Phase Relationships Between Body Components of Odontocete Cetaceans in Relation to Stability and Propulsive Mechanisms
WEST CHESTER UNIV PA DEPT OF BIOLOGY
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For thunniform lunate-tail swimmers, propulsive movements were considered to be restricted to the caudal oscillating hydrofoil effectively minimizing drag. Previous reports on dolphin swimming have indicated substantial displacements of points along the body which oscillate in the vertical plane. To examine these vertical oscillations, video analysis was used to study the motions of the rostrum, pectoral flipper, caudal peduncle, and fluke tip for seven odontocete cetaceans. Animals swam over a range of speeds of 1.4 to 7.3 mls. For each species, oscillatory frequency of the fluke tip increased linearly with swimming speed. Peak-to-peak amplitude remained constant with respect to swimming speed for all species. Mean peak-to-peak amplitude ranged from 0.02 to 0.06 body length at the rostrum and 0.17 to 0.25 body length at the fluke tip. Oscillations of the rostrum were nearly in phase with the fluke tip with phase differences of -9.41 to 32.95 degrees, respectively. Flipper oscillations trailed fluke oscillations by 60.93 to 123.43 degrees. The lower range in amplitude at the rostrum compared to the fluke tip reflects increased resistance to vertical oscillation at the anterior end due to increased body stiffness and resistance on the flippers.