Temporal changes in sighting density indices of baleen whales in CCAMLR Subareas 48.1 and 48.2 based on three circumpolar sighting surveys

This paper examines temporal changes in distribution and sighting density indices of krill-eater baleen whales in Subareas 48.1 and 48.2. This paper was prepared in response to a suggestion in EMM-15 that an analysis of historical cetacean surveys in IWC Area II could provide a context for at-sea observations of cetaceans. Sighting data examined in this study were obtained during a series of Antarctic sighting cruises for whale assessment purposes organized by the International Whaling Commission Scientific Committee (IWC SC) in the context of the research programs ‘International Decades of Cetacean Research’ (IDCR) and Southern Ocean Whale and Ecosystem Research (SOWER), which were organized into three circumpolar surveys (CPI, II and III) between 1978/79 and 2009/10 austral summer seasons. CPI, CPII and CPIII data in Subarea 48.1 corresponded to years 1982/83, 1989/90 and 1993/94+1999/00, respectively while that in Subarea 48.2 those corresponded to years 1981/82, 1986/87 and 1997/98, respectively. The density indices in both subareas suggested that humpback and fin whales were more frequently observed in CPIII than in CPII while that Antarctic minke whale showed an inverse trend. These observations are consistent with abundance estimates trend in humpback and Antarctic minke whales. Two issues are of importance for management of krill under the FBM. The first is the development of the stock abundance of whales in relevant subareas for krill management, and the second is on the concentration of whales in the krill fishing/top predators feeding areas, and the impact on land-based predators.