Study

Improving selectivity of the Baltic cod pelagic trawl fishery: Experiments to assess the next step

  • Published source details Madsen N., Tschernij V. & Holst R. (2010) Improving selectivity of the Baltic cod pelagic trawl fishery: Experiments to assess the next step. Fisheries Research, 103, 40-47

Actions

This study is summarised as evidence for the following.

Action Category

Modify the configuration of a mesh escape panel/window in a trawl net

Action Link
Marine Fish Conservation

Fit mesh escape panels/windows to a trawl net

Action Link
Marine Fish Conservation
  1. Modify the configuration of a mesh escape panel/window in a trawl net

    A replicated, controlled study in 2000 of areas of seabed in the Bornholm Deep, Baltic Sea, between Poland and Sweden (Madsen et al. 2010) found that trawl nets fitted with square mesh escape windows either in the bottom or top of the codend did not affect cod Gadus morhua selectivity, compared to a standard codend with no square mesh windows. Overall, the length at which cod had a 50% chance of escape was similar between trawl types (bottom windows: 44.6–50.3 cm, top window: 49.3–50.3 cm, no windows: 48.0–49.3 cm). However, this decreased with increasing catch weights in bottom windows in one of two cases, and with no window in one of two cases. In addition, more cod escaped with bottom windows in one of two cases (top: 6,906 fish, bottom: 18,765 fish, none: 13,202 fish) and with a top window in the other case (top: 27,616 fish, bottom: 17,026 fish, none: 16,089 specimens). Trials were conducted on two commercial fishing vessels in April–June 2000. A total of 18 trawl deployments were completed using a trawl net with a 122 mm square mesh top window fitted into a 122 mm mesh codend, 16 tows with two 122 mm square mesh windows fitted into the bottom of a 122 mm mesh codend, and 17 tows using a trawl net with a standard 136 mm mesh codend. Full gear specifications are given in the original paper. Tow duration was 8–11 hours at a speed of 2.5–2.6 knots and depths of 91–95 m. A cover was applied to each codend to retain and sample escaped cod.

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

    A replicated, paired, controlled study in 2000 of a pelagic area in the Baltic Sea, Denmark (Madsen et al. 2010) reported that three of three configurations of pelagic trawl codends, including two with square mesh escape windows, allowed large proportions of Atlantic cod Gadus morhua to escape, and reduced the catches of undersized cod compared to an existing type of square mesh window codend. Data were not tested for statistical significance. High numbers of cod escaped from each of the tested codends relative to the numbers retained; codend with bottom escape windows (escaped: 17,026–18,765, retained 1,998–5,466); large diamond mesh codend (escaped: 13,202–16,089, retained: 2,317–3,228); and top window codend (escaped: 6,906–27,616, retained: 6,906–27,616). Compared to the square mesh codend in use by the fishery (Bacoma), catches of undersized (<38 cm) cod in the three test codends were reported to be reduced to 0.1–1.4% from 5.4%. Trials were conducted by two commercial vessels around the Bornholm Deep in the main pelagic cod fishery season, April–June 2000. Data was collected from 10–11 deployments of each of three codend types on one vessel and 6–7 on the other (total 51). Tow duration was 8–11 h at 2.5 knots and 90–95 m depth. The three codends tested were: a codend with two 125 mm bottom square mesh escape windows; a codend with one 125 mm top escape window; and a standard diamond mesh codend of 135 mm mesh (see paper for gear specifications). Covers installed over the codends sampled escaping fish catch. Lengths of all fish in the covers and codends were measured. Data for the 110 mm Bacoma codend were taken from a previous study (7).

Output references

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