The
flatback sea turtle (
Natator depressus) is a
sea turtleSea turtles are marine reptiles that inhabit all of the world's oceans except the Arctic.-Distribution:...
that is
endemicEndemism is the ecological state of being unique to a defined geographic location, such as an island, nation or other defined zone, or habitat type; organisms that are indigenous to a place are not endemic to it if they are also found elsewhere. For example, all species of lemur are endemic to the...
to the
continental shelfThe continental shelf is the extended perimeter of each continent and associated coastal plain. Much of the shelf was exposed during glacial periods, but is now submerged under relatively shallow seas and gulfs, and was similarly submerged during other interglacial periods. The continental margin,...
of
AustraliaAustralia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
. Flatback turtles belong to the
CheloniidaeCheloniidae is a family of turtles belonging to the sea turtle superfamily Chelonioidea.-Extant genera:*Genus Caretta**Loggerhead sea turtle *Genus Chelonia**Green sea turtle *Genus Eretmochelys...
, or sea turtle, superfamily and are the only species found in the genus
Natator.
Taxonomy and etymology
This species is within a
monotypicIn biology, a monotypic taxon is a taxonomic group with only one biological type. The term's usage differs slightly between botany and zoology. The term monotypic has a separate use in conservation biology, monotypic habitat, regarding species habitat conversion eliminating biodiversity and...
genus,
Natator, in the
CheloniidaeCheloniidae is a family of turtles belonging to the sea turtle superfamily Chelonioidea.-Extant genera:*Genus Caretta**Loggerhead sea turtle *Genus Chelonia**Green sea turtle *Genus Eretmochelys...
family; the name means "swimmer," in Latin.
Depressus, the species indicator (the second part of the scientific name) means "flat" in Latin. It refers to the flatness of the Flatback's shell. The
Bardi peopleThe Bardi people are the Indigenous Australians from the area north of Broome and parts of the Dampier Peninsular in the Kimberley region of Western Australia.Djarindjin, Lombadina and One Arm Point are three Bardi communities in the area....
called this animal
barwanjan, and it was known to the Wunambil as
madumal.
Range and habitat
Flatback turtles are usually found in bays, shallow, grassy waters,
coral reefCoral reefs are underwater structures made from calcium carbonate secreted by corals. Coral reefs are colonies of tiny living animals found in marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. The polyps...
s,
estuariesAn estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....
and
lagoonA lagoon is a body of shallow sea water or brackish water separated from the sea by some form of barrier. The EU's habitat directive defines lagoons as "expanses of shallow coastal salt water, of varying salinity or water volume, wholly or partially separated from the sea by sand banks or shingle,...
s on the northern coast of Australia and off the coast of
Papua New GuineaPapua New Guinea , officially the Independent State of Papua New Guinea, is a country in Oceania, occupying the eastern half of the island of New Guinea and numerous offshore islands...
.
The species may feed off
IndonesiaIndonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
and
Papua New GuineaPapua New Guinea , officially the Independent State of Papua New Guinea, is a country in Oceania, occupying the eastern half of the island of New Guinea and numerous offshore islands...
, but it nests only in
AustraliaAustralia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
. Nesting occurs across the top half of Australia, from
Exmouth-Further reading:* Western Australia. Ministry for Planning. Exmouth-Learmonth structure plan. Perth, W.A. : Western Australian Planning Commission...
in Western Australia to
Mon Repos Conservation ParkMon Repos Conservation Park is a turtle rookery located on Queensland's central coast, 14 km east of Bundaberg. Mon Repos hosts the largest concentration of nesting marine turtles on the eastern Australian mainland and supports the most significant nesting population of the endangered loggerhead...
in
QueenslandQueensland is a state of Australia, occupying the north-eastern section of the mainland continent. It is bordered by the Northern Territory, South Australia and New South Wales to the west, south-west and south respectively. To the east, Queensland is bordered by the Coral Sea and Pacific Ocean...
. The most significant breeding site is Crab Island in the western
Torres StraitThe Torres Strait is a body of water which lies between Australia and the Melanesian island of New Guinea. It is approximately wide at its narrowest extent. To the south is Cape York Peninsula, the northernmost continental extremity of the Australian state of Queensland...
. Breeding may also occur on the islands of the southern
Great Barrier ReefThe Great Barrier Reef is the world'slargest reef system composed of over 2,900 individual reefs and 900 islands stretching for over 2,600 kilometres over an area of approximately...
, and on mainland
beachA beach is a geological landform along the shoreline of an ocean, sea, lake or river. It usually consists of loose particles which are often composed of rock, such as sand, gravel, shingle, pebbles or cobblestones...
es and offshore islands north of
Gladstone- Education :Gladstone has several primary schools, three high schools, and one university campus, Central Queensland University. It is also home to CQIT Gladstone Campus.- Recreation :...
.
Anatomy
The
carapaceA carapace is a dorsal section of the exoskeleton or shell in a number of animal groups, including arthropods such as crustaceans and arachnids, as well as vertebrates such as turtles and tortoises. In turtles and tortoises, the underside is called the plastron.-Crustaceans:In crustaceans, the...
of the adult is on average 90 centimetres (35.4 in) long. It is low domed, the edge is upturned and has four pairs of
costalIn vertebrate anatomy, ribs are the long curved bones which form the rib cage. In most vertebrates, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the chest cavity. They serve to protect the lungs, heart, and other internal organs of the thorax...
scales—fewer than other marine turtles. The upper parts are an olive-grey, while it is more pale ventrally. A single pair of scales are located at the front of the head, which also distinguish this species.
Nesting
The Flatback turtle is unusual because it lays fewer but larger eggs than other
sea turtleSea turtles are marine reptiles that inhabit all of the world's oceans except the Arctic.-Distribution:...
species. Like other species, its females emerge onto the
beachA beach is a geological landform along the shoreline of an ocean, sea, lake or river. It usually consists of loose particles which are often composed of rock, such as sand, gravel, shingle, pebbles or cobblestones...
on which they hatched more than 30 years before and make their way up the beach to lay their eggs.
Male turtles never return to shore, since mating occurs at sea, taking around 1.5 hours. The female digs a pit using her front
flippersA flipper is a typically flat limb evolved for movement through water. Various creatures have evolved flippers, for example penguins , cetaceans A flipper is a typically flat limb evolved for movement through water. Various creatures have evolved flippers, for example penguins (also called...
to clear away the topmost layer of dry sand. She then uses her rear flippers to dig a small egg chamber. After laying a
clutchA clutch of eggs refers to all the eggs produced by birds or reptiles, often at a single time, particularly those laid in a nest.In birds, destruction of a clutch by predators, , results in double-clutching...
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 seasonThe nesting season is the time of year during which birds and some other animals, particularly some reptiles, build nests, lay eggs in them, and in most cases bring up their young. It is usually in the spring....
—totaling 1-4 nests. They nest only every 2–3 years. There are around 54 eggs in each clutch, and the rookeries are usually small.
These eggs are vulnerable to predation by
dingoThe Australian Dingo or Warrigal is a free-roaming wild dog unique to the continent of Australia, mainly found in the outback. Its original ancestors are thought to have arrived with humans from southeast Asia thousands of years ago, when dogs were still relatively undomesticated and closer to...
es, sand
goannaGoanna is the name used to refer to any number of Australian monitor lizards of the genus Varanus, as well as to certain species from Southeast Asia.There are around 30 species of goanna, 25 of which are found in Australia...
s (
Varanus gouldii) and an introduced pest species—the
foxThe red fox is the largest of the true foxes, as well as being the most geographically spread member of the Carnivora, being distributed across the entire northern hemisphere from the Arctic Circle to North Africa, Central America, and the steppes of Asia...
. 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 its range.
Hatching
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
birdBirds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s and
crabTrue crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
s. However, even the sea is not safe.
SharkSharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
s and
fishFish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
patrol shallow waters, waiting to prey upon hatchlings. Scientists estimate only 1 of 100 turtles live to become an adult. However, once these turtles become adults there are very few organisms that predate them. Its
survivorship curveA survivorship curve is a graph showing the number or proportion of individuals surviving at each age for a given species or group...
is known as Type III because hatchlings endure high mortality rates, while adults thrive.
Feeding
The Flatback turtle eats a variety of organisms such as
seagrassSeagrasses are flowering plants from one of four plant families , all in the order Alismatales , which grow in marine, fully saline environments.-Ecology:...
, marine invertebrates including mollusks,
jellyfishJellyfish are free-swimming members of the phylum Cnidaria. Medusa is another word for jellyfish, and refers to any free-swimming jellyfish stages in the phylum Cnidaria...
and
shrimpShrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...
and also
fishFish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
es. It also consumes of soft
coralCorals are marine animals in class Anthozoa of phylum Cnidaria typically living in compact colonies of many identical individual "polyps". The group includes the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.A coral "head" is a colony of...
,
sea cucumberSea cucumbers are echinoderms from the class Holothuroidea.They are marine animals with a leathery skin and an elongated body containing a single, branched gonad. Sea cucumbers are found on the sea floor worldwide. There are a number of holothurian species and genera, many of which are targeted...
s and other soft-bodied creatures.
Conservation
The species is considered vulnerable to extinction in
Western AustraliaWestern Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...
, but the Red list of the IUCN regards it as data deficient and unable to be correctly assessed.
The Australian flatbacks in the northwest of Kimberley face immediate threats from industrial development and need the world's attention.
External links