A population of Hood Island giant tortoises, which once dwindled to just over a dozen, has recovered on the Galapagos island of Española, says a team of scientists led by Prof James Gibbs of the State University of New York’s College of Environmental Science and Forestry.
Two Galapagos giant tortoises engage in a dominance display. Image credit: Aaron Logan / CC BY 2.0.
The Hood Island giant tortoise (Chelonoidis hoodensis or Chelonoidis nigra ssp. hoodensis) is one of the 14 subspecies of the Galapagos giant tortoise (Chelonoidis nigra).
This subspecies once numbered in the thousands of individuals but dropped to just 15 (12 females and 3 males) by the 1960s due to historical exploitation of tortoises throughout the archipelago.
Between 1963 and 1974, all survivors were brought into captivity and to date more than 1,500 of their captive-raised offspring have since been released onto the island of Española, in the southeastern sector of the Galapagos Archipelago.
Successful reproduction of repatriated Hood Island giant tortoises was first documented in 1990 suggesting the repatriated population might become self-sustaining.
Now there are some 1,000 individuals breeding on their own.
“The population is secure. It’s a rare example of how biologists and managers can collaborate to recover a species from the brink of extinction,” explained Prof Gibbs, who is the first author of the paper published in the open-access journal PLoS ONE.
He and his colleagues assessed the Hood Island giant tortoise population using 40 years of data from tortoises marked and recaptured repeatedly for measurement and monitoring by members of the Galapagos National Park Service, Charles Darwin Foundation, and visiting scientists.
But there is another side to the success story: while the tortoise population is stable, it is not likely to increase until more of the landscape recovers from the damage caused by feral goats.
“Population restoration is one thing but ecological restoration is going to take a lot longer,” Prof Gibbs said.
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Gibbs JP et al. 2014. Demographic Outcomes and Ecosystem Implications of Giant Tortoise Reintroduction to Española Island, Galapagos. PLoS ONE 9 (10): e110742; doi: 10.1371/journal.pone.0110742
