'Unique' sighting of fin whales Dolphin spectacle baffles experts

Jeff Tierney, from Pontypridd, filmed the leatherback as he sailed back to Wales from Ireland on Sunday.

The turtle is the largest species of its kind and can grow up to nine feet (2.74m) long.

The world's biggest and oldest specimen was washed up on a Welsh beach in 1988. It had drowned after being trapped in fishing lines.

Mr Tierney told the BBC's Wales Today programme: "It let us come right up next to it. We were literally within two yards of it. We turned the engine off, got a tape out and started videoing.

"He seemed to be quite happy there bobbing up and down with us right next to him. It was absolutely fantastic."

Huge size

Experts say it is likely the turtle was trawling the waters for its favourite food, jellyfish, which are abundant in the warm sea of Carmarthen Bay.

Marine Biologist Howie Watkins said leatherbacks were no stranger to Welsh waters.

He said: "They regularly hunt as far north as the Arctic Circle and can be found in Canada as they search for their jellyfish food.

"They're able to do this because they're the only reptile that generates its own body heat - very much as we do. That combined with their huge size really is a great advantage to them."

The world's biggest recorded leatherback turtle was washed ashore on Harlech beach, Gwynedd, in September 1988 attracted worldwide attention.

At 100 years old, it was the oldest recorded turtle. It measured almost nine feet (2.74m) in length and weighed 914kg (2,015lb).

Mr Tierney said it had been an exciting year for marine life in Wales.

"We've had a pretty interesting summer: large numbers of dolphin spotted, a sun fish coming up from the tropics, other species of turtle, even a humped back whale turned up."