Science Says: Diet plays big role in how huge whales can get

Whales are big, but why aren’t y bigger? A new study says it’s basically about how many calories y can take in.

That’s conclusion of researchers who used small boats to chase down 300 whales of various species around world. y reached out with a long pole to attach sensors to creatures with suction cups, allowing m to record what animals were doing on ir dives for food.

results suggest body size is controlled by how whales capture prey and how much food is available, researchers reported Thursday in journal Science.

study included 90 blue whales, biggest animal ever to live. Size estimates vary, but American Cetacean Society says blue whales can grow about 100 feet (30 meters) long and weigh more than 100 tons (91,000 kilograms). study also included biggest whale with teeth, sperm whale, which can stretch about 60 feet (18 meters) long, group says.

When tood whales hunt, y capture one prey at a time, seeking m out in murky depths with a sonar-like detection. study found that as body size increases in such whales, y become progressively less efficient as y hunt — y recover fewer calories from ir meals per calorie burned in each dive. That results from limits on availability of prey.

“It looks like you cant be much bigger than a sperm whale” when hunting way it does, said Nicholas Pyenson of Smithsonian’s National Museum of Natural History, who was part of research.

blue whale can be bigger because it feeds in a much different and highly efficient way, study says. It opens its mouth wide and engulfs an immense volume of water, even bigger than its body size, as it swims along. n it closes its mouth and strains water out through a sieve-like filter, which traps huge amounts of tiny shrimp-like creatures called krill.

That “allows m to exploit a very large prey resource that’s very rich in a small amount of time,” said Jeremy Goldbogen of Stanford University, ar researcher. “y get a huge bang for buck.”

So why aren’t y even bigger than y are? Maybe blue whales are limited by seasonal nature of most nutritious krill patches, which grow gigantic and dense in summer, Goldbogen said. And calculations indicate that to sustain a blue whale that’s 115 feet (35 meters) long, “you’d need a density of prey that is just t seen anywhere in world,” Pyenson said.

But maybe re’s also some kind of limiting factor in how ir bodies function, Goldbogen said. He ted a recent study that found a blue whale’s heart beats up to 37 times a second after deep dives, and that appears to be about as fast as organ can pump.

Ar limiting factor could be a whale’s ability to process food it takes in, said Terrie Williams of University of California, Santa Cruz, who did t participate in research.

study provided a comprehensive look across big whale species, and success in collecting data “boggles mind,” she said.

“You try to go out and put a tiny tag on back of biggest animal in world,” she said.

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This Associated Press series was produced in partnership with Howard Hughes Medical Institute’s Department of Science Education. AP is solely responsible for all content.