EK60 Water Column Sonar Data Collected During DY1906

The Midwater Assessment and Conservation Engineering (MACE) program of NOAA Fisheries, Alaska Fisheries Science Center (AFSC), conducted acoustic-trawl (AT) stock assessment surveys on the Gulf of Alaska (GOA) shelf and associated bays during the late spring and summer of 2019 to estimate the distribution and abundance of walleye pollock (Gadus chalcogrammus). The survey was conducted 30 May - 7 August aboard NOAA Ship Oscar Dyson, a 64 meter stern trawler equipped with acoustic and oceanographic instrumentation. The primary acoustic instrument for the survey was a Simrad EK60 split-beam echosounder system utilizing five frequencies (18, 38, 70, 120, and 200 kHz). The vessel departed Kodiak, Alaska on 30 May and conducted the survey in three legs with all port calls in Kodiak; the project was completed in Kodiak on August 7. Leg 1 of the project was conducted 30 May \u2013 20 June on the Gulf of Alaska (GOA) shelf from the Islands of Four Mountains to outer Shumagin Trough including Sanak Trough, Morzhovoi Bay, Shumagin Islands area, and Mitrofania area. The leg 2 surveys were conducted 25 June \u2013 16 July in Shelikof Strait, Alitak Bay, Barnabas Trough, Chiniak Trough, and on the Alaska shelf. The leg 3 surveys were conducted 19 July \u2013 7 August and included Marmot Bay, Resurrection Bay, Prince William Sound, and the Alaska shelf from Kodiak to Yakutat Bay. Calibrations of the echosounder system were conducted in Kalsin Bay, Kodiak Island, Alaska at the start and end of the cruise; no significant differences in gain parameters or transducer beam pattern characteristics were noted between the two calibrations.