Fine-scale kinematics and energetics

: a detailed insight into the biomechanical strategies of cetacean locomotion

Abstract

Efficient locomotion is critical for active foraging and migrating animals promoting numerous morphological, mechanical and behavioural adaptations for improved performance. While biologging devices have enabled fine-scale studies of movement performance in wild animals, analysis of the resulting data is challenging. This thesis presents an integrated approach to quantifying the swimming movements of cetaceans. These movements generate specific acceleration and body rotations due to propulsor displacement, both of which are sensed by body-mounted accelerometers, but analyses of swimming animals have largely ignored the second component. To address this, I developed a kinematic processing method that combines data from body-mounted magnetometers to separate the acceleration components. Validation with a more conventional gyroscopic approach shows that the magnetometer-method is effective and so offers a low-power solution for kinematic studies enabling smaller/longer duration tags. The application of the new method revealed a novel stroke-and-glide gait, used towards the end of foraging dives by three beaked whale species, which involves a faster and more energetic stroke possibly recruiting anaerobically-powered fast-twitch fibres. A broader study of swimming in 11 free-ranging cetacean species covering a 3000:1 mass range, showed that, as predicted, mass-specific force production decreases approximately with mass⁻¹^/³, whereas methods that ignore body rotations overestimate force production in large animals. Combining the magnetometer method with a stroking hydrodynamic model applied to dive descents, I also found evidence that Cuvier’s beaked whales control lung volume by inhaling more air during deep vocal foraging dives versus shallower and shorter silent dives. Finally, FFT analysis of acceleration signals suggests that cetaceans usually produce bursts of thrust at the stroking rate but under high force loading they may be able to produce thrust at twice the stroke cycling rate, possibly enhancing locomotor efficiency. These results provide a more complete picture on the swimming strategies that cetaceans adopt to promote locomotor efficiency.

Date of Award	30 Nov 2016
Original language	English
Awarding Institution	University of St Andrews
Supervisor	Mark Johnson (Supervisor) & Patrick James Miller (Supervisor)