Baleen whale prey consumption based on high-resolution foraging measurements

Baleen whales influence their ecosystems through immense prey consumption and nutrient recycling 1 – 3 . It is difficult to accurately gauge the magnitude of their current or historic ecosystem role without measuring feeding rates and prey consumed. To date, prey consumption of the largest species has been estimated using metabolic models 3 – 9 based on extrapolations that lack empirical validation. Here, we used tags deployed on seven baleen whale (Mysticeti) species ( n = 321 tag deployments) in conjunction with acoustic measurements of prey density to calculate prey consumption at daily to annual scales from the Atlantic, Pacific, and Southern Oceans. Our results suggest that previous studies 3 – 9 have underestimated baleen whale prey consumption by threefold or more in some ecosystems. In the Southern Ocean alone, we calculate that pre-whaling populations of mysticetes annually consumed 430 million tonnes of Antarctic krill ( Euphausia superba ), twice the current estimated total biomass of E. superba 10 , and more than twice the global catch of marine fisheries today 11 . Larger whale populations may have supported higher productivity in large marine regions through enhanced nutrient recycling: our findings suggest mysticetes recycled 1.2 × 10 4 tonnes iron yr −1 in the Southern Ocean before whaling compared to 1.2 × 10 3 tonnes iron yr −1 recycled by whales today. The recovery of baleen whales and their nutrient recycling services 2 , 3 , 7 could augment productivity and restore ecosystem function lost during 20th century whaling 12 , 13 .