AFSC/RACE/MACE: Combining eastern Bering Sea bottom trawl and midwater acoustic surveys to assess semi-demersal fishes

Walleye pollock (Gadus chalcogrammus) in the eastern Bering Sea (EBS) are assessed during the summer using an acoustic-trawl (AT) survey for the midwater component of the stock, and a bottom trawl (BT) survey for the demersal component. The surveys are generally conducted at similar times and over roughly the same area (the BT survey does actually extend into shallower areas than the AT survey). The goal of this project is to develop an efficient AT-BT hybrid survey approach, which would be conducted from the same set of vessels to assess the targeted species from both surveys. Acoustic data are collected annually since 2006 from the BT survey vessels to estimate an index of walleye pollock abundance that agrees well with AT survey estimates. Efforts are currently underway to collect walleye pollock size composition data from trawl hauls conducted in midwater conducted by the BT survey chartered vessels. These catch data will ultimately be used to convert acoustic data into fish abundance estimates. The BT survey acoustics-based walleye pollock abundance index has been formally used in the EBS stock assessment model since 2011.

Walleye pollock in Alaskan waters support one of the largest single-species fisheries in the world and the largest in the United States by volume. Catches of pollock in Alaskan waters ranged from 850 thousand to 1.36 million tons from 2009 – 2013, with an ex-vessel value ranging from $299.7 – 495.9 million for the same time period. Information from fishery independent surveys (AFSC BT and AT surveys in the EBS and Gulf of Alaska) provide critical data inputs for the stock assessment and management needs of this fishery. Because the costs to conduct the EBS BT survey (ca. $1.7 million) and AT survey (ca. $0.95 million) is substantial, efficiently combining the two as proposed above will result in greater survey efficiencies and thus dramatic savings to NOAA.