State of the Environment Report 2007
Many terms are used to describe introduced and native animals (Table B3.1). There are many types of animals introduced in WA, including different groups - birds, mammals, reptiles, amphibians, fish, crustaceans, molluscs, worms and insects.
Introduced animals that become established in Australia generally have a number of characteristics that allow them to survive and spread. These include having a similar climate between their native geographic range and their introduced location, a history of establishing invasive populations elsewhere in the world, a high reproductive rate, a generalist diet and an ability to live in modified landscapes (Hart & Bomford, 2006).
Introduced animals cause environmental impacts because natural ecological constraints on them (such as predation, competition from other species, diseases and parasites) are often absent. If not adequately managed or quarantined, introduced animals have the potential to escape into the environment and breed if environmental conditions are favourable. Many are an environmental problem because they can compete with native animals for food and habitat; predate on native animals; destroy or degrade habitats; overgraze; carry and spread harmful diseases and parasites; and can inter-breed with native species producing hybrid animals. Some introduced animals are considered problems for human health (e.g. they carry diseases or are toxic) and some are considered pests to the agricultural, pastoral, plantation and construction industries.
There is limited data for introduced animals in WA, but reliable information exists for introduced mammals at a large scale (Figure B3.1). The highly populated areas of the Swan Coastal Plain have the most introduced mammals, while forested areas of the South West, the northern agricultural area, the Gascoyne-Murchison, the Carnarvon basin and the Pilbara also have a high count of introduced mammals. There is corresponding evidence that native mammals have undergone significant range contractions (especially the Carnarvon Basin and the Jarrah Forest bioregions), and significantly reduced native mammal diversity in arid and semi-arid regions (especially Yalgoo and Nullarbor bioregions) (Commonwealth of Australia, 2002). There are comparatively fewer introduced mammal species in the central deserts and Kimberley, where climatic factors and remoteness may help limit the spread of introduced mammals. There are no bioregions in WA with less than four identified introduced mammals.
![Figure B3.1: Number of introduced mammal species found in each terrestrial bioregion. [Data source: Department of Conservation and Land Management [ver. 2005]. Analysis: Department of Conservation and Land Management. Presentation: EPA.]](/site/files/images/Figure-B3.1_Large.jpg)
Some surveys for agricultural and pastoral animal pests have been undertaken to determine the approximate distribution and density across WA (Figure B3.2). The effects of introduced herbivores in the rangelands are often associated with overgrazing and land degradation. Large herbivores in particular (especially camels, horses and donkeys) have serious detrimental effects in arid and semi-arid environments (causing soil erosion, disturbing wetlands, eating vegetation). It was estimated that there were 238 000 feral camels in WA in 2005 (Ward et al., 2005). The density of camels was about 5 times higher in desert regions than in the pastoral zone in inland WA (0.23/km2 compared to 0.05/km2) (Ward et al., 2005). Camel densities in the Little Sandy Desert region were an average of 0.26/km2, with lower densities at an adjoining pastoral station (Ward et al., 2006). The camel population of central Australia is thought to be increasing at approximately 10% per year and doubling every eight years (Edwards et al., 2004). The number of donkeys in the Kimberley was very high in the past, but control measures have now reduced the population to near eradication (Department of Agriculture and Food, 2006b). The number of donkeys in the Pilbara and desert regions remains of concern.
Goats are most abundant in the Mid West and are causing considerable environmental damage, especially as they are becoming popular as livestock in this area. Surveys in 1987 and 1990 showed that goat populations were increasing by 18% per annum in WA even though commercial harvesting was occurring (Southwell & Pickles, 1993). Wild pigs are a problem in the South West forested areas, near Geraldton, and are particularly abundant and increasing in the Kimberley. At present, no control program for pigs is currently in place in the Kimberley although pigs are culled opportunistically in areas where the donkey eradication program is in progress (Department of Agriculture and Food, 2006b).There is evidence that they are being deliberately introduced to some areas to provide game for recreational shooters.
![Figure B3.2: Level of impact on native ecosystems of selected introduced animals by bioregion. [Data source: Woolnough et al. (2005). Presentation: EPA.]](/site/files/images/Figure-B3.2_Large.jpg)
Some introduced animals are relatively restricted in range and have limited effect on native species. For example, the Indian palm squirrel was introduced to Perth Zoo in 1898 and has gradually spread to South Perth and surrounding suburbs, but is not known to affect native species (M Massam, Department of Agriculture and Food, pers. comm.). However, others are ubiquitous and immensely damaging. For example, house mice have spread in agricultural and bushland areas, competing with native rodents and birds for food sources and nesting areas, and potentially transmitting diseases.
The decline in populations and extinction of small and medium-sized mammals has been attributed to predation by cats and foxes, the introduction of herbivores (especially rabbits, sheep and cattle) and changed fire regimes (Maxwell et al., 1996). Research shows that foxes have the highest triple bottom line impact (negative economic, environmental and social consequences) in the agricultural region, while cats have the greatest environmental impacts (Woolnough et al., 2005). Feral pigs and cats were key species thought to have increased in distribution and abundance in the agricultural region between 2000 and 2005. In the pastoral region, there have been reports of an increase in distribution and abundance of wild dogs (however these are indistinguishable from dingoes), leading to increased control efforts. The population of rabbits in the rangelands has declined in recent years as a result of the spread of rabbit haemorrhagic disease (Edwards et al., 2004). Feral cats are widely distributed across WA and predate on a wide variety of native animals.
Other groups of animals have not been as well studied as mammals, but it is likely that many other species are affected by introduced animals. For example, there has been a loss of ant biodiversity in the Perth metropolitan area over the last 15 years, and there is circumstantial evidence that this is due to increased populations of two invasive ant species, namely the coastal brown ant (Pheidole megacephala) and the Argentine ant (Linepithema humile) (Heterick et al., 2000). The distribution of these species is known to have changed and increased over time, but has not been re-mapped since 1986 (Figure B3.3).
Island populations of native species are at particularly high risk from introduced animals as they are usually small in size, have limited options to escape predators, and have few alternatives in the face of direct competition for resources.
![Figure B3.3: Distribution of coastal brown and Argentine ants in metropolitan Perth. [Data source: Majer & Brown (1986). Presentation: EPA. Note: Distributions in 1986 are shown here, however, it is likely that both species have increased their range since then.]](/site/files/images/Figure-B3.3_Large.jpg)
The pressures exerted by introduced animals differ according to geographical area, population density and interactions with other species. The presence of an introduced animal represents a threat to local biodiversity and can cause a number of environmental impacts (Table B3.2). The Global Invasive Species Database has compiled a list of 100 of the worst invasive species from across the world. Many are present in WA (Table B3.2). The list is compiled to recognise species that have shown very high invasive ability in various places around the world, either demonstrating a very high impact in small areas (such as islands) or less visible damage over a large area. These species tend to be well adapted to living close to humans or in human-modified environments. Some introduced animals have been recognised by the State agencies as posing a risk to agricultural or fisheries production, and have been restricted from entry or movement within WA.
Many potential invaders are known and represent a significant risk to the State's environment if they become established here (e.g. cane toads, Indian mynas, starlings, red-eared slider turtles and red imported fire ants) (Table B3.3). All of these animals have been recognised for their invasive potential in other parts of the world and are listed as being the world's 100 worst invasive species. In addition, most have also been recognised under State legislation and are prevented from entry into WA.
![Table B3.3: Animals that represent a high risk to biodiversity in WA. [Data source: numerous papers and websites; Global Invasive Species Database (2007); Department of Agriculture and Food (2006a); Note – In WA species can be declared under the Agriculture and Related Resources Protection Act 1976 – there are a variety of categories including entry prohibited, subject to eradication in the wild, keeping prohibited, entry subject to Departmental permits or conditions, numbers will be reduced or controlled, keeping subject to Departmental permits or conditions and the requirement for a management program]](/site/files/images/Table-B3.3_Large.jpg)
Cane toads were deliberately introduced into north Queensland in 1935 in an unsuccessful attempt to control sugar cane beetles. Since then they have spread widely through Queensland, northern New South Wales and the Northern Territory. Cane toads eat a wide variety of prey items, breed opportunistically, are able to produce more offspring than native frogs, and develop rapidly in tropical conditions. They tolerate a broad range of environmental and climatic conditions, and occupy many different habitats where they compete for resources with native species. Most significantly, cane toads reproduce in high numbers and all life stages (from egg to adult) are highly toxic to native vertebrate predators (especially quolls, large lizards and freshwater crocodiles). Climate-based modelling of the potential distribution of cane toads across Australia (Figure B3.4) indicates that populations could migrate and establish in the Kimberley, and could survive if introduced to the South West (particularly in a warming climate). The current frontline of the cane toad advance is in the Victoria River area of the Northern Territory, approximately 120 kms from the WA border (Department of Environment and Conservation, 2006c). Recent data suggests that cane toads are moving about 55 kilometres per year towards the WA border due to evolving for competitive advantage, or entering an environment more favourable to spread (Phillips et al., 2007).
![Figure B3.4: Modelled potential geographic distribution of cane toads in Australia based on two climate scenarios: (a) long-term average climate; and (b) the 2030 climate change scenario. [Data source: Sutherst et al. (1995); Presentation: Sutherst et al. (1995). Note: The climatic suitability of each location for permanent colonisation is proportional to circle area.]](/site/files/images/Figure-B3.4_Large.jpg)
The red imported fire ant is a new addition to the list of invasive species in Australia, first detected in Brisbane in 2001. The ant is an aggressive predator and preys on ground-dwelling and nesting animals including insects, frogs, reptiles, birds and mammals (Moloney & Vanderwoude, 2002; Davis & Grimm, 2003); and can damage native flora (by eating it directly or reducing populations of beneficial animals). The ants have a dangerous sting that can cause severe pain and death of affected organisms, including humans. Introduction of the red imported fire ant to WA could cause significant economic loss through damage to plants (roots, fruits or crops), ingestion by livestock, and damage to underground cabling and pipes (Davis & Grimm, 2003). Modelling of the potential range of red imported fire ants in Australia (Figure B3.5) indicates that climatic conditions are suitable for spread along coastal parts of the Kimberley and South West, and further inland if water is available.
![Figure B3.5: Potential range of red imported fire ants in Australia with (a) natural rainfall and (b) irrigation. [Data source: Sutherst & Maywald (2005). Presentation: Sutherst & Maywald (2005).]](/site/files/images/Figure-B3.5_Large.jpg)
The hot desert climate of central Australia provides a natural barrier to the movement of many animals from the rest of Australia into the South West. In comparison, the Kimberley has less natural protection from other parts of northern Australia, with the wet season providing an opportunity for some animals to travel long distances between neighbouring wetlands and watercourses. Animals which successfully spread from their place of introduction to surrounding habitats are often disturbance specialists or prefer to live in human-modified landscapes. Transport networks also present many opportunities for the introduction of new species in cars or in freight transported by vehicles, aircraft, trains or ships. Quarantine and inspection services play an important role in preventing incursions into WA.
Preventing the entry of new animal species into WA and the early detection and eradication of incursions if they do occur is the first line of defence. If new incursions are discovered before they become established, eradication is possible. Eradication may not be possible for introduced animals that are widely distributed, so activities need to focus on controlling their spread. Control measures may include:
Although the task is far from complete, WA leads the other states in eradication of introduced animals on islands. Six exotic mammals (fox, feral cat, goat, rabbit, black rat and house mouse) have been eradicated from more than 45 islands in a series of projects since the 1960s (Burbidge & Morris, 2002). Effort has been directed at black rats, and more than 30 islands are now clear of this species, but eradication of other introduced species on islands is still required. Removal of introduced bird species (particularly tree and house sparrows, Indian mynas, house crows, Indian ringnecks and European starlings) has been successful - but repeat incursions still occur. Some vertebrates (whose numbers are too large for eradication) are confined to small areas of the State, largely through control activities of the Department of Agriculture and Food. These are typically species with potential for large population growth, such as the sulphur-crested cockatoo and Indian palm squirrel.
Quarantine: The role of the Australian Quarantine and Inspection Service is to prevent entry of introduced animals (as well as plants and pathogens) to Australia in incoming luggage, cargo and mail, or associated imported goods. The Western Australian Quarantine and Inspection Service (part of the Department of Agriculture and Food) aims to prevent pest and disease incursions from other parts of Australia. A system of risk assessment is now used to assess species proposed for import, to ensure that only those posing an insignificant level of risk are allowed to enter the State.
Legislation: The Agriculture and Related Resources Protection Act 1976 is administered by the Department of Agriculture and Food on behalf of the Agriculture Protection Board. The Act allows for management of listed (declared) animals in order to protect primary industries and related resources. All land managers are responsible for controlling declared animals, irrespective of whether the land is public, municipal or private. A Biosecurity and Agriculture Management Bill has been drafted, with the aim of replacing 17 existing Acts in the Agriculture portfolio. The drafted Act seeks to establish a modern biosecurity regulatory scheme to prevent serious pests, weeds and diseases that impact primary production, the environment or public amenity from entering the State, and to minimise the spread and impact of any that are already present. The bill was passed by the Lower House of Parliament in 2006 and has been introduced to the Upper House.
Threat abatement plans: Eight of the 16 key threatening processes listed under Commonwealth legislation (the Environment Protection and Biodiversity Conservation Act 1999) concern introduced animals. Threat abatement plans provide for research, management and any other actions necessary to reduce the impact of a listed key threatening process on a threatened species or ecological community. Current plans concern cats, rabbits, foxes, goats and pigs (draft).
Eradication and control: The Department of Environment and Conservation operates the Western Shield program which uses poisoned baits to control predators (foxes and cats) on about 3.5 million hectares of land across the South West (Department of Conservation and Land Management, 2005b). Native mammals can be re-introduced following predator baiting and trapping efforts. Western Shield has been credited with bringing at least 13 native fauna species back from the brink of extinction (Department of Conservation and Land Management, 2003d). Project Eden was established in the Shark Bay World Heritage area in 1995 to address declining populations of many native animals. It involved removal of introduced animals (goats, rabbits, foxes and cats) and re-introduction of native animals (bilby, rufous hare wallaby, banded hare wallaby and western barred bandicoot). In addition, introduced animal control is an integral part of conservation reserve management, and management of threatened species and communities, undertaken by the Department of Environment and Conservation across the State.
The Department of Environment and Conservation began the Saving Our Species program in 2006 and adds to Western Shield and other introduced animal control programs. It targets introduced animals in areas where they are known to have an impact on biodiversity and where it is feasible to eradicate or significantly reduce populations. Projects include: wild dog control in the rangelands and parts of the eastern Wheatbelt; pig control on the Darling Scarp and Swan Coastal Plain and in the forests around Manjimup and Lake Muir; goat control in Kennedy Range, Cape Range and Kalbarri national parks; fencing some of the conservation estate in the north of the State; fencing former pastoral lands purchased for conservation in the Goldfields and Midwest regions; camel, donkey, wild horse and wild cattle control in the western Little Sandy Desert and at a nature reserve in the Kimberley; a camel survey in Rudall River National Park; donkey control in some areas of the Pilbara; starling control on the south coast; and control of introduced bird species in the metropolitan area and around Albany and Denmark.
Natural Heritage Trust/National Action Plan for Salinity and Water Quality (NHT/NAP): These are two Commonwealth Government programs that aim to ensure environmental (on-ground) improvements occur via a targeted strategic approach at the regional level. All regional natural resource management groups have identified introduced animals as a problem and have initiated a wide range of actions to control them.
Management activities: The Department of Agriculture and Food coordinates surveillance and undertakes eradication and control activities, but mostly for introduced animals that can harm agricultural and pastoral production. Introduced animals that have a negative affect on native species and ecosystems are sometimes a lower priority than those impacting agricultural production. Many private landholders undertake control of introduced animals and procedures have been established to assist their efforts.
The State Cane Toad Initiative run by Department of Environment and Conservation funds the activities of several organisations to prevent the entry of the cane toad to WA including the Stop the Toad Foundation, Kimberley Toadbusters and Frogwatch (Northern Territory). The Kimberley Toadbusters, Stop the Toad Foundation and teams from State government agencies have been able to catch and destroy large numbers of toads in the Northern Territory to try and slow or stop their entry to WA (a total of about 260 000 toads were removed between 2005 and March 2007, L Scott-Virtue, Kimberley Toadbusters, pers. comm.). Efforts have focussed on physical collection and destruction of toads, but other methods such as cane toad traps and barrier fences are also being developed for areas that are hard for humans to regularly access.
Research: The Department of Agriculture and Food, Department of Environment and Conservation and CSIRO have current and ongoing programs that address control of introduced animals, particularly predators. Until recently, CSIRO conducted research into threatened species, in particular the reasons for their decline and techniques for re-establishment. The Department of Agriculture and Food has been researching methods for control of vertebrate pests including investigation of the sensitivity of non-target species to 1080 (a toxic compound also found in legume plants native to WA); investigating biological control of rabbits (myxomatosis and rabbit haemorrhagic disease); developing control strategies and techniques, baits and poisons for rabbits, foxes, birds and wild dogs.
Invasive Animals Cooperative Research Centre: was launched in 2005 by the Commonwealth Government to build on the work of the Pest Animal Control Cooperative Research Centre to counteract the impact of invasive animals through the development and application of new technologies and by integrating approaches across agencies and jurisdictions. It is the first time that research, industry, environmental, commercial and government agencies will work together to create and apply solutions for invasive animal threats.
Biodiversity Conservation Strategy: The Department of Environment and Conservation has released A 100-year Biodiversity Conservation Strategy for Western Australia: Blueprint to the Bicentenary in 2029. Public submissions were requested and a final biodiversity conservation strategy is in preparation (Department of Environment and Conservation 2006a).
Local governments: Many local governments have policies and strategies to prevent the spread of stray and feral cats including licensing, limiting the number of cats per household and a subsidy for cat sterilisation. The Perth Biodiversity Project is coordinated by the Western Australian Local Government Association to help local governments protect and manage natural areas, including the impacts of invasive animals.
Failure to control introduced animals is likely to result in further loss of biodiversity and further decline or extinction of native species or ecosystems. Introduced animals have been implicated in the extinction of 10 native mammal species in WA (Department of Conservation and Land Management, 2003d) and the decline in population and range of many others (Commonwealth of Australia, 2002). Introduced animals are also adversely affecting birds (Olsen et al., 2006), and many other groups for which detailed analysis has not been done. Introduced animal control needs to be consistent and sustained, and a proactive approach is required to prevent new introduced species becoming established. With increasing human population and associated travel, transport and trade, the risk of introducing new species is likely to grow (Convention on Biological Diversity, 2005). The potential cost of introduced animals is enormous, and includes costs of control measures, loss of biodiversity and damage to agricultural, forestry, pastoral and construction industries, in addition to effects on public health and amenity. For example, the environmental costs alone (i.e. not including the economic costs) of foxes and cats across Australia is estimated to be about $190 and $144 million respectively (McLeod, 2004).
5.12 Finalise and enact the Biodiversity Conservation Bill and the Biosecurity and Agricultural Management Bill.
5.13 Finalise and implement the draft A 100-year Biodiversity Conservation Strategy for Western Australia.
5.14 Expand current programs for introduced animal surveillance and control (such as Western Shield, Save Our Species and cat and herbivore control).
5.15 Expand sound biological control of introduced animals to include environmentally damaging species to the same extent as agriculturally damaging pests.
