Modify the design/attachments of a shrimp/prawn W-trawl net
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
Background information and definitions
Fishing can impact subtidal benthic invertebrates through species removal or habitat damage from fishing gear coming into contact with the seabed (Collie et al. 2000). Trawling is a method of fishing that involves pulling a cone-shaped fishing net (trawl) through the water behind one or more boats. Trawling can be particularly damaging to benthic invertebrates as they are dragged along the seabed (mid-water trawls can also sometimes accidentally come into contact with the seabed). In addition, trawl nets, and in particular W-trawls used in the prawn/shrimp/nephrops fishery, can catch a considerable number of unwanted organisms, including non-commercially targeted species and organisms under the legal-size limit. To reduce the level of disturbance to the seabed and the amount of unwanted organisms caught, the design and/or attachments of the W-trawl net can be modified, for instance by securing the netting at the wing ends, pulling the top tongue of the net forward, modifying the attachment of the ground chain or by using a combination of such modifications (Balash et al. 2016).
Balash C., Sterling D. & Broadhurst M.K. (2016) Progressively evaluating a penaeid W trawl to improve eco-efficiency. Fisheries Research, 181, 148–154.
Collie J.S., Hall S.J., Kaiser M.J. & Poiner I.R. (2000) A quantitative analysis of fishing impacts on shelf‐sea benthos. Journal of Animal Ecology, 69, 785–798.
Supporting evidence from individual studies
A replicated, paired, controlled study in 2014 in Moreton Bay, Australia (Balash et al. 2016) found that four designs of W-trawl nets caught less non-commercial unwanted catch of crustaceans (discard) compared to a traditional Florida Flyer trawl net. All designs of W-trawls caught smaller amounts of crustacean discard than the traditional trawl (design 1: 1.5 vs Florida Flyer: 5.2 kg/ha; design 2: 5.6 vs 7.6; design 3: 4.9 vs 6.7; design 4: 6.9 vs 9.4). All designs of W-trawl caught lower amounts of the commercially targeted prawn species compared to the traditional trawl (27–39% reductions). In February 2014, unwanted catch from four W-trawl designs were compared to that of the Florida Flyer trawl during paired simultaneous 15–60 min deployments (one net of either one of the four designs on one side of the vessel, one Florida Flyer net on the other; 10–13 deployments/design). Design 1: unmodified W-trawl. Design 2: W-trawl with secured netting at the wing ends. Design 3: design 2 with the top tongue pulled forward and one chain link removed from each side of the ground chain. Design 4: design 3 further modified at wing ends (fitting “Dan lenos”). See paper for technical details. All nets were fitted with batwing otter boards, a “turtle-excluder device” (escape panel), and a “bycatch reducing device” (“fisheye”). At the end of each haul, catches were sorted into commercially targeted catch, commercial unwanted catch (large crabs, squid and octopus), and crustacean discard, and all were weighed.Study and other actions tested