Square mesh panels in North Sea demersal trawls: separate estimates of panel and cod-end selectivity

Published source details O’Neill F.G., Kynoch R.J. & Fryer R.J. (2006) Square mesh panels in North Sea demersal trawls: separate estimates of panel and cod-end selectivity. Fisheries Research, 78, 333-341.
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This study is summarised as evidence for the following.

	Action	Category
	Fit mesh escape panels/windows to a trawl net Action Link

Fit mesh escape panels/windows to a trawl net

A replicated, paired, controlled study in 2001 on bottom fishing grounds in the North Sea off Scotland, UK (O'Neill et al. 2006) found that square mesh escape panels fitted to bottom trawl nets reduced the unwanted catch of small haddock Melanogrammus aeglefinus and whiting Merlangius merlangus, compared to standard trawl nets, and the effect varied with position of the panel in the net. For all three panel positions, average relative catch rates of haddock and whiting smaller than 30 cm were lower in nets with square mesh escape panels than nets with no panels (data presented as average catch ratios by length). Whiting catches in nets with panels positioned 6–9 m and 9–12 m from the codend were similar and lower than panels positioned 3–6 m away and no statistical differences were found for haddock between panel positions. In addition, the selection length of haddock (the length at which half of fish of that size will escape and half will be retained) of panel nets was higher than no panel nets across all configurations (3–6 panel: 27.9 cm, 6–9 panel: 30.4 cm, 9–12 cm: 29.9 cm; no panel: 16.6 cm). Data were collected from a total of 30 trawl deployments of one of four test nets (panel or no panel) fished simultaneously with a small mesh (40 mm) control codend. Four 100 mm diamond mesh codends were tested: three with 90 mm square mesh panels inserted in either the codend or extension at 3–6, 6–9 and 9–12 m from the codend, and one with no panel (see paper for specifications). Tows were carried out on commercial fishing grounds 65 miles north-east of Fraserburgh in March 2001. Tows were 90–150 minutes at 2.4–3.3 knots. Seven or eight tows were completed with each test net. Codend catches of the target species, haddock and whiting, were sorted, weighed and the lengths of a subsample measured.

(Summarised by: Chris Barrett)