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Federal Register / Vol. 86, No. 109 / Wednesday, June 9, 2021 / Notices
generally correlated with distance to shore, and sea otters typically remain within 1 to 2 km 0.62 to 1.24 mi of shore Riedman and Estes 1990. They tend to be found closer to shore during storms, but they venture farther out during good weather and calm seas Lensink 1962; Kenyon 1969. In the 14
aerial surveys conducted from 1995 to 2012 in Southeast Alaska, 95 percent of otters were found in areas shallower than 40 m 131 ft Tinker et al. 2019.
Areas important to mating for the Southeast Alaska stock include marine coastal regions containing adequate food resources within the 40-m 131-ft depth contour.
The most recent estimate of the number of sea otters in the Southeast Alaska stock is 25,584 otters standard error = 3,679; Tinker et al. 2019. The estimate was developed using a Bayesian hierarchical modeling framework based on survey and harvest count data. The survey data comprised results from 14 aerial surveys conducted in Southeast Alaska from 1995 to 2012, totaling more than 20,000 km 12,427
mi of aerial transects. The Service conducted large-scale surveys in cooperation with the U.S. Geological Survey in 2003 and 2010 in southern Southeast Alaska from Kake to Duke Island and Cape Chacon and in 2002
and 2011 in northern Southeast Alaska from Icy Point to Cape Ommaney. In these aerial surveys, transects were flown over high-density otter habitat <40-m 131-ft ocean depth with a spacing of 2 km 1.2 mi between transects and low-density otter habitat 40- to 100-m 131- to 328-ft ocean depth with a spacing of 8 km 5 mi between transects.
Otter densities within the Southeast Alaska stock have been calculated for 24
subdivisions Tinker et al. 2019. The density of otters in the affected subdivisions ranged from 0.175 to 1.333
otters per km2. Distribution of the population during the proposed project is likely to be similar to that detected during sea otter surveys, as work will occur during the same time of the year that these surveys were conducted.
The documented home range sizes and movement patterns of sea otters illustrate the types of movements that could be seen among otters responding to the proposed activities. Sea otters are non-migratory and generally do not disperse over long distances Garshelis and Garshelis 1984. They usually remain within a few kilometers of their established feeding grounds Kenyon 1981. Breeding males stay for all or part of the year in a breeding territory covering up to 1 km 0.62 mi of coastline while adult females have
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home ranges of approximately 8 to 16
km 5 to 10 mi, which may include one or more male territories. Juveniles move greater distances between resting and foraging areas Lensink 1962; Kenyon 1969; Riedman and Estes 1990; Estes and Tinker 1996. Although sea otters generally remain local to an area, they are capable of long-distance travel.
Otters in Alaska have shown daily movement distances greater than 3 km 1.9 mi at speeds up to 5.5 km per hour km/hr; 3.4 mi per hour mi/h Garshelis and Garshelis 1984.
Potential Effects of the Specified Activities Exposure of Sea Otters to Noise We do not expect the operations outlined in the Description of Specified Activities and Geographic Region and described in the applicants petition to lead to take from vessel presence or anthropogenic presence. The tracklines for the vessels will not physically enter low-density or high-density sea otter habitat. Thus, we do not anticipate humanotter interactions that would lead to Level B harassment or other forms of take.
The operations have the potential to result in take of sea otters by harassment from noise. Here, we characterize noise as sound released into the environment from human activities that exceeds ambient levels or interferes with normal sound production or reception by sea otters. The terms acoustic disturbance or acoustic harassment are disturbances or harassment events resulting from noise exposure. Potential effects of noise exposure are likely to depend on the distance of the otter from the sound source and the level of sound the otter receives. Temporary disturbance or localized displacement reactions are the most likely to occur. No lethal take is anticipated, nor can the Service authorize lethal take through an Incidental Take Authorization.
Therefore, none will be authorized.
Whether a specific noise source will affect a sea otter depends on several factors, including the distance between the animal and the sound source, the sound intensity, background noise levels, the noise frequency, the noise duration, and whether the noise is pulsed or continuous. The actual noise level perceived by individual sea otters will depend on distance to the source, whether the animal is above or below water, atmospheric and environmental conditions as well as aspects of the noise emitted.
From the discussion below, we expect the actual number of otters experiencing
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Level B take due to harassment by noise to be 27 or fewer. While individual otters may be taken more than once, the total number of incidental takes of sea otters is expected to be less than 49.
Sea Otter Hearing The NSF/LDEOs 36-airgun array will produce sound frequencies that fall within the hearing range of sea otters and will be audible to animals.
Controlled sound exposure trials on southern sea otters E. l. nereis indicate that otters can hear frequencies between 125 Hz and 38 kHz with best sensitivity between 1.2 and 27 kHz Ghoul and Reichmuth 2014. Aerial and underwater audiograms for a captive adult male southern sea otter in the presence of ambient noise suggest the sea otters hearing was less sensitive to high-frequency greater than 22 kHz and low-frequency less than 2 kHz sound than terrestrial mustelids but was similar to that of a California sea lion Zalophus californianus. However, the subject otter was still able to hear lowfrequency sounds, and the detection thresholds for sounds between 0.1251
kHz were between 116101 dB, respectively. Dominant frequencies of southern sea otter vocalizations are between 3 and 8 kHz, with some energy extending above 60 kHz McShane et al.
1995; Ghoul and Reichmuth 2012.
Exposure to high levels of sound may cause changes in behavior, masking of communications, temporary or permanent changes in hearing sensitivity, discomfort, and injury to marine mammals. Unlike other marine mammals, sea otters do not rely on sound to orient themselves, locate prey, or communicate underwater; therefore, masking of communications by anthropogenic sound is less of a concern than for other marine mammals.
However, sea otters do use sound for communication in air especially mothers and pups; McShane et al. 1995
and may avoid predators by monitoring underwater sound Davis et al. 1987.
Thresholds have been developed for some marine mammals above which exposure is likely to cause behavioral disturbance and injuries Southall et al.
2007; Finneran and Jenkins 2012; NMFS
2016. However, species-specific criteria for sea otters has not been identified.
Because sea otter hearing abilities and sensitivities have not been fully evaluated, we relied on the most similar proxy to evaluate the potential effects of noise exposure.
California sea lions otariid pinnipeds have a frequency range of hearing most similar to that of southern sea otters Ghoul and Reichmuth 2014
and provide the closest related proxy for
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