Study

Giant tortoise Geochelone gigantea translocation to Curieuse Island (Seychelles): success or failure?

  • Published source details Hambler C. (1994) Giant tortoise Geochelone gigantea translocation to Curieuse Island (Seychelles): success or failure?. Biological Conservation, 69, 293-299.

Summary

The only species of wild giant tortoise on Indian Ocean islands survive on Aldabra Atoll. Here a population of Geochelone gigantea recovered to 150,000 individuals, but recently declined following food depletion. To aid conservation and provide a tourist attraction, tortoises were translocated over several years (from 1978-1983) to Curieuse Island (280 ha; 3.4 × 2 km max. dimensions) in the Seychelles archipelago. This paper evaluates the cumulative success of these translocations, based upon a census undertaken in 1990.

Between 1978 and 1983, 251 (possibly 255) tortoises were released: 95 in May 1978; 78 in April 1980, and between 75 and 79 in 1982. Each was marked with a numbered disk. Three adults from nearby Aride (where introduced earlier) were released in 1983. Tortoises were monitored by visiting scientists and the resident warden. Sporadic population censuses provided minimum estimates of numbers.
 
A census in 1986 suggested a population decline. In 1990, the most detailed survey since translocation was undertaken, and translocation success of tortoises reintroduced to Frégate Island (Seychelles) was briefly appraised.

In 1990, 117 tortoises were found on Curieuse (73 adult males; 38 adult females; and 6 juveniles derived from breeding on the island). Some adults were diseased. Low growth and reproductive rates suggest resource saturation, even at the present low density. Whilst endemic vegetation had not suffered due to tortoise grazing/browsing, tortoises were shown to spread non-native plants (via droppings).
 
Recruitment to five years of age was very low, probably due predation by non-native predators. Curieuse has a large population of brown rats Rattus rattus. Whilst there was no direct evidence of rats excavating ‘wild’ tortoise nests and predating eggs or hatchlings, captive hatchlings on Curieuse have been killed by rats. Feral cats Felis catus also occur throughout the island (as indicated by scats).
 
Poaching also occurs. Giant tortoises are regarded by some as a delicacy, and five or more dismembered carapaces were found; at least two had been killed since 1986. In contrast, giant tortoises have reproduced successfully on the cat- and rat-free Seychelles islands of Aride and Frégate.
 
It seems that the translocations to Curieuse will ultimately fail to establish a viable giant tortoise population.
 
 
Note: If using or referring to this published study, please read and quote the original paper, this can be viewed at: http://www.sciencedirect.com

Output references
What Works 2021 cover

What Works in Conservation

What Works in Conservation provides expert assessments of the effectiveness of actions, based on summarised evidence, in synopses. Subjects covered so far include amphibians, birds, mammals, forests, peatland and control of freshwater invasive species. More are in progress.

More about What Works in Conservation

Download free PDF or purchase
The Conservation Evidence Journal

The Conservation Evidence Journal

An online, free to publish in, open-access journal publishing results from research and projects that test the effectiveness of conservation actions.

Read the latest volume: Volume 18

Go to the CE Journal

Discover more on our blog

Our blog contains the latest news and updates from the Conservation Evidence team, the Conservation Evidence Journal, and our global partners in evidence-based conservation.


Who uses Conservation Evidence?

Meet some of the evidence champions

Endangered Landscape Programme Red List Champion - Arc Kent Wildlife Trust The Rufford Foundation Save the Frogs - Ghana Bern wood Supporting Conservation Leaders National Biodiversity Network Sustainability Dashboard Frog Life The international journey of Conservation - Oryx British trust for ornithology Cool Farm Alliance UNEP AWFA Butterfly Conservation People trust for endangered species Vincet Wildlife Trust