There are several threatening processes that have contributed to the decline in abundance and distribution of the Growling Grass Frogs (GGF). These include:
- Habitat loss, fragmentation, and degradation
- Altered flooding regimes
- Disease and pathogens
- Presence of invasive fish species
Habitat loss, fragmentation, and degradation
Urbanisation, land conversion for agriculture, overgrazing by livestock, and the colonisation of habitat by invasive species are considered the major processes contributing to the destruction, fragmentation, and degradation of the GGFs habitat state-wide.
As Winton Wetlands is a conservation reserve and is actively managed, the threat of habitat loss, fragmentation, and degradation of GGF habitat within the reserve is minimal. In fact, we will continue to enhance the habitat to support the reintroduced population of GGFs.
Altered flooding regimes
Localised extinctions of GGF populations coincide with altered flooding regimes and the inundation of GGF habitat, due to the diversion of water for agriculture, and the conversion of wetlands ecosystems to dams and reservoirs.
It is likely that the construction of the Lake Mokoan Dam and the inundation of the wetlands led to the extinction of the species within Winton Wetlands. The decommissioning of the dam has seen the ongoing restoration of the landscape’s hydrology, and the revival of the ephemeral nature of the wetlands. As it stands, the wetlands once again provide suitable habitat for the GGF.
Diseases and pathogens
Chytridiomycosis, the infectious disease caused by the chytrid fungus, is considered a major threat to frog populations across south-eastern Australia and is responsible for the decline and extinction of many amphibian populations and species globally.
Chytrid fungus is present within GGF populations state-wide. However, certain environmental factors can limit the chytrid load within a population. Chytrid is less prevalent in populations of GGFs that inhabit warmer, more saline water. Furthermore, the diurnal basking behaviour of the GGF assists with the management of chytrid load.
Through sampling, we are aware that chytrid is present within the source and release sites. To reduce the chytrid load on the translocated individuals and to prevent the introduction of new strains of chytrid into Winton Wetlands, all captured GGFs will be pre-screened for Chytrid and undergo a quarantine period for the treatment of chytrid prior to release.
The release site has been actively modified to enhance availability of basking sites which contains warm, and relatively saline water that is not suitable for the survival of chytrid fungus. Theoretically, the release site will therefore act as an environmental refuge for GGF from Chytridiomycosis.
Presence of invasive fish species
Through the predation of GGF eggs and tadpoles, and degradation of aquatic vegetation, several invasive fish species including European carp (Cyprinus carpio) and Eastern Gambusia (Gambusia holbrooki) threaten the remaining GGF populations. To minimise the negative impact of invasive fish on the reintroduced GGF population, we will actively reduce invasive fish at Winton prior to the release of the GGFs by undertaking electrofishing and carp mustering activities.
We anticipate that by reducing the number of invasive fish present within the release site we will help to improve the reproductive success of the reintroduced GGF population.