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.