KOJESZEWSKI, T.B.*; FISH , F.E.: Kinematics of swimming in the Florida manatee

Swimming of the Florida manatee Trichechus manatus latirostris was studied to determine the performance of an aquatic mammal using the undulatory mode.The propulsive movements of captive manatees were examined at Sea World, FL and the Lowry Park Zoo, FL.As the animals swam rectilinearly past a viewing window in their tank, the swimming movements were recorded with a digital video camera at 60 Hz.Lateral views of the animals swimming via dorsoventral undulations of the caudal flukes were observed.The body length for each individual was measured and used as the scale to determine the displacement and velocity of the animal and flukes.Individual animals were identified to associate swimming performance with body morphology.The video records were analyzed using the Peak Performance video analysis system (Motus 2000).The kinematics obtained from the analysis were applied to Lighthill’s bulk momentum model to calculate power output and propulsive efficiency.Animals swam slowly in the subcarangiform mode, producing a caudally moving undulatory wave of one body length. Stroke frequency was 0.33-0.46 Hz and peak-to-peak amplitude of the fluke tip was 0.25-0.36 L.Propulsive efficiency was calculated as 0.65.The calculated values for propulsive efficiency were less than those for cetaceans but greater than those for drag-based paddlers.The undulatory mode of the manatee is intermediate in hydrodynamic performance between drag-based and lift-based mammalian swimmers.According to a transition model of the evolution of aquatic mammals, increasing propulsive efficiency would coincide with increasing aquatic habits.The results suggest that ancestral aquatic mammals could have followed changes in swimming modes from drag-based paddling to body and tail undulation to lift-based oscillation of caudal fluke with increasing propulsive efficiency.