SEASONAL DISTRIBUTION AND MIGRATION OF THE COMMON MACKEREL IN THE SOUTHWESTERN JAPAN SEA AND THE EAST-CHINA-SEA

Seasonal changes in the distribution of the common mackerel were examined using catch statistics of the Japanese large purse seine fishery (years of 1974-1988). Concentrations with high CPUE appeared in the southwestern Japan Sea in November-December. They expanded to the waters near Cheju island in January-April, but only remained in the southwestern Japan Sea near May. Concentrations in this sea almost disappeared in summer. The Tsushima current stock was estimated to move southwards from autumn to winter and move northwards from the wintering area after spring. Some yearly variations of the time to start migration were observed. The density index of the wintering group was proposed to describe the yearly fluctuation of this stock. It was estimated that the size of this stock has decreased since 1977, and its distribution area has also reduced. Concentrations also appeared in the middle and southern East China Sea, which was considered to belong to the East China Sea stock. Due to the lack of data, a migration pattern of this stock was presented as a preliminary result.