Giant, krill-eating whales could grow even bigger if the size and availability of their prey (猎物) could keep up, a new study finds.
Whales are the heaviest animals to have ever lived on our planet. These marine giants evolved from dog-sized four-legged land creatures and grew nearly 10,000 times bigger in the past 50 million years or so, according to Nicholas Pyenson, head of fossil marine mammals at the Smithsonian's National Museum of Natural History.
Creatures benefit from having a bigger size in a number of different ways, whether it's not getting eaten by smaller creatures or having the ability to keep warm and travel great distances more efficiently. Still, some whale species are bigger than others, and they do have some limits to their size.
To find out what these limits are, researcher attached multisensor equipment to many types of whales. The researcher also assessed prey type and quantity using different methods. For baleen whale prey，they used acoustic(声学的) equipment to test the density (密度) of krill patches. For toothed whales, they looked at the size and quantity of squid (鱿鱼) beaks and otoliths (parts of the inner ear) found in the stomachs of beached whales.
Putting all the data together, they could determine how much energy the whales were likely to get back from the food. For toothed whales, the limiting factor seems to be the size of their prey. Sperm whales were found to feed mostly on medium-sized squid—possibly because there aren't as many giant squid in the ocean. Baleen whales, like blue whales swallow massive mouthfuls of krill or other small creature. But these small creatures only appear in large concentrations for a few months per year in some areas, which may be the limiting factor for the growth of the largest whales.
A researcher said that it's not completely clear that baleen whales have finished growing. "Perhaps several million years into the future we'll see something even larger than a blue whale."
