Jody Gibbons, 27, recorded the video of Sunday afternoon, while walking beside the Cattawade Sluice. Experts think the beast, estimated to measure 4ft to 5ft, could be a shallow water smoothound shark. Mr Gibbons, who was with his father at the time, said: "It was unbelievable to actually see something like that down this way. "I saw this fin popping out of the water. As I got closer I saw it was a shark." University of Southampton shark expert, Dr Ken Collins thinks the shark may be a smoothhound, which commonly swim close inshore.