Dubbo’s two weirs are choking the Macquarie River, and hurting native fish stock levels. Fish ways must be built, and become mandatory in all weirs if fish populations are to return to anywhere near pre European settlement levels.
Australian native fish require unimpeded access along waterways in order to survive and reproduce. Freshwater fish move within waters at different times to access food and shelter, to avoid predators, and to seek out mates. Of the 83 species of freshwater fish in south eastern Australia, over half migrate at least once as part of their life cycle. Some species can migrate thousands of kilometers while others only move a short distance.
Barriers to fish passage prevent the migration of native fish species and can have severe implications for these populations. In extreme cases, barriers can result in localised extinctions. This has occurred for golden perch populations above several large weirs and dams.
Fish passage barriers can adversely impact native fish by:
#1 interrupting spawning or seasonal migrations
#2 restricting access to preferred habitat and food resources
#3 increasing the chance of predation and disease
#4 reducing genetic flow between populations through population fragmentation.
The cumulative effect of barriers to fish passage has been identified as a Key Threatening Process to the continuing survival of several species of native fish in Australia .
Fish ways are constructed by creating a series of pools and small steps with rocks. The fish are able to move to the other side of a barrier by swimming into the small pools, resting and then swimming up or down the step into the next pool.
Since 1999, Melbourne Water has reconnected more than 230 kilometers of rivers and creeks through the construction of 20 fish ways, and it is hoped that smaller towns in NSW such as Dubbo will follow.
An experimental manual fish way at Balranald Weir was constructed and in the first four weeks almost 8,000 fish were observed using the fishway. NSW DPI and Balranald Shire Council have now successfully sought funds from the Environmental Trust to automate the fishway to provide permanent benefits to the ecology of the Lower Murrumbidgee River.
Many local river users, conservationists and the environmentally aware, hope that Dubbo council will consider installing fish ways with a carp trap in both of Dubbo’s weirs, which are currently halting the natural migration and breeding cycle of our native fish.