Galapagos once exterminated invasive goats to save giant tortoises

Conservationists have deployed a series of measures to kill 140,000 goats in 7 years, helping the Galapagos giant tortoise recover.

By the late 20th century, the giant Galapagos tortoises that inhabited the archipelago of the same name off the coast of Ecuador were in danger of extinction. Their numbers had dwindled from more than 250,000 individuals in the 16th century to just 3,000 by the 1970s, largely due to human hunting. The tortoises were relatively slow and poorly protected, making them easy to collect and keep on ships, where they could survive for a year without food, providing fresh meat for sailors. In addition to overhunting, humans had introduced the biggest invasive species to the fragile ecosystems of the islands: the goat. These seemingly harmless herbivores devoured all available vegetation, including many rare ones, and competed with native animals for scarce resources. As the goats cleared the islands of vegetation, the Galapagos tortoises began to disappear.

Giant tortoise on the Galapagos Islands. (Photo: Flickr).

In 1995, authorities decided to eradicate goats in the Galapagos to save the islands' native flora and fauna. Two years later, Project Isabela was devised, which would eradicate goats and donkeys on Isabela, pigs, goats and donkeys on Santiago, and goats on Pinta.

In 1999, a team of snipers scoured three islands for footprints and shot the goats from helicopters. It was one of the most advanced eradication programs of its time. Within a few years, 90% of the goats were wiped out with relative ease. But as the goats became fewer, they became harder to spot. The remaining goats learned to be wary of hunters, and began hiding in bushes, caves, or lava tubes. The remaining 10% became increasingly difficult to eliminate. To completely eradicate the goats, hunters had to resort to a different method called the 'Judas goat.'

A herd of several hundred goats is collected, sterilized, injected with hormones that cause them to be in long-term heat, fitted with radio-tracking collars, and released on the islands. Because goats are social animals, they instinctively seek out other goats. By tracking the Judas goats, hunters can track the remaining goats. Once they find a herd, they shoot all but the Judas goats, leaving them to continue searching for more goats that may be hiding. The carcasses are left to decompose so that the beneficial nutrients the goats consume on the island can be returned to the soil. Taking the goat meat away would remove the nutrients from the island forever, according to Dr. Karl Campbell, operations manager for the Isabela project.

Over 200 Judas goats were deployed on Santiago Island and another 770 on the larger island of Isabela over two years. By 2006, they were the only goats left on the target islands. The invasive goats numbered only 20-30 on Santiago Island and 266 on Isabela. They were allowed to live on the islands for monitoring purposes.

After the Galapagos Islands were cleared of goats, vegetation began to recover. Small trees began to grow from the stumps the goats left behind. Highland shrubs, forest trees, cacti, and many endemic species increased in number. Combined with captive breeding, the giant tortoise population also recovered.

Project Isabela is the world's largest island reforestation effort to date. Over seven years, more than 140,000 goats were wiped out from half a million hectares of land at a cost of $10.5 million. The last few hundred were the most difficult and expensive to eradicate. The success of Project Isabela prompted conservationists to undertake eradication on three other islands. Using a combination of aerial shooting, hunting dogs, and Judas goats, they eliminated another 10,000 goats between 2006 and 2009.