Murray River restoration increases native fish populations

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Research has shown that providing woody habitat ("snags") for fish in the Murray River increases  the population size of native doesn't just draw them in from elsewhere.

WHILE any angler will tell you that instream habitat and its restoration is essential for the recovery of native fish, a debate has been raging in the scientific community about its effectiveness.

In particular, scientists have been arguing about the effectiveness of what is sometimes referred to as the "honeypot effect" - when we add habitat for fish in a large river, does the number of fish increase, or do the fish already present simply move to the new habitat?

A team of scientists from the Arthur Rylah Institute, University of Melbourne, University of Canberra, the Federal Government, and Flinders University have finally answered this question, but it wasn’t simple, quick, or easy.

In a publication released today in the scientific journal Ecological Applications, Dr Jarod Lyon and his team describe how they took a large-scale approach, in terms of time, effort and space. They studied 110 km of the Murray River over seven years, and with partners at NSW Department of Primary Industries installed more than 4450 "snags" (mainly large pieces of wood), recorded more than 10 thousand fish, and analysed more than six million records of tagged fish.

This work shows that providing woody habitat ("snags") for fish in the Murray River did indeed result in an increase in the population size of native fish.

“We found a three-fold increase in the abundance of Murray cod, and a doubling of abundance of golden perch, in the reach of river where habitat restoration was done, compared to sites where habitat remained constant’, said Dr Lyon.

‘This was certainly an encouraging finding”, he continued.

‘In addition, abundances of the target species in the adjacent reference sites remained stable, indicating that the numbers of fish across the whole study area had increased, rather than just the same fishes just moving around’.

The comprehensive study included a range of methods to track the fish populations over time, including electrofishing surveys, mark-recapture, and telemetry tracking. Anglers also provided important data by sharing their catch records within a valuable science citizen-science program.

Professor Corey Bradshaw from Flinders University, who was a collaborator on the study, said ‘Restoring degraded freshwater ecosystems like the embattled Murray-Darling Basin is an expensive and colossal task, so knowing that our restoration attempts actually work to increase the number of native fish gives us hope that we can keep these unique species around well into the future’.

‘These results give great confidence to river managers that installing woody habitat really does help native fish populations thrive and delivers substantial benefits to the communities using them’, Dr Lyon said.  

‘Under most climate-change scenarios, we are looking at a future where there will be increased pressure on Australia’s limited water resources’ said Dr Lyon. ‘We need to look at a range of options for restoring fish populations in our waterways — it will take a mix of interventions to do this, and it is vital for managers to know that we can apply habitat restoration that works’, he said.

The large-scale, long-term study also provides a valuable and useful example of how we can assess other interventions in our rivers, such as installing fish passage or delivering water for the environment, all of which are designed to support better, healthier, thriving native fish populations.

This work was funded by the Murray-Darling Basin Authority’s The Living Murray Program and was a partnership with NSW Department of Primary Industries.

The paper, ‘Increased population size of fish in a lowland river following restoration of structural habitat’ by JP Lyon, TJ Bird, J Kearns, S Nicol, Z Tonkin, CR Todd, J O’Mahony, G Hackett, S Raymond, J Lieschke, A Kitchingman, and CJA Bradshaw was published in Ecological Applications

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