to the overall distribution of animals in the area and their use of the habitat. Feeding behavior is not likely to be significantly impacted as prey species are mobile and are broadly distributed throughout the survey area; therefore, marine mammals that may be temporarily displaced during survey activities are expected to be able to resume foraging once they have moved away from areas with disturbing levels of underwater noise. Because of the short duration (two survey days) and temporary nature of the disturbance and the availability of similar habitat and resources in the surrounding area, the impacts to marine mammals and marine mammal prey species are not expected to cause significant or long-term fitness consequences for individual marine mammals or their populations.

Additionally, the acoustic “footprint” of the proposed survey would be very small relative to the ranges of all marine mammals that would potentially be affected. Sound levels would increase in the marine environment in a relatively small area surrounding the vessel compared to the range of the marine mammals within the proposed survey area. The seismic airguns would be active 24 hours per day throughout the duration of the proposed survey. However, the very brief overall duration of the proposed survey (2 survey days) would further limit potential impacts that may occur as a result of the proposed activity.

Of the marine mammal species that are likely to occur in the survey area, the following species are listed as endangered or threatened under the ESA: humpback whale (Central America and Mexico Distinct Population Segments), sei whale, fin whale, blue whale, sperm whale, and Guadalupe fur seal. The take numbers proposed for authorization for these species (table 7) are minimal relative to their modeled population sizes; therefore, we do not expect population-level impacts to any of these species. Moreover, the actual range of the populations extends past the area covered by the model, so modeled population sizes are likely smaller than their actual population size. Lastly, as previously described, meaningful impacts from the seismic survey are even less likely to occur for high-frequency cetaceans ( e.g., delphinids), as this group is relatively insensitive to sound produced at the predominant frequencies in an airgun pulse. The other marine mammal species that may be taken by harassment during SIO's seismic survey are not listed as threatened or endangered under the ESA or depleted under the MMPA. There is no designated critical habitat for any ESA-listed marine mammals within the survey area.

There are no rookeries, mating, or calving grounds known to be biologically important to marine mammals within the survey area, and there are no feeding areas known to be biologically important to marine mammals within the survey area.

In summary and as described above, the following factors primarily support our preliminary determination that the impacts resulting from this activity are not expected to adversely affect any of the species or stocks through effects on annual rates of recruitment or survival:

• No Level A harassment, serious injury, or mortality is anticipated or authorized;

• The proposed activity is temporary and of very short duration (3 days total with 3 days of planned survey activity);

• The anticipated impacts of the proposed activity on marine mammals would be temporary behavioral changes due to avoidance of the ensonified area, which is relatively small (see tables 4 and 5);

• The availability of alternative areas of similar habitat value for marine mammals to temporarily vacate the survey area during the proposed survey to avoid exposure to sounds from the activity is readily abundant;

• The potential adverse effects on fish or invertebrate species that serve as prey species for marine mammals from the proposed survey would be temporary and spatially limited and impacts to marine mammal foraging would be minimal; and,

• The proposed mitigation measures are expected to reduce the number and severity of takes, to the extent practicable, by visually and/or acoustically detecting marine mammals within the established zones and implementing corresponding mitigation measures ( e.g., delay; shutdown).

Based on the analysis contained herein of the likely effects of the specified activity on marine mammals and their habitat, and taking into consideration the implementation of the proposed monitoring and mitigation measures, NMFS preliminarily finds that the total marine mammal take from the proposed activity will have a negligible impact on all affected marine mammal species or stocks.

As noted previously, only take of small numbers of marine mammals may be authorized under sections 101(a)(5)(A) and (D) of the MMPA for specified activities other than military readiness activities. The MMPA does not define small numbers and so, in practice, where estimated numbers are available, NMFS compares the number of individuals taken to the most appropriate estimation of abundance of the relevant species or stock in our determination of whether an authorization is limited to small numbers of marine mammals. When the predicted number of individuals to be taken is fewer than one-third of the species or stock abundance, the take is considered to be of small numbers (see 86 FR 5322, January 19, 2021). Additionally, other qualitative factors may be considered in the analysis, such as the temporal or spatial scale of the activities.

The number of takes NMFS proposes to authorize is below one-third of the modeled abundance for all relevant populations (specifically, take of individuals is equal or less than 2 percent of the modeled abundance of each affected population, see table 7). This is conservative because the modeled abundance represents a population of the species and we assume all takes are of different individual marine mammals, which is likely not the case. Some individuals may be encountered multiple times in a day, but PSOs would count them as separate individuals if they cannot be identified.

There is no abundance information available for the CA/WA/OR stock of dwarf sperm whale. However, the take numbers proposed for authorization are sufficiently small (one take by Level B harassment) that we can safely assume that they are small relative to any reasonable assumption of likely population abundance for this stock.

Based on the analysis contained herein of the proposed activity (including the proposed mitigation and monitoring measures) and the anticipated take of marine mammals, NMFS preliminarily finds that small numbers of marine mammals would be taken relative to the population size of the affected species or stocks.

There are no relevant subsistence uses of the affected marine mammal stocks or species implicated by this action. Therefore, NMFS has determined that the total taking of affected species or stocks would not have an unmitigable adverse impact on the availability of such species or stocks for taking for subsistence purposes.

Section 7(a)(2) of the ESA of 1973 (16 U.S.C. 1531 et seq. ) requires that each Federal agency insure that any action it authorizes, funds, or carries out is not likely to jeopardize the continued existence of any endangered or threatened species or result in the destruction or adverse modification of designated critical habitat. To ensure ESA compliance for the issuance of IHAs, NMFS consults internally whenever we propose to authorize take for endangered or threatened species.

NMFS is proposing to authorize take of humpback whale (Central America and Mexico Distinct Population Segments), sei whale, fin whale, blue whale, sperm whale, and Guadalupe fur seal which are listed under the ESA.

The Permits and Conservation Division has requested initiation of section 7 consultation with the Interagency Cooperation Division for the issuance of this IHA. NMFS will conclude the ESA consultation prior to reaching a determination regarding the proposed issuance of the authorization.

As a result of these preliminary determinations, NMFS proposes to issue an IHA to SIO for conducting a marine geophysical survey in the Cascadia Subduction Zone in the Northeast Pacific Ocean, provided the previously mentioned mitigation, monitoring, and reporting requirements are incorporated. A draft of the proposed IHA can be found at: https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-research-and-other-activities.

We request comment on our analyses, the proposed authorization, and any other aspect of this notice of proposed IHA for the proposed marine geophysical survey. We also request comment on the potential renewal of this proposed IHA as described in the paragraph below. Please include with your comments any supporting data or literature citations to help inform decisions on the request for this IHA or a subsequent renewal IHA.

On a case-by-case basis, NMFS may issue a one-time, 1-year renewal IHA following notice to the public providing an additional 15 days for public comments when (1) up to another year of identical or nearly identical activities as described in the Description of Proposed Activity section of this notice is planned or (2) the activities as described in the Description of Proposed Activity section of this notice would not be completed by the time the IHA expires and a renewal would allow for completion of the activities beyond that described in the Dates and Duration section of this notice, provided all of the following conditions are met:

• A request for renewal is received no later than 60 days prior to the needed renewal IHA effective date (recognizing that the renewal IHA expiration date cannot extend beyond 1 year from expiration of the initial IHA).

• The request for renewal must include the following:

(1) An explanation that the activities to be conducted under the requested renewal IHA are identical to the activities analyzed under the initial IHA, are a subset of the activities, or include changes so minor ( e.g., reduction in pile size) that the changes do not affect the previous analyses, mitigation and monitoring requirements, or take estimates (with the exception of reducing the type or amount of take).

(2) A preliminary monitoring report showing the results of the required monitoring to date and an explanation showing that the monitoring results do not indicate impacts of a scale or nature not previously analyzed or authorized.

• Upon review of the request for renewal, the status of the affected species or stocks, and any other pertinent information, NMFS determines that there are no more than minor changes in the activities, the mitigation and monitoring measures will remain the same and appropriate, and the findings in the initial IHA remain valid.

A description of the potential effects of the specified activity on marine mammals and their habitat for the activities for which an authorization of incidental take is proposed here may be found in the Notice of the Proposed IHA for the initial authorization (89 FR 53046, June 25, 2024). NMFS has reviewed the monitoring data from the initial IHA, recent draft Stock Assessment Reports, information on relevant Unusual Mortality Events, and other scientific literature, and determined that there is no new information that affects our initial analysis of impacts on marine mammals and their habitat.

A detailed description of the methods and inputs used to estimate take for the specified activity are found in the Notice of the Proposed IHA for the initial authorization (89 FR 53046, June 25, 2024). Specifically, the source levels, days of operation (reduced to 15 days in this renewal), and marine mammal density/occurrence data applicable to this authorization remain unchanged from the previously issued IHA. Similarly, the stocks taken, methods of take, and types of take remain unchanged from the previously issued IHA. The number of takes, reduced to a subset of the intial IHA (smaller number of piles and days pile driving), are indicated below in table 2.

The proposed mitigation, monitoring, and reporting measures included as requirements in this authorization are identical to those included in the Federal Register notice announcing the issuance of the initial proposed IHA, and the discussion of the least practicable adverse impact included in that document remains accurate (89 FR 53046, June 25, 2024; 89 FR 66057, August 14, 2024). The following measures are proposed for this renewal:

(a) The Holder must employ Protected Species Observer (PSO)s and establish monitoring locations. The Holder must monitor the project area to the maximum extent possible based on the required number of PSOs, required monitoring locations, and environmental conditions.

(b) Monitoring must take place from 30 minutes prior to initiation of pile driving activity ( i.e., pre-start clearance monitoring) through 30 minutes post-completion of pile driving activity.

(c) Pre-start clearance monitoring must be conducted during periods of visibility sufficient for the lead PSO to determine that the shutdown zones are clear of marine mammals. Pile driving may commence following 30 minutes of observation when the determination is made that the shutdown zones are clear of marine mammals.

(d) If a marine mammal is observed entering or within the shutdown zones, pile driving activity must be delayed or halted. Pile driving must be commenced or resumed as described in condition 4(e) of this IHA.

(e) If pile driving is delayed or halted due to the presence of a marine mammal, the activity may not commence or resume until either the animal has voluntarily exited and been visually confirmed beyond the shutdown zone, or 15 minutes have passed without re-detection of the animal.

(f) Specific measures for avoiding take of killer whales and humpback whales:

(i) Prior to the start of pile driving activities each day, the Holder must contact the Orca Network to obtain the latest sightings information for killer whales and humpback whales.

(ii) The Holder must delay or halt pile driving activities if Southern Resident Killer Whale (SRKW), unidentified killer whale ( i.e. transient) or humpback whales are sighted within the vicinity of the project area and are approaching the Level B harassment zones during in-water activities.

(iii) If a SRKW, unidentified killer whale, or humpback whale enters the Level B harassment zone undetected, in-water pile driving must be suspended immediately upon detection and must not resume until the animal exits the Level B harassment zone or 15 minutes have passed without re-detection of the animal.

(g) Pile driving activity must be halted (as described in condition 4(d) of initial IHA) upon observation of either a species for which incidental take is not authorized or a species for which incidental take has been authorized but the authorized number of takes has been met, entering or within the harassment zone.

(h) The Holder, construction supervisors and crews, PSOs, and relevant Phillips 66 staff must avoid direct physical interaction with marine mammals during construction activity. If a marine mammal comes within 10 meters of such activity, operations must cease and vessels must reduce speed to the minimum level required to maintain steerage and safe working conditions, as necessary to avoid direct physical interaction.

As noted previously, NMFS published a notice of a proposed IHA (89 FR 53046, June 25, 2024) and solicited public comments on both our proposal to issue the initial IHA for Ferndale Refinery Dock Maintenance and Pile Replacement Project Activities in Ferndale, Washington and on the potential for a renewal IHA, should certain requirements be met. No public comments were received following the notice announcing the proposed issuance of the initial IHA (89 FR 53046, June 25, 2024).

The proposed action is identical to that of the initial authorization in terms of effects. The minor change of four additional piles does not modify our findings. The same marine mammals are affected, and the potential effects and estimated take are a subset of the initial IHA. Mitigation and monitoring remain the same as the initial authorization.

With a subset of estimated take, the extensive analysis, as well as the associated findings included in the prior documents remain applicable. We found that the previous IHA had a negligible impact, and with the issuance of a renewal, the taking would be small relative to population size.

NMFS has preliminarily concluded that there is no new information suggesting that our analysis or findings should change from those reached for the initial IHA. Based on the information and analysis contained here and in the referenced documents, NMFS has determined the following: (1) the required mitigation measures will effect the least practicable impact on marine mammal species or stocks and their habitat; (2) the authorized takes will have a negligible impact on the affected marine mammal species or stocks; (3) the authorized takes represent small numbers of marine mammals relative to the affected stock abundances; (4) Phillip 66's activities will not have an unmitigable adverse impact on taking for subsistence purposes as no relevant subsistence uses of marine mammals are implicated by this action, and; (5) appropriate monitoring and reporting requirements are included.

Section 7(a)(2) of the Endangered Species Act of 1973 (ESA: 16 U.S.C. 1531 et seq. ) requires that each Federal agency ensure that any action it authorizes, funds, or carries out is not likely to jeopardize the continued existence of any endangered or threatened species or result in the destruction or adverse modification of designated critical habitat. To ensure ESA compliance for the issuance of IHAs, NMFS consults internally whenever we propose to authorize take for endangered or threatened species. No incidental take of ESA-listed species is proposed for authorization or expected to result from this activity. Therefore, NMFS has determined that formal consultation under section 7 of the ESA is not required for this proposed action.

As a result of these preliminary determinations, NMFS proposes to issue a renewal IHA to Phillips 66 for conducting the Ferndale Refinery Dock Maintenance and Pile Replacement Project in Ferndale, Washington, from August 9, 2025 through August 8, 2026, provided the previously described mitigation, monitoring, and reporting requirements are incorporated. A draft of the proposed and final initial IHA can be found at https://www.fisheries.noaa.gov/permit/incidental-take-authorizations-under-marine-mammal-protection-act. We request comments on our analyses, the proposed renewal IHA, and any other aspect of this notice. Please include with your comments any supporting data or literature citations to help inform our final decision on the request for this renewal IHA.

Title and OMB Number: Defense Federal Acquisition Regulation Supplement (DFARS) part 225, Foreign Acquisition, and Defense Contractors Performing Private Security Functions Outside the United States; OMB Control Number 0704-0549.

Affected Public: Businesses or other for-profit and not-for-profit institutions.

Respondent's Obligation: Required to obtain or retain benefits.

Frequency: On occasion.

Number of Respondents: 10.

Responses per Respondent: 4.

Annual Responses: 40.

Average Burden per Response: 0.5 hour.

Annual Burden Hours: 20.

Needs and Uses: Geographic combatant commanders are required by section 862 of the National Defense Authorization Act for Fiscal Year 2008, as amended, to establish procedures and assign responsibilities for ensuring that contractors and contractor personnel report certain security incidents when performing private security functions in covered operational areas. The clause at DFARS 252.225-7039, Defense Contractors Performing Private Security Functions Outside the United States, requires contractors and subcontractors performing private security functions in designated operational areas outside the United States to comply with 32 CFR 159 and any orders, directives, and instructions contained in the contract on reporting the following types of incidents to the geographic combatant commander if and when they occur:

(a) A weapon is discharged by personnel performing private security functions.

(b) Personnel performing private security functions are attacked, killed, or injured.

(c) Persons are killed or injured or property is destroyed as a result of conduct by contractor personnel.

(d) A weapon is discharged against personnel performing private security functions or personnel performing such functions believe a weapon was so discharged.

(e) Active, non-lethal countermeasures (other than the discharge of a weapon) are employed by personnel performing private security functions in response to a perceived immediate threat.