Leatherback Turtle
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Leatherback Turtle

Common name: Leatherback Turtle
Scientific name: Dermochelys coriacea
Length: 1.4 to 1.6 m
Weight: 300 to 900 kg (660 to 2,000 lb)
Population: estimated at approximately 25,000
Distribution: worldwide, from tropical oceans to subpolar seas; egg-laying sites on tropical beaches
Issue: overexploitation of eggs, disturbance of egg-laying sites, fishing equipment, plastic pollution, overfishing
IUCN Red List status: critically endangered

Description
The Galápagos tortoise is the largest living tortoise (land-dwelling turtles), along with the Aldabra giant tortoise (Aldabrachelys gigantea). The species is endemic to the Galápagos Islands, an archipelago of 14 volcanic islands off the coast of Ecuador, in the Pacific Ocean. (The islands’ name comes from the old Spanish word meaning “saddle” because the shell of the giant tortoises reminded 16th-century explorers of the saddles used by the Spanish.) When Europeans discovered the islands in 1535, the population was thought to be about 250,000 individuals. Today, it is about 20,000, but in the 1970s, it was as low as 3,000.

The species is split into 11 existing subspecies on the archipelago’s main islands. At least one subspecies (Chelonoidis nigra nigra), and as many as four in all, has gone extinct in the wild; one other (Chelonoidis nigra abingdoni) was until recently is represented by only one a single living individual,: “Lonesome George,.” but he died on June 24th 2012 at an estimated age of 100.

Two to three million years ago, the ancestor of these reptiles came to the archipelago from the South American continent, 950 km away. Having first colonized the nearest and oldest islands (San Cristóbal and Española), the species later spread west to the more distant and younger islands. The subspecies are differentiated by the different conditions that prevail on the various islands in the archipelago. Their legendary size is likely a characteristic they share with their ancestors, since large body size would increase their chances of survival during a long voyage, such as their crossing between the continent and the islands. Their long necks would also have allowed them to better hold their heads out of the water to breathe. Their gigantism also helps them conserve water, adapt to dry climates and long periods without food, and tolerate wide temperature fluctuations. Fossils found in South America would appear to confirm these ideas.

The Galápagos tortoise has a broad bony shell that is dull brown in colour. Lichen may even grow on it, evidence of the relative slowness of these animals. For protection, they can withdraw their head and forelimbs inside the shell. Some scientists believe that the shell, which arches up in front like a saddle, and the long neck are adaptations to elevated food sources, such as the fruit of the prickly pear cactus, typical of arid climates. Other researchers believe that it is a competitive trait among males, individuals with the longest necks having better reproductive success.

Galápagos tortoises lead a relatively slow-paced life, eating herbaceous plants, grasses, and shrubs in their environment. During the day, they may move at 0,3 km/h toward volcanic plateaux, where they have access to drinking water, warm-water springs to wallow in, and an abundance of plants. In the evening, they generally return to the lowland plains along paths used by generations of tortoises. As cold-blooded animals, they prefer warm, dry areas. They spend about two hours a day sunbathing, their dark shells storing warmth and releasing it later.

Breeding season is between January and August. Males are able to detect a scent given off by females. Once a potential mate has been located, the male will follow her and dominate her until mating begins. Nesting generally takes place between June and December. Females build a nest in the sunny lowlands to ensure the eggs are warm enough for incubation. They produce about 10 eggs, which they cover with soil using their powerful hind legs. Incubation time varies from three to eight months, depending on ambient temperature and subspecies. Once the eggs hatch, the young tortoises are on their own. Most young die within their first 10 years of life. Sexual maturity is achieved after about 20 years.
Galápagos tortoises enjoy remarkable longevity. They generally live over 100 years, and the record in captivity is 177 years.

The subspecies are as follows (see map):
1. Chelonoidis nigra vandenburghi. Population: 6,320. IUCN status: vulnerable
2. Chelonoidis nigra porter. Population: 3,391. IUCN status: endangered
3. Chelonoidis nigra vicina. Population: 2,574. IUCN status: endangered
4. Chelonoidis nigra chathamensis. Population: 1,824. IUCN status: vulnerable
5. Chelonoidis nigra darwini. Population: 1,165. IUCN status: endangered
6. Chelonoidis nigra becki. Population: 1,139. IUCN status: vulnerable
7. Chelonoidis nigra hoodensis. Population: 860. IUCN status: critically endangered
8. Chelonoidis nigra microphytes. Population: 818. IUCN status: vulnerable
9. Chelonoidis nigra guntheri. Population: 694. IUCN status: endangered
10. Chelonoidis nigra duncanensis. Population: 532. IUCN status: extinct in the wild
11. Chelonoidis nigra abingdoni. Population: 01 (Lonesome George died on June 24, 2012). IUCN status: extinct in the wild

Threats
Over the centuries, Galápagos tortoises have been hunted for their meat and oil. Slow-moving and rather harmless animals, they were easy to catch and, once turned onto their shell, could survive for months on a ship before being eaten by the sailors. In addition to overexploitation, which reduced the total population to some 3,000 individuals by the 1970s, another threat has loomed in recent decades: introduced species such as dogs, cats, rats, goats, and pigs, which have quickly become invasive. Today, this is the most significant threat to the tortoise, since the predators eat the young turtles and the plant eaters eat the plants the tortoises feed on. Hunting is now prohibited, and major efforts have been taken over the past 30 years to preserve the different subspecies. And while several of the Galápagos tortoise subspecies are considered endangered, since 1986 the species as a whole has been listed by the IUCN as “vulnerable” rather than “endangered.” So there is room for hope.

Did you know?
Harriet, a Galápagos tortoise collected by Charles Darwin himself in 1835, died at the Australia Zoo, north of Brisbane, in 2006. She belonged to the subspecies Chelonoidis nigra porter and was over 175 years old!

REFERENCES: Red List of Threatened Species of the International Union for Conservation of Nature (IUCN) and Encyclopedia of Life.

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