Norske pigghåundersøkelser i 1963
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- Fisken og havet (1958- ) 
The present article is an account of the Norwegian investigations of the spur-dog in 1963. The results of the tagging experiments are considered with respect to the distribution of the recaptures in time and localities. A new feature in recent years is the regular long lining for spur-dog on the South-Western part of the Norwegian coast in the autumn which last year (1963) extended into the Skagerak (Oslofjord). Tag returns indicate that the fish belong to the common (North European) oceanic stock. From a quantitative analysis of the tagging data it appears that the estimate of the average total instantaneous mortality rate in the years 1960-1963 amounts to 0. 72, and this high figure is interpreted as a danger signal. A certain measure of the catch per unit of effort was obtained from various dealers by comparing the landings with the amount of bait used. The series, comprising the years 1957-63, shows a heavily declining stock. Using Schaeffer's model for stock assessment, the obtained series of catch/effort, and the catch statistics from Northern Europe, a maximum equilibrium catch of about 50 000 tons is found. This level was, practically speaking, reached in 1961. The available data are not considered sufficient for a precise stock assessment; but one important fact does emerge: The present exploitation of the stock of Squalus acanthias in European waters is undoubtedly very high.