Interaction between oceanography, krill and baleen whales in the Ross Sea and adjacent waters, Antarctica in 2004/05

A joint survey of the R/V Kaiyo Maru and the Japanese Whale Research Program under Special Permit in the Antarctic (JARPA) was carried out to study the interactions between oceanographic conditions, and the distribution of krill as prey and baleen whales as predators in the Ross Sea and its adjacent waters, Antarctica, in austral summer of 2004/05. Results indicated close interactions between the thermal conditions, krill and baleen whale distributions. The oceanography of the surface layer was summarized as an oceanographic environmental index that integrated the mean temperature from 0 to 200 m in depth (ITEM-200). Distribution of ITEM-200 was used as background information for comparing with distribution patterns of each species. Antarctic krill (Euphausia superb) mainly distributed in the Antarctic Surface Water (ASW) area (ITEM-200 = 0 to -1°C) and extended in the Shelf Water (SW) area (less than ITEM-200 = -1°C). Ice krill (Euphausia crystallorophias) clearly distributed in SW but not ASW. Humpback whales (Megaptera novaeangliae) mainly distributed in the Antarctic Circumpolar Current (ACC) waters with high density around ITEM-200 = 0°C near the Southern Boundary of ACC and their distribution slightly extended in ASW. Antarctic minke whales (Balaenoptera bonaerensis) mainly distributed in ASW and SW with a high density around ITEM-200 = -1°C in the continental shelf slope frontal zone. The interaction between distributions of krill and baleen whales with ITEM-200 could yield quantitative information to identify the boundary of distributions of Antarctic krill and ice krill for biomass estimations using acoustic data in the surveys. Finally we summarized a conceptual model of interaction between oceanography relating water mass and circulation pattern of the oceanic surface layer with ITEM-200, as well as the distribution and abundance of krill and baleen whales.