The Antarctic minke whale (Balaenoptera bonaerensis) is the most abundant baleen whale species in the Southern Ocean. Quantitative information on prey consumption of whales is useful to understand their feeding ecology and role in the Antarctic marine ecosystem. The purposes of this study were 1) to investigate the feeding habits of Antarctic minke whales based on information on prey species in stomach contents, and 2) to estimate the amount of prey consumed by whales, accounting for some uncertainties. The analysis is based on the data from whales taken by JARPA (Japanese Whale Research Program under Special Permit in the Antarctic: 1989/90-2004/05) and JARPAII (2005/06-2013/14) in the Indo-Pacific region of the Antarctic (35°E-145°W). Sampling of Antarctic minke whales was conducted in the austral summer seasons, mainly in the months from December to March. The Antarctic minke whales fed mostly on Antarctic krill (Euphausia superba) in offshore area, and on ice krill E. crystarollophias in coastal (shallow) area on the continental shelf such as the Ross Sea and Prydz Bay. Daily prey consumption by the whales in each reproductive status group was estimated using an energy-requirement approach. Based on the results obtained by three equations combined and Monte Carlo simulations, the daily prey consumptions per capita of Antarctic minke whales were 207.1kg and 353.3kg for immature and mature males; and 229.3kg and 397.0kg for immature and mature females, respectively. The CVs of the daily prey consumption consumed by whales per capita were in the range 0.35-0.39. Consumption was equivalent to 4.9-6.3 % of body weight. The total per capita prey consumptions during the feeding season were 24.8 and 42.4tons for immature and mature males, 27.5 and 47.6tons for immature and mature females, respectively. Total prey consumptions of krill by Antarctic minke whales during the feeding season (120days) were estimated at 1.5 and 4.6 million tons in Areas IV and V, respectively. It is expected that the output of this study will assist the understanding of the role of the Antarctic minke whale in the ecosystem and development of ecosystem models.
Dr Tsutomu Tamura (Japan)
Dr Taro Ichii (Japan)