The effects of Nordmøre-grid bar spacings on catches in a Brazilian artisanal shrimp fishery

Published source details Silva C.N.S., Broadhurst M.K., Dias J.H., Cattani A.P. & Spach H.L. (2012) The effects of Nordmøre-grid bar spacings on catches in a Brazilian artisanal shrimp fishery. Fisheries Research, 127-128, 188-193.
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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
	Fit a size-sorting escape grid (rigid or flexible) to a prawn/shrimp trawl net 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 2010 of a sandy seabed area in the Atlantic Ocean, off Brazil (Silva et al. 2012) found that using a different configuration of size-sorting escape grid (decreased bar spacing) in shrimp nets in a traditional canoe-trawl fishery did not reduce the total catches of non-target fish compared to a standard bar spacing. The average catch weight of all ray-finned fish (Teleostei) combined was similar between narrower grid bar spacings (20 mm and 17 mm) compared to the standard 24 mm (17 mm: 1.0 kg/30 min, 20 mm: 1.3 kg/30 min, 24 mm: 1.2 kg/30 min). In addition, commercial target catches of seabob shrimp Xiphopenaeus kroyeri were similar between grid bar spacings (17 mm: 5.5 kg/30 min, 20 mm: 5.0 kg/30 min, 24 mm: 5.5 kg/30 min). Data were collected in April–June 2010 from 24 paired trawl deployments on a powered fiberglass canoe rigged with two identical trawl nets (26 mm codend). One trawl was fitted with a plastic grid (Nordmøre type) of one of three different bar spacings: 17 mm, 20 mm and an existing 24 mm. The other trawl had no grid. The grid trawls were alternately compared against each other and the no grid trawl (see original paper for gear specifications). Codend catches were separated by groups of organisms and the numbers and weights of each group recorded.

(Summarised by: Leo Clarke)
Fit a size-sorting escape grid (rigid or flexible) to a prawn/shrimp trawl net

A replicated, paired, controlled study in 2010 of a sandy seabed area in the Atlantic Ocean, off Brazil (Silva et al. 2012) found that shrimp trawl nets fitted with rigid size-sorting escape grids (Nordmøre) did not catch fewer unwanted fish in a canoe-trawl fishery, compared to conventional trawls with no grids, regardless of grid bar spacing. For three of three grid bar spacings, the average catch weight of all unwanted fish (see paper for list of species) was similar between trawl nets (grid: 1.0–1.3 kg/30 min, no grid: 1.2 kg/30 min). Numbers of four of four fish species with sufficient data were similar between nets (grid: 8–55 fish/30 min, no grid: 6–35 fish/30 min), but trawls with grids retained smaller sizes of two of those species (grid: 8.0–8.4 cm, no grid: 8.9–9.0 cm). In addition, there was no significant difference in the weights of retained target seabob shrimp Xiphopenaeus kroyeri catches (grid: 5.0–5.4 kg/30 min, no grid: 4.8 kg/30 min). In April–June 2010, data was collected from 24 paired deployments of each of six net pairings, towed in <15 m depth by a motorized canoe rigged with two identical trawls. Three conventional trawl nets were fitted with aluminium Nordmøre grids with 17-, 20- or 24 mm bar spacings and tested against each other and against one conventional net without a grid (see paper for specifications). Codend catches were counted and weighed by species.

(Summarised by: Leo Clarke)