Mismatch in Management: The Effect of Trawl Size and Codend Material on Size Selectivity in the Icelandic Trawl Fishery for Cod

The Icelandic fisheries management regulates mesh sizes of demersal whitefish trawls as 135 mm and sets a reference length for undersized fish. Fishing area is closed temporary if more than 25% of the cod is below 55 cm.

After observing low codend selectivity on a commercial trawler, a selectivity experiment for cod was conducted in September 2013, comparing bottom trawls of different sizes and designs, with two different codends with 135 mm mesh sizes. The codends were of PE materials of different stiffness with twine diameters of 2 x 6 mm (10.4 gm^-1) and 2 x 6.2 mm (15.85 gm^-1). There were strong interactions between trawl size and codend stiffness. Trawl size affects size selection no less than the codend. The L50's were unexpectedly low or below 37.5 cm in all cases and decreased with increasing trawl size and codend stiffness. It is of concern that those gear combinations are common for the fleet, and that the L50's are far below the reference length of 55 cm for cod. Regardless of trawl size, we conclude that the mesh size regulations are not in line with the management aims of avoiding catches of cod below 55 cm.