Whales eat (and poop) more than we thought
Whales are, by weight, the largest animals to exist in the history of life on Earth. They can weigh up to twice that of the largest dinosaurs with blue whales weighing in around 150 tonnes. Up to now, we didn’t know exactly how much food a whale was eating but new research published in Nature found that whales are eating up to three times more than we first thought.
A team of researchers from Stanford University investigated the feeding habits of 321 whales over seven different species using state-of-the-art technology. Previous methods involved crude metabolic modeling and experiments at whaling stations weighing the insides of a whale’s stomach. Lead author Matthew Savoca explained, ‘‘we hadn’t measured on a living whale how much food it was eating".
To measure how much food a living whale eats, the team counted the number of gulps taken by a whale during feeding using a suction cup tag the size of a rugby ball that is able to sense when water is taken in. The tags work in a similar manner to sensors in our smartphones, and are able to detect motion with very high resolution. Researchers assessed the size of the gulp through analysing aerial images obtained by drones. Finally, the team probed the density of prey in the water using an echo-sounder which works analogously to how dolphins and bats assess their prey using reflected sound waves. Combining the number of gulps, size of gulps and density of prey allows for an estimate as to how much food these whales are eating. The answer turns out to be around 10-20 % of their body weight on feeding days, which is far higher than initial estimates.
The significance of these results lies in the key role whale poop plays in ocean ecosystems. Whale poop is critical for nutrient recycling, returning components such as iron to the water for smaller creatures like plankton and phytoplankton to feed on. More poop means more plankton leading to more krill and more fish in our oceans. "Ecosystems with whales are more productive than ecosystems without" says Savoca. Not only do these findings expand our understanding of whale ecology but also in our understanding of their role in marine ecosystems.
Savoca comments on the team's findings, “we need a world with whales and this work helps expand our understanding of why that is so.”