574 



Fishery Bulletin 88(3), 1990 



Site description 



This study was conducted in the Exuma Cays, Baha- 

 mas, at two sites characterized by turtlegrass Thalas- 

 sia testudinum Konig and known juvenile queen conch 

 populations (Wicklund et al. 1988). The first site (CBC) 

 was located 1.5 km west of Children's Bay Cay (23° 

 44.3'N, 76°04.5'W). The second site (SR) was located 

 just southwest of Shark Rock (23°45.0'N, 76°07.5'W), 

 a rock outcrop off the southern end of Norman's Pond 

 Cay. There is a gradient in depth at both sites from 

 a shallow sand bar (< 1 .0 m) to a depth of approximately 

 3.5 m, accompanied by a gradient in seagrass and 

 detritus biomass (Table 1). Tidal range in the area is 

 approximately 1 m and both sites are subject to strong 

 reversing tidal currents, sometimes exceeding 50 cm/ 

 second. 



Conch density was highest (~2.0/m-), near the popu- 

 lation centers, decreasing in density towards their 

 peripheries. At each site three transects were made, 

 each separated by approximately 50 m. Divers were 

 towed by a small boat around each site to place buoys 

 on the edges of each population. Transects were then 



positioned through the population centers, parallel to 

 the depth gradient. Transect lengths were an average 

 of 61 m at CBC and 142 m at SR. Stations marked by 

 stakes were placed along each transect (5 for CBC and 

 7 for SR) from bare sand to the highest density sea- 

 grass. Thalassia shoot density was used to set all sta- 

 tions of equivalent number in similar habitats for both 

 sites. Station 1 of each transect was placed on bare 

 sand, with no seagrass or detritus. Stations 2, 3, 4, and 

 5 were placed in the following approximate shoot den- 

 sities, respectively: 70, 300, 550, and 700 shoots/m^. 

 Stations 6 and 7 at SR were characterized primarily 

 by increasing accumulated detritus and higher seagrass 

 biomass and not increasing shoot density. 



Methods and materials 



Field measurements 



Counts were made in July 1988 and February 1989 to 

 test for seasonal differences in conch distribution. In 

 February at CBC we found that the center of the 

 population had moved north of its July location, and 



