AbStrclCt. Stock enhancement 



with hatchery-reared juvenile queen 

 conch, Strombus gigas L., has been sug- 

 gested as a means to rehabilitate over- 

 fished populations in Florida and the 

 Caribbean region. A 15-month field ex- 

 periment was conducted in the Baha- 

 mas to compare the survival, growth, 

 morphology, and behavior of hatchery- 

 reared and wild juvenile conch (85-120 

 mm shell length). Two experimental 

 sites were established. Site CI con- 

 tained a resident conch population 

 whereas few conch occurred naturally 

 at site C2. Survival was higher for wild 

 conch than for hatchery-reared conch. 

 After 7 months, 28% of the original wild 

 conch were recovered compared with 

 only 99c of the hatchery-reared conch. 

 Thin shells, short spines, and low burial 

 frequency in hatchery-reared conch 

 may have caused them to be more vul- 

 nerable to predators. In a tethering ex- 

 periment, about twice as many hatch- 

 ery conch were killed as wild conch, but 

 the difference was not significant inside 

 enclosures. Survivorship was higher at 

 the site with resident juveniles, prob- 

 ably because of density-dependent pro- 

 tection from predation. After a period 

 of high mortality in free-ranging conch 

 during the first two months, tag recov- 

 ery curves for both stock types reached 

 a plateau. Also, near the end of the 

 study, shell characteristics of wild and 

 hatchery conch were identical as was 

 survivorship. Analysis of movement 

 patterns indicated that both stock types 

 moved toward the natural population 

 center. Although survivorship was 

 higher at the site with resident conch, 

 growth rates for both stock types were 

 often lower at this site. Algal foods may 

 have been more abundant at the site 

 without conch because of lower grazing 

 pressure. Athough highest mean daily 

 growth occurred at 1.0 conchm 2 , 

 growth rates of conch enclosed at 0.5, 

 1.0, and 2.5 individuals m" 2 were not 

 significantly different in most cases. 

 Growth rates were higher for wild 

 conch than for hatchery conch. In sum- 

 mer, free-ranging and tethered wild 

 conch grew twice as fast as hatchery- 

 reared conch. Success in rehabilitating 

 depleted queen conch populations will 

 require the release of high quality, 

 hatchery-reared juveniles in large num- 

 bers in appropriate habitats. 



Experimental outplanting of juvenile 

 queen conch, Strombus gigas: 

 comparison of wild and 

 hatchery-reared stocks 



Allan W. Stoner 

 Megan Davis 



Caribbean Marine Research Center, 805 E. 46th Place 

 Vera Beach, Fl_ 32963 



Manuscript accepted 4 October 1993 

 Fishery Bulletin 92:390-411 ( 1994) 



390 



Widespread depletion of natural 

 fishery stocks, particularly in in- 

 shore coastal and estuarine habi- 

 tats, has resulted in increasing in- 

 terest in enhancement and restora- 

 tion of wild populations through 

 releases of hatchery-reared indi- 

 viduals. Among the molluscs, rela- 

 tively sedentary bivalves such as 

 oysters, Crassostrea spp. (Burrell et 

 al., 1981; Goodwin 1 ), clams, Merce- 

 naria mercenaria (Flagg and 

 Malouf, 1983), mussels, Mytilus 

 edulis (Dare and Edwards, 1976), 

 and giant clams, Tridacna spp. 

 (Heslinga et al., 1984; Heslinga and 

 Watson, 1985 ) have been restocked 

 most successfully. Experimental re- 

 seeding of scallops, Argopecten and 

 Patinopecten spp. (Saito, 1984; Ao- 

 yama, 1989; Tettelbach and Wen- 

 czel, 1991) and abalone, Haliotis 

 spp. (Kojima, 1981; Saito, 1984; 

 Uki, 1984; Searcy and Salas, 1985; 

 Tegner and Butler,1985; Tong et al., 

 1987; Ebert, 1989; Emmett and 

 Jamieson, 1989) also show promise. 

 Queen conch, Strombus gigas, is 

 one of the most important fishery 

 species in the Caribbean region 

 (Brownell and Stevely, 1981; Berg 

 and Olsen, 1989), with an estimated 

 annual value of 30 million U.S. dol- 

 lars (Appeldoorn and Rodriquez, 

 1993). Heavy fishing for queen 

 conch in shallow water habitats has 

 resulted in a decline of this species 

 throughout most of its biogeogra- 



phic range (Appeldoorn et al.,1987; 

 Appeldoorn and Rodriguez, 1993), 

 and the U.S. fishery has been closed 

 completely since 1986 (Berg and 

 Olsen, 1989). Mariculture has been 

 suggested as a way to rehabilitate 

 queen conch populations (Berg, 

 1976; Siddall, 1984a; Davis et al., 

 1987), and research efforts during 

 the past two decades have made it 

 possible to culture large numbers of 

 juvenile conch for stock enhance- 

 ment (Brownell, 1977; Ballantine 

 and Appeldoorn, 1983; Hensen, 

 1983; Laughlin and Weil, 1983; Cruz, 

 1986; Davis et al., 1987; Heyman et 

 al., 1989; Creswell,1993; Davis, 

 1993). Unfortunately, field outplants 

 of hatchery-reared stock have met 

 with little success because of very 

 high mortality (Appeldoorn and 

 Ballantine, 1983; Laughlin and Weil, 

 1983; Appeldoorn, 1985; Marshall et 

 al., 1993; Dalton, 1993). Also, little is 

 known about the relative viability of 

 wild and hatchery-reared conch. 



This study uses a large-scale 

 outplant experiment, together with 

 enclosure and tether experiments, 

 to compare the survival, growth, 

 morphology, and behavior of hatch- 

 ery-reared and wild juvenile conch 

 released into a well-studied nursery 



Goodwin, W.F. 1981 Use of seed oysters to 

 supplement oyster production in southern 

 North Carolina. Report, North Carolina 

 Division of Marine Fisheries, NCDMF - 

 Project - 2/314-R, 109 p. 



