Post-mortem studies have revealed that 42 dead porpoises washed up between 1991 and 1993 were killed by 'massive multiple trauma' inflicted when they were rammed by dolphins.
Although fighting is common among the cetacean group, which includes porpoise and dolphin, it is usually limited to within an individual species."It is well-known that dolphins attack other dolphins when they are establishing a social hierarchy," said Harry Ross, who heads the Scottish Agricultural College veterinary team which is investigating the deaths. 'But I have never heard of what has happened here anywhere else in the world.'
About 150 bottle-nosed dolphins live in the Moray Firth, joined every year by several hundred porpoise passing through from the north Atlantic. Though more numerous, porpoises only reach a third of the size of an average 12-feet dolphin.
The vets' suspicions were raised after they examined 105 porpoise carcasses form around Scotland between 1991 and 1993 and found 42 had suffered severe internal injuries. Some also had knife-like marks on their skin.
Mr Ross is now helping biologists to work out why the dolphins have turned nasty. Dr. Peter Evans, a cetacean expert at Oxford University, said one explanation could be territorial jealousy, another conflict over food.
'We ruled out fishing gear, jetskis and oil exploration equipment,' said Mr Ross. Tests taken using the jaw of a dead bottle-nosed dolphin proved an exact match with the knife-like marks.
'It was hard to believe, but the proof was there. It was a salutary reminder that they are wild animals.'