“Imagine a lower Murray where fishers can reliably catch and release 20kg Murray cod. Where fish and other aquatic animals thrive in a healthy river. This is the natural and cultural heritage of the Murray River and restoring it is well within our means. The clincher is that a lot of this can be done with little or no extra water from the Murray Darling Basin Plan.”
This is the vision of Dr Martin Mallen Cooper – internationally renowned fisheries scientist and Director of OzFish Unlimited.
The vision comes from studying the history of the river, combined with sophisticated computer modelling. Surprisingly, it shows that the river was flowing all the time, even in droughts (see The Land article and scientific paper in Ecohydrology). But now the Murray River between Lock 1 (Blanchetown) and Lock 11 (Mildura) is a series of weir-pools. A distance of 700 kms (see figure below).
The running river that existed is gone and the species that like faster flows, like Trout Cod, Macquarie Perch and Murray crayfish are gone too – while Murray Cod have severely declined. Faster flows are not only good for adult fish but essential to enable larvae to drift into suitable nursery habitats, especially for species like Golden Perch (Callop) and Silver Perch. Unfortunately, carp love these pool environments and are presently thriving in the lower Murray.
The good news is that it is easy to bring back the running river of the lower Murray and give native fish populations a huge boost – by lowering or removing a weir the river changes from a weirpool back to its natural state as a running river, with the same flow (see diagram below). The river becomes a complex habitat that swirls around snags, creating perfect conditions for ambush predators like Murray cod. All this, with no extra environmental water.
It will not be possible to achieve the changes needed without consulting with irrigators and addressing the issues that lower weir-pools might mean for their pumps. It will also not be possible without consulting with Murray River tourist boat operators on trying to avoid potential impacts on boat access up and down the River. Finally, salinity would also need to be managed as a lower river level may draw in more salt – it would likely take many years to reach a natural balance.
But if it could happen, we would see a major resurgence in native fish numbers, with more tourists coming to fish, catching and releasing one of the world’s largest freshwater fish – the mighty Murray cod.
Read the newspaper article HERE
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