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Fishery Bulletin 92(1), 1994 



siphonal groove and 35 mm in from the edge of the 

 shell, according to the methods of Appeldoorn (1988) 

 and Stoner and Sandt (1992). Shell length was 

 measured from the tip of the spire to the end of the 

 siphonal canal in both adults and juveniles. Re- 

 peated measures made by different persons showed 

 that both length and lip thickness measurements 

 were made to ±1 mm. Differences in length-fre- 

 quency and thickness-frequency distributions 

 were tested with the non-parametric Kolmogorov- 

 Smirnov test. 



Morphological differences between bank and shelf 

 populations were tested with canonical discriminant 

 function analysis from shell length and lip thickness 

 data. This multivariate technique is well suited for 

 differentiating two types where individual charac- 

 teristics do not separate the types. The analysis 

 computes a third variable Z, which is a linear func- 

 tion of both variables (length and thickness, in this 

 case) such that the equation for the new line maxi- 

 mizes the distance between the two types ( Sokal and 

 Rohlf, 1969). The significance of the discriminant 

 function Z was determined with the Hotelling- 

 Lawley trace test statistic (Morrison, 1976). Results 

 of the canonical analysis were then examined to 

 determine what percentage of the individuals were 

 correctly classified according to collection site. 



Observations were also made on general shell 

 thickness (particularly in juveniles), length of api- 

 cal spines and resultant shell diameter, and num- 

 ber of spines per whorl. None of these characteris- 

 tics were quantified systematically. 



Shell growth experiment 



Early observations suggested that shell phenotypes 

 were different between shelf and bank conch. Adults 

 from the shelf appeared to be longer and to have 

 thicker shell lips than those from the bank. Juve- 

 niles from the shelf were more narrow, thin-lipped, 

 and had shorter apical spines than those on the 

 bank (Martin-Mora, 1992). To examine the potential 

 relation between shell morphology and growth rates, 

 juveniles were tagged in two different nursery sites: 

 in the well-studied nursery west of Children's Bay 

 Cay and in seagrass areas off Charlie's Beach in the 

 northeast cove of Lee Stocking Island (Fig. 1). Ju- 

 veniles were individually marked with spaghetti 

 tags (Floy Tag & Manufacturing Co.) tied around the 

 spire and measured to the nearest millimeter with 

 calipers. Charlie's Beach conch between 108 and 150 

 mm (mean=137 mm, n=281) were measured and 

 released in the last week of August 1990. Children's 

 Bay Cay conch, somewhat smaller than the Charlie's 

 Beach conch (106 to 133 mm, mean=118 mm. 



n=292), were tagged and released in early Septem- 

 ber 1990. Conch from both populations were 

 remeasured for shell length five months later, at the 

 end of February 1991. Forty-eight conch were recov- 

 ered at Charlie's Beach and 135 were recovered at 

 the Children's Bay Cay site. Daily growth rate was 

 calculated for individuals by dividing increase in 

 length by the number of days between measure- 

 ments. Differences in growth rate between the two 

 sites were evaluated by using the Mann-Whitney U- 

 test. 



Results 



Conch densities and abundance 



Densities of adult queen conch in the survey area 

 were highest between 15 and 20 m depth on the 

 island shelf (Table 1) with nearly 88 conch/ha 

 (Fig. 2). Density was also high between the 10- and 

 15-m isobaths. In both of these depth zones densi- 

 ties of adults were highly variable, but there was no 

 apparent pattern across transect lines. There was 

 a highly significant difference in the density of adult 

 conch in the survey zones (Kruskal-Wallis test, 

 H adj =36.195, P<0.001KFig. 2). No conch were found 

 deeper than 25 m, despite an abundance of appar- 

 ently suitable habitat of sand and algae-covered 

 hard-bottom. Adults were most sparsely distributed 



50 



20 • 



10  



o 

 c 



If) 

 c; 

 v 

 Q 



U 



C 



o 

 O 



120  

 100  



80 

 60 

 40 



20 

 



r+-. 



Eh 



Inner Outer 



Bank 



•- «- CN 



^ Depth 



in (Meters) 



Shelf 



Figure 2 



Density of queen conch, Strombus gigas, on the 

 Great Bahama Bank and in six different depth 

 zones of the island shelf hear Lee Stocking Island, 

 Bahamas. Values are ± mean standard error of the 



