Protecting rockfish through gear design: development of a selective flatfish trawl for the U.S. west coast bottom trawl fishery

Abstract

This study evaluated the potential to reduce the bycatch of rockfish (Sebastes spp.) in a flatfish trawl fishery by developing a selective trawl that separates flatfish from rockfish using differences in their behavior as the trawl net approaches. Using an alternate haul, randomized block design, we compared catches between a commonly used combination trawl and a newly designed, low-rise trawl incorporating a "cutback" headrope. For most of the target flatfish species, the experimental trawl had a 25–59% higher catch rate (kilograms) than the control net (P < 0.05), consistent with greater footrope length in the experimental trawl. Increased catches of some small rockfish, skates, and sablefish (Anoplopoma fimbria) were also observed (P < 0.05). The catches of many larger roundfish and rockfish species, including canary rockfish (Sebastes pinniger), redstripe rockfish (Sebastes proriger), Pacific hake (Merluccius productus), and shortspine thornyhead (Sebastolobus alascanus) more than 25 cm long, were reduced from 34 to 97% in the experimental trawl (P < 0.05). Under weak-stock management conditions, in which the bycatch of overfished rockfish species limits directed flatfish fisheries, trawl designs that permit nontarget species to escape before entrainment can significantly reduce bycatch mortality and prevent premature closures of directed flatfish fisheries.