A new research paper, published July 17 in Proceedings of the Royal Society B, reveals previously unknown details of how great white sharks 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.
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.
The original article can be found here.