Friedlander and Ziemann: Impact of hatchery releases on recruitment of Po/ydacty/us sexfilis 



33 



and eggs are dispersed and hatched offshore (Lowell. 

 1971). Larvae and juveniles are pelagic up to about 6 cm 

 FL, at which size they enter inshore habitats including 

 surf zones, reefs, and stream entrances (Santerre and 

 May, 1977; Santerre et al., 1979). Newly settled young Pa- 

 cific threadfin, locally called "moi-lii" (Lowell, 1971; Tinker, 

 1982), appear in shallow waters in summer and fall where 

 they are the doininant member of the nearshore surf zone 

 fish assemblage (Ziemann et al.'-). 



Pacific threadfin is a popular and much sought-after 

 sport fish that also supports a small subsistence fishery 

 in Hawaii (Santerre et al., 1979; Leber et al., 1998). It is 

 presently an important species in the Hawaii recreational 

 fishery because of its reputation as one of the best tasting 

 fishes in Hawaii (Hosaka, 1990) and its high market value 

 (wholesale market price over US$3.00 per kilogram). A 

 species prioritization study conducted early in the stock 

 enhancement research program in Hawaii identified Pa- 

 cific threadfin as the top candidate for stock enhancement, 

 based partly on the decline of its stocks, its high market 

 value, and importance in the recreational fishery (Oceanic 

 Institute-'). As part of the Stock Enhancement of Marine 

 Fish in the State of Hawaii (SEMFISH) program funded 

 by the National Marine Fisheries Service, juvenile Pacific 

 threadfin were released in nursery habitats along the wind- 

 ward coast of Oahu between 1993 and 1997 to evaluate the 

 contribution of hatchery-reared fish to the local fishery. 



2 Ziemann. D. A.. A. M. Friedlander. and P. Craig. 1998. En- 

 hancement of Pacific threadfin Polydactylus sexfilis in Hawaii. I. 

 Release optimization. Stock Enhancement of Marine Fish in the 

 State of Hawaii (SEMFISH). Phase K, 152 p. Oceanic Insti- 

 tute, 41-202 Kalanianaole highway, Waimanalo. HI 96795. 



^ Oceanic Institute. 1989. Selection of marine finfish species 

 for stock enhancement in Hawaiian waters, 78 p. The Oce- 

 anic Institute. Makapuu Point, 41-202 Kalanianaole Highway, 

 Waimanalo. HI 96795. 



Leber et al. (1998) demonstrated site-specific potential suc- 

 cess in stocking progi-ams for juveniles in 1993-94. The pur- 

 pose of this article is to provide long-term tracking of 

 catches to determine the contribution of hatchery-produced 

 fish versus wild stocks in the recreational fishery on the 

 windward side of Oahu. 



Methods 



The culture of Pacific threadfin at the Oceanic Institute 

 (01) is described by Ostrowski et al. ( 1996). Most fish were 

 released into coastal waters between day 60 for small 

 juveniles (70-85 mm FL) and day 90 for larger juveniles 

 (130-150 mm FL). 



During each of five release years, 10,000 to 100,000 juve- 

 niles (per release site) were sorted by size and released in 

 multiple lots over 3-5 months; the total number released 

 per release site usually varied between years (Table 1. 

 Fig. 1). Over the five release years, a total of 430,994 Pacific 

 threadfin fingerlings were released. Before release, all fish 

 received coded wire tags (Northwest Marine Technology, 

 Inc., Shaw Island. WA: Jefferts et al., 1963) in the snout 

 area to identify release lots by release size, date, and loca- 

 tion. Approximately 5** of each release lot was retained in 

 culture at OI to determine tag retention rates. Fish were 

 examined monthly from 1 to 6 months until tag loss rates 

 stabilized ( i.e. when the number lost had not increased since 

 the previous month). Tag retention rates varied from 93% 

 to 99'7r. All calculations of tag recovery rates were based on 

 coded-wire-tag data adjusted for tag retention rates. 



We conducted a roving creel sui-vey. encompassing all 

 release areas, intermittently from 1994 to 1998 on the 

 windward side of Oahu 1) to determine if released Pacific 

 threadfin were surviving and being caught in the fishery, 2) 

 to estimate Pacific threadfin CPUE in the recreational fish- 

 ery, and 3) to inform fishermen about the Pacific threadfin 



