While one of the giant reptiles - called Aikanti - has rocketed across the Atlantic, travelling more than 3000 kilometers in 10 weeks, the other - Kawana - was caught in a fisherman's gill net and perished before she was able to get to the open sea.
Aikanti and Kawana were fitted with satellite tracking devices in Surinam, South America, as part of WWF's ongoing marine turtles tracking programme which is attempting to establish the routes travelled by these extraordinary animals and help find out where these creatures interact with fishing activities.
Both Aikanti and Kawana were female leatherbacks, fitted with the transmitters by WWF staff and Sky TV presenter Charlotte Uhlenbroek for the Sky One programme Final Chance to Save, which will be shown at 8pm on Sunday (September 18).
The transmitters - which are about the size of a mobile phone and are attached with a series of harnesses that look a little like a very small back-pack - were attached when the turtles came ashore to lay their eggs in late June this year. The transmitters will last for up to three years, and the harnesses are designed with a link that corrodes and breaks over a period of two-three years, so that the animal is not stuck with the device for life.
Aikanti is now just off the coast of Africa - you can follow Aikanti's progress here.
Leatherbacks - the world's biggest turtles, measuring up to 2.5m and weighing up to 900kg - are regular visitors to UK waters, where they feast on the abundant jellyfish around our coast. The biggest leatherback ever recorded was washed up on the coast of Wales in 1988.
Andrew Lee, Director of Campaigns for WWF-UK said: The tragic death of Kawana highlights the vital need for fishing gear that does not harm other sea life, like leatherback turtles. WWF has been working around the world to persuade fishermen to use innovative solutions - like circular fish hooks that reduce turtle bycatch, but still catch fish, and fishing nets which use Turtle Excluding Devices. We can only hope that Aikanti's journey takes her to a far, far better place than Kawana."
Charlotte Uhlenbroek said: "It is essential that we take action to prevent these magnificent creatures from being lost forever. This really could be our final chance to save the leatherback turtle."