Baleen whales are among the largest creatures to ever exist on earth. But much of their lives are spent eating tiny shrimp-like creatures called krill, which they pull out of the ocean in huge bite-size pieces. To fuel their huge bodies and planetary migrations, they have to eat millions and millions of tiny crustaceans.
But how much exactly? It turns out that scientists who study whales have almost no idea how much they eat, how much poop they are doing, and what the loss of that poop may have done to ecosystems when Whaling companies have killed millions of whales over the past 100 years.
âWe don’t remember how the world once was because we’ve changed it outside of those baselines,â says Nick Pyenson, a paleontologist at the Smithsonian’s Museum of Natural History who studies marine mammals and co-author of a new study in Nature who proposes to answer these questions. âJust as we have no cultural memory for the carrier pigeons hiding the sun, or the scale of American bison. We don’t know what the oceans looked like when there were a lot more whales.
The sheer size of these creatures makes their study, as well as their poo, a unique challenge.
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âThey are huge animals, many of them the size of a school bus or an airplane,â says Matthew Savoca. âThey feed well below the surface where we can’t see them. You cannot keep them in captivity and feed them measured food. So, at first, what seems rather simple becomes quite difficult.
Previous estimates, says Savoca, did not look directly at the whale. Instead, they took the diet of small mammals, like dolphins, and basically increased it based on the size of the whales, or estimated based on the stomach contents of dead whales.
In the new study, to get a number based on stronger physical data, the team used decades of recordings from different sources: they tracked whales with GPS beacons, which allowed them to record every time a whale pounced on prey. They used drones and sonar to measure whale mouths and the size of krill swarms, which gave an estimate of how much a whale could pick up in one sip.
To their surprise, they discovered that whales eat a lot more than previously thought. By way of comparison, previous estimates had shown that all baleen whales off the Pacific coast of North America ate 2 million metric tonnes of seafood each year. The new research found that instead, each species of whale probably eats 2 million metric tonnes, and the total catch is three times or more.
A whale-sized paradox
But this finding raises another question. Industrial whaling in the 19th and 20th centuries pushed many whales to the brink of extinction, with the worst impacts on the Southern Ocean around Antarctica. In just a few decades, humans have killed about 99 percent of the world’s blue whales. All these whales had to eat something. But existing populations of prey species, and krill in particular, are nowhere near large enough to support these whales, especially if they are eating more than previously thought.
This question is not new. When the whales disappeared, fishing experts expected krill populations to explode as they were no longer consumed en masse. And for a brief period, seal and penguin populations in the Southern Ocean increased, suggesting there was more krill to be had. But then the krill populations collapsed.
The new research suggests a resolution of the puzzle of where the krill has gone, known as the Krill Paradox. While whales eat a lot more than previously thought, they also poop more. Whale poo is serious business: a single blue whale eats around 16 tonnes of krill per day and ejects volcanic amounts of poop. And this poo is full of iron. Iron is scarce in the Southern Ocean, and the bounty of whale poo could cause an explosion in the growth of tiny algae and creatures at the bottom of the food chain. These in turn would feed huge swarms of krill, which would feed the whales.
In an accompanying essay, Victor Smetacek, a longtime researcher of marine microorganisms at the Alfred Wegener Institute Helmholtz Center for Polar and Marine Research says that the region’s first European sailors described “the surface of the sea. as being colored red by the swarming of krill, and reported that the water from feeding whale streams extended from horizon to horizon. (Smetacek was not involved in the article, but previously wrote articles on the relationship between iron and whales.)
âWhen whales eat and poop, they do so at the top of the water column,â Pyenson explains. âSo instead of these nutrients just falling to the bottom of the sea and then being locked away, these nutrients are resuspended,â a process Smetacek likens to plowing the nutrients in a field.
But take out the whales, which recycle iron, and the whole food web collapses.
If true, that would make whales not a competitor to human fishing, but the key to thriving swarms of krill and fish. âIf you let the whales return to their pre-whaling level,â Pyenson explains, âour numbers tell you that there should be an immense amount of recovery of functions for marine ecosystems. “
The implication, according to Smetacek, is that we have to start the whole recovery process with iron: Seeding the Southern Ocean could trigger a “green wave” of growth that would feed a rebounding whale population.
But Maria Maldonado, who studies the movement of metals in ocean ecosystems at the University of British Columbia, believes the research overestimates the role of whales in this story. His research has already shown that even in the 1900s, whales would only have contributed 1 / 1000th of the iron produced by microorganisms. âThese guys, the little guys, are the ones who really do it all,â she says.
Her 1900 estimates, she notes, are consistent with those of the new newspaper. âIt’s a very sexy story,â she says, but she doesn’t think it shows whales are a transformative source of iron.
Evgeny Pakhomov, an ocean ecologist at the University of British Columbia and co-author of Maldonado’s research, agrees. Noting in an email to PopSci that the timing of the decline in ocean productivity does not match the decline of whales, he said. And there are global processes, like climate change, that overshadow the impacts of whales on krill.
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It could just be that the loss of whales and the loss of krill happened for different reasons, and the paradox is a coincidence of timing. (Although the root cause is always human industry.) âNo one ever said whale poo didn’t matterâ¦ but other processes are much more important. â¦ Ultimately, if anyone says that eliminating whales as natural fertilizers is responsible for the decline in productivity in the Southern Ocean, it is totally one-sided and largely incomplete.
Savoca agrees that microorganisms almost certainly contain more iron. âI think the problem here is the behavior of the whales, in terms of processing and moving this iron,â he says. He and Smetacek both believe that the iron from whale poo has a different impact on the ecosystem, allowing it to stay near the surface, rather than sinking to the bottom of the ocean.
Where researchers agree, however, is that the whales must have done Something to the ocean that we no longer see. âWe don’t think whales are a big contributor to recycling iron,â says Maldonado, âbut we really think they shaped the ecosystem. She says that over the past few decades, populations of salps – tiny jellyfish-like creatures – have proliferated, while krill has declined, which could be linked to whales.
That’s the key point: We know whales were so big and voracious that their massive destruction left a gaping hole in the ecosystems they once shaped. But without knowing the shape of this hole, we will not be able to help it heal.