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Climate change adds to frog woes

Frog and lizard scientists add their voices to the call for climate change action to save species from extinction 

By 2085 climate change could mean life is a 60-year long boys’ weekend for tuatara. Temperature can dictate whether tuatara eggs hatch as female or male. In a warming world males will briefly emerge from eggs as the lonely, functionally extinct winners.

It would be an ignominious end for a species whose roots go back to the dinosaur age. 

Last week, almost a thousand attendees from around the globe descended on Dunedin for the 9th World Congress of Herpetology. Held every four years, the event is like the Olympics for those who study reptiles and amphibians.

The 600 plus presentations included debate on the fragile state of the world’s amphibians and reptiles.  Around 40 percent of amphibians are threatened with extinction. Reptile species are under similar pressure. 

University of Otago Zoology Professor Phil Bishop, the congress director, said a recurring thread in presentations was the threat of climate change.

“It is highly likely that we will observe many species going extinct in front of our very own eyes in the next decade.”

New Zealand used to have seven frog species. Three are now extinct and the remaining four are threatened with, or at risk of, extinction.

“Climate change is one of those topics where people generally throw their arms up and say ‘there’s nothing we can do’ but we’ve had enough of not doing anything. We really need to be pushing the people who can do something about it.”

The congress released a declaration calling for all governments to acknowledge the accumulated evidence of global climate change and take immediate action to mitigate future impact. This includes increasing protection for biodiversity and wild places. 

As a group, the congress also made a commitment for its events to become 100 percent carbon neutral in future and serve locally sourced food with limited meat and dairy.

Climate change adds pressure to the numerous issues facing amphibians and reptiles.

University of Otago Professor Phil Bishop wears this shirt as a provocative conversation-starter to highlight the insect-eating and food source role frogs play in ecosystems. Photo: Supplied

Bishop said the biggest issue facing amphibians worldwide was loss of habitat.

“Whether it’s habitat destruction, or habitat alteration by climate change, or habitat fragmentation, that’s the main issue.”

Frogs are cold-blooded and can’t regulate their body temperature themselves, relying on the environment around them. There are fears the pace of warming temperatures might prove too much. 

“If we could just stop messing around with their habitat, a lot of amphibians would be safe.”

The fires in Australia highlight another concern. With habitat burnt, any survivors of species are easy pickings for predators such as feral cats. Studies show they will travel some distance to hunt in sites which have been recently burnt. For those which escape the flames and predators and manage to establish a new population there's the issue of in-breeding.

Previous studies of Australian frog life after bushfire revealed genetic diversity within the population had decreased. With just a small number of adults surviving the fires, populations had become inbred meaning they were likely to be more vulnerable to future threats.

Fires last year near Otago affected the habitat of the jewelled gecko. Modelling shows the number of fire risk days in eastern parts of New Zealand will increase with climate change. Photo: Carey Knox

Disease is a threat which has become a major concern.

“They’re getting a number of infectious diseases. I liken this to the thousand straws which break the camel’s back. With a whole number of stressors, amphibians being subjected to emerging diseases, [is] the last nail in the coffin, just knocking them down so they become extinct.”

One disease, chytrid fungus is well known. However, presentations at the conference highlighted another virus which may prove to be more of a danger than first thought. 

Ranavirus: The new killer on the block

Skin ulcers, limbs dropping off, emaciation and haemorrhaging are all symptoms of ranavirus. 

Once caught, there’s no cure and the result is often fatal.

The disease affects amphibians as well as reptiles and fish and has been found in the United Kingdom, United States and parts of Asia and Australia. 

Research in the UK shows warming temperatures caused by climate change have increased the spread and severity of the virus. When the weather warms to 16°C, outbreaks increase.

So far, ranavirus hasn’t been found in New Zealand frogs. With an active exotic fish pet trade Bishop expects it’s just a matter of time before it’s found here. 

With no cure available the hope seems to be for species to eventually develop immunity to the virus.

The suffocating fungus 

One of the well known issues facing amphibians is the chytrid fungus. This affects how the creatures breathe through their skin and effectively suffocates them. 

Referred to as an amphibian apocalypse the fungus is estimated to have caused the extinction of around 90 amphibian species as well as be responsible for a decline in numbers of around 500 different species.

Bishop said a strain of the fungus hit New Zealand in the mid 1990s to early 2000s. Hardest-hit were introduced species and the native Archey’s frog.

Studies since then have shown our native frogs have an immunity to the strain present here. Frogs exposed to the pathogen show no signs of disease. Within 10 weeks the frogs are pathogen-free.

“If we could close all our borders to make sure no other disease got into New Zealand, we’re safe from a chytrid fungus point of view because all our frogs seem to be able to cure themselves.”

The concern is the arrival of a different strain of the fungus. The strain which is causing the most problems worldwide isn’t here yet and Bishop worries every time he hears of any accidental frog or cane toad incursion. 

Climate change is likely to alter where the fungus is found. Preferring cool, wet environments, it’s likely to move up mountains at the same time amphibians beat an upward escape from warming temperatures.

"There seems to be a lot of emerging infectious diseases which were tolerated by amphibian populations that seem to not be tolerated anymore."

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