In November 2009, a group of veterinarians, working with the Galapagos National Park (GNP), prepared 39 hybrid tortoises slated to be the pioneer group to initiate the return of tortoises to Pinta Island. Project Pinta is a multi-year project aimed at the restoration of the island following the successful eradication of goats on Pinta in 2003. While complete island restoration will require the eventual repopulation of Pinta with a reproductive tortoise population, scientists and managers are awaiting the final results from genetic analyses of a massive sampling of tortoises before making the final selection of which tortoises to use. To initiate the return of tortoises, critical ecosystem engineers during this important period of vegetative recovery, a special group of tortoises will be released onto Pinta. To ensure that this group of hybrid tortoises will not compromise any future efforts to reestablish a reproductive population, veterinarians sterilized them.
Members of the team that participated in the tortoise sterilization project.
The role of giant tortoises in natural ecosystems
Research on giant tortoises in Galapagos during the last 40 years has demonstrated many ways in which tortoises play a major role in Galapagos ecosystems. Given their size, movement patterns, and use of resting forms (hollowed-out beds created by tortoises for resting), tortoises can affect both the pattern and structure of vegetation. In addition, grazing by tortoises can help maintain open areas within forests. Studies of the Galapagos tomato and other plant species have shown a marked increase in germination rates following passage through the gut of tortoises. Besides scarification of seeds, tortoise scat can provide a rich substrate for germination and growth. Studies have shown that seeds consumed by tortoises may take from a few days to weeks to be deposited, allowing for seed dispersal over distances of several kilometers. Probably more than any other native species in Galapagos, tortoises have a major impact on the structure and composition of their environment.
Tortoises are needed back on Pinta. With the eradication of goats in 2003, vegetation grew back quickly but without tortoises to engineer the recovery. Shade-loving plant species are becoming more and more abundant, reducing the available habitat for native and endemic sun-loving species. Pinta needs a natural habitat engineer, the giant tortoise, to ensure a balanced recovery and to fully restore the island to its near pristine condition.
While awaiting the final results of the genetic survey, conservation managers took steps to initiate the return of tortoises to Pinta through the use of sterilized adult hybrid tortoises currently held in captivity. This is considered the best short-term solution to initiate a more balanced recovery.
Captive tortoises in Galapagos
During the years following the establishment of the GNP and the Charles Darwin Foundation (CDF) in 1959, several giant tortoises that had been maintained by private parties were returned to the Tortoise Center on Santa Cruz. For the first several years, these tortoises were allowed to reproduce, potentially creating hybrid tortoises with ancestry from more than one island. This practice was discontinued in 1976, as hybrid tortoises could never be returned to the wild given the GNP goal of maintaining natural biodiversity as close to pristine conditions as possible. However, as a result of reproduction prior to 1976, a group of hybrids remains in captivity.
In addition to the tortoises at the Center, Margret Wittmer, one of the original settlers on Floreana, had several tortoises brought to that island and held them in captivity. These tortoises were also allowed to reproduce. At the time of Mrs. Wittmer’s death, the 32 remaining tortoises, which are primarily hybrids, were moved to a corral on Floreana managed by the GNP.
In the 1990s, genetic analyses of Galapagos tortoises provided sufficient data to determine the ancestry of all tortoises in captivity at the Tortoise Center and on Floreana. Many were shown to be hybrids. Until now their prospects of ever being returned to the wild were slight. Given their longevity, they would remain captive for well over 100 years.
Why use captive tortoises on Pinta?
Project Pinta will eventually involve the reestablishment of a reproductive population of tortoises on Pinta, with tortoises genetically close to the original Pinta tortoise. In the meantime, the smaller captive tortoises on Santa Cruz and Floreana (most adapted to the Pinta ecosystem) provide an excellent short-term solution to the critical conservation problem on Pinta – ensuring a balanced recovery of the native vegetation in the absence of goats. By sterilizing the tortoises, they can finally be returned to the wild to live out their days in a natural setting without contaminating the gene pool of the final tortoise population, and at the same time play the much needed role of ecosystem engineer.
In early November 2009, US-based veterinarians traveled to Galapagos to help the GNP with the tortoise sterilizations. The group included: Dr. Joseph Flanagan (Houston Zoo); Dr. Steve Divers, Dr. Emi Knafo, and Jason Norman (College of Veterinary Medicine, University of Georgia); and Dr. Sam Rivera (Zoo Atlanta). The team was joined by Dr. Pamela Martinez, a local veterinarian working with the GNP. Karl Storz Veterinary Endoscopy, Ellman Radiosurgery, and Envisionier loaned more than $70,000 in surgical equipment. Galapagos Conservancy Science Advisor, Dr. Linda Cayot, and Head of the Department of Conservation and Sustainable Development of the GNP, Washington Tapia, organized the project. Galapagos Conservancy provided the necessary funding for the veterinary team to undertake the sterilization work. Continental Airlines donated international travel. GNP personnel worked alongside the sterilization team and provided logistical support.
Thirty-nine tortoises (14 females and 25 males) were successfully sterilized. The tortoises recovered rapidly and are now housed together in a corral at the Tortoise Center. They will be released onto Pinta during the wet season of 2010, sometime between March and May. Their movements, foraging, and impact on vegetation will be monitored.
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