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On 25 September, a beluga whale has been seen feeding in the river Thames near London. Experts have speculated that storms may be one of the reasons why it has travelled so far from home.
Belugas normally live in freezing Arctic and subarctic waters, and are rarely seen off the coast of Britain. This animal's appearance in the Thames is an unusual - and worrying - sight.
Without a closer investigation of the whale, it is impossible to confirm what has brought it this far south, but disturbances in weather patterns could be a possible cause.
Richard Sabin, marine mammal expert at the Museum, has been monitoring the whale closely. He says, 'There is a theory that this appearance in the river could be linked to severe storm systems, both the recent two in the UK and the hurricane in the US.
'There has been speculation in the past that stormy weather can cause whales to become disorientated and confused and to make navigational errors. This animal is so far away from where it should be, but the reason for this extralimital sighting isn't clear.'
Well this is as close as it gets folks - but hey its a Beluga Whale in the Thames WOW! Exciting but sadly more heartbreaking - i wish it all the luck in the world, it will need it #beluga #thames #wildlifecameraman #uk pic.twitter.com/mkAZK7VdM0— richard taylor-jones (@rtaylorjones) September 25, 2018
Onlookers spotted the white whale at noon on 25 September, when it was seen feeding around barges near Gravesend in Kent.
Experts think it is likely that the beluga has come from the direction of Svalbard off Norway. It looks to be a grown adult at roughly five metres long.
It is not unusual for belugas to travel up rivers, but they normally don't venture so far south of the Arctic. They are not an open-water species, instead preferring to spend time around coasts. The whales also don't need deep water to feed, and can find food in just a few metres of shallow water.
Between 1793 and 1932, there were less than a dozen reported sightings of belugas in British waters. More recently the animals have been seen off the coasts of Northumberland, Scotland and Northern Ireland. This week's sighting is the most southerly record of a beluga in the UK.
Other cetaceans have also appeared in the UK, far outside of their usual habitat.
Dr Chiara Bertulli, Sightings Officer at the Sea Watch Foundation, adds, 'In the last decade, we have recorded sightings of cetacean species that are completely outside of their normal habitat, like the bowhead whale - a species largely confined to the Arctic regions - which was sighted off the Isles of Scilly in February 2015.
'One possible explanation for the recent bowhead whale records is that ice melt is causing the ice to fragment, causing icebergs and pack ice to drift south from the Arctic. The welcome increase in the size of the West Greenland whale population may also be a contributory factor for why this individual appeared some 2,000 miles from its normal range.'
Concerns are growing for the safety of the visiting whale. At the time of writing, the beluga has been in the same location for more than 24 hours, which Richard says is a worrying sign.
There is a risk that it won't find enough food, and that it will be too exhausted to complete the return journey home. Belugas are also social animals, normally spending time in pods.
Richard says, 'We all want this whale survive and return to its pod. But it is a long way to swim, and it may not have the energy if it hasn't been feeding properly.
'The positive thing is that belugas can feed on a wide range of prey, including marine worms, squid, crustaceans and many species of fish, so hopefully it is finding enough to eat in the river.'
Marine-adapted animals do not fare well in freshwater environments like the Thames.
Richard says, 'Most species of cetaceans are adapted to life in marine environments. Estuaries such as the Thames Estuary are transition zones between marine and freshwater. Though belugas can be found in estuaries up around the Arctic, they may develop metabolic problems if they spend too much time in freshwater systems.'
If the beluga doesn't make it back out to sea, a rescue attempt may begin. It would be initiated by British Divers Marine Life Rescue and the RSPCA, who are currently monitoring the animal's progress. The charities will only intervene if the whale appears to be in distress.
Experts have urged the public to stay away from the whale, and not to approach it in a boat or to attempt a rescue.
If it dies, the Zoological Society of London (ZSL) and the UK Cetacean Strandings Investigation Programme will be first on the scene to conduct a post-mortem examination.
Eventually, its carcass will be brought to the Natural History Museum, where it can be dissected and examined. The Museum's world-leading marine mammal collection contains beluga skeletons dating back to the early nineteenth century.
Richard says, 'If the beluga doesn’t survive and we are able to collect the carcass, we would use a range of different analytical techniques to try to build up a long-term picture of the animal's diet, movements and general health.
'The data would be added to those which we have collected from other historical specimens, allowing us to track changes in this species over time.
The Museum's research collection only contains one beluga specimen from the UK, an individual that stranded near Stirling in the Firth of Forth, Scotland, in 1932. It was a young male, measuring just over 2.5 metres (eight feet and six inches). The entire animal was sent to the Museum after it died, and it now provides an invaluable reference for marine biologists and other researchers.
This isn't the first time an unusual whale species has appeared in the Thames. It's been just over a decade since a northern bottlenose whale swam into the River Thames and drew thousands to watch the dramatic rescue attempt.
On 19 January 2006, a six-metre-long female northern bottlenose whale swam into the River Thames in London. It had ventured a long way from its home in the deep waters of the North Atlantic.
In 1949 two narwhals (a close relative of belugas) also appeared in the river, having travelled from the Arctic. A female was found stranded in the River Medway in Kent, and a male made it all the way into the lower reaches of the Thames. The female was collected and incorporated into the Museum's research collection.
It could be that these two animals were suffering from disease or became disorientated, losing their way and growing weaker as they travelled further south. It is also possible that their appearance was related to an extreme cold weather event in the same year.