Western Australia’s unique freshwater fish are in trouble, say scientists at Murdoch University’s Centre for Fish and Fisheries Research.
A number of freshwater fish species are now listed as threatened and require "specific conservation consideration".
Murdoch University Research Fellow Dr Stephen Beatty and his team have undertaken an extensive study of the Ellen Brook and Brockman River – the major tributaries of the Swan Canning Riverpark –for the Ellen-Brockman Integrated Catchment group.
Dr Beatty said the research team had good evidence that there had been large declines in numbers of unique native fish throughout the south-west.
"The main impacts on the fresh water habitats are inputs of nutrients, loss of river bank vegetation, feral fishes, in-stream barriers and groundwater extraction," he said.
"We have found that fresh groundwater input into rivers can be very important in providing habitat for freshwater fish, so the extraction of too much groundwater is a threat along with reduced rainfall due to climate change.
"Secondary salinisation has resulted in only 44 per cent of the flow of the 30 largest rivers in the south-west being fresh.
"More noticeably, there have been major declines in the geographical range where many species can now be found due to increases in salinity in the majority of rivers," he said.
The study recommended two species for specific conservation consideration, the Black-stripe Minnow and Western Mud Minnow. Each has only two remnant populations north of the Bunbury region, including sites in the Ellen Brook catchment.
Dr Beatty said saving these fish species was extremely important.
"We believe that these two species may have been found more widely on the Swan Coastal Plain but loss of habitat such as destruction of wetlands, alteration of rivers and introduction of feral fish has caused them to disappear.
"Protecting and improving the condition of our remaining freshwater systems is the only long-term, sustainable solution to halting the decline of our unique freshwater fish and crayfish."
Dr Beatty said much effort was going into increasing the water quality of the Ellen and Brockman Rivers to in turn improve the quality of the Swan River.
"The Ellen Brook and Brockman River study, funded by Lotterywest, was designed to provide a baseline for managers so that future declines, or improvements, of populations of fish, crayfish and mussels can be determined," he said.