A huge leatherback turtle was spotted off the Portland coast - after it was first mistaken for a basking shark.

The rare turtle was seen devouring a barrel jellyfish at Shambles Bank over the bank holiday weekend.

Sightings of leatherback turtles - the largest of all living turtles - are rare, and it has been four years since one was last spotted in Dorset.

Video credit: Mike Lewis

Residents Mike Lewis and Keith Moore saw the creature when they were out on their fishing boat.

Mike said: "Our first thought was that it was a basking shark but as we got closer, we soon realized it was a turtle – about 1.5 to 2m in length, and it appeared to be feeding on a large barrel jellyfish just below the surface.

"We made sure it wasn’t in distress or tangled up and watched it until it disappeared. We’ve fished around Portland for over 30 years and seen porpoises, dolphins and seals, so this was a red-letter day for us."

It's thought that the turtle could have come into shallower waters in pursuit of its prey - jellyfish, which have been present in large numbers around the Dorset coast all summer.

Dorset Wildlife Trust's coastal marine centre assistant, Sarah Hodgson, said: "We were really excited to hear about this sighting of a leatherback turtle.

"These are incredibly rare visitors to the Dorset coast. With so many barrel jellyfish about this year, the turtle’s favourite food, there’s always a possibility that these magnificent marine giants might turn up, and Mike and Keith were very lucky to witness this."

Leatherback turtles are ocean wanderers and visit UK waters in the summer to feast on jellyfish. There are seven global species of turtle and this is the biggest species, and the most frequently recorded in the UK. They can weigh up to 1500 pounds and are the largest sea turtle species found in the ocean. Globally, they are listed as being vulnerable to extinction with many populations critically endangered and at risk of extinction.

Marine conservationists are particularly concerned about turtles eating plastic found in the ocean, mistaking it for food.

Dorset Wildlife Trust says marine turtles are protected by law, so care should be taken if one is seen. They are slow swimmers, so they need plenty of space.

Report marine wildlife sightings to the trust at via Twitter at @DWTMarine, Facebook/dorsetwildlife, Instagram/dorsetwildlife or email kimmeridge@dorsetwildlifetrust.org.uk.

To see the full video, visit dorsetwildlifetrust.org.uk/turtle-sighting