Relative selectivity of Greenland halibut (Reinhardtius hippoglossoides, Walbaum) by trawls, longlines and gillnets

Selectivity parameters for Greenland halibut (Reinhardtius hippoglossoides, Walbaum) were calculated from trawl and gillnet catches in the Norwegian s cientific fisheries for greenland halibut. Within the chosen individual are as and seasons, our data show no trend in length distribution with depth. A trouser-trawl selectivity experiment gave an L-50 at 42 cm in a 135 mm cod ends. A selectivity analysis of the gillnets using a log normal model showe d maximum probability of retention for lengths of 46.8-73.5 cm for 140-220 mm stretched meshes. By using expected catch proportions and life history p arameters, the selectivity in longline and trawl was shown to be bell-shape d, both gears losing both the smallest and largest fish. Calculated estimat ed life-history parameters were biased by sampling gears, giving slower gro wth and larger Loo for females caught in gillnets. The maturation length (M -50) Of female Greenland halibut was largest in trawl catches, smallest for gillnet catches. The sex ratio in the gillnet catches was shown to be a di rect function of mesh size. These analyses will provide a better understand ing of possible sampling bias when sampling a stock by means of only one ty pe of gear. (C) 1999 Elsevier Science B.V. All rights reserved.