Combining bottom trawl and acoustic data to model acoustic dead zone correction and bottom trawl efficiency parameters for semipelagic species

We present a modeling method that combines acoustic and bottom trawl abundance measurements and habitat data to estimate acoustic dead zone (ADZ) correction and bottom trawl efficiency parameters. Bottom trawl and acoustic measurements of walleye pollock (Theragra chalcogramma) abundance and available habitat data from the eastern Bering Sea are used to illustrate this method. Our results show that predictions of fish abundance in the ADZ can be improved by incorporating bottom habitat features such as depth and sediment particle size, as well as pelagic habitat features such as water temperature, light level, and current velocity. We also obtain predictions for trawl efficiency parameters such as effective fishing height, density-dependent trawl efficiency, and catchability ratio between trawl and acoustic data by modeling bottom trawl catches as a function of acoustic measurements and the environmentally dependent ADZ correction. We conclude that catchability of walleye pollock for either survey is spatially and temporarily variable. Our modeling method can be applied to other semipelagic species to obtain estimates of ADZ correction and bottom trawl efficiency parameters.