The effect of grid spacing on size selectivity of shrimps in a pink shrimp trawl with a dual-grid size-sorting system

Published source details He P. & Balzano V. (2012) The effect of grid spacing on size selectivity of shrimps in a pink shrimp trawl with a dual-grid size-sorting system. Fisheries Research, 121-122, 81-87.
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This study is summarised as evidence for the following.

	Action	Category
	Use a different design or configuration of size-sorting escape grid/system in trawl fishing gear (bottom and mid-water) Action Link

Use a different design or configuration of size-sorting escape grid/system in trawl fishing gear (bottom and mid-water)

A replicated, paired, controlled study in 2009 of a fished area of seabed in the Gulf of Maine off Portland, USA (He & Balzano 2012, same experimental set-up as He & Balzano 2011 and He & Balzano 2013) found that using a different configuration of size-sorting escape grid in a dual-grid system (decreased bar spacing in a secondary grid designed to reduce the catches of small target shrimp) had no effect on the capture of non-commercial target finfish, compared to a standard bar spacing. There were no differences in average catch rates of the three main unwanted finfish species and all other unwanted finfish catch combined between a narrower 9 mm grid bar spacing and a standard 11 mm grid bar spacing: silver hake Merluccius bilinearis (narrow: 3.8 kg/h, standard: 4.3 kg/h), long rough dab Hippoglossoides platessoides (narrow: 1.3 kg/h, standard: 1.2 kg/h), witch flounder Glyptocephalus cynoglossus (narrow: 0.4 kg/h, standard: 0.3 kg/h), and all other finfish (narrow: 0.4 kg/h, standard: 0.5 kg/h). In addition, average catch rate of the commercial target species Northern shrimp Pandalus borealis were similar (narrow: 82.7 kg/h, standard: 77.8 kg/h). Data were collected in between 20 April and 2 May 2009 from 24 comparative deployments (1 h) using a commercial shrimp trawl net modified to have two codends. In each codend, one of two rectangular size-sorting grids with different grid spacing (9 mm and 11 mm) were fitted. In both codends, the size-sorting grid was installed in front of a standard grid (Nordmøre), creating a dual-grid system (see paper for gear specifications). Catches in each codend were sorted and weighed by the main non-target finfish and commercial target shrimp species.

(Summarised by: Natasha Taylor)