EK60 Water Column Sonar Data Collected During DY1503

Acoustic-Trawl Survey of Walleye Pollock in the Gulf of Alaska (DY1503, EK60). The Midwater Assessment and Conservation Engineering (MACE) program of NOAA National Marine Fisheries Service (NMFS), Alaska Fisheries Science Center (AFSC) conducted an acoustic-trawl (AT) stock assessment survey in the Shelikof Strait, Marmot Bay, and Chirikof shelf break areas of the Gulf of Alaska (GOA) during late winter/early spring of 2015 to estimate the distribution and abundance of walleye pollock (Gadus chalcogrammus). The survey was conducted 15-31 March (Marmot Bay, 15-16 March; Shelikof Strait 17-23 March; Chirikof shelf break, 23-24 March), starting and ending in Kodiak, Alaska. The survey was conducted aboard NOAA Ship Oscar Dyson, a 64 meter stern trawler equipped with acoustic and oceanographic instrumentation. The primary instrument for the survey was a Simrad EK60 split-beam echosounder system utilizing five frequencies (18, 38, 70, 120, and 200 kHz).