In these ozone-depleted times, most of us reach for a T-shirt or a bottle of sunscreen to protect us from the sun's ultraviolet radiation. Whales don't have those luxuries—and they're paying the price. Researchers have found numerous cases of sunburned and blistered skin on whales in the wild, sparking concern that the thinned ozone layer may be causing skin cancer in these animals.
"Most people think that whales can't get sunburned because of their dark skins," says Karina Acevedo-Whitehouse, a wildlife molecular epidemiologist at the Institute of Zoology in London. "But in the last decade, there have been increasing reports about skin lesions on whales and dolphins." Although some of the lesions may be due to pathogens, such as fungi and viruses, Acevedo-Whitehouse thought it likely that ultraviolet radiation (UVR) plays a role, too. UVR produces specific changes, including DNA damage, in skin cells, making it possible to identify the sun as the culprit.
Acevedo-Whitehouse, along with graduate student Laura Martinez-Levasseur of Queen Mary, University of London and colleagues, photographed and collected skin samples from more than 150 individuals of three cetacean species—sperm whales (Physeter macrocephalus), blue whales (Balaenoptera musculus), and fin whales (B. physalus)—in the Gulf of California over a 3-year period. The three species vary in the amount of pigmentation in their skin, with blue whales being the lightest in color and fin whales the darkest. In the lab, the researchers analyzed the skin biopsies, collected from darts shot at the whales, and identified numerous lesions that carried the telltale hallmarks of sun overexposure, including increased production of microvesicles, particles that help repair damaged tissue, and melanin pigments. As the team reports online today in the Proceedings of the Royal Society B, 95% of the samples contained cells with sun damage; in 56% of the samples, the damage extended through every layer of skin, including the lowest, basal layer.
And, just as in humans, the lighter-skinned blue whales suffered more from the sun's rays, whereas the darkest whales, the fin whales, had the fewest abnormalities. Although darker than blue whales, sperm whales had almost the same amount of sun damage, perhaps because they spend more time at the surface breathing between dives, the researchers speculate. Also like fair-skinned humans, the blue whales seemed to respond to the sun's rays by producing more pigmented cells, which help repair sun-damaged skin and protect it from UVR.
Over the 3-year study period, the number of blue whales with blisters increased by 56%, suggesting that the ongoing ozone depletion may be causing more skin damage in whales, the team reports.
"The whales are being hammered by UV rays every day, every time they surface," says Acevedo-Whitehouse, who is continuing to study the long-term effects of UVR on the whales. "The big question now is whether their cellular repair mechanisms are being exceeded," which could lead to chronic health problems, including cancer. She notes, however, that her team has not found a case of skin cancer in any of the samples of whale skin it has examined thus far.
"It's a very important paper because it gives us a tool to recognize UVR-caused lesions in whales," says Marie-Françoise Van Bressem, a veterinary scientist and specialist on cetacean diseases at the Peruvian Centre for Cetacean Research in Pucusana. "It is easy for us to forget about UV rays because we can protect ourselves against [them]," she adds. "But the whales can't. They remind us: Ozone depletion is happening."