Simply adding water is not the solution to the complex environmental issues facing the Murray Darling Basin.
With limited resources available our focus must shift from the simplistic approach of removing water from productive use, which is not delivering the environmental outcomes sort but is turning once thriving communities into ghost towns, to adopting complementary measures which deliver real environmental outcomes.
If complementary measures, such as those listed below, are not adopted many of the environmental outcomes being sort under the Basin Plan will never eventuate.
a) Carp control through the release of the Carp Herpes virus
Carp make up around 80% of the fish biomass in the Murray Darling Basin, and cost up to $500 million annually. Studies have demonstrated that Carp impact on water quality, plankton levels, algal bloom incidence, native fish, macrophytes and water birds.
Research has shown that a carp specific virus known as Cyprinid herpesvirus 3 is highly effective on carp present in Australia. International case studies indicate the virus will kill 70-100% of carp in a naïve population within a very short time. The virus also has been shown to only affect Common carp and Koi carp (same species), thought will not cause disease in other fish species, birds, reptiles, amphibians, mammals or crustacea.
Environmental flows deliver benefits to some desirable ecosystem components, but are well known to increase carp breeding efficacy if delivered onto floodplain habitat during warmer months.
The Australian Government have announced a $15 million investment, in order to undertake the necessary work to develop a plan to release a carp-specific herpes virus into waterways.
In order to ensure that carp numbers do not rebuild after release it will be necessary to employ additional measures to suppress carp and promote recovery of native fish communities. Carp impact significantly on aquatic ecosystems, but are not the only factor contributing to the decline of native species. Additional threats include:
- Degradation of habitat and water quality;
- Historical overfishing;
- Thermal pollution; and
- Barriers to migration
Significant social and economic benefit derived from improved inland fish resources are likely to occur as a result of this single measure.
To ensure the legacy of outcomes delivered through the carp biocontrol program, and environmental flow delivery it is recommended that a program of complimentary measures be employed to promote recovery of native fish recovery, including:
- Re-establish populations of locally extinct native fish species through re-stocking following carp removal
- Mitigation of cold water pollution at four priority dams
- Restoration of native fish habitat along river reaches within priority river valleys throughout the MD Basin
- e-connect fish migration along the full length of the Barwon Darling River system in the northern MD Basin.
b) appropriate management of cold water pollution
The importance of water temperature for breeding, feeding, growth and larval survival in native fish species has been well understood now for over a decade, as is the impact of cold water pollution on aquatic organisms and river health in the Murray Darling Basin. A recent study noted that mortality levels in Murray cod eggs can reach 100% at 13 degrees Celsius, and that low water temperatures can dramatically reduce growth rates in species including Freshwater catfish and Murray cod, and can cause up to 30% mortality in Silver perch. All of these species are listed under either national or state environmental legislation. Over 2700km of riverine environment is now understood to be affected by thermal pollution in the Murray-Darling Basin.
Fortunately, off-the-shelf solutions such as installation of a thermal curtain as done in Lake Burrendong, have been shown to rapidly correct thermal pollution and are cost effective.
c) improvement of fish migration through fishways along the Barwon-Darling
Many native fish species are now known to migrate during various life stages, and barriers to migration are now listed as a key threatening process in state and Commonwealth threatened species legislation.
Reinstatement of fish passage at 13 barriers in the main stem Darling, Barwon, Paroo and Warrego Rivers would reinstate continuous access to over 5180 km of river system. This outcome would exceed the Sea to Hume program, which is lauded as one of the largest ecological rehabilitation projects undertaken in Australia.
d) restoration of native fish habitat
Healthy habitat is vital to the health of native fish communities. Numerous studies throughout Australia have demonstrated the value of restoring fish habitat for native fish communities. In the Condamine River, habitat improvement along the Dewfish Demonstration Reach resulted in significant increases in Golden perch (5 x increase), Murray cod (from absent to captured every survey), Spangled perch, Bony bream (11 x increase), Carp gudgeon (1200 x increase), and Murray-Darling Rainbowfish (60 x increase).
Re-snagging in the lower Murray resulted in a threefold increase in Murray cod, and was estimated to significantly increase overall population size
e) feral animal control in wetlands such as the Narran Lakes, Gwydir Wetlands and Macquarie Marshes.
Feral pigs are one of Australia’s most successful and widespread invasive species. Their success is largely due to their omnivorous diet, comprising mostly green grasses and herbs. They also eat a variety of native vertebrate species including reptiles, amphibians, birds and mammals.
Feral pigs have occurred in the Macquarie Marshes since 1896. Important wildlife species that may be susceptible to predation by feral pigs also occur in the marshes, including snipe, stork and ibis. Studies undertaken on the stomach content of feral pigs in the Macquarie Marshes show that feral pig diet includes grasses, roots, ferns, fruits, crops, frogs, lizards, snakes, turtles, birds, mammals, invertebrates and carrion. Five different vertebrate species were found including eastern bearded dragon, barking mash frog, green tree frog, spotted marsh frog and De Vis banded snake.
In recent years’ pig populations in the Gwydir and Macquarie Marshes have exploded. Partly due to the delivery of environmental water to wetland areas during dry-sequences, which is believed to be providing beneficial opportunity for feral animals to survive during drought.
Weeds are well known as a significant threat to Australia's natural environment and primary production industries. They displace native species, contribute significantly to land degradation, and reduce farm productivity. Aquatic weeds continue to spread through flooding, moving the plants to other waterways. Many aquatic weeds have been introduced or have colonised new waterways.
Invasive species, including weeds, animal pests and diseases, represent the biggest threat to biodiversity after habitat loss. Weed invasions change the natural diversity and balance of ecological communities, threatening the survival of many plants and animals as the weeds compete with native plants for space, nutrients and sunlight.