Study

Potential use of a Nordmøre grid for by-catch reduction in a Portuguese bottom-trawl multispecies fishery

  • Published source details Fonseca P., Campos A., Mendes B. & Larsen R.B. (2005) Potential use of a Nordmøre grid for by-catch reduction in a Portuguese bottom-trawl multispecies fishery. Fisheries Research, 73, 49-66

Actions

This study is summarised as evidence for the following.

Action Category

Fit mesh escape panels/windows and a size-sorting grid (rigid or flexible) to a trawl net

Action Link
Marine Fish Conservation

Fit a size-sorting escape grid (rigid or flexible) to a fish trawl net

Action Link
Marine Fish Conservation
  1. Fit mesh escape panels/windows and a size-sorting grid (rigid or flexible) to a trawl net

    A replicated study in 2003 of an area of seabed in the Atlantic Ocean off Portugal (Fonseca et al. 2005) found that bottom trawl nets fitted with a square mesh escape window in addition to a rigid size-sorting escape grid, enabled the escape of high proportions of undersized commercially targeted and non-target fish species, and the main means of escape (window or grid) varied between bottom and mid-water dwelling species. Data were not statistically tested. The proportion (by number) of individuals of commercially targeted fish below their respective minimum landing sizes that escaped was 62–79% (grid) and 8–15% (square mesh window) for two bottom dwelling species; and 0–14% (grid) and 60–100% (window) for two pelagic commercial species. For non-target species, the percentage (by weight) of escaped individuals of one bottom dwelling species was 48% (grid) and 1% (window), and for two pelagic species the grid excluded 13–17% and the window 17–72%. In September 2003, a total of 26 trawl net deployments were done by research vessel off the north west coast of Portugal at 40–150 m depth. Trawl nets were fitted with either a Nordmøre grid (plastic, 1.5 × 1 m, 30 mm bar spacing) on its own (17 hauls), or a Nordmøre grid and a square mesh window (1.8 m long, 50 mm mesh size) inserted just behind the top section of the grid (9 hauls). A ‘flapper’ net guided catch to the bottom of the grid, the upper 40 cm of which had no bars to allow retained catch to pass into the codend, while catch that passed through the grid (excluded) was retained by an inner net. A cover attached over the square mesh window collected fish escaping through the meshes of the window (see original paper for gear specifications). Fish collected in the codend, inner net and cover were sampled.

  2. Fit a size-sorting escape grid (rigid or flexible) to a fish trawl net

    A replicated study in 2003 in an area of seabed in the Atlantic Ocean off Portugal (Fonseca et al. 2005) reported that fish trawl nets fitted with a size-sorting escape grid (a modified Nordmøre grid system) had a variable effect on the reduction of unwanted and/or undersized fish catch in a multi-species fishery, and the effect differed by ecological group. Data were not tested for statistical significance. In general, unwanted/undersized individuals of three of three bottom-dwelling (demersal) species escaped in higher proportions by number (unwanted lesser-spotted dogfish Scyliorhinus canicula: 48%, hake Merluccius merluccius: 62%, pouting Trisopterus luscus: 79%) than four of four species pelagic species that inhabit the upper water layers (unwanted blue whiting Micromesistius poutassou: 13%, unwanted longspine snipefish Macroramphosus scolopax: 17%, undersized horse mackerel Trachurus trachurus: 14%, undersized Atlantic mackerel Scomber scombrus: 0%). Of legally sized commercial species, 10% of hake and horse mackerel, 76% of pouting and 9% of Atlantic mackerel were retained. Data were collected in September 2003 from 17 trawl deployments off the north west coast of Portugal at 40–150 m depths. Trawl nets were fitted with a 1.5 × 1 m plastic grid with 30 mm bar spacing in front of the codend. A ‘flapper’ net guided catch to the bottom of the grid. The upper 40 cm had no bars to allow catch not sorted out by the grid into the codend. An inner cover fitted over the grid retained catch that passed through the grid and would otherwise escape under commercial operations via an opening in the net (see paper for gear specifications).

Output references

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