Fluctuations in Year-class Strength of Japanese Spanish Mackerel in the Central Seto Inland Sea.

Abstract

The abundance of larval and juvenile Japanese Spanish mackerel Scomberomorus niphonius in Hiuchi-nada, the central part of the Seto Inland Sea, and its adjacent waters, was investi-gated by net sampling from 1983 to 1988. The relationships between larval/juvenile abundance, CPUE of subsequent 1-year-old fish and oceanographic conditions were examined. There was a significant, positive correlation between the abundance of juveniles and the CPUE of subsequent 1-year-old fish, although no such correlation occurred between postlarval abundance and either the abundance of juveniles or the CPUE of subsequent 1-year-old fish. This indicates that significant mortality occurs throughout the larval stages and that year-class strength seems essentially determined by the juvenile stage. A strong year-class seems to occur when the boundary between stratified Hiuchi-nada, the spawning area, and vertically well mixed adjacent regions becomes obscure in June