Influence of spring river flow on the recruitment of Japanese seaperch <em>Lateolabrax japonicus</em> into the Chikugo estuary, Japan

The estuarine turbidity maximum (ETM) zone is considered to serve as a predation refuge for fish during the early life stages due to the high turbidity and high prey concentration. River flow can be one of the important determinants for survival of early life stages of estuarine dependent fish because it affects both the physical and biological properties of the ETM. We tested the hypothesis that fluctuation of river flow explains the variability in recruitment of Japanese seaperch Lateolabrax japonicus around the ETM region of the Chikugo River estuary, upper Ariake Bay, Japan. Japanese seaperch recruitment showed a 43.3-fold fluctuation from 1990 to 2000 and was inversely correlated with the mean daily river flow of the Chikugo River in March. The recruitment was high and variable in years of low March river flow and was poor in years of high March river flow. We conclude that high river flow potentially decreases Japanese seaperch recruitment in the Chikugo River estuary by blocking the larval migration into the river and by increasing the probability of larval dispersion to the downriver/upper bay areas, where potential predators (jellyfish and Sagitta spp.) were more abundant, and prey (Sinocalanus sinensis) availability and turbidity were lower