Flatback Turtle
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| Flatback Turtle | ||||||||||||||
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| Natator depressus (Garman, 1880) |
The Flatback Turtle, Natator depressus, is a sea turtle that is endemic to the continental shelf of Australia.
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[edit] Anatomy
The carapace of the adult is on average 90 cm long. This is low domed, the edge is upturned and has four pairs of costal scales - fewer than other marine turtles of the region. An olive-grey colour is found on the upper parts, and it is paler underneath. A single pair of scales are located at the front of the head, which also distinguish this species.[1]
They can grow up to one meter in length.
[edit] Distribution
Flatback turtles are found in coastal waters. The species may feed in the waters off Indonesia and Papua New Guinea, but it nests only in Australia. Nesting occurs across the top half of Australia, from Exmouth in Western Australia to Mon Repos in Queensland. The most significant breeding site is Crab Island in the western Torres Strait. Breeding may also occur on the islands of the southern Great Barrier Reef, and on mainland beaches and offshore islands north of Gladstone.
[edit] Ecology and life history
[edit] Habitat
Flatback turtles are usually found in bays, shallow, grassy waters, coral reefs, estuaries and lagoons on the northern coast of Australia and off the coast of Papua New Guinea.
[edit] Trophic ecology
The Flatback Turtle is known to be rather broad in its eating habits and can eat a variety such as seagrass, marine invertebrates (such as mollusks, jellyfish and shrimp) and fish. It also is known to be a consumer of soft coral, sea cucumbers and other soft-bodied creatures.[1]
[edit] Nesting
The Flatback turtle is unusual because it lays fewer, but larger eggs than the other sea turtle species. Females emerge onto the beach on which they hatched more than 30 years ago and make their way up the beach to lay their eggs. This takes around an hour and a half. The female digs a pit using her front flippers to clear away the topmost layer of dry sand,. She then uses her rear flippers to dig a small egg chamber. After laying between 50 and 75 eggs she covers them first with her hind flippers, and then flings sand back with her front flippers. Females will lay a clutch of eggs around every 16-17 days during the nesting season, with between one and four nests being laid in total. They will only nest every 2-3 years. There are around 54 eggs in each clutch, and the rookeries are usually small.[1]
These eggs are vulnerable to predation by dingoes, sand goannas (Varanus gouldii) and the introduced pest species - the fox. An altered ecology at known nesting sites, such as Port Hedland, have resulted in disturbances to the breeding behaviour of the turtle. Adult specimens are also found in the nets of fishing trawlers, and are still consumed by the indigenous peoples of its distribution range.[1]
Male turtles never return to the shore, as mating occurs at sea.
[edit] Hatching
Hatching is the most dangerous time for flatback turtles. Guided by the low, open horizon, the newborns make a dash for the sea. Only safety in numbers will protect them from birds and crabs. However, even the sea is not safe. Sharks and fish partol shallow waters, waiting to gobble up the babies. Scientists estimate only 1 out of 100 turtles live to become an adult. However, as these turtles become adults there are very few organisms that hunt these fascinating creatures. The survivorship curve is known as a type III because there is high mortality for these animals as hatchlings but there is a very low mortality rate as they become older.
[edit] Naming and taxonomic history
This species is contained by a monotypic genus, Natator, that is found in the Cheloniidae family. depressus, the species indicator (the second part of the scientific name means "flat" in Latin. This refers to the flatness of the Flatback's shell.
The Bardi people called this animal barwanjan, and it was known to the Wunambil as madumal.[1]
[edit] Conservation
The species is considered vulnerable to extinction in Western Australia,[1] but the Red list of the IUCN notes that is data deficient and unable to be correctly assessed.[2]
If this species is not protected, it is likely that these turtles will become extinct in the foreseeable future. If this species disappears, the ecosystems it is a part of will surely crumble. The seagrasses these turtles feed on are breeding grounds for certain organisms that can only survive if the grass is kept short, much like the grass in our front yard. The organisms that thrive in the seagrass would die out, causing a chain reaction of the organisms that feed off them to die out, and so on.
[edit] See also
- Chelonioidea. The sea turtle superfamily.
[edit] References
- ^ a b c d e f Burbidge, Andrew A [2004]. Threatened animals of Western Australia. Department of Conservation and Land Management, 110, 114. ISBN 0 7307 5549 5.
- ^ Red List Standards & Petitions Subcommittee (1996). Natator depressus. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 12 May 2006. Database entry includes a lengthy justification of why this species is listed as data deficient
