Size selection and release of juvenile monkfish Lophius vomerinus using rigid sorting grids

Published source details Maartens L., Gamst K.A. & Schneider P.M. (2002) Size selection and release of juvenile monkfish Lophius vomerinus using rigid sorting grids. Fisheries Research, 57, 75-88.
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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 study in 2000 of an area of seabed in the South Atlantic Ocean, off Namibia (Maartens et al. 2002) reported that fitting rigid size-sorting escape grids to a fish trawl reduced the amount of unwanted young monkfish Lophius vomerinus, relative to the retained catches. Data were not tested for statistical significance. Across four grid designs, 59–68% of the monkfish catch was released through the grids and the vast majority were fish smaller than 31 cm (data reported as length frequency distributions). In addition, of the four grids tested, fewer fish were released by the Sort-V single grid with circular openings of 115 mm (59%) and the EX-it grid with circular openings of 130 mm (61%) compared to the Sort-V single grids with circular openings of 120mm (64%) and 130 mm diameter (68%). Data were collected in February 2000 from 40 trawl deployments of 2 h and in 314–379 m depths. Four rigid sorting grids: an EX-it multiple-panel grid with circular openings of 130 mm diameter and Sort-V single grids with circular openings of 115 mm, 120 mm and 130 mm diameter, were tested in a commercial monkfish diamond mesh trawl net (see paper for specifications). Small mesh covers attached over the grids and inside the codend collected the escaped and retained catches. Fish were sorted and depending on size of catch all, or a subsample, of lengths measured.

(Summarised by: Chris Barrett)