2008-06-13

Nick Tomlinson, skipper of the fishing boat Lenten Rose, had not felt anything like it in the 35 years he has been working the waters off the Cornish coast.

"I'm used to the big military guns going off but this was something different - bang, bang, bang, very close, very loud. The vibrations went through the boat and up through my backbone. The whole boat was shuddering."

As Tomlinson's boat was rocking 12 miles out, an extraordinary drama was playing out in muddy little coastline creeks near Falmouth. Around 70 dolphins had suddenly headed for shore and dozens became trapped in mud and slime. Rescuers tried to keep the distressed mammals wet by draping damp tarpaulin and seaweed over them. They guided some back out to sea but 26 perished in the sticky shallows.

Marine scientists are astounded at Monday's tragedy - the biggest mass stranding of dolphins for many years. Multiple strandings of dolphins, porpoises and whales do happen frequently in other parts of the world. In the UK the number of strandings of cetaceans has doubled to more than 700 over the past 10 years. But this increase is generally put down to the creatures becoming entangled in fishing nets and usually only involves a few individuals or a small group.

Unusual spring

Over the next few weeks scientists from the Zoological Society of London will try to pinpoint the cause of this week's stranding. The government has given them extra money to help them unravel the mystery.

But meanwhile in Cornwall, the rumours are flying, fuelled by the experiences of the likes of Nick Tomlinson. Were the dolphins terrified by explosions of some sort? Could sonar from naval vessels have spooked them? Is the military testing secret equipment?

Even before the dolphins headed for land it had been an unusual spring off the coast of south Cornwall. Northerly winds rather than the prevailing south-westerly ones whipped in and the plankton bloom, a crucial food source, came very late. Fishermen say this has caused a dearth of smaller fish such as whitebait, sardines and herrings, which in turn makes life difficult for predators such as dolphins.

After this unusual spring came an unusual weekend. Leonora Burtt, of Falmouth, went out diving in the bay on Sunday and noticed a lack of large commercial vessels. "It struck me as very odd. There are always large tankers around but all we could see was an unusual-looking naval vessel. It was strangely quiet. I was told by a fisherman that a submarine was around as well. It was as if the area had been cleared for something."

On Monday news of the strandings started reaching the authorities. A tree surgeon turning up for work had seen the dolphins "thrashing" in Porth Creek, upstream from St Mawes. Dolphins were found in two other creeks.

Darryl Thorpe, a local vet and a member of the British Divers Marine Life Rescue organisation, said his initial reaction was disbelief. "This doesn't happen in UK with dolphins," he said.

Throughout the day rescuers worked to save the creatures they could, put down the ones they could not and line the bodies up ready for post-mortem examinations. It was grisly work.

One of the rescuers, Rory Goodall, described how he was covered in milk from three lactating female dolphins. "It was terrible," he said. Intriguingly he also said he felt "tremors" that agitated the shallow water. "It was a very strange feeling - something odd was going on out there," he said.

It is easy to rule out some theories. Pathologists have said there was no sign the animals had been trapped in nets. The idea that a killer whale had scared them into the shallows has been largely dismissed - a pod of orcas would have been spotted.

The theory most of those involved in the rescue seem to be settling on is that they may have come closer to the coast than they normally would hunting because of the lack of food and then been terrified into the shallow water. The question is what frightened them.

Ministry of Defence officials say there was no "major exercise" in the area but "low level ship movements". A spokesman confirmed a survey vessel was using sonar 20 miles off Falmouth on Sunday but said it was "extremely unlikely" this would have affected the dolphins.

Gunnery exercises

There were gunnery exercises on Friday and Monday afternoon. This tallies with Goodall and Tomlinson's reports of tremors and vibrations. The MoD says no firing was going on at the times the dolphins actually headed to shore and insists the firing on Monday was routine - but both Goodall and Tomlinson are experienced seagoers and maintain that what they felt was unusual.

The Whale and Dolphin Conservation Society believes sonar or explosions could have frightened the dolphins or caused them to become disorientated. It has called for the navy to suspend the use of sonar in the area while the stranding is investigated and to release details of its activities off Cornwall.

Marine biologists are increasingly convinced that exposure to sonar leads to strandings. One of the most striking studies was carried out in Spain after a mass stranding of beaked whales in the Canary Islands. Scientists concluded the whales had died after surfacing too quickly and suffering a form of bends because they had been frightened by naval sonar.

But a major concern is that the reason for the dolphins' deaths may never be found. The fear is that if something else is endangering the dolphins, whole populations could be wiped out.
Getting stranded

· Cetaceans - whales, dolphins and porpoises - have always become stranded. In 1927 168 false killer whales were beached on the north-east coast of Scotland.

· In the last 12 years the number of strandings in the UK has increased dramatically from 360 in 1994 to 741 in 2006. Possible causes include marine pollution, infectious diseases, starvation, fewer prey, accidental collisions with boats, and noise pollution such as dredging and sonar. But the most significant cause is believed to be entanglement in fishing nets.

· Cornwall sees by far the largest number of strandings. The majority here occur from December to February. The Outer Hebrides and the coast of Gwynedd, Wales, are also hotspots.

· According to the Natural History Museum the biggest mass stranding this century was in March 2003 when 29 cetaceans - the species is not known - were spotted in the sea off Dorset. These were believed to have become tangled in netting. In November 2001 16 common dolphins were stranded in Looe in Cornwall - again they were believed to have been entangled.

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