Abstract
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Release-recapture studies were conducted with Pacific threadfin, Polydactylus sexfilis, the
species given highest priority for stock-enhancement research in Hawaii. Their purpose was to evaluate recruitment
potential, dispersal, growth, and differential recapture rates of cultured fingerlings released into shoreline
juvenile nursery habitats along the windward (eastern) coast of Oahu, Hawaii. We varied fish size at release,
release site, and the seasonal timing of releases using a balanced, randomized-block experimental design. After
releases of 20,000 tagged Pacific threadfin in 1993 and about 81,000 in 1994, we recaptured 1705 cultured juveniles
in net collections made over a 17-mo period. Presence of cultured fish in net samples depended strongly on the
interactive effects of release variables. Size at release had an important effect on recapture rates at all release
sites, but this effect varied seasonally. At one of the release sites, larger fish apparently had better survival
after winter releases and smaller fish had better survival alter summer and fall releases. Release site affected
dispersal patterns, recruitment, and recapture rates. The percentage of cultured fish in samples of Pacific
threadfin taken 8 months after release varied from 0% to 64%. Cultured fish showed strong site fidelity at some
sites, weak at others. What we considered "pilot"-scale releases clearly were large enough to approach swamping wild
recruitment at Kahana Bay. A key question from this study is how many cultured juvenile Pacific threadfin the Kahana
Bay site can support without displacement of wild individuals. |