Collaborative Research: Weddell Seal Foraging: Behavioral and Energetic Strategies for Hunting Beneath the Antarctic Fast-Ice

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Davis 9614857 Fuiman 9708151 Williams 9618384 To forage efficiently beneath the extensive, unbroken fast ice along the Antarctic coast, Weddell seals (Leptonychotes weddellii)have adapted to an environment that is very challenging for an air-breathing predator. These adaptations enable Weddell seals to hunt for prey at depth while holding their breath for 20 minutes or longer. This is analogous to a lion or other large terrestrial predator holding its breath while it locates, pursues and captures prey. In addition, Weddell seals must return to the same hole at the end of a dive or know the location of other breathing holes. Failure to locate a breathing hole will result in a seal's death by drowning. This study will investigate the behavioral and energetic adaptations that enable Weddell seals to forage in the Antarctic fast-ice environment. To achieve this goal,the underwater behavior, locomotor performance (swimming velocity, stroke frequency and amplitude, and three dimensional movements)and energy metabolism of Weddell seals will be measured during foraging dives. 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 will be tested. Until now, it has not been possible to investigate the foraging behavior of marine mammals in detail. To accomplish this study, a small video system and data logger will be attached to the seals' backs and oxygen consumption will be measured during voluntary dives from an isolated ice hole in McMurdo Sound, Antarctica. Placing an instrumented seal in an isolated ice hole is a standard protocol for studying the diving behavior of Weddell seals. The video system and data logger will record 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, compass bearing, water tem perature, stomach temperature and ambient sound. Computer analysis of data on depth, swim speed and bearing will enable investigators to reconstruct the three-dimensional, underwater path of seals'dives. This new technology is fully operational and has been used on other marine mammals. Observing the foraging behavior and prey of marine mammals has been and continues to be a major obstacle to the advancement of studies on their foraging ecology. The Weddell seal may be the single best species in which to study the foraging behavior and energetics of deep diving pinnipeds because: 1) data is available on their diving ability, 2) the isolated-ice-hole protocol in McMurdo Sound enables recorders to be attached and recovered reliably, and 3) they make daily foraging dives when placed in the isolated ice hole. 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. In addition, this study will greatly advance our understanding of the foraging ecology of Weddell seals as large predators in the Antarctic fast-ice environment.