Meeting Abstract
The forces that dolphins can produce by oscillation of the tail flukes have been debated for 80 years. Hydrodynamic analyses of the force production by the flukes have modeled these propulsors as rigid structures. The flukes, however, are composed of flexible elements including collagen fibers, which are arranged in a complex organization. The arrangement of the collagen fibers provides the flukes with both rigidity and flexibility. We investigated the effect of chordwise bending within the flukes of bottlenose dolphins (Tursiops truncatus) and determined how swimming effort could affect shape change of the flukes. Two adult male dolphins were video recorded from a lateral view as they statically pushing against a load cell at three levels of effort (Low: 61-98 N; Medium: 107-210 N; High: 314-527 N). While oscillatory frequency increased with increasing effort, heave amplitude remained constant. To measure the flexibility of the flukes, a Flex Index was computed as the ratio of the length of the chordline to the length of the camberline, where a value of one indicated a straight or unbent fluke. The Flex Index decreased with increasing effort. Average values of Flex Index were greater at the transitions between up-stroke and down-stroke compared to mid-stroke, particularly as effort increased. The flukes are flexed throughout the stroke cycle, which can have implications in the generation of propulsive force and efficiency.
