Assessment of dual selection in grid based selectivity systems

Published source details Sistiaga M., Herrmann B., Grimaldo E. & Larsen R.B. (2010) Assessment of dual selection in grid based selectivity systems. Fisheries Research, 105, 187-199.
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This study is summarised as evidence for the following.

	Action	Category
	Use a larger mesh size Action Link

Use a larger mesh size

A replicated, controlled study in 2009 of an area of seabed in the Barents Sea off the coast of northern Norway (Sistiaga et al. 2010) found that increasing the mesh size of a trawl codend fitted with a size-sorting escape grid, resulted in a similar size-selectivity of cod Gadus morhua and haddock Melanogrammus aeglefinus compared to a codend with a conventional smaller mesh size. The average length at which fish had a 50% chance of escape was similar between a larger (140 mm) diamond mesh codend and a smaller (135 mm) diamond mesh codend for both cod (large: 49 cm, small: 46 cm) and haddock (large: 45 cm, small: 43 cm). Data were collected in March 2009 from 28 deployments on a survey vessel: 12 hauls with a 140 mm diamond mesh codend and 16 with a 135 mm diamond mesh codend. Both trawl nets also had a size-sorting escape grid (“Sort-V”, 55 mm bar spacing, upper escape opening) in front of the codend (see original paper for gear specifications). Covers fitted over both the grid escape opening and codend collecting fish escaping from these areas. The lengths of cod and haddock >30 cm in codend and cover catches were recorded.

(Summarised by: Chris Barrett)