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Federal Register / Vol. 86, No. 38 / Monday, March 1, 2021 / Notices Sea otter abundances outside of the area covered by surveys were inferred/
estimated as follows.
North and Mid subregions 40100m 131328-ft depth contour: While 95
percent of sea otters are observed within the 40-m 131-ft depth contour, otters do occur farther off shore see Pearson 2019 for specific instances off Washington coast, thus lower density otter habitat was delineated between the 40- and 100-m 131- and 328-ft depth contours. To calculate the density of otters in lower density 4010-m or 131
328-ft habitat, we multiplied the density of the adjacent high-density habitat by 0.05.
North and Mid subregions >100-m 328-ft depth contour: Pearson 2019
observed two sea otters 1 in 2017 and 1 in 2018 in waters >100-m 328-ft
depth contour in the Mid subregion. We do not have a reasonable method for determining the density of otters in the waters this deep and far offshore, thus for the purposes of calculating the number of otters that may be exposed, we assumed 2 otters could be in the waters >100-m 328-ft depth contour in the Mid subregion.
South subregion: Includes the area from Grays Harbor south to Oregon/
California border. This subregion was further divided into three areas because of the differences in transects and sea otter observations: Grays Harbor to Washington/Oregon border, Northern Oregon, Southern Oregon. There are no systematic surveys conducted south of Grays Harbor, but there are consistent reports of individuals as far south as
Cape Blanco, Oregon unpublished FWS
data; Jim Rice, Oregon State University, pers. comm. We do not have data to inform a density estimate for these areas; however, in our best professional judgment we estimated that a minimum of four sea otters may be in the south subregion at the time of the project.
Pearson 2019 observed one sea otter in waters >100-m 328-ft depth contour in the South subregion. We do not have a reasonable method for determining the density of otters in the waters this deep and far offshore, thus for the purposes of calculating the number of otters that may be exposed in the Grays Harbor to WA/OR border, we assumed two sea otters could be at any depth. In Oregon, we assumed one otter in each of the two areas, which could be at any depth.

TABLE 1ESTIMATED SEA OTTER ABUNDANCE AND DENSITIES FOR THE ANALYSIS AREA
High density <40 m
Lower density 40100 m
Subregion
North
Mid
South

The area impacted in each subregion and depth contour was multiplied by the estimated otter density to determine the number of otters that would experience Level A and Level B sound levels Tables 2 and 3. The total number of takes was predicted by estimating the projected days of activity in each subregion and depth contour using the reduced transects supplied by NSF. In several areas, the length and direction of the proposed survey transect lines make it highly unlikely that impacts will occur on only 1 day.
In these instances, we estimated the days of disturbance based on the number of passes of the survey transect lines.

Abundance estimate
Area km2

Density
Abundance estimate
Area km2

549
2,236

456
1,434

1.2
1.56

27
112

556
2,060

The following assumptions were pertinent to our estimate of harassment take see above for specific rationale:
No otters will occur >100-m 328-ft depth contour in North subregion.
Visual observers will not be able to see sea otters in poor weather conditions and will not be observing at night. When visual observers are not able to effectively observe sea otters, there would be no mitigation shutdown applied.
When visual observers are not able to observe sea otters they could be exposed to harassment that has the potential to injure Level A or disturb by causing disruption of behavioral patterns Level B. For the purposes of this analysis, we applied our best professional judgment and erred on the
Density 0.05
0.05
4

side of the species, attributing the harassment to Level A. In the areas where a density estimate cannot be used to differentiate the number of otters exposed to Level A or Level B, we attributed the harassment to Level A.
During the project, only two sea otters will be in the waters offshore of Southwest Washington between Grays Harbor and Washington/Oregon border.
These two sea otters may be in waters >100 m 328 ft, thus harassment was assigned at Level A conditions.
During the project, only two sea otters will be in the waters offshore of Oregon. These two sea otters may be in waters at any depth contour, thus harassment was assigned at Level A
conditions.

TABLE 2ESTIMATED NUMBER OF NORTHERN SEA OTTERS ENSONIFIED BY SOUND LEVELS GREATER THAN 232 dBRMS
LEVEL A DUE TO THE PROPOSED ACTIVITIES
Take was calculated by multiplying the area ensonified in each subregion by that subregions sea otter density or specific estimate, then multiplied by the projected days of ensonification
Subregion
Habitat type
Density otters/km2

Area impacted km2

Estimated take/day
Projected days of take
North

High <40m
Low 40100 m
Offshore >100 m
High <40 m
Low 40100 m
Offshore >100 m

1.2
.05
0
1.56
0.05
2 otters

0
0
0 0

0
0
0 0
2

2

Mid

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