抄録
As a drift-net or a long-line is made adrift by the oceanic currents, and is scarcely influenced by the wind, it may be regarded as an excellent current-drag. If we record the positions and the instants, when the fishing-appliances of this kind are put into and hauled up from the sea, we can easily estimate the average current during their driftage. In such cases, the accurate determination of positions by aiming at the land-objects or some heavenly bodies is desirable and the time of drift should last at least about half a day in order to eliminate the tidal currents or any accidental fluctuations. These are, however, by no means difficult in practice, far easier than handling instruments such as current-meters in the open sea.
Employing such a method the writer investigated: -
(i) The currents in the Kurosiwo-area based on the records of long-line fishing of “Maguro” (Thunnus thynnus), those in Oyasiwo-area on the records of the drift-net fishing of herrings and of “Samma” (Cololabis saira), and those in the intermediate-area between Oyasiwo and Kurosiwo based on the records of the drift-net fishing of “Samma” and the long-line fishing of “Maguro” from 1928 to 1933 (Fig. 1).
(ii) The currents in the Japan Sea along the west coast of Hokkaidô estimated from the drift-net fishing of herrings from February to May every year from 1924 to 1930 (Fig. 1 and Tab. 1).
The currents thus estimated coincide well with the results obtained in other ways, proving the correctness of the method adopted (Fig. 1). Furthermore by means of this method, some conditions of fisheries, such as the catch (Fig. 2), can very conveniently be studied, correlating with the currents in question.
