For the second consecutive winter, frogs across Australia are dropping dead in large numbers due to reasons yet unidentified, scientists have warned as they called for further research to unravel the causes and impacts of the die-off.
“Last winter, thousands of dead and dying frogs were found across Australia. In the last few weeks, as it’s cooled, we’ve started getting scarily similar reports,” reptile conservation biologist Jodi Rowley from the University of New South Wales in Sydney tweeted on Monday.
To help understand the scale and cause of these deaths, researchers have asked people living in the continent to send any reports they have of sick or dead frogs to the Australian Museum.
Scientists, including Dr Rowley and Karrie Rose from the University of Sydney, say they have already started receiving emails this year reporting dwindling numbers of some frogs and the deaths of others.
While sick, old, or injured frogs are likely to die as their immune system slows down in winter, researchers say they began to worry last year as such reports increased in late June and July.
Such a crash in frog populations could have “very real consequences” with the potential to impact entire ecosystems, they said.
Amid Covid-19-induced lockdowns, since scientists were unable to venture out to investigate the frog deaths themselves, they sought help from local communities.
They reportedly aligned the public with local veterinary clinics to examine the frogs for care and diagnostic sample collection.
Scientists wrote in The Conversation that a “remarkable 1,600 people” found sick or dead frogs across Australia.
They said that each of these reports often described dozens of dead frogs spanning over 40 species, with the total mortality count extending in the thousands. Threatened species such as the green and golden bell frog (Litoria aurea) and the giant barred frog (Mixophyes iteratus) were among those that died last year.
While a majority of the reported dead frogs belonged to the green tree frog species, scientists speculate this could be because this species tends to hang around houses and is spotted more.
There are “many possible suspects” that could be causing these die-offs, scientists say, adding that amphibian chytrid fungus is “certainly involved”.
The fungus, implicated in the mass deaths of frogs as well as other amphibians, spread across the world in the last 120-150 years from Asia via newly established trade and transportation links, and was likely most amplified during the Korean war in the early 1950s.
Studies have shown that it kills frogs, newts, salamanders, and other amphibians by attacking their skin, which they use to breathe.
It may have already led to the extinction or near-extinction of over 200 amphibian species with warmer temperatures caused by climate change likely favouring its spread to new areas.
A 2019 study, published in the journal Science, said the fungus had caused the decline of over 500 amphibian species across five continents — the Americas, Europe, Africa and Australia — between 1965 and 2015, making it the largest ever die-off attributable to a single disease.
However, researchers are unsure if the fungus is acting alone in the current frog die-offs in Australia.
“We’ve been testing for parasitic, bacterial, viral, and fungal pathogens. These tests include looking for pathogens known to kill frogs, and also looking for possible novel pathogens, which is by far the harder task,” scientists said.
They said the likely role of toxins is also being assessed.
