Sonar devices on board Naval vessels was today blamed for the death of 26 dolphins who died when they swam up a river in Cornwall.

But initial post-mortem examinations of seven of the animals revealed no clues as to the cause of the mass stranding.

The animals appear to have been well-fed and there were no obvious signs of disease or poisoning.

Dead Dolphin
British Divers Marine Life Rescue have suggested that the sonar used by military ships had disorientated the Common dolphins.

But the British Divers Marine Life Rescue have suggested that the sonar used by military ships had disorientated the Common dolphins.

However chairman Alan Knight conceded: "We can find no conclusive evidence as to why the stranding took place or why they stranded in such numbers at different locations."

Rescuers were today still searching for any dolphins who might still be stranded.

The sea mamals died when they became trapped in the shallow waters of the Percuil River yesterday.

Lifeboat crews and members of the BDMLR managed to rescue seven of the animals and help them to rejoin their pod in deeper waters.

By the time emergency teams could reach them, the majority of these once graceful creatures were already beyond help.

Even after one of the biggest marine animal rescue operations ever mounted in the UK, only the lucky ones would survive.

From the moment they headed up a tidal estuary from the deep waters of the south Cornish coast, they were virtually doomed.

Yet for several hours they kept coming. Wave after wave made the fateful journey along the receding waters of the Percuil River, near Falmouth, yesterday - either in pursuit of food, it is thought, or in response to the call of those which were already dying.

The result was one of the most horrific scenes to confront coastguards and animal rescue groups for years - the worst mass stranding in nearly three decades.

A total of 26 dolphins died and several were in such poor condition they had to be put down.

Falmouth lifeboat crewmen managed to return five to deeper water but it is believed they may simply have returned later.

Only seven of those treated or rescued could be saved - two of them were towed to sea on stretchers attached to boats.

Grim task: The recent heatwave caused a massive bloom of algae in shallow waters which attracts bait fish, but the dolphins may have become confused in rivers and shallow estuaries

No one knew for certain why they came. The normal habitat of these striped dolphins is deeper offshore water where fish, squid and shrimps are plentiful. Their playground is the freedom of the seas.

But the world of these most enchanting and intelligent mammals has long held many mysteries for mankind. Yesterday, none was any closer to being solved.

One by one the carcasses were stretched out side by side on dry land.

Rescuers fought back tears as the bodies of others lay lifeless or helpless on the shore. One described the scene as ' carnage'. Another said the stranding was 'almost beyond comprehension'.

The dolphins, among nature's most graceful and spectacular swimmers, began heading inshore some time during yesterday morning. Had anyone caught sight of them in the early hours, they might have thought they were in for the kind of marine cabaret that enthralled Cornwall a year ago, when a pod of 40 striped dolphins was sighted off Land's End.

They can leap spectacularly high out of the water and travel in large groups, often of 100 or more and sometimes up to 3,000.

A few months later, 50 bottlenose dolphins thrilled holidaymakers off St Austell with an aquatic ballet of tail-walking and back-flips.

But yesterday brought only scenes of death after the first stranded dolphins were reported at 8.30pm.

Coastguards, rescue teams and marine wildlife organisations worked side by side in the biggest such operation since 1981, when 20 pilot whales beached on the east coast of England.

RNLI Helmsman Dave Nicoll revealed how his crews struggled desperately to save the stranded dolphins. 'We have been trying to help those who are alive and have already succeeded in getting five back into the water,' he said. 'But there are still some caught on the shore and they are very sick. It's a horrible scene of carnage with bodies everywhere.'

At one stage, boats attempted to block the estuary entrance. It proved to be no obstacle.

Daryl Thorpe, a British Marine Life Rescue co-ordinator, said: 'The boats are trying to stop them getting up the river but we're surrounded by them - it's incredible.'

From a boat towing one victim out to sea on a stretcher, he added: 'I've never seen anything like it.'

So why might so many come ashore en masse? One theory is that hot weather in the South-West produced an unusually big algae bloom in the estuary, which attracted large numbers of fish. These, in turn, then attracted hungry dolphins.

Ironically, it was the same hot weather which created so many casualties - the baking sun rapidly dehydrated the dolphins, which need water to keep their skins moist.

Other possibilities are that one dolphin became lost or stranded and sent out a distress call, picked up by fellow dolphins for miles around. Such is the dolphin's family-unity that loyalty often takes precedence over danger.

Or perhaps it was caused by a simple navigation glitch.

Sometimes a dolphin's sophisticated echo-location system can get confused, causing it to become temporarily lost.

Recent strandings elsewhere have been blamed on interference from naval sonar, and Falmouth has a large Royal Navy base.

Most likely, however, is that the answer will never be known for certain. And a sad but intriguing mystery will remain with the dolphins.

The investigation continues.