Project Summary
The primary objective of this study is to investigate the behavioral and energetic adaptations that enable Weddell seals (Leptonychotes weddellii) to forage in the Antarctic fast- ice environment. To achieve this goal, we will examine the underwater behavior, locomotor performance (swimming velocity, stroke frequency, and three-dimensional movements) and energy metabolism of Weddell seals during foraging dives. We will test hypotheses on general foraging strategies, searching behavior, searching mechanics, modes of swimming, metabolic costs of foraging, and foraging efficiency for different environmental conditions and prey type. Until now, there has been no other technology or widely accepted technique to investigate the details of the foraging behavior of marine mammals.
To accomplish this study, we will attach a small video system and data logger to the seals' backs and measure oxygen consumption during voluntary dives from an isolated ice hole in McMurdo Sound. Placing an instrumented seal in an isolated ice hole is a standard protocol for studying the diving behavior and physiology of Weddell seals and one with which the authors are very experienced. The video system and data logger records video images of the seal's head and the immediate environment in front of the animal. In addition, the instrument will record time, depth, swim speed, bearing, water temperature, stomach temperature, and ambient sound. Computer analysis of data on depth, swim speed and bearing will enable us to reconstruct the three-dimensional, underwater path of seals’ dives. This new technology is fully operational and has been tested on ocean-trained bottlenose dolphins (Tursiops truncatus) and a free-ranging elephant seal (Mirounga angustirostris).
This project, like other recent applications of undersea video technology, will yield unparalleled insight into the activities of animals at sea. The hypotheses we propose are simple in contrast to those developed for terrestrial vertebrates and small fish. However, so little is actually known about the foraging behavior of marine mammals that our results will provide the necessary foundation for further, more sophisticated questions and hypotheses. The proposed study will investigate both behavioral and energetic aspects of foraging to obtain a better understanding of the special challenges of obtaining food resources at depth while being constrained by limited access to atmospheric oxygen. The proposed work will greatly advance our understanding of the foraging ecology of Weddell seals as large predators in the Antarctic fast-ice environment.