Adult leatherback turtle. Photo: Col Limpus, EHP.
Common name: leatherback turtle, leathery turtle
Scientific name: Dermochelys coriacea
Conservation status: This species is listed as Endangered in Queensland (Nature Conservation Act 1992) and Vulnerable nationally (Environment Protection and Biodiversity Conservation Act 1999). It is ranked as a critical priority under the Department of Environment and Heritage Protection Back on Track species prioritisation framework.
Leatherback turtle hatchling. Photo: Col Limpus, EHP.
The leatherback turtle is the largest marine turtle, growing up to a length of 3m. The carapace (upper part of the shell covering the back of the turtle) of the adult is covered by a thick, smooth, leathery skin and is strongly pointed at the rear. It is usually a uniform dark brown or black above, sometimes with paler marbling on the back or with longitudinal rows of small, fine dots and usually with pale white, pink or cream spots and blotches on the sides. The throat and lower sides of neck are white, pale cream or pink mottled and blotched with dark brown or black and whitish or pinkish-white below. A series of seven prominent longitudinal ridges occur on the carapace (including the outer lateral pair) and four ridges along the plastron. The front flippers are large and lack claws. Breeding males and females are similar in appearance, but males have a longer tail.
The hatchlings are black with five distinct ridges on the shell. The average carapace length of a hatchling is 5.8cm and each hatchling weighs about 46g.
Habitat and distribution
The leatherback turtle has the widest distribution of any marine turtle, occurring in tropical, temperate and sub-polar waters from the North Sea and Gulf of Alaska in the Northern Hemisphere, to Chile and New Zealand in the Southern Hemisphere. Leatherback turtles occur in tropical and temperate waters of Australia. Large numbers of leatherback turtles feed off the southern Queensland and New South Wales coasts and off Western Australia's coast, south of Geraldton, but they are less abundant in the tropical waters of northern Australia. The best place in Queensland to see leatherback turtles is Wreck Rock, north of Bundaberg.
Most sightings are along the more heavily populated eastern seaboard of Australia where large adults are found year round in larger bays, estuaries and rivers. The frequency of sightings suggests that the species actively seeks out temperate feeding grounds, rather than simply straying to the south.
Life history and behaviour
Most leatherback turtles found in Australian waters breed in neighbouring countries, particularly in Java and along the northern coast of Irian Jaya, Papua New Guinea and the Solomon Islands. This species is thought to live at least 30 years or more.
No large rookeries have been recorded in Australia. Scattered nesting occurs along the southern Queensland coast from Bundaberg to Roundhill Head and along the coast of Arnhem Land from Coburg Peninsula to Maningrida, including Croker Island. Breeding in Australia occurs mostly during December and January. Females lay on average about 83 large eggs and 47 small yolkless eggs per clutch. Turtle eggs require temperatures in the range of 23-33oC throughout incubation. As with other species of marine turtles, the sex of the hatchlings is determined by nest temperature. Males result from cooler temperatures and females from warmer temperatures.
Leatherback turtles are carnivorous and feed mainly in the open ocean on jellyfish and other soft-bodied invertebrates. Many casual observers have seen these turtles feeding on unidentified jellyfishes (apparently Catostylus mosaicus) and on bluebottles or Portuguese Man'o'War Physalia utriculus along the coast of New South Wales. These turtles have a number of adaptations which allow them to venture into cold water to forage for food. These include a large adult body size, a thick layer of fatty tissue and some ability to regulate their temperature to prevent excess cooling. Foraging occurs throughout the water column, from the surface layer to depths of several hundred metres. Deep diving in leatherback turtles is assisted by other adaptations that conserve oxygen, such as the ability to slow their heart rate and to direct blood flow away from non-vital body organs while diving.
Although little is known about the population status of leatherback turtles in Queensland, it appears to be declining based on a decline in nesting at traditional sites. The main threats to leatherback turtles are:
- Entanglement and drowning in commercial fishing gear such as drift nets, gill nets and longlines. Pelagic longline bycatch has been implicated as a proximate cause for the decline in Pacific leatherback turtle populations.
- Ingestion of marine debris
- Boat strike which can kill marine turtles especially in estuaries, sandy straits and shallow inshore areas. Damage to the carapace may lead to death or disruption to feeding and breeding.
- Pollution and changes to important turtle habitats, especially coral reefs, seagrass beds, mangrove forests and nesting beaches.
A national recovery plan for marine turtles in Australia exists and is currently under review. This plan identifies the management actions necessary to recover marine turtle species in Australia, including:
- Implementing management actions to address key threats affecting successful turtle nesting such as marine debris, light pollution, invasive species, bycatch, boat strike, and vehicle damage to nesting sites.
- Identifying habitats critical to the survival of marine turtles.
- Establishing monitoring programs for marine turtle populations including monitoring of nesting beaches and marine turtle strandings.
- Working with Traditional Owner Groups to improve the sustainability of turtle harvesting.
- Raising awareness of marine turtles and involving the community in their protection.
The department’s marine turtle conservation program includes, research, monitoring (including turtle tagging and satellite tracking), studies of nesting and feeding sites and threat abatement actions.
A community awareness program about the effect of light sources around nesting sites is being implemented. The program promotes the use of alternative lighting and protection of nesting sites to local councils through the ‘Cut the glow to help turtles go’ campaign.
The department is currently delivering turtle biology and conservation training to Indigenous Groups. Indigenous rangers in a number of communities are now collecting turtle monitoring data to help with the conservation of marine turtles.
The Queensland Government responds to stranded marine animals as a high priority, and this work involves active partnerships with volunteer and rehabilitation centres. Information is collected on each stranding event and an annual report on marine strandings is available.
What can you do to help this species
- Report sick, injured, dead and/or tagged marine turtles to the RSPCA Qld on 1300 ANIMAL (1300 264 625). Queensland Government officer in the relevant region will be contacted with your information and will determine the appropriate response.
- Remember that rubbish you throw away can find its way to the sea, where turtles can mistake things such as plastic bags for jellyfish. Plastic swallowed by mistake can cause blockages of the stomach and intestines of marine animals such as turtles.
- Follow the regulations relating to "go slow areas for turtles and dugong" including operating vessels off the plane and not undertaking motorised water sports. Many turtles are struck by propellers of speeding boats and this can cause injury and death.
- Be careful not to damage seagrass by careless anchoring or operating of a vessel in shallow water where boat wash or propeller damage can occur.
- Take care when fishing, don’t leave behind discarded fishing lines and use non-stainless steel hooks.
- Check crab pots regularly. Set your pots to avoid loose rope floating about in the water and ensure your pot entrances are not large enough to trap a turtle. Familiarise yourself with the guidelines on how to make a new crab pot, or learn how to correctly modify an existing one.
Environment Australia and Marine Turtle Recovery Team 2003. Recovery plan for marine turtles in Australia. Department of the Environment and Heritage, Canberra.
Department of the Environment and Heritage 2005. Protected marine species identification guide. Department of the Environment and Heritage, Canberra.
Department of Sustainability, Environment, Water, Population and Communities. 2013. Dermochelys coriacea Leatherback turtle: in the Species Profile and Threats Database.
A biological review of Australian marine turtles: 6. Leatherback Turtle Dermochelys coriacea (see availability( http://www.ehp.qld.gov.au/wildlife/watching/turtles/publications.html#document_availability ))