Whales are showing signs of acute sun damage that researchers believe is due to rising levels of ultra violet radiation.
The research by British and Mexican researchers and published today in Proceedings of the Royal Society B suggests that continued depletion of the ozone layer could put whales at risk of developing skin cancers.
Researchers from the University of London , the Instituto Politecnico Nacional , and the Universidad Autonoma de Queretaro photographed and took skin biopsies from over 150 fin, blue and sperm whales in the World Heritage listed Gulf of California.
The ocean-going life of a whale is one of almost constant sun exposure. Although they dive for some food, much of their socialising, feeding and breeding time is spent very near the surface, where the clear water provides little protection from burning UV radiation.
Over millions of years whales have evolved skin repair mechanisms to cope with sunburn, but the new research suggests that increasing UV radiation coming into the tropics where the whales live could be overwhelming their natural defences.
Rapidly increasing blisters and lesions
The researchers say the photos and skin biopsies show "widespread evidence of epidermal damage commonly associated with acute and severe sunburn".
Over half the whales tested had 'sunburn cells' in their skin - these are cells which form when the DNA is damaged by UV radiation.
Most alarmingly, when the researchers tracked the formation of sun-induced skin blisters in Blue Whales over time, they found the number of blisters had increased significantly in just three years.
They suggest that rising UV levels as a result of ozone depletion are to blame for the observed skin damage, in the same way that human skin cancer rates have been on the increase in recent decades. The Cancer Council of Australia says the rate of skin cancer in women rose 6.8% in the decade between 1993-2003 and for men, it rose 18.7%.
With UV radiation expected to increase 4% in the tropics and up to 20% in the poles over the next few decades, the researchers say the thinning ozone layer poses a 'significant and rising threat' to cetaceans.
Since the hole in the Antarctic ozone layer was discovered in the 1970s, ozone levels have shrunk by up to 70% in the worst seasons. Although the CFCs which damaged the ozone layer were banned in 1987, ozone levels are not expected to recover for another 40-50 years.
Dr Nick Gales who is the Leader of the Australian Mammal Centre at the Australian Antarctic Division says Australian whale researchers have also seen higher levels of blisters and lesions in whales over the past few years.
The blisters are around 10cm wide, and occur across the back and sides of the whales where the skin is most exposed to the sun.
Dr Gales said blisters have also been seen in dolphins and are particularly common in the pygmy blue whales found off the coast of southern Victoria and Rottnest Island in West Australia.
"It would be useful to look at long term photo identification catalogues [taken of whales by researchers in the past] in a more random stratified way, to look for evidence for increases in skin lesions, and to also take advantage of strandings to look at their histology.
"With the increase in UV, it may lead to increases in some kind of cancers that are life threatening to the whales. It's something we need to look more carefully at."