EK60 Water Column Sonar Data Collected During DY1803

Acoustic-Trawl Surveys of Walleye Pollock (Gadus chalcogrammus) in the Gulf of Alaska (DY1803, EK60). 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 and Marmot Bay areas of the Gulf of Alaska (GOA) in the late winter/early spring of 2018 to estimate the distribution and abundance of walleye pollock (Gadus chalcogrammus). This survey was conducted 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 conducted an acoustic system calibration in Captains Bay, Dutch Harbor, Alaska on 12 March and departed Dutch Harbor on 13 March transiting toward Shelikof Strait. The Shelikof Strait survey was conducted 15-21 March followed by the Marmot Bay survey 21-22 March. A post-cruise calibration of the echosounder system was conducted at the end of the cruise on 23 March in Kalsin Bay, Kodiak Island, Alaska. The vessel returned to its homeport of Kodiak, Alaska on 23 March ending the cruise.