カツヲの漁況諸因子との關係

Abstract

Some tentative studies of the fishing conditions of “Katuo”, Euthynnus vagans (LESSON), as a function of several oceanographic elements, including surface temperature, are given here. The fishing locality of “Katuo” moves from the region off Nozimazaki in May, passing off Tyosi in June, to the region off Kinkwazan in July. The paths seem to follow the warm branches of currents, which are recognizable by the tongs of isotherms either at the surfase or at the subsurface of 100m depth. The concentration of the shoals seems to be defined not only by the surface water temperature but also by the vertical distribution of vertical tem-perature gradient in the uppermost 100m layer. The paths also have close bearing to the migration of sardine shoals and to the distribution of copepoda, both being the natural food fauna for “Katuo” In the sea-region south off Kagosima Pref., the catch of “Katuo” varies with salinity throughout the periods from March to September (Fig. 6). The value of transparency and of salinity giving the mode for the catch are shown in Figs. 5 and 7.