454 



Fishery Bulletin 94(3). 1996 



portion (at least 20%) of the juvenile striped mullet 

 in net samples 4 months after release; 2) there was 

 a persistence of cultured fish in net samples through- 

 out the study; and 3) growth was comparable to mea- 

 sured rates in wild juveniles. If these criteria were 

 met, it would be reasonable to assume that cultured 

 fish had substantially affected juvenile recruitment 

 at the study site. 



This study was conducted in and around fresh 

 water tributaries, the preferred nursery habitat for 

 striped mullet. Striped mullet are catadromous and 

 begin to move out of their nursery habitats as they 

 approach maturity (Blaber, 1987). In Hawaii, year- 

 ling juveniles begin to move out of the intertidal zone 

 and out of shallow shore zones of streams by about 

 February or March (Major, 1978; Leber, 1995; Oce- 

 anic Institute 4 ). Striped mullet reach advanced 

 sexual development in fresh water but must migrate 

 to the sea to spawn (Blaber, 1987). Annual recruit- 

 ment into inshore nursery habitats of young-of-the-year 

 wild mullet occurs in spring in Hawaii (Major, 1978). 



Methods 



Hatchery releases 



Striped mullet were spawned from wild 

 broodstock at The Oceanic Institute and 

 reared to fingerling size for spring and 

 summer releases. Batches of striped 

 mullet eggs were hatched about every 

 six weeks over a five-month period. Lar- 

 val striped mullet from each batch were 

 hatched and cultured in 5,000-L cylin- 

 drical tanks with conical bottoms for 45 

 days. Stage-1 juveniles (45 days old, 20 

 mm TL) were transferred to 8,000-L cir- 

 cular tanks and nursed for 40 days to 

 stage-2 juveniles (85 days old, 40 mm 

 TL). Stage-2 juveniles were transferred 

 to 30,000-L circular tanks and nursed 

 to tagging size (45-130 mm TL). In cul- 

 ture tanks, growth rates averaged 0.5 

 mm TL/day. 



A release-recapture experiment was 

 performed to evaluate recapture rates 

 of cultured striped mullet. Release mag- 

 nitude, release location, release season, 

 and size of fish released were deter- 

 mined from results of 1990 and 1991 



pilot studies in Kaneohe Bay (Leber, 1995; Leber et 

 al. 3 ). During 4 May through 29 May 1992, and again 

 from 13 July through 7 August 1992, juveniles were 

 harvested from culture tanks, graded into five dif- 

 ferent length groups (ranging from 45 mm to 130 mm 

 TL) by using commercial bar graders and tagged with 

 binary coded-wire tags (CWT) (Northwest Marine 

 Technology, Inc., Olympia, WA). Prior to tagging, fish 

 were provided a 2-day period to recover from stress 

 of harvesting and size grading. About 80,500 tagged 

 fish were released into Kaneohe Bay. 



Tags identified year and season of release, SAR, 

 release habitat, release lot (date), and number offish 

 released per treatment condition. Fish were tagged 

 in batches, with a different code for each season-SAR- 

 site-lot combination. Tags were implanted in the 

 snout area with an automatic injector with head 

 molds designed specifically for striped mullet. 



For each release season and SAR combination, the 

 experiment was replicated with three release lots at 

 each of two release locations in Kahaluu Stream (Fig. 

 1), where the greatest recruitment of wild mullet in 

 Kaneohe Bay had been reported (Leber, 1995; Oce- 

 anic Institute 4 ). In May, fish of all five size intervals 

 were released in each lot (45-60 mm; 60-70 mm; 70- 

 85 mm; 85-110 mm; and 110-130 mm). Only fish of 



Oceanic Institute. 1991. Stock enhancement 

 of marine fish in the State of Hawaii (SEMFISH 

 Phase III). Annual report to NMFS, June 

 1990-June 1991. Waimanalo, Hawaii, 107 p. 



Figure 1 



Map of Kaneohe Bay showing pilot study release sites and nursery habitats where 

 monthly cast-net collections were conducted. In this study, all releases were made 

 at Kahaluu Stream, a principal nursery habitat for striped mullet in Kaneohe Bay. 



