Temporal Aspects of Population Dynamics and Dispersal Behavior of the West Indian Topshell, Cittarium Pica (L.), at Selected Sites in the Exuma Cays, Bahamas
Abstract:Population dynamics of unexploited stocks of the West Indian topshell, Cittarium pica, were studied from October, 1983, to December, 1985, in the Exuma Cays, Bahamas. Snails were tagged at two sites of high population density to examine temporal aspects of natural mortality, growth, and recruitment, while reproduction and activity pattern were monitored at separate sites. At the site of highest density (8.42 ± 0.97 snails˙m–2, 95% confidence interval), mortality was highest for small snails and showed significant temporal variation (total releases = 561). At the site of lowest density (4.35 ± 0.47 snails˙m–2) no size or temporal effects on mortality were demonstrated (total releases = 386). For both sites combined, the median annual instantaneous rate of natural mortality (M) for small snails (10–50 mm shell width) was 1.05 (95% confidence limits = 0.43–2.07), while for large snails (> 50 mm) it was 0.59 (0.00–1.23). At the site of highest population density, growth rates appeared to vary seasonally with lowest rates occurring during winter. At this site L∞ was estimated at 91.15 cm and K at 0.3028. Growth rates were highest at the site of lowest population density where a decrease in growth rate coincided with a bloom of filamentous benthic intertidal algae. The annual average von Bertalanffy growth parameters L∞ and K at the Patter site were 96.60 cm and 0.3648, respectively. Gonadal development peaked during summer. For three consecutive years, annual peaks in recruitment occurred during summer at both sites, demonstrating that the population size-frequency modes identified represent year classes. The species tends to be nocturnal and moves only small distances. After 255 days the median displacement along the shore by snails at a sheltered site was 7.5 m and the largest displacement was 33.5 m (N = 33). The snails showed size-specific zonation with small individuals higher on the shore than large ones. While snails 10–70 mm in shell width migrated strongly with the semidiurnal tides, animals either smaller or larger than this size range did not.
Document Type: Research Article
Publication date: September 1, 1990
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