Engineering development of flexible selectivity grids for Nephrops

Published source details Loaec H., Morandeau F., Meillat M. & Davies P. (2006) Engineering development of flexible selectivity grids for Nephrops. Fisheries Research, 79, 210-218.
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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 2002 of a seabed area in the Bay of Biscay, France (Loaec et al. 2006) found that prawn trawls fitted with an experimental flexible size-sorting escape grid caught less discarded catch (fish and invertebrates) compared to a small-mesh trawl net without a grid. Data were not tested for statistical significance. The amounts of discarded catch (that included large quantities of horse mackerel Trachurus trachurus plus debris) were lower in nets with grids in five of six hauls (with: 12–32 kg, without: 14–51 kg) and higher in one of six (with: 59 kg, without: 32 kg). The total amount of discarded catch in all hauls was 161 kg in nets with grids and 184 kg in nets without grids. In addition, grid-fitted nets caught 88% fewer (with: 114 ind, without: 950 ind) undersized individuals of the target species Norway lobster Nephrops norvegicus, but also 61% less (with: 1033 individuals, without: 2632 individuals) of marketable size. A total of six, 2.5 h paired trawl deployments were done from a research vessel, simultaneously towing a trawl net fitted with a flexible grid (polyurethane) and a conventional trawl net with a fine-mesh inner lining. The grid had 20 mm bar spacing and was fitted at a 45° angle. Full details of trawl design are provided in the original study.

(Summarised by: Leo Clarke)