THE USE OF MARK-RECAPTURE TO ESTIMATE FLORIDA APPLE SNAIL (POMACEA PALUDOSA SAY) DENSITY IN WETLAND HABITATS

Estimating Florida apple snail (Pomacea paludosa Say) abundance in wetlands is difficult due to the complex structure of the habitat. We have used throw traps for sampling snails, but significant limitations to this approach prompted investigation of alternative methods. Here, we deployed funnel traps in a mark-recapture study to estimate apple snail density in three habitat types. We compare and contrast the data quality and logistics associated with this approach to those associated with throw traps. We captured and marked 1,420 snails in our sampling grids. Density estimates based on the grid area ranged from 0.13 – 0.43 snails | m2. These 'naïve' density estimates were 19–30% higher than those adjusted to account for snails moving in and out of the grid. Capture probabilities (p̂) varied between sampling grids, and we illustrate why it can be misleading to compare counts of animals without adjusting for p̂. The funnel trap approach proved especially advantageous over throw traps in densely vegetated habitats. However, no clear advantage exists in areas with relatively sparse vegetation. Although both approaches have their limitations, which we discuss in detail, the mark-recapture approach using funnel traps accommodates a wider range of habitat types.