Selectivity and escapement behaviour of five commercial fishery species in standard square- and diamond-mesh codends

Published source details Frandsen R.P., Madsen N. & Krag L.A. (2010) Selectivity and escapement behaviour of five commercial fishery species in standard square- and diamond-mesh codends. ICES Journal of Marine Science, 67, 1721-1731.
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This study is summarised as evidence for the following.

	Action	Category
	Use a square mesh instead of a diamond mesh codend in a trawl net Action Link

Use a square mesh instead of a diamond mesh codend in a trawl net

A replicated, controlled study in 2006–2007 in two fished areas of seabed in the Kattegat and the Skagerrak, Denmark (Frandsen et al. 2010) found that a standard square mesh codend improved the size-selectivity of a bottom trawl net for three roundfish species, but not one flatfish species, compared to a standard diamond mesh codend. Overall, the length at which 50% of fish were predicted to escape was greater in the square mesh compared to the diamond mesh codend for roundfish: Atlantic cod Gadus morhua (26–27 cm vs 15–17 cm), haddock Melanogrammus aeglefinus (26 cm vs 15 cm) and whiting Merlangius merlangus (33 cm vs 18 cm); but it was lower for plaice Pleuronectes platessa (square: 14–15 cm, diamond, 19–20 cm). Catch comparison trials were done on multi-species fishing grounds (Norway lobster Nephrops norvegicus, cod and plaice) on two commercial twin-trawl vessels in September 2006 (18 deployments) and August 2007 (6 deployments). Two codends were tested, towed simultaneously each haul, and interchanged between left and right sides: a commercial square mesh (70 mm) and a commercial diamond mesh (90 mm). Hauls were 1–4 h at 32–184 m depth. Small mesh covers (36 mm) were attached over each codend and collected fish escaping from the upper and lower parts of the codend in separate compartments.

(Summarised by: Chris Barrett)