Using composite square-mesh panels and the Nordmøre-grid to reduce bycatch in the Shark Bay prawn-trawl fishery, Western Australia

Published source details Broadhurst M.K., Kangas M.I., Damiano C., Bickford S.A. & Kennelly S.J. (2002) Using composite square-mesh panels and the Nordmøre-grid to reduce bycatch in the Shark Bay prawn-trawl fishery, Western Australia. Fisheries Research, 58, 349-365.
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This study is summarised as evidence for the following.

	Action	Category
	Fit mesh escape panels/windows and a size-sorting grid (rigid or flexible) to a trawl net Action Link
	Fit a size-sorting escape grid (rigid or flexible) to a prawn/shrimp trawl net Action Link

Fit mesh escape panels/windows and a size-sorting grid (rigid or flexible) to a trawl net

A replicated, paired, controlled study in 2000 in an area of soft seabed in the Indian Ocean, off Western Australia (Broadhurst et al. 2002) found that the effect of prawn trawl nets fitted with square mesh escape panels and rigid grids on non-target fish catch compared to a standard net, varied with the position of the escape panel. Compared to a standard net, trawl nets with the square mesh panel located in the rear section of the codend further away from the grid, reduced the non-target catches of two of seven non-commercial, and two of three commercial fish species, by between 50–76% in number and 47–73% by weight (see original paper for species individual data). Catches of the five other species were similar between the nets. No differences in non-target catches of the 10 fish species were found between the net with a grid and panel located forward of the codend (nearer the grid) and the standard net (see original paper for species individual data). In addition, the total catch weights of the target prawns Penaeidae were reduced in both grid/panel nets, by 12–14%. In August 2000, two sets of 10 paired trawl deployments (40 min each) were done in Shark Bay using one of two designs of modified trawl and a standard trawl net (47 mm diamond mesh, no grid or panel) simultaneously. The modified trawl nets were standard nets fitted with a Nordmøre rigid grid (100 mm bar spacing) located in front of the codend, and a square mesh escape panel (47, 94 and 155 mm mesh sections) at either the rear or front section of the codend (see original paper for gear specifications). All catch was sorted, counted, and weighed.

(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 2000 of an area of sand/mud seabed in the Indian Ocean, off western Australia (Broadhurst et al. 2002) found that a prawn trawl net fitted with a rigid size-sorting escape grid did not reduce the catches of seven of seven non-commercial and commercial fish species, or the amount of overall unwanted catch (fish and invertebrates), compared to an unmodified standard trawl net. Average catch numbers of six of six non-commercial and one of one commercial fish species (see paper for individual species data) were similar in nets with a grid to nets without a grid (with: 10–284 fish/tow, without: 5–266 fish/tow) and species weights were also similar (data reported as statistical model results). Average weight of all non-target catch was similar between nets (with: 55 kg/tow, without: 58 kg/tow). In addition, the average weight of all target prawn species Penaeidae was reduced (with: 11 kg/tow, without: 13 kg/tow). In August 2000, ten 40-min paired trawl deployments were done on established prawn fishing grounds in Shark Bay. A trawl codend end fitted with an aluminium Nordmøre grid (100 mm bar spacing, 45° angle, top escape opening) was towed simultaneously with a standard codend. All codend catches were sorted, counted and weighed and the species caught in sufficient numbers analysed.

(Summarised by: Leo Clarke)