A new study has looked at a shark's changing buoyancy over time to track the depletion of its fat reserves during its long migration.
Before a shark makes a long trip, it has a snack – a seal snack.
Scientists have found that the great white shark makes its 2,500-mile-long journey through the western Pacific only after feasting on seal fat and packing the oil in its gargantuan liver. That oil is the shark's sole sustenance during the food-scarce haul from California to Hawaii.
“Scientists have known that the size of sharks' livers fluctuates widely, and that this variation reflects food availability,” says Salvador Jorgensen, a post-doctoral research associate at Stanford University and Monterey Bay Aquarium and a co-author on the study, published in Proceedings of the Royal Society B.
“We have been able to finally demonstrate that a well-fed white shark in our aquarium becomes more buoyant with increasing energy stores, and in the wild, the sharks are using those stores to fuel vast migrations,” he said.
Many animals pillage from stored fat during migrations – some birds double their body weight in packed fat before departing for a long trip south. Great white sharks are one of nature’s greatest migrators, making month-long journeys of more than 2,500 miles from coastal areas abundant with seals to offshore waters, where food is scarce. Still, it had been unclear if sharks packed fat for the sea jaunt or hunted their way through the trip.