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    Relationships between oceanographic environment and distribution of krill and baleen whales in the Ross Sea and adjacent waters, Antarctica in 2004/05

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    M. Naganobu, S. Nishiwaki, H. Yasuma, R. Matsukura, Y. Takao, K. Taki, T. Hayashi, Y. Watanabe, T. Yabuki, Y. Yoda, Y. Noiri, M. Kuga, K. Yoshikawa, N. Kokubun, H. Murase, K. Matsuoka, T. Iwami and K. Ito (Japan)

    We have surveyed the ecological interactions between the oceanography and biological ecosystem in the Ross Sea and its adjacent waters with a joint survey the R/V Kaiyo Maru and the Japanese Whale Research Program in the 2004/05 austral summer. We compared the relationship between the geographical distribution of the main biological prey and predator populations such as krill including other zooplankton and fishes as well as baleen whales with an oceanographic environment index (namely MTEM-200 which is the averaged temperature in degrees Celsius from the surface to 200 m; note all temperatures given below are MTEM-200 values). - Antarctic krill mainly distributed in the waters between 0 to -1℃ of MTEM-200, which approximated the area covered by the Antarctic Surface Water (ASW) zone, and slightly extended in the waters less than -1℃ of the Shelf Water (SW) zone. Ice krill distributed in the waters colder than -1℃ (SW) but did not ℃ cur in ASW (warmer than -1℃ ). Other zooplankton and fishes also showed distribution patterns that could be approximately segregated patterns with MTEM-200. Humpback whales mainly distributed in the waters warmer than 0℃, which agreed with the Antarctic Circumpolar Current (ACC) zone, with a high density around 0℃ near the Southern Boundary of ACC. Antarctic minke whales mainly distributed in the ASW and SW zones with high density around -1 ℃ in a continental shelf slope frontal zone. The interaction between distributions of krill and baleen whales with MTEM-200 could give quantitative information to identify the boundary of distribution of Antarctic krill and ice krill for biomass estimations using acoustic data. We summarized a geographical image between oceanography relating water mass and circulation pattern of the surface layer with MTEM-200, the distribution and abundance of krill and baleen whales. We conclude that this is useful for characterizing the Ross Sea and adjacent waters ecosystem and comparing other areas in the Antarctic Ocean.