1. National Institute of Polar Research, 1-9-10 Kaga, Itabashi, Tokyo 173-8515, Japan
2. Laboratory of Applied Zoology, Faculty of Agriculture, Hokkaido University, Kita-9, Nishi-9, Kita-ku, Sapporo 060-8589, Japan
3. Japan Science and Technology Corporation, Domestic Research Fellow,Hokkaido National Fisheries Research Institute, Katsurakoi 116, Kushiro-shi 085-0820, Japan
4. Laboratoire d'Océanographie Physique, Muséum National d'Histoire Naturelle, 43 rue Cuvier, 75231 Paris Cédex 05,France
5. Centre d'Ecologie et Physiologie Energétiques, Centre National de la Recherche Scientifique, 23 rue Becquerel, 67087 Strasbourg Cédex,France