The surveys come after two significant flood events in early 2022, and scientists are concerned the seagrass loss could trigger an increase in dugong and green sea turtle strandings.

James Cook University TropWATER Centre is leading the monitoring of 2300km2 of seagrass meadows – one of the largest and most important areas of seagrass in eastern Australia – in partnership with the Department of Environment and Science (DES).

TropWATER Professor Michael Rasheed said there had been drastic reduction of seagrass when compared with previous extensive mapping.

“Our boat surveys show there’s almost no seagrass visible in the 2m to 17m depth range for much of the deeper meadows, and these sites have previously recorded extensive areas of seagrass,” he said.

“There were some areas of sub-tidal seagrass but these were confined to the deepest areas in the northern part of the bay.

“We also used helicopters to assess more than 1300 intertidal sites throughout the Great Sandy Straits and while some sites had seagrass the cover was typically less than one percent of the seafloor offering scant resources for dugong and turtle.”

Prof Rasheed said the last comprehensive mapping of the entire area was more than 20 years ago, and surveys now were critical to help understand what seagrass resource remains to support dugong and turtle feeding as well as assess the potential for recovery over the coming months.

“However, we are in the low season for seagrass growth and about to enter the recovery period for seagrasses, so we hope to return to these waters in September/October, the normal seasonal peak for seagrasses, to look at how much of the seagrass has recovered.

“The good news is that there is still some seagrass remaining and this can provide the source for recovery in the coming months if conditions are favourable.”

In 1991 the same region experienced back-to-back floods causing more than 1000 km2 of seagrass loss.

Sediment in the floodwaters is known to reduce light and smother seagrass meadows, potentially depleting the main food source for dugong and turtles in the area.

The following year saw the highest recorded mortality of dugong, including a 20 per cent decline in dugong calves.

Queensland Parks and Wildlife Service Senior Ranger Dan Clifton said rangers had seen an increase in marine strandings within the Great Sandy Marine Park over the past 12 months, with the recent floods contributing to the issue.

“Since July 2021 we have recorded more than 240 stranded marine turtles and 22 stranded dugongs in this area as a result of different factors including boat strike and poor health,” Senior Ranger Clifton said.

“These numbers are significantly greater than the long-term average in the area.

“We have also recently seen large, mature green turtles presenting with an ulcerative skin disease affecting the carapace and flippers. This is currently being investigated by leading authorities to determine causes so we can respond accordingly.

“The issues currently faced by marine wildlife in the Great Sandy Marine Park demonstrate the importance of ongoing research and surveys so that we can identify and respond to threats and how critical it is that we protect our precious ecosystems.”

Alongside the seagrass monitoring, TropWATER researcher and dugong expert Dr Chris Cleguer is trialling the use of drones to monitor the body condition of the dugongs in the area.

“Extensive seagrass loss can have dramatic impact on dugongs and sea turtles. Dugongs may stop breeding, some will move and some will die,” he said.

“Assessing changes in the body condition of dugongs can help us monitor the health of the animals following the flooding events in the Hervey Bay region.

“Drones are increasingly used as a low-cost, non-invasive approach to obtain morphometric measurements of marine mammal body size. It’s been done for whales and manatees, and now we’re starting to collect data to do the same for dugongs.”

The large-scale monitoring also includes the collection of sediment samples from the seafloor to better characterise the fine sediment that surrounds the seagrass meadows and the source of these sediments.

TropWATER researchers and rangers from Queensland Parks and Wildlife Services will today finish the 14-day assessment of deep-water and shallow-water habitats across Hervey Bay and the Great Sandy Strait, using aerial and boat surveys.

Final results from the survey will be available in the coming months.

Water samples taken from the lower Burdekin River by a James Cook University-led team of researchers and analysed for environmental DNA (eDNA) confirmed the presence of the Irwin’s turtle at many sites along the river, which has not been formally recorded in the area for more than 25 years.

The turtle, first discovered in the Burdekin catchment by the late Steve Irwin and his father Bob in the early 1990s, is among a number of freshwater species which uses its cloaca (equivalent to its bum) to breathe while underwater, thus able to stay submerged underwater for longer.

Centre for Tropical Water and Aquatic Ecosystem Research (TropWATER) Director Professor Damien Burrows and Research Officers Dr Cecilia Villacorta-Rath and Jason Schaffer teamed up with a State Government agency, a consultancy firm and Traditional Owners to survey the Burdekin, Bowen and Broken rivers for the elusive turtle.

“Until this rediscovery, we didn’t have any formal records to prove that the Irwin’s turtle was still living in the lower Burdekin River, and that river has changed a lot since the construction of the Burdekin Falls Dam,” Prof Burrows said.

“It’s reassuring to know they are still living there.”

The survey findings, co-authored by the JCU team and the Department of Regional Development, Manufacturing and Water’s Thomas Espinoza and Bernie Cockayne, were published this week in BMC Ecology and Evolution journal following two years of research comprising three separate survey periods over 2020 and 2021.

Funded by the National Environmental Science Program, 37 sites were investigated across the three river catchments, some of which involved the use of helicopters to get in and out.

Prof Burrows said eDNA technology was vital to the rediscovery of the turtle in the lower Burdekin River and had the potential to revolutionise how researchers tracked and located both aquatic and land-based animals.

“Previously, it’s been very difficult to sample for the Irwin’s turtle because they only live in places where there are crocodiles, or in upland tributaries which are very hard to access,” he said.

“They also don’t come into traps easily and the water they are living in in the Burdekin isn’t clear so you can’t put in underwater cameras to see them.

“But now with eDNA, all we had to do was take a water sample and analyse for their DNA.”

With the new process, DNA itself can be extracted and amplified directly from environmental samples such as soil, sediment and water without having to catch the target organism.

Dr Villacorta-Rath said while the eDNA samples taken by the team could not determine the age of the turtles found in the lower Burdekin and other rivers surveyed, the results were potentially game-changing.

“With the original site samples that we took in 2020, we had the beginnings of the story, but we needed to investigate further and go closer to the dam and see where was the uppermost distribution of the species,” she said.

“We don’t know anything about the demographics of this population, but the fact we have found their eDNA now, despite the dam being built in the 1980s, could point to adult Irwin’s turtles being able to survive in these more turbid water conditions.

“This rediscovery has now challenged the previous hypothesis that the species could not survive in these conditions.”

The information gathered will also help the State Government as it evaluates a proposal to build a dam in the upper reaches of Broken River at Urannah Station