Size selectivity patterns in the North-east Arctic cod and haddock fishery with sorting grids of 55, 60, 70 and 80 mm

Steel sorting grids are widely used in the North-east Arctic fisheries as excluding devices for juvenile fish. Sorting grids with four different bar spacings, 55, 60, 70 and 80 mm, were tested in sea trials during February–March 2006 and 2007. Cod and haddock were the target species. The study shows that there is little variation in the selectivity parameters when increasing bar spacing from 55 to 60 or 70 mm for haddock (2.7 cm in the l50 while the SR is fairly constant around 5 cm). For cod, no differences were found between the 55 and the 60 mm grids or the 70 and 80 mm grids, but the first two differed from the latter. The mean l50 increases from 56.08 to 73.33 cm and the mean SR from 7.46 to 14.28 cm when the bar spacing is increased from 55 to 80 mm. The selection curves move to the right and tend to lose sharpness, and the 95% confidence areas increase gradually as the bar distance of the grid is widened. The relationship between the l50 and grid bar spacing, based on this and previous studies, was determined to be linear for both cod and haddock.