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Federal Register / Vol. 86, No. 38 / Monday, March 1, 2021 / Notices which data are available. Sea otters and pinnipeds share a common mammalian aural physiology Echteler et al. 1994;
Solntseva 2007. Both are adapted to amphibious hearing, and both use sound in the same way primarily for communication rather than feeding.
NMFS criteria for Level A harassment represents the best available information for predicting injury from exposure to underwater sound among pinnipeds, and in the absence of data specific to otters, we assume these criteria also represent appropriate exposure thresholds for Level A harassment of sea otters.
For otariid pinnipeds, PTS is predicted to occur at 232 dB peak or 203
dB SELcum cumulative sound exposure level for impulsive sound, or 219 dB SELcum for non-impulsive continuous sound NMFS 2018.
Exposure to unmitigated in-water noise levels between 125 Hz and 38 kHz that are greater than 232 dB peak or 203 dB
SELcum for impulsive sound or 219 dB
SELcum for non-impulsive continuous sound will be considered by the Service as Level A harassment. NMFS predicts that marine mammals are likely to be behaviorally harassed in a manner considered Level B harassment when exposed to underwater anthropogenic noise above received levels of 120 dB re 1 mPa rms for continuous e.g., vibratory pile-driving, drilling and above 160 dB re 1 mPa rms for nonexplosive impulsive e.g., seismic airguns or intermittent e.g., scientific sonar sources NMFS 2018.
Thresholds based on TTS can be used as a proxy for Level B harassment.
Based on studies summarized by Finneran 2015, NMFS 2018 has set the TTS threshold for otariid pinnipeds at 188 dB SELcum for impulsive sounds and 199 dB SELcum for non-impulsive sounds. Thus, using information available for other marine mammals, specifically otariid pinnipeds, as a surrogate, and taking into consideration the best available information about sea otters, the Service has set the received sound level underwater of 160 dB re 1
mPa rms as a threshold for Level B
harassment for sea otters based on the work of Ghoul and Reichmuth 2012, McShane et al. 1995, Riedman 1983, Richardson et al. 1995, and others.
Exposure to unmitigated impulsive inwater noise levels between 125 Hz and 38 kHz that are greater than 160 dB re 1 mPa rms will be considered by the Service as Level B harassment.
Exposure to Project ActivitiesBased on the studies on sea otters in Washington, California, and Alaska, we believe sea otters spend between 40 and 60 percent of a 24-hour period with at
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least a portion of their body underwater foraging, other diving, or grooming behaviors that result in the head being underwater and forage both diurnally and nocturnally Esslinger et al. 2014, Laidre et al. 2009, Yeates et al. 2007, Tinker et al. 2008. Seismic survey activities can operate 24 hours/day and otters may be exposed at any time. Any single point along the transects could be above thresholds for a maximum of 6.5
hours, during which time sea otters in that area would engage in underwater behaviors and would be exposed to underwater sound. Some areas along the transects will be ensonified more than once.
Because sea otters spend a considerable portion of their time at the surface of the water, they are typically visually aware of approaching boats and are able to move away if the vessel is not traveling too quickly. The noise of approaching boats provides an additional warning, thus otters should be able to detect the vessels and paddle away, rather than be startled and go subsurface. Because the R/V Langseth would be traveling relatively slowly 4.5
knots during the surveys, it is unlikely that sea otters would suffer injury or death from a vessel collision. Otters that may be foraging may be startled by the remotely operated vehicle deployed to retrieve OBNs in waters >60 m 197 ft along three transects perpendicular to the Oregon coast.
The potential for exposure to all activities is likely to be limited to where the vessel is operating in waters <1,000
m 3,280 ft deep, as we do not anticipate otters to be farther offshore.
Off the Washington coast, females primarily forage and rest in waters <40
m 131 ft, but males spend less time foraging close to shore and rest farther offshore than females Laidre et al.
2009, venturing as far offshore as 58 km 36 mi Pearson 2019. Within the waters adjacent to Washington and northern Oregon to Tillamook Head, the ensonified zone would not penetrate the waters between shore and the 40-m 131-ft depth contour, thus sea otters that may be exposed are more likely to be the males that occur farther offshore.
The otters along the Oregon coast are presumed to be males, based on stranding data FWS unpublished data.
NSF and LDEO have proposed measures to minimize the chances of sea otter exposure to the seismic surveys.
Along the Washington coast in waters <200 m 656 ft deep, the airgun array would operate only during daylight hours. The airgun startup would be ramped in order to alert otters that are underwater, in the hope they would move away. Prior to airgun startup and
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during airgun operations, visual observers would be employed during daylight hours, in order to establish a 500-m 1,640 ft exclusion zone. Any sea otter observed in this zone would lead to a shutdown of the airgun array.
However, there will be gaps in the visual coverage, in particular during nighttime operations in Oregon and beyond 200 m 656 ft in Washington. In addition, under poor weather conditions and some good weather conditions, observers cannot be 100 percent effective and may not detect a sea otter in, or about to enter, the exclusion zone.
Further, visual observations cannot cover the entirety of the area with sound levels that may cause behavioral changes. The lack of ability to fully monitor the ensonified area means an otters may go unobserved and be exposed to underwater noise that results in Level A and/or Level B harassment.
Potential Effects of the Proposed Activity on Northern Sea Otter Habitat Physical and biological features of habitat essential to the conservation of sea otters include the benthic invertebrates crabs, urchins, mussels, clams, etc. eaten by otters and the shallow rocky areas and kelp beds that provide cover from predators. Important sea otter habitat areas of significance in the NSF and LDEO project area include coastal areas within the 40-m 131-ft depth contour where high densities of otters have been detected, although deeper waters may be important for male sea otters. A number of recent reviews and empirical studies have addressed the effects of noise on invertebrates Carroll et al. 2017, sea otter prey, with some studies showing little or no effects and others indicating deleterious effects from exposure to increased sound levels. Given the shortterm duration of sounds produced by each component of the proposed project, it is unlikely that noises generated by survey activities will have any lasting effect on sea otter prey see the Services draft EA USFWS 2020 for further information. The MMPA allows the Service to identify avoidance and minimization measures for affecting the least practicable impact of the specified activity on important habitats. Although sea otters within this important habitat may be impacted by geophysical surveys conducted by NSF and LDEO, the project, as currently proposed, is not likely to cause lasting effects to habitat.
Potential Impacts of the Proposed Activity on Subsistence Needs The subsistence provision of the MMPA does not apply to northern sea otters in Washington and Oregon.

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