日本近海におけるブリの資源生態に関する研究‐Ｉ ブリ来遊量の長期傾向

Abstract

The yearly changes in catches of the yellowtail Seriola quinqueradiata in the coastal waters of Japan are analyzed. The results obtained are as follows: 1) Long-term trends of fish catches from 1947 to 1986 show different patterns among regions. 2) From the age-composition of catch in each region, older fish were more often caught in the southern regions than in the northern regions of Japan, while the reverse was the case with younger fish. 3) The migration of adult fish into the waters of Japan has been decreasing since the mid-1960's, sharply in the northern regions and gradually in the southern regions. 4) However, the recruitment of young 0-1 year-old fish has remained nearly constant since 1970 along the coast of the Sea of Japan. These results suggest that the distributional/migrational range of adult fish has been in a process of reduction and restriction to the southern regions since the mid-1960s, due to the decrease in its stock size, and that an unexploited spawning stock exists near the East China Sea and reproduces most of the young fish migrating into the Sea of Japan.