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J. Moll. Stud. (1999), 65, 195-208
© The Malacological Society of London
1999
A Comparison of Sampling Techniques for Quantifying Abundance of the Florida Apple Snail (Pomacea Paludosa Say)
Department of Wildlife Ecology and Conservation, Florida Cooperative Fish and Wildlife Research Unit University of Florida, Gainsville, FL 32611-0450 USA
Despite the long recognized importance of apple snails (Pomacea paludosa Say) in Florida wetland food webs, surprisingly little is known about their life history and ecology. The paucity of information is due, in part, to the lack of a validated sampling technique. In this study, we compared the effectiveness of a dip net, bar seine, and suction dredge in extracting apple snails from 1-m2 throw traps. We also evaluated the reliability of egg cluster counts as an index of snail abundance.
The bar seine was eliminated as a suitable extraction method based on poor performance in densely vegetated habitats. The suction dredge appeared slightly less sensitive than the dip net to habitat differences with regards to both marked snail recovery and higher yield of free-ranging (unmarked, not previously extracted) snails. Our results indicate that the probability of recovering snails from throw traps can be considerably less than 1.0, and that recovery probabilities vary among sites and habitats. Therefore, without reliable estimates for the fraction of animals recovered, density estimates, especially comparisons among sites and habitats, are not reliable.
We found no relationship between egg cluster counts and estimates of snail density. The high degree of temporal and spatial variability in egg production precludes the use of egg clusters as a reliable index of apple snail abundance.
(Received 15 April 1998; accepted 30 June 1998)