Designs for swimming : morphometrics and swimming dynamics of several cetacean species

Swimming is the only mode of locomotion available to whales and dolphins. Although all cetaceans live in an aquatic environment, large differences exist between the behavioural ecologies of different species: corresponding variation in morphology and in dynamical swimming characteristics is expected between species. -- Morphological variation was examined within a sample (n=35) of harbour porpoise (Phocoena phocoena) to determine the values of several geometric parameters (including body volume, body surface area, volumetric coefficient, fineness ratio, fluke surface area, fluke aspect ratio and fluke sweep angle) for mature animals. Harbour porpoise showed significant variation in several non-dimensional parameters with age, suggesting that other cetacean species may display similar variation. In general, juvenile harbour porpoise displayed lower fineness ratios and lower fluke aspect ratios than adult harbour porpoise: these results imply a lower propulsive efficiency for juvenile porpoise. -- The morphologies of sexually mature harbour porpoise were statistically compared with a sample (n=3) of Atlantic white-sided dolphins (Lagenorhynchus acutus). Harbour porpoise were found to have significantly lower fineness ratios than Atlantic white-sided dolphins, indicating a fatter body and a higher drag coefficient. Harbour porpoise also displayed higher fluke aspect ratios. This suggests that the flukes of the harbour porpoise may have a higher propulsive efficiency than those of Atlantic white-sided dolphins, although the white-sided dolphins' high fluke sweep angles may compensate for their lower aspect ratio. -- The morphologies of harbour porpoise and Atlantic white-sided dolphins were qualitatively compared with several other cetacean species. The largest between-species differences were observed for volumetric coefficient, fluke aspect ratio and the ratio of body surface area : fluke area. These morphological differences may reflect differences in relative swimming performance. -- Dynamical swimming parameters, including swimming speed, fluke oscillation frequency, and stride length, were measured from videotape for a harbour porpoise, an Atlantic white-sided dolphin and two long-finned pilot whales (Globicephala melas). Limited data on heave amplitude and maximum pitch angle of the flukes were also measured for the harbour porpoise and the white-sided dolphin. The results were compared with data from fish and cetacean swimming studies. The observed animals displayed a linear relationship between swimming speed and fluke oscillation frequency. Stride lengths were found to remain constant within species, and to vary significantly between species. The upstroke and downstroke of the flukes were found to be equally long for all speeds measured. -- Finally, a statistical method to test the hypothesis of wave energy absorption by whales was developed, and the method was applied to the track of a long-finned pilot whale when corresponding wave conditions were known. The whale was not found to increase its swimming speed or to adjust its heading with respect to wave direction in response to favourable wave conditions. Possible reasons for these results are reviewed.