Fantastic feasts and where to find them : using biologging to investigate foraging behaviour of marine megafauna across a range of spatiotemporal scales

Abstract

Understanding the strategies animals use to locate, select, and capture prey can guide more robust conservation efforts. In marine megafauna, foraging is often inferred from infrequent surface positions using biotelemetry tags. In this thesis I argue that finer-scale measurements of predator movements, prey availability and behaviour are critical to understanding foraging decisions. To explore this I used multi-sensor, high-resolution biologging tags on three megafauna species and compared optimal foraging predictions to actual behaviour over a hierarchy of spatiotemporal scales. At the landscape scale, I studied a central-place forager, the harbour seal, which accesses distant and nearshore prey although the relative importance of these resources is poorly understood. I found that prey encounter rates were similar for the two resources but while prey were distributed extensively offshore, inshore foraging was concentrated in just a few discrete patches. I suggest that the trade-off between accessibility and conspecific competition may influence site selection. At the patch scale, I studied a bulk-filter feeder, whale sharks, which are presumed to be highly-selective to offset the energetic cost of this strategy. Using novel sonar tags to record fine-scale behaviour and prey densities, I found that sharks did not selectively harvest rare dense patches. Instead, a less-selective strategy with continual-patch assessment may be advantageous when prey density is highly heterogenous. At the scale of prey captures, I studied the sensory and locomotor responses of an echolocating predator to evasive prey. Results revealed rapid responses to prey movements which scale with the acceleration of prey, enabling this energetically constrained mammal to reliably capture high-energy prey. Within each study, detailed biologging measurements were critical to understanding factors influencing foraging choices and capabilities. Such data help define the plasticity with which predators can respond to changing prey distribution, density, and performance, and provide critical insights to focus effective conservation actions.