Turtle preservation plan for Bibra Lake

City of Cockburn backed research by Murdoch University PhD student Anthony Santoro over the past 18 months has revealed the unsustainably high death rate of the lake’s south-western snake-necked turtles (Chelodina colliei).

“The rate of adult turtle mortality and nest predation witnessed is extremely unsustainable and if it continues, the risk of local population extinction will drastically increase,” Mr Santoro said.

“But the good news is that the City of Cockburn is working on several fronts to halt the turtle’s dangerous decline in numbers.

“Several nesting refuges and fresh sand will be installed on the lake’s western side, the feral animal control program has been ramped up and a campaign to educate drivers to slow down on roads near wetlands during the September-February turtle nesting season will start soon.”

Several nesting refuges installed on the lake’s western fringe will help the threatened reptiles which are being snapped up by two fox families caught on the researcher’s covert wildlife cameras.

In the last year, Mr Santoro located 135 nests at Bibra Lake targeted by foxes and birds, and it was likely these nests represented a majority of the turtle’s reproductive potential.

He said another common cause of turtle deaths at the lake was vehicle strike, with 15 turtles killed on Progress Drive in a single night last October.

“I also found 25 dead adult turtles at Bibra Lake during the 2018 nesting season. These turtles and those killed on Progress Drive were all mature females, likely to have been on nesting movements,” Mr Santoro said.

City of Cockburn Environment Manager Chris Beaton said Mr Santoro’s research was vital and timely to safeguard the future of the lake’s treasured turtle population.

“We run annual feral animal control programs at our conservation reserves, including Bibra Lake, targeting foxes, rabbits and feral cats.

“We completed a fox control program in April and May and will run a second round in the lead-up to turtle nesting season in August. We will continue to run programs just prior to nesting season in those wetland reserves known to have turtles,” Mr Beaton said.

“We’ve installed a number of turtle nest refuges at Bibra Lake this year. They are designed to provide a safe environment away from predators where females can lay their eggs which will be protected until hatching time.   “We will also position Variable Message Boards on Progress Drive and Hope Road during the nesting season to encourage drivers to slow down. Long term, we will investigate a fauna underpass to go under Progress Drive.

“We will also provide more funds for GPS trackers for the turtles so we can monitor their movements and behaviours to help us locate and protect their nests.”

Mr Beaton said the City would continue to support Mr Santoro’s PhD research including application of glow in the dark powder to the hatchlings this year, to track their journey from nest to wetland.

“This will increase our knowledge on how long it takes hatchlings to get from nests to the wetland, what habitats they travel through, and how many successfully make the journey,” Mr Beaton said.

“Mr Santoro is also helping us develop a citizen science program so the local community can help monitor the turtles and hopefully increase their numbers. Watch this space.”   Mr Santoro said the level of turtle mortality happening at Bibra Lake was likely to be happening at other Perth wetlands.

“During my honours research at Bibra Lake, I caught about 80 turtles, half of which were female. During my current PhD research, I caught 220 turtles, but only 40 of these were females,” he said.

“This shift from equal sex ratios to heavily male dominated, suggests that female mortality is starting to affect the population.”

Studies show that turtles and tortoises are in trouble globally with nearly 60 per cent of species threatened by climate change, predation, habitat reduction and modification, pollution and disease.

For his PhD research, Mr Santoro is also studying Chelodina Wetlands at Murdoch University, and North Lake Reserve, managed by the Department of Biodiversity, Conservation and Attractions.

His research shows the reptiles move around a lot at dawn and dusk in fringing lakeside vegetation but appear to be relatively sedentary during the day.