Like the tanned hides of human sunbathers, whale skin appears to be vulnerable to damage from the ultraviolet radiation in sunlight, according to a recent study.
Although they live underwater, whales can't avoid sun exposure; they must surface to breathe, and, like us, they have no fur or feathers to protect them from the ultraviolet radiation that travels through the atmosphere's protective ozone layer.
"Whales are being exposed to the sun, and they are having acute sunburn damage. But we also found they are able to respond to that either by producing more pigment or increasing the rate of apoptosis," said Karina Acevedo-Whitehouse, a wildlife molecular epidemiologist from the Zoological Society of London and a study researcher. Apoptosis is programmed cell death; it is a natural protective measure that removes damaged cells.
In recent years, scientists have been seeing an increase in skin lesions among marine mammals. Although other factors cannot be ruled out, the depletion of the ozone layer by pollutants is a likely culprit, according to the researchers, who also saw an increase in blisters among blue whales over the three years they collected data.
Even though whales have the means to respond to UV exposure, however, it's not clear whether human-caused ozone depletion has created an increase that outstrips their ability to adapt, according to Acevedo-Whitehouse.
The researchers collected skin samples and high-quality photographs of various whales in the Gulf of California: blue whales (whose skin is a mottled white and gray), dark gray sperm whales and darker fin whales. The researchers looked for lesions and microscopic abnormalities that have been associated with ultraviolet damage in humans and laboratory animals.
Fin whales, whose skin had the most pigment, had the fewest lesions and other abnormalities. However, sperm whales did not fare much better than their paler-skinned relatives, the blue whales. The researchers believe this has something to do with sperm whales' surfacing patterns. Unlike blue and fin whales, who surface for only a minute or two at a time, sperm whales spend more time floating at the surface, breathing and socializing, and thus soaking up harmful ultraviolet rays, for as much as hours at a time, according to Acevedo-Whitehouse.
The article was published in the journal Proceedings of the Royal Society B.