Stocking Effectiveness of Flounder Paralichthys olivaceus in Miyako Bay evaluated by a Fish Market Census

This paper assesses the effectiveness of the annual releases (1987-1992) of flounder evaluated by a census of the commercial landings at the Miyako Fish Market, Iwate Prefecture, from 1988 through 1995, where nearly all the flounders fished in the area adjacent to Miyako Bay are landed. Flounders landed were classified into wild or hatchery released individuals by the difference in the pigmentation on the eyeless side of the body. Total length of all the released and almost all the wild individuals which were landed were measured. And we estimated age composition of released flounder. As a result, from the 611 thousand flounder seeds released from 1987 through 1992, a total of 77, 681 were commercially landed, and a contribution rate of the released flounder to the total landings were between 16.5% and 52.7%. The recapture rate of released seed for each annual release was estimated at between 5.9% and 23.3%, and the ratio of the total landing cash value to the cost of seeds, including personnel and facilities required prior to release were evaluated at between 0.46 and 1.96. We suggest that improvement of the post-release survival rate may significantly improve the economic returns.