1. National Institute of Polar Research, Itabashi, Tokyo 173-8515, Japan
2. Laboratory of Applied Zoology, Faculty of Agriculture, Hokkaido University, Sapporo, Hokkaido 060-8589, Japan
3. Department of Biology, Faculty of Science, Osaka City University, Sugimoto, Sumiyoshi, Osaka 558-8585, Japan
4. School of Polar Science, Graduate University for Advanced Studies, Itabashi, Tokyo 173-8515, Japan
5. CSIRO Wildlife and Ecology, G.P.O. Box 284, Canberra 2601, Australia