They are famed for their epic voyages across the world’s roughest oceans.
But until now, nobody quite appreciated just how good leatherback turtles were at navigation.
In a new study, scientists have discovered that the gigantic females can swim for thousands of miles in a perfectly straight line.
Following a course that would be the envy of a state-of-the-art cruise liner, the turtles make the transatlantic journey from Central Africa to South America using the shortest possible route.
Exactly how turtles can swim in a straight line remains a mystery to biologists.
However, they are thought to use a combination of vision – relying on the position of the stars and sun – and a sense of the Earth’s magnetic field, to steer their way.
The findings come from a study led by the Centre for Ecology and Conservation at Exeter University.
Over five years, the researchers tagged 25 females with satellite tracking devices strapped or drilled to their shells as they left their hatching grounds in Africa to seek food across the Atlantic.
They discovered three migratory routes – including one 4,699 mile journey straight across the Atlantic from Gabon to the coastal waters off southern Brazil and Uruguay that took 150 days.
Dr Matthew Witt, who published the findings in the journal Proceedings of the Royal Society B, said: ‘Despite extensive research carried out on leatherbacks, no-one has really been sure about the journeys they take in the South Atlantic until now.
‘What we’ve shown is that there are three clear migration routes as they head back to feeding grounds after breeding in Gabon, although the numbers adopting each strategy varied each year.
‘We don’t know what influences that choice yet, but we do know these are truly remarkable journeys – with one female tracked for thousands of miles travelling in a straight line right across the Atlantic.’
Female leatherbacks begin their first migrations as newly hatched youngsters.
After a few weeks splashing around in the coastal waters near their hatching grounds, they seek out feeding grounds rich in jellyfish and other gelatinous food, travelling thousands of miles in the process.
After a few years building up strength, they swim back to the beaches were they were born to lay up to 150 eggs at a time in holes dug in the sand.
After a breeding year – during which they can lay up to 1,000 eggs – they head back to the feeding grounds for another few years to build up their reserves before returning to the nesting beaches.
In the Pacific, the number of leatherback turtles has plummeted in the last three decades.
One nesting colony in Mexico has declined from 70,000 in 1982 to just 250 by 1999.
The reason for the fall is not clear. However, egg harvesting and fishing have been blamed.
In the Atlantic, population levels have been more stable.
The new study was carried out with the help of Parcs Gabon, the Wildlife Conservation Society, the Marine Turtle Partnership for Gabon, the Trans-Atlantic Leatherback Conservation Initiative and WWF.
Dr Howard Rosenbaum, Director of the Wildlife Conservation Society’s Ocean Giants Program, said: ‘This important work shows that protecting leatherback turtles—the ancient mariners of our oceans—requires research and conservation on important nesting beaches, foraging areas and important areas of the high seas.
‘Armed with a better understanding of migration patterns and preferences for particular areas of the ocean, the conservation community can now work toward protecting leatherbacks at sea, which has been previously difficult.’
Biologists hope the data will help to conserve the turtles, who spend virtually all their lives at sea and can grow to more than 6ft long.
Written by David Derbyshare