The Florida apple snail has been a difficult species to collect or sample in natural settings due to 1) its cryptic coloration; 2) its aquatic habitat, which often includes dense emergent vegetation; and 3) its relatively low density (usually <1 snail/m²).  The only conspicuous signs of apple snail presence are egg clusters on emergent vegetation and piles of empty shells left by predators. 

The best method to use to collect/sample for apple snails depends upon the purpose of the work.  For example, to

• Collect snails (e.g., for voucher specimens or use in lab studies):  Wire funnel traps.

• Estimate snail density:  Throw traps, with dip net for extraction.  Also, wire funnel traps may be used in a mark-recapture framework in high stem density habitats (e.g., cattail).

• Monitor individual snails to answer life history/ecological questions:  Telemetry and mark-recapture.

• Monitor reproductive status of a population:  Egg cluster counts.

• Examine habitat preferences:  Throw traps, egg cluster counts, telemetry, and mark-recapture.

If the purpose of the work is to estimate apple snail densities, whether using throw trap sampling or mark-recapture, a concurrent estimation of the capture probability (CP) is important.  In throw trapping, this is the proportion of snails in a trap that are actually captured.  The density estimate is adjusted by dividing by CP (see Darby et al. 1999; Karunaratne et al. 2006).  A CP is obtained by marking snails and placing them in the throw trap before removing vegetation in the trap.  If only half of the snails are recovered, for example, the CP is 0.5.  When conducting a mark-recapture study, CP is estimated by the computer models used (e.g., Program CAPTURE or SURVIV).  More information on capture probability is provided in the website subsections "Throw Traps with Dip Net Extraction” and “Mark-Recapture.”

The potential for using egg clusters as an index of snail abundance has been examined because egg clusters are conspicuous and easy to count.  However, to date the procedure has not proven reliable (Darby et al. 1999; Darby and Ren 2004).  Exploration of a method is ongoing, but even if it can be proven reliable under certain situations, it could not be used during certain times of year (when snails are not laying eggs) or in some habitats or hydrologic conditions (during extremely low water or dry down conditions). 

The various methods to collect, sample, or monitor apple snails are described on subsequent pages.

Literature Cited:

• Darby, P.C., R.E. Bennetts, J.D. Croop, P.L. Valentine-Darby, and W.M. Kitchens.  1999.  A comparison of sampling techniques for quantifying abundance of the Florida apple snail (Pomacea paludosa Say).  Journal of Molluscan Studies 65: 195-208.

• Darby, P.C. and A.K. Ren.  2004.  The potential utility of apple snail egg clusters in the context of an Everglades restoration performance measure.  Abstract, p. 101, First National Conference on Ecosystem Restoration, December 6-10, 2004, Lake Buena Vista, FL.

• Karunaratne, L.B., P.C. Darby, and R.E. Bennetts.  2006.  The effects of wetland habitat structure on Florida apple snail density.  Wetlands 26(4): 1143-1150.