Decline... The growling grass frog. Photo: Dr Geoff Heard
MELBOURNE'S expanding urban growth boundary is forecast to hit remnant populations of one of the state's most endangered frogs, just as new figures show an almost 30 per cent drop in growling grass frog populations over the past decade.
Results of a Melbourne University survey released to The Age found the growling grass frog suffered ''significant and unsustainable population decline'' around Melbourne, due largely to a loss of habitat, drought and disease.
The survey compared population data recorded at 152 sites across Melbourne's north in 2001-02 and in 2011-12.
Dr Geoff Heard surveys a site at Merri Creek in Donnybrook, which is home to the frog. Photo: Wayne Taylor
Geoff Heard, research fellow at Melbourne University's school of botany, said in the decade to 2012 there had been a 29 per cent decline in growling grass frog populations in this area.
''We had anticipated a decline but a third over a decade is really quite a severe decline,'' Dr Heard said.
''If this trend continues in coming decades, we will lose them from many areas around Melbourne.''
In the first survey, the frog was found at 58 sites. In the second survey, completed this year, it was located at only 41 sites.
Dr Heard said while the growling grass frog had persisted at 30 sites, it had become locally extinct at 28 sites. Two of the wetland sites surveyed in 2001-02 - in Wollert north of Melbourne - have since been drained for use as landfill sites and another two - Aurora Estate in Epping and Botanica Park Estate in Bundoora - have been developed for housing.
However, the growling grass frog was discovered to have colonised 11 new sites.
Found in Melbourne's south-east, north, west and south-west suburban fringes, the frog - a fist-sized amphibian with dark olive to bright emerald-green or brown colouring - is classified as endangered in Victoria and vulnerable nationally. Earlier this month, the Baillieu government announced an expansion of the urban growth boundary, which includes the establishment of six new suburbs to Melbourne's north, west and south-east.
The suburbs will house more than 100,000 people over the next 30 years.
''There are four main areas around the city where the frog occurs and they all unfortunately coincide with where the government proposes to build new suburbs,'' Dr Heard said.
''While urbanisation is going to go ahead, there are things we can do. We must protect high-quality wetlands and make sure they are not degraded, we need to maintain significant parkland along our creeks and we need to invest heavily in constructing new wetlands to offset the impacts of urbanisation.''
The Baillieu government is yet to release its revised biodiversity plans, which will need approval by the Commonwealth government.