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Federal Register / Vol. 86, No. 167 / Wednesday, September 1, 2021 / Notices to be used on the concrete piles, the noise levels would be lower than either the 66- or 84-inch caisson. The Navy estimated the Level B harassment isopleth for this source at 350 m, smaller than the Practical Spreading Loss model prediction of 575 m. Given the uncertainty discussed above, we used the 575 m distance for the Level B harassment isopleth.
Marine Mammal Occurrence, Take Calculation, and Take Estimation In this section, we provide the information about the presence, density, or group dynamics of marine mammals that will inform the take calculations.
Here we describe how the information provided above is brought together to produce a quantitative take estimate.
We examined two approaches towards estimating the Level B take for the requested six marine mammal
species within the project area at Naval Base Point Loma. The first approach was using our standard approach of using species density multiplied by isopleth size. The second approach utilized daily sightings from monitoring reports produced from past Navy projects at Naval Base Point Loma NAVFAC SW, 2015a; NACFAC SW, 2017; NAVFAC SW, 2018.
Density estimates for any specific area assumes that the species in question are evenly distributed across the entire site, which is rarely the case. Using the first approach for this project, we examined the use of densities, using an overall density for San Diego Bay, within a much smaller and definitive area specifically Naval Base Point Loma.
This approach, in combination with the predicted Level B harassment isopleths, yielded take estimates that were determined to not be conservative
enough in nature for these activities and activity source levels as compared to the results of the in situ measurements included in the Navys Compendium NAVFAC SW, 2020 and as discussed above. Furthermore, the take estimates produced from this method did not appropriately account for group size of all marine mammal species as the density estimate was for a much larger area consisting of a primarily offshore environment and assumed a much larger distribution of marine mammals.
Therefore, this approach was not utilized and will not be discussed further.
The second approach utilized average daily sightings from the Year 15
monitoring reports from IHAs that were previously issued NAVFAC SW, 2015a;
NACFAC SW, 2017; NAVFAC SW, 2018. This information was provided by the Navy in Table 6.

TABLE 6MONITORING RESULTS FROM THE NAVYS YEARS 15 PROJECTS AT NAVAL BASE POINT LOMA IN SAN DIEGO, CALIFORNIA
Year 1 project 10 days; potential El Nino year
Year 2 project 100 days; El Nino year
Species Average/
day
Average group size
2,229
25
83
19

229.9
2.5
8.3
19

2.2
1.1
2.4
6.3

n/a n/a
n/a n/a
n/a n/a
Total California sea lions
Harbor seal
Bottlenose dolphins
Common dolphins
Pacific white-sided dolphins
Northern elephant seals
Year 3 project 59 days
Average/
day
Average group size
7,507
248
695
850

75.1
2.5
7.0
8.5

1.4
1.0
2.8
2 42.5

27
1

0.3
1

3.9
1

Total
Year 4 project 152 days
Average/
day
Average group size
483
25
25
n/a
8.2
0.4
0.4
n/a
1.3
1.0
1.9
n/a
n/a n/a
n/a n/a
n/a n/a
Total
Year 5 project 49 days
Average/
day
Average group size
2,263
88
67
n/a
14.9
0.6
0.4
n/a
1.7
1.1
2.7
n/a
n/a n/a
n/a n/a
n/a n/a
Total
Average/
day
Average group size
618
28
13
n/a
12.6
0.6
0.3
n/a
1.3
1.0
2.2
n/a
n/a n/a
n/a n/a
n/a n/a
Total
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These estimates were chosen for the second method in which to estimate take of marine mammals for this action.
1 Same individuals was observed hauled out on a beach twice.
2 This includes four sightings of groups of 100+ animals outside of San Diego Bay. When these observations are eliminated, the average group size is 6.75 animals observed inside of San Diego Bay.

The Year 1 and 2 monitoring reports demonstrated marine mammal estimates during a potential and known El Nino year, respectively. Because of this, these values were likely not representative of the typical conditions around Naval Base Point Loma and were not preferred.
California sea lions, harbor seals, and bottlenose dolphins were recorded during all other years. Within these, Year 4 was considered the most conservative as these activities consisted of the longest duration 152
days with the highest number of sightings for these species. Therefore, for these species we used the Year 4
average daily values.
Pacific white-sided dolphins were only recorded during Year 2. While these estimates are likely not fully representative of the typical distributions of Pacific white-sided dolphins around San Diego Bay, they will serve as the basis for our conservative take estimates for this species. Common dolphins were
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observed in Years 1 and 2; however, the length of the project period in Year 2
100 days was considered more representative than the Year 1 project 10 days. Therefore, the values from the Year 2 estimates were used for common dolphins. A single Northern elephant seal was only recorded to have hauled out on a beach twice during all Year 1
5 work. Due to this, no average daily estimates were present for analysis;
however, some discretionary take is authorized in the event Northern elephant seals are present during this action.
For all species excluding Northern elephant seals, these daily sightings were extrapolated over the number of days of pile removal activities 84.
This second approach yielded larger and more conservative Level B take estimates, but more realistic for particular species occurrence and group size given the data was previously collected at the location of this project for similar or the same species during past projects. Here we describe how the
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information provided above is brought together to produce a quantitative take estimate.
By following this daily occurrencebased approach using past sightings at Naval Base Point Loma, we will expect that 15 California sea lions, 1 harbor seal, 9 common dolphins, 1 Pacific white-sided dolphin, and 1 bottlenose dolphin will be sighted per day.
Multiplication of the above daily occurrences times the number of pile removal days planned 84 results in the Level B harassment take of 1,260
California sea lions, 84 harbor seals, 756
common dolphins, 84 Pacific whitesided dolphins, and 84 bottlenose dolphins see Table 7 for final estimates.
The Navy has noted that northern elephant seals are very rarely seen in this area, with the only true record being of a hauled out and distressed juvenile during the Year 2 IHA
NAVFAC SW, 2015a. As a precaution that a greater number of northern elephant seal may occur around Naval
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