Whale size limited by calories they eat

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

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

The results suggest body size is controlled by how whales capture prey and how much food is available, researchers reported Dec. 12 in the journal Science.

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

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

“It looks like you cannot be much bigger than a sperm whale” when hunting the way it does, said Nicholas Pyenson of the Smithsonian’s National Museum of Natural History, who was part of the research.