Dermochelys coriacea (Leatherback turtle)
Leerrug-seeskilpad [Afrikaans]
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Family: Dermochelyidae > Genus: Dermochelys
Identification
A very distinctive species with its spindle-shaped body and
leathery, unscaled, keeled carapace (the protective covering on top of the
animal). It is the largest species of chelonian (the group containing the
turtles, terrapins and tortoises) in the world and one of the largest living
reptiles; it is exceeded in size only by a few large species of crocodile. The
largest individual yet recorded was 2.56 m long and weighed 916 kg.
Distribution and habitat
The Leatherback turtle is pelagic, living in the open sea,
and is found in oceans worldwide. Although living in the surface waters most of
the time, these turtles are also able to dive to depths of over 900 m. Unlike
most other reptiles, it is endothermic (warm-blooded), thus being able to
generate internal heat to keep its body warmer than its surroundings. This
capability, along with the insulation provided by a protective thick and oily
skin, has resulted in the Leatherback turtle being superbly adapted to cold
water conditions. As a result, it occurs not only in tropical and subtropical
seas but also penetrates into the cool seas such as into the Gulf of Alaska and
around Scandinavia.
Life cycle
- A female comes ashore on beaches at night, digs a hole in the sand above
the high water mark, lays 46-160 eggs, covers them up and returns to the
sea.
- She lays 4-7 clutches in a season, 9-10 days separating each clutch.
- In South Africa, leatherbacks breed along the coast in northern
KwaZulu-Natal and egg laying is from late October to late January.
- After an incubation period of 50-78 days (depending on temperature
and humidity), the hatchlings emerge, dig out of their nest, and make their
way down to the sea. Hatching takes place from late December to early April
in South Africa.
- They reach sexual maturity after 13-14 years, by which time their
carapace length has reached about 1.25 m. They can live for 30 years or
more.
Food
The Leatherback turtle feeds mainly on jellyfish but also
on other surface-dwelling soft-bodied invertebrates, including
pyrosomes (Davenport and Balazs 1991) and cephalopods.
Ecological interactions
- Eggs are eaten by a variety of animals including monitor lizards (Varanus
– leguwaan in Afrikaans),
monkeys and
mongooses. Harvesting of eggs by
people has caused drastic declines in populations.
- Hatchlings are exposed to extensive predation in their journey from the
nest into the sea, being attacked by various predatory birds and mammals.
Once in the water, they are caught by seabirds (e.g.
frigatebirds,
gulls)
and by carnivorous fishes and squids.
- In the sea, both juveniles and adults are attacked by sharks and adults
can be eaten by killer whales (Orcinus
orca).
Status
The World leatherback turtle population dropped from about
115 000 adult females in 1982 to about 25 000 in 1996, constituting a 78%
reduction in numbers. This decrease has been caused by excessive harvesting of
eggs, killing of adult females on beaches to obtain oil or for eating,
entanglement of adults in fishing nets, and capture of adults on long-line
hooks. They also die quite frequently from consuming plastic packets and bottles
floating in the sea, which they seem to mistake for jellyfish. This serious
situation for leatherbacks is being addressed through: (1) legislation
prohibiting egg collecting and killing of females; (2) CITES regulations that
prohibit international trade in all sea turtle products; and (3) the creation of
coastal reserves in breeding areas. The capture and death of these turtles
through fishing practices has yet to be addressed adequately.
Links
Publications
- Davenport J, Balazs GH. 1991. 'Fiery bodies' - are pyrosomas an
important component of the diet of leatherback turtles? British
Herpetological Society Bulletin 37: 33-38.
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