Scientists have reintroduced green and golden bell frogs to the Australian Capital Territory for the first time since the species became locally extinct four decades ago.
The first cohort of 25 frogs was released on Tuesday morning, a milestone for conservation of the animals, whose numbers have been devastated by the chytrid fungal disease that has wiped out 90 amphibian species in 50 years.
Associate Prof Simon Clulow of the University of Canberra, one of the researchers who led the project, said it felt “quite incredible and really significant to return [the species] back to this region for the first time in almost 50 years”.
“As far as we’re aware, it went extinct [in the ACT] by about 1981,” he said.
The 25 frogs, released at Mawson Ponds, are about 14 months old and have been immunised against chytridiomycosis, a disease caused by two fungal species.
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Tuesday’s reintroduction was the first of 15 releases at wetland sites around Canberra, which will total about 375 frogs.
Each frog is microchipped and even named, with help from volunteers involved in the project. “We’ve had some creative ones,” said Dr Jarrod Sopniewski, a postdoctoral research fellow at the University of Canberra. “We have a James Pond and Dua Leaper.”
To give the amphibians the best chance of survival, the team has dug 60 “frog spas” – four at each wetland site – and also installed 180 “frog saunas”.
The frog saunas and spas would “provide little pockets of disease refuge in the wetlands for the offspring that are eventually produced, because of course the offspring aren’t immunised”, Clulow said.
Frog saunas – in this case, perspex pyramids covering a three-level tower of black-painted bricks – are hoped to provide refuges for the frogs at temperatures lethal to the chytrid fungi.
“The pathogen itself is quite susceptible to elevated temperature – it doesn’t like temperatures over 25C; 27 or 28C is quite lethal to it,” Clulow said. “A lot of Australian frogs … prefer those temperatures – the green and golden bell frog likes to be about 30C.”
Sopniewski said trial saunas had been installed for over a year in Canberra. “Even when the temperatures are barely reaching 10C here, we’re still [passively] getting into the high 20s on a sunny day.”
The green and golden bell frog grows up to 8.5cm in body length and spends most of its time close to ground level. Formerly common along Australia’s east coast, it is considered endangered in New South Wales.
Despite the ravages of chytrid, green and golden bell frogs have been observed to survive in isolated pockets along the east coast, often in areas with slightly higher water salinity, Clulow said.
Building on that discovery, the scientists have installed satellite ponds around large wetlands – what they call “frog spas” – in which the water is slightly more salty. A salt concentration of about three parts per thousand “is more than enough to negatively affect the chytrid, but is absolutely fine for frogs to use”, Sopniewski said.
The goal is to have 200 frogs at each of the 15 sites. “One female can have up to 8,000 eggs, so their population growth should start really rapidly if our interventions against chytrid are helping those initial founders survive and reproduce,” Sopniewski said.
“It’s almost like letting your children go out into the world themselves,” he added. “A bit daunting, but overwhelmingly exciting.”
