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San Cristóbal giant tortoise population estimated at more than 6,000 individuals

December 20, 2016

San Cristobal Tortoise Census

After analyzing data collected in November by the expedition to survey the giant tortoise population of San Cristóbal Island (Chelonoidis chathamensis) — the first ever on this island — the population has been estimated at approximately 6,700 individuals, with a high percentage of juveniles and females. These results indicate that, from an ecological perspective, the species is in the process of recovery. This tortoise population experienced catastrophic decline in previous centuries due to exploitation, with recovery severely restrained for many decades due to introduced predators, competitors, and vegetation change. From an estimated historical population between 12,000 and 25,000 individuals, only 500-700 animals were estimated in the population by the early 1970s.

Watch a Video on the San Cristóbal Tortoise Census

Throughout a two-week period, a team of 70 people conducted a comprehensive census of the population of giant tortoises on San Cristóbal Island. The team included Galapagos National Park rangers (of the Ministry of the Environment) and scientists from Galapagos Conservancy; the two organizations lead the Giant Tortoise Restoration Initiative (GTRI). The field team covered approximately 58 square miles of the island, from the boundary between the National Park and the agricultural area in the western end of the island to the far northeastern tip of the island at Punta Pitt. They marked a total of 1,938 tortoises: 359 males, 499 females, 928 juveniles, and 152 hatchlings. The results of the census, using the mark:recapture method, provided the estimated total number of more than 6,000 individuals.

Blood samples were also collected from approximately 400 tortoises. These samples will be analyzed at Yale University to help determine the health of the population from a genetic perspective.

The field team discovered that the tortoise population is currently expanding its range into the highlands of San Cristóbal Island. Currently the agricultural area, this area was an important part of tortoise habitat prior to human presence.

Walter García, the Minister of the Environment, commented, “The results of this research expedition provide great news for Ecuador and the world. The work demonstrates that the conservation measures of the environmental authority, executed by park rangers during decades of hard work, have been effective for the management of this species.”

The data obtained also permit the creation of a map of the current and potential range of this population. An important discovery was that despite the extreme drought and lack of food, a high number of hatchlings (152 observed) survive.

“The GTRI works with all giant tortoise populations of the Archipelago,” said Wacho Tapia, the Galapagos Conservancy scientist who led the expedition and coordinates the research. “One of our priorities, however, is to study the lesser known species, like the San Cristóbal giant tortoise. This work will generate sufficient knowledge to allow the Galapagos National Park Directorate (GNPD) to implement effective management measures to ensure the conservation of not only the tortoise population but also the ecosystem they inhabit. As ecosystem engineers, giant tortoises, through their activities and movements, contribute to the ecological integrity of their islands.”

During the expedition, the environmental authority not only found a growing population of giant tortoises in good condition, they also located 69 individuals of Calandrinia galapagosa and 1,049 Lecocarpus leptolobus, both island endemic plants found only on San Cristóbal and both Critically Endangered, according to the Red List of the International Union for the Conservation of Nature (IUCN).

The Director of the Galapagos National Park, Walter Bustos, indicated that the field work and the data obtained provide stimulus to continue investing technical efforts, funding, and personnel in the conservation of Galapagos ecosystems.

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