I recently obtained an explosive document which reveals that introduced fish species such as carp and trout have been a major cause of native fish extinctions in the Murray Darling Basin (MDB).

The document is explosive because it makes it plain that the Government’s attempts to create ‘healthy working rivers’ in the MDB, of which Western NSW is an integralpart, will fail if the Government’s strategy is too simply take productive water away from communities.

The Ministerial Advice from the Commonwealth Government’s Threatened Species Scientific Committee calling on the Government to list introduced fish as a key threatening process under the EPB&C Act was rejected on the 11/11/11 by the Federal Environment and Water Minister , Tony Burke. The document does not say why.

The Ministerial advice states that; ‘In Australia, 43 non -native freshwater fish species occur in the wild, and of these, 34 have established populations. Five of the species established in Australia were nominated by the International Union for Conservation of Nature (IUCN) as among the world’s 100 most invasive species. These are: carp, Mozambique tilapia, eastern gambusia, rainbow trout and brown trout.’

The Ministerial Advice makes it very clear that introduced fish have caused the local extinctions of some native fish and are continuing to threaten native fish and frog populations through predation, disease, habitat loss and competition for food

In the Macquarie Valley, the Ministerial Advice highlights the devastating impact that introduced fish like carp are having on native fish, particularly the Silver Perch.

Carp are causing considerable damage to the health and water quality of creeks and rivers in the Macquarie Valley. A female carp can lay one million eggs in a breeding season and can reach sexual maturity at twelve months. Over their natural range, carp live up to 15 years, with reports of individuals living up to 24 years. Males live longer than females.

The Ministerial Advice highlights; ‘The introduction of diseases and parasites through introduced native and non-native species may pose a significant threat to local fish populations. Live aquarium fish are the greatest risk group for introducing aquatic animal diseases in Australia. (A review in 2008) showed that 21 ornamental fish species harboured disease agents alien to Australia.

Key examples of this include:

  • Aquarium fish led to the spread of the goldfish ulcer disease that was introduced via infected goldfish, and which subsequently spread to native fish.
  • Lernaea is an introduced parasite that burrows into the fins of infected fish, or in finely-scaled species, into the skin itself. Carp and introduced trout are effective vectors of the parasite. Lernaea infestations are often fatal for native fish species.
  • Introduced redfin perch are the main host for Australia’s first recorded finfish virus. EHNV is highly pathogenic to a number of native species, including Macquarie perch, mountain galaxias and silver perch.

The advice to the Minister points out native fish and frog numbers will continue to decline unless action is taken to address the impact of introduced fish species.

In its current form, the Murray Darling Draft Basin Plan is half pregnant, and is setting up the Commonwealth Environmental Water Holder to fail miserably in its key task of delivering a ‘healthy river system’.

The Draft Basin Plan offers no solutions to problems of invasive fish species, riparian vegetation, urban pollution, or cold-water pollution.

Just adding water is not a solution to a complex web of environmental problems in the basin and complementary Natural Resource Management action is critical.

The Sustainable Rivers Audit (used by Governments to rate the health of 23 River Valleys in the MBD) shows the hydrology of eighteen of the twenty -three Valleys is rated as moderate to good, or good.

The Audit says it confirms the well-known decline of native fish in the Basin, and states; ‘common carp were overwhelmingly dominant, being 58% of total fish biomass’ across the 23 valleys, as a result, fish health in 20 of the valleys rates extremely poor –poor.

The Government’s own expert body on feral pests, the Invasive Animals CRC, is warning carp numbers in the Lower Darling have already exploded by 4000 percent in the past year.

Communities in western NSW are getting short changed in the current round of water reforms. Without access to water, communities have no hope. To date the Government has failed miserably to clearly enunciate what it believes it is trying to achieve by simply returning water to the environment.

Unless the Government broadens its efforts beyond simply removing productive water from communities, carp and trout will continue to decimate our native fish and frog population and a healthier river system will remain an impossible dream.