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Results of the acoustic-trawl surveys of walleye pollock (Gadus chalcogrammus) in the Gulf of Alaska, February-March 2016 (DY2016-02 and DY2016-04)
  • Published Date:
    2017
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Results of the acoustic-trawl surveys of walleye pollock (Gadus chalcogrammus) in the Gulf of Alaska, February-March 2016 (DY2016-02 and DY2016-04)
Details:
  • DOI:
    doi:10.7289/V5/AFSC-PR-2017-02
  • Corporate Authors:
    Alaska Fisheries Science Center (U.S.)
  • Series:
    AFSC processed report ; 2017-02
  • Document Type:
  • Description:
    Scientists from the Midwater Assessment and Conservation Engineering (MACE) Program of the Alaska Fisheries Science Center's (AFSC) Resource Assessment and Conservation Engineering (RACE) Division conducted acoustic-trawl (AT) stock assessment surveys in the Gulf of Alaska (GOA) during late winter and early spring 2016 to estimate the distribution and abundance of walleye pollock (Gadus chalcogrammus) within several of their main spawning grounds. These pre-spawning pollock surveys covered the Shumagin Islands, Sanak Trough, and Morzhovoi and Pavlof Bays (DY2016-02; 13-17 February) and Shelikof Strait and Marmot Bay (DY2016-04; 14-24 March). Prior to 2001, these efforts have focused on the Shelikof Strait area, which has been surveyed annually since 1981 (except 1982, 1999, 2011). The shelf break near Chirkof Island and Marmot Bay are also regularly surveyed during the Shelikof survey cruises. The first survey of the Shumagins occurred in 1994, and this area has been surveyed annually since 2001 (except 2004, 2011). Sanak Trough, Morzhovoi Bay, and Pavlof Bay have also been regularly surveyed during the Shumagin survey cruises. Average surface water temperatures ranged from 3.9 °C (Pavlof Bay) to 5.7 °C (Marmot Bay) in these areas. Mean temperatures declined by about 0.3 °C in the Shumagin Islands and increased about 0.7 °C in Shelikof Strait compared to 2015. The walleye pollock biomass estimate for the winter 2016 Shumagin Islands survey was 20,706 metric tons (t), with an additional 17,098 t estimated for the Sanak, Morzhovoi, and Pavlof areas. The walleye pollock biomass estimate for the winter 2016 Shelikof Strait area was 665,059 t, with an additional 37,161 t estimated for the Marmot area. This breaks down to estimates of 34,619 t, 530,438 t, and 174,967 t in International North Pacific Fisheries Commission areas 610, 620, and 630, respectively. Pollock between 35 and 45 cm fork length (FL), which is indicative of age-4 fish, contributed to most of the biomass in all areas. For example, 90% of pollock biomass from the Shumagin Islands survey area and 88% of pollock biomass from the Shelikof Strait survey area came from this age class. Fish weight at length was lower in fish > 40 cm FL compared to winter GOA surveys in previous years. A second abundance analysis was conducted in which backscatter was attributed to other species where possible. [doi:10.7289/V5/AFSC-PR-2017-02 (http://dx.doi.org/10.7289/V5/AFSC-PR-2017-02)]

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