EK80 Water Column Sonar Data Collected During DY2102

The Midwater Assessment and Conservation Engineering (MACE) program of NOAA Fisheries, Alaska Fisheries Science Center (AFSC), conducted acoustic-trawl (AT) stock assessment surveys in the Shelikof Strait area of the Gulf of Alaska (GOA) in the late winter of 2021 to estimate distribution and abundance of walleye pollock (Gadus chalcogrammus). These surveys were conducted aboard NOAA Ship Oscar Dyson (built in 2003, 64 meters, 2500 tons, 3100 hp), a research stern trawler equipped with acoustic and oceanographic instrumentation. The primary water column acoustic instrument for the survey was a Simrad EK80 split-beam scientific echosounder system utilizing five frequencies (18, 38, 70, 120, and 200 kHz). The vessel departed Kodiak, Alaska on 2 March and conducted the Shelikof Strait survey 3-10 March, and the Marmot Bay survey 13-15 March. A calibration of the EK80 echosounder was conducted prior to starting the surveys on 2 March in Kalsin Bay, Kodiak Island, Alaska and a follow-up post-cruise calibration was conducted in Kalsin Bay, Kodiak Island, Alaska on 15 March. Trawl operations were conducted using an LFS1421 mid-water trawl net.