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
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
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.
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