Fluctuations of abundance and survival rate during the egg and larval stages of Japanese anchovy Engraulis japonicus in the Seto Inland Sea (1980–2007)

In order to understand the processes affecting early survival of the Japanese anchovy Engraulis japonicus population in the Seto Inland Sea, we examined the monthly fluctuations in the abundance and survival rates from eggs to recruits (15-day-old larvae, 13 mm in standard length fish, defined as 1-month-old fish) during their main spawning season from 1980 to 2007. The abundance of the yolksac larvae positively correlated with the abundance of eggs, but the abundance of recruits did not significantly correlate with the abundance of yolksac larvae. These results imply that the survival rate during the egg stage is relatively stable, but that the rate during the larval stage is variable. Of the three most recent decades (1980s, 1990s and 2000s), the abundance of recruits was highest in the 1980s. The decrease in the abundance of recruits after the 1990s can be considered to have occurred through a decline in survival rate during the larval stage because there were no significant differences in egg abundance, yolksac larval abundance, and survival rates during the egg stage in the three decades of the study period.