The effect of twine thickness on cod-end selectivity of trawls for haddock in the North Sea

Published source details Lowry N. & Robertson J.H.B. (1996) The effect of twine thickness on cod-end selectivity of trawls for haddock in the North Sea. Fisheries Research, 26, 353-363.
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This study is summarised as evidence for the following.

	Action	Category
	Use a different twine type in a trawl net Action Link

Use a different twine type in a trawl net

A replicated, controlled study in 1993 in a seabed area in the North Sea, UK (Lowry & Robertson 1996) found that using a thinner twine thickness in a fish trawl codend improved the size-selectivity of haddock Melanogrammus aeglefinus compared to thicker twine. The length at which haddock had a 50% chance of escaping was lower with thinner twine thickness (thin: 25 cm, thick: 24 cm). The authors noted the difference would be expected to be larger if the two codends had been of the same mesh size. Data were collected in the Moray Firth off Fraserburgh in June 1993 from 13 experimental trawl deployments by a commercial trawler in depths of 91–100 m (2 h duration, 2.5 kn speed). Separate deployments of two codends with different twine thicknesses were tested, 3.5 mm (7 hauls) and 5.2 mm (6 hauls). Measured mesh size was 95 mm for the thin twine and 100 mm for the thick twine. A small mesh cover attached over each codend collected fish escaping through the meshes. Codend and cover catches were recorded, and haddock lengths measured.

(Summarised by: Chris Barrett)