Mark-Recapture Study on Mangrove Terrapins in the Big Sable Creek Complex within Everglades National Park
We marked a total of 300 terrapins. We captured 24 animals in crab pots on the first sampling trip (November 2001), but thereafter captured terrapins only with dip nets.
Systematic surveys of the tidal creeks in the BSC complex during both daylight and nighttime hours around low tides revealed that terrapins predominately use the upper headwater portions of the creeks (i.e., first-order streams).
The female: male sex ratio was 1.0:1.2 (only slightly male-biased), and females were on average about 3 times larger (by mass) than males (sexual size dimorphism was apparent).
Most (80%) of the females captured and almost all (94%) of the males captured in the Everglades were adults, according to both methods of counting annual rings on the plastral scutes and straight plastron lengths (SPL). Despite consistent and equal sampling efforts, we did not capture any females or males less than 3 years of age in this habitat.
However, recapture rates were high, and many individuals were recaptured within meters of their original capture location. Such data are suggestive of high site fidelity, which radiotracking confirmed for females.
We detected no significant differences between sexes in survival and/or capture probabilities. The annual adult survival estimate was 0.79 (95% CI = 0.60-0.91). The estimated capture probability in Winter was 0.28 (95% CI = 0.18-0.42) whereas the estimated capture probability in Summer was 0.53 (95% CI = 0.41-0.64). Model averaging indicated a mean probability of capture of 0.41.
We used JOLLY Model B to estimate population size. The mean adult population point estimate was 1545.3 individuals (95% CI = 1261.6-1828.9). Without the extremely high variance in sampling period 2, mean abundance of adult terrapins in BSC was 1391.2, mean variance was 2750.1, mean SE was 52.4, and the 95% CI range was 1288.5-1493.8.
Microsatellite genetic analysis showed that terrapins in BSC are more similar to terrapins in Florida Bay rather than to terrapins from St. Petersburg, Florida (Gulf coast).
ONGOING AND FUTURE WORK
Further analysis of mark-recapture data will allow for determination of effects of hurricanes (i.e., Hurricane Wilma, October 24, 2005) on terrapin survival and capture probabilities.
Genetic analysis is ongoing for this population to determine hurricane effects on allele frequencies over time.
(Please use the links to the left for additional information pertaining to this data.)
U.S. Department of the Interior, U.S. Geological Survey
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Last updated: 15 January, 2013 @ 12:42 PM(HSH)