162 



Fishery Bulletin 90(1), 1992 



23°42 



ye-os 



Figure 1 



Map of the Lee Stocking Island, Bahamas, study site showing plankton sampling sta- 

 tions (*). RS = location of the Reproductive Site, where observations and plankton col- 

 lections were made; RC = Rat Cay cut; AC = Adderley Cay cut; CBC = Children's 

 Bay Cay nursery site. 



(called "mounds"), each sur- 

 rounded completely by bare 

 sand, were examined. All of the 

 mounds (designated with the 

 letter "M" in Fig. 2) were located 

 at depths of 18 m at the base with 

 tops between depths of 12 and 

 14m. (2) Sand habitats were 

 divided into two major regions. 

 Si is the extensive sand flat be- 

 tween the 10 m reef front and the 

 mound zone. S2 is the sand area 

 within the mound zone. (3) Rub- 

 ble and boulder areas are found 

 at the base of the 10 m reef in a 

 narrow band, with an extensive 

 boulder field (Bl) at the south- 

 east end of the study site. The 

 mounds and rubble, particularly 

 in the Bl area, are covered with 

 a turf of green algae (primarily 

 Cladophoropsis spp.), plus abun- 

 dant erect forms such as Hali- 

 meda spp. An area of mixed 

 hardground, sand, and coral 

 heads (HI) extends to the north 

 and east of the study site. 



Island, there is a coral ledge at which depths increase 

 rapidly from 10 to 18 m. Beyond the ledge is a 1km- 

 wide platform with a gradual slope from 18 to 24 m. 

 Seaward from the platform, depth increases rapidly to 

 the deep basin of Exuma Sound. This geomorphology 

 is typical of the western side of the Exuma Sound. 

 Highest number and density of adult S. gigas occur on 

 the 18m-deep platform, which is beyond the normal 

 free-diving range of conch fishermen. In this area, more 

 than 99% of the conch are sexually mature (Stoner and 

 Sandt 1992). In the colder months, the conch are found 

 on algae-covered hardbottom; they move to sand for 

 mating and egg-laying in the summer. 



A study site of approximately 12 ha surface area on 

 the 18 m platform was chosen for the investigation of 

 reproductive behavior and habitat association in adult 

 conch (Fig. 2). The particular location, north of the 10 m 

 coral ledge, was selected because of an abundance of 

 adult conch and close proximity of feeding and spawn- 

 ing habitats (Stoner and Sandt 1992). A scale map of 

 the site was constructed from compass bearings and 

 distances measured by scuba divers along the sides of 

 primary habitat features or boundaries. Figure 2 shows 

 all prominent features between the coral ledge and the 

 23m isobath. 



Observations on reproductive behavior were made 

 in three habitat types (1) Five hard-bottom domes 



Reproductive activity 



Reproductive behavior was surveyed for 14 months, 

 on a monthly basis during the period of highest activ- 

 ity (March-October 1988) and at 6-8 week intervals 

 during January-February 1988 and November 1988- 

 February 1989. Longer sampling intervals were used 

 in the winter because preliminary observations near 

 Lee Stocking Island in previous years indicated that 

 no reproductive behavior occurs between November 

 and March. During each survey, spanning 5-15 days, 

 a scuba diver search for adult conch was made on 

 mounds Ml, M3, M4, and MS, in the boulder area (Bl), 

 in the rubble area (at the base of the coral ledge), and 

 in both sand zones SI and S2. During each survey 

 period, all conch were counted on each of the mounds 

 and at least one-half of the Bl area was examined. Very 

 few conch were found on M2 and this mound was aban- 

 doned early in the study. After determining that most 

 reproductive activity occurred on sand and not on hard- 

 ground or rubble (Table 1), the sampling protocol was 

 modified to locate at least 100 individuals on sand for 

 each survey. During winter months, less than 100 

 conch were located on sand in several days searching; 

 however, 100-300 animals were observed per month 

 during most of the reproductive season. 



