Diet plays big role in how huge whales get
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 Thursday 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 sonarlike 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.
The blue whale can be bigger because it feeds in a much different and highly efficient way, the study says. It opens its mouth wide and engulfs an immense volume of water, even bigger than its body size, as it swims along. Then it closes its mouth and strains the water out through a sievelike filter, which traps huge amounts of tiny, shrimplike creatures called krill.
That “allows them to exploit a very large prey resource that’s very rich in a small amount of time,” said Jeremy Goldbogen of Stanford University, another researcher. “They get a huge bang for the buck.”