サンゴ海,タスマニア海におけるビンナガの漁況経年変化の原因について-I

海区別の釣獲率経年変化と年令組成の関係

抄録

The authors studied the monthly and annual variation of hook rate of albacore and the relation between difference of age composition by sub-areas and the annual variation of hook rate of the fish in the Coral and Tasman Seas, and obtained following results:
1. The hook rate of the fish declined in the sub-areas B, D and E from July to December, increased in the sub-areas F and G in the same period and increased from September to December after declined from July to September in the sub-area C (Figs. 2 and 3).
2. Hook rate was high in the sub-area G in 1956 and 1959, was high in the sub-areas A, D and E in 1954, 1957 and 1960, and was high in the sub-areas B and C in 1954, 1958 and 1961 (Fig. 4 and Table 1).
3. Almost all fish were six-year-olds in the sub-areas A and B, majority were five-year-olds followed by six-year-olds in the sub-areas D and E, and four-year-olds dominated occupying nearly a half in the sub-areas F and G (Fig. 5).
4. From the relation between difference of high hook rate year and that of age composition between sub-areas, it is thought that high hook rate might have been brought by dominant year class and that high hook rate might have moved to northern sub-areas as dominant year class moved to northern sub-areas.