Flatback sea turtle

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Flatback sea turtle
Natator depressus.jpg
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Testudines
Family: Cheloniidae
Genus: Natator
McCulloch, 1908
Species: N. depressus
Binomial name
Natator depressus
(Garman, 1880)

The flatback sea turtle (Natator depressus) is a sea turtle endemic to the continental shelf of Australia. The flatback turtle belongs to the sea turtle superfamily Cheloniidae and is the only species found in the genus Natator. Its common name comes from its flattened carapace compared to other species of sea turtle.

Adult flatback turtles have a low-domed carapace, with upturned edges, which is approximately 90-95cm long.[2] The carapace is olive to grey coloured and the plastron is cream coloured.[2] Flatback hatchlings have grey carapaces with the scutes distinctively outlined in black. The plastron and the edges of the carapace are white.[2]

Taxonomy and etymology[edit]

This species is within a monotypic genus, Natator, in the family Cheloniidae; the name means "swimmer" in Latin. Depressus, the specific name, means "flat" in Latin. It 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.[3]

Range and habitat[edit]

Map showing four nesting sites, spread across Australia's northeast coast
Natator depressus distribution map: Red circles show major nesting sites.

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.

The species may feed off Indonesia and Papua New Guinea, but it nests only in Australia. Nesting occurs across the northern half of Australia, from Exmouth in Western Australia to Mon Repos Conservation Park 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.

Anatomy[edit]

The carapace of the adult is on average 90 cm (35 in) long. It is low-domed, the edge is upturned, and has four pairs of costal scales—fewer than other marine turtles. The upper parts are an olive-grey, and more pale ventrally. A single pair of scales is located at the front of the head, which also distinguish this species.[3]

Life history[edit]

A flatback turtle hatchling crawls to sea
Underside of an adult flatback

Nesting[edit]

The flatback turtle is unusual because it lays fewer but larger eggs than other sea turtle species. They lay up to 55 eggs a time, three times during the breeding season. Male turtles never return to shore, since mating occurs at sea, taking around 1.5 hours. 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 a clutch of between 50 and 75 eggs, she covers them first with her hind flippers, and then flings sand back with her front flippers. Females lay eggs every 16–17 days during the nesting season—totaling one to four nests. They nest only every two to three years. Around 54 eggs are laid in each clutch, and the rookeries are usually small.[3]

These eggs are vulnerable to predation by dingoes, sand goannas (Varanus gouldii) and an introduced pest species—the red fox. An altered ecology at known nesting sites, such as Port Hedland, has disturbed breeding behavior. Adult specimens are also found in the nets of fishing trawlers, and are still consumed by indigenous peoples across their range.[3]

Hatching[edit]

Flatback hatchlings are the largest of any turtle. Hatching is the most dangerous time for flatbacks. Guided by the low, open horizon, newborns dash for the sea. Only safety in numbers protects them from birds and crabs. However, even the sea is not safe. Sharks and fish patrol shallow waters, waiting to prey upon hatchlings. Scientists estimate only one of 100 turtles lives to become an adult.[citation needed] However, once these turtles become adults, very few organisms prey on them. Their survivorship curve is known as type III because hatchlings endure high mortality rates, while adults thrive.

Adaptations[edit]

Flatback hatchlings are fairly large compared to other sea turtles making it harder for predators to eat them. The light reflected off the water from the sky guides them to the sea. Their smooth shells and paddle-like flippers help them speed through the water as fast as 29 kph.

Ecology[edit]

Feeding[edit]

The flatback turtle eats a variety of organisms, such as seagrasses, marine invertebrates, including mollusks, jellyfish and shrimp, and fishes. It also consumes of soft corals, sea cucumbers and other soft-bodied creatures.[3]

Conservation[edit]

The species is considered vulnerable to extinction in Western Australia,[3] but the Red List of the IUCN regards it as data deficient and unable to be correctly assessed.[1]

The Australian flatbacks in the northwest of Kimberley face immediate threats from industrial development.[4]

References[edit]

  1. ^ a b Red List Standards & Petitions Subcommittee (1996). "Natator depressus". IUCN Red List of Threatened Species. Version 2.3. International Union for Conservation of Nature. Retrieved 14 May 2011. 
  2. ^ a b c Limpus, Colin (2007). A Biological Review of Australian Marine Turtles. 5. Flatback turtle Natator depressus (Garman). Queensland: The State of Queensland. Environmental Protection Agency. 
  3. ^ a b c d e f Burbidge, Andrew A (2004). Threatened animals of Western Australia. Department of Conservation and Land Management. pp. 110, 114. ISBN 0-7307-5549-5. 
  4. ^ Sea Turtle Restoration Project : Australia's Sea Turtles

External links[edit]