Population decline off the Japanese sardine Sardinops melanostictus owing to recruitment failures

The Japanese sardine Sardinops melanostictus started to decline after 1989. Recruitment to age 1 population was small in four year-classes from 1988 to 1991. The population decline after 1989 resulted from recruitment failures in 4 consecutive years. Egg production was high in the years of poor recruitment. The recruitment failures were caused not by a reduction in reproductive output but by low survival between egg stage and age 1 recruitment. Abundance of post first-feeding larvae positively correlated with egg and yolksac larval abundance. Mortality at the first-feeding stage was not so variable as to destroy correlations between the abundance of early life stages. The population of age 1 recruits did not correlate with the abundance of post first-feeding larvae. Recruitment of the sardine was not fixed by the end of the first-feeding stage. Cumulative mortality through the early life stages, rather than relatively instantaneous mortality at the first-feeding stage, is thought to be responsible for the recruitment success or failure and eventual population fluctuations of the sardine.