Dare to differ : individual foraging success in marine predators, from the largest seal to small penguins

Abstract

The oceans are undergoing rapid alterations due to human activities, making it crucial to predict how ecosystem shifts will affect marine predators. Short-term indicators of the fitness consequences of a changing environment, such as individual foraging performance, are essential to guide timely conservation measures but there is a dearth of methods for quantifying the individual foraging strategies and efficiency of aquatic animals. This thesis documents the development of three innovative multi-sensor biologging devices and explores their application to uncover the foraging performance of Southern Ocean predators. A tag containing wide-bandwidth light and movement sensors was developed to measure anti-predator bioluminescent signals emitted by prey as they are hunted by southern elephant seals. Results indicate that some seals target large aggregations of bioluminescent prey, but inter-individual variability is wide. The need for details on the prey size, quality and ease of capture prompted the development of a miniature sonar and movement tag to study both the biotic environment of marine predators and their feeding interactions. Using proxies for prey type, behaviour and capture success, I identified prey types associated with differing rates of body condition improvement in southern elephant seals, providing evidence in marine predators that individual prey selection strategies are linked with longer-term energy gains. A miniature sound and movement tag was developed to record foraging and provisioning behaviour of macaroni penguins and to examine how performance in daily feeding trips influenced subsequent chick provisioning. Using the same device, I combined proxies for swimming speed, posture and foraging activity to infer prey types in the Antarctic fur seal and explored individual foraging performance in years of contrasting prey availability. These new methods are applicable to a range of marine predators while the ecological results provide key information to help predict population trajectories under changing climate and fisheries scenarios.