Total selectivity of a commercial cod trawl with and without a grid mounted: grid and codend selectivity of north-east Artic cod

Published source details Kvamme C. & Isaksen B. (2004) Total selectivity of a commercial cod trawl with and without a grid mounted: grid and codend selectivity of north-east Artic cod. Fisheries Research, 68, 305-318.
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This study is summarised as evidence for the following.

	Action	Category
	Fit a size-sorting escape grid (rigid or flexible) to a fish trawl net Action Link

Fit a size-sorting escape grid (rigid or flexible) to a fish trawl net

A replicated, paired, controlled study in 2001 of bottom fishing grounds in the Norwegian Sea off Norway (Kvamme & Isaksen 2004) found that a fish trawl net fitted with rigid a size-sorting escape grid did not improve the size-selection of unwanted Atlantic cod Gadus morhua compared to a conventional trawl net with no sorting grid. The length at which cod had a 50% chance of escape was similar between trawl nets with a sorting grid (53 cm) and conventional trawls without a grid (49 cm) and the selection range (the difference between the lengths at which 25% and 75% of cod were retained) was 10 cm for both the grid and codend. In addition, the proportion of the 34% of cod below the minimum landing size (47 cm) entering the gear was reduced to 8% in the catches with a grid mounted and 12.0% in the catches without a grid. Data were collected in June and July 2001 west of Bear Island. Trawl deployments were done of a standard 135 mm diamond mesh codend fitted with a stainless steel sorting grid (single grid system - modified Sort-V) with 55 mm bar spacing fitted in the upper trawl panel ahead of the codend (9 tows), and a standard 135 mm diamond mesh codend with no grid (18 tows). Covers over the sorting grid escape opening and the codend retained the escaping catch. Full details of trawl designs are provided in the original study.

(Summarised by: Leo Clarke)