Temporal variation of seasonality of egg production and the spawning biomass of Pacific anchovy, Engraulis japonicus, in the southern waters of Koreain 1983-1994

Embryonic mortality, egg production and the spawning stock biomass of Pacif ic anchovy, Engraulis japonicus, off Southern Korea during 1983-1994, and t heir biological response to oceanographic features in spring and summer, we re analysed. The instantaneous mortality rate (IMR) of embryonic stages dec reased in spring and increased in summer, with a range of 0.33-1.23 day(-1) in spring and 0.78-1.69 day(-1) in summer. Egg production in summer was th ree times that during spring and production was low in the late 1980s. Mean lengths of yolk-sac larvae and adult females were greater in spring than i n summer, whereas spawning fraction and spawning stock ratio (spawning biom ass:adult biomass) were lower in spring than summer. Estimated mean spawnin g stock biomass ranged from 141 x 10(3) to 380 x 10(3) MT in spring and fro m 221 x 10(3) to 557 x 10(3) MT in summer. Statistically, the seasonal and long-term trends of embryonic mortality, egg production and spawning stock biomass of Pacific anchovy can be explained largely by spring warming, summ er cooling and by less abundant zooplankton in the late 1980s.