The image of the bottlenose dolphin as a friendly creature has been dented by new evidence that shows it attacking and killing its cousin the porpoise.
Hard evidence was provided by Mr. Mike Hancox, a local man, who captured an attack on film.
"I was very shocked," he said. "At first I thought the two dolphins were playing with a salmon."
"But when it was looked at more closely I could see them flipping up a porpoise with their beaks and battering it when it landed on its back on the water. "This destroys the myth of the cuddly, Flipper-type dolphin and puts them in the category of wild animals sustaining themselves by instinct and protecting their territory," he said.
Ms Sally Wilson, the series producer, said: "The dolphins pack one hell of a punch."
"They play with porpoises in the same way that killer whales play with seals. The kill can take up to 45 minutes."
"Although the porpoises are bitten, no part of them is eaten by the dolphins."
Mr Ben Wilson, from an Aberdeen University research team studying dolphins in the firth, said:
"The dolphins and porpoises have similar diets. But that does not explain the ferocity of the interaction. It could be some sort of recognition problem. Dolphins are afraid of big sharks and this could be leading them to attack porpoises.
"Other theories are that it is aberrant behaviour in two dolphins or that there is some sort of stress exerted in the firth which leads to this behaviour."
There have been reports of isolated incidents of dolphins attacking porpoises off the coast of British Columbia and in the Pacific. Dolphins do attack each other, particularly when they are held in captivity and try to establish a social hierarchy. Mr Chris Stroud, of the Whale and Dolphin Conservation Society, said:"Dolphins evolved 35 million years ago and this seems to be very recent and unusual behaviour. "In the Moray Firth there has been increased boat traffic, pollution and oil and gas exploration and it could be that this had altered the ecological balance there. "If dolphins feel that their food stock is under threat then they tend to defend their territory and themselves," he said.
Well i didn't know that !