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Whales tan too. Just like us, they do it to protect themselves from powerful ultraviolet radiation.

A study of skin samples taken from blue, fin and sperm whales in Mexico's Gulf of California found that the blue whales show the most obvious tanning effects. Samples were collected between January and June from 2007 to 2009.

Blue whales migrate annually between the Arctic and the Gulf of California. The team, led by Mark Birch-Machin of Newcastle University, UK, found that their grey skins darken with melanin as ultraviolet radiation intensifies from February to May in the Gulf.

Birch-Machin and his colleagues also found that damage to mitochondrial DNA in skin cells dropped as the whales' skin darkened, demonstrating that melanin protects them against UV-induced DNA damage, just as it does in humans.

Perma-tanned

But neither fin nor sperm whales appeared to change colour noticeably. Unlike blue whales, which migrate annually between the Arctic and Mexico, fin whales live in the Gulf of California all year round, and so are permanently exposed to high UV levels. They had the darkest skin with the highest melanin content.

Sperm whales spend long periods at the sea surface. For sun-factor protection, they rely on melanin and a substance called heat-shock protein 70, which repairs proteins damaged by UV light. "The amount of UV they're exposed to would overwhelm pigments alone," says Birch-Machin.

He says the results are the first to show from analysis of DNA and skin that animals rely on pigments too for sun protection. Karina Acevedo-Whitehouse of the Zoological Society of London, reported the first sighting of sunburnt whales three years ago . Birch-Machin says that whether sunburn leads to melanomas in whales – as has been documented in trout – is not known.

Journal reference: Nature Scientific Reports, DOI: 10.1038/srep02386

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