Choosing anterior-gear modifications to reduce the global environmental impacts of penaeid trawls

Abstract

Globally, penaeid-trawl fisheries are faced with three broad sustainability issues: (1) large bycatches; (2) acute benthic-habitat impacts; and (3) high energy consumption. Most resolution efforts have focused on i above, and via bycatch reduction devices (BRDs) installed in the posterior trawl (codend), which typically reduce total bycatches by 30–70%, but are poorly adopted owing to few perceived benefits by fishers. While mandated BRDs will remain a feature of selective penaeid trawling, solutions to habitat impacts and high energy consumption require changes to the anterior trawl, including the spreading mechanisms (e.g. otter boards, beams and sleds), ground gears, and net designs. Further, because such components ultimately determine which organisms enter the codend, it should be feasible to structure anterior-trawl modifications to address all three sustainability issues, including improving selection. We sought to review the feasibility of such an approach here, and located fifty-eight relevant articles: of which 45, 11 and 23 directly or indirectly focused on reducing bycatch, habitat impacts and energy consumption, respectively. Considering these articles, we propose a protocol for holistically improving the environmental efficiency of penaeid trawling involving: (1) selecting the most appropriate multi-net configuration; (2) reducing otter-board angle of attack to ~20°; (3) minimising twine area; and (4) optimising horizontal-trawl opening. Compared to conventional configurations, choosing alternatives within the above protocol could reduce total unwanted bycatches and habitat contact by >70%, while concomitantly lowering drag/fuel costs by >20%. The latter outcome might improve selective penaeid-trawl adoption among global fishing fleets.