Selectivity experiments with sorting grids in the North Sea brown shrimp (Crangon crangon) fishery

Published source details Polet H. (2002) Selectivity experiments with sorting grids in the North Sea brown shrimp (Crangon crangon) fishery. Fisheries Research, 54, 217-233.
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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 study in 1996–1997 of bottom fishing grounds in the North Sea off Belgium and the Netherlands (Polet 2002) found that shrimp trawl nets fitted with a rigid size-sorting escape grid (a Nordmøre grid) reduced the overall amount of fish catch and allowed the majority of undersized fish to escape capture. Across all trials, overall catch numbers of fish species were reduced by 72–75% in nets with a grid compared to without. For four of four species (plaice Pleuronectes platessa, sole Solea solea, whiting Merlangius merlangus and cod Gadus morhua) high percentages of the fish escaping through the grid opening were below the minimum landing sizes (data presented as length frequency distributions and selection curves). In addition, catches of undersized and marketable brown shrimp Crangon crangon were reduced by 17–45% and 15% respectively. Trawl deployments were made on a research vessel in November 1996 (24 tows) and during three trips on a commercial trawler in July and September 1997 (10 tows). An 8 m commercial shrimp beam trawl net was fitted with an 80 × 60 cm Nordmøre grid and top escape opening. The grid had 12 mm bar spacing in November 1996 and 14 mm spacing subsequently. Covers retained any catch passing through the codend and grid escape opening. All catch (codend and covers) was sorted, counted and lengths recorded. Full trawl details are given in the original study.

(Summarised by: Leo Clarke)