Central Australia has largely avoided many of the typical impacts to aquatic ecosystems experienced elsewhere, ie, no dams are present, although they are still occasionally proposed. This is probably as a result of central Australia's isolation and very low population density. Despite this, numerous impacts threaten the integrity of central Australia's unique aquatic ecosystems.
A total of eight exotic and translocated species have been recorded from central Australia. This includes the recent translocation of three native fish, Murray cod, Murray-Darling golden perch, and silver perch either by local landholders or government agencies for angling purposes. Five exotic species, damnbusia, swordtails, one spot livebearers, goldfish, and carp have been recorded. Only three exotics are still present; damnbusia, goldfish, and carp. The impacts of exotic fishes have been low, primarily because natural flow regimes have been maintained and the area is naturally variable with few permanent habitats. This could easily change if a predatory species adapted to this environment is released. While no impacts have yet been shown for translocated native fish, the potential for disaster through hybridisation with congeners is very serious. Two of the translocated species have closely related species in central Australia. If hybridisation occurs between local and translocated stocks, this could weaken the fitness of unique locally adapted stocks. This could lead to a decrease in native fish populations and an irreplaceable genetic loss.
Unfortunately, the isolation of this area allows considerable illegal fishing to continue largely undetected (primarily gill nets, although dynamite is still sometimes utilised). Many locals when they want fish, put a gill net out until they have caught sufficient numbers. Others, however, may take commercial quantities and transport them to interstate markets. Due to the low number of waterholes present during drought, this can cause a particularly severe reduction in year classes of fish susceptible to capture in gill nets.
Naturally, considerable sediment probably entered the system. However, this has most likely increased since the introduction of rabbits and the overstocking of livestock since the late 1800's. This is known to cause an overall loss in vegetation which increases soil erosion. While no direct impacts relating to this have been reported in Australia, it is likely to have caused some siltation to waterholes and changes to nutrient dynamics although, these rivers naturally carried large quantities of sediment.
Australia contains the largest populations of feral animals in the world including, goats, camels, horses and donkeys as well as domesticated sheep and cattle. Aside from causing soil erosion and the loss of vegetation they foul waterholes through their faeces or carcasses, which can make waterholes uninhabitable to fish (Pierce 1993). Because of the paucity of water, introduced herbivores congregate in the riparian zone and on floodplains; these areas are trampled and heavily overgrazed.
A commercial fishery was recently established at Lake Hope on the lower Cooper Creek for Lake Eyre golden perch. This was allowed on the basis that this was a temporary lake/waterhole which was isolated from the system and would inevitably dry out. This has not been shown to be accurate. If this practice were expanded to include other waterholes, fish populations could easily be decimated due to the limited number of refuges present. A key consideration is the role of ephemeral waterbodies in sustaining fish populations in an exceptionally variable system. To what extent do these populations rely on the rare recruitment opportunities provided by inundation of the outlying sites? What are the evolutionary implications of harvesting the colonising populations in these outliers? Unfortunately, no biological studies have been completed to ascertain the sustainability and management of these practices.
There have been numerous proposals in the past to dam several rivers and divert the water into the Murray-Darling system where water is used mainly for irrigation. Dams are also frequently proposed for flood control on the Todd River above Alice Springs. Fortunately all have been defeated so far. There are at present no catchment management arrangements for any rivers, and there is considerable resistance by the upstream state governments to consider the needs of water users downstream in South Australia.
Pierce, B. E. 1993. "Up the creek" South Australia's channel country and its major waterways. SAFISH Magazine. 17(4): 4-8. (previously published by the South Australian Fisheries Department)
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This file was last modified: 18 March 2003