Blue whales, humpbacks, and other baleen whales eat up to three times more than previously thought. This is what American, Danish and South African biologists write temper nature. They fitted the whales with a transmitter to locate their hunting sites and calculate the density of prey there. This indicates that the animals eat up to 30 percent of their body weight daily. This has dire consequences for their ecosystem and may explain the mysterious “krill paradox”.
Baleen whales (Mysticeti) are the largest animals on Earth. Their balls – rows of floppy “hairs” – enter the nutrient-rich ocean waters filled with fish and krill, a type of shrimp-like plankton. But exactly how much they eat remains a guess. Based on the stomach contents of dead whales and computer models, scientists previously concluded that the animals eat about 5 percent of their body weight daily. The current researchers wrote that this estimate is too low based on their observations of 321 live baleen whales from seven species.
The more whales eat, the more they excrete. Whale droppings are rich in nutrients, including nitrogen and iron. While baleen whales often feed relatively deep in the water, they usually defecate during breathing periods, near the surface of the water. The crustaceans in turn provide food for the phytoplankton. These phytoplankton ensure additional carbon dioxide uptake2 From the air, they serve as a source of food, for example krill. In this way it ends up indirectly to the whales.
The authors estimate that whales around Antarctica ate up to 430 million tons of krill per year before large-scale whaling began there around 1910. This massive food intake resulted in about 12,000 tons of recycled iron. But between 1910 and 1970, whale numbers plummeted so much that whales recycle only 1,200 tons of iron annually.
The long-unexplained krill paradox: Fewer whales and fewer krill – their food
This decrease in recycling may explain the krill paradox. For many years, biologists have puzzled over how the amount of krill has fallen so sharply since whaling. They expected that the dwindling of the whale population would lead to a massive increase, but it turned out that the opposite was true: along with whales, the krill disappeared. The authors wrote that if whales are already generating a “green wave” of extra life with their droppings, rising whale numbers may also increase krill densities.
If the presence of iron had such a critical effect on krill’s abundance, we could even use it to protect the environment, marine biologist Victor Smetasek wrote in an accompanying editorial. temper nature. Smetasek, professor emeritus at the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research, believes that scientists should experiment with “seeding” more iron in the oceans. “From our ability to imitate the iron fertilization of whales” […] to feed the krill and with it the whales.” And who knows, he hopes to write, that this will eventually lead to a richer life in the ocean.
A version of this article also appeared on NRC on the morning of November 4, 2021
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