INVESTIGATING THE IMPACTS OF TROUT AND CHYTRID FUNGUS ON SPOTTED TREE FROG POPULATIONS

Photo: M. West 

The Australian Spotted Tree Frog (Litoria spenceri) is one of the many amphibian species currently in decline, probably due to:

Predation of tadpoles by trout: Introduced Rainbow and Brown Trout now occur throughout the range of the Spotted Tree Frog, and prey on their tadpoles. Trout appear to have significantly reduced population densities, and caused range contractions and possibly local extinctions, in Spotted Tree Frogs.

Chytridiomycosis: This disease is caused by the chytrid fungus, and has been found in populations of Spotted Tree Frogs and sympatric species, such as the Rocky River Frog (Litoria lesueuri). Its impacts on populations are unclear: it has probably caused the extinction of at least one high-density Spotted Tree Frog population in a trout-free stream, but other infected low-density populations have not become extinct. Chytridiomycosis does not appear to severely affect the Rocky River Tree Frog.

Matt West, Dr Graeme Gillespie and Dr Mick McCarthy from Zoos Victoria and the University of Melbourne are conducting a project to quantify the impacts of these threats on Spotted Tree Frog populations in north-east Victoria.

AIM

The project aims to understand the relative demographic significance and potential interactive impacts of trout and chytrid fungus on two Australia frog species: the Spotted Tree Frog and Rocky River Tree Frog. This information will then be used to review the current status and distribution of the Spotted Tree Frog, and so develop effective management strategies for this Critically Endangered species.

METHODS

Research is currently being undertaken in mountain streams throughout north eastern Victoria.

Spotted Tree Frog and Rocky River Tree Frog populations are being monitored to:

• Evaluate and compare the prevalence of chytrid fungus where one or both species of frog occur.
• Evaluate the transmission of chytrid fungus within and between these frog species.
• Determine the differential effects of trout predation and chytrid fungus on Spotted Tree Frogs.

This information will be used to:

• Construct mathematical population models to examine the relative influences of trout and chytrid on the demography and population declines of these frog species.
• Inform future management, including the prioritization of key threatening processes for targeting management action.

RESULTS

This project commenced in November 2009.  Preliminary results will be uploaded soon.

PROJECT OUTCOMES

Data collected in this project will be used to refine population models, and so determine the relative importance of trout and chytrid fungus in population declines. Ultimately this knowledge will assist in refining conservation strategies for the Spotted Tree Frog and other amphibian species affected by multiple threats.

PROJECT PARTNERS

• Zoos Victoria 
• University of Melbourne
• Department of Sustainability and Environment
• Parks Victoria 
• Department of Environment, Climate Change and Water 

FOR MORE INFORMATION:

- on this project - click here to email Matt West (Principal Investigator).

- on the Spotted Tree Frog - click to follow links to:

• Zoos Victoria Spotted Tree Frog Conservation Program
• Action Statement (Victoria)
• Recovery Plan (NSW)
• IUCN Red Listing

- on other Zoos Victoria research involving the Spotted Tree Frog - click here.