Results of the acoustic-trawl survey of Walleye pollock (Gadus chalcogrammus) in the Gulf of Alaska, June - August 2015 (DY2015-06)
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Results of the acoustic-trawl survey of Walleye pollock (Gadus chalcogrammus) in the Gulf of Alaska, June - August 2015 (DY2015-06)
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    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 an acoustic-trawl (AT) survey of the Gulf of Alaska (GOA) shelf to estimate the distribution and abundance of walleye pollock (Gadus chalcogrammus) in summer 2015. Previous surveys of the GOA have also been conducted by the MACE program during the summers of 2003, 2005, 2011, and 2013. The 2015 survey covered the shelf from the Islands of Four Mountains to Yakutat Trough including many bays and troughs. Surface water temperatures across the GOA shelf averaged 12.2° C, overall, approximately 1.6° C warmer than in 2013, which was the only other survey with comparable coverage. The pollock biomass estimate for the entire survey area was 1,606,171 metric tons (t). The majority of the pollock biomass was observed on the continental shelf (66%), Shelikof Strait (18%), east of Kodiak Island in Chiniak (2%) and Barnabas Troughs (6%), and in Marmot Bay (3%). The majority (79%) of the biomass in the survey area was from age-3 fish (~30-45 cm fork length [FL]). Fish weight at length was approximately 10% lower in fish greater than 40 cm FL in 2015 compared to the average weight of fish from surveys conducted in the GOA in summer of previous years. Backscatter was attributed to other species when trawl verification, frequency differentiation, or other methods made it possible. A biomass estimate was calculated for Pacific ocean perch (Sebastes alutus, 438,545 t), and euphausiid (primarily consisting of Thysanoessa inermis, but also including T. spinifera, T. raschii, and Euphausia pacifica) backscatter distribution and abundance relative to previous surveys was estimated. [doi:10.7289/V5/PR-AFSC-2017-03 (]
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