Theme D: Developing optimal release strategies
41. OBAMA'S FLOUNDERING: POST-RELEASE ABILITIES, CHARACTERISTICS, AND ASSESSMENT OF CAGE CONDITIONED JAPANESE FLOUNDER, PARALICHTHYS OLIVACEUS
Michelle L. Walsh1,2, Hiroshi Fujimoto3, Takeo Yamamoto3, Tatsuya Yamada3, Youiti Takahashi3, Yoh Yamashita2
1 University of New Hampshire, Department of Biological Sciences, Durham, NH, 03824, USA
2 Kyoto University
3 National Center for Stock Enhancement (NCSE), Obama Station
michelle.walsh@unh.edu
Conditioning is the process of providing individuals reared for stock enhancement with some degree of "natural" experience prior to release. Conditioning flatfish before release may increase successful recruitment to the fishery, as fish trained for the "wild" may transition more easily and successfully upon release. Predator-free acclimation cages may help flatfish adjust to the wild environment, establish burial skills, begin pigment change, recover from transport stress, and experience natural (live) food sources before true release. Since 2008, Obama Station, National Center for Stock Enhancement, has conducted pre-release, experimental acclimation cage conditioning for Japanese flounder (N = 13 000 - 80 000) in both the Takahama and Obama portions of Wakasa Bay, Japan. Recaptured fish were acquired through a cooperative effort between researchers and local fishermen (both commercial and recreational). The overall objective was to describe how the characteristics of released flounder changed with acclimation cage exposure as well as to determine how recapture rates compared between conditioned and nonconditioned fish.
To date, more conditioned fish have been recaptured via fishermen's catch than non-conditioned fish. Within the first month of release, conditioned fish slightly led the advancement towards the mouth of the bays in 2008 (1-2 days) and 2010 (18 days), but movements were similar in 2009. Laboratory experiments revealed that conditioned fish exhibited enhanced burial abilities and begin feeding almost immediately, while non-conditioned fish took up to 2 full days before accepting live (goby) prey (Fig. 1). When subjected to adult Japanese flounder and crab predators, conditioned fish exhibited higher survival than non-conditioned fish. However, there was no difference in overall growth (determined by total body length and otolith measures) between conditioned and non-conditioned fish.
Initial observations suggest that non-feeding individuals recollected near the release sites (mostly non-conditioned fish) 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. These results show that acclimation cage conditioning can favorably alter the attributes of released fish. This work has powerful implications for Japanese flounder stocking strategies and may be applicable to other flatfish stocking efforts.
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