Stoner and Ray: Strombus gigas in a marine fishery reserve 



557 



20 

 10 







40 

 30 

 20 

 10 

 



30 



20 



10 

 



30 i 



20 j 



10 







Shell structure Pairwise Kolmogorov- 

 Smirnov tests showed differences in fre- 

 quency distributions of shell length in 

 the MFR between adult conch on the 

 bank and those at each depth interval 

 <P<0.002 in all cases) except 2.5-5 m 

 (P=0.14). Adult conch from the sound, 

 always >150 mm, tended to be longer 

 than those from the bank (Fig. 2). The 

 length mode for sound conch ranged 

 from 180-189 mm (at 5-10 m and 10- 

 15 m) to 210-219 mm (at 15-20 m and 

 at 25-30 m, where the largest indi- 

 vidual [265 mm] was found). Conch at 

 the deepest interval were relatively 

 large, and mean shell length increased 

 18 mm between the 10-15 m and 25- 

 30 m intervals. A bimodal distribution 

 was observed in the three deepest in- 

 tervals, with a low frequency of 200-209 

 mm conch in all cases. Mean shell 

 length for all conch from the sound was 

 202 mm (SD=21 mm, n =524), compared 

 with 188 mm (SD=20 mm, n=213) for 

 conch on the bank. An intersite compari- 

 son showed significant differences in 

 frequency distributions of shell length 

 between the MFR and the fished area 

 for conch living at each depth interval 

 but not for those on the bank (Fig. 2). 

 Adult conch from the shelf in the fished 

 area had longer shells than those from 

 theshelfintheMFR. 



Pairwise Kolmogorov-Smirnov tests 

 also showed differences in frequency 

 distributions of shell lip thickness in the 

 MFR between adult conch on the bank 

 and those at each depth interval 

 (P<0.001 in all cases) because those on 

 the bank had relatively thin shell lips. 

 All bank adults had shell lips <28 mm 

 thick, and 31% were <8 mm (Fig. 3). Lip 

 thickness values were >16 mm for most 

 adults in the sound, and <5% of the 

 conch at each of the three depth inter- 

 vals to 15 m had lip thickness <8 mm. Beyond 15 m 

 no thin-lipped conch were measured. Mean lip thick- 

 ness for all conch from the sound was 24 mm (SD=7 

 mm, n=524), compared with 12 mm (SD=6 mm, 

 n=213) on the bank. 



An intersite comparison showed significant differ- 

 ences in frequency distributions of shell lip thick- 

 ness for conch living on the bank and at each depth 

 interval (P<0.001 in all cases) except for those at 5- 

 10 m (P=0.08) (Fig. 3). Compared with conch in the 



Bank 



pH- 



D 188 120(213) 

 • 187 ±17(472) 

 P=0 05 



IT 



10=*=- 



Shelf 5-10 m 



D 200 ±20 (144) 



• 221 ±26(57) 



P<0 001 



Shelf 10-15 m 



D 194 ±19 (148) 



• 226 ±24 (229) 



P<0 001 



Shelf 20-25 m 



D 209 ±20 (70) 

 • 233 ±17 (100) 

 P<0 001 



<140 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 

 Shell length (mm) 



Figure 2 



Frequency distribution of shell length of adult conch on the bank and at 6 

 depth intervals in Exuma Sound on the island shelf near WW in the ma- 

 rine fishery reserve (columns) and in the fished area near LSI (points). 

 Each value on the x-axis represents a range of sizes starting with the lower 

 end of the size interval (e.g. 150-159 mm). Mean shell length (±SD) and 

 sample size in parentheses are also given for each distribution. Values for 

 LSI are adapted from Stoner and Schwarte ( 1994). P-values are for intersite 

 comparisons (Kolmogorov-Smirnov tests). 



MFR, conch in the fished area tended to have thin- 

 ner lips in shallow water (bank, and sound <5 m) 

 and thicker lips in deeper water. 



Juvenile surveys 



Juvenile conch were never observed at depths >15 

 m in the Exuma Sound at either study area, and they 

 were infrequently observed (mean <6/ha) in shal- 

 lower water in the MFR (Fig. 4). Highest density of 



