The energy that whales spend during feeding may exceed what they get from their prey, keeping the body size of the Earth’s largest animals in check, according to a study.
The study, published in the journal Science, noted that the size to which whales grow is limited by prey availability, and some of the marine mammals have evolved a strategy to achieve the largest body sizes of any animal to have ever lived on the Earth.
The researchers, including those from the Smithsonian National Museum of Natural History in the US, sought and tagged whales, porpoises, and dolphins of various sizes — from 5-foot-long harbour porpoises to gigantic blue whales.
They used multi-sensor tags temporarily affixed via suction cups, reaching from their boats with long poles to stick them on to the animals’ backs.
The results of the study revealed that the relationship between body size, and energetic payoff depended on what feeding strategy a whale had evolved to use.
The researchers explained that whales were either filter feeders — which gulped down schools of prey, and strains them from ocean water — or instead, toothed hunters that caught prey individually.
“Energy is a key currency for all life, and we wanted to know how energy gain compares to energy use in foraging whales with different body sizes and feeding strategies,” said Jeremy Goldbogen, study co-author from Stanford university in the US.
“The ratio of energy gain relative to energy use reveals a whale’s foraging efficiency and that provides clues as to why different whales are big and why they aren’t bigger,” Goldbogen said.
The scientists explained that blue whales, humpbacks, and other filter-feeding whales used baleen — rows of flexible hair-like plates in their mouths — to strain krill and other small prey from ocean water.
These whales seek out dense patches of their prey, and almost always consumed more calories than they expended while feeding.