Bulk release of southern corroboree frog eggs boosts wild species survival hopes in Kosciuszko National Park

A milestone has been reached in the NSW Snowy Mountains with the largest release of eggs from the critically endangered southern corroboree frog.

The tiny yellow and black patterned frog found in Kosciuszko National Park is considered to be one of Australia's most iconic amphibians, but there is thought to be only about 50 remaining in the wild.

More than 3,407 eggs have been recently released into the park, in a bid to bring the species back from the brink of extinction.

"It's a really significant milestone," Zoos Victoria threatened species biologist Deon Gilbert said.

"This is the most amount of eggs we've been able to produce since the recovery program started back in 2001."

The southern corroboree frog, which measures up to 3 centimetres in length, or around the size of a 20-cent coin, has been under threat since the late 1980s.

It was listed as endangered in 1996 and critically endangered since 2009.

Its key threat is a fatal disease caused by the amphibian chytrid fungus, but it's also impacted by drought, bushfires, climate change and feral species.

Zoos Victoria's Melbourne Zoo and Healesville Sanctuary, along with Taronga Zoo, have taken part in the official breeding program to bolster the population over the past two decades.

They have previously produced about 2,000 eggs annually for release, so the latest release of 3,407 is about a 70 per cent increase.

'Wild-fit' frogs

The latest batch of eggs was meant to go out all at once in early May, but a dry autumn meant some eggs had to wait until more rain fell and conditions improved.

Amphibian specialists from the zoos and the NSW government returned to remote areas of the park on Friday to release the remaining 800 eggs.

"There's now been enough rain and the pools are full of water," said Dr David Hunter, senior threatened species officer at the NSW Department of Climate Change, Energy, the Environment and Water.

"The challenge for us now is to continue to establish more effective techniques to keep them alive more broadly in Kosciuszko."

Some of the eggs have been released into protected "disease-free" enclosures, but others went directly into the wild in former known breeding sites and ideal wet habitats.

This was done in the hope that the frogs could develop a greater immunity to the chytrid fungus.

"We want wild-fit frogs to survive and breed, and one of the best ways to do that is to get them back to the wild as soon as possible," Mr Gilbert said.

"We look at both strategies so we're not putting all our eggs in one basket."

Back from the brink

The latest release of eggs follows in the footsteps of yearly excursions to Kosciuszko to boost the species' population.

Captive-bred adult frogs have been released into disease-free enclosures in the park since 2013, but those areas were destroyed in the 2019-2020 Black Summer bushfires.

The enclosures have since been rebuilt to better withstand natural disasters, and 100 captive-bred frogs were released into the park in 2022 while a further 100 were released in 2023.

The continued efforts to reintroduce frogs, tadpoles and eggs over the years have been hailed as invaluable to the survival of the species.

'It's not over-exaggerating that without that work, the species would already be extinct," Mr Gilbert said.

The ongoing success of the captive-breeding program and improved knowledge about the frog is giving more confidence to those involved.

"Time is on our side, we have lots of options," Mr Gilbert said.