Containers holding more than 1,600 of endangered species’ eggs placed in remote areas of Mt Kosciuszko national park

A few days before the United Nations released a report warning that 1 million species, including 40% of all amphibians, could become extinct within decades, staff from Melbourne zoo were nursing chilled containers of frogs’ eggs to be taken to remote areas of sphagnum bog in the Mt Kosciuszko national park.

The containers held 1,673 fertilised eggs of the critically endangered southern corroboree frog, a species near the top of Australia’s extinction watchlist.

The eggs were packed into sphagnum moss for transport. Half were placed in one of 22 special disease-free areas that had been cleared of chytrid fungus, which is responsible for wiping out much of the wild population. The other half were placed in protected tubs in the wild, out of which the tadpoles will be able to climb once the eggs metamorphose.

That will not happen until spring. The tadpoles, which come out of their eggs as soon as they are released into the water, will spend the cold winter months nestled into the moss beneath a layer of snow and ice.

Facebook Twitter Pinterest Melbourne zoo has released a record 1,673 eggs of the critically endangered southern corroboree frog into Mt Kosciusko national park. Photograph: Melbourne Zoo.

It has been a record breeding season for the zoo, and the largest release of eggs since the program began in 2001. In collaboration with Sydney’s Taronga zoo and Healesville sanctuary about 3,000 southern corroboree frogs have been released this year.

Melbourne zoo has a breeding population of about 50 male frogs and 70 females, the oldest of which was captured as a tadpole in Kosciusko in 1999.

For the past several weeks of the breeding season, carers at the zoo have been gathering the clear eggs and chilling them to slow down their development so they can be released together.

“We use the sophisticated equipment of a wine chiller to keep them at a temperature of 8C,” the amphibian supervisor Damian Goodall says. “It’s a lot easier to transport them as eggs than as tadpoles.”

Tadpoles, he says, need to be “carried in bags, like fish” which is not conducive to either bumpy 4WD travel or being dropped via helicopter.

The release into the water mimics the natural process of water rising in the bogs at the end of summer, Goodall says, so the eggs often begin to hatch as soon as they are released.

Conservationists who monitor the site in spring say they have heard the calls of male corroboree frogs in areas where the tadpoles had been released, and which had been bare of wild frogs for years.

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“If we weren’t doing any of these releases, pretty much this species would be extinct, because a lot of the more crowded sites where there used to be huge communities now don’t have any males calling,” Goodall says.

He says the wild population of the southern corroboree frog, the closely related northern corroboree frog and the Baw Baw frog plummeted following bushfires about 15 years ago that burned out their habitat. All three critically endangered species were then crowded out of their traditional habitat by the smooth toadlet, an abundant native species that carries the deadly chytrid fungus.

The three frog species are on a list of 21 priority native species for Zoos Victoria, 16 of which are subject to a captive breeding program. All but four are Victorian natives; the others are priority national species such as the Tasmanian devil and Lord Howe Island phasmid.

Dr Marissa Parrott, a reproductive biologist, says Zoos Victoria has made a commitment that no Victorian terrestrial vertebrates will go extinct on its watch. “The UN report is terrifying but it’s not going to change what we are doing because we are already there,” Parrott says. “We already know how bad the situation is and we are already fighting extinction for these species that are on the brink.”