Study

Alternative codends to reduce bycatch in Chilean crustacean trawl fisheries

  • Published source details Queirolo D., Erzini K., Hurtado C.F., Ahumada M. & Soriguer M.C. (2011) Alternative codends to reduce bycatch in Chilean crustacean trawl fisheries. Fisheries Research, 110, 18-28

Actions

This study is summarised as evidence for the following.

Action Category

Fit a size-sorting escape grid (rigid or flexible) to a prawn/shrimp trawl net

Action Link
Marine Fish Conservation

Use a square mesh instead of a diamond mesh codend in a trawl net

Action Link
Marine Fish Conservation

Fit mesh escape panels/windows to a trawl net

Action Link
Marine Fish Conservation

Use a larger mesh size

Action Link
Marine Fish Conservation
  1. Fit a size-sorting escape grid (rigid or flexible) to a prawn/shrimp trawl net

    A replicated, controlled study in 2008–2009 of a seabed area in the Pacific Ocean off Chile (Queirolo et al. 2011) found that shrimp trawl nets fitted with a rigid size-sorting escape grid allowed more unwanted fish to escape capture than conventional trawl nets with no grid. The total percentages in number of unwanted catch (fish and invertebrates combined) that escaped capture was higher in trawls with a grid fitted (25%) than in trawls without a grid (2–3%). The percentage number of catch that escaped capture was also higher in trawls with a grid fitted than trawls without a grid for Chilean hake Merluccius gayi gayi (48 vs 1%), Aconcagua grenadier Coelorinchus aconcagua (20 vs 0–3%), cardinalfish (Apogonidae) (80 vs 1–4%) and elasmobranchs (Elasmobranchii) (39 vs 0%). Escapees were similar in trawls with and without a grid for cusk-eel Ophidiidae (100 vs 94%). Thirty-nine trawl deployments were made using two trawl nets with 56 mm diamond mesh codends, either with or without a rigid grid. The grid was a metal Nordmøre grid (1.2 × 0.8 m) with 35 mm bar spacing and top escape opening, fitted at a 45° angle in front of the codend. A mesh guiding panel guided catch to the grid. Covers over the grid opening collected the escaping catch. All codend and cover catches were sorted and weighed separately.

  2. Use a square mesh instead of a diamond mesh codend in a trawl net

    A replicated, controlled study in 2008–2009 in bottom fishing grounds in the Pacific Ocean, off Chile (Queirolo et al. 2011) found that the effect of crustacean trawl nets fitted with square mesh codends on reducing discarded fish catch, varied with mesh size as well as mesh configuration, compared to a reference diamond mesh codend. In one of two target fisheries for crustaceans, escape rates (by weight) of Chilean hake Merluccius gayi gayi and bigeye flounder Hippoglossina macrops (the two main non-target fish species) were higher in both 70 mm square mesh and diamond mesh (D70) codends than the 56 mm diamond (D56) mesh codend (hake, square: 36%, D70: 16%, D56: 0%; flounder, square: 28%, D70: 17%, D56: 1%). For the other target crustacean fishery, main non-target fish escape rates (by weight) were higher in a 56 mm square mesh codend than a 56 mm diamond mesh codend for eelpout Zoarcidae spp. (99 vs 26%) only, and were similar between the codends for: Chilean hake (3 vs 0%), aconcagua grenadier Coelorinchus aconcagua (17 vs 3%) and cardinalfish Apogonidae spp. (19 vs 4%). However, they were all higher in a 70 mm diamond mesh codend than the 56 mm diamond mesh codend. Retained and escaped catches were compared between four codends of different mesh size (56 or 70 mm) and mesh configuration (square or diamond), and a reference 56 mm diamond mesh codend (see paper for gear specifications). In total, 84 trawl deployments were made in December 2008 in traditional crustacean fishing grounds using commercial vessels. A small mesh (32 mm) cover attached over each codend during deployment collected the escaped catch.

  3. Fit mesh escape panels/windows to a trawl net

    A replicated, controlled study in 2008–2009 of bottom fishing grounds in the Pacific Ocean off Chile (Queirolo et al. 2011) found that crustacean trawl nets fitted with square mesh escape panels did not allow more unwanted fish to escape capture than nets without, however, nets with a panel and increased codend mesh size did. In the first of two trials, the average escape rates of Chilean hake Merluccius gayi gayi and bigeye flounder Hippoglossina macrops were similar in 56 mm mesh codends with and without a panel, and higher in 70 mm codends with a panel (56 mm/panel: 3–8%, 70 mm/panel: 14–23%, 56 mm/no panel: 1%). In the second trial, the average escape rates of four of four fish species/groups (Aconcagua grenadier Coelorinchus Aconcagua, cardinalfish Apogonidae, Chilean hake and cusk-eel Ophidiidae) were similar in 56 mm codends with and without a square mesh escape panel (panel: 1–88%, no panel: 0–94%). Fish data were collected from two trials in December 2008 (37 tows) and June-July 2009 (40 tows). Three codend types were tested: a 56 mm diamond mesh codend with an 80 mm mesh square mesh top escape panel (both trials), a 70 mm diamond mesh codend with an 80 mm mesh square mesh top escape panel (trial one), and a 56 mm diamond mesh codend without a panel (both trials). In both trials, the codends tested were changed after two or three tows, and the order used was randomized. Covers over the escape panels and sampled the escaping catch. Fish caught in large enough quantities were analysed.

  4. Use a larger mesh size

    A replicated study in 2008–2009 in an area of fished seabed in the Pacific Ocean off Chile (Queirolo et al. 2011) found that crustacean trawls with larger mesh codends allowed more unwanted fish to escape than smaller mesh codends. The average percentage number of escaped fish was higher using larger 70 mm mesh compared to 56 mm mesh: in four of four comparisons for Chilean hake Merluccius gayi gayi (3–38 vs 0–1%) and bigeye flounder Hippoglossina macrops (8–27 vs 0–1%), and in one of one comparison for Aconcagua grenadier Coelorinchus aconcagua (44 vs 3%), cardinalfish Apogonidae (51 vs 4%) and eelpout Zoarcidae spp. (96 vs 26%). A total of 101 trawl deployments were made by three commercial vessels targeting three different crustacean species during two experiments in December 2008 and June–July 2009. Trawls were fitted with either a 70 mm diamond or square mesh codend and compared with deployments of a 56 mm diamond mesh codend. Small mesh covers over each codend collected the fish escaping through the meshes.

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