Other common names: Australian
Flatback, Flatback Seaturtle (Witherington, 2006)
The Flatback
Sea Turtle, Natator depressus, is a medium
sized sea turtle with an elliptical, flattened shell characterized
by upturned edges. Its olive-gray shell has a thin, waxy
surface that can easily be damaged. Its range is much more
restricted than other sea turtles, as it is found only
in the waters surrounding Australia. It is the only sea
turtle with no pelagic phase.
Female flatbacks weigh from 70 to 80 kg (155 to 175 lbs)
and their shell is about 85 to 95 cm (33 in to 37 in) in
length (Witherington, 2006). Males are generally a bit smaller.
Their bodies are olive-gray with a creamy white underside.
Flatbacks have a lower dome than other sea turtles, thus
giving them their name. The upturned edges of their shell
often collect sand when they flip sand backwards while concealing
their nests. The keratin which covers the scutes of this
turtle is so thin that blood can be drawn by running a fingernail
firmly across its shell.
Flatback sea turtles were once thought to be a variation
of Green
Sea Turtles, Chelonia mydas, and were originally
placed in the same genus. Like Green Sea Turtles, they have
one pair of long prefrontal scutes between their eyes, and
four pairs of lateral scutes on their shell. The tracks they
leave while nesting also resemble green sea turtle tracks.
These similarities notwithstanding, flatbacks are now recognized
as being very distinctive from Green Sea Turtles with their
own genus. Features that distinguish them from Green Sea
Turtles are their non-pelagic behavior and limited range,
their distinctive flattened shells, their larger head and
shorter flippers, and the smaller scales on their flippers.
Flatback sea turtles are endemic to Australia, with their
northern range extending to southern Papua New Guinea. They
inhabit the east and west coasts of Australia only as far
south as the warmest temperate areas. Their preferred habitat
is shallow, murky waters with muddy bottoms away from coral
reefs. All nesting sites are thought to be in Australia.
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| Picture of Australian flatback
sea turtle, Natator depressus,
heads back to ocean after nesting
in beach dunes, Curtis Island, Queensland,
Australia. |
Image
#: 004040 |
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Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Reptilia
Order: Testudines
Suborder: Cryptodera
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Flatbacks feed on soft-bodied invertebrates, such as sea
cucumbers, soft coral, squid and jellyfish. As sea cucumbers
are common in their preferred habitat, they may be considered
the fatback’s main food source.
Flatbacks exhibit some unique sea turtle characteristics.
They often bask in the sun at the ocean’s surface, providing
a perch for seabirds. They have also been found laying eggs
in daylight. Their shells generally do not become fouled
with barnacles, possibly as a consequence of natural chemicals
covering their waxy scutes.
Flatback sea turtles reach adulthood at about 20 years of
age, and females nest on the same beach where they were born.
They lay eggs once every one to four years during the Australian
summer, in November and December, and lay up to four clutches
in a season. There are an average of 54 eggs to a clutch,
a number which is half that of other sea turtles. The eggs,
however, are larger than those of other species, and the
hatchlings emerge larger than any sea turtle species except
the leatherback. It takes 50 to 55 days for hatchlings to
emerge.
Because flatback hatchlings are larger than other sea turtle
hatchlings, they have a better chance of surviving attacks
by crabs, gulls and fish when they leave the nest. They are
also strong swimmers, which allows them to fight ocean currents
and remain near the Australian shore where they spend most
of their lives.
Flatback sea turtles and turtle nesting sites are well protected
by the Australian government, but large numbers of these
turtles are picked up in shrimp trawlers in international
waters. Since 2000, shrimp trawlers have been required to
use TEDs (Turtle Excluder Devices), which should help reduce
flatback drownings. While aboriginal people consume some
turtles and their eggs, they are not considered a serious
threat to this species, as the numbers taken are low. Predators
of flatback turtle eggs include pigs, foxes, rats, dingos,
lizards, herons and crocodiles. Hatchlings are eaten by pelicans,
sea eagles, sharks and crocodiles.
The IUCN lists the flatback sea turtle as Data Deficient,
which means the organization lacks enough information to
detail the risk of extinction for this species. Because of
the flatback’s limited range, many scientists fear they are
most at risk if sudden changes occur to their habitat.
• Flatback Sea Turtle information assembled from published
and on-line sources by Kevin
Miller on Dec. 24, 2006 for Seapics.com.
Sources:
Perrine,
D. Sea Turtles of the World, Voyageur Press, 2003.
Ripple,
J. Sea Turtles, Voyageur Press, 1996.
Witherington,
B. Sea Turtles, Voyageur Press, 2006.
http://marinebio.org/species.asp?id=316 |
