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The Endangered Galapagos Giant Tortoise

Text Courtesy of the World Conservation Monitoring Centre
Photos © Jeff Waugh

The Giant Galapagos Torrtoise

Geochelone elephantopus (Harlan 1827)

Synonyms: Chelonoidis species

Order: TESTUDINES
Family: TESTUDINIDAE


SUMMARY

Occurs on most islands in the Galapagos group (Ecuador) in the east Pacific. Populations severely depleted in nineteenth century through overcollection by whaling ships for stores. Natural reproduction presently reduced (and in some populations prevented) by introduced mammal predators. Important captive breeding and rearing projects are being carried out at the Charles Darwin Research Station. Strictly protected in the Galapagos, which were declared a National Park in 1959. Listed on Appendix I of CITES.


DISTRIBUTION

Restricted to the Galapagos Islands (Archipiélago de Colon) (Ecuador), astride the equator in the east Pacific (See Population section for further details).


POPULATION

Populations are isolated on different islands, or on Isabela by impassable lava flows. They have traditionally been treated as subspecies of Geochelone elephantophus but it has recently been proposed (1) that they might be more appropriately treated as full species of the genus Chelonoidis. Pending further discussion the more conservative arrangement is retained here. Population details for each subspecies are summarised below.


G. e. abingdoni

Formerly restricted to the southern slopes of Pinta (Abington Island) (3,10). Only one known individual is alive ("Lonesome George"), and is currently maintained at the Charles Darwin Research Station. This population was severely depleted by whalers and fishermen, and the introduction of goats in 1958 resulted in massive destruction of vegetation (12,14). Tortoise droppings, probably not more than a few years old, were found in the island in 1981, so there is a possibility that a second individual of this subspecies still exists (16). Further investigations are planned for 1982.

G. e. becki

Northern and western slopes of Volcano Wolf, Northern Isabela (Albermarle). Present population may be as many as 2,000. Reproduction appears to be successful despite the presence of black rats and feral cats, but the impact of these predators is not known (8,13).

G. e. chathamensis

Now confined to northeast San Cristobal (Chatham). Present population between 500 and 700. Heavily exploited and completely eliminated over much of its original range (3). Effective reproduction is now prevented by trampling of nests by feral donkeys, and the destruction of young by feral dogs (6,8,13). Eggs from wild nests have been removed for incubation and rearing to the Charles Darwin Research Station (5). In 1979 139 juveniles had been returned to the island and 13 were held at the station (13).

G. e. darwini

West-central San Salvador (James Island). Large numbers of tortoises were removed from the island in the early nineteenth century by whaling vessels, and introduced goats reduced the coastal lowlands to deserts, restricting the remaining tortoises to the interior (8). The sex ratio is strongly imbalanced in favour of the males (8) and most nests and young are destroyed be feral pigs (4,8). It is estimated that reproductive success diminished about 50 years ago and ceased altogether about 30 years ago (8). Some nests are now protected by lava corals and since 1970 eggs have been transported to the Charles Darwin Research Station for hatching and rearing. 115 individuals have been re-released on San Salvador (13).

G. e. elephantopus

Cerro Azul, Eastern Isabela (Albemarle). Range overlaps with G. e. guentheri and it may eventually be shown that these two taxa should be combined (6,8). This population was depleted by seamen in the last two centuries and by extensive slaughter in the late 1950's and 60's by employees of cattle companies based at Iguana Cove. Present population may number as many as 700 individuals. Although mating and nesting still occur naturally, very few young individuals are found, suggesting that predation by local feral dogs, cats and pigs is almost total (6,8). Eggs and hatchlings are removed to the Charles Darwin Research Station. Since 1971, 114 indiviuals have been returned to the island (13).

G. e. ephippium

Southwestern slopes of Pinzon (Duncan Island). Although relatively undisturbed by whalers, fairly large numbers of tortoises were removed by expeditions in the latter half of the nineteenth century and early this century (2,8). Present population is about 150 adults. Since the introduction of black rats some time before 1900, there has been no natural recruitment. Despite the age of the remaining population the females are still laying fertile eggs. Since 1965, eggs have been transported to the Charles Darwin Research Station for hatching and rearing. So far 182 young tortoises have been returned to the island (13).

G. e. galapagoensis

Floreana (Charles Island). Extinct. Formerly abundant but heavily exploited by visiting ships and a penal colony in the last century (8).

G. e. guentheri

Volcano Sierra Negra, Isabela (Albemarle). Severely depleted by settlement and exploitation for tortoise oil which continued until the 1950s. 300-500 individuals remain, divided into two groups by settlements. About 300 occur in the east and 200 over the western and southwestern slopes (4,13). Reproduction seems successful in the east but in the western-southwestern area pigs, dogs, rats and cats are present as predators (6).

G. e. hoodensis

Formerly Espanola (Hood). This population was very heavily exploited by whalers in the nineteenth century. The population appears to have collapsed around 1850 (8). 14 adults (2 males, 12 females) were found in the early 70's and are now held at the Charles Darwin Research Station as a breeding colony. Mating had not occurred naturally for some time because the individuals were so scattered that they did not meet. 129 young have now been produced. 79 have been returned to the island and 50 are held at the Station (13).

G. e. microphyes

Southern and western slopes of Volcano Darwin, Isabela (Albemarle). Present population between 500 and 1,000 individuals (8), heavily exploited in the nineteenth century by whaling vessels. Reproduction appears to be successful. The effect of populations of rats and cats needs to be investigated (13).

G. e. phantastica

Fernandina (Narborough Island). Only one specimen has ever been found, probably extinct (8).

G. e. porteri (Syn. G. e. nigrita).

The main population occurs in southwest Santa Cruz (Indefatigable Island) with a very small population in the northwest (8). Total population estimated at 2,000-3,000. Depleted by heavy exploitation for oil at least until the 1930s (3,8). Reproductive success has been severely hampered for many years by the presence of feral dogs and pigs (6,8,9,13). Approximately 15-20 hatchlings have been raised at the Charles Darwin Research station annually.

G. e. vandenburghi

Caldera and southern slopes of Volcano Alcedo, Central Isabela (Albemarle). The largest population in the archipelago, possibly numbering as many as 5,000 individuals. Reproduction successful at present (6,8,13).


HABITAT AND ECOLOGY

Dome-shaped carapace from Santa Cruz A very large species which may reach a carapace length of 122 cm (4 feet) and weight of 227 kg (500 lb) on the larger islands (8). Males are much larger than females (8). The different populations exhibit marked differences in size and shape. The populations may be divided roughly into two groups. Those from the smaller, drier islands tend to be smaller (females average 27 kg, males 54 kg) and have 'saddleback' carapaces (elevated above the neck and flared or reverted above the hind feet) and longer, thinner limbs. Conversely those from the larger, wetter islands are larger with dome-shaped shells (8). The saddleback would appear to be a modification allowing the tortoises to reach up and browse on the taller vegetation. This is particularly important since on the drier islands with tortoise populations the Opuntia cactus (a major source of water) has evolved an arborescent form (8). Mating appears to occur at any time of the year although it does have seasonal peaks. Almost any kind of green vegetation is taken as food, including Hippomane mancinella which is highly poisonous to most creatures (8). When possible G. elephantopus spends long periods of time partially submerged in pools; this may be both a thermoregulatory response and a protection from mosquitoes and ticks. At night this species may dig itself into soft ground or vegetation (8).


THREATS TO SURVIVAL

Feral goats threaten tortoise survival Populations, particularly on the more accessible islands, were severely depleted by passing ships (particularly whalers) taking tortoises on board for supplies. A total of over 15,000 tortoises is recorded in the logs of 105 whaling ships between 1811 and 1844 (12). Increased settlement in the 20th century encouraged commercial hunting of tortoises for oil and extensive collecting for museums (3). Introduced mammals now pose the greatest threat to the tortoises. Feral pigs, dogs, cats and black rats are extremely effective predators whilst feral goats, donkeys and cattle compete for grazing. Goats have had particularly drastic effects upon the natural vegetation (6).


CONSERVATION MEASURES TAKEN

In 1959, Ecuador declared all uninhabited areas in the Galapagos to be a National Park, and made it illegal to capture or remove many species from the islands, including tortoises or their eggs; in 1970, it became illegal to export any Galapagos tortoises from Ecuador, regardless of whether they had been reared in captivity or the wild, or whether from continental Ecuador or the islands; United States Public Law 91-135 (December 5 1969) automatically prohibits importation of Galapagos tortoises into the U.S.A. because their export from Ecuador has been declared illegal (4). A 1971 decree makes it illegal to damage, remove, alter or disturb any organism, rock or other natural object in the National Park (6). The Galapagos National Park Service systematically hunt feral predators and competitors where necessary. Some nests are protected by lava corrals and the eggs of many of the populations are taken from the wild and hatched and reared at the Charles Darwin Research Station. Juveniles that have reached a size that ensures a good chance of survival are returned to their original ranges (5,13).

Geochelone elephantopus is listed on Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Appendix I listing requires that trade in the taxon and its products is subject to strict regulation by ratifying states and international trade for primarily commercial purposes is prohibited.


CONSERVATION MEASURES PROPOSED

Present efforts should be continued. A more radical programme of feral mammal eradication might be employed in some areas; in particular an effective means of controlling the Black Rat Rattus rattus is needed (3,11). Further attempts should be made to find a mate for the captive male G. e. abingdonii. Electro-ejaculation followed by artificial insemination of a female with a similar shaped carapace might be considered (11).


CAPTIVE BREEDING

A breeding colony of G. e. hoodensis is held at Charles Darwin Research Station. One hundred and twenty-nine young had been produced by 1979 (see Population section) (13). Eggs of G. e. elephantopus, G. e. darwini, G. e. ephippium, are hatched and young reared at the station (see Population section). In 1980 223 individuals (of which 72 had been bred in captivity), were held in 54 collections; 125 of these were not identified subspecifically in available sources. Seventy-one were identified as G. e. elephantopus, 50 of these were bred in a major breeding project at Honolulu Zoo. Three male G. e. becki were held at Zurich, one male and two females of G. e. guentheri were held at Sydney and 21 G. e. porteri were held in 10 collections (15).


REMARKS

This account is largely based on a draft kindly provided by Réne Honegger (Curator of Herpetology, Zürich Zoo, and former Compiler, Amphibia and Reptilia Red Data Book).

This species is of great historical scientific interest since, by illustrating a correlation between geographic isolation and morphological divergence, it was instrumental in the formation of Darwin's concept of evolution through natural selection.

It has recently been proposed (1) that several taxa usually recognized as subgenera of Geochelone should be elevated to generic rank, in this case as Chelonoidis. This usage is not yet widespread. Also see first paragraph of Population section, above.


REFERENCES

Bour, R. (1980). Essai sur la taxinomie des Testudinidae actuels (Reptilia, Chelonii). Bull. Mus. natn. Hist. nat. Paris. 4e sér., 2, section A, no 2: 541-546.
Hendrickson, J.R. (1966). The Galapagos tortoises Geochelone Fitzinger 1835 (Testudo Linnaeus 1758 in part). In Bowman, R.I. (ed.) The Galapagos: Proc. Galapagos Int. Sci. Proj. Univ. Calif. Press, Berkeley and Los Angeles, pp. 252-257. Not seen, cited in (3).
Honegger, R. (1979). Draft Red Data Book accounts for G. elephantopus subspp.
MacFarland, C.G. and Black, J. (1971). The law and the Galapagos. Int. Turtle and Tortoise Soc. J. 5(4): 36-37. Not seen, cited in (3).
MacFarland, C.G. (1979). Pers. comm. to J.R. Hendrickson. Not seen, cited in (2).
MacFarland, C.G., Villa, J. and Toro, B. (1974). The Galapagos Giant Tortoises (Geochelone elephantopus) I. Status of the Surviving Populations. Biol. Consv. 6(2): 118-133. Not seen, cited in (3).
MacFarland, C.G., Villa, J. and Toro, B. (1974). The Galapagos Giant Tortoises (Geochelone elephantopus) II: Conservation Methods. Biol. Consv. 6(3): 198-212. Not seen, cited in (3).
Pritchard, P.C.H. (1979). Encyclopedia of Turtles. T.F.H. Publications, Hong Kong and New Jersey.
Snow, D.W. (1964). The giant tortoises of the Galapagos Islands. Their present status and future chances. Oryx. 7: 277-290. Not seen, cited in (3).
Swingland, I.R. (1981). In litt.
Swingland, I.R. (1981). Report on 1st meeting of IUCN/SSC Specialist Group held 1-2 October. Oxford U.K.
Townsend, C.H. (1925). The Galapagos tortoises in their relation to the whaling industry. A study of old logbooks. Zoologica. 4: 55-135. Not seen, cited in (3).
Villa, J.L. (1979). In litt. Not seen, cited in (3).
Weber, D. (1971). Pinta, Galapagos: Une Ile à sauver. Biol. Consv. 6(2): 118-133. Not seen, cited in (3).
Olney, P.J.S. (Ed.) (1981). International Zoo Yearbook. Vol. 21 Zoological Society of London.
Laurie, A. (1982). Pers. comm., 21 June.

For further information, contact: the Information Officer,
e-mail: info@wcmc.org.uk; Tel: +44 (0)1223 277314

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