Stoner and Ray: Strombus gigas in a marine fishery reserve 



553 



at the southern end of the chain (Fig. 1C), and the 

 MFR was 87 km north near Waderick Wells in the 

 Exuma Cays Land and Sea Park (Fig. IB). Our ob- 

 jectives were 1 ) to test the perceived benefits of an 

 MFR by quantifying differences in densities of adults, 

 juveniles, and larvae; 2) to consider physical-oceano- 

 graphic mechanisms for such differences with respect 

 to the open nature of the population; 3) to compare 

 abundance patterns with data reported from other 

 regions; 4) to determine sources of adult conch; and 

 5) to make management recommendations for a spe- 

 cies that has been heavily exploited in many Carib- 

 bean locations. 



and Olsen, 1989; Appeldoorn, 1994a), queen conch 

 was considered commercially threatened worldwide 

 in 1983 (Wells et al., 1983) and, in 1992, it was added 

 to Appendix II of the Convention on International 

 Trade in Endangered Species (CITES). Fisheries 

 have been closed seasonally or for multiyear periods 

 in areas of Venezuela, Colombia, Belize, Mexico, 

 Cuba, and the U.S. Virgin Islands. Despite closure 

 in Florida (since 1985) and Bermuda (since 1978), 

 stock recovery has been slow (Appeldoorn, 1994a). 



Methods 



Subject species 



The natural history of the queen conch is relatively 

 well known. The species is indigenous to subtropical 

 and tropical waters of the western Atlantic from Ber- 

 muda and southern Florida to Venezuela and 

 Trinidad (Abbott, 1974). Several egg masses, each 

 containing -400,000 eggs, are laid by females on 

 clean sand during the summer season (Robertson, 

 1959; Stoner and Sandt, 1992). Larvae hatch in 3-5 

 d and live in the upper 5-10 m of the water column 

 for 16-28 d, feeding on phytoplankton (Brownell, 

 1977; Davis et al., 1993; Stoner and Davis, in press, 

 a). Vertical migration appears to be slight (Barile et 

 al., 1994), and the larvae drift passively on near-sur- 

 face currents (Stoner and Davis, in press, b). Genetic 

 studies (Mitton et al., 1989; Campton et al., 1992) 

 and analysis of queen conch larval life history and 

 ocean currents in the Caribbean region (Davis et al., 

 1993) suggest that larvae can travel long distances 

 to colonize seagrass nursery grounds where they 

 settle and feed. 



Young conch feed on seagrass detritus and algae 

 ( Randall, 1964; Stoner and Waite, 1991 ) and migrate 

 into deeper water with age (Weil and Laughlin, 1984; 

 Stoner and Schwarte, 1994). At 3.5-4 yr, queen conch 

 reach sexual maturity, cease to grow in shell length, 

 and begin to form the characteristic flared shell lip 

 that thickens with age (Egan, 1985; Appeldoorn, 

 1988). Longevity is at least 6-7 yr (Berg, 1976) and 

 may reach 26 yr in deep-water habitats (Coulston et 

 al., 1987). Fishing regulations in the Bahamas pro- 

 hibit the taking of any nonlipped (i.e. juvenile) queen 

 conch and the use of SCUBA gear for any kind of 

 fishing. A general lack of conch at depths >30 m has 

 been attributed to low abundance of plant foods at 

 such depths (Randall, 1964; Adams, 1970). 



In 1990, the economic value of queen conch taken 

 from the Caribbean region was estimated at $40 

 million (US) (Appeldoorn, 1994a). However, as a re- 

 sult of severe overfishing throughout its range (Berg 



Study sites 



The Exuma Cays island chain comprises more than 

 100 small islands that extend northwest to south- 

 east in the central Bahamas, separating Exuma 

 Sound from the Great Bahama Bank (Fig. 1). The 

 bank is a shallow platform covered with sand and 

 seagrass meadows. In the sound, the island shelf 

 extends from land out 1-3 km to a steep shelf edge 

 beginning at -30 m depth. At both Lee Stocking Is- 

 land (LSI) (Fig. 1C), where fishing is allowed, and at 

 Waderick Wells (WW) (Fig. IB), within an MFR, habi- 

 tats in the depth range of 2.5-15 m include sand, 

 coral rubble, algal-gorgonian hard-bottom, and 

 seagrass. The hard-bottom is covered with the short 

 turf of the green alga Cladophoropsis sp. in many 

 subtidal locations. Beyond 15 m, the habitat is mostly 

 sand and large coral ridges with some hard-bottom. 

 Most of the rocky eastern shore of WW lacks beaches, 

 and water depth close to shore is typically 2 m. At 

 LSI, small sandy beaches lie in protected coves at 

 certain locations between rocky headlands. 



Water exchange between the bank and sound oc- 

 curs through numerous passes that separate the is- 

 lands, creating extensive tidal flow fields on the bank. 

 At LSI (Fig. 1C), most queen conch reproductive ac- 

 tivity occurs in the sound on the island shelf, where 

 adults live in highest densities and juveniles are rare 

 (Stoner and Schwarte, 1994). Larvae are carried 

 through the tidal passes and settle onto the bank 

 (Stoner et al., 1994; Stoner and Davis, in press, b) 

 (Fig. 1, B and C). Discrete juvenile aggregations, with 

 densities of 0.1-1.3 conch/m 2 (most >80 mm shell 

 length), occur on the bank in the same general loca- 

 tions year after year (Wicklund et al., 1991; Stoner 

 and Ray, 1993; Stoner et al., 1996) and may cover 5- 

 600 ha. Most aggregations are located within 5 km 

 of inlets on the Great Bahama Bank in beds of the 

 seagrass Thalassia testudinum (Stoner et al., 1994). 



The Exuma Cays Land and Sea Park, recognized 

 as a protected area in 1958, extends 40 km along the 



