Evaluation of a Selective Flatfish Trawl and Diel Variation in Rockfish Catchability as Bycatch Reduction Tools in the Deepwater Complex Fishery off the U.S. West Coast

Abstract We tested the potential of a selective flatfish trawl to reduce bycatch of slope rockfish in the upper continental slope bottom-trawl fishery (250–500 m) on the U.S. West Coast. The trawl we tested differed from typical slope trawls in that it was a low-rise, two-seam trawl with a severely cut back headrope. We used an alternate haul, randomized block design to compare catches of the experimental trawl with those of a typical four-seam, high-rise trawl and to examine diel changes in catch rates for both trawls. The experimental trawl produced catches similar to the control trawl for all commercially valuable flatfish, except arrowtooth flounder Atheresthes stomias, which was reduced 24%. Catches of most rockfish and roundfish were significantly reduced in the experimental trawl (50–94% depending on species). However, the catches of darkblotched rockfish Sebastes crameri and redbanded rockfish S. babcocki were not reduced significantly in the experimental trawl. Nighttime catches were reduced 30–99% for most rockfish species, the greatest reductions occurring in the experimental trawl. The large nighttime catch reduction for several rockfish species for both trawls along with no catch reduction in Dover sole Microstomus pacificus, suggests that fishing only at night may be a viable bycatch-reduction strategy for some rockfish species. The diel and depth-related variation in catch rates we noted for the selective flatfish trawl indicates that catches by this trawl may be especially sensitive to physical and environmental factors such as time of day, depth, or turbidity.