IT is well known that the annual yield of the sea fisheries varies very much from year to year. An example of such variation is shown in Fig. 1 in which the broken curve shows the number (in millions) of skrei—spawning cod (Gadus callarias)—caught in the Lofoten fishing area of northern Norway in the years 1885–1958. It is obvious that such fluctuations make the planning of the fishing industry very difficult and that reliable forecasts would be helpful, even if they are only rough approximations.