Fishery Bulletin 92(1). 1994 



(Stoner, unpubl. data). However, our morphological 

 analyses of conch suggest that very few conch us- 

 ing the bank for a nursery actually reach the off- 

 shore spawning sites. Furthermore, similarities in 

 length frequency and shell morphology between ju- 

 veniles found immediately off the east (windward) 

 side of the Cays on isolated seagrass beds and adults 

 in deep water suggest that the small aggregations 

 of juveniles found on the shelf serve as the primary 

 source for the offshore reproductive stocks. Given 

 that mating and egg-laying are rare on the Great 

 Bahama Bank, it is likely that recruitment to bank 

 nurseries is sustained by deep-water reproductive 

 populations (Wicklund et al., 1991; Stoner et al., 

 1992; Stoner and Sandt, 1992). 



Differences in shell morphology between bank and 

 shelf conch are not well understood but appear to 

 be related to growth rate. Alcolado (1976) reported 

 that large, thin shells and short spines in queen 

 conch in Cuba were associated with rapid growth. 

 A similar phenomenon may explain the shell differ- 

 ences observed in this study. Juveniles in the 

 nearshore shelf environment of Charlies' Beach 

 grew rapidly and had the large, thin-shelled, short- 

 spined morphotype typical of the shelf adults. The 

 small, thick-shelled, long-spined conch on the bank 

 had growth rates less than half of those on the shelf. 

 A recent transplant experiment at Lee Stocking Is- 

 land demonstrated that shell form and spination in 

 juvenile conch is an environmentally mediated char- 

 acteristic associated with habitat type and indi- 

 vidual growth rate (Martin-Mora, 1992). 



The large size of the deep-water reproductive 

 stock may explain high productivity of queen conch 

 in the Exuma Cays. It is likely, however, that abun- 

 dance of conch in the region is now dependent upon 

 the small, isolated pockets of fast-growing juveniles 

 that inhabit the nearshore shelf habitat during the 

 first two or more years of life then recruit to deep- 

 water reproductive populations. Stoner and Sandt 

 (1992) found that the adult population at an 18-m 

 deep site off Lee Stocking Island was relatively 

 stable between 1988 and 1991, but most individu- 

 als were old and thick-lipped. The predominance of 

 old conch in deep water may or may not be a func- 

 tion of low recruitment rates from shallow water in 

 recent years, and the significance of shallow-water 

 spawning to conch abundance is unknown. 



In an comparison of data from Glazer and Berg 

 (in press.), densities of queen conch in the Exuma 

 Cays are 10 to 100 times higher than those reported 

 for many other localities in the Caribbean region. 

 This may be related to geographic differences in 

 habitat quality, recruitment processes, and fishing 

 methods. The Exuma Cays probably represent a 



particularly efficient system for retaining conch lar- 

 vae because of unique geographic and oceanographic 

 conditions such as an alongshore current and nu- 

 merous tidal inlets leading to nursery grounds 

 (Stoner et al., in press), but fishing methods can play 

 a large role in the population structure of queen 

 conch. Fishing in the Bahamas is restricted to free- 

 diving and limited diving with surface-supply air for 

 adults with flared shell lips; therefore, conch deeper 

 than 10 m are rarely exploited. Depth distribution 

 of queen conch near Lee Stocking Island suggests 

 that virtually every conch in the Exuma Cays is 

 within the range of SCUBA divers and that popu- 

 lations of S. gigas could be decimated quickly if the 

 fishery were opened to this latter gear. On the other 

 hand, if the source of deep-water conch is shallow- 

 water nurseries, protection of deep-water reproduc- 

 tive stocks only delays the effects of overfishing, and 

 certain nurseries should be protected as well. Analy- 

 sis of larval transport and recruitment processes will 

 be crucial to the sound management of this already 

 threatened commercial species. 



Acknowledgments 



This research was supported by a grant from the 

 Undersea Research Program of NOAA, U.S. De- 

 partment of Commerce. We thank P. Bergman, G. 

 Donnly, R. Gomez, J. Lally, D. Mansfield, M. Ray, 

 V. Sandt, D. Wicklund, and E. Wishinski for assis- 

 tance in the field work. R. I. Wicklund prompted us 

 to examine the important juvenile stocks off the 

 windward beaches. The manuscript was improved 

 with helpful criticism by R. Appeldoorn, R. Hardy, 

 E. Martin, M. Ray, and an anonymous reviewer. 



Literature cited 



Alcolado, P. M. 



1976. Crecimiento, variaciones morfologicas de la 

 concha y algunos datos biologicos del cobo 

 Strombus gigas L. (Mollusca, Mesogas- 

 tropoda). Acad. Ciencias de Cuba, Inst, de 

 Oceanol. No. 34, 36 p. 

 Appeldoorn, R. S. 



1988. Age determination, growth, mortality, and 

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 Strombus gigas L., off Puerto Rico. Fish. Res. 

 6:363-378. 

 Appeldoorn, R. S., G. D. Dennis, and O. 

 Monterrosa-Lopez. 



1987. Review of shared demersal resources of Puerto 

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