Flora & Fauna
Early European explorers were very impressed by the richness and diversity of native animals across the Darling catchment, even though they had difficulty capturing and keeping specimens.
It took until the 1950s to realize the total diversity of animals along the Darling. In total, 113 species have been recorded in the catchment, 101 of these are native.
Marsupials are the dominant group with 50 species, but native rodents and bats are strongly represented. Only one species, the rare Pilliga Mouse, is restricted to the Darling catchment and is confined to a small area near the catchment’s eastern boundary (the Pilliga scrub).
The most common native animals include kangaroos, bandicoots, koalas, wallabies, betongs,
dunnarts, bilbys and possums. It also includes 19 species of native rodents, and 25 species of bats, flying foxes and dingos. The dingo is the only native carnivore occurring along the Darling.
At least 25 of the original 101 species of native animals have disappeared; eight are extinct. Most of these were small mammals susceptible to degradation of habitat and the introduced animals.
The 12 introduced animals are all regarded as pests. Rats, foxes, cats, rabbits, horses, donkeys, camels, deer, pigs and goats were introduced by European settlers for various reasons. Camels were commonly used for transport around Broken Hill, Bourke and Wilcannia, and were part of the Burke and Wills expedition that travelled through Menindee in 1860. Donkeys were used as pack animals and on pastoral stations until the early 20th century. Most introduced animals have extensive but patchy distribution along the Darling and numbers now depend very much on climate and food sources.
Rabbits arrived in the 1880s and resulting plagues contributed to broad-scale depletion of native grasses, shrubs and trees. Rabbit populations were decimated in the late-1950s by myxomatosis and again in the 1990s by calicivirus. By 2001, rabbit numbers appeared to be at their lowest along the Darling for several decades.
There are several threats to native animals along the Darling. Sheep and cattle have reduced vegetation cover and food for native animals; wind erosion has destroyed burrows; the removal of trees impacted on tree-dwelling species such as koalas and gliders. It is likely that in the next 50 years, remnant colonies of possums, gliders and bats that depend on tree hollows for shelter may disappear as older and mature trees are not replaced.
Foxes and feral cats have had a significant impact on small and medium-sized native animals. Bounties offered on wallabies and kangaroos since the 1880s and poisoning to control rabbits have also reduced native animal populations. While some animals will thrive in the modified environments along the Darling, introduced and feral animals are key threats and will need to be addressed if declines in native animal numbers are to be reversed. Innovative solutions may also be required, such as commercial use of kangaroos and commercial tree production.
Reptiles and frogs have always been important to people along the Darling. However, there has been relatively little research on reptiles and amphibians and this lack of information hampers their effective management.
Reptiles and frogs inhabit all parts of the Darling catchment and 241 species have been recorded. Many are true arid or semi-arid specialists which are also widely distributed across central Australia. Each species is well adapted to the climate and landscape, but the many changes brought about by human occupation and modification are putting pressure on these animals.
Limited understanding of the species and their environments make it difficult to predict the future impact of these changes.
WATER BIRDS AND WETLANDS
The Darling catchment contains both permanent and ephemeral wetlands. Wetlands are the ‘hot spots’ of biodiversity on a river system and include features such as billabongs, clay pans, floodplains, lakes, lagoons, marshes and swamps. However, some wetlands have also been created by artificial water storages and watering points.
Most wetlands rely on water delivered by rivers or creeks. Changes to river flows fundamentally affect their ecology. Wetlands are the ‘hot spots’ of biodiversity along rivers and are sometimes described as the ‘kidneys’ of river systems. They remove sediment from water; improve water quality; and slow floods down. They provide valuable breeding sites and food sources for thousands of plants, animals, reptiles, birds and fish. Without wetlands along the Darling, there would be fewer of plants, animals, reptiles, birds and fish.
There are nearly 20 spectacular wetlands within the Darling catchment. Some, like the Macquarie Marshes, cover extensive areas, others are small and less well-known. However, regardless of their size, these wetlands literally teem with life during wet periods. The Macquarie Marshes have been listed as RAMSAR wetlands and are wetlands of international significance.
Sadly, our current knowledge of how wetlands work and their value is limited. However, one aspect that has been reasonably well-studied are water birds. About 20 percent of Australia’s birds are water birds and many of these can be seen on the wetlands and waters of the Darling River. They include pelicans, cormorants, darters and grebes. There are small wading birds such as sandpipers and ducks, and large wading birds such as ibis, brolgas, herons and egrets.
Water bird species and numbers depend on particular wetlands and what is happening to wetlands elsewhere. For example, the presence of Black-tailed native hens on a wetland along the Paroo River may depend on what is happening on Cooper Creek further to the west.
Wetlands and water birds need water. The most important issue for their conservation is the impact of river regulations and diversion of water for human and economic use. While most wetlands receive too little water, a small number receive too much. The most obvious along the Darling are the Menindee Lakes. This area would have originally supported many species of water birds but now mainly supports only fish-eating birds. Many aquatic plants do not establish in such wetlands, reducing the feeding habits for Black swans and herbivorous waterbirds.
Fortunately, a few wetlands in the Darling catchment remain unaffected by river regulation and diversion. These include the wetlands of the Paroo and Warrego rivers that still maintain their status as free-flowing rivers.
As well as droughts and river regulation, there are other threats to wetlands. These include livestock, pollutants, feral plants and animals, weeds, levees and roads and lakebed and floodplain cropping.
The Darling River contains 30 fish species including seven alien (introduced) species The fish species are similar to those of the southern rivers of the Murray-Darling Basin.
Fish were an important food for Aboriginal communities along the Darling and were used not just for daily food, but for large celebrations. Aboriginal people caught fish with nets and poison, by hand, with spears and hooks, and in stone traps. The Brewarrina fish traps are the best remaining example of these stone fish traps.
The relative abundance of native fish in the Darling River is different in several ways to other rivers in the immediate area. Native species such as Western carp gudgeon, Bony herring and Golden perch, and alien species such as carp, goldfish and redfin are more common in the Darling than in the Murray.
Another unusual feature of Darling River fish is that the number of species decreases as you move downstream. This pattern also occurs in the Paroo and Warrego rivers. This happens because the river flow in the Darling is reduced downstream of Bourke, whereas in other river systems, river flows increase in downstream reaches. As a result, the lower Darling contains fewer fish species than might be expected.
It also appears that fish along the Darling have adapted to a wider range of variable living conditions and have not developed the strong habitat relationships characteristic of more predictable river systems such as the Murray River. It is important to note however, that 23 native fish species in the Darling is fairly typical of similar size rivers flowing through semi-arid regions elsewhere in the world.
Native fish species include the large and more well-known species such as Murray cod, Golden perch and Bony herring. However the smaller but less well-known native fish are just as important and include Western carp gudgeon, Purple spotted gudgeon, Rainbow fish and Olive perchlet.
The Darling River offers various habitats for native fish, providing food, shelter from predators, breeding sites and migration corridors that all fish need at different stages of their life cycles. River flows play a vital role in the ecology of these fish. The flows create habitat, and determine when fish move out of the main channel onto floodplains to breed. Flow is also critical in supplying nutrients that in turn support food for native fish.
Weirs along the Darling can disrupt flow patterns for many kilometres upstream, reducing habitats and creating conditions that are more favourable to alien fish. Weirs are also barriers o fish movement. Most native fish need to migrate at various stages of their life cycle, but mainly for spawning. Golden perch and Murray cod have been recorded as travelling very large distances along the Darling. However, such movement can be disrupted by weirs.
Although none of the original fish species in the Darling River are known to be extinct, six are under threat. Murray hardyhead and Trout cod are classified as endangered; Silver perch, Darling River hardyhead and Murray jollytail are vulnerable; the Purple-spotted gudgeon is in a low risk category. Two other species of concern are Hyrtl’s tandan (a small catfish recorded in the Paroo and Warrego rivers and Menindee Lakes), and the Dwarf flathead gudgeon.
Despite the changes that have occurred since white settlement, some fish species along the Darling are present in relatively large numbers and do not appear to have experienced population declines.
There are a number of current threats to native fish, including changed river flows; cold water pollution; fishing; barriers to migration (weirs, culverts and levee banks); pesticides; loss of habitat; impact of alien fish; and land use. Fewer floods along the Darling and the alienation of floodplains from the main river artery has had a detrimental affect by preventing fish getting into wetlands to breed, and by reducing the amount of nutrients and food in the river.
Recreational fishing is a popular sport and pastime on the Darling River. Murray cod and Golden perch are the most popular fish.
There is increasing interest in improving populations and habitats for native fish. This is reflected in the establishment of native fish demonstration reaches between Bourke and Brewarrina, and at Wilcannia. A new fish ladder has been built at Burtundy Weir between Pooncarie and Wentworth, and there are plans for other fish ladders at weirs along the Darling River. These projects have been funded through catchment management authorities (CMAs), the Department of Primary Industries, and the Murray-Darling Basin Authority (as part of its 50-year Native Fish Strategy).
The fish resources of the Darling River are not as degraded as those in the Murray River and other Murray-Darling Basin waterways. Providing threats to native fish can be addressed, fish will retain their valued position in the cultural heritage of Darling River communities.