Habitat selection of stone and starry flounders in an estuary in relation to feeding and survival

Juveniles of both stone flounder Platichthys bicoloratus and starry flounder Platichthys stellatus utilize estuaries as nursery grounds. To understand their habitat selection and the functions of habitats such as food supply, we defined the seasonal distribution of recently settled fish of these species in shallow nursery areas and investigated their feeding habits in the Natori River estuary, Japan. Distribution of stone flounder was limited to the lower estuary (<3 km upriver from the mouth) and stone flounder were most abundant near the mouth. Recently settled starry flounder were first detected further upstream in areas characterized by low salinity <10 and by the absence of the predatory sand shrimp Crangon uritai. Early juvenile stone and starry flounders consumed mainly siphons of the bivalve Nuttallia olivacea and the mysid Neomysis awatschensis, respectively; however, 1- and 2-yr-old fish of both stone and starry flounders fed mainly on the bivalve siphons. These results indicate that habitat selections of juvenile stone and starry flounders enable utilization of preferred prey and predator avoidance, respectively, and that non-overlap of these species' habitats results in avoidance of inter-specific competition for food between these two species.