Acoustic-Trawl Surveys to Assess Walleye Pollock In Alaska: Challenges Faced and Progress Made

Large-scale acoustic-trawl surveys have been regularly conducted for over three decades by researchers at the NOAA, Alaska Fisheries Science Center (AFSC) to assess walleye pollock (Theragra chalcogramma) in Alaska.  Research within the AFSC acoustics program (MACE) has addressed several of the challenges associated with both the acoustics and trawling aspects of these surveys.  Acoustic issues include species classification of the acoustic data, fish avoidance to survey vessels, and in situ target strength measurements.  Large trawls typically form an integral part of acoustic surveys to confirm the species identity of backscatter and to collect other biological information needed to convert the echo integral into numbers and weight of animals per unit area.  MACE staff have also made significant progress in evaluating the selectivity of the large midwater trawls used during their acoustic surveys as well as in developing other direct sampling tools to help interpret the acoustic backscatter data.  This presentation will highlight these and other recent advanced technologies and methods that are being developed and used by the MACE program to improve acoustic-trawl surveys in Alaska and elsewhere.