Using acoustic data from fishing vessels to estimate walleye pollock (Theragra chalcogramma) abundance in the eastern Bering Sea

Eastern Bering Sea walleye pollock (Theragra chalcogramma) support one of the world's largest fisheries. Because of walleye pollock's high recruitment variability and relatively short life span, timely and accurate abundance indices are needed for fisheries management. Walleye pollock are surveyed biennially with an acoustic-trawl (AT) survey and annually with a bottom trawl (BT) survey. The latter tracks the demersal portion of the population using chartered fishing vessels, whereas the AT survey tracks the younger, midwater portion using research vessels and is critical for evaluating prerecruit abundances. Acoustic data collected from commercial fishing vessels conducting the BT survey were analyzed to provide information on midwater walleye pollock abundance at relatively low cost. A retrospective analysis of AT survey data identified a suitable index area to track midwater walleye pollock abundance. The BT survey acoustic data in that area tracked the AT survey abundance and captured its broad spatial patterns. This study is unique because commercial vessel acoustic data were used to estimate a new annual abundance index whose performance can be evaluated by a biennial research vessel survey. The new index will benefit managers by providing more accurate information on near-term abundance trends when dedicated research ship time is not available.