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.

Influence of illumination and temperature upon flatfish reactivity and herding behavior: Potential implications for trawl capture efficiency

“…For example, bycatch of Pacific halibut often curtails fishing effort in other Alaskan flatfish fisheries. If it can be adequately demonstrated that the initial behavioral response of halibut at night causes them to rise further off the bottom than do rock sole, then use of low-rise trawls (King et al, 2004;Hannah et al, 2005) may facilitate halibut escape, reducing bycatch and thereby allowing expanded effort on the targeted species. Lastly, these conclusions are based upon the study of sub-adult individuals.…”

A review of flatfish behavior relative to trawls

“…Alternatively, flatfish may simply rise to a height that allows them to fall back into the net without contacting the footrope (Bublitz, 1996). Again, these maneuvers occur close to the seafloor, typically <1 m (Main and Sangster, 1981;Bublitz, 1996;Rose, 1996;King et al, 2004). This contrasts with the net entry behavior demonstrated by many roundfish (Main and Sangster, 1981;Wardle, 1993;Rose, 1996).…”

Trophic and fishery interactions between Pacific hake and rockfish: effect on rockfish population rebuilding times

“…Scientists and managers are addressing each of these issues as related to conservation of Pacific rockfish Sebastes spp. Recent examples include modified trawl gear that reduces bycatch of some rockfish yet maintains or increases flatfish catch (King et al 2004), the linking of bocaccio rockfish Sebastes paucispinis recruitment to oceanographic conditions (Tolimieri & Levin 2005), and a theoretical study suggesting that lingcod Ophiodon elongatus predation on juvenile bocaccio can reduce the efficacy of nearshore marine protected areas designed to rebuild bocaccio stocks (Mangel & Levin 2005).…”