The Ministry of Defence is being asked to explain the mysterious deaths of several whales who washed up after suffering from the bends.
Scientists tracking the recent Nato war games, Joint Warrior, off the Scottish coast have recorded an alarming number of sonar contacts.
It’s thought sonar waves can frighten deep-diving whales, forcing them to surface too quickly.
This could lead to symptoms similar to decompression sickness – known as the bends – which human divers often suffer from.
Joint Warrior is the largest military exercise in Europe, bringing together all three of the British armed forces and troops from 13 other nations.
The two-week war exercise sees troops practice crisis and conflict situations they could realistically encounter in operations against other nations, terrorists and pirates.
Most of the training took place around Scotland’s northern coasts, and included live-firing at ranges such as Cape Wrath in Sutherland.
Investigators from the Scottish Marine Animal Strandings Scheme (SMASS) said the recent spate of beaked whale strandings was unusual.
Some had an ‘unusually high number’ of gas bubbles in their tissues, which could suggest they had the bends.
The first two cases were Sowerby’s beaked whales – also known as North Sea beaked whales – who were alive when they stranded on the Lothian coast.
SMASS said: ‘Given how sensitive beaked whales are to underwater noise, specifically naval sonar, we have to consider noise-mediated decompression sickness as a possible cause for these two strandings.
‘We are therefore in the process of trying to find data on sources of noise in this region, including putting a request for activity logs to the MoD following the recent Joint Warrior naval exercises.’
Three other cases involved northern bottlenose whales, including one in Stornoway on the Western Isles and two in the Clyde sea lochs.
Scientists aboard a Hebridean Whale and Dolphin Trust (HDWT) research vessel tracked the Joint Warrior exercise, which ended on October 15, using hydrophones and other equipment.
HDWT said: ‘We are concerned about how these exercises and training scenarios may be impacting the whales, dolphin and porpoise in our waters.
‘Military sonar used during these exercises can disturb cetaceans, who live in a world of sound, relying on their hearing to navigate, find food and communicate with one another.’
The researchers said the noise was so loud that some crew members could hear the sound coming from headphones left in a neighbouring room.
Naval sonar is still being investigated as a cause over the deaths of 90 whales who mysteriously washed up along the Scottish, Irish and Icelandic coasts in 2018.
A spokeswoman for the MoD said the Navy does all it can to ensure sonar is not damaging marine life.
She said: ‘The MoD takes its environmental responsibilities very seriously; environmental impacts are always considered in the planning of military exercises.
‘During the planning of the exercise Environmental Impact Assessments have been produced and findings implemented where required, such as for the use of active sonar and live weapons.’
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