Royal Navy's sonar testing may have killed dolphins off Cornish coast

13 April 2012

The Royal Navy had been testing sonar equipment only miles from the bay where dozens of dolphins met an agonising death.

Another theory is that killer whales could be to blame for the shocking deaths of the dolphins.

The Ministry of Defence has admitted that a survey vessel was mapping the seabed 12 miles off the Cornish coast when the creatures swam to their deaths.

The admission will fuel suspicions that sonar caused the dolphins' sophisticated echo-location system to become scrambled, driving them to shallow waters where they suffered a slow and horrific death.

Post mortem: Scientists have so far failed to explain why 26 Common dolphins died after beaching themselves

Post mortem: Scientists have so far failed to explain why 26 Common dolphins died after beaching themselves

But the MoD said it was 'extremely unlikely' its warship was to blame because the sonar system was a low-powered and short-range device.

Officials also denied reports that the Navy was carrying out gunnery practice at the time of Monday's mass beaching in the Falmouth Bay area.

The dolphins were fit, healthy and carried no obvious signs of disease when they became trapped at four points in and around the bay.

Post-mortem tests have revealed evidence they were 'scared ashore'.

British Divers Marine Life Rescue (BDMLR) said many of the dolphins had no fish in their stomach, which adds weight to the theory that they were panicked by an underwater disturbance.

A common reason for the animals being stranded is when they are chasing fish - but if they were feeding, there would be clear evidence of it, a BDMLR spokesman said.

Tony Woodley, spokesman for BDMLR, said: 'Very few had anything in their stomachs.

'That adds weight to the theory that they were scared ashore.

'It is another unusual factor in this extremely unusual stranding.'

It is also possible that killer whales scared the pod of dolphins into the shallows.

In all, more than 100 deep-sea-dwelling common dolphins strayed into Falmouth Bay, a popular training ground for vessels from the Navy's Devonport base in nearby Plymouth. More than 30 became stranded and dozens more became distressed in shallow water, in one of the worst scenes to confront coastguards and animal rescue groups for years.

Although many dolphins were saved, 24 died and two were put down.

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

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

Some of the most likely explanations for the stranding include the inquisitive and sociable creatures being disorientated by Naval sonar or frightened ashore by an explosion.

Several residents have reported hearing loud explosions late on Sunday and there are claims the Navy was carrying out live firing exercises.

Alan Knight, chairman of the British Divers Marine Life Rescue organisation, said: 'We can find no conclusive evidence as to why the stranding took place or why they stranded in such numbers at different locations. My personal conclusion is that there was some sort of disturbance that has caused the animals to panic.'

Shipping movements in the area, mining and military exercises were all being investigated, he said.

Trevor Weeks, also of the BDMLR, said residents had reported hearing a pair of large explosions on Sunday evening.

He said: 'If the Navy was doing any testing or sonar work or anything under water, that could be a cause of why they came into the estuary. Even something like an earthquake could cause a problem.

'A lot of whales or dolphins strand because they are injured or ill. The postmortem examinations have shown the animals to be fit and healthy and no obvious sign of illness or injury.'

He added that failure to find fish in the animals' stomachs dispelled the theory that they were lured into the estuary by shoals of fish feeding on algae there.

Experts continued to examine the dolphins

Experts continued to examine the dolphins

Dr Paul Jepson, one of a team from London Zoo carrying out the post-mortems, said: 'Effects of manmade noise from the oil and gas industry, and from naval warships using sonar to look for submarines, have been linked with the standings of some species of whales and dolphins.'

Possible theory: Killer whales could be to blame for the shocking deaths

Possible theory: Killer whales could be to blame for the shocking deaths

Other theories include the dolphins swimming into the estuary to escape predation by a killer whale.

Some dolphins did survive on the Percuil river in Cornwall yesterday

Some dolphins did survive on the Percuil river in Cornwall yesterday

The creatures' innate sense of family could also have been to blame. Gill Bell, of the Marine Conservation Society, said: 'If one of them was sick and stranded itself after getting disorientated, they would have gone after it to try to assist.'

Preliminary tests have been carried out on 11 dolphins. Further tests, including searches for viruses and poisons, could take months to complete and may never yield a conclusive cause of death.

The Navy said it had not carried out any shelling exercises in the area since Friday June 6 - three days before the beaching.

Disruption: Some experts have blamed the Royal Navy, who were carrying out live firing exercises involving a submarine, for the deaths (file picture)

Disruption: Some experts have blamed the Royal Navy, who were carrying out live firing exercises involving a submarine, for the deaths (file picture)

The MoD confirmed that a Navy survey vessel was testing its sonar some 12 miles off Falmouth at the time of the incident. But officials insisted the sonar was a short-range seabed mapping system, lacking the power to affect marine mammals several miles away.

Royal Navy spokesman Captain Mike Davis-Marks said: 'I doubt a dolphin would hear it more than half a mile away. It's extremely unlikely it would have played a part in this incident. We can't be categorical, but there is no evidence of any of our vessels' sonars ever playing a part in beaching incidents like this.'

Factfile: Possible causes of the dolphin tragedy

  • Sonar signals scrambled the dolphins' echo-location system
  • Killer whales scared the dolphin pod into the shallows
  • An explosion frightened them into shallow water
  • They fled to the cost to escape predation by a killer whale
  • They were swimming to the aid of an injured pod mate
  • They were chasing fish feeding on algae thriving in the warm water

Create a FREE account to continue reading

eros

Registration is a free and easy way to support our journalism.

Join our community where you can: comment on stories; sign up to newsletters; enter competitions and access content on our app.

Your email address

Must be at least 6 characters, include an upper and lower case character and a number

You must be at least 18 years old to create an account

* Required fields

Already have an account? SIGN IN

By clicking Create Account you confirm that your data has been entered correctly and you have read and agree to our Terms of use , Cookie policy and Privacy policy .

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.

Thank you for registering

Please refresh the page or navigate to another page on the site to be automatically logged in