Post-Release Performance and Assessment of Cage-Conditioned Japanese Flounder, Paralichthys olivaceus, in Wakasa Bay, Japan

Abstract

Conditioning is the process of providing individuals reared for stock enhancement with some degree of “natural” experience prior to release. Conditioning flatfish in predator-free cages may help adjustment to the wild. From 2008–2010, the Obama Laboratory conducted pre-release, experimental cage conditioning for Japanese flounder in both the Takahama and Obama portions of Wakasa Bay, Japan. Recaptured fish were acquired through a cooperative effort between researchers and local fishermen. The objectives were to describe how characteristics of released flounder changed with cage exposure and to determine how recapture rates compared between conditioned and non-conditioned fish. Significantly more conditioned fish were recaptured than non-conditioned fish in Obama Bay in 2010 (p < 0.05). In 2008 and 2009, recapture rates of conditioned and non-conditioned flounder followed the same trend, although these were not significantly different. Laboratory experiments revealed that conditioned fish had significantly better burying abilities (p < 0.001) and enhanced feeding abilities compared to non-conditioned fish. This study is the first to examine flatfish conditioning strategies using market data and shows that cage conditioning can favorably alter the attributes and recapture rates of released fish.

Keywords:

• hirame
• stocking
• predator-free enclosure

ACKNOWLEDGMENTS

This project was funded by the J. W. Fulbright Commission via the Institute of International Education (IIE)—U.S. Department of State, the East Asia and Pacific Science Institute (funded through a joint effort of the National Science Foundation and the Japan Society for the Promotion of Science), the Field Science and Education Center of Kyoto University, and the Japan Sea National Fisheries Research Institute, Fisheries Research Agency. We are ever grateful for the assistance of professors, students and staff at Maizuru Fisheries Research Station and Obama Laboratory, especially R. Masuda, Y. Kai, M. Ueno, S. Akiyama, S. Matsui, K. Minami, M. Oshima, and K. Tokuda. Comments, advice, and analyses assistance from E. Fairchild, W. H. Howell, B. Galuardi, J. Hargreaves, C. Neefus and two anonymous reviewers were vital to the quality of this work. We especially thank all the fishermen.