A dead shark similar to the Great White which some claim they have seen off the Cornish coast has been washed ashore.
The trust says Porbeagles can be mistaken for Great Whites
But the Porbeagle shark, found at Gunwalloe on the Lizard, is probably not the Great White lookalike allegedly seen off St Ives, say experts.
Predatory Porbeagles are commonly mistaken for the feared Great White and at 5ft (1.5m) long it is about the same size as the St Ives shark.
Cornwall Wildlife Trust said it may have been caught in fishing gear.
Holidaymaker Richard Fletcher, from South Yorkshire, filmed a shark breaching in the water near a pod of dolphins close to Porthmeor Beach in St Ives on Saturday, raising fears people would stay away from the county's beaches.
The National Marine Aquarium in Plymouth where the shark is being examined, said it was "probably not" the one filmed off St Ives.
Douglas Henderson told BBC News it was "quite likely" a larger, mature Porbeagle that was filmed and mistaken for a great white.
"The dead shark was a juvenile only about 1.5m, whereas the one in the photo was about 3m."
Mr Henderson said Great Whites grow to about 5 or 6m, and adult Porbeagles about 3m.
The Wildlife Trust said many families gathered around the Porbeagle shark, while others continued to surf and swim, showing no apparent concern or fear.
Marine conservation officer Joana Doyle said Porbeagles, which can often be mistaken for Great Whites, are now critically endangered in the north east Atlantic.
"The Porbeagle does not pose any threat to humans. In fact, it is us that threaten their survival."