The 2019-2020 Black Summer bushfires caused untold devastation to people and wildlife, but a team of researchers say something of a miracle has risen from the ashes in the Snowy Valleys region of NSW.
They have recently determined three rare Macquarie perch from the only remaining population in the NSW Murray catchment mysteriously defied the odds and survived the horrific water conditions caused by the combination of bushfires followed by severe storms.
The unexpected discovery has been welcomed by the NSW Department of Primary Industries (DPI), which despite organising a rescue operation just days after the bushfires struck, and conducting several months of surveying to locate the Macquarie perch, thought the rare population had been completely wiped out.
The first Macquarie perch spotted since the bushfires was reported in March 2021 by a spray contractor undertaking willow control works around a creek.
Researchers from Charles Sturt University and NSW DPI quickly went to investigate the sighting and were delighted to discover three Macquarie perch at two separate locations within the river system.
NSW DPI Murray-Darling Unit Fisheries manager Luke Pearce said the findings were a welcome surprise after the long journey the research team had been on to protect the species.
Just three days after the bushfires initially ravaged the area surrounding Mannus Creek, the NSW DPI Fisheries team desperately surveyed the water to see if any perch survived the blaze.
“To our relief, the Macquarie perch were still present and had largely survived the initial fire front,” said Mr Pearce.
“But with the storms forecast for the following week, it became a race against time to try to capture as many perch out of water.
“We quickly set up a rescue operation, but the conditions were terrible and after five days of sampling, only 10 were captured and taken to the Narrandera Fisheries Centre for safe keeping.”
The following week, the rescue operation was set to return, but the runoff from the storms had caused the dissolved oxygen levels in the water to be zero and the conditions meant the researchers could not rescue any more fish.
In the months that followed, researchers used funding from the Federal Government’s National Bushfire Recovery Fund through Murray Local Land Services to quantify the changes in the Mannus Creek habitat and determine if there were any Macquarie perch remaining after the bushfires.
A fisheries researcher at Charles Sturt University’s Institute for Land, Water and Society (ILWS) in Albury-Wodonga, Dr Katie Doyle, and fellow ILWS researcher Cameron McGregor worked on the project together.
“The first fish sampling efforts in February 2021 were looking grim and, much to our disappointment, there were no Macquarie perch detected despite significant effort – approximately 1020 net hours and 18,000 seconds of electrofishing,” said Dr Doyle.
“We started to think the population was likely lost.”
Dr Doyle said that given these results, the decision was made not to release the 10 rescued Macquarie perch back into Mannus Creek, but rather use them to boost the number and genetic diversity of the nearby Adjungbilly Creek.
“What started out as a story of real despair and fear that we had lost a very significant and important population has now turned into a story of hope as we have seen these fish survive what we thought was a certain death,” she said.
“How these Mannus Creek fish survived the fire, and the polluted water conditions from the flush of ash and sediment from the storms that followed, is nothing short of a miracle.
“Now that we have confirmed these rare perch are still present, it is essential we do everything we can to ensure they recover and have the best chance of survival.”
In a joint collaboration between Charles Sturt University, NSW DPI Fisheries and Murray Local Land Services, the researchers have already started implementing an action plan to ensure the fish population survives.
They have been working with the Victorian Fisheries Authority to introduce 2500 Macquarie perch fingerlings to the area in the hope of boosting the genetic diversity of the population and aiding with their recovery.
Murray Local Land Services has also organised a weed control program and some planned habitat enhancement and bank stabilisation works to be undertaken throughout the year to improve conditions.
“The final action in our plan is removing alien fish species, predominantly redfin perch and carp, from the creek,” said Dr Doyle.
“This is being completed by Charles Sturt University researchers and is aimed at reducing competition for the limited resources and predation. We believe it is a vital component to the recovery of Macquarie perch in the post-fire environment.”