Chief Reporter
Anti-submarine war games off the Westcountry coast were the "most probable" cause for the mass stranding of 26 dolphins on the region's coast, scientists have concluded.
The pod of dolphins beached themselves at four separate locations around the Percuil River, near Falmouth, in June 2008 after an international military exercise involving surface ships and a submarine.
At the time, conservationists said they believed the worst mass stranding of the marine mammals in UK waters was the result of the dolphins being panicked by an underwater disturbance.
Those fears have now been backed by a four-year investigation by scientists which ruled out every other cause for the incident. The findings, published in the journal PLOS One, follow post-mortems on the short-beaked common dolphins involved.
Dr Paul Jepson, of the Institute of Zoology, who led the research funded by the Department for Environment, Food and Rural Affairs, said that a group of up to 60 dolphins swam into the bay three or four days before the stranding, probably to escape the disturbance caused by the anti-submarine sonar.
He said the dead dolphins, most of which were infants, had been in good health and ruled out other potential causes of death.
"The mass stranding may have been a two-stage process where a large group of dolphins entered the bay, possibly to avoid a perceived acoustic threat," reported Dr Jepson.
"After three or four days, a second disturbance occurred, causing them to strand en masse.
"The international naval activities are the only established cause which cannot be eliminated and is ultimately considered the most probable, but not definitive, cause."
The mass stranding resulted in distressing scenes as rescuers attempted to refloat many of the animals. While 26 dolphins died in the event, a similar number were successfully herded back into water.
Many blamed the use of mid-frequency sonar, used by the military to detect hidden vessels, which has been associated with past strandings of marine mammals.
A study published in 2009 by the Zoological Society of London (ZSL) said a definite cause for the stranding could not be found, although the dolphins could have reacted to a "trigger" event or suffered an "intrinsic error of navigation".
Research by Cornwall Wildlife Trust Marine Strandings Network and British Divers Marine Life Rescue, published at the same time, did not blame the naval exercise.
But it added: "It is possible that the second wave of panic, when the dolphins came into Falmouth harbour, may have been caused by naval helicopters which were flying around that time."
Conservation groups have repeatedly called for the Ministry of Defence to redesign exercises to safeguard wildlife.
Sarah Dolman, head of policy at Whale and Dolphin Conservation Society, said: "This stranding is a game-changer and leads us to call for a re-evaluation of military activities."
However, a Royal Navy spokesman said: "We do not agree with the conclusion of this report. Even its own extensive investigation has found no evidence to show naval activity was responsible. Naval training has taken place in the area for over 60 years and active sonar has been in use throughout that time without any similar reported mass strandings. The Royal Navy is committed to taking all reasonable and practical measures to mitigate effects on marine animals."