An assessment of the Swedish grid and square-mesh codend in the English (Farn Deeps) Nephrops fishery

Published source details Catchpole T.L., Revill A.S. & Dunlin G. (2006) An assessment of the Swedish grid and square-mesh codend in the English (Farn Deeps) Nephrops fishery. Fisheries Research, 81, 118-125.
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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 trawl nets and use a square mesh instead of a diamond mesh codend Action Link
	Fit a size-sorting escape grid (rigid or flexible) to a prawn/shrimp trawl net Action Link

Fit a size-sorting escape grid (rigid or flexible) to trawl nets and use a square mesh instead of a diamond mesh codend

A replicated, paired, controlled study in 2006 of an area of seabed in the North Sea, UK (Catchpole et al. 2006) found that prawn trawl nets fitted with a rigid size-sorting escape grid and a square mesh instead of a diamond mesh codend, reduced the catch of all sizes of unwanted whiting Merlangius merlangus and the overall amounts of plaice Pleuronectes platessa, small cod Gadus morhua and small haddock Melanogrammus aeglefinus, compared to a standard trawl (no grid, diamond mesh codend). Average catch numbers of whiting of all length groups (11–41 cm) were reduced with a grid and square mesh codend (with: 0–23 fish/tow, without: 5–254 fish/tow). Average catch numbers of plaice, haddock and cod were lower for up to half of the length groups in nets with a grid and square mesh codend (plaice, with: 4–12 fish/tow, without: 1–22 fish/tow; haddock, with: 0 fish/tow, without: 4–52 fish/tow; cod, with: 0–2 fish/tow, without: 4–45 fish/tow). These included the smaller size groups of haddock and cod (see paper for data by length group). In addition, catches of marketable sizes of the target species Norway lobster Nephrops norvegicus were reduced in trawls with a grid and square mesh codend (with: 0.8–0.9, without: 1.2–2.0 baskets/trawl) but discards were also lower (with: 0.5, without: 2.4 baskets/trawl). In March 2006, a total of 10 paired deployments were made by a twin-rig vessel in the Farn Deeps Nephrops fishing ground off the coast of England. The vessel towed two trawl nets simultaneously: one 80 mm Nephrops trawl fitted with a metal grid (Swedish grid) and a 70 mm square mesh codend; and one standard 80 mm Nephrops trawl net with a 85 mm diamond mesh codend.

(Summarised by: Khatija Alliji)
Fit a size-sorting escape grid (rigid or flexible) to a prawn/shrimp trawl net

A replicated, paired, controlled study in 2005 of a seabed area in the North Sea, UK (Catchpole et al. 2006) found that prawn trawl nets fitted with a rigid size-sorting escape grid resulted in less non-target catch of most sizes of whiting Merlangius merlangus and plaice Pleuronectes platessa, but more small cod Gadus morhua and haddock Melanogrammus aeglefinus, compared to standard trawls without a grid. Average numbers of whiting (with: 25–126 fish/tow, without: 77–356 fish/tow) in the size ranges 20.6–35.5 cm (98%) and plaice (with: 0–8 fish/tow, without: 1–22 fish/tow) between 20.6–40.5 cm (91%) were lower with the grid than the standard trawl. Fewer cod of marketable size (35 cm) were caught in the trawl net with a grid (with: 0 fish/tow, without: 0–10 fish/tow), but average numbers of small cod (10.6–20.5 cm) were higher (with: 67–120 fish/tow, without: 25–64 fish/tow). More small haddock (10.6–15.5 cm) were caught with the grid (with: 20 fish/tow, without: 14 fish/tow) and catches above this size were typically similar (with: 0–12 fish/tow, without: 0–10 fish/tow). In addition, numbers of marketable sizes of the target species Norway lobster Nephrops norvegicus were greater in trawls with a grid (with: 3.8–4.4, without: 3.0–3.9 baskets/trawl) and total discards lower (with: 1.3, without: 1.7 baskets/trawl). In November 2005, a total of 12 paired deployments towing both a standard trawl net fitted with a metal grid (Swedish grid) and a standard trawl net were conducted in the Farn Deeps Nephrops fishing ground off the coast of England.

(Summarised by: Khatija Alliji)