Why the world needs more whale poop
“It all collapsed when the whales were taken out.”
Bigger than any dinosaur that ever existed, blue whales can reach 110 feet long and weigh up to 190 tons.
These giants, alongside other cetacean species like humpback and grey whales, are part of a group known as baleen whales. Together, they are some of the world’s largest animals.
You might suspect that animals of this size eat a lot. However, new research suggests baleen whales eat even more than previously estimated — three times more.
This also means they poop more. And according to scientists, this is very good news for the rest of us.
These findings were published Wednesday in the journal Nature.
How the discovery was made — Baleen whales typically feed on clusters of small fish or crustaceans, including krill. Whale poop, in turn, is an essential source of nutrients for ocean ecosystems.
But due to their size and feeding habits, it’s been hard to gauge just how much food they consume. This has hindered conservation efforts.
“If we want to protect whales and make sure they are thriving in modern oceans, then knowing how much food they need to survive and reproduce is critical,” lead author Matthew Savoca, a postdoctoral scholar at Stanford University, tells Inverse.
Previous estimations were likely inaccurate because they either relied on metabolic models on much smaller animals, like dolphins, that were studied in captivity or were based on the contents within dead whales’ stomachs.
“Occasionally when whales were killed, people would open their stomachs and weigh the contents inside,” Savoca says.
By contrast, this study team used direct measurements of baleen whales in the Atlantic, Pacific, and Southern Oceans to determine how much krill they ate — and how much they subsequently defecated. Using tagging methods and acoustic measurements, researchers gathered field data on more than 300 whales across seven species of baleen whales.
Based on their observations of daily feeding behavior, scientists calculated the amount of prey (like swarms of krill) the whales consumed, as well as the number of nutrients recycled back into the ocean through feces.
What they found — Prior studies suggested baleen whales consumed less than five percent of their body weight each day.
Instead, Savoca’s research finds that baleen whales consume three times more prey than scientists previously realized.
Across all baleen whale species studied, whales consume an average of 5 to 30 percent of their body weight each day. The scientists found fin whales and humpback whales populations in the northeastern Pacific Ocean alone require more than two metric tons of krill each year.
“In brief, if whales eat more than we thought, then they also recycle more nutrients — i.e. poop — than we thought.”
But the amount and type of prey consumed depends on the whale. For example, an adult eastern North Pacific blue whale (Balaenoptera musculus) will consume 16 tons of krill on feeding days, while the North Atlantic right whale will likely eat five tons of small zooplankton.
Meanwhile, humpback whales prefer a more complex palate and alternative between eating anchovy and krill. All this food translates to one thing: way more poop.
“In brief, if whales eat more than we thought, then they also recycle more nutrients — i.e. poop — than we thought,” Savoca says.
Why these findings matter — The study team wasn’t calculating how much whales eat and poop for the fun of it.
“While it may just seem like a fun trivia fact, knowing how much whales eat is an important aspect of ecosystem function and management,” Savoca says.
Whales provide important nutrient recycling services in ocean ecosystems. When they poop, they recycle nutrients — including iron — back into the sea. These nutrients are then consumed by smaller ocean creatures like phytoplankton, which helps to keep oceans healthy.
“It's not that these whales add more iron —or other nutrients — to the system, they just convert it from within the bodies of their prey, to in the seawater itself, where it could, in theory, fertilize phytoplankton — the base of all open ocean food webs.”
But while whale poop has enormous effects on global ocean ecosystems, recent research suggests the decline in whales has been slowing down that global conveyer belt of nutrient recycling.
Whale hunting caused baleen whale populations to drop precipitously between 1910 to 1970. In turn, remaining whales consumed less prey than what could have been possible, recycling fewer nutrients.
The researchers estimate that pre-1900s whale hunting, baleen whales in the Southern Ocean consumed 430 million tons of Antarctic krill annually. That’s two times as much krill as exists today.
“Baleen whales were maintaining the krill stocks on which they were feeding,” Victor Smetacek, the author of a related perspective on the study, tells Inverse. Smetacek is a researcher at the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research.
“It all collapsed when the whales were taken out,” Smetacek said.
This new study highlights the essential, fragile role of whales in ocean ecosystems — especially now that scientists know baleen whales are contributing much more to these ecosystems than previously realized.
What’s next — While some baleen whale populations, like the humpback whale, have made remarkable recoveries in recent years, others aren’t faring nearly so well.
For example, a recent report suggests the North Atlantic right whale population declined by eight percent over the past year, hitting its lowest numbers in two decades. The decline of baleen whales means less nutrient recycling for oceans.
To get the ocean to a place where it could have been if this decline never happened, we would “need to mimic the whales by adding iron artificially from ships,” Smetacek says.
Savoca hopes his study spotlights the ecological significance of baleen whales and aids in conservation efforts. He stresses that simple changes, like regulations to slow down shipping traffic along common whale routes, can have “big positive effects.”
“We are trying to use the information we have learned to try and conserve whales, and help them recover,” Savoca says.
Abstract: Baleen whales influence their ecosystems through immense prey consumption and nutrient recycling1–3. It is difficult to accurately gauge the magnitude of their current or historic ecosystem role without measuring feeding rates and prey consumed. To date, prey consumption of the largest species has been estimated using metabolic models3–9 based on extrapolations that lack empirical validation. Here, we used tags deployed on seven baleen whale (Mysticeti) species (n = 321 tag deployments) in conjunction with acoustic measurements of prey density to calculate prey consumption at daily to annual scales from the Atlantic, Pacific, and Southern Oceans. Our results suggest that previous studies3–9 have underestimated baleen whale prey consumption by threefold or more in some ecosystems. In the Southern Ocean alone, we calculate that pre-whaling populations of mysticetes annually consumed 430 million tonnes of Antarctic krill (Euphausia superba), twice the current estimated total biomass of E. superba10, and more than twice the global catch of marine fisheries today11. Larger whale populations may have supported higher productivity in large marine regions through enhanced nutrient recycling: our findings suggest mysticetes recycled 1.2 × 104 tonnes iron yr−1 in the Southern Ocean before whaling compared to 1.2 × 103 tonnes iron yr−1 recycled by whales today. The recovery of baleen whales and their nutrient recycling services2,3,7 could augment productivity and restore ecosystem function lost during 20th century whaling.