Fattened livers prep white sharks for extreme migrations

Reserves enable long journey from California to Hawaii and back

11:02am, July 17, 2013

BIG TANK  A young white shark temporarily residing at the Monterey Bay aquarium gave researchers a chance to test a virtual gas gauge designed to see how the fish draw down energy stores during their epic migrations. 

A white shark’s big fat liver, which can plump up to more than a quarter of an animal’s body weight, turns out to be the fuel tank for extreme migrations.

White sharks (Carcharodon carcharias) in the eastern Pacific take a springtime swim from California to Hawaii and return in late summer. A one-way, 4,000-kilometer trip takes about a month.

By combining data from two kinds of tracking tags attached to the animals, an unusual analysis shows that sharks fatten up for the demands of migration much the way birds do, says Gen Del Raye of the University of Hawaii in Manoa.

As the sharks use up calories stored as oily lipids, their bodies lose buoyancy. The tracking data revealed signs that during the trip to Hawaii sharks sink progressively faster during glides, Del Raye and his colleagues report July 17 in the Proceedings of the Royal Society B. Tagged sharks on the California coast didn’t change in glide trajectories.

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