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How Canberra's turtles could help solve the carp problem

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Flaviemys purvisi

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By Finbar O'Mallon
20 December 2018

A predator-proof sanctuary in the middle of Gungahlin may house the solution to Canberra's carp clean-up problem: the eastern long-neck turtle.

Canberra's recent spell of wet weather has been prime time for the turtles, with softer soil making it easier to make nests and lay eggs as they migrate around the capital, including near Yerrabi Pond.

While the eastern long-neck turtle isn't endangered, University of Sydney associate professor in ecology Ricky Spencer warned their population was in decline nationally and they formed an important part of the ecosystem.

"They're the major vacuum cleaners of the river," Dr Spencer said.

He and a group of researchers are working with the CSIRO to see how effectively the turtles can eat up carp carcasses.

"If the carp herpes virus is released they will be the major scavengers that help with the clean-up," he said.

"There's no way that manually going around collecting dead carp throughout [NSW] and the ACT is going to be quite feasible in the time frame if the water quality gets terrible."

He said the next best scavengers to deal with dead carp were yabbies and then bacteria, but neither were anywhere near as efficient as the eastern long-neck turtle.

Dr Spencer is part of a group of ecologists and volunteers mapping the locations of the turtles inside the sanctuary, counting their numbers and helping protect their nests.

The population inside Mulligans Flat is booming thanks to the lack of predators, and it is hoped the sanctuary's turtles can be used to restock populations across NSW and the ACT.

At last count, the number of turtles inside Mulligans Flat was 600, Dr Spencer said.

Inside the sanctuary at Mulligans Flat on Friday, Woodland and Wetlands Trust Indigenous project officer Kristi Lee drove inside the electrified fence line looking for turtles.

The fence protects the turtles from foxes, feral cats and fast cars, but it also presents a problem.

"It's sort of a barrier to turtle migration," Ms Lee said.

The turtles follow migratory paths as they seek to lay eggs and forage around Canberra, but once they reach the fence they are unable to get past it and simply sit there.

Ms Lee said this was fine during the wet weather, but when it got sunny and hot the turtles could die of heatstroke.

A group of volunteers help patrol the fence line and help put the turtles back inside or outside the fence.

Ms Lee said it was important for the turtles to be able to follow their migratory instincts, but they faced risks outside the fence.

She said the long-neck turtle did have its own defence mechanism - it released a foul scent that was enough to make humans gag, but did not deter foxes.

"A fox might go, 'Wow, I want to eat you even more'," Ms Lee said.

The stench has earned the reptiles the common name of the 'stinker turtle', extra appropriate considering the perpetual grin the turtle wears - and has also bombed out Ms Lee's ute as she collects the reptiles from the fence line.

But thanks to the lack of predators inside the sanctuary, its native Australian species are thriving. Barely a minute after driving inside the electrified zone on Friday, Ms Lee stopped her ute to look at a shingleback lizard.

The jet-black variant of the species is only found in the ACT, and the one Ms Lee found was lazily crossing the dirt road.

"We have heaps of them in here. It's a breeding ground," she said.

"They're actually pretty cute because they mate with the same breeding pair for life."

Minutes later, she stopped her ute again after spotting an echidna by one of the dams which house the turtles.

"We have about 51 [echidnas] in here,"
she said, before noticing the one she had spotted hadn't been tagged.

"It looks like we've got 52,"
she said.
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