Stock size fluctuations in chub mackerel (Scomber japonicus) in the East China Sea and the Japan/East Sea

The stock size of chub mackerel ( Scomber japonicus ) in the East China Sea and the Japan/East Sea has shown a continuous decrease, with fluctuations, from 1975 to 1990. After a remarkable increase in 1992–96, the stock size fell to its lowest level in 1997–99. The spawning success (number of recruits/spawning biomass) fluctuates periodically with a period of several years, although there are no clear relationships between the spawning biomass and the number of recruits. Spawning success was inversely correlated with sea surface temperature (SST). On the contrary, the catch amount and the catch per unit effort (CPUE) of spotted mackerel ( Scomber australasicus ) has increased since 1997.