ESTIMATES OF ANNUAL SURVIVAL PROBABILITIES FOR ADULT FLORIDA MANATEES(TRICHECHUS-MANATUS-LATIROSTRIS)

The population dynamics of large, long-lived mammals are particularly sensitive to changes in adult survival. Understanding factors affectin g survival patterns is therefore critical for developing and testing t heories of population dynamics and for developing management strategie s aimed at preventing declines or extinction in such taxa. Few studies have used modern analytical approaches for analyzing variation and te sting hypotheses about survival probabilities in large mammals. This p aper reports a detailed analysis of annual adult survival in the Flori da manatee (Trichechus manatus latirostris), an endangered marine mamm al, based on a mark-recapture approach. Natural and boat-inflicted sca rs distinctively ''marked'' individual manatees that were cataloged in a computer-based photographic system. Photo-documented resightings pr ovided ''recaptures.'' Using open population models, annual adult-surv ival probabilities were estimated for manatees observed in winter in t hree areas of Florida: Blue Spring, Crystal River, and the Atlantic co ast. After using goodness-of-fit tests in Program RELEASE to search fo r violations of the assumptions of mark-recapture analysis, survival a nd sighting probabilities were modeled under several different biologi cal hypotheses with Program SURGE. Estimates of mean annual probabilit y of sighting varied from 0.948 for Blue Spring to 0.737 for Crystal R iver and 0.507 for the Atlantic coast. At Crystal River and Blue Sprin g, annual survival probabilities were best estimated as constant over the study period at 0.96 (95% CI = 0.951-0.975 and 0.900-0.985, respec tively). On the Atlantic coast, where manatees are impacted more by hu man activities, annual survival probabilities had a significantly lowe r mean estimate of 0.91 (95% CI = 0.887-0.926) and varied unpredictabl y over the study period. For each study area, survival did not differ between sexes and was independent of relative adult age. The high cons tant adult-survival probabilities estimated for manatees in the Blue S pring and Crystal River areas were consistent with current mammalian l ife history theory and other empirical data available for large, long- lived mammals. Adult survival probabilities in these areas appeared hi gh enough to maintain growing populations if other traits such as repr oductive rates and juvenile survival were also sufficiently high. Lowe r and variable survival rates on the Atlantic coast are cause for conc ern.