MEPS 281:275-281 (2004)  -  doi:10.3354/meps281275

3D diving behavior of Weddell seals with respect to prey accessibility and abundance

Yoko Mitani1,4,*, Yuuki Watanabe3, Katsufumi Sato1,5, Michael F. Cameron2,6, Yasuhiko Naito1

1National Institute of Polar Research, 1-9-10 Kaga, Itabashi, Tokyo 173-8515, Japan 2University of Minnesota, 100 Ecology, St. Paul, Minnesota 55455, USA 3Center for International Cooperation, Ocean Research Institute, The University of Tokyo, 1-15-1 Minamidai, Nakano,Tokyo 164-8639, Japan 4Present address: Department of Marine Biology, Texas A&M University at Galveston, 5007 Avenue U, Galveston,Texas 77551, USA
5Present address: International Coastal Research Center, The Ocean Research Institute, The University of Tokyo, 2-106-1 Akahama, Otsuchi, Iwate 028-1102, Japan
6Present address: National Marine Mammal Laboratory/NOAA, 7600 Sand Point Way NE, Seattle, Washington 98115, USA

ABSTRACT: The foraging behavior of predators is influenced by the distribution of prey at different spatial and temporal scales. In marine environments, aquatic animals move in 3 spatial dimensions; however, previous studies of the fine-scale movements of predators were limited to only the vertical component of diving behavior. Here, we have analyzed image data along the 3D dive paths of Weddell seals Leptonychotes weddellii to address the 3D nature of their interactions with prey at the spatial and temporal scales relevant to an individual predator. The 3D dive paths were calculated using acceleration and geomagnetic intensity data. A prey index was estimated using image data taken by digital still picture loggers. The descent and ascent phases of a dive were more linear than the bottom phase, and the prey index during the bottom phase was significantly higher than those during the descent and ascent phases. These results suggest that the bottom phase does indeed represent time spent foraging in a prey patch, and that the descent and ascent phases represent the transit between an ice hole and a prey patch. The 3D dive paths of individual seals were affected by the location of breathing holes in the ice and by the slope of local bathymetric features around their breeding colony. Our data suggest that once seals encounter prey, they dive no further, which minimizes their distance from the breathing hole and maximizes their time spent foraging.

KEY WORDS: Foraging behavior · 3D dive paths · Prey distribution · Prey availability · Weddell seal · Leptonychotes weddellii

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