Turtles and tortoises date back 220 million years, making them older than crocodiles and snakes. The Mary River turtle has one of the most ancient lineages of Australian turtles, its closest living ancestor lived about 50 – 60 million years ago.The Mary River is a dynamic river system. Most of the flow occurs during the Southern Hemisphere’s summer and early autumn when river heights can vary significantly, while during the winter months, the flow is relatively stable.
The Mary River turtle primarily inhabits riffle zones and pools in the river. It mostly forages for food in these riffle zones, it needs exposed rocks and logs for basking, open, sandy sites along the riverbank for nesting and nocturnal resting areas. These areas must be safe from predators.
The Mary River turtle has two ways to breathe. When it surfaces, it uses its lungs. But within its tail is a deep cavity lined with gill-like structures that are used for extracting oxygen from the water. This allows the turtle to stay submerged for longer periods and has led to it being known as a ‘bum-breather”. One hatchling has been recorded remaining submerged for 2.5 days in optimal temperature and oxygen conditions.
The Mary River turtle has very long back legs. Long legs are necessary to dig nesting chambers deep enough (about 13 – 15cm) to avoid the extreme temperatures that occur on the surface of the ground. At 15cm, the temperatures are conducive to embryo development and the soil remains moist for longer, both essential for successful incubation during the hot, dry Australian summers. Climate change is increasing the heat and drought stress of summer.
Forty years ago, Mary River turtles were sold as penny turtles through the pet trade, hatching just in time for Christmas. It takes about twenty years for a Mary River turtle to reach breeding age. Cats, dogs, foxes are known to prey on female freshwater turtles as they lay eggs, including the Mary River Turtle. Monitor lizards (aka goannas) also love feasting on freshwater turtle eggs. Consequently, the population of this species was plummeting even before it was recognised and described as a distinct species.
The Mary River is the sole habitat for the Mary River cod (Maccullochella mariensis), a species of temperate perch native to the coastal section of the river system. The Mary River cod is one of Australia’s most endangered fish.
The Mary River is also the most important remaining habitat for the Queensland lungfish (Neoceratodus forsteri), one of six extant species of the ancient air-breathing lungfishes that flourished during the Devonian period about 413 – 365 million years ago, and which is the most evolutionarily distinct of all.
Ten years ago, the Australian government ruled against the Queensland government’s proposed Traveston Crossing dam, which would have exterminated the Mary River turtle and the Mary River cod, and it would have driven the Queensland lungfish even closer to extinction.
Queensland Conservation was one of the leading community organisations opposing this calamitous proposal which would also have flooded sufficient of Queensland’s deepest and most fertile agricultural landscapes to impact on the long term food security of Brisbane without providing water security for that city which had prompted the Traveston Crossing proposal in the first place.
Queensland’s Tiaro and District Landcare volunteers now monitor Mary River turtle nest sites. They place a protective cover over each nest site to prevent foxes, wild dogs and monitor lizards from digging up the eggs and eating them.
If summer storms fail to arrive – an increasing risk as our climate warms – the extended hot, dry conditions threaten the developing eggs, so volunteers water the nests to prevent the eggs from desiccating.
Australia’s most unique freshwater turtle is fortunate to have the Mary River catchment group looking after the health of the river system to give the endangered Mary River turtle a better chance of survival.