標識放流結果からみた本邦太平洋沿岸のブリの回遊-II

漁獲統計,体長組成からの検討

抄録

In order to evaluate the results of the tagging experiments of yellowtails, Seriola quinqueradiata, which have been presented in the previous paper, the seasonal variation of catch and the length composition of each age group are analysed. The catch in the Tohoku Region (north of Chiba Prefecture) shows two waves, one from April to September corresponding to the northward migration and the other from October to March corresponding to the southward migration. A peak of the catch of the large sized fish from January to May in the Tokai-Nankai Region (south of Chiba Prefecture) indicates the active southward migration of the adults in the spring season. The length compositions show a clear difference in growth between the two regions over the ages from the latter half of I-age to early III-age. This difference is obscured for the fish of III-age and older. Such a phenomenon may be explained by segregation among young fish and intermingling among adults, which have been suggested by the tagging experiments. The conclusions obtained from the tagging experiments of yellowtails are endorsed by these analyses of the catch and length compositions.