The Effect on Juvenile Haddock By-catch of Changing Cod-end Twine Thickness in EU Trawl Fisheries
Abstract:The selectivity of North Sea haddock (Melanogrammus aeglefinus) was measured for 100 mm mesh trawl cod-ends made of three different twines: 4 mm double twine used commercially until the introduction of thicker twines during the 1990’s; 6 mm double twine and 8 mm single twine proposed by the European Commission as maximum thicknesses starting in January 2000. A significant difference in selectivity was found between the 4 mm double twine and the two thicker, stiffer twines. The 50% retention length was increased by almost 4 cm when using the thinner twine. Models of the selectivity of these cod-ends have been developed, taking into account small mesh size differences and using catch size as a variable and sea state and twine size as categorical variables.
The benefits of using a thinner twine cod-end are illustrated by showing the effect on the catch of juvenile and marketable fish from a typical North Sea population of haddock. The potential increases in survival of the 2 + and 3 + year classes of such a haddock stock are estimated to be 17% and 12% respectively.
Document Type: Research Article
Publication date: 1999-01-01
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