Population parameters of the witch flounder, Glyptocephalus cynoglossus (L.) (Pisces: Pleuronectidae), from Malangen, northern Norway

Abstract

The witch, Glyptocephalus cynoglossus (L.), is one of the commonest flatfish caught in the prawn trawl fisheries along the Norwegian coast, but despite commercial interest abroad, few are landed. There is a marked lack of published details of the population biology of witch in Norwegian waters. Accordingly, witch were sampled in November 1986 and February 1987 with a demersal prawn trawl at two localities (Aglapsvik and Hekkingen) from Malangen, northern Norway. Analyses revealed a 1:1 sex ratio up to approximately 9 years of age. There was a preponderance of females among older fish. Annual rates of instantaneous total mortality ( Z) varied from 0.24 to 0.76, depending on sex, locality and age. Growth rates (total length) of males and females were not found to be significantly different at Aglapsvik, while females had significantly greater rates of growth at Hekkingen. Von Bertalanffy growth function (VBGF) parameters for L ∞ and K varied from 39.3 to 46.9, and 0.15 to 0.23 respectively. Weight-length relationships were calculated and compared for male and female fish at the two localities. The data are compared and discussed with regard to knowledge of the biology of witch from other areas, especially Canada.