Stock structure of cod in the Møre area. In: The propagation of cod Gadus morhua L.: an international symposium, Arendal, 14 - 17 June 1983
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Recently several research projects have involved studies of cod in the Møre area. Due to a common sampling programme a large number of individual fish have been classified for biological and genetical characters. The genetical study included analyses of mature fish, juveniles and eggs/yolksac larvae, and all samples were analysed for polymorphic proteins by using electrophoresis combined with selective staining methods. A significant amount of heterogeneity, expressed as variation in genotype distributions and allele frequencies, was observed among cod samples from this area, suggesting a rather complex stock structure. Samples which were taken during spawning consisted of a mixture of Arctic and coastal cod. Some of these samples permitted comparisons between biological and genetic data. The correlation between otolith structure and the allele frequencies for the enzymes analysed was not as significant as in earlier studies on blood factors and blood proteins. Significant differences between the two groups of cod were detected for two proteins (lactate dehydrogenase and haemoglobin), confirming the results from earlier genetical studies of cod in this area. The variation observed in different samples of coastal cod was very complex and difficult to interpret in terms of a reliable stock model. At present, however, the genetical data on spawning samples of coastal cod indicate a distinct stock in the Smøla region. In the Sunnmøre region the preliminary analyses of cod eggs taken on the main spawning ground at different times suggest more than one spawning group. This new sampling approach seems to be very useful in studies of fish gene pools. With regards to the stock ' structure of coastal cod in this area, we feel that genetic analyses of cod eggs on locally distributed spawning grounds will provide the most reliable information.