A simulation model for estimating optimum stocking density of cultured juvenile flounder Paralichthys olivaceus in relation to prey productivity

Abstract

The determination of the optimum stocking density of hatchery-reared juveniles in relation to the carrying capacity of the nursery ground is important to the success of any stock enhancement programs. In order to estimate the surplus productivity of nursery grounds available to support hatchery-reared fish, a population growth model for juvenile Japanese flounder Paralichthys olivaceus was developed by extending an ecophysiology-based model on growth of juvenile fishes. Parameters of the model were adjusted using field-collected data from Ohno Bay in northeastern Japan. This model predicted the optimum stocking density, namely the maximum number of hatchery-reared juvenile Japanese flounder released into the bay without decreasing the growth of conspecific wild juveniles owing to food limitation. The optimum stocking density for juveniles of 89mm total length was estimated to be 2000 individuals per 250,000m2 in Ohno Bay in 1989. Under the model, the most important factors affecting the optimum stocking density of Japanese flounder were the abundance of mysids and wild juveniles at the time of release. The effect of abundance of a competing flatfish species on growth of wild Japanese flounder was less important.