Some of the animals have two thirds of the visible parts of their bodies covered in lesions, while in others the normally smooth dark skin has turned orange or is pitted like corroded aluminium.
A scientific survey of 10 other groups of the same species, the bottlenose dolphin, Tursiops truncatus, has found that there are some skin irregularities in all of them, but that the Scottish animals, on which a tourist trade in the Inverness area is based, are by far the most seriously affected. Nearly all the 130 animals in the colony are suffering.
The research, to be published in the Proceedings of the Royal Society, has so far found no link between the skin disease and pollution, but may indicate one with water temperature and salinity.
The Moray Firth dolphins are the most northerly resident group of the species in the world and live in colder and less saline water than any others. "They are a group on the edge," said Paul Thompson, a senior lecturer in zoology at Aberdeen University, who leads the study of them with a colleague from the University of St Andrews, Ben Wilson.
The researchers have so far been unable to detect the agent causing the skin disease - whether it is a virus, bacterium or fungus - or whether it is affecting the dolphins' behaviour. As wild dolphins are so difficult to study, they cannot even detect whether it is causing them discomfort. But it is certainly ugly in appearance. "Some of them do look pretty grotesque," Mr Thompson said.
The disease came to light when the Scottish researchers began photographing and studying the dorsal fins of individual dolphins in order to recognise them. They then organised the worldwide survey to see if it was prevalent elsewhere.
Bottlenose colonies were studied in Portugal, Ireland, Brittany, Croatia, the United States and New Zealand, as well as Britain's other resident colony in Cardigan Bay in Wales, and a smaller number of animals off the Cornish coast. All were found to have some skin disease.
The Cardigan Bay animals were also quite badly affected, but the dolphins of the Moray Firth were by far the worst hit.
"It is a cause for concern, as this is a very small colony, and it highlights their vulnerability," Mr Thompson said.
The Moray Firth animals have already been observed exhibiting unusual behaviour as well as unusual skin conditions - they are known to attack and kill porpoises, apparently from sheer aggression, and last year it was revealed that they have even attacked their own young. But no connection can so far been drawn between the two phenomena, Mr Thompson said.Reuse content