Killer whales with yellow skin restore their white patches after migrating to warmer waters to molt.

John Durban/National Oceanic and Atmospheric Administration; Holly Fearnbach/SR3

By Virginia Morell

Some people travel across oceans to seek warm, healing waters in spas or coastal resorts. It turns out that whales are likely making their annual migrations for much the same reason: to maintain healthy skin, according to a new study out today.

Scientists have long wondered why whales—baleens, such as humpbacks and blues, and toothed whales, such as sperm and killer whales—travel up to 18,840 kilometers every year between their feeding grounds in polar waters and warmer, tropical seas. Previously, researchers thought that after feeding in the Arctic or Antarctic, whales traveled to the tropics to give birth far from their usual predators.

To find out the real reason for the migrations, researchers led by Robert Pitman, a marine ecologist at Ore

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