Abstract
Based on the accurate records reported from the fishing-boats, about fifty in number, distributed on our Pacific side from 1936 to 1938, N-θ. curves of “Katuo” (or the curves of the frequency of the catch of “katuo” as ordinate against the surface water temperature as abscissa) were plotted and examined (Fig. 1). (1) N-θ curve referred to the sea-district off North-eastern Japan shows asymmetrical form, with a clear maximum lying on it, which can be considered as the result of deformation of a normal curve having equal area, as plotted by a dotted line in Fig. 1. On the higher temperature side of N-θ curve, another small and some-what vague maximum is seen, which also corresponds to a smaller probability curve. The asymmetrical deviation of the curve to the lower temperature is explained by the accumulation of shoals of “Katuo” on the line of convergence (Cold Wall) corresponding to the polar front which is especially distinguished in summer. (2) In the southern, Dunan and Satunan, seadistricts, of Japan, N-θ curves are represented by the combination of two or three probability curves approximately.
