Permalink : http://hdl.handle.net/2115/61067

JaLCDOI : 10.14943/bull.fish.66.1.39

KEYWORDS : Sea cucumber;Growth;Survival rate;Artifical reef;Stock enhancement

The objective of this study was to follow growth and survival of the Japanese sea cucumber Apostichopus japonicus juveniles released into artificial reefs, and to verify practical effectiveness of the artifical reef to reduce early disapperance of released juveniles and an overall effect of the juvenile release to enhance the sea cucumber stock. We set up the artifical reefs near a breakwater in Esashi, sowthwestern coast of Hokkaido, where juveniles of sea cucumber were almost unoberved. To examine effective size of the reef, we prepared four types of the artificial reefs on the basis of size, and released 1-year old juveniles into them. The censuses were conducted ten times from June 2008 to July 2011 by SCUBA diving. The juveniles grew in average from 16 mm to 77 mm in standard body length during three years of the survey, and the growth rate became lower inversely depending on size of the artifical reefs. The number of juveniles decreased by about 36% after a month from the release and remained until 16 months after that. It then declined to 17% over the next 18 months. The juveniles in the larger artificial reefs showed better survival rates but lower growth rates comparing with those in the smaller ones. Considering increase in the number of the larger sea cucumber around the breakwater after 3 years of the release, it seems more likely that grown-up juveniles moved from the artificial reefs toward an offshore natural habitat, and they might keep about 30% survival rate during the 3 years. These results suggest that the release with artifical reefs makes a certain level of effect to increase the sea cucumber stocks.