They are renowned as the world's greatest ocean wanderers, spending a lifetime exploring the most obscure waters.
So when a World Wildlife Federation team from Britain tagged a giant leatherback turtle with a satellite-tracking device in South America last year, they hardly expected the critically endangered creature to turn up a few miles off the Cornish coast more than a year later.
But the transmitter revealed that Aikanti, a 1.5m-long female turtle, made a 7,000-mile journey from Suriname to Britain.
After swimming in British waters for the past few days, she has now begun the homeward journey to the South American beach of her birth, to lay eggs.
Aikanti was fitted with the device in South America in June las year, as part of a WWF project to monitor the movement and threats to Atlantic species. The turtle's route to Britain initially took her to the west African coast, and from there to Portugal and the Bay of Biscay.
Rob McNeil, part of the team that tagged Aikanti, said that it was astonishing she had turned up in the UK. Food and ocean currents probably drew her to British waters, which are rich in jellyfish, he said.
"We were very lucky to have tagged a turtle that came to the UK. It goes to show what spectacular endurance these animals have," Mr McNeil said.
Mark Wright, chief scientist for WWF-UK, said that it was not uncommon for leatherbacks to venture to Britain.
"These are creatures that most people associate with tropics, but they visit the UK fairly regularly," he said. "The biggest leatherback ever found, which was about 2.5m long, was washed up on Harlech beach in Wales in the 1990s.
"It is essential that the world takes steps to keep these visitors to Britain from extinction."
Leatherbacks are solitary travellers and spend their lives in the world's seas in an average lifespan of 80 years, although some survive for more than 100. They endure long journeys by adjusting their body temperature. Only females can be tagged while they come to beaches to lay eggs - males never venture on land. Another female, Kawana, who was also tagged as part of the WWF project, died less than a mile from the Suriname beach after being caught in a discarded fishing net.
Thousands of leatherbacks are believed to be killed by abandoned fishing gear or long-line fisheries. While the species has survived for more than 100 million years, only a total of about 34,000 nesting females remain.
Estimates show the species is declining rapidly, especially in the Pacific. In the past 20 years, adult female numbers have slumped to 2,300, making the Pacific leatherback the world's most endangered marine turtle.
Aikanti's arrival in the UK coincides with tonight's edition of Extinct on ITV, featuring marine turtles in South America.Reuse content