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Federal Register / Vol. 86, No. 106 / Friday, June 4, 2021 / Notices
Detailed Description of Specific Activity The procedures to be used for the proposed survey would be similar to those used during previous seismic surveys by LDEO and would use conventional seismic methodology. The surveys would involve one source vessel, the R/V Langseth. R/V Langseth would deploy an array of 36 airguns as an energy source with a total volume of 6,600 in3. The array consists of 36
elements, including 20 Bolt 1500LL
airguns with volumes of 180 to 360 in3
and 16 Bolt 1900LLX airguns with volumes of 40 to 120 in3. The airgun array configuration is illustrated in Figure 211 of NSF and USGSs Programmatic Environmental Impact Statement PEIS; NSFUSGS, 2011.
The PEIS is available online at:
www.nsf.gov/geo/oce/envcomp/usgsnsf-marine-seismic-research/nsf-usgsfinal-eis-oeis-with-appendices.pdf. The vessel speed during seismic operations would be approximately 4.2 knots kn 7.8 km/hour during the survey and the airgun array would be towed at a depth of 12 m. The receiving system would consist of OBSs and a towed hydrophone streamer with a nominal length of 15 km OBS and multi-channel seismic MCS shooting. As the airguns are towed along the survey lines, the hydrophone streamer would transfer the data to the on-board processing system, and the OBSs would receive and store the returning acoustic signals internally for later analysis.
Approximately 60 short-period OBSs would be deployed and subsequently retrieved at a total of 123 sites in multiple phases from a second vessel, the Canadian Coast Guard ship John P.
Tully CCGS Tully. Along OBS
refraction lines, OBSs would be deployed by CCGS Tully at 10 km intervals, with a spacing of 5 km over the central 40 km of the fault zone for fault-normal crossings. Twenty-eight broadband OBS instruments would also collect data during the survey and would be deployed prior to the activesource seismic survey, depending on logistical constraints. When an OBS is ready to be retrieved, an acoustic release transponder pinger interrogates the instrument at a frequency of 811 kHz;
a response is received at 11.513 kHz.
The burn-wire release assembly is then activated, and the instrument is released from its 80-kg anchor to float to the surface. Take of marine mammals is not expected to occur incidental to LDEOs use of OBSs.
The airguns would fire at a shot interval of 50 m approximately 23 s during MCS shooting with the hydrophone streamer approximately 42

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percent of survey effort, at a 150-m interval approximately 69 s during refraction surveying to OBSs approximately 29 percent of survey effort, and at a shot interval of every minute approximately 130 m during turns approximately 29 percent of survey effort.
Short-period OBSs would be deployed first along five OBS refraction lines by CCGS Tully. Two OBS lines run parallel to the coast, and three are perpendicular to the coast; one perpendicular line is located off Southeast Alaska, one is off Haida Gwaii, British Columbia, and another is located in Dixon Entrance. Please see Figure 1 for all location references.
Following refraction shooting of a single line, short-period instruments on that line would be recovered, serviced, and redeployed on a subsequent refraction line while MCS data would be acquired by the Langseth. MCS lines would be acquired off Southeast Alaska, Haida Gwaii, and Dixon Entrance. The coastparallel OBS refraction transect nearest to shore would only be surveyed once at OBS shot spacing. The other coastparallel OBS refraction transect on the ocean side would be acquired twice, once during refraction and once during reflection surveys. In addition, portions of the three coast-perpendicular OBS
refraction lines would also be surveyed twice, once for OBS shot spacing and once for MCS shot spacing. The coincident reflection/refraction profiles that run parallel to the coast would be acquired in multiple segments to ensure straight-line geometry. Sawtooth transits during which seismic data would be acquired would take place between transect lines when possible; otherwise, boxcar turns would be performed to save time. Both reflection and refraction surveys would use the same airgun array with the same discharge volume.
There could be additional seismic operations associated with turns, airgun testing, and repeat coverage of any areas where initial data quality is substandard, and 25 percent has been added to the assumed survey line-kms to account for this potential.
Note that the location of some tracklines has been modified from the original proposal as represented in Figure 1 and reflected in the take estimation analysis see Estimated Take. However, these minor modifications do not substantively impact the location of survey effort or the proportion of survey effort in different depth bins and, therefore, the original take estimates remain accurate.
In addition to the operations of the airgun array, a multibeam echosounder MBES, a sub-bottom profiler SBP,
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and an Acoustic Doppler Current Profiler ADCP would be operated from R/V Langseth continuously during the seismic surveys, but not during transit to and from the survey area. Take of marine mammals is not expected to occur incidental to use of the MBES, SBP, or ADCP because they will be operated only during seismic acquisition, and it is assumed that, during simultaneous operations of the airgun array and the other sources, any marine mammals close enough to be affected by the MBES, SBP, and ADCP
would already be affected by the airguns. However, whether or not the airguns are operating simultaneously with the other sources, given the other sources characteristics e.g., narrow downward-directed beam, marine mammals would experience no more than one or two brief ping exposures from them, if any exposure were to occur. Proposed mitigation, monitoring, and reporting measures are described in detail later in this document please see Proposed Mitigation and Proposed Monitoring and Reporting.
Description of Marine Mammals in the Area of Specified Activities Sections 3 and 4 of the application summarize available information regarding status and trends, distribution and habitat preferences, and behavior and life history, of the potentially affected species. Additional information regarding population trends and threats may be found in NMFS Stock Assessment Reports SARs;
www.fisheries.noaa.gov/national/
marine-mammal-protection/marinemammal-stock-assessments and more general information about these species e.g., physical and behavioral descriptions may be found on NMFS
website www.fisheries.noaa.gov/findspecies.
Table 1 lists all species with expected potential for occurrence in the survey area and summarizes information related to the population or stock, including regulatory status under the MMPA and Endangered Species Act ESA and potential biological removal PBR, where known. For taxonomy, we follow Committee on Taxonomy 2020.
PBR is defined by the MMPA as the maximum number of animals, not including natural mortalities, that may be removed from a marine mammal stock while allowing that stock to reach or maintain its optimum sustainable population as described in NMFSs SARs. While no mortality is anticipated or authorized here, PBR and annual serious injury and mortality from anthropogenic sources are included here
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