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Home › Sea Life Facts › Marine Species › Vertebrates › Turtles › Flatback Turtle

Facts about Australian Flatback Sea Turtle

[Sea Turtle Phylum: Chordata] [Class: Reptilia] [Order: Testudines] [Superfamily: Chelonioidea]

Flatback turtles have the smallest geographical range of all marine turtles. Despite being listed as vulnerable more than ten years ago (1994), they remain as the least studied with limited factual data available.

This guide contains essential information about the flatback sea turtle (Natator depressus), such as where they still exist, what they eat, and how they reproduce.

Flatback Sea Turtle Habitat and Distribution

Generally, the only place to find flatback turtles is the continental shelf and coastal waters of northern Australia, southern Indonesia, and PNG (Papua New Guinea).

They are most abundant along the Australian coastline, especially their nesting sites in Western Australia, Queensland, and Northern Territory.

Unlike the other sea turtle species, Natator depressus avoids migratory behaviour and tends to stay in shallow water (less than 60 metres).

They distance themselves from vibrant coral reefs, preferring the sandy bottom habitats of shallow bays, sheltered lagoons, and estuaries.

Pro Tip: They don't undertake the long oceanic voyages that are common in other species of sea turtle. Instead, the Australian flatback sea turtle (Natator depressus) spends most of the day time floating and swimming at the surface of tropical and subtropical oceans.

Characteristics of Flatback Sea Turtles

The most distinctive feature of the flatback turtle is its flattened shell, (called a carapace in the anatomy of a sea turtle). The oval shaped shell is also quite smooth and the edges are slightly upturned.

Even though the upper part has pale grey and olive green colouring, the underside (called a plastron) tends to be more of a cream or off-white colour.

They have a large head and the flippers (used for swimming and building nests) are also large with a single claw on each forelimb. Whereas, the hawksbill sea turtle (Eretmochelys imbricata) has two claws on each of the front flippers.

But here's the kicker:

The dorsal section of the carapace in flatback turtles is made of soft keratin. Thus, unlike other sea turtle types, it offers less protection against their main predators in the wild (e.g. sharks and grouper fish).

Flatback Turtle Size and Weight

After reaching full maturity, adult flatback turtles can grow up to ninety (90) centimetres long (35 inches) and weigh around ninety (90) kilograms (198 pounds).

Fun Fact: The leatherback sea turtle (Dermochelys coriacea) is a lot bigger (up to 3 metres long) and even heavier (up to 500 kilograms).

What Do Flatback Turtles Eat?

Not having any teeth means marine turtles need to use their beak-like mouth to grab their favourite food, usually seaweed, algae, sea anemones (Actiniaria), and jellyfishes (cnidarians).

Even though some species focus on certain types of prey, and the diet tends to change as some get older, most of the omnivorous feeders are also known to eat soft-bodied invertebrates, including mollusks, sea cucumbers, and shrimps.

How Do Sea Turtles Reproduce?

When baby sea turtles reach maturity, from the age of ten, they reproduce through a process that starts off in the ocean but will end on a sandy beach.

Mating in the Ocean

By and large, turtles mate in a shallow coastal area sometime between spring and summer. Their mating process actually occurs in water, so the male will use its claws and tail to grasp the female.

However, because the females are able to store sperm from more than one male, they can use it to fertilise their eggs over several nesting events.

Nesting on a Natal Beach

The nesting behaviour of Natator depressus only takes place in northern Australia - on exposed beaches with large sand dunes. In November and December, females return to the exact same beach where they previously hatched to lay their eggs.

During the cover of darkness, she will crawl onto the sand and use her front flippers to dig a large egg chamber. In fact, the eggs of the female Australian flatback sea turtle are the biggest among the species and can be up to five (5) centimetres (2 inches) in diameter.

After she lays her eggs (up to 50), the clutch starts to hatch after several weeks of incubation (between 48 and 66 days) depending on the air temperature. Females can nest multiple times per season and it typically occurs every two to three years.

Hatching and Survival Rates

Despite emerging under the cover of darkness, and guided only by the moonlight, the hatchlings scurry their way toward the relative safety of the ocean.

Threats and Predators

A variety of terrestrial and aquatic threats, especially their natural predators (requiem sharks), means only a small number of hatchlings will actually survive and get a chance to expand the population.

Terrestrial Threats

In Australia, saltwater crocodiles prey on female flatback turtles when they are nesting on the beach. In addition, a clutch of hatchlings will need to avoid lizards, sea birds, dingoes, feral pigs, and red foxes.

Aquatic Threats

After reaching the shallow coastal waters of the ocean, baby turtles will be preyed upon by crabs, large predatory fish, and sharks.

Moreso, bycatch in fishing gear and industrial development continues to cause habitat destruction and irreversible damage to the nesting habitats of the most vulnerable sea turtles, almost to the point of complete extinction.

In fact, according to figures released by the 'Sea Turtle Conservancy', the current population estimate for nesting female sea turtles is less than 21,000.

Interesting Fact: The Australian flatback sea turtle is the only marine turtle that does not undergo the "oceanic pelagic phase of development" (also known as the lost years) in early life.

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