Stoner and Davis: Outplanting queen conch, Strombus gigas 



403 



for equivalent mortality rates mea- 

 sured in tether experiment I. Most ex- 

 periments showed that growth rates 

 were lower at site CI than at C2 with 

 certain exceptions ( Table 11 ). A signifi- 

 cantly higher growth rate was found 

 at CI in wild conch during the second 

 enclosure experiment, and equivalent 

 growth rates were found in hatchery- 

 reared conch in the same experiment. 

 Growth rate did not differ between 

 sites during fall in free-ranging conch. 



0-20 



O 

 6 



0.15 



0.10 



005 



Discussion 



Importance of seed stock quality 



Stock enhancement and rehabilitation 

 depend upon the ability of fisheries 

 managers to place viable seed animals 

 in optimal habitats at appropriate 

 times (Stoner, in press). Hatcheries in 

 the Turks and Caicos Islands, Belize, 

 Mexico, and Florida are now produc- 

 ing juvenile queen conch with the ex- 

 pectation that hatchery-reared conch 

 will be seeded into local waters for res- 

 toration of depleted resources. Re- 

 leases of hatchery-reared conch in sev- 

 eral small-scale pilot programs have 

 been relatively unsuccessful in terms 

 of conch survival (Appeldoorn and 

 Ballantine, 1983; Appeldoorn, 1984; 

 Iversen et al., 1986; Coulston et al., 

 1987; Rathier, 1987; Davis et al., 1992), but it is un- 

 known whether low survivorship was related to char- 

 acteristics of the habitat or the outplanted conch. The 

 only published field comparison of wild and hatch- 

 ery-reared queen conch (Marshall et al. 2 ) showed that 

 hatchery-reared conch may be more vulnerable to 

 predation than are wild conch. Additionally, Jory and 

 Iversen ( 1988) found that hatchery-reared conch may 

 have shells with lower breaking strengths than those 

 of wild conch. The present study shows that poten- 

 tial differences in physiology, behavior, morphology, 

 and survival must all be considered. 



Differences in growth rate between wild and hatch- 

 ery-reared conch at Children's Bay Cay study sites 

 are surprising given that the hatchery conch had 

 been in a field grow-out enclosure with natural sub- 

 strata and food for 6 months. Several explanations 



0.20 

 0.15 

 0.10 



>> 0.05 

 TO 



Period I 

 April - May 1 990 



_ 



020 



015 



0.10 



1 0.05 



E 0.5 1.0 2.5 0.5 1.0 2.5 



—' hatchery wild 



£ Site C1 



CO 



cc 



0.5 1.0 2.5 0.5 1.0 2.5 



hatchery wild 



Site C2 



Penod II 

 May -July 1990 



* 



0.20 



- 0.15 



0.10 



0.05 



0.5 10 2.5 

 hatchery 



05 



1.0 2.5 



wild 



0.5 1.0 2.5 



hatchery 



0.5 



1.0 2.5 

 wild 



Site C1 



Site C2 



Density (#conch/m 2 ) 



Figure 1 1 



Growth rate comparisons for enclosure experiment I. Hatchery-reared 

 and wild queen conch, Strombus gigas, were held at three different 

 densities at sites CI and C2. Values are mean ± SD for average growth 

 rates in two replicate enclosures. 



2 Marshall, L. S., Jr., C. Cox, and R. N. Lipcius. 1992. Survival of 

 wild and hatchery-reared juvenile queen conch in natural 

 habitats. Unpubl. manuscr. 



Table 7 



Seagrass components in 24 cages at the beginning 

 and end of enclosure experiment I. Thalassia biom- 

 ass included all above-ground live blades. Thalassia 

 detritus included senescent and decomposing 

 seagrass blades retained in a 3 mm mesh bag. Val- 

 ues are mean ( ± SD). 



Seagrass components 



March 1990 



July 1990 



Thalassia shoot density 

 (shoots-m -2 ) 



Thalassia biomass 

 (g dry wt-m~ 2 ) 



Thalassia detritus 

 (g dry wtm -2 ) 



674.1 (±92.2) 



77.2 (±18.5) 



649.3 (±79.8) 



107.2 (±37.5) 



317.9 (±131.7) 324.32 (±25.4) 



