Australian Marine Turtles

Australia is home to six of the world’s seven marine turtle species: Green, Hawksbill, Leatherback, Loggerhead, Olive Ridley, and Flatback.

AusTurtle works primarily in the Northern Territory, where the Timor Sea and Beagle Gulf support all six species. These waters are rich, shallow, and productive — but not ideal for swimming thanks to crocodiles, stingers, and the occasional tiger shark. Watching from a boat or beach is strongly recommended.

AusTurtle Fast Facts

SpeciesFlatbackOlive Ridley

Scientific nameNatator depressusLepidochelys olivacea

Adult size80–100 kg35–50 kg

AppearanceGrey–olive carapace, upturned edgesOlive-brown, heart-shaped shell

DietJellyfish, sea cucumbers, soft-bodied invertebratesCrabs, molluscs, fish, jellyfish

Lifespan~50 years~50 years

AusTurtle cuteness rating1010

Flatback Turtle — Australia’s Own

The Flatback Turtle (Natator depressus)** is the only sea turtle found exclusively in Australian waters. Feeding grounds extend into Indonesia and PNG, but all known nesting beaches occur only in Australia — across Queensland, the NT, and Western Australia.

Flatbacks are also the least studied sea turtle species in the world, which makes every data point collected on Ngulbitjik valuable.

A brief history of “discovering” the Flatback

Before the 1880s, Flatbacks were mistaken for oddly shaped Green Turtles. Even into the 20th century they were considered a subspecies. It wasn’t until 1988 that researchers confirmed Flatbacks are genetically distinct and more closely related to Hawksbills and Loggerheads.

Appearance

Australia is known for literal species names — Brown Snake, Redback Spider, Black Cockatoo — so it’s fitting that the Flatback is named for its broad, low-profile carapace. Key features:

Grey to olive-green shell
Smooth texture with upturned edges
Adult size 80–95 cm, up to 100 kg

Nesting and reproduction

Nest every 2 years
Lay 2–3 clutches per season
~50 eggs per clutch — the lowest of any marine turtle
Eggs weigh 70–80 g (billiard-ball sized)
Incubation 50–60 days
Hatchlings: ~6 cm, ~43 g — the largest hatchlings relative to adult size of any sea turtle

Flatback hatchlings can have blue or green eyes. Early research suggests cooler nests may produce blue-eyed hatchlings, warmer nests green — but the jury is still out. AusTurtle volunteers have strong opinions on this, and none of them agree.

Where they nest

Flatbacks nest across northern Australia, including:

Barrow Island
Eighty Mile Beach
Cape Dommett
Mudabullangana Beach
Ngulbitjik (Bare Sand Island) — AusTurtle’s primary monitoring site

Bare Sand Island is a small/medium rookery. (Insert your actual annual nesting estimate here.)

Life in the water

There are no underwater photos of Flatbacks from our NT sites — because everything in the water here is trying to eat something. This is also why in-water behaviour is poorly understood. Satellite tracking is the safest way to study them, unless you can find a volunteer with a death wish.

Olive Ridley Turtle

Identifying Turtle Tracks on Bare Sand Island

Flatback and Olive Ridley tracks are easy to tell apart once you know what to look for.

Flatback

Track width: 90–100 cm
Breaststroke pattern — both front flippers move together
Deep, wide body pit

Olive Ridley

Track width: 70–80 cm
Alternating flipper marks
Narrower, more compact body pit

Field guides and guidelines

Marine Turtle Watching Community Guidelines, 11th October 2016, Department of Tourism and Culture. Northern Territory Government.

Marine wildlife of WA's north-west; Identification guide, March 2018, Department of Biodiversity, Conservation and Attractions. Western Aurstalian Government.

Marine turtles of the Kimberley Coast, October 2018, Department of Biodiversity, Conservation and Attractions. Western Australian Government.

Queensland Marine Turtle Field Guide, 2016, Queensland Parks and Wildlife Service. Nest to Ocean Turtle Protection Progaram. Australian and Queensland Governments.

Plans and Stategies

Recovery Plan for Marine Turtles in Australia, 2017, Department of the Environment and Energy. Commonwealth of Australia.

Queensland Marine Turtle Conservation Stategy, May 2018, Conservation & Biodiversity Operations Branch Department of Environment and Science. Queensland Government.

Reef 2050 Long-Term Sustainability Plan, July 2018, Department of the Environment and Energy. Commonwealth of Australia.

Sea Turtle resources

Quail Island Group;The Defence Force is cleaning up the Quail Island Group of unexploded bombs from its 30 years as a military training ground. 2011. Laetitia Lemke. Guinea, ABC News

Munitions Solutions; Quail Island Air Weapons Range Unexploded Ordnance (UXO) Hazard Reduction Project Newsletters. G-tek Pty Ltd.

Blood Chemistry of Nesting Flatback Turtles (Natator depressus): Baseline Results Prior to Offshore Oil and Gas Development. Authors: Michael L. Guinea, Nirmala W. Nath, Dean J. Wright & Andrew M. Raith

The Distribution and Status of Marine Turtle Nesting in the Northern Territory. Authors: Ray Chatto & Bryan Baker (2008)

Diet and Feeding Biology of Adult Olive Ridley (Lepidochelys olivacea) and Loggerhead (Caretta caretta) Sea Turtles in Fog Bay, Northern Territory, Australia. Authors: Shaun P. Conway & Michael L. Guinea

Lunar Phase and Tidal Influence on Peak Timing of Nesting Flatback Sea Turtles (Natator depressus), Northern Territory, Australia. Author: Sarah Drescher (2018)

Behavioral Responses of Sea Turtles, Saltwater Crocodiles, and Crested Terns to Drone Disturbance. Authors: Elizabeth Bevan, Scott Whiting, Tony Tucker, Mick Guinea, Andrew Raith &Ryan Douglas

A Biological Review of Australian Marine Turtles. 1. Logger Turtle Caretta caretta (Linnaeus).

Author: Colin J. Limpus (2008)

A Biological Review of Australian Marine Turtles. 2. Green Turtle Chelonia mydas (Linnaeus).

Author: Colin J. Limpus (2008)

A Biological Review of Australian Marine Turtles. 3. Hawksbill Turtle Eretmochelys imbricata (Linnaeus).

Author: Colin J. Limpus (2009)

A Biological Review of Australian Marine Turtles. 4. Olive Ridley Turtles Lepidochelys olivaea (Eschscholtz).

Author: Colin J. Limpus (2008)

A Biological Review of Australian Marine Turtles. 5. Flatback Turtle Natator depressus (Garman).

Author: Colin J. Limpus (2007)

A Biological Review of Australian Marine Turtles. 6. Leatherback Turtle Dermochelys coriacea (Vandelli).

Author: Colin J. Limpus (2009)

Tonic Immobility: An Ethical, Easy and Safe Means of Sea Turtle Restraint. Author: Michael L. Guinea.

Scientific Journals
A Comparison of Hatchling Locomotor Performance and Scute Pattern Variation between Two Rookeries of the Flatback Turtle (Natator depressus). Authors: Elizabeth L. Sim, David T. Booth, Colin J. Limpus, and Michael L. Guinea (2014)

The Impact of Extended Preovipositional Arrest on Embryonic Development and Hatchling Fitness in the Flatback Sea Turtle. Authors: Chloe C. Rings, Anthony R. Rafferty, Michael L. Guinea & Richard D. Reina (2014)

Measuring behavioral responses of sea turtles, saltwater crocodiles, and crested terns to drone disturbance to define ethical operating thresholds. Authors: Elizabeth Bevan, Scott Whiting, Tony Tucker, Michael Guinea, Andrew Raith & Ryan Douglas (2018)

Brochures
Sea Turtles of the Northern Territory. AusTurtle Inc. 2006.

Posters
Charles Darwin University Sea Turtle Rehabilitation Centre.

Conference and Workshop Proceedings
Marine Turtle Conservation and Management in Northern Australia. Proceedings of a Workshop held at the Northern Territory University Darwin, 3–4 June 1997.

Proceedings of the Third Australian Marine Turtle Symposium held at Territory Wildlife Park, Berry Springs. Darwin 22 - 24 August 2016.

Maps
Cox Peninsula and Bynoe Harbour - Use and Access Map. Northern Land Council. March 2018.

2072 Grose Island. Reproduced by Australian Army Topo Svy Coy AIF March 1944.

Kenbi Open Area Declaration Map. Northern Land Council. September 2016.