A shark expert has dismissed claims of an "unusually large" shark photographed off the coast of Cornwall over the weekend.
The image of what looks like a large fin was taken by Jacquie Williams at around 11am on Sunday in Gunwalloe, near Porthleven - pictured around 30 metres from the coast.
Her son-in-law posted the picture on Facebook, warning swimmers to "proceed with extreme caution", saying: "It doesn't look like the average basking shark."
One local told Cornwall Live: "Either way, dangerous or not, it's unusual to see any type of shark inshore this time of year and with a fin that size."
Speculation grew on social media over what species of shark it could be and the danger it poses, but marine expert Dan Jarvis says the discovery is not what people think.
“This photo is a seal, it’s just sleeping in an upright position, they can look like fins sometimes. It’s amazing that it’s got this far," he told Yahoo News UK.
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"People see something and they’re not sure what it is, people post it on Facebook and say I think it could be a shark, then it’s reported that it is a shark and it could be dangerous."
Jarvis, director of welfare and conservation at the British Divers Marine Life Rescue charity, said that while a number of shark species can be spotted off Britain's coast - and often in fishing nets - they rarely pose a threat to swimmers.
“Some are quite big, none of them are particularly dangerous unless people want to go and mess about with them and provoke them.”
Basking sharks, which feed on plankton, are among the largest likely to be found swimming around the UK. They can grow up to 30ft long and are sometimes mistaken by beachgoers as great whites, Jarvis added.
Following an interview about a sighting of a blue shark in shallow water near Trelissick beach last summer, Jarvis said he'd been misquoted by many media outlets as saying he was worried about harm to humans.
In reality, he said the incident was "worrying" because it suggested the shark may have had health problems, he told Yahoo News UK.
Blue shark attacks on humans are described on the British Sea Fishing website as "extremely rare", with only four fatal and 25 non-fatal attacks having been confirmed.
UK-based charity the Shark Trust says there have been no “unprovoked” shark bites in British waters since 1847, when records began.
“There are a number of shark species to be found around the UK, none of them are dangerous to humans," Jarvis added.
"The only time these animals tend to be aggressive humans is if they have been provoked in some way.”
Some marine biologists have suggested that changes in water temperatures brought by global warming could lead to new species of sharks being attracted to the UK coast.
However, others could be driven away, says Jarvis, who points out that basking shark sightings off the south coast are much rarer now as their food source has migrated towards colder waters in Scotland.
He added that thresher and mako sharks could migrate more frequently from the Bay of Biscay to the UK as a result of global warming.
Although they are very rare, shark attacks are not completely unheard of in the UK.
In early August last year, the Penzance Coastguard Rescue Team was dispatched to help a snorkeler who was believed to have sustained a shark bite. The swimmer had suffered a leg injury and was passed to the care of an ambulance team.
According to a comprehensive report on reported shark sightings by Carbon Brief, the prospect of larger sharks - such as tiger sharks - appearing in UK waters is not beyond the relams of possibility, but something that there is, as of yet, no evidence of.
While climate change may indeed push some shark species away from the equator and closer to the poles - potentially including UK waters as well - sharks would also need to rely on the correct habitat in which to thrive, such as the availability of food.
Dr Peter Cotton, a marine biologist from the University of Plymouth, told Carbon Brief: “The main reason that they are not regular visitors here is that there is relatively little for them to eat. Of course, if climate change increases the number of tuna in the UK, there will be something to eat.”