ミッドウェー・ハワイ諸島周辺とマーシャル・ファンニング諸島周辺に於けるメバチの漁況と体長の周期変化,両周期変化間及び両漁場間の関係

Abstract

1) Fishing condition (rate-of-catch) in sub-areas, A, B and C (Fig. 1) changes periodically; in sub-areas A and B good fishing season is from December to February while in sub-area C nice fishing period lasts from December up to June of next year. 2) Fork-length composition (fork-length frequency) in sub-areas A, B, C and D changes periodically (Fig. 3). In sub-areas A and B, young stage fish occupy most of the frequency from December to March in odd years, small-sized fish do so from December to March in even year, and large-sized fish do so from April to November. In sub-areas C and D, medium-sized fish are dominant from July to December and so are large-sized fish from January to June in the body-length formation. 3) Most part of the frequency is occupied by young stage or small-sized fish in period of nice fishing and by large-sized fish in period of poor fishing in sub-areas A and B. Majority of the frequency is occupied by large-sized fish in period of good fishing in subarea C and by medium-sized fish in period of poor fishing. 4) It is presumed that fish group that has been spawned and has grown in sub-areas C and D is recruited to young stage or small-sized fish groups in sub-areas A and B, young stage or small-sized fish groups in sub-areas A and B are recruited to medium-sized fish group in subareas C and D, and large-sized fish groups in sub-areas A and B and in those C and D interchange with each other.