Conservation group Whale and Dolphin Conservation has asked the Ministry of Defence to detail what military movements took place off the Scottish and Irish coasts in December.
That month a naval chase took place aided by American planes after a periscope was spotted in waters off Faslane, where Royal Navy submarines normally surface as they head in or out of the base, home to Britain’s nuclear deterrent.
But since the search experts have been baffled by an increasing spate of mystery deaths around the west coast of Scotland, including several by the world’s deepest diving mammal.
Scientists at the Hebridean Whale and Dolphin Trust say they have now received 15 reports since mid-December of stranded Cuvier’s beaked whales, a species that is rarely seen due to its offshore distribution.
The strandings have occurred down the west coast between Scotland and Ireland including two on Mull, South Uist, Benbecula, Tiree and Kintyre.
In addition other species of whale and dolphin have washed ashore along the west coast, including a killer whale on the Uists.
Now conservationists want to know if sonar in particular – which can damage cetaceans and has been suspected in past strandings – was used in the submarine hunt.
Dr Andrew Brownlow, head of the Scottish Marine Animal Stranding Scheme, said he was still waiting for the MoD’s response.
“WDC has asked the MoD for answers, which will be passed on to me,” he said. “They want to know what military activity was taking place in the area at the time.
“It is possible that these strandings are linked to certain military activity. It is something we are looking at. But the animals were so badly decomposed we shall probably never know the answer,” he said.
Samples from some of the dead Cuviers have been sent to Dr Brownlow for analysis.
Dr Conor Ryan, sightings and strandings officer for HWDT, added: “What we do know is that there has been a large and sudden cluster event.
“It may be biological or it may be man made? We are concerned because we have not known anything like this for the last six to eight years. We do not know why and we may never know, especially given the state of the animals.”
Cuvier’s whales can grow up to 23ft-long and are widely distributed in tropical to cool temperate waters. Northern Scotland represents their northern-most limit.
The species is the current world-record holder for the longest and deepest known dive for a mammal – down to 2992 metres for two hours and 17 minutes. The pressure at this depth is 300 kg per square centimetre.
Other than the pair of teeth in adult males, beaked whales are toothless and are thought to use suction to catch their prey.
In a statement on its website, WDC said: “The mass stranding of rare, deep-diving whales along the coast of Ireland last December could be linked to a reported search by British navy warships for a suspected Russian submarine.
“Eight rarely sighted Cuvier’s beaked whales have been found off the Irish coast in recent weeks together with a number of common dolphins, a minke whale, a sperm whale, pilot whales, a fin whale, and harbour porpoises. The total of 33 whales and dolphins washed up dead on Irish shores so far this year is a record. Last year a number of Cuvier’s beaked whale deaths in Crete were thought to be due to military exercises in the area. Investigations following Britain’s largest mass dolphin stranding in 2008 concluded that the only realistic cause was military exercises taking place in the area at the time. Noise pollution threatens whale and dolphin populations, interrupting their normal behaviour, driving them away from areas important to their survival, and at worst injuring or sometimes even causing their deaths. For whales and dolphins, ‘listening’ is as important as ‘seeing’ is for humans, yet there are still no international regulations regarding noise pollution in the world’s seas.”