北西部太平洋に於けるビンナガマグロ漁場動態に関する研究-1-
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概要
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Albacore schools moving southward in the winter-spring period in the Northwest Pacific Ocean adjacent to Japan are divided into the surface swimming tunas by pole fishing, and the deep swimming tunas by long line fishing. We know that the migration of albacores in the winter-spring period is the seasonal migration. Now, from the analysis of the fishery reports on the albacore fishing for the period 1951-1956 regarding the seasonal migration of albacore tunas between the latitudes 25° N and 40° N, and the longitudes 130° E and 180° E, the principal information obtained by this work are as follows :- 1) It is found that the optimum temperatures in the albacores' "life zones" are variable, but there is a tendency to show a higher optimum temperature for large-sized tunas, and a lower temperature for small-sized tunas, seeing from their body weights (Fig. 2), and the water zones under 16.3°C and over 22.8°C are regarded as "environmental resistance"*, or "environmental barrier", which prevent the albacores' migration, and also the formation of fishing grounds, in which the present methods of pole and long line fishing are exercised (Fig. 2). 2) It seems that albacores moving southward in winter, and northward in early spring have the "life zones", which indicate the different optimum temperatures, namely, the higher temperature for large-sized tunas, and the lower temperature for small-sized tunas, 3) Paragraph 2 makes it clear that principally in the North Pacific Current Area, northward the Subtropical Convergence Line, the "habitat segregation" is also made for albacores as emphasized by Dr. IMANISHI and Dr. KAGI (Fig. 2, Fig. 3). 4) It can be said that the large-sized albacores migrating southward in winter precede the small-sized albacores, and vice versa in spring. * Include a general Idea of the resistance in the Science of electricity.
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