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One of the goals of the Giant Tortoise Restoration Initiative is to re-establish reproductive tortoise populations on islands where humans caused their extinction. Tortoises went extinct on Floreana and Santa Fe Islands in the mid-1800s and on Pinta Island in 2012, with the death of Lonesome George.
Over the last two decades, genetic analysis of Galapagos tortoises — both from the wild and from museum specimens — has opened a window of opportunity for cutting-edge conservation to restore tortoise populations to islands where they are extinct. This is an important component of island restoration, as these growing tortoise populations will provide ecosystem “engineering” by trampling vegetation, opening areas, and dispersing seeds, which helps to recover ecosystem processes and provides improved habitat conditions for other native species.
The repopulation of Santa Fe Island with giant tortoises began in 2015. The Santa Fe tortoise species went extinct before any complete specimens were collected — thus an official description and scientific name do not exist. Genetic analysis has confirmed, using museum specimens of pieces of tortoises collected on Santa Fe, that this was a separate species, and has identified the Española tortoise as the species most closely related to the extinct Santa Fe species.
Tortoise repatriations to Española Island were suspended in 2013 while habitat studies and potential management are completed. A decision was then made to release the young Española tortoises produced in the Santa Cruz Tortoise Center onto Santa Fe, given their genetic similarity to the original Santa Fe tortoise. The first group of 201 juvenile tortoises ranging in age from 5-8 years old was released in the interior of the island in June 2015. Additional cohorts of juvenile tortoises are released annually. Follow-up surveys of these tortoises show near 100% survival and continued dispersal of individuals throughout a larger area. Ongoing research will focus on potential competition with the Santa Fe land iguana and the mid- to long-term impacts of the tortoises on the vegetation.
The tortoises of Floreana went extinct a decade or two after Charles Darwin’s visit in 1835, with the last individuals most likely harvested for food. Geneticists from Yale University have identified hybrid tortoises on Wolf Volcano (on northern Isabela Island) with partial Floreana tortoise ancestry. Apparently, whalers abandoned a mixture of Galapagos tortoises there in centuries past. In November 2015, 19 tortoises with partial Floreana ancestry were transferred from Wolf Volcano to the Tortoise Center on Santa Cruz. An additional four tortoises already in the Center were also identified as having partial Floreana tortoise ancestry. A breeding program, initiated with 20 of these tortoises in 2017, will provide young tortoises to be released onto Floreana in the future. With a healthy tortoise population, genetically similar to the original species, the island will undergo a broader ecological restoration engineered by the released tortoises.
The restoration of the tortoise population is part of the larger Floreana Restoration Project, which will include the eradication of the introduced rodents and cats as a necessary step prior to the first release of tortoises into the wild, and the return of other species no longer present on the island (e.g., mockingbirds and snakes).
Tortoises were thought to be extinct on Pinta Island for most of the first half of the 20th century. Then Lonesome George was sighted in 1971 and transported to the Santa Cruz Tortoise Center in 1972. Since then there have been extensive searches both on Pinta and in the world’s zoos for another Pinta tortoise. None was ever found. When Lonesome George died in June 2012, the species was officially extinct. As with the Floreana tortoise, a few tortoises have been found on Wolf Volcano with partial Pinta ancestry. Unfortunately, the number is not sufficient for initiating a breeding program. Additional searches, however, may discover more, or it may be that a replacement species, genetically similar to the Pinta tortoise, will be used.
Goats, introduced on Pinta in 1959, destroyed the vegetation. Their eradication in 2006 was the first step in restoring the Pinta ecosystem. Giant tortoises, the “engineers” of Galapagos terrestrial ecosystems, were considered a vital component of the ongoing process of ecosystem restoration. To provide a “bridge” until a decision is made as to which tortoises should be used to start a reproductive and self-sustaining population on the island, 39 adult tortoises with mixed ancestry from islands with healthy tortoise populations were sterilized and released onto Pinta in May 2010. These tortoises were monitored for two years. They expanded their range and are impacting the vegetation and maintaining open trails. This will help ensure a successful re-establishment of a reproductive tortoise population on Pinta in the future.
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