How much do whales eat? World’s largest animals eat three times more krill than we thought

Baleen whales are the largest animals on Earth, and they are even hungrier than we had assumed, which has huge implications for marine ecosystems

By Chen Ly

Baleen whales, the largest animals in the world, eat three times more prey than previous estimates suggested. The discovery implies that these whales play a larger role in sustaining marine ecosystems than we had thought.

Matthew Savoca at Stanford University in California and his colleagues tracked 321 tagged baleen whales from seven species, including the blue whale (Balaenoptera musculus), the fin whale (Balaenoptera physalus) and the humpback whale (Megaptera novaeangliae). The researchers followed these whales throughout the Atlantic, Pacific and Southern Oceans and estimated their feeding patterns using aerial photographs of the whales’ foraging areas and acoustic measurements of prey density, primarily crustaceans such as Antarctic krill (Euphausia superba).

The team found that the average amount of prey consumed per day by the seven baleen species was between 5 and 30 per cent of their body mass – a range that is three times higher than previous average estimates.

In the Southern Ocean, the team estimated baleen whales ate around 430 million tonnes of krill per year before industrial whaling began in the early 20^th century. This is twice the estimated mass of krill in our oceans today.

“This new higher estimate is important for the functioning of ocean ecosystems because whales act as giant nutrient recycling plants,” says Savoca, “By consuming even more prey than previously thought in most cases, they are also pooping more, and that poop is actually marine fertiliser.”

This fertiliser sparks the growth of marine plants, including phytoplankton, and provides food for krill and other small fish.

Emma Cavan at Imperial College London, who wasn’t involved in the study, says: “It is counter-intuitive to think that if there are more krill predators, there will be more krill. But it highlights just how complex biology is, as actually the presence of whales may have fertilised the Southern Ocean with nutrients, thereby stimulating phytoplankton growth, which is the food the krill eat. It really is a true circle of life, and we are only just beginning to understand it.”

The study highlights the important role that recovering whale populations play in restoring marine ecosystem functions.

“There’s a variety of passive and active things to encourage whale recovery, such as more regulations and marine protected areas in our oceans,” says Savoca.

Journal reference: Nature, DOI: 10.1038/s41586-021-03991-5

Sign up to Wild Wild Life, a free monthly newsletter celebrating the diversity and science of animals, plants and Earth’s other weird and wonderful inhabitants