Appropriate release number of juvenile red spotted grouper, Epinephelus akaara, into nursery reef and fishing port habitats
2007
Okumura, S.(National Center for Stock Enhancement, Takamatsu (Japan). Yashima Station)
Six nursery reefs of ca. 20cubic m were installed off Shiraishi Island, central Seto Inland Sea, Japan in July 2000. Juvenile red spotted grouper were released into the reefs on October 2001. The densities of released juveniles were arranged at three levels, 500, 1,000 and 2,000 fish per reef. Part of the reef was salvaged from each reef three times to estimate the number of residual fish. The numbers of residual fish were directly proportional to the numbers of released fish until one month after release; however they were nearly even among the three levels at four months after release. Retention rates were inversely proportional to the released number. Release experiments into a fishing port were carried out in Ishima West Port located in central Seto Inland Sea, Japan. A total number of 15,000 and 1,500 juveniles were released into the port on October 1998 and November 1999, respectively. Respective recapture operation took place 16 and 28 days after the release using 16 and 20 fishing traps in the port. CPUE were 0.38 and 0.05 directly proportional to the number of released juveniles.
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