The Yearly Fluctuation of Survival Indices before and after Shirasu, the Larval Stage, of Japanese Sardine from 1979 to 1992 off the Pacific Coast of Japan

Abstract

We investigated the yearly fluctuation of survival indices before and after shirasu (post larval Japanese sardine) stage, from 1979 to 1992, comparing the relative abundance of shirasu with the annual egg production and with the year-class strength of Japanese sardine off the Pacific coast of Japan. The relative abundance of shirasu was estimated, using the catch data from the shirasu boat seine in Enshu-nada and Atsumi-gaikai area, off Shizuoka and Aichi Prefecture, and the location of Kuroshio Current axis. Between egg and shirasu stage from 1979 to 1985, and between shirasu stage and recruitment from 1979 to 1987, the survival indices were high on average though widely fluctuated. However, the former indices after 1986 and the latter indices after 1988 were consistently low. Except after 1988 when both stages' survival indices were low, it was observed that the survival index before the shirasu stage is higher than that after the shirasu stage is low and vice versa.