Study

Escape mortality of trawl caught Baltic cod (Gadus morhua) — the effect of water temperature, fish size and codend catch

  • Published source details Suuronen P., Lehtonen E. & Jounela P. (2005) Escape mortality of trawl caught Baltic cod (Gadus morhua) — the effect of water temperature, fish size and codend catch. Fisheries Research, 71, 151-163

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 1998 of seabed in a coastal bay in the Baltic Sea, Sweden (Suuronen et al. 2005) found that the survival of cod Gadus morhua escaping from trawl nets fitted with two different configurations of square mesh escape panels was similar compared to a standard trawl net with no escape window. Survival of escaped cod was 96-100% from a trawl with a single square mesh panel in the top of the codend, 92–100% from a trawl with two square mesh panels mounted on either side of the codend below the side seams, and 93-100% from a standard trawl with no escape panel. In addition, the number of fish with skin injuries was similar between trawl types (data reported as statistical results). Results where seawater temperatures were relatively high (>9oC) were excluded. In August-September 1998, a total of 19 trawl deployments were done: four with a 105 mm knotless square mesh top panel (Bacoma window) fitted in a standard 120 mm diamond mesh trawl codend, eight with a codend with 105 mm square mesh escape panels on both sides, and seven with a standard trawl net of 105 mm diamond mesh codend. Full gear specifications are given in the original paper. Deployments were carried out on a twin-rig fishing vessel for 3 h each at 30-55 m depth. Cod escaping through the square mesh panels were collected in cages attached to the end of the trawl nets, towed to the seabed and kept in cages for 12–14 days, after which survival and visible skin damage were recorded.

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

    A replicated, controlled study in 1997-1998 in a coastal bay in the Baltic Sea, off Sweden (Suuronen et al. 2005) found that survival of cod Gadus morhua escaped from trawl nets fitted with square mesh escape panels (two types) was similar to cod escapee survival from a standard diamond mesh trawl. Survival of cod escaped from codends with square mesh escape panels was not statistically different from a standard codend (two side square panels: 25–100%, one large top panel: 96–100%, standard: 42–100%). In addition, the survival of all escapees decreased with unusually high seawater temperatures in the bay (normal <10°: 92–100%; high >15°C: 25–100%). Data were collected in Hanö Bay from 30 trawl deployments of 3 h at 30-55 m depths on a commercial bottom trawl vessel in August 1997–April 1998. Three codend types were tested: a Danish type 105 mm side escape window codend (14 tows); a 105 mm square mesh top-panel codend (Bacoma window) (four tows) and a standard 120 mm diamond mesh codend (12 tows). Escapee cod were collected in cages attached to the end of the trawl during the last 20 minutes of each tow, kept on the seabed for 5–14 days, after which survival was recorded.

Output references

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