LONESOME GEORGE'S death in the Galapagos Islands may have signalled the end of the Pinta Island tortoises, but a related subspecies on a neighbouring island has been saved from extinction. The huge success of the rescue mission suggests that similarly endangered species may have a chance, too.
The Galapagos boast the world's largest and most iconic tortoises. Throughout history, pirates and whalers have fed on the animals, and introduced pest species like goats to the islands, destroying the tortoises' habitat. "Goats are very problematic," says Michel Milinkovitch at the University of Geneva, Switzerland. "They eat everything." As a result, the giant-tortoise population of Española Island dwindled to near extinction four decades ago. In a bid to rescue it, conservationists in 1971 began collecting all the tortoises they could find on Española - just 14 - and took them to nearby Santa Cruz island to breed in captivity. They were joined by a 15th tortoise from San Diego Zoo in California.
In total, this breeding colony comprised 12 females and 3 males. Meanwhile, conservationists cleared Española of goats. Baby tortoises were hand-reared until they were about 5 years old before being taken to Española in batches. The programme was widely regarded as a success story. Since its inception, over 1700 tortoises have been reintroduced.
A true measure of success, though, is how well the animals are coping on the island - whether they are able to survive and breed when left to their own devices. All the new tortoises were born from the same 15 animals, so genetic diversity is thought to be low. That can cause a problem, as inbred animals die younger, have poor fertility, and are often more vulnerable to environmental changes. "There's always a big risk that the animals don't survive or don't breed," says Milinkovitch.
To investigate how well the tortoises were doing, Milinkovitch and his colleagues carried out a genetic analysis of all tortoises on Española, searching for tortoises born on the island.
Eighteen years ago, none of the tortoises on Española had been born there. From blood samples collected in 2007, the researchers have now found that about a quarter of the tortoises are native, the offspring of reintroduced animals (Evolutionary Applications, doi.org/jts).
"We're really excited," says Milinkovitch. "The habitat is restored, the species is thriving and the animals are breeding happily. We can now safely say that the species is saved."
"It certainly looks like it," agrees Richard Griffiths at the University of Kent, UK, though researchers will have to check back in a couple of generations' time to be sure.
Jean-Christophe Vié, deputy director of the International Union for Conservation of Nature's Species Programme, is more cautious: "I'm not sure you can ever say a species is completely safe." He gives the example of white and black rhinos in Africa, which were recently rescued from the brink of extinction. But, since the start of this year, around 500 are thought to have been poached. "It's fragile," he says. But Vié adds that the early success of the tortoise programme is encouraging. "We need these kinds of successes. What is really important here is that you can do something about this extinction crisis. There is always hope."
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Giant tortoises bounce back in the Galapagos
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Giant tortoises bounce back in the Galapagos
