IMPACT OF HATCHERY RELEASES ON THE RECREATIONAL FISHERY FOR PACIFIC THREADFIN (Polydactylus sexfilis) IN HAWAII

Alan M. Friedlander and David A. Ziemann

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

Fishery Bulletin, in press

The Pacific threadfin (Polydactylus sexfilis) was traditionally reserved for the ruling chiefs in ancient Hawaii and is today considered one of the premier local food fishes. Despite catch limits, seasonal closures, and size limits, catches of Pacific threadfin have declined dramatically over time, particularly around the more populated coastal areas. Pacific threadfin was identified as the top candidate for stock enhancement in Hawaii, based partly on the decline in stocks, high market value, and importance in the recreational fishery. As part of a stock enhancement program for Pacific threadfin, over 340,000 fingerlings of various sizes were implanted with coded wire tags and released in nursery habitats along the windward coast of Oahu between 1993 and 1997. Because few Pacific threadfin were present in roving creel surveys conducted between 1994 and 1998, Oahu fishermen were offered a $10 reward for each Pacific threadfin (hatchery-reared and wild) caught. A total of 1,882 Pacific threadfin were recovered from the reward program between March 1998 and May 1999. This total included 163 hatchery-reared fish, an overall contribution of 8.7% to the fishery. The percentage of hatchery-reared to wild fish was as high as 71% in areas where the releases were conducted. Hatchery-reared fish were recovered on average 11.5 km (SD = 9.8 km) from the release site, but larger movements were observed with individuals recaptured as far away as 42 km from release sites. Average age for hatchery-reared fish was 495 days (SD = 168.6 days) with the oldest fish recovered being 1,021 days old. Cultured Pacific threadfin juveniles survived and recruited successfully into the recreational fishery, accounting for 10% of fishermen's catches on the windward side of Oahu. Recruitment to the fishery was highest for the 1997 release year; few recruits from prior releases were observed. The presence of a few large, fully-developed females in the recreational fishery suggests hatchery-reared fish can survive, grow and reproductively contribute to the population. These data support an increase in the minimum size limit for the fishery from 7 inches (177 mm) to 11 inches (280 mm), and suggest that an upper size limit may also be appropriate. Implementation of an enhancement program focused on juveniles and perhaps large females, as a component in an integrated fishery management strategy, could speed the rate of recovery.