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NOAA Technical Memorandum NMFS-AFSC-238

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Results of cooperative research acoustic surveys of walleye pollock (Theragra chalcogramma) in the western Gulf of Alaska from September 2007 to September 2011

Abstract

In 2007, the Alaska Fisheries Science Center (AFSC) initiated a cooperative survey to assess the abundance of walleye pollock (Theragra chalcogramma) with local fishermen in the western Gulf of Alaska. The purpose of the survey was to estimate the abundance and distribution of walleye pollock in relatively small bathymetrically-complex areas using local fishing vessels active in the pollock fishery. The use of fishing vessels as a sampling platform provides more extended seasonal coverage in a restricted spatial area, in contrast to the large-scale assessment surveys conducted by the AFSC.  The AFSC contracted and equipped a local 58 foot (18 m) trawler for the project.  Originally the scope of the project was to evaluate the feasibility of conducting acoustic-trawl surveys of pollock using local fishing vessels.  This was successfully completed and the project expanded to include other objectives: evaluation of transect density in bathymetrically complex regions in the western Gulf of Alaska, temporal variability of pollock density during replicate transects, including day/night transects, the timing of fish migration to spawning areas, and relationships between pollock adult, young-of-the-year, and euphausiid density, and the distribution of foraging humpback whales (Megaptera novaeangliae).  This report summarizes the estimates of abundance and distribution of walleye pollock in areas covered by cooperative acoustic-trawl surveys conducted aboard the fishing vessel FV Temptation during September and January in 2007-2011. It also summarizes physical oceanographic and biological composition observations, initial findings from ancillary data collections of marine mammal observations, and dual-frequency differencing techniques to discriminate different types of acoustic backscatter.

                                                           
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