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Comeback seen for endangered giant tortoise

Oct. 28, 2014
Courtesy of SUNY College of 
Environmental Science and Forestry
and World Science staff

A popula­t­ion of en­dan­gered gi­ant tor­toises, which dwin­dled to just 15 a half-cen­tu­ry ago, has re­cov­ered on the Galapa­gos is­land of Es­pañola, ac­cord­ing to a new re­port.

It’s “a true sto­ry of suc­cess and hope in con­serva­t­ion,” with about 1,000 tor­toises breed­ing on their own, said the lead au­thor, James P. Gibbs, a bi­ol­o­gist at the State Uni­vers­ity of New York Col­lege of En­vi­ron­men­tal Sci­ence and For­est­ry.

Es­pañola gi­ant tor­toise. (Credit: James P. Gibbs, SUNY-ESF)


The Galapa­gos Na­t­ional Park Serv­ice started in­tro­duc­ing captive-bred tor­toises to the is­land af­ter the popula­t­ion bot­tomed out. 

Now the en­dem­ic Es­pañola gi­ant tor­toises are said to be re­pro­duc­ing and re­stor­ing some of the ec­o­log­i­cal dam­age caused by fe­ral goats brought to the is­land in the late 1800s.

“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,” said Gibbs, whose find­ings are pub­lished Oct. 28 in the research jour­nal PLoS One

Gibbs and col­la­bo­ra­tors as­sessed the tor­toise popula­t­ion us­ing 40 years of da­ta from tor­toises marked and re­cap­tured re­peat­edly for meas­ure­ment and mon­i­tor­ing.

But there’s an­oth­er side to the sto­ry, he said: the tor­toise popula­t­ion, while sta­ble, is un­likely to grow more un­til the land­scape re­cov­ers from the dam­age in­flicted by the now-gone goats. “Popula­t­ion restora­t­ion is one thing but ec­o­log­i­cal restora­t­ion is go­ing to take a lot longer.” 

Af­ter the goats de­voured all the grassy vegeta­t­ion and were sub­se­quently re­moved from the is­land, more shrubs and small trees have grown, he ex­plained. This hin­ders both the growth of cac­tus, a vi­tal part of a tor­toise’s di­et, and the tor­toises’ move­ment. Chem­i­cal anal­y­sis of the soil, done by Mark Teece, a chem­ist at the col­lege, in­di­cates a pro­nounced shift from grasses to woody plants on the is­land in the last cen­tu­ry.

The shrubs and trees al­so in­hib­it the move­ments of the en­dan­gered waved al­ba­tross, said Gibbs: the plants make it hard for the un­gainly sea birds to take flight. “This is a mi­rac­u­lous con­serva­t­ion suc­cess ac­com­plished by the Galapa­gos Na­t­ional Park Serv­ice,” said Gibbs, “but there is yet more work to fully re­cov­er the ec­o­sys­tem up­on which the tor­toises and oth­er rare spe­cies de­pend.”


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A population of endangered giant tortoises, which dwindled to just 15 a half-century ago, has recovered on the Galapagos island of Española, according to a new report. It’s “a true story of success and hope in conservation,” with about 1,000 tortoises breeding on their own, said the lead author, James P. Gibbs, a biologist at the State University of New York College of Environmental Science and Forestry. The Galapagos National Park Service started introducing captive-bred tortoises to the island after the population bottomed out. Now the endemic Española giant tortoises are said to be reproducing and restoring some of the ecological damage caused by feral goats that were brought to the island in the late 19th century. “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, “ said Gibbs, whose findings are published Oct. 28 in the journal PLoS One. Gibbs and collaborators assessed the tortoise population using 40 years of data from tortoises marked and recaptured repeatedly for measurement and monitoring. But there’s another side to the story, he said: while the tortoise population is stable, it’s unlikely to increase until more of the landscape recovers from the damage inflicted by the now-eradicated goats. “Population restoration is one thing but ecological restoration is going to take a lot longer.” After the goats devoured all the grassy vegetation and were subsequently removed from the island, more shrubs and small trees have grown, he explained. This hinders both the growth of cactus, a vital part of a tortoise’s diet, and the tortoises’ movement. Chemical analysis of the soil, done by Mark Teece, a chemist at the college, indicates a pronounced shift from grasses to woody plants on the island in the last century. The shrubs and trees also inhibit the movements of the endangered waved albatross, said Gibbs: the plants make it hard for the ungainly sea birds to take flight. “This is a miraculous conservation success accomplished by the Galapagos National Park Service,” said Gibbs, “but there is yet more work to fully recover the ecosystem upon which the tortoises and other rare species depend.”