MEPS 242:275-284 (2002)  -  doi:10.3354/meps242275

Fine-scale three-dimensional spatial use by diving, lactating female Weddell seals Leptonychotes weddellii

Mark A. Hindell1,*, Robert Harcourt2, Joseph R. Waas3, David Thompson4

1Antarctic Wildlife Research Unit, School of Zoology, University of Tasmania, PO Box 252-05, Hobart, Tasmania 7001, Australia
2Marine Mammal Research Group, Graduate School of the Environment, Macquarie University, Sydney, New South Wales 2109, Australia
3Department of Biological Sciences, University of Waikato, Private Bag 3105, Hamilton, New Zealand
4Sea Mammal Research Unit, Gatty Marine Laboratory, University of St Andrews, St Andrews, Fife, KY16 8LB, United Kingdom

ABSTRACT: Despite the importance of fine-scale spatial use in understanding an animal¹s foraging ecology, these data cannot readily be collected for free-ranging marine mammals. We used an acoustic positioning system to quantify, for the first time, the fine-scale 3-dimensional (3D) spatial use of free-ranging Weddell seals swimming under ice. Unlike many other phocid species, lactating Weddell seals spent up to 25% of their time diving. Given the limited foraging range imposed on the seals by the fast ice upon which they breed, this could lead to prey depletion and even inter-specific competition. The seals focused their underwater activity on a relatively small region associated with a steep bottom contour, using the entire water column, with very little time spent at the bottom. This behaviour is consistent with feeding on bentho-pelagic prey such as Pleurogramma antarcticum. The 3D profile of individual dives consisted of the seals making simple, directed dives which gradually converged with the ocean floor. There was some variation from this pattern, usually associated with increased searching time. Such focused foraging activity may result in local prey depletion and intra-specific competition.

KEY WORDS: Three-dimensional tracking · Acoustic tracking · Habitat use · Intra-specific competition · Weddell seals

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