The effect of varying cod-end circumference, inserting a ‘flexi-grid’ or inserting a Bacoma type panel on the selectivity of North Sea haddock and saithe

Published source details O’Neill F.G., Graham N., Kynoch R.J., Ferro R.S.T., Kunzlik P.A. & Fryer R.J. (2008) The effect of varying cod-end circumference, inserting a ‘flexi-grid’ or inserting a Bacoma type panel on the selectivity of North Sea haddock and saithe. Fisheries Research, 94, 175-183.
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This study is summarised as evidence for the following.

	Action	Category
	Decrease the circumference or diameter of the codend of a trawl net Action Link
	Fit mesh escape panels/windows to a trawl net Action Link

Decrease the circumference or diameter of the codend of a trawl net

A replicated, paired, controlled study in 2002 of an area of fished seabed in the northern North Sea off Norway (O'Neill et al. 2008) found that decreasing the codend circumference of a bottom fish trawl improved the size-selectivity of haddock Melanogrammus aeglefinus, and for saithe Pollachius virens in one of two cases, compared to a standard larger circumference. For haddock, the length at which fish had a 50% chance of escape was greater for both small (60 meshes) and intermediate (80 meshes) circumferences compared to the larger standard 100 meshes (small: 37–45 cm, intermediate: 33–45 cm, standard: 27–40 cm). For saithe, the length at which fish had a 50% escape likelihood was higher (41–65 cm) in the small 60 mesh circumference codend compared to the standard 100 mesh codend (40–77 cm), but the 80 mesh codend did not differ from either (40–49 cm). Data were collected from 22 paired deployments on a twin-rig trawler in August–September 2002. Diamond mesh (120 mm nominal size) codends of three circumferences (60 meshes, 80 meshes and standard 100 meshes) were tested each deployed alongside a small mesh (50 mm) trawl to measure size-selectivity. After each haul haddock and saithe number and length from each codend were recorded, and randomly sub-sampled when catches were high.

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

A replicated, controlled study in 2002 of a seabed area in the North Sea, Norway (O'Neill et al. 2008) found that a fish trawl codend fitted with a square mesh escape panel improved the size-selection of haddock Melanogrammus aeglefinus, compared to a standard trawl codend without an escape panel, and had similar size-selectivity as standard trawl codends with reduced circumferences. The length at which fish had a 50% chance of escape (selection length) was higher in a codend with an escape panel (41.8–46.6 cm) than without in a standard 100 mesh circumference codend (27.0–39.7 cm) and similar to two codends with decreased mesh circumferences (60 meshes: 37.1–44.7 cm, 80 meshes: 32.6–44.7 cm). Data were collected from 23 trawl deployments on fishing grounds west and south west of Bergen in August–September 2002 using a twin-rig trawler. Four codend types were tested: a 120 mm diamond mesh codend fitted with a Bacoma-type 110 mm square mesh panel; and three 120 mm diamond mesh cod-ends of 100 (standard), 80 and 60 open meshes in circumference (see paper for specifications). Test codends were towed alongside a small mesh (50 mm) codend.

(Summarised by: Chris Barrett)