Published: 11 January 2012

Northern Australia’s disappearing native mammals

John Woinarski

The Northern Australian landscape is a spectacular, vast and wild place. It is a land of crocodiles, dingoes and endless bush. It forms a refuge for many wildlife species that have disappeared or declined in other parts of the continent, such as bush stone-curlews and nailtail wallabies.

Paperbark forest in the wet season, Kakadu National Park: in the ten years from 2001–11, native mammal populations in the park have dropped by 75 per cent.

Credit: Sally Greenaway/Parks Australia

Much of the landscape is still managed as it has been for tens of thousands of years by Indigenous landowners. The environment seems little changed since European settlement, and has few human inhabitants.

But look more closely, and a different picture emerges. A series of recent studies I’ve been involved with – along with researchers from the Northern Territory Department of Natural Resources Environment the Arts and Science, and Charles Darwin University – have revealed that some key areas in the North are fast losing species.

Much of the work has been concentrated in Kakadu National Park. Since 2001, we have been surveying 136 sites across the park. Over that time, mammal populations have dropped by an average of 75 per cent. The number of sites classified as ‘empty’ of mammal activity increased from 13 per cent in 1996 to 55 per cent in 2009. Similar declines have occurred in many other areas of Northern Australia.

Let me give you one example. Australia was once home to three species of rabbit-rats (Conilurus species). These are elegant docile rodents, much like guinea-pigs, but with long, beautiful, tufted tails – very sweet-looking creatures. Most Australians would never have heard of them, let alone seen them.

Their fate is symptomatic. One species, from north-eastern Australia, disappeared without ever having been recorded as a living animal in the scientific record. Its existence is known only from remains in owl pellets and from subfossils¹ that have been dated to as recent as the last century. Another species, from south-eastern Australia, became extinct very soon after the arrival of livestock, cats and foxes.

Given the comparative lack of environmental modification in Northern Australia, we may have thought the third, and sole surviving, species – the brush-tailed rabbit-rat, which occurs across the north of the continent – to be secure. It turns out this presumption is false. During the period of my research, the species has disappeared from many areas: including, it seems, its previous stronghold in Kakadu National Park.

The sole surviving rabbit-rat species, the brush-tailed rabbit rat, Conilurus peniccilatus, is disappearing at an alarming rate.

Credit: Kym Brennan

It seems as if we are witnessing in Northern Australia the wave of extinctions that previously occurred elsewhere on this continent. It’s a frightening prospect: one that will likely deprive Australia of some important elements of its natural heritage and erode the area’s integrity.

I’ve been working with researchers from the Australian Wildlife Conservancy, the Western Australian Department of Environment and Conservation and CSIRO to describe the geographic pattern and rate of this decline and to understand its causes, so that we can attempt to manage these factors.

Our research indicates that parts of the rugged north Kimberley and some islands seem to have retained their mammal fauna. The decline of species elsewhere may be due to a complex mix of fire, feral cats, pastoralism and cane toads, with the first two factors the most important.

In an important recent advance, we have manipulated fire, cat predation levels and cattle densities to tease out the relative impacts of these factors. In this way, management can be most efficiently directed to the most effective action. These large-scale experiments are being supported by the Australian Research Council, the National Environmental Research Program, Kakadu National Park and the Kimberley Science and Conservation Strategy.

In Northern Australia, we have the rare luxury and responsibility – denied to us in many other parts of Australia – of attempting to maintain an intact natural environment, to retain those wildlife species that have existed in this country for hundreds of thousands or millions of years. This is an opportunity we must not squander. It is a test of our capacity as researchers – and of our capabilities as environmental managers – to accurately read and understand landscapes, and give those species under our stewardship the best chance of escaping extinction.

Dr John Woinarski is an internationally recognised researcher in the field of biodiversity. His focus includes threatened species, biogeographic patterning of plants and animals, and the impacts on biodiversity of land use changes and other potential threats. He has developed effective wildlife survey protocols that are now employed as standard practice within the Northern Territory and elsewhere in northern Australia. Dr Woinarski has applied his knowledge to conservation planning, and design and implementation of conservation actions collaboratively with Aboriginal landowners and pastoralists. He is currently writing a book on Australia’s most recent mammal extinction – the Christmas Island pipistrelle.

¹ Remains that have not been fully fossilised and still contain organic material.

Published: 11 January 2012

Managing the future of the north’s aquatic biodiversity

Bradley J. Pusey

Northern Australia features prominently in visions for Australia’s future. Plans for capturing, storing and transporting the region’s water to make it available for increased agricultural development in the region and elsewhere are frequently proposed. But what is our current understanding of the biodiversity, and the ecological functions and services and of the northern region, and how might these assets be affected by such development?

A comb-crested Jacana, one of the 30 per cent of the nation’s waterbird species that are recorded in the northern region.

Credit: With permission of MV Jackson

The recently published book, Aquatic Biodiversity in Northern Australia: patterns, threats and future, by the Tropical Rivers and Coastal Knowledge (TRaCK) research consortium, examines the biodiversity of northern Australia’s freshwater ecosystems, its dependency on the natural water regime and how increased water use might be managed to avoid future degradation of the region’s sensitive ecology.

TRaCK is comprised of leading tropical river researchers from five Australian Universities (Charles Darwin University, University of Western Australia, Griffith University, Australian National University and James Cook University), federal research organisations (Geoscience Australia, eriss, AIMS, CSIRO), State governments of Queensland, Western Australia and the Northern Territory, and the Northern Australian Indigenous Land and Sea Management Alliance (NAILSMA). More than 30 researchers from TRaCK contributed to the book.

Northern Australian freshwater ecosystems sustain a very rich and distinctive biodiversity. Although it comprises only 17 per cent of the continent’s land area, the region contains a large proportion of the nation’s aquatic plants and animals.

For example, waterbird diversity accounts for about 30 per cent of the nation’s waterbird species, whereas freshwater fish account for almost 60 per cent. A third of the nation’s frog species, and half the turtle species, are also found in northern Australia, as are many water dependent lizards, snakes and of course, crocodiles.

A graphic flutterer (<i>Rhyothemis graphiptera</i>).

A graphic flutterer (Rhyothemis graphiptera).

Credit: With permission of J Clark

Such high biodiversity is perhaps not surprising as the region’s freshwater ecosystems sit within a savanna landscape of globally significant ecological integrity¹.

Moreover, northern Australia contains the highest concentration of free-flowing rivers in the world². Consequently, the biological systems of northern Australia’s swamp, wetlands and rivers remain relatively pristine and capable of supporting such biodiversity riches. Importantly, the connectivity of different parts of the riverine landscape (for example, headwaters, main channels, floodplains and estuaries) and between the riverine and near-shore marine environment, remains largely intact across the region, allowing the free passage of organisms, nutrients, carbon and energy necessary to sustain high biodiversity.

A view across the majestic Hann River in the Fitzroy River catchment (Western Australia).

Credit: TRaCK

“Hot-spots” of biodiversity vary between taxanomic groups, making effective conservation and protection measures difficult. The national reserve system currently does not adequately cover the distribution of all aquatic biota. For example, up to 80 per cent of all species examined had less than 5 per cent of their total distribution contained within existing protected areas.

Also of significance is the high rainfall of the region – more than 1 million gigalitres per year! This means that the area’s rivers transport huge volumes of water. The Mitchell River in Queensland, for example, conveys an average of 24 000 megalitres a day, more than any other river in Australia.

Such high flows and abundant rainfall also mean a great diversity of aquatic ecosystem types, across a huge area. For example, floodplain wetlands are so vast that they may cover about 25 per cent of the catchment area of some basins. They are hotspots of biological production which is later transported widely throughout river systems and is, therefore, of enormous ecological, cultural and economic significance.

Measuring fish during fish surveys on the Daly River, Northern Territory.

Credit: TRaCK

However, despite the huge amount of rainfall, it is highly seasonal and often unpredictable in incidence and volume. Most of northern Australia incurs an annual water deficit (rainfall minus evapotranspiration) of about 1000mm. This places extreme pressure on the region’s biota and greatly limits production. Most rivers cease to flow, often for periods of up to nine months, and contract back to series of isolated refugial waterholes. Such large contractions in available aquatic habitat constrain the development and maintenance of high biodiversity.

In intermittent rivers (the dominant river type across the region), aquatic species are either forced to retreat to these refuges, which become increasingly less hospitable as the dry season progresses, or seek shelter underground. Refugial waterholes often persist only when in contact with shallow groundwater.

A prawn shell on cracking clay, Fitzroy River, Northern Territory. The northern region is characterised, and tested, by extremes of wet and dry.

Credit: TRaCK

Groundwater is also critical in sustaining high levels of biodiversity in larger rivers. For example, the highest levels of fish biodiversity are found only in those rivers that have perennial flow sustained by groundwater contributions during the dry season (for example the. Daly, Mitchell, Wenlock and Jardine rivers).

Groundwater resources have been identified as suitable for development and exploitation in order to support agricultural expansion. The 2009 Northern Australia Land and Water Science Review³ suggested that further development of agriculture in northern Australia would most likely be of a mosaic style, where agriculture would be confined to areas defined by the coincidence of suitable soils and exploitable groundwater.

A helicopter being used by TraCK researchers to rapidly collect water samples from a remote area of the Fitzroy River, Western Australia

Credit: TRaCK

Such a development option is less likely to have negative impacts on freshwater biodiversity than broad-scale agriculture and large-scale water capture and diversion schemes, which are sometimes proposed.

A greater focus on sustainable use of resources and a greater appreciation of the values of aquatic biodiversity from economic, cultural and spiritual perspectives suggest that alternative visions for the future of northern Australia are gaining traction. These visions recognise that the economic value from commercial fishing, recreational fishing and tourism more generally, is significant.

Similarly, the substantial dependence of Indigenous household economies on riverine production (for example fish, crustaceans, and birds etc. are used for food), represents another, significant form of economic value.

Combined with the central cultural and spiritual importance of the region for Indigenous peoples (about 60 per cent of the population), this multiplicity of values require that the maintenance of healthy aquatic ecosystems and the rich and productive biodiversity they sustain is key to a sustainable future for the north.

Horticultural development on the Daly River, Northern Territory.

Credit: TRaCK

A set of guiding principles for improved management of aquatic biodiversity was proposed by the book’s authors. These are:

Prioritise and protect high value aquatic ecosystems;
Address current threats;
Explore development options and their consequences carefully;
Improve planning processes to secure environmental water allocations;
Improve the available information base; and
Improve public awareness and engagement.

Although visions of the future are useful, a clear focus on the present is critical. Aquatic systems across the north are currently threatened by feral animals (including pigs, buffalo, and alien fishes), weeds, altered fire regimes and a range of other diffuse pressures including resources extraction. We need to urgently and efficiently develop counter measures to these immediate threats to limit further and potentially widespread degradation of the region’s unique riches, and to ensure its broader values and future are assured.

Bradley J. Pusey is a researcher at the Tropical Rivers and Coastal Knowledge (TRaCK) research consortium, and editor of Aquatic Biodiversity of Northern Australia: patterns, threats and future. 2011. Charles Darwin University Press, Darwin.

¹ Woinarski J, Mackey B, Nix H, and Traill B. 2007. The Nature of Northern Australia: Natural Values, Ecological Processes and Future Prospects, ANU E Press, Canberra.
² Vörösmarty C J, McIntyre P, Gessner M, Dudgeon D, Prusevich A, Green P, Glidden S, Bunn S E, Sullivan C, Reidy C, and Davies P M (2010). Global threats to human water security and river biodiversity. Nature 467:555–561.
³ Stone P. (2009). Northern Australia Land and Water Science Review. Final report to the Northern Australia Land and Water Taskforce, CSIRO Publishing, Canberra.

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