CARRYING CAPACITY FOR HATCHERY-REARED PACIFIC THREADFIN (POLYDACTYLUS SEXFILIS) IN NATIVE NURSERY HABITATS IN HAWAI'I

David A. Ziemann and Alan M. Friedlander

The Oceanic Institute, 41-202 Kalanianaole Hwy., 
Waimanalo, HI 96795 USA
ziemannda@oceanicinstitute.org

Transactions of the American Fisheries Society , in press

As part of a stock enhancement program for Pacific threadfin (Polydactylus sexfilis) in Hawaii, over 380,000 fingerlings were tagged and released in sandy shoreline nursery habitats along the windward coast of Oahu between 1993 and 1998. A variety of stocking densities and release habitats provided an opportunity to examine density-dependent effects on survival, growth, and migration patterns over a range of conditions. More than 250,000 threadfin were released into Kahana Bay, with numbers per release ranging from 10,000 to 99,000 fish. Kailua Bay served as a release site from 1996 to 1998 with release numbers ranging from ca. 15,000 to 97,000 fish. Catch rates of hatchery-reared threadfin in Kahana Bay increased with stocking density up to 40,000 fish, and then declined with larger releases. Adjacent sites showed a linear increase in catch rates of hatchery-reared fish with increased stocking density in Kahana Bay, supporting the hypothesis that high stocking density resulted in emigration to nearby habitats. Density-dependent growth of hatchery-reared threadfin in Kahana Bay was evident from declining growth rates with increased stocking density. The release of ca. 97,000 fish in Kailua, a much larger bay, did not appear to affect the growth of hatchery-reared threadfin during the 1997 release year. Knowledge of the carrying capacity of nursery habitats has important implications for development of successful stock enhancement strategies. In order to maximize the effectiveness of stocking programs in environments with limited resources, a strategy of more small releases at many sites may be more productive than large releases at a few sites.