Abstract
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.
Highlights
Japanese seaperch Lateolabrax japonicus is a euryhaline marine fish of commercial importance that is widely distributed in the coastal waters of Japan and Korea
The importance of the estuarine turbidity maximum (ETM) zone is widely recognised in estuaries of different parts of the world because it serves as a predation refuge for fish during the early life stages due to the high turbidity, and as their feeding ground due to the high prey concentration
This suggests that an increase in river flow may decrease Japanese seaperch recruitment in the Chikugo River estuary through a density-independent process, as reported in other estuarine dependent fishes (Turner and Chadwick, 1972; Hayman and Tyler, 1980; Crecco and Savoy, 1984; Rulifson and Manooch III, 1990; Strydom et al, 2002; Whitefield, 2005; Shoji et al, 2006b)
Summary
Growth analyses using larval otolith microstructure have shown that temperature in the northern part of Ariake Bay and larval growth were high but the recruitment was poor in the years of high winter flow (Shoji et al, 2006b) This suggests that an increase in river flow may decrease Japanese seaperch recruitment in the Chikugo River estuary through a density-independent process, as reported in other estuarine dependent fishes (Turner and Chadwick, 1972; Hayman and Tyler, 1980; Crecco and Savoy, 1984; Rulifson and Manooch III, 1990; Strydom et al, 2002; Whitefield, 2005; Shoji et al, 2006b)
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