© AP
The Cuvier's beaked whale is the world's deepest diving mammal.
Experts say they are baffled by a spate of mystery deaths around the west coast of Scotland by the world's deepest diving mammal.

Scientists at the Hebridean Whale and Dolphin Trust says it has received many reports over the past two weeks from members the public of stranded cetaceans. Five were of Cuvier's beaked whales, a species that is rarely seen due to its offshore distribution.

"Despite being rarely seen however, they are native to Scotland, preferring offshore deep-water canyons and seamounts where they hunt for squid," said the trust.

"To our southwest in Ireland, the Irish Whale and Dolphin Group have recorded similarly high numbers of Cuvier's beaked whales. In December, five were found dead along the west and north coast which accounts for almost 10 per cent of all the records of this species since records began.

"This brings to 10 the number dead Cuvier's beaked whales found in Scotland and Ireland since December. Many more will go undetected as the carcasses may sink or end up in very remote locations.

"There are no obvious clues as to what is causing such a sudden increase in strandings of this species. While the very intense storms of mid-December may be partly to blame, this does not explain why we are finding just one deep-diving species in such high numbers.

"A similar peak in strandings during 2008 comprised a mix of species - including Sowerby's beaked whales and pilot whales - but the underlying cause of this unusual mortality event (of 57 whales) was never determined."

The HWDT appealed to people to report any dead cetaceans to it.

"Strandings provide a rare an unique insight into the lives of these poorly understood animals, and may help us to establish more effective conservation measures towards their protection," it said.

Among the places where Cuvier's beaked whales have recently beached are at Borve Point on Benbecula in the Outer Hebrides.

The Scottish Marine Animal Strandings Scheme has only 37 records of strandings of the species in Scotland in the past 25 years.

The whale can grow up to 23 feet and is 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 dive for a mammal - down to 2992 metres for a staggering two hours and 17 minutes. The pressure at this depth is 300 kg per square centimetre.

Squid form the main part of the Cuvier's beaked whale diet, although they also consume fish and crustaceans.

They can dive for over 30 minutes to reach deep-dwelling prey. Other than the pair of teeth in adult males, beaked whales are toothless and are thought to use suction to catch their prey.

There are no global population estimates for the Cuvier's beaked whale although they are generally thought to be one of the most abundant of the beaked whale species.

The main threats include the accumulation of toxic pollutants in whale tissue and organs, entanglement in fishing nets and marine litter, and noise disturbance.

They may also swallow plastic bags mistaken for prey, which can accumulate in the stomach of the animal causing starvation and eventual death.