Aldabrachelys gigantea hololissa
| Seychelles giant tortoise | |
|---|---|
 | |
| A preserved specimen, from when it was believed to be extinct. | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Order: | Testudines |
| Suborder: | Cryptodira |
| Superfamily: | Testudinoidea |
| Family: | Testudinidae |
| Genus: | Aldabrachelys |
| Species: | A. gigantea |
| Subspecies: | A. g. hololissa |
| Trinomial name | |
| Aldabrachelys gigantea hololissa (GÜNTHER, 1877) | |
| Synonyms[1] | |
| |
The Seychelles giant tortoise (Aldabrachelys gigantea hololissa) is a tortoise subspecies in the genus Aldabrachelys.
It inhabited the large central granitic Seychelles islands, but was slaughtered in vast numbers by European sailors and settlers. By around 1840 it was presumed to be extinct, along with the Arnold's giant tortoise, a species which shared the same islands.
It was recently rediscovered. Currently, a little over a hundred individuals exist. Many had been reestablished in the wild on forested islands such as Silhouette, but were evicted in 2011 by the Seychelles Islands Development Company (IDC).[2]
Description
The three Aldabra-Seychelles giant tortoise species can be distinguished based on carapace shape, however, many captive animals may have distorted carapaces and so may be difficult to identify.
The Seychelles giant tortoise (A. g. hololissa) is broad, flattened on the back and with raised scutes, it is usually a brownish-grey color. In comparison, the true Aldabra tortoise (A. g. gigantea) is a roundly-domed, black-colored species. [3]
Life history
Large tortoises are among the longest-lived animals on the planet. Some individual Aldabra giant tortoises are thought to be over 200 years of age, but this is difficult to verify because they tend to outlive their human observers. Adwaita was reputedly one of four brought by British seamen from the Seychelles Islands as gifts to Robert Clive of the British East India Company in the 18th century, and came to Calcutta Zoo in 1875. At his death in March 2006 at the Kolkata (formerly Calcutta) Zoo in India, Adwaita is reputed to have reached the longest ever measured life span of 255 years (birth year 1750).[4] Today, Jonathan, a Seychelles giant tortoise, 184 years old, is thought to be the oldest living giant tortoise, and Esmeralda, 170 years old, the second oldest, since the death of Harriet at 176, a Galapagos giant tortoise. Esmeralda is an Aldabra giant tortoise.
A roughly 184-year-old tortoise on Saint Helena, named Jonathan, is believed to be a survivor of this species (as well as potentially the oldest living land creature in the world).[5]
Morphotype
This is a controversial species possibly distinct from the Aldabra giant tortoise. The species is a morphologically distinctive morphotype, but is considered by many researchers to be either synonymous with or only subspecifically distinct from that taxon. This identification is based primarily on morphological characters. Published molecular identifications are unclear with several different indications provided by different data sources.[6]
It is a domed grazing species, differing from the Aldabra tortoise in its broader shape and reduced ossification of the skeleton; it differs also from the other controversial giant tortoise in the Seychelles, the saddle-backed morphotype (Arnold's giant tortoise).
It was apparently extirpated from the wild but is now known only from 37 adults, including 28 captive, and 8 on Cousine Island, 6 of which were released in 2011 along with 40 captive bred juveniles. Captive reared juveniles show that there is a presumed genetic basis to the morphotype and further genetic work is needed to elucidate this.[7][8][9]
Extinction and rediscovery
Originally, several different species of giant tortoise inhabited the various islands of the Seychelles. Large and slow, the tortoises were also reportedly friendly with little fear of man. Sailors and settlers slaughtered thousands and swiftly drove most populations to extinction.
Though generally assumed that the Aldabran tortoise was the only one to have survived over-exploitation in the Seychelles, it is occasionally, most recently in 1995, suggested that some Seychelles granitic island tortoises survived in captivity. The report of oddly shaped captive tortoises prompted the Nature Protection Trust of Seychelles to examine the identity of the living tortoises. Examination of museum specimens of the 'extinct' Seychelles species by Dr. Justin Gerlach and Laura Canning confirmed that some living tortoises did show characteristics of the supposedly extinct species.[10] Some recently published scientific papers on the genetics of the Seychelles and Indian Ocean tortoises provide conflicting results. Some studies suggest only one species (with multiple variants) was ever present in the islands, whilst others suggest three distinct, but closely related species. These different views derive from studies of different genes.
Conservation
With DNA testing, tortoises of the "extinct" species were identified and were acquired by the Nature Protection Trust of Seychelles for conservation. They were brought to Silhouette Island and the captive-breeding program was initiated in 1997. For several years the female tortoises produced infertile eggs. In November 2002 eggs laid by a young female started to hatch.[11] By the time the NPTS was evicted, they had produced 40 juveniles of the Seychelles giant tortoise.[7][8][12]
The decision of the Islands Development Company to evict NPTS from Silhouette island by March 2011 and the incomprehensible refusal to permit wild tortoises to live on the island forced them to remove and find new homes for the tortoises.
Fortunately, the privately managed island of Cousine agreed to provide a new home for the Seychelles tortoises.[2] In April 2011, the Seychelles giant tortoises went to Cousine.[2] Cerf Island also has one free-ranging adult.[9] Had they been able to release them on Silhouette island, they would have established separate wild populations, now they will be mixed with the Aldabra tortoises that are already on the islands.[2]
NPTS take consolation from the fact that they have produced a new generation of many young tortoises which will live on for at least 100 years. In that time there may be an opportunity to establish pure populations of these tortoises; fortunately, these animals live longer than short-term management and development perspectives.[9]
References
- ↑ Aldabrachelys gigantea at the Reptarium.cz Reptile Database. Accessed 05 June 2015.
- 1 2 3 4 "Moving giant tortoises". Retrieved 5 June 2015.
- ↑ "The identification of Seychelles giant tortoises". Retrieved 5 June 2015.
- ↑ BBC News - South Asia (2006-03-23). "'Clive of India's' tortoise dies". BBC News. BBC Online. Retrieved 2014-01-23.
- ↑ Kettle, Sally (13 March 2014). "Meet Jonathan, St Helena's 182-year-old giant tortoise". BBC News. Archived from the original on 2014-04-09.
- ↑ "Release of Arnold's giant tortoises Dipsochelys arnoldi on Silhouette island, Seychelles; By Justin Gerlach" (PDF). Retrieved 7 June 2015.
- 1 2 "Tortoises". Retrieved 6 June 2015.
- 1 2 "Tortoise reintroduction". Retrieved 5 June 2015.
- 1 2 3 "Aldabrachelys hololissa, 061". Retrieved 7 June 2015.
- ↑ "Giant tortoises". Retrieved 5 June 2015.
- ↑ "Hatchings". Retrieved 7 June 2015.
- ↑ "Tortoise news". Retrieved 7 June 2015.