Potential energy gain by whales outside of the Antarctic: prey preferences and consumption rates of migrating humpback whales (Megaptera novaeangliae)

The humpback whale (Megaptera novaeangliae) makes annual migrations from Antarctic feeding grounds to tropical breeding grounds. The extent to which it feeds during migration is unknown, but thought to be very low. Whether an animal feeds during migration is likely dependent on prey availability and on the ease with which it can capture the available prey. This study used digital tags (DTAGs) and concurrent prey sampling to measure how changes in the depth and type of prey influenced the lunge feeding rates and the amount of energy consumed by migrating humpback whales. Whales targeting krill lunged at significantly higher rates than whales targeting fish; however, the depth of the prey did not influence lunge rate. The observed lunge rates when feeding on krill, to the best of our knowledge, are higher than any previously reported rates of whales feeding. Estimates of the energetic content of the prey ingested revealed that whales may consume between 1.2 and 3.4 times their daily energy requirements per day while feeding on krill during migration, but less when feeding on fish. This suggests that whales may begin to restock energy supplies prior to reaching the Antarctic. Determining how often this high rate of energy intake occurs along the migratory route will assist with understanding the contribution of migratory energy intake to annual energy budgets.