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One of the most notable species on Curieuse that also highly promotes the island as a tourist destination is the Giant Aldabra Tortoise. There are only a few populations of Aldabra tortoises left in the world, specifically in the Galapagos Islands, Madagascar, Mascarene Is, and Seychelles. It is thought that these creatures were dispersed to these areas by floating as well as relocation by humans. The tortoises can last about six months without food or water, allowing them to travel long ways and survive. However, the population of Aldabra tortoises on Curieuse appeared as a relocation of the tortoises to a new island in order to promote tourism and scientific studies. Between 1978 and 1982, almost 300 tortoises were relocated to the island, but nearly half were stolen or killed by 1986. GVI monitors and records data annual from each tortoise in the current population to gain an understanding of their growth rates, behaviors, and chance of long term survival as a population on Curieuse.

group of small turtles in a sandy cage

The Seychelles National Parks Authority’s ranger station on Curieuse has the largest concentration of these tortoises on the island. The adult tortoises roam freely to nearly all areas of the island, sometimes several kilometres from the station up steep rocky paths, while the juvenile and hatchling tortoises stay in a protected hatchery at the station to protect against poachers and predators such as rats, cats, and mangrove crabs. To discourage theft, each tortoise heavier than four kilograms has a Passive Integrated Transponder tag. Hatchlings will receive a temporary monitoring tag at about six to eight months when they weigh about 90 to 150 grams.

During a typical tortoise survey, we will search for tortoises without marking on their shells, indicating that it has been about six months or more since it was last scanned and recorded. Once the tortoise is scanned and identified by number, we can look back to its previous data and compare new measurements before rewriting its number. The third dorsal scoot, dorsal Aldabra (a rigid marking within the third dorsal), width, length, white lines between scoots, and toenails are measured and recorded. Additionally, the tail and plastron (underbelly of the shell) are checked to determine gender. A short tail and a flat plastron indicate a female. A long tail and a concave plastron indicate a male. In order to check these characteristics, the tortoise must be standing. In the case of a stubborn tortoise, someone will stroke the back of its neck until the tortoise slowly stands up, allowing someone to quickly feel the underside the shell to determine concavity and check the length of the tail. The GPS location is also taken to observe movements between recordings throughout the year. Since little is known about this population, including the ages of nearly all of the adult tortoises, it is important that GVI continues to monitor these tortoises. Through the research so far, GVI can monitor average growth rates of the juveniles, females, and males for each year’s census and estimate only a 1-2% success rate in reproduction on the island. They are also studying correlations between tortoise size and sexual maturity of males (development of long tails and concave plastrons) and toenail length and body size, as well as looking into what the best methods of tagging and marking the tortoises are.