White Sharks Rely on Liver Oil for Buoyancy and Fuel for Long Journeys [VIDEO]

Great white sharks use fat and oil stored in their livers to provide buoyancy and fuel non-stop journeys exceeding 2,500 miles, according to researchers from Stanford University's Hopkins's Marine Station and Monterey Bay Aquarium.

Other creatures, such as birds and whales, are known to power long journeys using fat stores, but the recent study was the first ever to show the characteristic present in sharks. The find suggests that great white sharks, which have a reputation as voracious eaters, fill up once before a long trek, rather than chowing down on prey along the way.

"We have a glimpse now of how white sharks come in from nutrient-poor areas offshore, feed where elephant seal populations are expanding - much like going to an Outback Steakhouse - and store the energy in their livers so they can move offshore again," said researcher Barbara Block, a Stanford professor of marine sciences.

"It helps us understand how important their near-shore habitats are as fueling stations for their entire life history."

Whales and sea lions build up blubber, which acts as fuel for long migrations, much like a bear will increase its fat stores before going into hibernation. But until now, it was poorly understood how sharks managed long journeys of their own without building up stores of blubber. Researchers studied a well-fed white shark in captivity at the Monterey Bay Aquarium. They documented over time a steady increase in buoyancy as the shark's body mass increased, presumably due to the increase in oils stored in its liver.

Then, the researchers looked at white sharks in the wild to identify points of "drift diving," in which the shark passively descends while momentum carries it forward. By measuring the sharks' rate of descent during drift dives, researchers were able to estimate the amount of oil in the sharks' livers. Quicker-descending sharks had less oil in the liver, whereas more buoyant sharks were determined to have more oil in the liver. The free-swimming sharks consistently decreased in buoyancy over time, indicating a gradual, but steady, depletion of oil reserves.

"Sharks face an interesting dilemma," said Sal Jorgensen, a research scientist at the Monterey Bay Aquarium. "They carry a huge store of energy in the form of oil in their massive livers, but they also depend on that volume of oil for buoyancy. So, if they draw on those reserves, they become heavier and heavier."

The researchers' findings are published in Proceedings of the Royal Society B.