Many native fish species within the Murray-Darling Basin have declined dramatically in distribution and abundance. Declines in the population of fish species often occur suddenly. There is potential for the extinction of some species in the future. There is a need to take urgent action to reverse this trend of endangerment, for both individual species and fish communities as a whole. Research undertaken through the Native Fish Strategy has focused on identifying critical habitat for native species, and threats to the sustainability of their populations, so that we can take action to recover them. Areas of high conservation value have been identified with this work informing environmental water plans and other regional conservation activities.
Forecasting of future fish population trends and the implementation of actions to reverse trends towards endangerment is an area for ongoing work. While it is important that specific legislative requirements are provided to manage species under threat, it is also important to recognise that appropriate management arrangements for all fish need to be implemented. Further, it is easier and more economical to maintain healthy populations than it is to restore depleted populations.
The Basin already contains at least 11 introduced fish species in the wild, some in pest proportions, and further introductions are inevitable over time. Both the abundance and attributes of some introduced fish continue to cause damage to habitats and populations of native species. Most attention has been given to carp and trout because they are the largest and visibly most abundant, but there are many other species that can have impacts through predation, competition and disease. The risk of further introductions into the Basin— especially from aquariums and nearby rivers outside the Basin—also needs to be considered. Precautionary approaches, to minimise the risk of future introductions, and pest management principles, to address existing introductions, should be applied across the Basin.
The focus of all management of introduced fish species should be on reducing the impacts of such fish on native species, rather than on complete eradication of numbers. The best approach to reducing such impacts is an integrated one that combines a range of techniques. For example, with carp, appropriate techniques could include rehabilitating the wetting and drying cycles for floodplain wetlands, commercial exploitation, and the installation of screens and fish traps to prevent adult fish migrations. There is unlikely to be one ‘silver bullet’ that can solve any single introduced species problem. Control of alien species needs to be part of an overall river rehabilitation process.