Meeting Abstract
Oscillation of the flukes is the primary mechanism of propulsion by cetaceans. The flukes are composed of collagen fibers without any rigid skeletal elements. Small cetaceans, such as dolphins, have been shown to possess limited chordwise and spanwise flexibility in the flukes under load. The present study was initiated to determine the flexibility of the flukes in large cetaceans. The fluke oscillations of the humpback whales (Megaptera novaeangliae) were video recorded as the whales swam leisurely in the waters about Rarotonga in the Cook Islands. The fluke oscillations of adult and neonate whales were examined two-dimensionally from lateral views using ImageJ. To measure the degree of chordwise bending of the flukes, a Flex Index was calculated as ratio of the chord length to the camber line length, where a value of unity indicted no flexing. The largest amount of flexing was measured at the end of each half stroke with values for the Flex Index of 0.94 and 0.92, for the adult and neonatal whales, respectively. When the fluke is halfway between the extreme positions of the stroke cycle, the Flex Index was measured as 0.97 for both the adult and the neonate. The data indicate that there was effectively no difference in the flexibility between the flukes of adult and neonatal humpback whales. Despite the absence of rigid skeletal elements within the flukes, large cetaceans, such as the humpback whale, possess relatively stiff flukes when swimming. As the flukes of both small and large cetaceans exhibited similar degrees of flexibility, the stiffness of the flukes appears to be size independent.
