Experts have clashed over the existence of Great White Sharks off the UK coast.
Great White Shark: Vagrant visitor?
Speculation is mounting amid a series of claimed sightings by holidaymakers and fishermen and a new documentary on BBC One on Sunday.
Marine biologist Douglas Herdson, from the National Marine Aquarium in Plymouth, rejected claims of sightings.
But shark conservationist Richard Peirce says the weight of anecdotal evidence convinces him that Great Whites are in UK waters.
Mr Herdson said: "Temperature and conditions here are all fine, and I'm sure they have been here in the last 3-4,000 years, but they are now so rare it is very unlikely.
"Shark populations such as blue sharks in the North Atlantic have crashed over the past few years.
"All the intensive fishing in the Bay of Biscay, catching hundreds of thousands of sharks including one Great White 40 years ago, means I very much doubt they are here now."
In 2003 Richard Peirce set off from Padstow in Cornwall with the intention of spotting a Great White, but returned without a sighting.
Mr Peirce, from Bude, told BBC News: "There is no scientific evidence, but there is very strong anecdotal evidence and the case is much stronger than that portrayed in the programme.
"I am almost certain that Great White Sharks appear off the coast.
"My view is that there is strong circumstantial evidence that we get occasional vagrant visitors."
Lobster fisherman Brian Bate, from Padstow, is convinced he saw a Great White several years ago.
He said: "I saw this big thing breach out of the water.
"He looked like he was tail towards me. I could see his back and as he came up he twisted sideways.
"I thought, 'What was that?'. It was quite a size to come leaping out of the water."
Sharks: Great Whites in Great Britain is showing on BBC One this Sunday at 1900 BST.