Depth distributions and time-varying bottom trawl selectivities for Dover sole (Microstomus pacificus), sablefish (Anoplopoma fimbria), and thornyheads (Sebastolobus alascanus and S-altivelis) in a commercial fishery

We estimated size-specific depth distributions and commercial bottom trawl fishery selectivities for Dover sole (Microstomus pacificus), shortspine th ornyhead (Sebastolobus alascanus), longspine thornyhead (S. altivelis), and sablefish (Anoplopoma fimbria) along the U.S, west coast. Depth distributi ons are size-specific because fish migrate ontogenetically to deep water: W ith ontogenetic migration, fishery selectivities of commercial bottom trawl s depend on depth of fishing because large fish ale most common in deep wat er. Depth distributions were similar for northern and southern areas and fo r males and females. Results show ontogenetic migration in sablefish, sugge st a possible weak ontogenetic migration in longspine thornyhead, and confi rm ontogenetic migration patterns already reported for Dover sole and short spine thornyhead. Fishery selectivities varied among species, between areas , and changed dramatically over time for most species as fishing effort mov ed into deep water: Our approach used biological data collected during rese arch bottom trawl surveys but was generally not affected by size selectivit y of bottom trawl survey gear. Uncertainty in our commercial bottom trawl s electivity estimates was mostly from length-specific capture probabilities (or vulnerabilities) for fish in the path of commercial bottom trawls. Our estimates complement selectivity estimates fi om stock assessment models. T he approach may be useful whenever the geographic distribution of fish depe nds on size ol age, fishing effort is not randomly distributed geographical ly, and sun ey estimates of fish density, bathymetric data, and commercial fishing effort information ar e available.