西南太平洋の大型ビンナガとその鉛直分布との関係

概要

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It has been known that the large-sized albacore appear in the western South Pacific Ocean during summer, and its hooked depth is generally deeper than the other tunas. How-ever, there are many unknown facts which are related to differences in the biological charac-teristics of albacore at various swimming depths. The authors studied the albacore and its vertical distribution, using data collected by means of the long-line and the vertical long-line. The results are summarized as follows: 1) Length frequency distribution of the albacore showed similarities for every year. 2) Most of the fish were mature during the season in this area. 3) The sex ratio is nearly ?? 3: ?? 7 for every year. 4) The albacore inhabited over a wide range in the vertical zone, and it was not related to the growing stage. However, it seemed that mature fish tend to be distributed in the deeper water layers.