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Federal Register / Vol. 86, No. 109 / Wednesday, June 9, 2021 / Notices
the zone of ensonification. The ensonification zone in which noise levels exceed thresholds for Level A
harassment is often referred to as the
Level A harassment zone. The Level B
harassment zone likewise includes areas ensonified to thresholds for Level B
harassment of sea otters and extends
from the sound source to the 160-dB
isopleth.

TABLE 1SUMMARY OF THRESHOLDS FOR PREDICTING LEVEL A AND LEVEL B TAKE OF NORTHERN SEA OTTERS FROM
UNDERWATER SOUND EXPOSURE IN THE FREQUENCY RANGE 125 HZ38 KHZ
Injury Level A threshold
Disturbance Level B
threshold
Marine mammals Impulsive 1

Non-impulsive 1
All
Sea otters
1 Based
232 dB peak; 203 dB SELCUM

219 dB SELCUM 2

160 dBRMS.

on National Marine Fisheries Service acoustic exposure criteria for take of otariid pinnipeds NMFS 2018.
= cumulative sound exposure level.

2 SEL
CUM

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Evidence From Sea Otter Studies The available studies of sea otter behavior suggest that sea otters may be more resistant to the effects of sound disturbance and human activities than other marine mammals. For example, at Soberanes Point, California, Riedman 1983 examined changes in the behavior, density, and distribution of southern sea otters that were exposed to recorded noises associated with oil and gas activity. The underwater sound sources were played at a level of 110 dB
and a frequency range of 50 Hz to 20
kHz and included production platform activity, drillship, helicopter, and semisubmersible sounds. Riedman 1983
also observed the sea otters during seismic airgun shots fired at decreasing distances from the nearshore environment 50, 20, 8, 3.8, 3, 1, and 0.5
nautical miles nm at a firing rate of 4
shots per minute and a maximum air volume of 4,070 in3. Riedman 1983
observed no changes in the presence, density, or behavior of sea otters as a result of underwater sounds from recordings or airguns, even at the closest distance of 0.5 nm <1 km or 0.6 mi.
However, otters did display slight reactions to airborne engine noise.
Riedman 1983, 1984 also monitored the behavior of sea otters along the California coast while they were exposed to a single 1,638-cm3 100-in3
airgun and a 67,006-cm3 4,089-in3
airgun array. Sea otters did not respond noticeably to the single airgun, and no disturbance reactions were evident when the airgun array was as close as 0.9 km 0.6 mi.
While at the surface, turbulence from wind and waves attenuates noise more quickly than in deeper water, reducing potential noise exposure Greene and Richardson 1988; Richardson et al.
1995. Additionally, turbulence at the waters surface limits the transference of sound from water to air. A sea otter with its head above water will be exposed to
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only a small fraction of the sound energy travelling through the water beneath it. The average time spent above the water each day resting and grooming varies between male and female sea otters and seasonally. Esslinger et al.
2014 found in the summer months i.e., the season when the proposed action will take place, female otters foraged for an average of 8.78 hours per day, while male otters foraged for an average of 7.85 hours per day. Male and female sea otters spent an average of 63
to 67 percent of their summer days at the surface resting and grooming. The amount of total time spent at the surface may help limit sea otters exposure during noise-generating operations.
Sea otters generally show a high degree of tolerance to noise. In another study using prerecorded sounds, Davis et al. 1988 exposed both northern sea otters in Simpson Bay, Alaska, and southern sea otters in Morro Bay, California, to a variety of airborne and underwater sounds, including a warble tone, sea otter pup calls, killer whale calls, air horns, and an underwater noise harassment system designed to drive marine mammals away from crude oil spills. The sounds were projected at a variety of frequencies, decibel levels, and intervals. The authors noted that certain noises could cause a startle response and result in movement away from a noise source. However, the effects were limited in range no responses were observed for otters approximately 100200 m 328656 ft from the source of the stimuli, and otters stopped moving away as a result of the stimuli within hours or, at most, 3 to 4 days.
In locations that lack frequent human activity, sea otters appear to have a lower threshold for outward signs of disturbance. Sea otters in Alaska have exhibited escape behaviors in response to the presence and approach of vessels.
Behaviors included diving or actively swimming away from a boat, hauled-out
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sea otters entering the water, and groups of sea otters disbanding and swimming in multiple different directions Udevitz et al. 1995. Sea otters in Alaska have also been shown to avoid areas with heavy boat traffic but return to those same areas during seasons with less traffic Garshelis and Garshelis 1984. In Cook Inlet, otters drifting on a tide trajectory that would have taken them within 500 m 0.3 mi of an active offshore drilling rig tended to swim to change their angle of drift to avoid a close approach despite near-ambient noise levels from the work BlueCrest 2013.
Individual sea otters in Southeast Alaska will likely show a range of responses to noise from NSF/LDEOs survey equipment and vessels. Some otters will likely show startle responses, change direction of travel, diving, or premature surfacing. Sea otters reacting to survey activities may divert time and attention from biologically important behaviors, such as feeding. Some animals may abandon the survey area and return when the disturbance has ceased. Based on the observed movement patterns of wild sea otters i.e., Lensink 1962; Kenyon 1969, 1981;
Garshelis and Garshelis 1984; Riedman and Estes 1990; Estes and Tinker 1996, we expect some individuals, independent juveniles, for example, will respond to NSF/LDEOs proposed survey by dispersing to areas of suitable habitat nearby, while others, especially breeding-age adult males, will not be displaced by vessels.
Consequences of Disturbance The reactions of wildlife to disturbance can range from short-term behavioral changes to long-term impacts that affect survival and reproduction.
When disturbed by noise, animals may respond behaviorally e.g., escape response or physiologically e.g., increased heart rate, hormonal response Harms et al. 1997; Tempel and
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