太平洋東部赤道付近におけるメバチの漁況経年変化の原因について-V

Abstract

The author compared the distribution of surface water temperature and transparency between high temperature period (Feb. to July) and low temperature period (Aug. to Jan.) and between high temperature year (1957 to 1960) and low temperature year (1961 to 1963) in the eastern tropical Pacific Ocean, lat. 20°N to 20°S and long. 100°W to 150°W, and got the following results: 1) There were two colder waters in this area, one of which is in northern area north of lat. 10°N or 15°N and another of which is in southern area south of lat. 5°N. The south edge of the northern colder water moved toward south in high temperature period and the southern colder water extended toward west in low temperature period (Figs. 3 and 4). 2) It is thought that the surface water temperature in the area from lat, 10°N to 10°S is influenced by the southern colder water. 3) Shallower transparency water corresponded to the colder water and deeper transparency water corresponded to the warmer water in the area of lat. 10°N to 10°S and long. 100°W to 150°W, and the shallower transparency water extended toward west in the low temperature period (Fig. 5). 4) The colder water and shallower transparency water extended in the low temperature year in the area of lat. 10°N to 10°S and long. 100°W to 150°W. 5) It is supposed that these phenomena were brought about by up-welling in the equatorial area and that the up-welling brought up so much nutrient salts that larvae of big-eyed tuna could have much food. These phenomena decreased the death rate of the larvae and so the dominant year class of the fish appeared.