Researchers have discovered that the range of one of Western Australia's rarest freshwater fishes, Balston's Pygmy Perch, could have declined by as much as 25 per cent.
Murdoch University's Freshwater Fish Group & Fish Health Unit and the University of Western Australia's Centre of Excellence in Natural Resource Management recently surveyed more than 70 sites across the south-west where the Balston's Pygmy Perch is historically found.
"We found that it was missing from almost a quarter of the catchments sampled," said Mark Allen, a scientist from Murdoch University's Freshwater Fish Group.
"The species appears to have been lost from the King River, Kalgan River, Turner Brook, Dombakup Brook, Marbelup Brook and Moore River."
Balston's Pygmy Perch is endemic to the south-west corner of the state, historically occurring from the Moore River north of Perth to Two Peoples Bay near Albany.
The species is highly susceptible to habitat disturbance, in particular land clearing.
"Our results showed that the abundance of Balston's Pygmy Perch tends to decline as the scale of land clearing increases in catchments," Mr Allen said.
"Migration barriers such as dams and weirs and declining flows due to water abstraction and climate change are also a threat.
"It is also highly sensitive to the presence of introduced species and only rarely occurs in the same rivers as Trout, Redfin Perch and Eastern Gambusia."
Numbers of Balston's Pygmy Perch are still in reasonable abundance within a belt of predominantly forested land stretching from Margaret River to Denmark and two previously unknown populations were discovered.
"We were excited to find two previously unknown populations, one in the Meerup River and another in part of the Frankland River," Mr Allen said.
While the discovery of these new populations is encouraging, the overall declining trend has scientists concerned for the future prospects of the species.
"The results of this study confirmed our suspicions that remaining populations tend to be confined to relatively pristine systems and that's a concern as pressures on the environment increase due to a growing human population and reduced future rainfall," said Mr Allen.
The Department of Fisheries Western Australia recently listed the Balston's Pygmy Perch as a protected species that it not to be taken.
In 2006 Balston's Pygmy Perch was listed as vulnerable under the Environment and Biodiversity Conservation Act 1999 when scientists from Murdoch University revealed its restricted distribution and extremely low abundance in the wild.
The survey of Balston's Pygmy Perch is part of a collaborative project with the Department of Fisheries Western Australia on threatened freshwater fishes in the state's south-west supported by the South West Catchments Council and the South Coast NRM and jointly funded by the Australian and Western Australian Governments.
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