A SPATE of deaths of the world’s deepest-diving mammal around the west coast of Scotland has left marine experts baffled.
Scientists at the Hebridean Whale and Dolphin Trust (HWDT) and Scottish Marine Animal Stranding Scheme (SMASS) say an unusually large number of Cuvier’s beaked whales have been found dead over the past couple of weeks.
The species, also known as the goose-beaked whale, is rarely seen due to its hunting grounds being around 80 miles offshore, but five carcasses were found washed up on Scottish shores in December.
This amounts to a five-fold increase in the number of annual strandings reported for the species in each of the previous three years.
Last month’s “weather bomb”, an unidentified disease or even interference from sonar operations at sea have all been considered as potential causes, but scientists say evidence is conflicting since only a single species appears to have been affected. The badly decomposed state of the corpses has meant post-mortem examinations have also failed to provide any pointers.
“There are no obvious clues as to what is causing such a sudden increase in strandings of this species,” said Dr Conor Ryan, sightings and strandings officer for HWDT.
“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.”
There was a similar unexplained spike in strandings during 2008, although there was a mix of deep-diving species among the 57 fatalities.
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SMASS director Dr Andrew Brownlow said: “We don’t receive many reports of them and to receive so many over the western seaboard is unusual.
“First of all, do these have a single origin? Is there something that has happened at a single place that has cause a lot of deaths, and the bodies have gradually been moved by tides and currents and are now washing up on beaches?
“The recent massive storm surge and huge swell will have scoured the eastern Atlantic and brought things from a long way out to sea and dumped them on western shores.
“However, if it was simply a question of weather and we happened to be a catchment area because a westerly was pushing dead animals on to the beaches when normally they would sink, we would expect lots of other whales as well.
“This is making us believe that perhaps there is something specifically affecting this species.”
Dr Ryan said an Irish whale and dolphin group had also recorded similarly high deaths of Cuvier’s beaked whales, which can grow up to 23 feet long.
Five were found dead along the west and north coast in December, accounting for almost 10 per cent of all known strandings of the species since records began.
The SMASS has only recorded 37 strandings of the species in Scotland in the past 25 years – 17 of these during the 2008 spike.
Recent beachings were on the Isle of Mull, the coast of Sutherland and Borve Point on Benbecula, in the Outer Hebrides.
The Cuvier’s whale holds the world record for the longest and deepest dive for a mammal – down to 2,992 metres for a staggering two hours and 17 minutes. The pressure at this depth is 300kg per square centimetre.
There are no global population estimates for the species, although they are generally thought to be one of the most abundant of the beaked whales.
Deepest diver can live for up to 40 years
Cuvier’s beaked whale (Ziphius cavirostris) is the only member of the genus Ziphius and is the most widely distributed of the beaked whales.
One animal has been recorded diving down to 9,816ft (2,992 metres) below the waves, which is around 6.75 times the height of the Empire State Building.
The creature has a robust, cigar-shaped body similar to other beaked whales.
It can grow up to 23ft (7 metres) long and can weigh 5,500lb (2,500kg).
The whale has a small dorsal fin and flippers to prevent drag while swimming.
It lives for around 40 years and feeds on different species of squid and deep sea fish.
Cuvier’s whales can be found in a number of different deep offshore waters from the tropics to cool seas.
It is thought there may be over 100,000 of the creatures in seas across the world.
The whale gets its name from the anatomist George Cuvier – who first described its imperfect skull, in 1804.
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