Figure 1. Percentage of American alligator clutches that experienced flooding during incubation in canal (n = 13 and 30) and interior (n = 35 and 24) habitats at A.R.M. Loxahatchee National Wildlife Refuge during 2000 and 2001, respectively. [larger image]

The Comprehensive Everglades Restoration Plan (CERP) includes the proposed removal of canals that fragment the Everglades wetland landscape. Dense populations of American alligators (Alligator mississippiensis) exist in canals throughout the system. Clutch and hatchling survival in canal and interior habitats at A.R.M. Loxahatchee National Wildlife Refuge (LNWR) were calculated during 2000 and 2001 to investigate the effects of canal habitats on alligator production. Data were collected from 112 nests and 779 hatchling alligators. Individuals from 57 hatchling pods were recaptured during this study.

No sampled clutches in the interior experienced flooding during 2000 and 2001 (fig. 1). However, most clutches in canal habitats were flooded or partially flooded (fig. 1). Nests were depredated by raccoons (Procyon lotor) at a higher rate during 2001 than 2000 (fig. 2). The number of clutches successfully producing at least one hatchling was greater during 2000 than 2001, and greater in interior than canal habitats (fig. 3). Survival probability estimates for 2000-cohort hatchlings for the first 6 and 13 months of life were 44 percent and 20 percent, respectively. Mean production per nest after 13 months was 2.4 + 0.5 in interior and 0.8 + 0.8 in canal habitats.

Compared to nests in interior habitats, canal nests were subjected to a larger range of water levels during clutch incubation and were more susceptible to flooding. Flooding was found to be the greatest risk to canal nests at LNWR. The majority of nests in LNWR interior habitats were on tree islands. High clutch mortality, small pod size, and overall low mean hatchling survival at LNWR, resulted in negligible production in canal habitats during 2000 and 2001. Comparatively high adult densities in canals at LNWR, and likely other areas of the Everglades, are sustained by immigration and high adult survival rates. Everglades canals appear to be population sinks for alligators and canal removal will probably not affect the overall population.

Figure 2. (left) Percentage of American alligator nests that experienced depredation during incubation in canal (n = 13 and 29) and interior (n = 33 and 24) habitats at A.R.M. Loxahatchee National Wildlife Refuge during 2000 and 2001, respectively. [larger image]	Figure 3. (right) Percentage of American alligator nests that successfully produced at least one hatchling during the hatch event in canal (n = 13 and 30) and interior (n = 36 and 35) habitats at A.R.M. Loxahatchee National Wildlife Refuge during 2000 and 2001, respectively. [larger image]

Contact: Matthew D. Chopp, Florida Cooperative Fish and Wildlife Research Unit, PO, Box 110430, University of Florida, Gainesville, FL 32611; Phone: 353-392-2861, email: chopp@ufl.edu

(This abstract was taken from the Greater Everglades Ecosystem Restoration (GEER) Open File Report 03-54)

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