A giant leatherback turtle has been spotted swimming four miles off the coast of Tenby.

Believed to be the largest species of turtle in the world, the leatherback is currently listed under the Endangered Species Act after its global population declined by 40 per cent over the past three generations.

But on Sunday afternoon Oscar Allen, along with his work colleagues Jack Lamont and Gareth Harris chanced upon the leatherback as they sailed four miles off the coast of Tenby.

“We were whelking and suddenly we saw the turtle directly ahead of us,” Oscar told the Western Telegraph. “It stayed with us for about three hours and it was massive.”

Despite the global decline in leatherback turtle numbers, reported sightings off the coast of Wales have increased over the last few years.

This is believed to be because the reptiles are drawn by the high numbers of jellyfish that are found off the coast of Pembrokeshire and Ceredigion.

Dr Peter Richardson of the Marine Conservation Society (MCS), has previously described the Welsh waters as ‘turtle heaven’.

The turtles nest in the Caribbean before travelling to UK waters to feed, and with the high number of jellyfish that have been reported in the Irish Sea throughout 2023, the turtles know that they’re onto a good thing.

"The waters around Wales are absolutely perfect for turtles," he said.  "So in many ways it’s a true turtle heaven."

The leatherback turtle giants are solitary ocean wanderers and, unlike other sea turtles, don’t mind the cold. As a result, they can dive to great depths where the water is a lot colder to get the first pick of all the deep-sea jellyfish.

They only get together with other turtles in order to breed, and they subsequently lay their eggs on beaches and leave them unsupervised.  As a result, the baby turtles have to make their way to the sea alone once they hatch.

Fully grown, they can measure up to 2.5 metres in length and can weigh-in at a staggering 916kg, or 144 stone. They can also look forward to a lengthy lifespan of up to 100 years.

The leatherback is listed as a Priority Species under the UK Post-2010 Biodiversity Framework and can be spotted around the UK between May and September.