HARBOUR porpoises found dead on the coast have Scotland are likely to have been the victim of vicious attacks by bottlenose dolphins.

The marine mammals show injuries including broken ribs, shoulder blades and spines, and brain haemorrhages caused by being “punched” and tossed around by the dolphins.

The number of porpoises washing up increases at this time of year as they come in to more contact with dolphins in inshore waters.

In the latest case, post mortem tests on a juvenile male that washed up at Golspie Beach in Sutherland last month, showed it had died as a result of trauma caused by an attack.

Marine biologist Mariel ten Doeschate of the Scottish Marine Animal Stranding Scheme (SMASS), said the reason for the attacks was unknown, but it could simply be for fun.

She said: “Around 40-60 per cent of the harbour porpoises we find for necropsy have died as a result of attacks by bottlenose dolphins.

“The dolphins do not eat the porpoises so it is not about predation. They tend to chase them around and grab them or punch them out of the water with their noses - and when they are dead they just leave them.

“Very often the ribs are broken and sometimes the spine. Some have had a broken scapula - the shoulder blade. The dolphins tend to grab hold of them at the scapula base and then throw the porpoise about, which causes brain haemorrhage.

“It is really quite violent. One animal had three focal breaks in the spine - it had literally been punched three times.”

Miss ten Doeschate said bottlenose dolphins in the north of Scotland were the “biggest in the world.

They grow up to 3.5m in length and are also “chunky” due to insulation for the cold waters.

Despite their friendly reputation, bottlenose dolphins have also been known to kill each other’s young.

She added: “They are highly intelligent animals but they are not always as friendly as they look.”

SMASS said there were a total of 51 strandings of different marine animals along the coast of Scotland in September.

They included 21 porpoises, dolphins and whales; 28 seals; and two leatherback turtles - one found dead on the Outer Hebridean island of Vatersay and the other off the coast of Arbroath, in Angus.

Many of the seals were young grey seals at the beginning of the pupping season.

A Northern bottlenose whale found near Ardentinny, in Argyll and Bute, was found to have drowned after becoming entangled in ropes off the west coast.

It was the first beaked whale of any species diagnosed with entanglement as the cause of death in the UK since records began in 1992.

Its skull, shoulder blade and pectoral fin were recovered by the National Museum of Scotland for its research collection.