Floods may ramp up fungus threat for frogs

Tracey Ferrier |

Jodi Rowley is working to understand what’s causing the deaths of many frogs across Australia.
Jodi Rowley is working to understand what’s causing the deaths of many frogs across Australia.

A biologist fears last year’s mysterious mass die-off of Australian frogs could be on the cards again this winter, amplified by the recent floods.

Jodi Rowley is still trying to work out why so many frogs were found sick, dying or dead across eastern Victoria, NSW and Queensland last winter.

She knows the skin-attacking amphibian chytrid fungus is at least involved, even if it’s not the full picture.

Most of the 350 frog carcasses collected and frozen for her last year by concerned citizens have since tested positive for the pathogen, which has caused frog extinctions worldwide including at least four in Australia.

That has Dr Rowley worried about the months ahead.

The recent floods have created the perfect conditions for the fungus to thrive through winter, when frogs’ immune systems are naturally suppressed by the cooler weather.

“We know that the amphibian chytrid fungus is at least involved in the die-off and weather conditions like this, where it hasn’t been super hot and has been very, very wet – it doesn’t bode well,” she says.

“The combination of the fungus-friendly conditions and the frogs’ immune systems slowing down means they might get sick.”

When the die-off began to reveal itself last July, Dr Rowley and her Australian Museum colleagues weren’t able to get into the field to investigate due to pandemic restrictions.

They only reason they’ve had any evidence to work with was because Australians didn’t mind storing little victims in their freezers until herpetologist and frog undertaker Tom Parkin could pick them up.

Things are much freer this year and researchers will be out monitoring frog health with a particular focus on NSW, which was heavily affected. They’ll also head into national parks to see what’s happening with threatened species.

Even so, Dr Rowley is hoping Australians will continue to help by reporting frog illness and deaths by emailing [email protected]

“The only way to help our frogs is if everyone’s involved. We hope very, very much that we’re not going to see dead and sick frogs turning up on people’s doorsteps again.”

Amphibian chytrid fungus is not a new threat in Australia and the pathogen is not always deadly. Some species seem to tolerate it well, and the fungus is often found in individuals that appear unaffected.

Jane Hall is a wildlife disease ecologist with the Australian Registry of Wildlife Health at the Taronga Conservation Society and is one of the detectives trying to unravel the die-off mystery.

She believes there’s something else going on besides the fungus.

“Free-ranging wildlife encounter pathogens all the time. Often they are able to fight those infection off but sometimes, if conditions are right, then things can go a little bit sideways and that’s when we get these unusual mortality events.”

Exposure to toxins, such as pesticides, is another avenue of inquiry but so far tests have not revealed anything that could explain the die off’s broad geographic range.

“Having so many that people notice is very unusual and that’s how we know that there is something awry going on out there,” Ms Hall says.

“There will be something that links a lot of these together and it’s just a matter of teasing things apart, sifting through the results, and trying to figure out the most reasonable story.”