MEPS 295:257-263 (2005)  -  doi:10.3354/meps295257

A comparison of prey richness estimates for Weddell seals using diving profiles and image data

Yoshihisa Mori1,*, Yuuki Watanabe2, Yoko Mitani3,5, Katsufumi Sato3,6, Michael F. Cameron4,7, Yasuhiko Naito3

1Department of Animal Sciences, Teikyo University of Science and Technology, 2525 Yatsuzawa, Uenohara, Yamanashi 409-0193, Japan
2The Ocean Research Institute, The University of Tokyo, 1-15-1 Minamidai, Nakano, Tokyo 164-8639, Japan
3National Institute of Polar Research, 1-9-10 Kaga, Itabashi, Tokyo 173-8515, Japan
4Department of Ecology, Evolution, and Behavior, University of Minnesota, 100 Ecology Building, 1987 Upper Buford Circle, St. Paul, Minnesota 55108, USA
5Present address: Texas A&M University at Galveston, 5007 Avenue U, Galveston, Texas 77551, USA
6Present address: International Coastal Research Center, The Ocean Research Institute, The University of Tokyo, 2-106-1 Akahama, Otsuchi, Iwate 028-1102 Japan
7Present address: National Marine Mammal Laboratory, NOAA 7600 Sand Point Way NE, Seattle, Washington 98115, USA

ABSTRACT: Diving animals such as seabirds and marine mammals are top predators foraging under water, and play an important role in the marine ecosystems through foraging behavior. Recently developed animal-borne digital video or still cameras have made it possible to directly observe and estimate the prey richness of a foraging patch with simultaneously recorded diving profiles. Optimal foraging theory suggests that patch residence time should be affected both by the time it takes to travel to a prey patch and the richness of the patch. Therefore, diving profiles obtained by animal-borne depth and time instruments may be used to calculate a relative index of the richness of a prey patch used by diving animals in the water column. We tested this hypothesis by comparing the indices of prey richness estimated from both dive profiles and image data using adult female Weddell seals Leptonychotes weddellii at breeding colonies in Antarctica. There was a positive correlation between these 2 values, indicating that dive profiles can be used effectively to calculate a relative index of prey richness at a prey patch used by diving animals.

KEY WORDS: Foraging · Patch residence time · Prey patch quality · Diving · Optimal model

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