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-I

Abstract

The authors studied the monthly and annual variation of hook rate (catch per 100 hooks) of big-eyed tuna in the tropical eastern Pacific Ocean. From the study, the following results are obtained: 1) Monthly variation of hook rate of the fish in the northern area than the equator differed by years, that is, there were years in which hook rate was high from March to September, years in which it was high in March and September and years in which it declined from March to September. The hook rate of the fish in the southern area than the equator was high in March and November but there are both years in which the March hooking-rate was higher than November hook rate and in which the November hook rate was higher than March hook rate. 2) The hook rate in the northern area than the equator was high in 1955 and 1960. In the southern area than the equator, the hook rate was high in sub-area SW in 1956, and 1961, in sub-area SM in 1958 and 1961, and in sub-area SE in 1958 and 1960, respectively. 3) In years before 1960, the hook rate in the eastern sub-area was higher than that in the western sub-area.