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Federal Register / Vol. 86, No. 106 / Friday, June 4, 2021 / Proposed Rules
transmits and receives at six frequencies ranging from 18 to 333 kHz.
2. Multibeam Echosounder and SonarMultibeam echosounders and sonars operate similarly to the devices described above. However, the use of multiple acoustic beams allows coverage of a greater area compared to single beam sonar. The sensor arrays for multibeam echosounders and sonars are usually mounted on the keel of the vessel and have the ability to look horizontally in the water column as well as straight down. Multibeam echosounders and sonars are used for mapping seafloor bathymetry, estimating fish biomass, characterizing fish schools, and studying fish behavior.
The NEFSC operates the Simrad ME70
system, which is mounted to the hull of the research vessels and emits frequencies in the 70120 kHz range.
3. Single-Frequency Omnidirectional SonarLow-frequency, high-resolution, long range fishery sonars operate with user selectable frequencies between 20
30 kHz, which provide longer range and prevent interference from other vessels.
These sources provide omnidirectional imaging around the source with three different vertical beamwidths available single or dual vertical view and 45
variable for tilt angles from 0 to 45 from horizontal. At the 30-kHz operating frequency, the vertical beamwidth is less than 7 and can be electronically tilted from +10 to 80, which results in differential transmitting beam patterns. The cylindrical multi-element transducer allows the omnidirectional sonar beam to be electronically tilted down to 60, allowing automatic
tracking of schools of fish within the entire water volume around the vessel.
The NEFSC operates the Simrad SX90
system.
4. Acoustic Doppler Current Profiler ADCPAn ADCP is a type of sonar used for measuring water current velocities simultaneously at a range of depths. Whereas current depth profile measurements in the past required the use of long strings of current meters, the ADCP enables measurements of current velocities across an entire water column. The ADCP measures water currents with sound, using the Doppler effect. A sound wave has a higher frequency when it moves towards the sensor blue shift than when it moves away red shift. The ADCP works by transmitting pings of sound at a constant frequency into the water. As the sound waves travel, they ricochet off particles suspended in the moving water, and reflect back to the instrument. Due to the Doppler effect, sound waves bounced back from a particle moving away from the profiler have a slightly lowered frequency when they return. Particles moving toward the instrument send back higher frequency waves. The difference in frequency between the waves the profiler sends out and the waves it receives is called the Doppler shift. The instrument uses this shift to calculate how fast the particle and the water around it are moving. Sound waves that hit particles far from the profiler take longer to come back than waves that strike close by. By measuring the time it takes for the waves to return to the sensor, and the Doppler shift, the profiler can measure
current speed at many different depths with each series of pings.
An ADCP anchored to the seafloor can measure current speed not just at the bottom, but at equal intervals to the surface. An ADCP instrument may be anchored to the seafloor or can be mounted to a mooring or to the bottom of a boat. ADCPs that are moored need an anchor to keep them on the bottom, batteries, and a data logger. Vesselmounted instruments need a vessel with power, a shipboard computer to receive the data, and a GPS navigation system so the ships movements can be subtracted from the current velocity data. ADCPs operate at frequencies between 75 and 300 kHz.
5. Net Monitoring SystemsDuring trawling operations, a range of sensors may be used to assist with controlling and monitoring gear. Net sounders give information about the concentration of fish around the opening to the trawl, as well as the clearances around the opening and the bottom of the trawl;
catch sensors give information about the rate at which the codend is filling;
symmetry sensors give information about the optimal geometry of the trawls; and tension sensors give information about how much tension is in the warps and sweeps. The NEFSC
uses the NetMind System which measures door spread and monitors the door height off of the bottom and operates at 30 and 200 kHz. The NEFSC
also uses a Simrad ITI Catch Monitoring System, which allows monitoring of the exact position of the gear and of what is happening in and around the trawl.

TABLE 2OPERATING CHARACTERISTICS OF NEFSC ACTIVE ACOUSTIC SOURCES
Active acoustic system
Operating frequencies
Maximum source level
Single ping duration ms and repetition rate Hz
Nominal beamwidth degrees
Orientation/directionality
Simrad EK500 and EK60
narrow beam echosounders.
Simrad ME70 multibeam echosounder.
Simrad SX90 narrow beam sonar.

18, 38, 70, 120, 200, 333
kHz; primary frequencies italicized.
70120 kHz

224 dB

Variable; most common setDownward looking
tings are 1 ms and 0.5 Hz.

7 at 38 kHz, 11 at 18 kHz.

205 dB

0.065 ms; 14 Hz

Primarily downward looking
140.

2030 kHz

219 dB

Variable

Omnidirectional

Teledyne RD Instruments ADCP, Ocean Surveyor.
Simrad ITI Catch Monitoring System.
Raymarine SS260 transducer for DSM300 surrogate for FCV292.
Simrad EQ50

75 kHz

224 dB

0.2 Hz

Downward looking

45 variable for tilt angles from 045 from horizontal.
30.

2733 kHz

214 dB

0.050.5 Hz

Downward looking

40.

50, 200 kHz

217 dB

Unknown

Downward looking

19 at 50 kHz, 6 at 200
kHz.

50, 200 kHz

210 dB

Variable

Downward looking

NetMind

30, 200 kHz

190 dB

Unknown

Downward looking

16 at 50 kHz, 7 at 200
kHz.
50.

Proposed mitigation, monitoring, and reporting measures are described in detail later in this document please see
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Proposed Mitigation and Proposed Monitoring and Reporting.

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Description of Marine Mammals in the Area of Specified Activities Sections 3 and 4 of NEFSCs LOA
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