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Fishery Bulletin 94(3), 1996 



IB). These particular tidal flow fields were emphasized 

 because adults on the island shelf probably originated 

 from nurseries in adjacent bank and shelf areas. 



To compare juvenile conch abundance at WW and 

 LSI, the percentage of the bank survey area occu- 

 pied by juvenile aggregations was calculated (ha of 

 aggregation/ha of bank area surveyed). Although this 

 index provides only a crude comparison of juvenile 

 abundance without quantitative data on animal den- 

 sity within the aggregations, our long experience with 

 juvenile aggregations in the Exuma Sound has shown 

 that aggregations rarely have <0.1 or >1.5 conch/m 2 . 

 General observations on densities were noted in our 

 1991 surveys at both sites. 



Larval surveys 



Surveys for queen conch larvae were conducted dur- 

 ing the primary spawning season (June through 

 August) at WW and LSI in order to provide informa- 

 tion on the production of larvae in the two areas and 

 to evaluate the supply of late-stage larvae. In 1993, 

 samples were collected on 5 dates ( 12 June, 30 June, 

 15 July, 4 August, and 22 August) at each site over 

 the island shelf at 1 inshore station (5-m isobath) 

 and at 1 offshore station (20-30 m isobath) (Fig. 1, 

 B-C). In 1994, samples were collected on 3 dates (22 

 June, 20 July, and 18 August) at only the offshore 

 stations, where highest concentrations of adults oc- 

 curred and where highest concentrations of late- 

 stage larvae were collected in 1993. Simultaneous 

 studies of spawning behavior at LSI and WW in 1995 

 showed that egg-laying is synchronous in the two 

 areas (Stoner and Ray, unpubl. data). 



Conical plankton nets (202-um mesh, 0.5-m mouth 

 diameter) were towed behind a 20-m vessel at 100 

 m/sec for replicated (n=2) 15-min tows. Because 

 queen conch larvae are found in the upper water col- 

 umn during the day (Stoner and Davis, in press, a), 

 nets were towed in the upper 1-2 m of the water 

 column at inshore sites. At offshore sites, replicated 

 15-min tows were made for ~5 min at each of the 

 following depths: 1 m, 2-3 m, and 5 m. The volume 

 of water filtered on each tow was calculated from a 

 calibrated flow meter (General Oceanics) secured in 

 the mouth of the net. Samples were preserved in 5% 

 formalin-seawater mixture. Strombid veligers were 

 sorted from the plankton with a dissecting micro- 

 scope and identified according to Davis et al. ( 1993). 

 The number of queen conch veligers per 10 m 3 of water 

 was calculated, and subsamples of veligers from each 

 tow were measured for shell length. The veligers were 

 classified as early-stage (<500 urn), mid-size (500- 

 900 um), or late-stage <>900 urn). Late-stage larvae 

 were metamorphically competent or nearly so. 



Results 



Adult surveys 



Variation in density and abundance There were 

 an estimated 208,500 adult conch in Exuma Sound 

 near WW within the MFR survey area, which com- 

 prised 2,167 ha (Table 1). Two-way ANOVA of the 5 

 depth intervals from 2.5 to 25 m revealed significant 

 differences both between the two different areas (Fj 63 

 = 16.62, P<0.001) and among zones (F 4 63 =3.87,'P 

 =0.007 ). The deepest interval (25-30 m ) was excluded 

 from analysis because adult conch were never ob- 

 served at that depth in the fished area. Interaction 

 between the two variables was not significant 

 (F 463 =1.48, P=0.218). 



Mean adult density was always higher, by as much 

 as 15 times, in the MFR than in the fished area for 

 each depth interval (Table 1). Maximum mean den- 

 sity (270 conch/ha) occurred at 10-15 m in the MFR. 

 This value was three times higher than the highest 

 density observed in the fished area near LSI (88 

 conch/ha at 15-20 m) and was significantly higher 

 than densities at all LSI depth intervals (Tukey test, 

 P<0.03) except 15-20 m (P=0.58). 



Although nearly half the survey area in the MFR 

 was 5-10 m deep (Table 1 ), adult densities were rela- 

 tively low at depths <10 m (0-49 conch/ha) and high 

 (>104 conch/ ha) at all deeper intervals, even at great- 

 est depth ( 122 conch/ ha at 25-30 m ). No adults were 

 observed at the two beach locations surveyed. 



Variation in conch density within depth intervals 

 was high and apparently related to island shelf struc- 

 ture. For example, density at 25-30 m was <6 conch/ 

 ha along transects D and E where the slope to the 

 shelf edge increased sharply from 15 m, whereas 

 density was 432 conch/ha farther north in transect 

 C, where the slope to 30 m was more gradual. 



The density of adult queen conch on the bank ad- 

 jacent to WW and Hall's Pond Cay in the MFR (53.6 

 conch/ha) was 31 times higher than that in the fished 

 area near LSI (1.71 conch/ha). Seventy-four percent 

 of all adult conch encountered on the bank near WW 

 were within 2 km of inlets; this general distribution 

 pattern was also evident at LSI. 



There was an estimated total of 174,100 adult 

 queen conch on the bank in the entire MFR survey 

 area (3,245 ha) (Table 1 ). This was 45.6% of the over- 

 all total for the shelf and bank. In the fished area, 

 there were only 6,816 adults in the bank area sur- 

 veyed (3,997 ha), and this number comprised a rela- 

 tively small portion of the overall total for the site 

 (8.3%). Most adult conch in the fished area (>87%) 

 were found in depths >10 m, whereas only 39% of 

 adult conch in the MFR were in depths >10 m. 



