EK80 Water Column Sonar Data Collected During DY2403

The Midwater Assessment and Conservation Engineering (MACE) program of NOAA Fisheries (NMFS), Alaska Fisheries Science Center (AFSC), conducted acoustic-trawl (AT) stock assessment surveys in the Shelikof Strait and Chirikof Shelf break areas of the Gulf of Alaska (GOA) 5-20 March, 2024, to estimate distribution and abundance of walleye pollock (Gadus chalcogrammus). The 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 these surveys was a Kongsberg EK80 split-beam scientific echosounder system utilizing five frequencies (18, 38, 70, 120, and 200 kHz). The vessel departed Kodiak, Alaska on 5 March and conducted the Shelikof Strait survey 6-17 March, and the Chirikof Shelf break survey 17-19 March. A calibration of the EK80 echosounder system was conducted during a previous survey (DY2401) on 4 February in Kalsin Bay, Kodiak Island, Alaska, and a post-survey calibration was conducted in Uyak Bay, Kodiak Island, Alaska, on 9 March. Trawl operations were conducted using an LFS1421 mid-water trawl net equipped with a Kongsberg FS70 trawl sonar.