Researchers reveal great white sharks' fuel for oceanic voyages: Liver oil

Jul 17, 2013 by Rob Jordan
This is a juvenile great white shark at the Monterey Bay Aquarium. Credit: Randy Wilder

New research shows that great white sharks power their non-stop journeys of more than 2,500 miles with energy stored as fat and oil in their massive livers. The findings provide novel insights into the biology of these ocean predators.

Great are not exactly known as picky eaters, so it might seem obvious that these voracious predators would dine often and well on their migrations across the Pacific Ocean. But not so, according to new research by scientists at Stanford University and the Monterey Bay Aquarium.

The researchers' findings, published July 17 in Proceedings of the Royal Society B, reveal previously unknown details of how power themselves and stay buoyant on non-stop trips of more than 2,500 miles. The discoveries have potentially broad implications for conservation and management of coastal waters.

"We have a glimpse now of how white sharks come in from nutrient-poor areas offshore, feed where 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 professor of and a senior fellow at the Stanford Woods Institute for the Environment. "It helps us understand how important their near-shore habitats are as fueling stations for their entire life history."

Just as bears put on fat to keep them going through long months of hibernation, ocean-going mammals such as whales and build up blubber to burn on their long migrations. Until now, little was known about how sharks, which carry fat in their massive livers rather than external blubber, make similar voyages.

This video is not supported by your browser at this time.

In a study initiated by a summer project of Stanford undergraduate student Gen Del Raye, researchers first looked at a well-fed juvenile great white shark 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 addition of stored oils in its liver.

The researchers then turned to detailed data records from electronically tagged white sharks free-swimming in the eastern Pacific Ocean. Using these data, which include location, depth and water temperature, the scientists identified periods of "drift diving," a common behavior of marine animals in which they passively descend while momentum carries them forward like underwater hang gliders.

By measuring the rate at which sharks sink during drift dives, the researchers were able to estimate the amount of oil in the animals' livers, which accounts for up to a quarter of their body weight. A quicker descent meant less oil was present to provide buoyancy. A slower descent equated with more oil.

"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."

Buoyancy consistently decreased over the course of each studied shark's migration, indicating a gradual but steady depletion of oil in the liver. In other words, they were primarily running on energy stored up before they embarked on their journeys.

"The most difficult thing about this research was finding a way to bring all of the different sources of data together into a coherent and robust story," said Del Raye.

Part of that story is the importance of calorie-stocked coastal feeding grounds, not just for mammals such as whales, but also for sharks readying for long-distance migrations. Could the same be true for other ocean animals such as sea turtles and a variety of fish? The study may help answer that question too through a novel technological approach that can be applied to ongoing studies of other large marine animals.

Explore further: Aging white lion euthanized at Ohio zoo

Related Stories

Agency says shark population is stable

Jun 30, 2013

The National Oceanic and Atmospheric Administration announced Friday that the northeastern Pacific Ocean population of great white sharks is not in danger of extinction and does not warrant listing under the Endangered Species ...

New eco study looks at Great white shark behavior

Apr 10, 2013

Many terrestrial animals are frequently observed scavenging on other animals– whether it is a hyena stealing a lion kill in the Serengeti or a buzzard swooping down on a dead animal. However, documenting ...

Fear of sharks helps preserve balance in the world's oceans

Jun 04, 2013

(Phys.org) —A prey's fear of a shark is critical to protecting ocean biodiversity, according to researchers at Florida International University. Without this fear, a cascading effect within the ecosystem could destabilize ...

Sharks stun sardine prey with tail-slaps

Jul 10, 2013

Thresher sharks hunt schooling sardines in the waters off a small coral island in the Philippines by rapidly slapping their tails hard enough to stun or kill several of the smaller fish at once, according to research published ...

Calif. great white sharks get protections for now

Feb 07, 2013

The most feared predator in the ocean received new protections today when a California commission decided the great white shark should be studied as a potential endangered species.

Recommended for you

A vegetarian carnivorous plant

Dec 19, 2014

Carnivorous plants catch and digest tiny animals in order and derive benefits for their nutrition. Interestingly the trend towards vegetarianism seems to overcome carnivorous plants as well. The aquatic carnivorous bladderwort, ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.