Royal Navy ships patrolling Westcountry coastal waters may be forced to turn off their sonar to prevent the stranding of whales and dolphins on beaches.
An internal report drawn up by the Ministry of Defence (MoD) suggests the Navy could be vulnerable to legal action and vessels should switch off the electronic devices if they detect marine mammals.
Officials insist there is still no hard evidence to prove the technology can harm whales, porpoises or dolphins.
But conservationists believe a large-scale offshore military training exercise was partly to blame for Britain’s worst mass stranding near Falmouth in 2008, where 26 dolphins died.
Ruth Williams, Cornwall Wildlife Trust’s marine conservation manager, said “the finger pointed most strongly ” at the Navy for the Falmouth stranding and welcomed the policy change as “really positive”.
“This is one of several mitigating measures the Navy is putting in place,” she added.
“They have some of the world’s leading software to determine where the highest cetacean activity is linked to Naval activity and if they use them all successfully as part of their tool box it will prevent this happening again.
“Initially (after the mass stranding) the barriers went up and they didn’t want to know, but having worked for two or three years those barriers have come down and they have accepted the need to work with us and fulfil their environmental duties.”
Scientists have established that some deep-diving whales and dolphins can suffer fatal doses of the bends – in which nitrogen dissolved in the blood expands to form bubbles – after being startled by the sound of sonar.
The MoD guidance is being drawn up by the environment department and will reinforce the European Union habitats directive, which prevents the deliberate disturbance of protected species. Crucially, it is believed the guidance will state that “deliberate” acts include those where the result of an action is “foreseeable”.
The report from the MoD’s defence nuclear environment and safety board, released under the Freedom of Information Act last year, revealed fears about potential consequences of the guidance.
“This would mean that [the] MoD would no longer be protected by claiming any harm caused was the unintended result of an otherwise legal action,” it said. “For example – using active sonar to locate a hostile submarine, knowing there are cetaceans in close proximity which may be harmed as a result.”
Experts say naval commanders already voluntarily switch off sonar in exercises if they know cetaceans are near.
The guidance could also affect the oil and gas industries which use high intensity sound to search for fossil fuel deposits beneath the seabed.
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