How Gal谩pagos giant tortoises have made a comeback
The are world-famous as a laboratory of biological evolution. Some 30 percent of the plants, 80 percent of the land birds and 97 percent of the reptiles on this remote archipelago are found nowhere else on Earth. Perhaps the most striking example is the islands鈥� iconic giant tortoises, which often live to ages over 100 years in the wild. Multiple species of these mega-herbivores have evolved in response to conditions on the island or volcano where each lives, in shell shape and size.
Over the past 200 years, hunting and invasive species reduced giant tortoise populations by an estimated 90 percent, destroying several species and pushing others to the brink of extinction, although a few populations on remote volcanoes remained abundant.
Now however, the tortoise dynasty is on the road to recovery, thanks to work by the , with critical support from nonprofits like the and advice from an international team of conservation scientists.
Together we are advancing a broad multiyear program called the , overseen by Washington Tapia, Linda Cayot and myself with major collaboration from at Yale University. Using many novel strategies, the initiative helps guide the Galapagos National Park Directorate to restore viable, self-sustaining tortoise populations and recover the ecosystems in which these animals evolved.
As many as 300,000 giant tortoises once roamed the Galapagos Islands. Whalers and colonists started collecting them for food in the 19th century. Early settlers introduced rats, pigs and goats, which preyed upon tortoises or destroyed their habitat. As a result, it was widely concluded by the 1940s that giant tortoises were headed for oblivion.
After the Galapagos National Park was established in 1959, park guards halted killing of tortoises for food. Next, biologists at what was then known as the did the first inventory of surviving tortoises. They also initiated a program to help recover imperiled species.
One species, the Pinz贸n Island tortoise, had not produced any juveniles for over 100 years because nonnative black rats were preying on hatchlings. In 1965 park guards started methodically removing eggs from tortoise nests, rearing the offspring to 鈥渞at-proof鈥� size in captivity and releasing them back into the wild. More than 5,000 young tortoises have been repatriated to Pinz贸n Island. . This program is one of the most successful examples of 鈥渉ead-starting鈥� to save a species in conservation history.
The Espa帽ola tortoise, which once numbered in the thousands, had been reduced to just 15 individuals by 1960. Park guards brought those 15 into captivity, where they have produced more than 2,000 captive-raised offspring now released onto their home island. All 15 survivors are still alive and reproducing today, and the wild population numbers . This is one of the greatest and least-known conservation success stories of any species.
Over the past 150 years, goats brought to the islands by early settlers overgrazed many of the islands, turning them into dust bowls and destroying forage, shade and water sources that tortoises relied on. In 1997 the Galapagos Conservancy launched , the largest ecosystem restoration initiative ever carried out in a protected area.
Over a decade park wardens, working closely with used high-tech hunting tactics, helicopter support and 鈥� animals fitted with radio collars that led hunters to the last remaining herds 鈥� to from virtually all of the archipelago.
Building on from Project Isabela, the Galapagos National Park Directorate and Island Conservation then eradicated nonnative rats from Pinz贸n Island in 2012, enabling tortoise hatchlings to survive and complete their life cycle again .
The argument for tortoise conservation has been strengthened by reconceptualizing giant tortoises as agents whose actions shape the ecosystems around them. Tortoises eat and disperse many plants as they move around 鈥� and they are more mobile than many people realize. By attaching GPS tags to tortoises, scientists with the have learned that tortoises migrate tens of kilometers up and down volcanoes seasonally to get to new plant growth and nesting sites.
As they move, tortoises crush vegetation. They may be an important factor in maintaining the native savannah-like ecosystems on the islands where they live. When tortoises are scarce, we think that shrubs sprout up, crowding out many herbaceous plants .
We need data to support this theory, so we have constructed an elaborate system of 鈥渆xclosures鈥� on two islands that wall tortoises out of certain areas. By in the tortoise-free zones to conditions outside of the exclosures, we will see just how tortoises shape their ecosystems.
Restoring ecosystems on islands where tortoises have gone extinct requires more drastic steps. Santa Fe Island lost its endemic giant tortoises more than 150 years ago, and its ecosystems are still recovering from a scourge of goats. Park managers are attempting to restore the island using an 鈥渁nalog,鈥� nonnative species 鈥� the genetically and morphologically similar Espa帽ola tortoise.
In 2015 the Galapagos National Park Directorate in the interior of Santa Fe Island. They all appear to have survived their first year there, and 200 more are scheduled for release in 2017. Espa帽ola tortoises are still endangered, so this strategy has the extra value of creating a reserve population of them on Santa Fe Island.
On Pinta Island, which also has lost its endemic tortoise, park managers have to serve as 鈥渧egetation management tools鈥� that can prepare the habitat for future introductions of reproductive tortoises. These initiatives are some of the first ever to use analog species to jump-start plant community restoration.
The endemic tortoises of Floreana Island are also considered to be extinct. But geneticists recently discovered that in a remote location on Isabela Island, tortoises evidently had been translocated from around the archipelago during the whaling era. In a major expedition in 2015, park rangers and collaborating scientists with shell features similar to the extinct Pinta and Floreana species.
Now the geneticists are exploring the degree of interbreeding of these 32 distinct tortoises between the extinct species and native Wolf Volcano tortoises. We are hoping to find a few 鈥減ure鈥� survivors from the extinct species. Careful and selective breeding of tortoises in captivity with significant levels of either Pinta or Floreana ancestry will follow to produce a new generation of young tortoises to be released back on Pinta and Floreana Islands and help their ecosystems recover.
Lonesome George, the last known living Pinta Island giant tortoise, died in 2012 after decades in captivity. His frozen remains were transferred to the United States and taxidermied by . Last month Lonesome George was returned to Galapagos once again, to be ensconced as the focus of a newly renovated park visitation center. Some 150,000 visitors each year will learn the complex but ultimately encouraging story of giant tortoise conservation, with a beloved family member resting back at home again.
鈥� is Professor of Vertebrate Conservation Biology and Director of the Roosevelt Wild Life Station, .
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