A new shrimp trawl combination grid system that reduces small shrimp and finfish bycatch

Published source details He P. & Balzano V. (2013) A new shrimp trawl combination grid system that reduces small shrimp and finfish bycatch. Fisheries Research, 140, 20-27.
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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, Atlantic Ocean, USA (He & Balzano 2013, same experimental set-up as He & Balzano 2011 and He & Balzano 2012) found that using a different type of size-sorting escape grid system (two grids) in shrimp trawl nets reduced the capture of unwanted finfish compared to a trawl net fitted with a conventional grid design. Overall, average catch rates of all unwanted finfish species, including smaller individuals of key species of commercial importance (see paper for list of species), was reduced by 33% in the trawl net with two grids compared to one grid (two grids: 23 kg/h, one grid: 33 kg/h). In addition, overall average catch rates of the target commercial species Northern shrimp Pandalus borealis were lower with the dual-grid system (two grids: 80 kg/h, one grid: 91 kg/h), but fewer smaller shrimp (<27 mm carapace length) were caught. Data were collected from 24 comparative trawl deployments done between 13 to 24 May 2009 on shrimp fishing grounds. A commercial shrimp trawl net modified with two codends was towed for 1 h at 135–163 m depth. One codend was fitted with an experimental combination grid system made from a rope grid - a 25 mm-spaced standard (Nordmøre) grid with two-thirds of the netting around it cut away and replaced with four ropes - and an additional 9 mm-spaced polyethylene grid in front of the rope grid. The other codend was the standard Nordmøre grid, with 25 mm bar (see paper for gear specifications). Numbers, weights and lengths of individuals of the non-target finfish and target shrimp species were recorded.

(Summarised by: Natasha Taylor)