The selectivity of the Swedish grid and 120mm square mesh panels in the Scottish Nephrops trawl fishery

Published source details Drewery J., Bova D., Kynoch R.J., Edridge A., Fryer R.J. & O’Neill F.G. (2010) The selectivity of the Swedish grid and 120mm square mesh panels in the Scottish Nephrops trawl fishery. Fisheries Research, 106, 454-459.
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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 prawn/shrimp trawl net Action Link
	Fit mesh escape panels/windows to a trawl net Action Link

Fit a size-sorting escape grid (rigid or flexible) to a prawn/shrimp trawl net

A replicated, paired, controlled study in 2009 in two areas of seabed in the North Sea, Scotland (Drewery et al. 2010) found that prawn trawls fitted with a rigid size-sorting escape grid caught fewer unwanted fish species compared to an unmodified reference trawl. A trawl net fitted with a grid caught lower overall numbers of six of six unwanted fish species (hake Merluccius merluccius, cod Gadus morhua, haddock Merluccius aeglefinus, whiting Merlangius merlangus, plaice Pleuronectes platessa and witch Glyptocephalus cynoglossus) than the unmodified trawl (data reported as statistical model outputs). In addition, overall catch rates of the target species Norway lobster Nephrops norvegicus were similar between trawl nets, but fewer lobster of legal landing size (> 41 cm) were caught in nets with a grid (data reported as statistical model results). In March and July 2009, a total of 22 paired trawl deployments were carried out in the South Minch and Fladen Grounds near Scotland, respectively. One trawl net (80 mm codend) fitted with a 1.52 × 0.36 m aluminium grid (Swedish grid) was towed simultaneously with a conventional trawl net with a small-mesh (40 mm) codend. The grid had 35 mm bar spacing, top escape opening and was positioned at a 45° angle 13 m in front of the codend. Trawls were deployed for 3–3.5 hours in depths 108–139 m and all catch counted, and lengths measured.

(Summarised by: Leo Clarke)
Fit mesh escape panels/windows to a trawl net

A replicated, controlled study in 2009 in two areas of seabed in the North Atlantic Ocean off Scotland, UK (Drewery et al. 2010) found that prawn trawl nets fitted with a square mesh escape panel typically reduced the catches of unwanted small commercially targeted roundfish compared to a small-mesh control trawl net without a panel, and for flatfish, the effect depended on panel position in the net. Data were reported as relative catch ratios and statistical test results. For both panel positions (6–9 and 12–15 m away from the codend), overall catch rates of smaller sizes of hake Merluccius merluccius, Atlantic cod Gadus morhua, haddock Melanogrammus aeglefinus, and whiting Merlangius merlangus were lower than the control net. Fewer small plaice Pleuronectes platessa were caught in the 6–9 m panel but more were caught in the 12–15 m panel net relative to the control. For witch Glyptocephalus cynoglossus, more were caught in the 6–9 m panel and similar numbers were retained in the 12–15 m panel net. Overall catch rates of target Norway lobster Nephrops norvegicus under 37 mm were reduced in both panel nets and rates of larger, legally sized Norway lobster (≥39 mm) were similar. In 2009, paired trawl deployments were carried out in the South Minch (July) and Fladen Grounds (March) around Scotland. Thirty-two twin-trawls were undertaken, simultaneously towing a test trawl net fitted with a 120 mm square mesh panel, 3.1 × 1.0 m and 80 mm diamond mesh codend, and a conventional trawl net with a small (40 mm) mesh codend. Fifteen trawl deployments were done with the panel positioned 6–9 m ahead of the codend and 17 with it positioned 12–15 m ahead of the codline. Trawl nets were deployed for 3–3.5 hours in 108–139 m depths and all catch counted and measured.

(Summarised by: Leo Clarke)