Title Case Studies in Flatfish Stock Enhancement: A Multi-Year Collaborative Effort to Evaluate the Impact of Acclimation Cage Conditioning for Japanese Flounder, Paralichthys olivaceus, in Wakasa Bay, Japan
Authers Michelle L. WALSH, Hiroshi FUJIMOTO, Takeo YAMAMOTO, Tatsuya YAMADA, Yoichi TAKAHASHI, and Yoh YAMASHITA
Keywords flatfish, hirame, Paralichthys olivaceus, Hottoke shi-iku, stock enhancement
Citation Bull. Fish. Res. Agen. No.35, 93-102, 2012
Abstract
Japan is the most active country in the world with respect to flatfish stock enhancement, both in the range of species and number of fish released. In Japan, Japanese flounder or hirame, Paralichthys olivaceus, is the primary species represented in the annual flatfish catch; thus, hirame has been a paramount choice for both aquaculture and stock enhancement for decades and is, in fact, the most important stocked marine finfish in Japan. A total of approximately 25 million Japanese flounder are released yearly from federal, prefectural, and local hatcheries throughout the country. Conditioning flatfish to the natural environment before release may increase successful recruitment to the fishery, as fish trained for “wild” conditions may transition more easily and successfully upon release. Since 2008, Obama Station, National Center for Stock Enhancement, has conducted pre-release experimental acclimation cage conditioning for Japanese flounder (N = 10,000-80,000) in both the Takahama and Obama portions of Wakasa Bay, Japan. Fish were reared via the “Hottoke shi-iku” method, a simplified rearing process that boosts cultivation efficiency of fingerlings by reducing rearing time and manpower. Recaptured fish were acquired through a cooperative effort between researchers and local fishermen (both commercial and recreational). To date, more conditioned fish have been recaptured via fishermen’s catch than nonconditioned fish. Initial observations suggest that non-feeding individuals captured near the release sites may be weaker and more likely to be caught by small boat beam trawl (towing speed 1-1.5 knots) than actively feeding, translocating fish. Thus, higher speed shrimp trawlers deeper in the bay (towing speed 3-3.5 knots) and set/fyke nets may be better, non-biased indicators of fitness and intermediate stocking success.
URI http://www.fra.affrc.go.jp/bulletin/bull/bull35/35-11.pdf