Late last year, 39 specially raised turtle hatchlings fitted with miniature sonar transmitters were deployed on a critical mission: to find out what was going on under the murky surface of the Mary River (Moonaboola) in southern Queensland. Their intelligence was intended to help solve the mystery surrounding the rapid decline of one of Australia’s most threatened reptile species.
Within days, years of work was gone in a flash. Two major floods surged through the river, one after the other. Expensive listening equipment was ripped up and destroyed by waters so powerful that trees were flung down the river like torpedoes. Months after the disasters, scientists and wildlife advocates are still struggling to understand the extent of the damage to fragile ecosystems and the endangered and vulnerable species they support. Their efforts were further complicated in May, when a third major inundation hit the river.
Marilyn Connell is doubtful whether any of the juvenile Mary River turtles and their high-tech backpacks will be found. “It’s a bit of a tragedy really,” says the co-ordinator of Tiaro Landcare, who has been fighting for 20 years to save the species from extinction. “We still need time for the river to go down further so that we can try to access and see if we can recover any more hydrophones, and see how many turtles have survived, if any.”
The Mary River turtle, Elusor macrurus, evolved 40 million years ago and is the only species of its genus. At maturity it is one of the biggest freshwater turtles in Australia, measuring more than 40 centimetres across the carapace, and it has an enormous tail. Affectionately known as a “bum-breather”, its ability to absorb oxygen through its cloaca allows it to stay underwater for days at a time. In 2018 the severely endangered species briefly gripped the public’s imagination as a “punk turtle” meme – complete with algae “mohawk” and a mocking grin – and inspired a fundraising concert and video featuring a turtle voiced by Cate Blanchett. But it’s still unclear what has been causing juveniles to disappear before they reach maturity. There are many suspects, including water and land degradation, predation by foxes and worsening droughts and floods. More data is needed to understand what is happening.
A dramatic strengthening of political will is also needed, as it emerged last week that one of the Coalition’s final acts in government had been to scrap recovery plans for 176 threatened species and habitats. The new Environment and Water minister, Tanya Plibersek, will face a long list of concerns, as conservationists and environmental scientists are also hoping for the prompt release of the five-yearly “Australia State of the Environment” report, which the Coalition was accused of sitting on ahead of the election, and a full response to the 38 recommendations in Graeme Samuel’s review of the Environment Protection and Biodiversity Conservation Act. A recovery plan for the Mary River has been gathering dust since 2014, Connell says.
Unlike the 2019-20 Black Summer bushfires, the impact of the historic floods on Australian wildlife has generated little publicity. This is partly because of the long delay before the worst impacts of starvation and disease will be apparent, but Connell also blames a lack of visibility for species that live below the surfaces of rivers and streams. The Mary River and its meandering tributaries are home to a large number of endangered and vulnerable species, including the ancient Queensland lungfish, a living fossil that has existed since the dinosaurs, and the Mary River cod. As the floods wrecked towns and cities, at the bottom of the bloated waterways, rocks and logs tumbled along at high velocity, turning the riverbed upside down and smashing delicate life to pieces. Plants, snails, sponges and any small creatures that didn’t make it into the safety of a shallow side-stream fast enough were swept up in the maelstrom.
And downstream at the river mouth, the floods brought further destruction. The sediment and debris scoured from the degraded banks of the Mary plumed like liquid mushroom clouds out into the Great Sandy Strait, blocking the light and sinking to the bottom. It smothered thousands of square kilometres of seagrass meadows that support one of Australia’s most important dugong populations.
A large-scale survey of seagrass, using boats and helicopters, has confirmed the worst: a massive loss of vegetation. Almost nothing remains in most of the previously mapped areas across Hervey Bay and the Great Sandy Strait. While a small amount of seagrass was detected at some sites, coverage was typically less than 1 per cent of the sea floor, according to Associate Professor Michael Rasheed from James Cook University’s TropWATER Centre.
To understand what could happen to the dugong population, scientists point to a similar event 30 years ago, when the area was hit by two floods and a cyclone in quick succession. Helene Marsh, emeritus professor at James Cook University and an authority on dugongs, said that in 1992 the population at Hervey Bay plummeted to about a 10th of its usual size, as many of the mammals moved out of the area in search of food. Many also died from starvation and calf counts decreased as mothers became too thin to reproduce or suckle their young. Ninety-nine carcasses were recovered, and that was likely just a fraction of the total loss, Marsh said.
“In 1992 the seagrass was lost very quickly, like has happened this time. But the carcasses mainly showed up six to eight months later, because it took a while for animals that have a lot of body fat to starve,” she said.
There’s hope for a quicker recovery in their food source than in 1992, however, as seagrass seed-stores under the sediment are believed to be relatively intact. A recovery may start to emerge during the peak growth season in September-October, meaning dugongs that migrated to greener pastures could soon start to return.
“One promising thing is those little bits of seagrass that we did find looked quite young and healthy in the rhizomes,” Rasheed said. “They looked like perhaps there have been recent germinations from seed … There’s good promise that we could see a bounce back in seagrass if conditions are favourable for their growth.”
Nevertheless, Marsh is concerned about shortages for the creatures scrounging for food along the wrecked coastline. And their survival could come under threat if climate change spurs more frequent extreme-weather events.
“Let’s imagine the seagrass comes back, the dugongs come back, and there’s serious floods again in three years or something like that, well, then it’s that frequency that can be very serious. Constant disruption to their breeding and to their mortality. And for very long-lived, slow-breeding animals, this is not good.”
Between November 2021 and April 2022, Queensland Parks and Wildlife Service rangers recorded 132 stranded marine animals including sea turtles and dugongs, compared with 47 strandings for the same period the year before. The numbers are “significantly greater” than the long-term average in the area, a spokesperson for the state’s Department of Environment and Science said, and the floods are a factor. “Rangers have also recently seen large, mature green turtles presenting with an ulcerative skin disease affecting the carapace and flipper.” The cause is still being investigated.
While the Mary River turtles have survived and recovered from major floods in the past, and some are believed to be up to 100 years old, their food supply and habitat will take years to fully recover from the latest setback. Marilyn Connell expects it will affect the turtle’s breeding patterns for at least two to three years, as they will struggle to eat enough protein to produce eggs. In the meantime, the turtles will continue their battle for survival against increasingly stacked odds. Once the flood damage has been properly assessed and funds secured, another batch of hatchlings will likely be raised and prepared to launch into the opaque waters to hear what the river is saying.
Hopefully when the time comes we will be more ready to listen.
This article was first published in the print edition of The Saturday Paper on June 11, 2022 as "River phoenix".
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