The influence of environmental factors on early life history patterns of flounders

The near-shore migration and settlement phases of Japanese and American flounders of the genus Paralichthys are compared and discussed relative to differences in coastal environments. Field sampling was conducted in Wakasa Bay, Kyoto Prefecture, Japan, where the shelf is narrow, estuarine habitat limited and tidal range slight, and in Onslow Bay, North Carolina, USA, where the shelf is broad, estuarine habitat extensive and tide relatively strong. Distribution of larvae and juveniles suggests Japanese flounder spawn in close proximity to nursery grounds relative to flounder in Onslow Bay. Sampling of planktonic and benthic flounder just seaward of nursery grounds resulted in capture of a wide range of developmental stages in Wakasa Bay (early planktonic to juvenile), but was limited to metamorphosing larvae in Onslow Bay. Vertical distribution of larvae during the night also differed between the Bays. At night most larvae in Wakasa Bay remained near the bottom regardless of tidal stage. In contrast, larvae in Onslow Bay exhibited selective tidal stream transport. Laboratory experiments conducted to examine the behaviour of recently captured wild and laboratory-reared larvae indicated that wild flounder from Onslow Bay had an endogenous rhythm of activity that corresponded to the tide at the time of capture. In contrast, wild flounder from Wakasa Bay and laboratory-reared larvae showed no distinct activity pattern. These results suggest that physical characteristics of the environment influence the early life history patterns of flounders by modifying behaviour of migrating larvae.