Study

The influence of twine tenacity, thickness and bending stiffness on codend selectivity

  • Published source details O'Neill F.G., Kynoch R.J., Blackadder L., Fryer R.J., Eryaşar A.R., Notti E. & Sala A. (2016) The influence of twine tenacity, thickness and bending stiffness on codend selectivity. Fisheries Research, 176, 94-99.

Actions

This study is summarised as evidence for the following.

Action Category

Use a different twine type in a trawl net

Action Link
Marine Fish Conservation

Use a larger mesh size

Action Link
Marine Fish Conservation
  1. Use a different twine type in a trawl net

    A replicated, controlled study in 2003 of bottom fishing grounds in the North Sea, UK (O'Neill et al. 2016) found that changing the thickness of twine (three diameters) in a trawl net codend did not improve the size-selectivity of unwanted haddock Melanogrammus aeglefinus or plaice Pleuronectes platessa. The lengths at which fish had a 50% chance of escaping capture were similar for all three twine thicknesses for both haddock (thin: 35–36 cm, medium: 35–36 cm, thick: 31–35 cm) and plaice (thin: 28.6–29.4 cm, medium: 28.6–30 cm, thick: 28.4–29.8 cm). Data were collected from 30 trawl deployments on a commercial fishing vessel east of Scotland in October 2003. Three twine sizes were tested (thin: 4.1 mm, medium: 4.6 mm, thick/conventional: 5.1 mm) during separate hauls and using the covered codend method to collect fish escaping through the meshes. Haul duration was 40–211 min. Haddock and plaice lengths were measured and if catches were large, subsampled.

    (Summarised by: Rosslyn McIntyre)

  2. Use a larger mesh size

    A replicated, controlled study in 2003 on bottom fishing grounds in the North Sea off Scotland, UK (O'Neill et al. 2016) found that a larger mesh size codend in a trawl net improved the size-selectivity of European plaice Pleuronectes platessa and haddock Melanogrammus aeglefinus compared to a smaller mesh codend. The size at which fish had a 50% chance of escape was greater with a larger 130 mm mesh codend, irrespective of twine thickness, than a smaller 120 mm mesh, for both plaice (large: 31–32 cm, small: 29–30 cm) and haddock (large: 34–39 cm, small: 32–36 cm). Data were collected in October 2003 from 30 deployments (40–210 min) of a standard commercial trawl net fitted with one of four different codends: a 130 mm diamond mesh codend (4.6 mm twine thickness, nine hauls), and three 120 mm diamond mesh codends of different twine thicknesses (4.1 mm, 4.6 mm and 5.1 mm, six to eight hauls each). Small mesh (17 mm) covers attached over each codend collected fish escaping through the meshes. All fish in the codends and covers were identified and weighed, and the lengths of haddock and plaice recorded. If catches were large, a subsample was measured.

    (Summarised by: Rosslyn McIntyre)

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