Rare or insufficiently known in Commonwealth territories (including Ashmore Reef, Australian Antarctic Territory, Christmas Island, Cocos Islands, Heard Island, McDonald Islands, Jervis Bay Territory and Norfolk Island). Common elsewhere..
Murray-Darling drainage, traverses four states and the Australian Capital Territory. Murray River turtles are found near headwaters at many locations west of the Great Dividing Range. Throughout its known distribution, from the Balonne, which runs into the Condamine before connecting to the Darling River, and in many other reaches running north to meet the Murray, these turtles display morphological variations. A polytypic species or species complex with distinctive populations also in Cooper Creek and Fraser Island. E. macquarii has been recorded in the Condamine-Balonne system
E. macquarii occurs primarily in rivers and waterbodies associated with rivers such as backwaters, oxbows, anabranchs and deep, permanent waterholes on the floodplains. This species appears to avoid shallow water. In one study it was not recorded from water less than 2 m deep. Its abundance is positively correlated with water depth, transparency, persistence and flow rate and negatively correlated with distance from the river,thus it prefers large, deep, clear, flowing, stable waterbodies in the Murray. Along the Murray River, there are countless lagoons and lakes with E. macquarii populations present. Some of these waterbodies are under continuous pressure (from a combination of man’s demand, little annual rainfall and extended droughts) and rely on rare floodwaters for any relief.
Meathrel et al., (2002) concluded habitat and dietary overlaps existed between C. longicollis, C. expansa and E. macquarii, suggesting strong competition for resources in large, permanent billabongs. All species preferred the more complex habitats in which to forage. During times of flood all turtles appeared to become opportunistic and consumed any food items available.
Turtles are slow growing and typically do not reach sexual maturity until about 15 years of age. Courtship and mating in captivity is known to occur from March to April.
Nesting occurs between mid- and late spring to early summer (late October – mid December). Females generally lay two or three clutches of eggs in a season, each clutch consisting of about 10 – 15 eggs, and taking six weeks to four months to hatch. Chessman (1978) considers that this species has the potential to lay 84 eggs in a season. Incubation period at Patho (Victoria) was recorded at 78 days. Incubation period appears to increase with decreasing temperatures. Thompson showed that temperatures did not influence the ratio of males to females and recorded incubation period of 48 days at 30°C.
Rainfall appears to be a critical determinant of nesting behaviour for E. macquarii . Rain may soften the ground and make nest excavation easier and thus faster, minimising the time that turtles spend on land and are exposed to predators. The species is said to nest in soils ranging from light sand to heavy clay, but ‘more frequently’ in lighter soils. Nest sites are usually in the open and from 2 – 40 m from the water. The same areas seem to be used for nesting by the population year after year. Nests are flask shaped and approximately 150 – 200 mm deep. The female, on completing her laying, makes an earthen plug to cover her nest.
E. macquarii eat both plants and animals (omnivore). Plant matter includes green algae, blue-green algae, diatoms, fungi and macrophtye shoots and leaves. Animal food consists mainly of invertebrates (e.g. crustaceans, molluscs) and also fish. Diet changes with size. Small turtles tend to eat more microorganisms and the substrate on which they grow.
Approved recovery plan for the Bellinger River Emydura (Emydura macquarii), which is a sub-species of the Emydura macquarii, lists as a potential threat reduced stream flow through extraction of water.
Predation is a major factor driving nest site selection for E. macquarii. Females prefer to nest in areas where offspring survival is greatest (i.e. not too close to shore due to flooding, not too far from shore due to increased predation during traverse across land), but when the risk of direct predation (on the female) is increased, they trade off minimising nest predation with survival by locating their nests closer to shore. Females consistently nest 10 – 15 m closer to shore in high-risk areas. The Murray population of E. macquarii contains a large number of old individuals. Juvenile recruitment is low due to predation.
Little annual rainfall, regular droughts (many extended), and chemical run-off from pastoral demand have changed much of the turtle's habitat.
^ Chessman, BC 1978, Ecological studies of freshwater turtles in southwestern Australia, Department of Zoology, Monash University.
^abc Chessman, BC 1988, 'Habitat preferences of freshwater turtles in the Murray valley, Vic and NSW', Australian Wildlife Research, vol. 15, pp. 485-491, CSIRO.
^ Georges, A 1993, 'Setting conservation priorities for Australian freshwater turtles', in D Lunney & D Ayers (eds), Herpetology in Australia: a diverse discipline, Surrey Beatty and Sons, Sydney, pp. 49-58.
^ Georges, A, White, M & Guarino, F 2003, 'Turtle populations and the impacts of fishing', Dryland River Refugia, vol. Newsletter 2, pp. 10-11, CRC for Freshwater Ecology, Canberra.