Mark-Recapture using Wire Funnel Traps

Please Note:   The information in this section is based on Valentine-Darby et al. (2008).

What it is:

• In general, mark-recapture is a sampling method in which animals are captured in the same area on multiple sampling occasions to estimate a population size or density (or other population parameters such as survival).  On each sampling occasion unmarked animals are marked and released, and marked animals (previous captures) are recorded and released.  A capture probability is calculated and used to estimate the population size. 

• Mark-recapture is a tool that has been used for many years with many different types of animals, particularly mammals and birds.

• To their knowledge, Valentine-Darby et al. (2008) were the first to use and report on this method (i.e., uniquely marking individuals, in a grid system) to sample apple snails.

• Mathematical models and computer programs are used to estimate population size. 

• Wire funnel traps (discussed in detail in the section called “Wire Funnel Traps”) are used to capture apple snails.  The traps are placed in a square or rectangular grid containing at least 100 traps (e.g., 10 rows of 10 traps; see picture below).    

  

What the method is used for:

• To estimate apple snail abundance or density in a particular area. 

• Can obtain concurrent information, such as capture probability, survival, distribution of snails within the grid, and distances moved (although distance/time is affected by being trapped).

• Can be used in a variety of wetland habitat types and across a range of plant densities.  Especially useful when sampling in densely vegetated habitats (e.g., dense cattail marsh; see picture below, circle shows location of field biologist in the grid). 

  

• Use of the traps does not require vegetation removal and results in minimal alteration of habitat.

• Less labor intensive and physically strenuous than throw trap sampling.

• Effects on snail movement due to temperature, water levels, and/or mating activity are accounted for by capture probability (CP)  estimates.

How they are used:

• See “Wire Funnel Traps” for set-up of individual traps.

• Traps are placed in water depths of 15 to 75 cm.

• Traps are placed 2.5 meters apart, as close to the substrate as possible.

• Traps are checked every 3 to 4 days.

• One person can set-up 100 funnel traps in 2.5-3.5 hours.  It takes 2 people ~2 hours to check traps, record data, mark, and return snails if about 20 “new” (newly caught) snails and 20 “old” (recaptured) snails are captured.  In higher density areas, it may take 2 people ~6 hours if 70-80 “new” snails and 40-50 “old” snails are captured.

• Tags are applied using a marine epoxy (as with radio transmitters).

         

• See Valentine-Darby et al. (2008) for more detail.

Their limitations:

• The mathematical/computer models used to analyze the data are complicated and interpretation may be difficult.

• Ineffective in deep water where snails are found near the surface in vegetation. 

• Extended periods of cold temperatures during sampling could lead to a low capture rate and/or low capture probability.  Snails were found to be less active when water temperatures were 20° C and below (Stevens et al. 2002).  Stevens et al. (2002) found no active snails in water below 13° C.

• May capture and injure non-target species (e.g., snakes, amphiumas).  See "Wire Funnel Trap Limitations."

• When not in use, a large storage space is required.

Literature Cited:

• Stevens, A.J., Z.C. Welch, P.C. Darby, and H.F. Percival.  2002.  Temperature effects on Florida applesnail activity:  implications for snail kite foraging success and distribution.  Wildlife Society Bulletin 30(1):75-81.

• Valentine-Darby, P.L., P.C. Darby, R.E. Bennetts, W.M. Kitchens, and H.F. Percival.  2008.  The use of mark-recapture to estimate Florida apple snail (Pomacea paludosa SAY) density in wetland habitats.  Florida Scientist 71(2):115-127.  

Related Publications:

• Darby, P.C., P.L. Valentine-Darby, H. F. Percival, and W.M. Kitchens.  2001.  Collecting Florida applesnails (Pomacea paludosa) from wetland habitats using funnel traps.  Wetlands 21(2): 308-311.