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Federal Register / Vol. 86, No. 171 / Wednesday, September 8, 2021 / Proposed Rules
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Steller sea lions during the spring AprilMay, summer JuneAugust, and fall SeptemberOctober, averaged 68, 110, and 56, respectively CCR
2001. A multi-year survey at NWSR
between 2000 and 2004 showed Steller sea lion numbers ranging from 175 to 354 in July M. Lowry, NMFS/SWFSC, unpubl. data. The SWFSC surveys document a consistent presence of Steller sea lions at NWSR in 11 out of 14 of yearly surveys between 1998 and 2017 with an average of 240 individuals Beth Jaime, NMFS, pers. comm., 2020.
The largest presence of Steller sea lions at St. George Reef is found on Southwest Seal Rock, approximately 6 km 3.7
miles from NWSR, with an average of 915 individuals observed among the SWFSC surveys unpublished data, Beth Jaime, NMFS/SWFSC, pers. comm., 2020. Southwest Seal Rock is a rookery that has contained up to 450 pups Wright et al. 2017. Adults with pups are known to relocate from there to NWSR in the fall. CCR 2001. Winter use of NWSR by Steller sea lions is thought to be minimal, due to inundation of the natural portion of the island by large swells.
Pacific Harbor Seal Harbor seals are widely distributed in the North Atlantic and North Pacific.
Phoca vitulina richardii inhabits coastal and estuarine areas from Mexico to Alaska Carretta et al., 2020 and is the only stock present in the action area.
In California, over 500 harbor seal haulout sites are widely distributed along the mainland and offshore islands, and include rocky shores, beaches and intertidal sandbars Lowry et al., 2005. Harbor seals mate at sea and females give birth during the spring and summer, although, the pupping season varies with latitude. Females nurse their pups for an average of 24
days and pups are ready to swim minutes after being born. Harbor seal pupping takes place at many locations and rookery size varies from a few pups to many hundreds of pups. The nearest harbor seal rookery relative to the proposed project site is at Castle Rock National Wildlife Refuge, located approximately located 965 m 0.6 mi south of Point St. George, and 2.4 km 1.5 mi north of the Crescent City Harbor in Del Norte County, California US Fish and Wildlife Service USFWS
2007.
CCR noted that harbor seal use of NWSR was minimal, with only one sighting of a group of six animals, during 20 observation surveys from 1997 through 2000 CCR 2001. They hypothesized that harbor seals may avoid the islet because of its distance
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from shore, relatively steep topography, and full exposure to rough and frequently turbulent sea swells. The SWFSC surveys did not record harbor seals at NWSR unpublished data, Beth Jaime, NMFS/SWFSC, pers. comm., 2020.
Potential Effects of Specified Activities on Marine Mammals and Their Habitat This section includes a summary and discussion of the ways that components of the specified activity may impact marine mammals and their habitat. The Estimated Take 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 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 how those impacts on individuals are likely to impact marine mammal species or stocks.
Acoustic and visual stimuli generated by: 1 Helicopter landings/takeoffs; 2
restoration activities e.g., painting, plastering, welding, and glazing; 3
maintenance activities e.g., bulb replacement and automation of the light system; and 4 human presence may have the potential to cause behavioral disturbance.
Noise This section includes a brief explanation of the sound measurements frequently used in the discussions of acoustic effects in this proposed rule.
Sound pressure is the sound force per unit area, and is usually measured in micropascals mPa, where 1 pascal Pa is the pressure resulting from a force of one newton exerted over an area of one square meter. Sound pressure level SPL is the ratio of a measured sound pressure and a reference level. The commonly used reference pressure is 1
mPa for under water, and the units for SPLs are dB re: 1 mPa. The commonly used reference pressure is 20 mPa for in air, and the units for SPLs are dB: 20
mPa.
SPL in decibels dB = 20 log pressure/reference pressure.
SPL is an instantaneous measurement expressed as the peak, the peak-peak, or the root mean square rms. Root mean square is the square root of the arithmetic average of the squared instantaneous pressure values. All references to SPL in this document refer to the rms unless otherwise noted. SPL

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does not take into account the duration of a sound.
Noise testing on the helicopter that has been used by the Society, a Robinson R66, as required for Federal Aviation Administration FAA
approval, required an overflight at 150
m 492 ft above ground level, 109 knots 202 km/hr and a maximum gross weight of 1,225 kg 2,700 lbs. The noise level measured on the ground at this distance and speed was 84.5 dB re: 20
mPa A-weighted. FAA testing also measured the sound levels on the ground for a typical helicopter takeoff and approach as 87.8 dB re: 20 mPa Aweighted Robinson 2017. Based on this information, we expect that the received sound levels at the landing area on the Stations caisson would be between 84.5 and 87.8 dB re: 20 mPa Aweighted. These sound levels are below the NMFS behavioral threshold for airborne pinniped disturbance 90 dB
for harbor seals and 100dB for all other pinnipeds NMFS 2016.
There is a dearth of information on acoustic effects of helicopter overflights on pinniped hearing and communication Richardson, et al., 1995 and to NMFS knowledge, there has been no specific documentation of temporary threshold shift TTS, let alone permanent threshold shift PTS, in free-ranging pinnipeds exposed to helicopter operations during realistic field conditions Baker et al., 2012;
Scheidat et al., 2011.
The primary factor that may influence abrupt movements of animals is engine noise, specifically changes in engine noise. The physical presence of aircraft could also lead to non-auditory effects on marine mammals involving visual or other cues. Airborne sound from a lowflying helicopter or airplane may be heard by marine mammals while at the surface or underwater. Responses by mammals could include hasty dives or turns, change in course, or flushing and stampeding from a haulout site. There are few well documented studies of the impacts of aircraft overflight over pinniped haulout sites or rookeries, and many of those that exist, are specific to military activities Efroymson et al., 2001. In 2008, NMFS issued an IHA to the USFWS for the take of small numbers of Steller sea lions and Pacific harbor seals, incidental to rodent eradication activities on an islet offshore of Rat Island, AK conducted by helicopter. The 15-minute aerial treatment consisted of the helicopter slowly approaching the islet at an elevation of over 1,000 ft 304.8 m;
gradually decreasing altitude in slow circles; and applying the rodenticide in a single pass and returning to Rat Island.

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