Habitat mapping with radiotelemetry data: Manatees and seagrass beds in southwest Florida

The Florida manatee (Trichechus manatus latirostris) is a federally endangered and Florida threatened species that inhabits most coastal waters of the state.  They are excellent indicators and sentinels of estuarine health, and are being used as a gauge of Comprehensive Everglades Restoration Project (CERP) success.  One of the habitat needs of manatees is seagrasses or other aquatic vegetation for forage.  Documentation of the extent and availability of seagrass forage is valuable for assessing habitat suitability and change.  Many waters in Florida are clear, and seagrass beds can be mapped from aerial imagery.  In southwest Florida, especially within the Ten Thousand Islands (TTI) area, waters are generally turbid, and attempts to map available seagrass beds have been largely unsuccessful.  Here, we analyzed GPS telemetry records from radio-tagged manatees tracked in the TTI region to delineate foraging areas.  We found distinct seagrass foraging areas in water of less than 3ft depth offshore of most islands, with total foraging area approximately four times the extent of previously mapped beds.  We will perform Bayesian analysis this summer to determine the likelihood of further forage areas not mapped by the animals, and stratified field sampling in 2008 to validate and refine the analysis.  This technique can be used as an efficient tool for monitoring changes in seagrass beds that may result from CERP efforts.