By-catch reduction in the brown shrimp, Crangon crangon, fisheries using a rigid separation Nordmøre grid (grate)

Published source details Graham N. (2003) By-catch reduction in the brown shrimp, Crangon crangon, fisheries using a rigid separation Nordmøre grid (grate). Fisheries Research, 59, 393-407.
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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 prawn/shrimp trawl net Action Link

Fit a size-sorting escape grid (rigid or flexible) to a prawn/shrimp trawl net

A replicated, paired, controlled study in 1993–1995 of two sandy/mud fishing grounds in the North Sea, UK (Graham 2003) found that fitting rigid size-sorting escape grids inside shrimp trawl nets reduced the catch of unwanted whiting Merlangius merlangus and plaice Pleuronectes platessa, compared to nets without grids. For three of three designs of grid, total catch numbers of whiting (with: 263–839, without: 586–4,923) and plaice (with: 850–3,074, without 1,304–5,504), were lower in nets with a grid than without, representing 55–85% reductions in catch for whiting and 35–44% for plaice. In addition, for one of one grid designs, the selection length (the length at which fish have a 50% chance of escape) increased with increasing grid bar spacing for both whiting (10 mm: 7.7 cm, 12 mm: 10.5 cm, 14 mm: 11.8 cm) and plaice (12 mm: 9.2 cm, 14 mm: 10.4 cm). Total overall losses (8–10%) of target brown shrimp Crangon crangon in nets with grids were not statistically different to nets without grids. Three fishing trials, each testing a different design of grid, were done in the Humber Estuary and off the Lincolnshire coast in November–December and February–March from 1993–1995. Paired trawl deployments (12–22 tows for each grid) were done on commercial shrimp vessels towing a trawl net fitted with a grid and a standard trawl net simultaneously for 0.5–2 h. Grids were made from steel or plastics with 12 mm bar spacings and had top opening escape holes (see paper for full specifications of trawl nets and grids). Two further plastic grids with 10- and 14-mm bar spacings were also tested using a small mesh cover over the grid escape opening to collect the escaping fish.

(Summarised by: Chris Barrett)