Feeding Habits and Prey Consumption of Antarctic Minke Whale (Balaenoptera bonaerensis) in the Southern Ocean

Abstract

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 ecosystem. The purposes of this study are 1) to investigate the feeding habit of Antarctic minke whales based on information on prey species, freshness and diurnal change in stomach contents, and 2) to estimate the amount of prey consumed by whales. Estimates are made for whales of different sexual maturity classes as it is expected that the energy requirements vary among them. The analysis is based on the data from whales taken by JARPA (Japanese Whale Research Program under Special Permit in the Antarctic) in a longitudinal sector between 35o E and 145o W, and south of 60o S. Sampling was conducted in the austral summer seasons from 1987/1988 to 2004/2005, mainly in the months from December to March. Daily prey consumption by the whales in each sexual maturity class was estimated using energy-requirement and energy deposition. The whales feed mainly before 05:00 h, which suggest that they cease to feed early in the day. Daily prey consumptions were estimated to be 83.7–325.5 kg, equivalent to 2.7–4.0% of body weight. The mean prey consumptions per capita during feeding season were 7.5 and 16.4 t for immature and mature male, 12.5 and 39.1 t for immature and mature female, respectively. In Area IV (70°–130°E), total prey consumptions of krill by Antarctic minke whales in 1999/2000 and 2001/2002 seasons were estimated to be 0.9 and 1.1 million t, respectively. In Area V (130° E–170° W including the Ross Sea), these estimates in 2000/2001 and 2002/2003 seasons were 3.9 and 4.1 million t, respectively. The estimations of feeding impact on krill resources by Antarctic minke whales in Areas IV and V were from 2.7 to 3.2%, and from 18.2 to 18.9% of krill biomasses, respectively. These results on prey consumption are important input data for the development of ecosystem modeling in the Southern Ocean.