Overview

Brief Summary

Biology

The breeding season of the flatback turtle varies depending on the location. For example, in southern Queensland, the flatback turtle begins mating in October and nesting occurs between October and January with a peak in December, while in northern Australia the flatback turtle nests between June and August. Each nesting season, the female lays between two and three clutches, 15 days apart (3). The female hauls herself out of the ocean, usually at night (2), and finds a suitable spot on the beach; most nests are constructed on top of dunes or as high as possible on seaward slopes (7). A hole is then excavated using alternate sharp jerks of the hind-flippers to throw sand away. Into the hole, measuring around 22 centimetres across and 30 centimetres deep, the female lays an average of 50 to 60 eggs within ten minutes. The hole is then filled with sand, and further sand is piled on top to form a mound. The female then leaves for the sea (2). Around six weeks later, the incubating eggs hatch and the hatchlings emerge from the nest chamber (2). The temperature at which the eggs have been incubating is critical; below 29°C and the clutch will be male, above 29°C and females are produced (3). The hatchlings instinctively head for the sea, fanning out as they run to the water rather than following each other (2). Unlike other sea turtles, flatback turtles do not spend any part of their life in the deep ocean, remaining instead in the surface waters of the continental shelf (3). Flatback turtles spend much of their day floating on the sea surface, basking in the sun, and it is not unusual to see birds resting on the turtle's back (2). While little is known about the diet of the flatback turtle (3), it is thought to be a predominantly carnivorous species (7), feeding on organisms that are found on the sea floor. This includes cuttlefish, hydroids, soft corals, crinoids, molluscs and jellyfish (3).
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Description

One of just seven species of sea turtle, the flatback turtle is distinguished by its restricted distribution and its very flat carapace, or upper shell (2). The fleshy carapace (3), which is composed of thin, bony scales (2), has an upwards turned rim, particularly towards the rear (2). The carapace may be grey, pale grey-green or olive in colour (3). The head and soft flippers are also olive-grey (2), while the underside is pale yellow (6). Flatback turtle hatchlings are olive-green with scales edged in black (3).
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Distribution

Continent: Asia Australia
Distribution: E Indian Ocean, SW/WC Pacific Ocean, coastal waters of the continental shelf off N/NE Australia  
Type locality: northern Australia
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Range

Having one of the most restricted ranges of any marine turtle (1), the flatback turtle is found only in the tropical waters of northern Australia, Papua New Guinea and Irian Jaya, and nests only in Australia (3).
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Ecology

Habitat

Habitat and Ecology

Habitat and Ecology
Terrestrial nest sites

Systems
  • Terrestrial
  • Marine
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Depth range based on 7797 specimens in 1 taxon.
Water temperature and chemistry ranges based on 5252 samples.

Environmental ranges
  Depth range (m): 0 - 12.8
  Temperature range (°C): 22.732 - 29.430
  Nitrate (umol/L): 0.090 - 0.757
  Salinity (PPS): 34.002 - 35.710
  Oxygen (ml/l): 4.377 - 4.954
  Phosphate (umol/l): 0.096 - 0.345
  Silicate (umol/l): 0.940 - 5.857

Graphical representation

Depth range (m): 0 - 12.8

Temperature range (°C): 22.732 - 29.430

Nitrate (umol/L): 0.090 - 0.757

Salinity (PPS): 34.002 - 35.710

Oxygen (ml/l): 4.377 - 4.954

Phosphate (umol/l): 0.096 - 0.345

Silicate (umol/l): 0.940 - 5.857
 
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Depth range based on 7797 specimens in 1 taxon.
Water temperature and chemistry ranges based on 5252 samples.

Environmental ranges
  Depth range (m): 0 - 12.8
  Temperature range (°C): 22.732 - 29.430
  Nitrate (umol/L): 0.090 - 0.757
  Salinity (PPS): 34.002 - 35.710
  Oxygen (ml/l): 4.377 - 4.954
  Phosphate (umol/l): 0.096 - 0.345
  Silicate (umol/l): 0.940 - 5.857

Graphical representation

Depth range (m): 0 - 12.8

Temperature range (°C): 22.732 - 29.430

Nitrate (umol/L): 0.090 - 0.757

Salinity (PPS): 34.002 - 35.710

Oxygen (ml/l): 4.377 - 4.954

Phosphate (umol/l): 0.096 - 0.345

Silicate (umol/l): 0.940 - 5.857
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

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The flatback turtle inhabits coastal waters over soft-bottomed sea beds (3). Like other marine turtles, its lays its eggs on sandy beaches, either on the Australian mainland or on offshore islands (2).
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Molecular Biology and Genetics

Molecular Biology

Barcode data: Natator depressa

The following is a representative barcode sequence, the centroid of all available sequences for this species.


There are 2 barcode sequences available from BOLD and GenBank.

Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.

See the BOLD taxonomy browser for more complete information about this specimen and other sequences.

TCCACTAACCACAAAGACATTGGCACCCTATATCTAATTTTCGGGGCCTGAGCAGGAATAGTTGGTACAGCGCTC---AGCCTATTAATCCGCGCAGAACTAAGCCAACCAGGAACTCTTCTAGGAGAT---GACCAAATCTACAATGTCATCGTTACAGCTCATGCTTTTATCATAATCTTCTTTATAGTTATACCAATCATAATTGGCGGCTTCGGAAACTGACTTGTTCCCCTAATA---ATTGGCGCACCAGATATAGCATTCCCACGTATAAACAATATAAGCTTTTGACTCCTGCCCCCCTCACTACTACTACTTCTAGCATCATCAGGAATTGAAGCAGGTGCGGGCACAGGCTGAACAGTATACCCCCCATTAGCCGGAAACCTAGCCCACGCCGGTGCTTCTGTAGACCTA---ACTATCTTCTCCCTCCACCTAGCCGGTGTATCCTCAATCTTAGGGGCCATCAACTTCATTACCACAGCAATCAACATAAAATCTCCCGCCATATCACAATACCAAACACCATTATTTGTATGATCCGTACTAATCACAGCTGTCCTATTATTACTTTCATTACCAGTACTAGCTGCA---GGCATTACCATACTACTTACAGACCGAAACCTAAATACAACCTTCTTCGATCCTTCAGGGGGAGGAGATCCAATCCTATACCAACACTTATTCTGATTCTTCGGTCACCCGGAAGTATACATCTTAATCCTCCCAGGATTTGGCATAATCTCCCACATTGTTACCTATTACGCTGGTAAAAAA---GAACCATTTGGCTATATAGGAATAGTTTGAGCAATAATATCC
-- end --

Download FASTA File

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Statistics of barcoding coverage: Natator depressa

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 3
Specimens with Barcodes: 12
Species With Barcodes: 1
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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
DD
Data Deficient

Red List Criteria

Version
2.3

Year Assessed
1996
  • Needs updating

Assessor/s
Red List Standards & Petitions Subcommittee

Reviewer/s

Contributor/s

Justification
This revised assessment is a ruling made by the Red List Standards and Petitions Subcommittee (S&PS) after considering all the material provided by the Marine Turtle Red List Authority in support of their 1996 listing and that provided by the petitioner against the listing. The ruling was the conclusion to an appeals process which was initiated following a petition against the 1996 listing of this species (for further details see the IUCN SSC web site).

This ruling is based on the information that was available in 1995, when the listing was made, and on the 1994 Red List Criteria, on which the listing was based. Thus, the S&PS did not consider information that became available after 1995, and the changes to the IUCN criteria that took effect in 2001. The rationale provided by the S&PS for the ruling is as follows:


The petitioner claimed that future reduction due to pollutants, pathogens, and introduced taxa (criterion A2e), due to reduction in area of occupancy (A2c), or due to exploitation by indigenous people (A2d) was not evident. The Marine Turtle Specialist Group (MTSG) justification referred to reported losses due to introduced foxes, feral dogs and pigs, reports of green turtle fibropapillomatosis in flatbacks, evidence of threats to habitat quality, and reports of accidental mortality by prawn trawling and coastal gill nets.

Although it is clear that there are reasons why some declines may be expected in the future, there is no quantitative evidence to suggest 20% decline in the next 3 generations. There is always going to be substantial uncertainty in using criterion A2 (future reduction) with long-lived species. This difficulty is further compounded here by lack of any specific quantitative information.

Thus, the S&PS believes that the information provided does not justify the use of criterion A2. However, considering that (as the MTSG states) this is one of the most poorly understood marine turtle species, and that the qualitative information provided suggests declines are possible, future reduction of 20% or more cannot be ruled out. For this reason, the S&PS decided that the appropriate listing for this species is Data Deficient (DD).

The justification by the MTSG also indicated that the flatback turtle has one of the most restricted geographic ranges of any marine turtle species. However, it did not provide data on the extent of occurrence or area of occupancy, and the listing was based on future reduction (criterion A2) not on restricted range (criterion B). Thus, the S&PS encourages the MTSG to assess this species in the future under Criterion B as well as Criterion A.

History
  • 1996
    Vulnerable (VU)
  • 1994
    Vulnerable (V)
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Status

Classified as Data Deficient (DD) on the IUCN Red List 2007 (1), and listed on Appendix I of CITES (4) and Appendix II of CMS (5).
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Threats

There is a large range of threats which may be affecting populations of the flatback turtle. Flatback turtle eggs and hatchlings are threatened by tourism and recreation disturbing nesting beaches, the effects of light pollution, and harvesting by indigenous people. They are also vulnerable to predation by feral pigs, particularly on the Cape York Peninsula (8). Adult flatback turtles are harvested for their meat, and face additional threats such as entanglement in lost or discarded fishing nets, ingestion of marine debris, being struck by boats, and being caught as by-catch. Flatback turtles comprise the majority of the turtle by-catch (59 per cent) in trawls in the Northern Prawn Fishery (8). However, as one of the most poorly understood marine turtle species, there is insufficient information to determine to what extent the flatback turtle may be affected by these threats, and thus it has been classified as Data Deficient on the IUCN Red List (1).
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Management

Conservation

The flatback turtle is classified as Vulnerable in Australia under the Environment Protection and Biodiversity Conservation Act 1999 (8), and there are a number of measures in place to protect the marine turtles of Australia. Much of the flatback turtle's habitat is protected. For example, 75 per cent of its nesting habitat is protected in Queensland and it occurs on the Great Barrier Reef, one of the world's most extensive protected areas. In addition, in an effort to reduce by-catch, Turtle Excluder Devices were made compulsory in the Northern Prawn Fishery in 2000, resulting in turtle mortalities being reduced to just five per cent of what they were in 1989-90 (8). A Recovery Plan for Marine Turtles in Australia was developed in 2003 and outlined a number of further measures necessary to reduce detrimental impacts on flatback turtles and other marine turtles of Australia. These included restricting boat speeds in areas of important marine turtle habitat, developing management plans for nesting beaches and a code of conduct for tour operators on beaches, as well as creating plans to ensure traditional indigenous harvests are undertaken in a sustainable manner (8).
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Wikipedia

Flatback sea turtle

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]

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 flatbacks in the area 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 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
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