Green turtle hatchling. Photo: EHP
Common name: green turtle
Scientific name: Chelonia mydas
Conservation status: this species is listed as Vulnerable in Queensland (Nature Conservation Act 1992) and nationally (Environment Protection and Biodiversity Conservation Act 1999). It is ranked as a critical priority under the Department of Environment and Heritage Protection (EHP) Back on Track species prioritisation framework.
Description: Green turtles are olive-green above, usually variegated with brown, reddish-brown and black. They are whitish or cream below. Hatchlings are shiny black above and white below, with white margins around the carapace (shell) and flippers. There are four costal scales on each side of the carapace (refer to the protected marine species identification guide for the green turtle). A mature green turtle can grow to a carapace length of more than one metre and weigh on average 150 kg. The green turtle is named for the greenish colour of its fat, created by its diet of seagrass.
Habitat and distribution
Green turtles occur in seaweed-rich coral reefs and coastal seagrass pastures in tropical and subtropical areas of Australia. In Australia there are seven separate genetic management units for the green turtle, and three of these occur in Queensland. The entire Great Barrier Reef area is an important feeding area for turtles which nest locally, as well as for those which nest in other regions and countries.
Life history and behaviour
Green turtles that nest on the Australian coast migrate from numerous feeding grounds dispersed through Indonesia, Papua New Guinea, Solomon Islands, Vanuatu, Fiji and New Caledonia as well as from Queensland, Northern Territory and western Australia. They make long migrations between feeding grounds and nesting beaches. Migrations recorded from nesting beaches in the southern Great Barrier Reef have exceeded 2600 km but the average migration is about 400 km.
In Queensland, the southern Great Barrier Reef has 13 major rookeries including North West, Wreck, Hoskyn and Heron Islands. Nesting occurs between late November and January in southern Queensland. The northern Great Barrier Reef has five major rookeries including Raine Island and nearby cays, and Bramble Cay in the Torres Strait. The south-eastern Gulf of Carpentaria has three major rookeries at Bountiful, Pisonia and Rocky Islands.
It takes a female green turtle 30-40 years to reach maturity. In general, female green turtles lay about 115 round, ping-pong ball sized, parchment-shelled eggs, per clutch. Each nesting season she returns to the beach to nest an average of five times at fortnightly intervals.
Diet: Adult green turtles feed mostly on seaweeds, seagrasses (e.g. Halophila ovata) and mangrove fruits, although immature green turtles are carnivorous.
Green turtle recovery
Green turtles destined for sale at the Fish Board in 1934. Photo: Queensland State Library 10651P
The upward trend in the green turtle nesting population at Heron island (EHP)
Adult female green turtle returning to the water after nesting. Photo: Col Limpus, EHP
Commercial harvesting of green turtles in southern Queensland was closed down in 1950 in response to scientific community and Government concerns over the depleted population.
The upward trend in the southern Great Barrier Reef green turtle population, as indicated by nesting numbers at the principal index beach of Heron Island, shows a three times increase in the annual nesting population after approximately one turtle generation since closure of commercial harvesting in 1950. This is one of the few green turtle populations of the world that is showing a strong increase in response to conservation measures.
This is a conservation success story worthy of celebration! It is the result of strong species protection, strong habitat protection (National Parks and Marine Parks), and fisheries managed to reduce bycatch. Conservation effort for the green turtle now means that:
- Greater than 90% of all marine turtle nesting in eastern Australia south of Torres Strait occurs in Queensland National Parks or Conservation Parks.
- 97% of the east coast of Queensland from Cape York to the New South Wales border is within Marine Parks, providing habitat protection of turtle foraging habitat and migratory routes.
At Mon Repos Conservation Park and Heron Island National Park, Queensland Government staff protect turtle nests during the nesting season, carry out research and monitoring, and raise public awareness.
In order to reduce the impacts of trawler fishermen on all marine turtles, the Queensland Government initiated a rebate scheme until 2010 to help fishermen start using more effective bycatch reduction devices on their nets. These include turtle exclusion devices (TEDs), which are a grid of bars at the neck of a trawl net that catches turtles and allows them to escape through an opening at the top or bottom of the net.
Although the green turtle population is recovering, it is still threatened by unsustainable hunting, boat strike, and drowning in crab pots.
- Unsustainable hunting: Hunting of green turtles removes individuals and the harvest of eggs affects recruitment. There is also considerable concern over the unsustainable numbers of green turtles being harvested in neighbouring countries and within northern Australian waters.
- Boat strike: Boat strike can damage or kill green turtles, especially in estuaries, sandy straits and shallow inshore areas, with damage increasing with boat speed. Damage to the shell may lead to death or disruption to feeding or breeding regime.
- Crab pots: Green turtles can drown after becoming entangled in commercial and recreational crab pots and their float lines. Trap types that cause an impact include round crab pots, collapsible pots, and spanner crab traps.
- Encourage indigenous communities to foster the sustainable use of turtle populations;
- Encourage boat users to ‘Go Slow for those Below’ and slow their boat speed in estuaries, sandy straights and shallow inshore areas; and
- Support the existing work by the Queensland Government who is working with the fishing industry to develop turtle-friendly crab-pots.
How can you help this species
To help this species you can:
- Decrease your boat speed in estuaries, sandy straights and shallow inshore areas, and remember to ‘Go Slow for those Below’; and
- Remember that rubbish you throw away can find its way to the sea. Plastic debris that is swallowed by mistake can cause blockages of the stomach and intestines of marine animals such as turtles.
Environment Australia and Marine Turtle Recovery Team 2003. Recovery plan for marine turtles in Australia. Department of the Environment and Heritage, Canberra.
Spotila, JR 2004. Sea turtles. The John Hopkins University Press, London.