Stoner et al.: Recruitment of Strombus gigas 
893 
T3 
CD 
Dead conch 
Z <5 5 10 15 20 25 30 35 40 
40 
30 
20 
10 
0 
<5 5 10 15 20 25 30 35 40 
Shell length (mm) 
Figure 3 
Length-frequency distribution for newly settled queen 
conch derived from all individuals, live and dead, col- 
lected from 11 dredge stations. Each value on the x axis 
represents a range of sizes starting with the lower end 
of the size interval (e.g. 5 represents 5. 0-9. 9 mm). 
Live conch density had a high positive correlation 
with xanthid density (r=0.825, P=0.002), marginellid 
density (r=0.695, P=0.02), and total predator den- 
sity (r=0.794, P=0.004), whereas relationships with 
densities of alpheids, portunids, and olivids were not 
significant (P>0.38). There were no significant rela- 
tionships with any of the predator families (P>0.15) 
for dead or total conch densities. 
Discussion 
Age of postlarvae and settlement dates 
The shell lengths of dredged newly settled conch pro- 
vide insight into when settlement occurred. Using 
the middle of the week-long sampling period as the 
Table 5 
Size range and mode for three crustacean and two mollus- 
can families of potential predators of newly settled conch 
collected at 11 dredge stations. 
Family 
Measurement 
Range 
(mm) 
Mode 
(mm) 
Xanthidae 
carapace width 
1.0-14.5 
1.5 
Alpheidae 
carapace length 
1.0-7. 8 
4.2 
Portunidae 
carapace width 
1.5-36.1 
3.4 
Marginellidae 
shell length 
1. 7-6.1 
3.2 
Olividae 
shell length 
2.0-11.6 
3.2 
endpoint (28 August 1992), we estimated a summer 
average growth rate of 0.39 mm/day (Ray and Stoner, 
1995), and considering settlement at 1.2 mm shell 
length (Davis, 1994), we determined that animals in 
the 10-15 mm modal size class would have settled 
3-4 weeks earlier, between 24 July and 5 August. 
The largest live individual (38.5 mm) would have 
settled on about 24 May, and the smallest (3.3 mm) 
would have settled on 23 August. Dead conch ranged 
from 1.5 to 44 mm SL. According to the same assump- 
tions, they would have been in the benthos for 1-110 
days at the time of death. Therefore, settlement re- 
corded in our samples began in early May and con- 
tinued through at least late August. It should be 
pointed out that our intent was to collect young conch 
as close to the peak settlement period as possible, 
near the end of August. However, it is known that 
larvae are present in the water column near Lee 
Stocking Island until at least late September (Stoner 
and Davis, 1997), and our collections probably do not 
represent total settlement at Shark Rock in 1992. 
There are three possible explanations for the fact 
that dredging yielded relatively few live conch out- 
side the 10-14.9 mm modal class. First, there could 
have been a major settlement event between late- 
July and early August. Queen conch larvae were col- 
lected at the Shark Rock nursery ground on 13 dates 
between late May and mid-September 1992 (Stoner 
and Davis, 1997); however, relatively few late-stage 
larvae were found in these collections, and it is im- 
possible with the available data to determine if the 
modal size of survivors resulted from a period of high 
settlement rate. Nevertheless, this is the most par- 
simonious explanation. Second, the high number of 
year-class 0 conch in the 10-14.9 mm range may also 
be related to high survivorship in conch settling be- 
tween late July and early August, compared to conch 
settling at other times. However, the steep decline 
in numbers of individuals with size could be a reflec- 
tion of the natural, high mortality of small conch (dis- 
