1-4-1-saving-the-critically-endangered-spotted-tree-frog-following-the-2019-20-bushfires-community-factsheet_v4

SAVING OUR SPECIES
The spotted tree frog is found 
in freshwater streams in 
northern-eastern Victoria and 
southern New South Wales. This 
Critically Endangered species 
has disappeared from 50% of 
its known former sites, is rare 
at all these remaining sites, and 
is expected to become extinct 
unless we intervene.
Non-native fish and chytrid fungus 
are the two key threats to its 
persistence. 
• Non-native fish (brown trout, 
rainbow trout, European carp 
and redfin perch) eat spotted 
tree frog tadpoles. The native 
fish species (blackfish) rarely 
eat the tadpoles. 
• Chytrid fungus causes a 
disease called chytridiomycosis 
that kills adult frogs, and frogs 
at earlier life stages. 
Bushfires can have devastating 
impacts on wildlife populations. 
Spotted tree frogs often use 
vegetation on the banks of 
mountain streams as shelter 
sites. If the frogs are sheltering in 
vegetation during bushfires, they 
can be killed when the vegetation 
burns, but they may also be killed 
by radiant heat if using other 
shallow shelter sites. Post-fire rain 
can wash ash, debris and sediment 
into mountain streams after fire 
events. When this material reduces 
dissolved oxygen in the water it is 
known as a blackwater event. 
Understanding the problem
 
KEY MESSAGES
• Spotted tree frogs have 
suffered major declines,  
are now Critically Endangered 
in Victoria and New South 
Wales, and will become  
extinct unless we take action.
• Before the 2019–20 bushfires 
remaining populations were 
rare and had low resilience, 
particularly due to predation 
by non-native fish and disease 
caused by chytrid fungus. 
• Spotted tree frogs can be 
killed during bushfire events, 
and their eggs and tadpoles 
can also be killed after fire if 
rainfall washes ash, sediment 
and debris into mountain 
streams, causing a black 
water event where this frog 
species breeds. 
• The 2019–20 bushfires burnt 
50% of sites used by spotted 
tree frogs, and high rainfall 
caused flooding and blackwater 
events after the fires.
• While the bushfire, post-fire 
flooding and blackwater events 
likely directly killed many frogs, 
eggs and tadpoles, a high 
proportion of frogs were also 
found to be infected by chytrid 
fungus during post-fire surveys.  
•  These post-fire surveys 
found that spotted tree frog 
populations were reduced  
to critically low numbers  
at severely burnt sites.
• The number of frogs at  
some sites were so low  
that researchers decided to 
salvage remaining individuals.
• Spotted tree frogs were 
collected from these sites, 
and neighbouring populations, 
to establish a captive 
conservation breeding  
and insurance population  
at Zoos Victoria.  
• The frogs collected were 
mostly juveniles and from 
multiple sites to reduce the 
potential impact on the 
remaining wild populations 
and to maximise the genetic 
diversity of the captive  
founder population.
• Captive-bred spotted tree frogs 
will eventually be released 
back to help increase the 
resilience of wild populations 
to existing threats like chytrid 
fungus, and future fire events. 
Saving the Critically Endangered spotted tree frog  
following the 2019–20 bushfires 
NESP Threatened Species Recovery Hub Project 1.4.1
 
A spotted tree frog nestled between  
burnt logs after the Black Summer Fires.   
Image: Matt West

Understanding the problem  
(continued)
Spotted tree frogs breed only in 
mountain streams, and if the post-
fire flooding causes a blackwater 
event when eggs and tadpoles 
are in the streams then an entire 
generation can be killed. 
Given that spotted tree frog 
populations are small, isolated 
and face multiple threats, they 
are unlikely to cope with severe 
bushfire events. This is because 
spotted tree frog populations are 
very unlikely to naturally recover 
if any event further reduces their 
recruitment rates. Furthermore, 
spotted tree frogs cannot 
recolonise sites, as the distance 
between all remaining populations 
is greater than the distance they 
can naturally disperse. Even low- 
to moderate-intensity bushfires 
may accelerate population 
declines of spotted tree frogs if 
fires reduce the survival of frogs 
and disrupt their breeding.
Severe drought up to spring 2019 
led to an extreme fire season in 
southern and eastern Australia. 
The 2019–20 bushfires burnt 
over 104,000 km2, including 
approximately 20% of the forest 
biomes, much of it severely. 
Aquatic habitats within and 
downstream of burnt areas  
were also heavily impacted.
Three billion reptiles, mammals, 
birds and frogs are estimated 
to have been impacted by the 
bushfires, and many were killed 
during the fires. Animals that 
survived the initial fire event 
may have later died from lack 
of resources (food, water, 
shelter), heavy sedimentation 
and water quality deterioration 
in aquatic environments, and 
increased exposure to predation, 
competition and disease.
Thirty-eight frog species, including 
the spotted tree frog, had 25% or 
more of their habitat burnt by the 
fires. Experts have predicted that 
in the absence of conservation 
action, the immediate and 
subsequent effects of the bushfire 
will drive a further 35-62% 
reduction in remaining spotted 
tree frog populations over the next  
10 years (or three generations). 
While the spotted tree frog 
is recognised as Critically 
Endangered in both Victoria and 
New South Wales, the recent 
fire event further supports 
recommendations that the 
national conservation status of 
spotted tree frogs (Endangered) 
also be up listed to Critically 
Endangered. 
Who is involved?
• Department of Agriculture, 
Water and the Environment
• Victorian Government 
Department of Land, Water 
and Planning 
• Forest Fire Management 
Victoria
• Parks Victoria
• The University of Melbourne 
• Zoos Victoria 
• Cadbury Freddo
• New South Wales Office of 
Environment, Energy and 
Science Saving Our Species 
Program
The impact of the 2019–20 bushfires on wildlife
A high percentage of spotted tree frogs were found to be infected with chytrid fungus 
after the Black Summer Fires. Image: Matt West

About chytrid
Chytrid fungus is found at the sites 
of all the remaining spotted tree 
frog populations. 
The fungus originated in south-
east Asia and spread around the 
world, likely arriving in Australia  
in the 1970s. 
Globally, chytrid has affected  
700 species of amphibian, with 
at least 500 of those suffering 
declines as a consequence. 
Chytrid has a free-swimming 
zoospore life stage that is 
microscopic and can persist  
in the environment. Not all frog 
species are equally affected by 
chytrid. Frog species that are  
less susceptible to infection  
and developing disease can 
carry and spread chytrid to 
the detriment of other, more 
susceptible, frog species. 
While we can treat individual frogs 
for chytrid infection in captive 
situations, we can’t yet eliminate 
chytrid from wild populations.
Captive insurance and 
conservation breeding programs 
can help protect species when 
their wild populations reach 
critically low numbers and their 
threats cannot be eliminated. 
Researchers from The University 
of Melbourne and Victorian 
Government Department of Land 
Water and Planning collected 27 
spotted tree frogs to establish a 
captive insurance and conservation 
breeding program at Zoos Victoria. 
The frogs were collected from 
four different sites to maximise the 
genetic diversity of the founders 
for the new breeding program. 
Three of these four populations 
had been affected by bushfire 
to differing degrees. At one site, 
researchers may have collected 
the last remaining individuals.
Mostly juvenile frogs were 
collected, as this was considered 
to have the least impact on  
the remaining wild populations.  
In addition, these juvenile frogs are 
expected to have a better chance 
of surviving to the adult stage in 
captivity than they do in the wild. 
Under current conditions, in the 
wild only around 0.4% of eggs 
produced by female spotted tree 
frogs survive to become adult 
frogs. Given that females produce 
around 500 eggs per year, this 
means that only around two of 
these will reach the adult breeding 
life stage. A key reason for the low 
survival of the eggs and tadpoles in 
the wild is because they are eaten 
by non-native fish. Furthermore,  
to contribute to the next 
generation, the adult frogs must 
also survive, avoid succumbing to 
chytrid infection, and then breed.
The collected spotted tree frogs 
will undergo a strict quarantine 
period at Zoos Victoria’s Healesville 
Sanctuary to ensure they are all 
chytrid-free before entering the 
captive-breeding program. 
New, specialised captive-breeding 
facilities are being constructed 
at Healesville Sanctuary and 
Melbourne Zoo thanks to the 
Australian Government’s Bushfire 
Recovery for Wildlife and their 
Habitats grant funding and 
donations received from the 
community after the fires and 
a special funding campaign by 
Freddo Frog. Once the captive 
frogs mature, the breeding 
program will help to produce  
frogs for future reintroduction  
and translocation trials at key  
wild release sites. Ultimately, 
we hope this will increase the 
resilience of spotted tree frogs  
to future fire events. 
Emergency salvage and establishing a captive conservation breeding colony
The spotted tree frog is highly susceptible to 
developing disease caused by chytrid fungus. 
Image: Matt West

Cite this publication as West, M, 2021. Saving the Critically Endangered spotted tree frog following the 2019–20  
bushfires. Project 1.4.1 community factsheet. NESP Threatened Species Recovery Hub, Brisbane. 
This research project was funded through the Australian Government’s Bushfire Recovery package for wildlife and their 
habitat, the Victorian Government’s Bushfire Biodiversity Response and Recovery program (Phase 1), Zoos Victoria and 
the Threatened Species Recovery Hub of the Australian Government’s National Environmental Science Program.
We will continue to monitor the 
fire-affected spotted tree frog 
populations to determine how 
they respond after the fires and  
to the other ongoing threats,  
and so that we can be ready  
if they need our help. 
To increase the resilience of 
spotted tree frog populations 
to future fire events we are also 
working to reduce the key threats. 
This includes reducing  
the numbers of non-native fish 
at one important site for the 
spotted tree frog. Changes in 
the spotted tree frog population 
will be assessed in response to 
non-native fish removal as part 
of a five-year (2021 to 2026) 
management trial. The trial is 
being conducted at a site of 
relative low value to anglers  
but high value to recovery  
of the spotted tree frog. 
Spotted tree frogs need urgent 
help to protect them from disease 
caused by chytrid fungus. We are 
trying to find some frogs that can 
survive chytrid infections, and 
undertaking research to discover 
the genetic mechanisms that  
help them survive.  
If we can identify these frogs, then 
we can selectively breed them 
in the new captive conservation 
breeding colony at Zoos Victoria. 
We plan to release spotted tree 
frogs back into the wild that 
can fight chytrid infections. 
Populations that can deal with 
chytrid are expected to be  
more resilient to future bushfire 
events. To achieve this, we  
need additional funding support. 
If you would like to help this 
critical research, please contact 
the spotted tree frog research 
team. 
West, M. & Johnson, G. (2021) BBRR Theme 1: Immediate reconnaissance – Activity AG1.1: Threatened reptiles 
and frogs. Post-fire assessment report: Spotted Tree Frog & Booroolong Frog. Bushfire Biodiversity Response 
and Early Recovery Program, Department of Environment, Land, Water and Planning, Hume Region, NE 
Victoria & University of Melbourne.
We encourage your feedback. Contact the research team: [EMAIL]
Severe bush fire, post-fire floods and disease appear to be accelerating spotted tree frog declines.  Image: Matt West
What else are we doing? And how can you help?
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