The spurdogs in the North Sea area in the Norwegian fishery and observations on changes in migration pattern.
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The Norwegian fishery of spurdog (Squalus acanthias L.), which started in 1930, has played a dominant part in the fishery for this species in Europe. During 1963-1968 a change occured in the behaviour of the spurdog stock. The spurdogs left the traditional fishing grounds, and this lead to a depression in the Norwegian fishery. New concentrations were discovered in the southern North Sea during the autumn 1968. Several tagging experiments, 1975-1979, indicate that the spurdogs in this area migrate to the area north of Scotland during the spring. Recaptures from taggings 1959-1966 together with information on Scottish spurdog catches during 1947- 1957, indicate that the spurdogs in the southern North Sea belong to the Scottish-Norwegian spurdog stock. During the last two years the Norwegian longline fishery for spurdogs has been greatly reduced. Length distributions indicate that maturing and mature females which constitute the main part of the Norwegian catch, were heavily reduced in numbers from 1975-1979. Research should be intensified to establish a basis for international regulation of the spurdog fishery.