Latitudinal comparison in the carrying capacity and function of nursery grounds for juvenile Japanese flounder using ecophysiological modeling

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Latitudinal variation in the carrying capacity and function of nursery grounds for juvenile Japanese flounder, Paralichthys olivaceus, was studied using ecophysiological modeling. 1. Pelagic larval and benthic juvenile Japanese flounder were collected in Wakasa Bay western Japan and Sendai Bay northern Japan. Flounder density was higher in Wakasa Bay than in Sendai Bay by 3-9 times in larvae and 30-60 times in juveniles indicating higher survival rate in northern Japan for larval flounder. 2. Flounder juveniles and mysids as the main prey of flounder juveniles were collected from southern to northern Japan and stomach contents of juveniles were examined. There was a clear tendency of lower juvenile flounder density and higher mysid abundance in northeastern areas than in southwestern areas. As a result, feeding rates and growth rates were higher in northeastern Japan, resulting in greater productivity of flounder juveniles. 3. The production ecology of mysids was studied to incorporate mysid production module into flounder sub-population growth model. 4. We developed a sub-population production model for juvenile flounder with the basis of an ecophysiology model. Using this model, we estimated the optimum stocking density above which the release of hatchery-raised juvenile flounder would restrict the growth of conspecific wild juveniles as food availability will begin to limit sub-population production. The model predicted a higher optimum stocking density in northeastern Japan. However, over-stocking was predicted to have occurred in several areas even in northeastern Japan.