Square mesh panels in demersal trawls: some data on haddock selectivity in relation to mesh size and position

Published source details Graham N. & Kynoch R.J. (2001) Square mesh panels in demersal trawls: some data on haddock selectivity in relation to mesh size and position. Fisheries Research, 49, 207-218.
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This study is summarised as evidence for the following.

	Action	Category
	Modify the configuration of a mesh escape panel/window in a trawl net Action Link
	Fit mesh escape panels/windows to a trawl net Action Link

Modify the configuration of a mesh escape panel/window in a trawl net

A replicated, controlled study in 1998 of a fished area of seabed in the North Sea, off Scotland, UK (Graham & Kynoch 2001) found that one of two square mesh escape panels located in the codend of a trawl net improved haddock Melanogrammus aeglefinus size-selectivity compared to a panel located in the extension piece or using no panel, but increasing the mesh size of the codend panel had no effect. The length at which haddock had a 50% chance of escaping (selection length) was greater with a square mesh panel of 80 mm mesh located in the codend of the trawl (26 cm), compared to an 80 mm square mesh panel located in the extension piece ahead of the codend (23 cm), and no panel fitted (23 cm). Haddock selection length in a codend panel with a larger mesh size of 100 mm was not significantly higher than the other three cases (30 cm). The authors noted this was probably due to the low catch rates with the 100 mm mesh window. Trials were conducted from a commercial fishing vessel in June 1998, using a twin trawl net. On the starboard side, nets with a 100 mm diamond mesh codend fitted with either a 100 mm square mesh panel, an 80 mm square mesh panel, an 80 mm square mesh panel in the 100 mm diamond mesh extension, or no panel were deployed. A trawl net with a 40 mm codend was towed on the port side. Full details of the trawl designs are provided in the original paper. In total, 16 valid trawl deployments of 60–210 min were completed at 2.6–3.3 knots and 70–81 m depth. Fish were identified and lengths measured.

(Summarised by: Chris Barrett/Natasha Taylor)
Fit mesh escape panels/windows to a trawl net

A replicated, paired, controlled study in 1998 on commercial fishing grounds in the North Sea, off Scotland, UK (Graham & Kynoch 2001) found that fitting a square mesh escape panel to a bottom trawl net improved the size selectivity of haddock Melanogrammus aeglefinus in one of two panel positions, compared to a net without a panel. The estimated length at which haddock had a 50% chance of escape was greater with a square mesh panel positioned in the codend (25.7 cm) than without a panel (23.0 cm), and similar when positioned in the extension piece in front of the codend (22.8 cm). In addition, increasing the mesh size of the square mesh escape panel to 100 mm from 80 cm resulted in a selection length of 30.28 cm, but too few fish were retained to test statistically. In June 1998, trials were done 45 miles east of Aberdeen from a commercial fishing vessel using a twin-trawl. One of four test nets was fished on one side of the trawl and a small mesh (40 mm) codend net on the other side. Test nets were all 100 mm diamond mesh codends: two with an 80 mm square mesh panel positioned in either the codend or extension piece; one with a 100 mm square mesh panel; and one without a panel. Sixteen valid deployments were made. Codend catches were sorted separately and lengths of all the haddock measured.

(Summarised by: Chris Barrett)