32 



Abstract— The Pacific threadfin (Po/v- 

 daclylus sexfilia) is considered one of 

 the premier Hawaiian food fishes but 

 even with catch limits, seasonal clo- 

 sures, and size limits, catches have de- 

 clined dramatically since the 1960s. 

 It was identified as the top candidate 

 species for stock enhancement in Ha- 

 waii, based on the decline in stocks, high 

 market value, and importance of the 

 fishery. 



In the stock enhancement program 

 for Pacific threadfin, over 430,000 

 fingerlings of various sizes were im- 

 planted with coded wire tags and re- 

 leased in nursery habitats along the 

 windward coast of Oahu between 1993 

 and 1998. Because few Pacific thread- 

 fin were present in creel surveys con- 

 ducted between 1994 and 1998, Oahu 

 fishermen were offered a $10 reward 

 for each threadfin that was caught ( for 

 both hatchery-reared and wild fish). 

 A total of 1882 Pacific threadfin were 

 recovered from the reward program 

 between March 1998 and May 1999, 

 including 163 hatchery-reared fish, an 

 overall contribution of 8.7'7r to the fish- 

 ery. Hatchery-reared fish accounted for 

 as high as 71% of returns in the release 

 areas. Hatchery-reared fish were recov- 

 ered on average 11.5 km (SD=9.8 km) 

 from the release site, although some 

 had moved as far away as 42 km. Aver- 

 age age for recovered hatchery-reared 

 fish was 495 days; the oldest was 1021 

 days. 



Cultured Pacific threadfin juveniles 

 survived and recruited successfully 

 to the recreational fishery, accounting 

 for lO'if of fishermen's catches on the 

 windward side of Oahu. Recruitment to 

 the fishery was highest for the 1997 re- 

 lease year; few juveniles from earlier 

 releases were observed. Presence of a 

 few large, fully developed females in the 

 recreational fishery suggested that 

 hatchery-reared fish can survive, grow, 

 and reproductively contribute to the 

 population. Implementation of an en- 

 hancement program that is focused on 

 juveniles and perhaps large females, as 

 part of an integrated fishery manage- 

 ment strategy, could speed the recovery 

 of this fish population. 



Impact of hatchery releases on the 

 recreational fishery for Pacific threadfin 

 iPolydactylus sexfilis) in Hawaii 



Alan M. Friedlander 



David A. Ziemann 



The Oceanic Institute 



Makapuu Point 



Walmanalo, Hawaii 96795 



E-mail address (for A M Friedlander) afnedlanderigoceanicinstituteorg 



Manuscript accepted 6 September 2002. 

 Fish. Bull. 101:32-43 (2003). 



Declining marine fish stocks worldwide 

 have led to an increased interest in 

 marine fish stock enhancement (Blan- 

 kenship and Leber, 1995; Schramm 

 and Piper, 1995; Leber et al., 1996; 

 Grimes, 1998; Howell et al., 1999). 

 Stock enhancement of marine fishes 

 has progressed since the late 1800s and 

 several successful marine fish stock 

 enhancement programs have been 

 documented; however, nearly all have 

 been directed toward temperate spe- 

 cies such as chum salmon (Kaeriyama, 

 1996 ), Japanese flounder ( Kitada et al., 

 1992), red sea bream (Imai et al., 1994; 

 reviewed by Masuda and Tsukamoto, 

 1998). and red drum (McEachron and 

 Daniels. 1995; McEachron et al., 1998). 

 In one successful marine fish stock 

 enhancement program in the tropics, 

 hatchery-reared striped mullet (Miigil 

 cephahis) successfully recruited to the 

 fishery, accounting for \'i'7( of the com- 

 mercial mullet catch in Kaneohe Bay, 

 Hawaii (Leber and Arce, 1996). 



The Pacific threadfin (Polydactylus 

 sexfilis), known locally as "moi," is the 

 only representative of the threadfin 

 family (Polynemidae) in Hawaii (Ran- 

 dall. 1996). The distribution of Pacific 

 threadfin extends throughout the Indo- 

 Pacific region from Madagascar (Bleek- 

 er, 1875) to the Ogasawara Islands of 

 southern Japan, east to Hawaii and 

 south to theTuamotu Archipelago (Ran- 

 dall et al, 1990; Myers. 1991). In an- 

 cient Hawaiian culture. Pacific thread- 

 fin were reserved for the ruling chiefs 

 and prohibited for consumption by com- 

 moners (Titcomb, 1972). Pacific threafin 

 were formerly harvested commercially, 

 but commercial catches have declined 

 steadily since the 1950s and have essen- 



tially ceased since 1968 when the daily 

 catch limit was restricted to 15 fish per 

 person. This decline in abundance, par- 

 ticularly around the more populated ar- 

 eas of the state, is likely the cumulative 

 result of years of chronic overfishing 

 (ShomuraM. Current regulations com- 

 prise the following: a catch limit of 15 

 fish per person per day; a minimum fish 

 size of 7 inch. TL (ca. 14.5 cm FL) for 

 caught fish; and a closed season from 1 

 June to 30 September. 



Pacific threadfin are typically found 

 over shallow sand flats, along high 

 wave-energy rocky shorelines, and in 

 sandy beach wash zone habitats (Ho- 

 saka, 1990; Leber et al.. 1998). They 

 can also be found in turbid water near 

 stream mouths and brackish mangrove 

 estuaries (Randall et al. 1990; Myers, 

 1991). Local fishermen call areas where 

 adult Pacific threadfin congregate "moi 

 holes" (Hosaka. 1990); these usually oc- 

 cur in shoreline caves or sandy depres- 

 sions and sand channels in the surf 

 zone among boulders or reef areas. 



Pacific threadfin are protandric her- 

 maphrodites, initially maturing as 

 males after a year at about 20-25 

 cm; they then undergo a sex reversal, 

 passing through a hermaphroditic 

 stage and becoming functional females 

 between 30 and 40 cm FL at about 

 three years of age (Santerre and May, 

 1977; Santerre et al., 1979; Szyper et 

 al.. 1991). Spawning occurs inshore 



' Shomura, R. 1987. Hawaii's marine fish- 

 ery resources: yesterday i 1900) and today 

 11986). Admin. Rep. H-87-21, 14 p. U.S. 

 Dep. Commer, NOAA, NMFS, South- 

 west Fisheries Science Center, Honolulu, 

 Hawaii 96822. 



