Finally we know how much krill whales eat – which also explains the puzzling krill paradox

Whales eat three times as much krill as previously thought. And that explains why the amount of krill decreased so much after intensive whaling. huh?

Krill is one of the main food sources for whales; we know that. But exactly how much krill do whales eat? Until recently, that was a big mystery. In a new study, researchers have attempted to answer that question. And it seems that the answer to that question has also solved another long-standing mystery: the marked decline in krill following intensive whaling in the last century.

Krill paradox

Between 1900 and 1970, unprecedented numbers of whales were killed by humans. You would say that this disastrous decline in whales probably led to an immense increase in krill. After all, their greatest enemy was largely gone. But that’s not what scientists saw. On the contrary. Surprisingly, the decline in whale numbers led to a decline in krill. This phenomenon is also known as the krill paradox.

Study

But now a new study sheds light on this puzzling mystery. And by studying how many krill whales slide in. The researchers placed tags on as many as 321 whales of seven different species that live in the Atlantic, Pacific and Southern Oceans. These tags, which look like suction cups, are placed on the whales’ backs and act as a kind of smartphone: complete with camera, microphone, GPS and a meter that tracks their movements. And these smart tags then gave the researchers insight into their eating habits.

Scientists examine a humpback whale by boat and drone in surface waters near the Antarctic Peninsula. Image: Duke University Marine Robotics and Remote Sensing under NOAA permit 14809-03 and ACA permits 2015-011 and 2020-016

Whales appear to have quite an appetite. Because the research shows that they eat no less than three times as much as thought. For example, an adult blue whale eats about 16 tons of krill per day during the foraging season. “That’s the weight of a full school bus!” says Matthew Scott Savoca in conversation with Scientias.nl. “Part of this has to do with the fact that baleen whales only eat about 100 days a year and fast the rest of the time. Something that is really remarkable for a warm-blooded animal that does not hibernate. So in order to survive and reproduce, they have to eat as much as possible during their summer feeding period.”

Ocean health

This discovery has far-reaching consequences. Because by underestimating how much whales eat, scientists have also underestimated the importance of these undersea giants to ocean health and productivity. Because whales eat more than expected, they also poop more. And whale droppings are a crucial source of nutrients in the ocean. For example, it is rich in iron, which in turn supports the flowering of carbon-absorbing phytoplankton. Previous research has also shown that whale droppings contain about 10 million times as much iron as Antarctic seawater. In addition, phytoplankton is back on krill’s menu. And so the circle is complete again.

Back to the krill paradox

It means that hungry whales and their droppings are very important for the health of the ocean. And that also explains the aforementioned krill paradox. Intensive hunting caused immense numbers of whales to disappear from the oceans. Fewer whales means less poop. A lack of whale droppings – and therefore iron – prevents the growth of phytoplankton. And less phytoplankton, in turn, means less krill.

Before whaling

These surprising findings led the researchers to study what the marine ecosystem looked like before industrial whaling that killed some 2 to 3 million whales. The researchers used existing estimates of the number of whales that used to live in the regions, combined with the new results, to determine how much the animals likely ate at the time. “Our calculations suggest that whales at the time consumed more food than all of today’s krill and global fisheries combined,” study researcher Nicholas Pyenson said in an interview with Scientias.nl. “The implication of these numbers is that whales supported many productive ocean ecosystems before whaling.”

The researchers therefore argue in their study for the recovery of the whale. Because this research undoubtedly underlines the crucial role they play in marine ecosystems. If we can restore whale populations to pre-whaling numbers, we can also restore important ecosystem functions that have been lost over the past 100 years,” Pyenson argues.

Oceanic Amazon

In addition, whales can also help to further contain climate change. Because, as mentioned, the iron-rich whale droppings feed the blooming of phytoplankton. Phytoplankton then absorbs CO2 during photosynthesis. And the more phytoplankton, the more CO2 is absorbed and stored in the ocean. This probably happened to a large extent before the disastrous whaling. “Our results suggest that whales’ contribution to global carbon removal was likely comparable in scale to the forest ecosystems of entire continents,” Pyenson said. “It’s no exaggeration to say we’ve lost an oceanic Amazon with whaling. Restoring the whale can therefore also offer a natural climate solution.”

recovery

This study unequivocally demonstrates how everything is interconnected and how the extermination of millions of whales has been devastating to the marine environment. So the recovery of the whale population can actually work wonders and help to boost declining fish populations. “More whales mean more productive oceans,” concludes Savoca. “And more whales are simultaneously supporting larger populations of fish and krill, not smaller ones.”

Now the question is whether we will be able to give the whale a hand. Especially now that the quality of the ocean is deteriorating further due to climate change. “Many of the solutions are in our own hands,” says Pyenson. “They relate, for example, to the economy and legislation. For example, declining numbers of whales in the North Atlantic can be largely attributed to collisions with ships and entanglement in fishing gear. However, this can be solved more easily than ocean acidification and warming seas.” Still, the researchers are hopeful. For example, Savoca suspects that the numbers of whales will certainly recover in the long run. “However, the question is on what time scale,” he says. “I hope within my life. But time will tell.”