A decline in huge baleen whales -- and, just as importantly, in whale poop -- has had major consequences for both the ocean ecosystem and the global climate, new research says.
Species such as the blue whale, humpback whale and right whale feed by gulping huge amounts of water that's strained through the animals' baleen -- structures that make up a huge filter feeding system inside the whales' mouths. These marine mammals are also the largest animals living on the planet today, making them nearly impossible to study in captivity. As a result, some basic biological knowledge about these big beasts, like exactly how much they eat, has never been rigorously studied by scientists.
An international team of researchers spent nearly a decade gathering data from seven species of baleen whales across three oceans using an arsenal of modern technology, including drones, underwater echo sounding equipment and tags (packed with a camera, microphone and sensors) that were suction-cupped to the whales' backs.
The team discovered that baleen whales eat way more than previously estimated -- three times more. That's a lot of filtered krill ending up in whale stomachs, which means even more whale poop going into the ocean than we thought. Before the era of industrial whaling in the 20th century greatly reduced baleen whale populations, certain parts of the world's oceans were quite literally swimming in shit.
And that's the problem: We could use a lot more of those whales and their poop right about now.
"Think of these large whales as mobile krill processing plants," said marine ecologist and Stanford University postdoctoral fellow Matthew Savoca in a statement. "Each fin whale or blue whale is the size of a commercial airliner. So, in the first half of the 20th century, before whaling, there were an additional one million of these 737-sized krill processing plants moving around the Southern Ocean eating, pooping and fertilizing."
Savoca is lead author on a study published in the latest issue of the journal Nature outlining the findings. The scientists also examine the lasting impact of large-scale whaling, which was greatly reduced starting over 50 years ago.
"Our results say that if we restore whale populations to pre-whaling levels seen at the beginning of the 20th century, we'll restore a huge amount of lost function to ocean ecosystems," said study co-author Nicholas Pyenson, from the Smithsonian's National Museum of Natural History. "It may take a few decades to see the benefit, but it's the clearest read yet about the massive role of large whales on our planet."
Specifically, the new results help explain the so-called krill paradox, which is that krill numbers mysteriously and counterintuitively declined after the numbers of their biggest predators -- baleen whales -- declined.
"This decline makes no sense until you consider that whales are acting as mobile krill processing plants," Savoca added.
When whales eat krill, they take in iron from the tiny animals and then release it when they defecate, making it available as fertilizer to phytoplankton near the ocean surface -- phytoplankton that, in turn, feed the krill. (Cue that old Circle of Life song.)
So more whales means more phytoplankton, which means more krill, which means more whales and a happy, healthy ocean. And there's a bonus: Phytoplankton also suck up climate change-accelerating carbon dioxide. The researchers estimate that restoring baleen whale populations to where they were in 1900 could remove 215 million metric tons of carbon.
"Our results suggest the contribution of whales to global productivity and carbon removal was probably on par with the forest ecosystems of entire continents, in terms of scale," Pyenson said. "That system is still there, and helping whales recover could restore lost ecosystem functioning and provide a natural climate solution."