EK60 Water Column Sonar Data Collected During DY1801

Acoustic-Trawl Surveys of Walleye Pollock (Gadus chalcogrammus) in the Gulf of Alaska (DY1801. EK601). 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 Gulf of Alaska (GOA) during the winter of 2018 to estimate the distribution and abundance of walleye pollock (Gadus chalcogrammus). These surveys were conducted aboard NOAA Ship Oscar Dyson, a 64 meter stern trawler equipped with acoustic and oceanographic instrumentation. The primary acoustic instrument for the surveys was a Simrad EK60 split-beam echosounder system utilizing five frequencies (18, 38, 70, 120, and 200 kHz). The vessel departed Kodiak, Alaska on 5 February and conducted the Shumagin Islands survey (including Shumagin Trough, Stepovak Bay, Renshaw Point, Unga Strait, and West Nagai Strait) 7-10 February. The Sanak Trough survey was conducted on 11 February followed by the Morzhovoi Bay survey on 11 February and Pavlov Bay on 12 February. A calibration of the echosounder system was conducted at the start of the cruise on 5 February in Kalsin Bay, Kodiak Island. The vessel returned to its homeport of Kodiak, Alaska on 15 February 2018.