Movements of radio-tagged manatees in Tampa Bay and along Florida’s west coast, 1991–1996

Abstract

Manatees wintering in Tampa Bay, Florida, were captured and fitted with satellite- and radio-telemetry equipment during a research project conducted from 1991 to 1996. Forty-four manatees were tagged after their capture in Tampa Bay; an additional 15 animals were tagged at other west coast locations. Locations of individual animals were estimated via satellite up to eight times per day, and observations of manatee locations were made in the field one or more times per week. These data were entered into a relational database and converted to a format accessible as points within a geographic information system (GIS). Seasonal densities of satellite locations were mapped for 33 manatees tagged in Tampa Bay. Within the bay, manatees aggregated at or near warm-water locations during winter. In other seasons, manatee density was highest in areas that had abundant sea grass and were close to fresh-water sources. Sequential data points for individual manatees were transformed into probable travel routes by using a GIS-based cost-path analysis. A map was created for each tagged manatee depicting estimated travel paths, and detailed descriptive information summarized major movements, tagging history, and physical characteristics. The travel patterns of male manatees were characterized by almost continual movement, often along predictable routes or circuits. Most males larger than 265 cm ranged 100 km or more away from Tampa Bay during non-winter months whereas smaller males remained in or near the bay. As males matured, their travel ranges appeared to expand. Female manatees used two general movement patterns. Small females and females with calves would use specific areas within a day’s travel of the warm-water sources for extended periods before moving to similar nearby areas for protracted stays. Females without calves and females longer than 330 cm with calves added long migrations between areas chosen for foraging.The ranges of some females extended south to Charlotte Harbor,the Caloosahatchee River,and the Everglades. Two tagged females traveled from Florida’s west coast to the east coast: one traveled south around the peninsula, and the other apparently moved east through Lake Okeechobee and the lock system.