Evaluation of a simple means to reduce discard in the Kattegat-Skagerrak Nephrops (Nephrops norvegicus) fishery: commercial testing of different codends and square-mesh panels

Published source details Krag L.A., Frandsen R.P. & Madsen N. (2008) Evaluation of a simple means to reduce discard in the Kattegat-Skagerrak Nephrops (Nephrops norvegicus) fishery: commercial testing of different codends and square-mesh panels. Fisheries Research, 91, 175-186.
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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
	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
	Use a larger mesh size Action Link

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

A replicated, paired study in 2003 of seabed areas in the Kattegat and Skagerrak, Northern Europe (Krag et al. 2008) found that changing the position of a square mesh escape panel in a Norway lobster Nephrops norvegicus trawl net did not reduce the catches of unwanted cod and other fish. The total number of small unwanted cod and the weight of other unwanted fish caught were similar in a trawl with a square mesh panel in the extension piece (ahead of the codend) compared to a square mesh panel in the middle of the codend (cod: 420–423 fish, all other fish: 1,567–1,590 kg). The total number of Norway lobster caught was lower in the trawl with a square mesh panel in the middle of the codend compared to the square mesh panel at the front of the codend (middle: 16,458, front: 19,735 lobsters). In August-September 2003, a total of 24 experimental trawl deployments were conducted in the North Sea by a vessel towing twin 80 mm diamond mesh trawl net codends. One of the two nets had a 90 mm square mesh panel in the top panel of the extension section of the codend (6–9 m from end), and the other had an identical 90 mm square mesh panel in the centre (3–6 m) of the top panel of the codend. Tow duration was 7 hours at a speed of 2.5 knots. All fish were identified and weighed, and the most abundant species were counted.

(Summarised by: Khatija Alliji)
Modify the configuration of a mesh escape panel/window in a trawl net

A replicated, paired study in 2003 on fishing grounds in the Kattegat and Skagerrak, northern Europe (Krag et al. 2008) found that increasing the mesh size of a square mesh escape panel in the codend of a Norway lobster Nephrops norvegicus trawl net did not typically reduce the amount of unwanted fish. For six of eight target fish species, numbers of unwanted small fish were similar between mesh sizes of the escape panel (90 mm: 391–1,161: 120 mm: 275–666) and lower with the larger mesh size for two species (90 mm: 188, 120 mm: 52). Weight of other unwanted fish catch was similar between escape panel mesh sizes (90 mm: 1,642 kg, 120 mm: 1,833 kg). In addition, nets with a larger escape panel mesh size had a lower overall number (9,739) and a lower number of small Norway lobster (5,168) compared to the smaller mesh size (overall: 10, 738, small: 6,175). In August-September 2003, two diamond mesh codends were tested, one fitted with a 90 mm mesh square mesh escape panel and one with a 120 mm square mesh escape panel. A total of 20 paired trawl deployments were done on a twin-trawl fishing vessel. Catches were sorted into commercial (lengths and weights) and non-commercial (weights) categories.

(Summarised by: Khatija Alliji)
Fit mesh escape panels/windows to a trawl net

A replicated, paired, controlled study in 2003 of an area of seabed in the Kattegat and Skagerrak, northern Europe (Krag et al. 2008) found that fitting a square mesh escape panel to the codend of a prawn trawl did not typically reduce the catches of undersized and discarded fish, compared to a trawl net without an escape panel. Total catch numbers of undersized fish were lower for two of eight species (see paper for list of species) in panel nets (with: 46–748, without: 86–1,017), similar for five species (with: 20–321, without: 20–307; for three species, total numbers across all sizes reported only) and higher for one (with: 41, without: 22). In addition, catch number of target Nephrops norvegicus below minimum landing size was reduced in panel nets (with: 10,479, without: 11,966) and was similar above (with: 6,771, without: 6,916). Data was collected in August and September 2003, from 24 trawl deployments by a single vessel towing two trawl nets side by side. One side was a 78 mm diamond mesh codend fitted with a 93 mm square mesh panel (93 mm) in the top panel of the extension section; the other side was a 78 mm diamond mesh codend with no escape panel. Side of vessel each net was towed was swapped every sixth tow. Tow duration averaged 7 h at 2.5 knots. Codend catches were sorted into commercial and non-commercial portions, counted and weighed.

(Summarised by: Khatija Alliji)
Use a larger mesh size

A replicated, paired, controlled study in 2003 in an area of seabed in the Skagerrak and Kattegat, Northern Europe (Krag et al. 2008) found that increasing the mesh size of a diamond mesh prawn trawl codend reduced the catches of undersized and discarded fish compared to a conventional smaller mesh size. For seven of seven commercial species, total catch numbers of undersized fish were reduced with the larger mesh size by between 59–92% compared to the standard mesh size (large: 1–130 fish, standard: 12–313 fish; see paper for species individual data). The total weight of other discarded fish was also lower with the larger mesh (large: 445 kg, 903 kg). Data were collected in August and September 2003, from 21 paired trawl deployments of an experimental 120 mm diamond mesh codend and an industry standard 90 mm diamond mesh codend. Deployments used a three-warp towing system and codends were swapped between sides of the vessel every sixth tow. Average tow time was 7 h at a speed of 2.5 knots.

(Summarised by: Khatija Alliji)