Progressively evaluating a penaeid W trawl to improve eco-efficiency

Published source details Balash C., Sterling D. & Broadhurst M.K. (2016) Progressively evaluating a penaeid W trawl to improve eco-efficiency. Fisheries Research, 181, 148-154.
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This study is summarised as evidence for the following.

	Action	Category
	Modify the design/attachments of a shrimp/prawn W-trawl net Action Link
	Modify the design or configuration of trawl gear (mixed measures) Action Link

Modify the design/attachments of a shrimp/prawn W-trawl net

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.

(Summarised by: Anaëlle Lemasson & Laura Pettit)
Modify the design or configuration of trawl gear (mixed measures)

A replicated, paired, controlled study in 2014 of a fished area of seabed in Moreton Bay in the Coral Sea, Australia (Balash et al. 2016) found that using a different design of prawn trawl (a ‘W-trawl’) reduced the quantities of unwanted fish in one of four cases, compared to a conventional trawl design. The catch rates of unwanted fish were lower in the first of four designs of W-trawl configuration compared to the conventional trawl (original: 5 kg/ha: conventional: 2 kg/ha). However, there were no differences in catch rates of unwanted fish between three subsequent modifications to the original W-trawl design and the conventional design (modified: 1–2 kg/ha, conventional: 2–3 kg/ha). In addition, target shrimp Penaeidae catches were reduced in all W-trawl designs compared to the conventional, by 27–80%. Trials were carried out by a double-rigged commercial vessel on trawl fishing grounds in Moreton Bay in February 2014. One of four designs of W-trawl were deployed in paired tows with a conventional trawl design (Florida Flyer). A total of 45 paired deployments were made (10 to 13 of each W-trawl design) and all trawls had a 42 mm diamond mesh codend (see original paper for gear specifications).

(Summarised by: Chris Barrett)