Study

Introduction of Aldabra giant tortoises Geochelone gigantea from Aldabra Atoll to the island of Curieuse, Seychelles

  • Published source details Stoddart D.R., Cowx D., Peet C. & Wilson J.R. (1982) Tortoises and tourists in the western Indian Ocean: the Curieuse experiment. Biological Conservation, 24, 67-80

Summary

To reduce tourist pressure on Aldabra giant tortoise Geochelone gigantea on their native Aldabra, a decision was made to attempt to establish a population to provide a tourist attraction within easy reach of Mahé (one of the main islands of the Seychelles archipelago). Also, if successful, it would mean re-establishment of giant tortoises in the Seychelles where the native Dipsochelys hololissa became extinct in the early 19th century. The hilly, 280 ha island of Curieuse (4.4 km long x 2 km wide; 4°16' S, 55º44' E) where Seychelles giant tortoises formerly occurred, was selected.

Releases: A total of 173 tortoises were introduced in two stages.  The first tortoises (101 of a range of sizes/sexes) were shipped on 4 April 1978, held at a quarantine station for about 5 weeks on Long Island, and 95 were released on Curieuse at the end of May. The tortoises were released on a plateau area (selected to limit initial dispersal) near the main settlement of Baie Laraie (and close to the Forestry Officer residence in order to reduce likelihood of poaching from nearby Praslin, 1.4 km distant). The second introduction was of 78 individuals on 10-11 April 1980. All animals were marked with numbered titanium discs on the lower right fourth scute.
 
Monitoring: Monitoring visits were made on 3 August, 23 November and 15 December 1978 (32 tortoises found). On 5-7 January 1979, 15 permanent vegetation monitoring sites was established, each photographed and the vegetation described in order to record the effects of tortoises over time. Subsequent sporadic monitoring visits were made in 1979 (3 days), 1980 (2 days) and 1981 (1 day).

Visits on 9 August 1979 and 9-10 January 1980 located 22 and 27 tortoises respectively; two tortoises on the latter date had traversed the island. The first hatchling tortoise was found in February 1980, and several were seen on 28 May 1981. At this time, 35 animals were found to have lost their discs (probably all 1978 releases). Four 1980 tortoises were found near the eastern point of the island: these had dispersed over a linear distance of more than 2 km over very rugged terrain in 12.5 months.
 
In January 1980, the 27 tortoises located were weighed; all showed considerable weight increases (average percentage increase ranged from 58-117%). These increases were much faster than would have been expected in the Aldabran source population.
 
By 20 March 1980 after 22 months, the only apparent impact of the tortoises on the vegetation was the formation of tracks and wallows in a small marsh.
 
 

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Output references

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