SINCE European settlement many changes have been made to the Murray River, and many of these changes have resulted in a completely different environment for native fish, river gums and other species dependant on the river for survival. In fact, experts estimate present levels of native fish communities in the Murray Darling Basin (MDB) are estimated to be 10 per cent of the pre-European settlement level, which is not sustainable in the long term.
Some of the changes to the South Australian section of the Murray include a system of weirs, which not only influence the flow in the main stem of the Murray, but also change water availability to many of the backwaters and floodplains in the region. Native fish require different flowing habitat for many aspects of their life history, including movement, feeding and reproduction.
Before the construction of the weirs, the unchanged main stem of the river would have had good river flows at 2,000 ML/day; however, the weir pool nature of the Murray at the moment means that for the same flows 20,000 ML/day of flow is required. This coupled with the recent prolonged drought conditions means that it has been a particularly difficult time for native fish in the last 10 years.
Notwithstanding that, many of the native fish species of the MDB are very resilient and have life history characteristics that mean they can survive long periods with zero to low flow, which also would have occurred prior to intervention by people of the river. For example Murray Cod are long living (up to 48 years old) and can move long distances to areas more suitable for survival and reproduction (hundreds of kilometres). Yabbies can survive several years in drought conditions by hibernating until the backwaters are inundated, then emerge and start breeding again.
High river flows which have occurred following recent rains in the MDB have provided a bumper harvest of yabby catch for recreational anglers in the South Australian Riverland. This has led to a shortage of nets within the region as more recreational fishers can access many more areas by road and foot. However, increases in recreational angling opportunities need not only happen in times of flood and high flow.
SARDI Aquatic Sciences researchers are looking at the relationship between native fish and flowing water in the lower Murray. This research has shown the importance, even in times of low flow, of the timing, duration, volume and variation of flow of water that is delivered for native fish like Murray cod, golden perch and yabbies. Recreational anglers who are passionate about preserving and catching native fish into the future should provide input through processes like the MDB Guide that will shape the future of water flow and fish production into the future.
This coupled with preservation and recovery of the environment through the MDB Native Fish Strategy means that the recreational angling experience in the South Australian section of the Murray will be maintained and enhanced in years to come.
