Leatherbacks can grow to up to 2m (6.5ft) long
The journeys of two leatherback turtles are being tracked online by scientists from the University of Exeter.
Dr Matthew Witt and Dr Brendan Godley, based at Tremough campus in Penryn, Cornwall, have put satellite tracking devices on the adult female turtles.
They hope their research will help government agencies to protect marine areas from the impacts of fishing, pollution and oil exploitation.
Since tracking began on 7 December the turtles have travelled 800 miles.
The leatherbacks, Noelle and Darwinia, nest off the coast of Gabon in western central Africa.
They can grow up to 2m (6.5ft) long
Leatherbacks are the most widely spread marine turtles
They eat jellyfish
The deepest recorded leatherback dive is 1.2km (3/4 mile)
By tracking them the scientists will be able to monitor their precise movements and observe how deep they dive.
The International Union for Conservation of Nature lists leatherback turtles as "critically endangered" because many of their key habitats are threatened by industrial fishing, oil exploitation and pollution.
Dr Witt said: "Our aim is that this will help inform management of fisheries and mineral exploration as well as feeding into ambitious plans to widen the network of marine protected areas in Gabon."
The project was funded by the British government's Darwin Initiative which aims to protect and enhance biodiversity around the world.