Long-term Fluctuations in Abundance of the Yellowtail Immigrants in the Coastal Areas of Japan

Abstract

We analyzed yearly changes in catches of the yellowtail Seriola quinqueradiata in set net fisheries in the adjacent waters of Japan and obtained the following results.
1) Long-term trends in fish catches show different patterns between growth stages.
2) The abundance of adult fish migrating into coastal areas of Japan has been decreasing since the 1950's, sharply in the northern (lower water temperature) regions and gradually in the southern (higher water temperature) regions.
3) However, young fish migrating into the waters of Japan has not been decreasing con-tinuously since the 1950's, and especially those migrating into southern coastal areas of Japan have increased since the mid-1970's.
From these results, we conclude that the distributional/migrational range of adult fish has been reduced and restricted to southern regions, due to a decrease in its stock size, and that the distributional range of young fish has also shifted toward the southern regions.