Securing the southern populations of the Growling Grass Frog in the Merri Catchment

20th January 2023
By Yasmin Kelsall


The Merri Creek at O’Herns Road looking south. 
An in-stream breeding location that is under threat via stormwater, water quality and predatory fish. 

The Growling Grass Frog (GGF), Litoria raniformis, subspecies major, once abundant across Victoria’s lowlands, is now considered Vulnerable, nationally. 

In the Merri Creek, this species is still present, but is highly threatened by development impacts. These have greatly intensified within the population’s most southern extent in the past 20 years.  In response to these pressures, the Merri Creek Management Committee (MCMC), along with other project partners, sought funds from the Growling Grass Frog Trust to create a strategy focusing on the portion of the catchment from Moomba Park in Fawkner (the southern-most know current extent of the species), through to Somerton, just below Aitken Creek in the north.  This area was chosen as it’s not currently covered by any other regional conservation process.  Another important motivation for the project was to find an appropriate scenario to maintain connectivity for a GGF population located at the Bolinda Road Quarry in Campbellfield. This will be almost completely encircled by a new development.

The strategy process to date has involved a background research and stakeholder engagement phase, resulting in a Background, Issues and Priorities paper and recently a Draft Strategy.  A Project Steering Group, comprising local council representatives, government department and land managers, as well as the MCMC, have guided the project.  Species expert, Dr Geoff Heard has also provided invaluable technical expertise.  Cultural consultation with the Wurundjeri Woi-wurrung Cultural Heritage Aboriginal Corporation has been an important aspect of the project.

Some key findings include:

  • There are seven known breeding populations within the study area and, broadly speaking, five metapopulation zones, one of which is no longer known to have an active population.  Habitat that supports the breeding populations includes four quarry holes, one in-stream location, and two stormwater wetlands.  Ephemeral offstream wetlands add to these locations in particularly wet years like we’ve recently seen.
  • The population of the GGF within the study site shows a long-term trend of decline, although this year has possibly seen increased occupation sites in comparison to drier years.
  • The overall decline is undoubtedly linked to increased urbanisation within the study site, particularly in the past 20 years.  While the extent of urbanisation may stabilise locally in the next 5-10 years, impacts from upstream development within urban growth areas will continue for decades. This will  likely render instream habitat unsuitable as core GGF habitat, affecting at least one breeding population and perhaps reducing its suitability as a dispersal corridor. As a result, offstream habitat is likely to become more important, particularly for breeding and sustaining GGF metapopulations.
  • In this system, groundwater volume and quality has been found to be important, as it supports GGF offstream habitat quality, particularly in quarry holes, as well as baseflow to instream habitat. 
  • Some of the most important off-stream habitat occurs in quarries. It will be critical to ensure that rehabilitation plans for quarries do not require infilling the quarry and that active quarries consider the needs of any resident GGF populations.
  • Instream habitat will remain important for connection and dispersal, but not as breeding or core habitat.  It is important to ensure that core, or linking, habitat is nearby, or accessible to instream habitats.
  • Stormwater wetlands have become surrogate habitat for the GGF at Frog Court, Barry Road and Horne Street.  This habitat is precarious, and these wetlands need to be ‘reset’ every 5-10 years or so.  The reset process needs to be well considered to ensure resident GGF populations are not compromised in this process.
  • GGF underpasses have shown little evidence of success within the study area.  These include 3 underpasses beneath Edgars Road and around 8 underpasses beneath the Craigieburn Bypass. This means the Edgars Creek population has been effectively severed from the Merri Creek population by the Craigieburn Bypass.
  • Habitat links that sit within an otherwise industrial or residential landscape, are yet to be proven effective within the study area.  Referral authorities should be made aware of the lack of evidence and accordingly apply the precautionary principle, rather than approving any such measures.  Further monitoring and research is also required. 

City of Whittlesea's Northern Quarry - a GGF breeding site

The draft Strategy contains a series of five maps that provide priority options for a variety of on-ground works.  These include a draft habitat link between the Bolinda Road Quarry site and the Merri, and numerous other potential supplementary habitat projects.  Supplementary habitat will normally involve building new, dedicated GGF wetlands.  In most cases, these would be located next to current breeding sites, like quarries and stormwater wetlands.  These projects will require large investment and ongoing maintenance, and need a dedicated and coordinated approach.

Other supporting activities include seeking improved water quality, reducing the impacts of excess stormwater, reducing shading of habitat sites and community engagement.

The next steps for the project area to:

  • Finalise the masterplan;
  • Work with City of Hume to develop the important GGF habitat link at Bolinda Road;
  • Continue to respond to development proposals;
  • Continue the Working Group to assist and oversee implementation of the plan;
  • Seek funding for implementation of priority projects; and
  • Advocate for improvements in policy and process where identified.

Again, a huge thank you to the Growling Grass Frog Trust for supporting this project, and everyone who has provided their knowledge, time and support so far.  Fingers crossed this strategy will assist in seeing this great frog growling abundantly once more! 

Image credits: Yasmin Kelsall

<< Previous | Next >>