And then there were ten… the June 24th, 2012 passing of “Lonesome George”, the only remaining Abingdon Island giant tortoise, has brought the number of extant Galápagos Islands tortoise subspecies down another notch from the original 12 to 15. Let’s look at who’s left, in all their long-lived, slow-moving glory.
Volcán Alcedo Tortoise
According to population estimates made by the Directorate of the Galápagos National Park in mid-2009, the overall number of giant tortoises is roughly 20,000 of which 6,320 belong to the Volcán Alcedo subspecies (Chelonoidis nigra vandenburghi). Though still considered Vulnerable by the IUCN Red List, Volcán Alcedo tortoises can be considered to be a success story in that the original estimated number of all subspecies of giant tortoise in the Galápagos Islands was roughly a quarter of a million, falling to a low of just 3,000 in 1974.
(image via: Tim Kenny)
Volcán Alcedo tortoises are native to the caldera and southern slopes of the Alcedo Volcano located on the central part of Isabela Island, the largest island in the Galápagos archipelago. Analysis of the tortoises’ DNA revealed a surprisingly low level of genetic diversity, a characteristic that may be the result of a natural catastrophe (likely a volcanic eruption) that occurred around 100,000 years ago.
Chatham Island Tortoise
Approximately 1,820 Chatham Island tortoises live in the northeastern portions of San Cristóbal (formerly Chatham) island. Designated as Vulnerable by IUCN, the Chatham Island tortoise (Chelonoidis nigra chathamensis) has made an impressive recovery helped by the fencing off of its prime habitat and the eradication of feral dogs in the 1970s.
(image via: Mikel.Hendriks)
Chatham Island tortoises are “giants” in the true sense of the word. Over an estimated 170-year lifespan they can grow to a maximum weight of 400 kg (880 lb), extending 1.8 meters (5.9 ft) in length from nose to tail tip.
Volcán Wolf Tortoise
About 1,150 Volcán Wolf tortoises inhabit the northern and western slopes of Volcano Wolf, the largest of the six component volcanoes that together make up Isabella Island. These officially Vulnerable tortoises have adapted to the harsh conditions around 1,707 meter (5,600 ft) high Volcano Wolf, conditions that may hinder the tortoises main predators: rats, feral pigs and dogs, donkeys and goats.
(image via: C.Nilsen)
A recent genetic analysis of the Volcán Wolf tortoise (Chelonoidis nigra becki) has shed light on a longstanding mystery: the tortoises exhibit a range of shell shapes varying from dome-shaped to saddle-backed. The latter may be hybrids of the now-extinct C. Elephantopus tortoise native to Floreana Island, located 200 miles away. Biologists theorize that 19th century whalers captured Floreana tortoises for food and later threw any “extras” overboard; the tortoises then swam to nearby Isabella Island and mated with Volcán Wolf tortoises.
Volcán Darwin Tortoise
Though there are only around 800 or so Volcán Darwin tortoises (Chelonoidis nigra microphyes), IUCN lists them as Vulnerable due to their reasonably successful reproduction rate in the wild. The tortoises are found on the rugged southern and western slopes of 1,325 meter (4,350 ft) high Volcano Darwin, located just south of Volcano Wolf on Isabella Island.
(image via: Bronx Zoo)
Volcán Darwin tortoises have relatively light-colored, brownish-gray carapaces that may have evolved to provide camouflage in their rocky habitat. They were extensively studied by Charles Darwin after his ship, HMS Beagle, laid anchor in a sheltered cove at the foot of the volcano that today bears his name.
Indefatigable Island Tortoise
Just under 3,400 Indefatigable Island tortoises roam the scrubby hills of Santa Cruz Island, with most tortoises congregating in the southwest and a separate group roaming to the northwest. The tortoises display a more lowland-type appearance with black, domed shells and comparatively shorter necks.
(image via: Wildlife of the Galapagos)
Recent studies point to the possibility of their actually being three distinct species of Indefatigable Island tortoise (Chelonoidis nigra porteri), creating a new challenge for biologists already struggling to boost the numbers of this officially Endangered giant tortoise.