The effect of strengthening bags on cod-end selectivity of a Scottish demersal trawl

Published source details Kynoch R.J., O’Dea M.C. & O’Neill F.G. (2004) The effect of strengthening bags on cod-end selectivity of a Scottish demersal trawl. Fisheries Research, 68, 249-257.
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This study is summarised as evidence for the following.

	Action	Category
	Modify the design or configuration of trawl gear (mixed measures) Action Link

Modify the design or configuration of trawl gear (mixed measures)

A replicated, controlled study in 2001 in an area of seabed in the North Sea, off the Orkney Islands, UK (Kynoch et al. 2004) found that modifying a bottom trawl by removing the strengthening bag (a large-mesh cover to prevent the codend from splitting when catch is heavy) improved the size-selectivity of haddock Melanogrammus aeglefinus at two mesh sizes. The length at which haddock had a 50% chance of escape was higher without a strengthening bag at both 110 mm codend mesh size (without: 31.4 cm, with: 31.4 cm) and 120 mm mesh codend (without: 34.3 cm, with: 32.4 cm). A total of 26 trawl deployments were completed on a commercial fishing vessel in June 2001: seven each with a 110 mm codend, with and without a strengthening bag, and six each with a 120 mm codend, with and without a strengthening bag (all diamond mesh). Hauls were 120–198 minutes at 68–87 m depth. The strengthening bag used 265 mm diamond mesh and 6 mm diameter twine (see original paper for full gear specifications). A cover attached over the codends sampled fish that escaped through the meshes. Codend and cover catches were sampled, and fish lengths recorded.

(Summarised by: Chris Barrett)