Scaling of oscillatory kinematics and Froude efficiency in baleen whales

Abstract

High efficiency lunate-tail swimming with high-aspect-ratio lifting surfaces has evolved in many vertebrate lineages, from fish to cetaceans. Baleen whales (Mysticeti) are the largest swimming animals that exhibit this locomotor strategy and present an ideal study system to examine how morphology and the kinematics of swimming scale to the largest body sizes. We used data from whale-borne inertial sensors coupled with morphometric measurements from aerial drones to calculate the hydrodynamic performance of oscillatory swimming in six baleen whale species ranging in body length from 5-25m (fin whale, Balaenoptera physalus; Bryde's whale, Balaenoptera edeni; sei whale, Balaenoptera borealis; Antarctic minke whales, Balaenoptera bonaerensis; humpback whales, Megaptera novaeangliae; and blue whales, Balaenoptera musculus). We find that mass-specific thrust increases with both swimming speed and body size. Froude efficiency, defined as the ratio of useful power output to the rate of energy input (Sloop, 1978), generally increased with swimming speed but decreased on average with increasing body size. This finding is contrary to previous results in smaller animals where Froude efficiency increased with body size. Although our empirically-parameterized estimates for swimming baleen whale drag was higher than that of a simple gliding model, oscillatory locomotion at this scale exhibits generally high Froude efficiency as in other adept swimmers. Our results quantify the fine-scale kinematics and estimate the hydrodynamics of routine and energetically expensive swimming modes at the largest scale.

Downsized: gray whales using an alternative foraging ground have smaller morphology

“…The smaller morphology of PCFG may also be related to foraging tactics employed on different prey and habitat types. Differences in skull and fluke morphology are associated with differences in habitat, feeding strategies, prey types, and hydrodynamics among baleen whales [77][78][79][80][81]. Gray whales are considered 'slow manoeuvrers' compared to other baleen whales, enabling them to employ flexible foraging tactics on various prey types [77,[82][83][84].…”

Round-trip migration and energy budget of a breeding female humpback whale in the Northeast Atlantic

“…However, we identified fewer resting days compared to what has been previously reported as optimal for energy conservation, calf growth and milk transfer rates (14% compared to 27% [6]). Routine swim speeds for baleen whales, i.e., the speed at which animals swim most efficiently based on physical adaptations, seem to converge around 2 ms -1 during transiting movements on feeding grounds [75,76]. Swim speeds slower than 2 ms -1 observed from tracking data may therefore be due to resting periods between swimming bouts not resolved at 6-hourly resolution.…”

“…For example, we use a fixed value for the drag coefficient (C d ) which has been estimated by previous studies. Substantial uncertainty exists around this value for most species, including humpback whales ( [6] but see [76] and [79]), and it also varies with many of the same factors mentioned above. Similarly, BMR cannot be directly measured for large freeranging marine animals, and there is disagreement on the relationship between size and metabolic cost for large animals [80,81], so we rely on estimates based on allometry.…”

UAVs for Science in Antarctica

“…Whales: Size and body conditions of killer whales were obtained by Durban et al (2021) [147] after aerial images acquired by multi-rotor UAVs being the measurement system, calibrated with a reference of known-length, to be approximately unbiased. The measurement of morphometric features of baleen whales after UAV flights coupled with data from whale-borne inertial sensors allowed Gough et al (2021) [148] to calculate the hydrodynamic performance of oscillatory swimming in six baleen whale species. The uncertainty in the estimation of the body condition of whales from photogrammetric derived parameters after UAV surveys along the coasts of the West Antarctic Peninsula and California are evaluated by Bierlich et al (2021) [149] through a Bayesian statistical model for three species of baleen whales with a range of body sizes (blue, humpback and Antarctic minke whales).…”