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

Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
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How is the evidence assessed?

Effectiveness

61%
Certainty

24%
Harms

0%

Calculating overall effectiveness category

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.}

Study locations

Key messages

One study examined the effects of modifying the design/attachments of a W-trawl net used in shrimp/prawn fisheries on unwanted catch of subtidal benthic invertebrate. The study was in Moreton Bay (Australia).

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (1 STUDY)

Unwanted catch overall abundance (1 study): One replicated, paired, controlled study in Moreton Bay found that four designs of W-trawl nets used in shrimp/prawn fisheries caught less non-commercial unwanted catch of crustaceans compared to a traditional Florida Flyer trawl net.

OTHERS (1 STUDY)

Commercial catch abundance (1 study): One replicated, paired, controlled study in Moreton Bay found that four designs of W-trawl nets used in shrimp/prawn fisheries caught lower amounts of the commercially targeted prawn species compared to a traditional Florida Flyer trawl net.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

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
Referenced paper
Balash C., Sterling D. & Broadhurst M.K. (2016) Progressively evaluating a penaeid W trawl to improve eco-efficiency. Fisheries Research, 181, 148-154.

Please cite as:

Lemasson, A.J., Pettit, L.R., Smith, R.K. & Sutherland, W.J. (2020) Subtidal Benthic Invertebrate Conservation. Pages 635-732 in: W.J. Sutherland, L.V. Dicks, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2020. Open Book Publishers, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

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This Action forms part of the Action Synopsis:

Subtidal Benthic Invertebrate Conservation

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Reduce the number or modify the arrangement of tickler chains/chain mats on trawl nets Action Link	Unknown effectiveness (limited evidence)	2	Synopsis Link
Fit a funnel (such as a sievenet) or other escape devices on shrimp/prawn trawl nets Action Link	Unknown effectiveness (limited evidence)	1	Synopsis Link
Use traps instead of fishing nets Action Link	Unknown effectiveness (limited evidence)	1	Synopsis Link