Voglio sapere a riguardo di…

30108

Federal Register / Vol. 86, No. 106 / Friday, June 4, 2021 / Proposed Rules
that utilize both depth strata deep divers. For each ecosystem area, the total number of line km that would be surveyed was determined, as was the relative percentage of surveyed line km associated with each source. The total line-kilometers for each survey, the dominant source, the effective percentages associated with each depth, and the effective total volume ensonified are given below Table 12.
From the sources identified in Table 2, the NEFSC identified six of the eight as having the largest potential impact zones during operations based on their relatively lower output frequency, higher output power, and operational pattern of use: EK60, ME70, DSM 300, ADCP Ocean Surveyor, Simrad EQ50, and Netmind 80 FR 39542. Further examination of these six sources considers operational patterns of use relative to each other, and which sources would have the largest potential impact zone when used simultaneously.
NEFSC determined that the EK60, ME
70, and DSM 300 sources comprise the total effective exposures relative to linekilometers surveyed acoustic disturbance takes are calculated for these three dominant sources. Of these dominant acoustic sources, only the EK
60 can use a frequency within the
hearing range of baleen whales 18k Hz.
Therefore, for NARW and all other baleen whales, Level B harassment is only expected for exposure to the EK60.
The other two dominant sources are outside of their hearing range.
Calculating volume of water ensonifiedThe cross-sectional area of water ensonified to a 160 dB rms received level was calculated using a simple spherical spreading model of sound propagation loss 20 log R such that there would be 60 dB of attenuation over 1,000 m. Spherical spreading is a reasonable assumption even in relatively shallow waters since, taking into account the beam angle, the reflected energy from the seafloor will be much weaker than the direct source and the volume influenced by the reflected acoustic energy would be much smaller over the relatively short ranges involved. We also accounted for the frequency-dependent absorption coefficient and beam pattern of these sound sources, which is generally highly directional. The lowest frequency was used for systems that are operated over a range of frequencies. The vertical extent of this area is calculated for two depth strata.
Following the determination of effective sound exposure area for transmissions considered in two
dimensions Table 11, the next step was to determine the effective volume of water ensonified at or above 160 dB rms for the entirety of each survey. For each of the three predominant sound sources, the volume of water ensonified is estimated as the athwartship crosssectional area in square kilometers of sound at or above 160 dB rms multiplied by the total distance traveled by the ship. Where different sources operating simultaneously would be predominant in each different depth strata, the resulting cross-sectional area calculated took this into account.
Specifically, for shallow-diving species this cross-sectional area was determined for whichever was predominant in the shallow stratum, whereas for deeperdiving species this area was calculated from the combined effects of the predominant source in the shallow stratum and the sometimes different source predominating in the deep stratum. This creates an effective total volume characterizing the area ensonified when each predominant source is operated and accounts for the fact that deeper-diving species may encounter a complex sound field in different portions of the water column.
Volumetric densities are presented in Table 12.

TABLE 11EFFECTIVE EXPOSURE AREAS FOR PREDOMINANT ACOUSTIC SOURCES ACROSS TWO DEPTH STRATA
Effective exposure area: Sea surface to 200 m depth km2

Active acoustic system EK60
ME70
DSM300

Marine Mammal Density As described in the 2015 proposed rule 80 FR 39542, marine mammals were categorized into two generalized depth strata: Surface-associated 0200
m or deep-diving 0 to >200 m. These depth strata are based on reasonable assumptions of behavior Reynolds III
and Rommell 1999. Animals in the shallow-diving strata were assumed to spend a majority of their lives >75

percent at depths of 200 m or shallower. For shallow-diving species, the volumetric density is the area density divided by 0.2 km i.e., 200 m.
The animals volumetric density and exposure to sound is limited by this depth boundary.
Species in the deeper diving strata were assumed to regularly dive deeper than 200 m and spend significant time at depth. For deeper diving species, the volumetric density is calculated as the
Effective exposure area: Sea surface to depth >200 m km2

0.0142
0.0201
0.0004

0.1411
0.0201
0.0004

area density divided by a nominal value of 0.5 km i.e., 500 m, consistent with the approach used in the 2016 Final Rule 81 FR 53061. Where applicable, both LME and offshore volumetric densities are provided. As described in Section 6.5 of NEFSCs application, level of effort and acoustic gear types used by NEFSC differ in these areas and takes are calculated for each area LME
and offshore.

TABLE 12MARINE MAMMAL AND VOLUMETRIC DENSITY IN THE ENSONFIED AREAS
Dive profile/vertical habitat
Common name
0200 m
I >200 m
LME area density per km2 1 2

LME
volumetric density per km3 3

Offshore ensity per km2 2 4

Offshore volumetric density per km3 5

Cetaceans NARW 6
Humpback whale
Fin whale

VerDate Sep<11>2014

17:49 Jun 03, 2021

Jkt 253001

PO 00000

X
X X

Frm 00030

Fmt 4701

Sfmt 4702

0.0030
0.0016
0.0048

0.0150
0.00800
0.02400

E:FRFM04JNP2.SGM

04JNP2

0
0 0.00005

0
0 0.00025