Assessment of animal pests in Tasmania


Detailed below is information on a range of introduced animals that have become established in Tasmania and are now considered as pests.

Foxes

The European red fox is thought to have been deliberately introduced into Tasmania around 2000. This environmental pest is the single most devastating introduced animal and threat to native vertebrate animals in Tasmania (and Australia).

The Fox Eradication Branch (established in 2002 by the Tasmanian Government) continues to manage the Fox Eradication Program with the prime aim of eliminating foxes from Tasmania, but also to ensure that this animal pest is not re-introduced into the State in the future (Internal linkDPIPWE 2009). As part of the eradication program, the project team aims to gain a better understanding of population trends of species at risk from fox predation, and foster broad community cooperation to support keeping Tasmania fox free. The DPIW website titled The Fox Free Tasmania (Internal linkDPIPWE 2009) provides an important source of information on fox sightings and the Fox Eradication Program.

Hard evidence to verify foxes in Tasmania (as opposed to other indicators such as reported sightings) has been increasing, with multiple discoveries of varying nature found since 2005. This hard evidence provides certainty of a fox presence. The most recent fox scats were confirmed from the Oatlands and Campbell Tow areas in March 2008. Locations of evidence confirming the presence of foxes in Tasmania is detailed in the Internal linkAnimal Pests and Diseases Indicator.

It is suspected from evidence and collective knowledge, that the density of a Tasmanian red fox population in Tasmania might be as low as one fox per 500 km2. Given that research in other parts of the world shows that once foxes are at a density of one per 25 km2 they are almost impossible to find, and once at one per 40 km2 the chances of finding them virtually collapse, the difficulty in providing hard evidence to confirm the presence of foxes in Tasmania is a difficult undertaking.

To date, the hard evidence indicates that foxes are established in areas associated with human settlement. They have been sighted across the north of Tasmania, down the east coast and throughout the Midlands to the south. There have also been credible reports of foxes in the Huon Valley area and around Geeveston and Franklin in the south of the State. In addition, one possible sighting of a fox is recorded in or near the (WWHA), which lies in the southwest of the State.

Cats

Cats (from the family Felidae) were most probably introduced into Tasmania by the first European settlers. Since this time, they have spread throughout most of the State and many offshore islands, and they may have been on King Island since 1802 and were first recorded on Macquarie Island in 1820 (Finzel in Internal linkTSN 2005 and Copson in Internal linkTSN 2005).

More recently, feral cats have been recorded in more remote areas, particularly in areas where human activities such as logging, road construction and bushwalking tracks have expanded. For example, a lactating female cat was destroyed near Melaleuca in southwest Tasmania in 2007 (Glenn Atkinson, pers. comm.). In addition, they are known to occur on 22 of the 69 islands on which feral or introduced animals have been recorded in Tasmania (Internal linkDPIWE 2005). See Internal linkIntroduced Species on Offshore Islands for further information on introduced animals to offshore islands.

The number of feral cats in Tasmania is not possible to calculate and their density in any one location is very variable. However, anecdotal reports estimate that the feral cat population in Tasmania may be as high as 150,000 and may have doubled in the past two years from 2005 to 2007. This may be associated with the Tasmanian devil (Sarcophilus harrisi) population being catastrophically reduced as a result of their susceptibility to the devil facial tumour disease (DFTD). It is thought that as Tasmanian devil numbers have fallen, feral cats have taken moved into the ecological niche once occupied by this species (Nicholas Mooney pers. comm.). Of great concern is the possibility of feral cats permanently establishing a new ecological equilibrium whereby Tasmanian devils are 'locked out' of their previous ecological niche. If this were to evaluate, the Tasmanian devil population may not be able to recover. The overall trend in the observed abundance of Tasmanian devils and feral cats in Tasmania is detailed in the Internal linkAnimal Pests and Diseases Indicator.

Although rabbits are usually the staple prey of cats in Tasmania, other food items include small mammals, birds, reptiles (particularly skinks), frogs, fish, invertebrates and on occasion, some plants (Internal linkDTAE 2007). In remote regions where fewer rabbits are found, cats mainly prey upon small native mammals and birds. In most areas of the State, native birds are particularly vulnerable to cat predation because they well out number introduced birds. For example, feral cats are believed to be a major threat to critically endangered orange-bellied parrots (Neophema chrysogaster) during their stop over on King Island. They can also transmit diseases such as toxoplasmosis to native animals, livestock and humans, potentially causing serious illness and even death.

It was estimated in 1990 that domestic and semi-domestic cats killed, but did not always eat, around 195,000 native and 228,000 introduced animals per year (Internal linkTrueman 1991). It is not known how many native and introduced animals cats currently prey upon, nor is it possible to fully quantify the impacts they have on ecosystems. What is known is that on smaller, remote offshore islands native species have been decimated or totally wiped out by cats. In addition, the Hobart Cat Centre accepts approximately 4,000 cats per year, and 90% of these animals are humanely destroyed (Internal linkDTAE 2007). People also now generally admit that cats do prey upon other animal species and that feral and stray cats are a significant environmental problem.

In Tasmania, areas where native species are most at risk from predation by feral cats and the ecosystems where this impact is likely, or known to be, greatest are identified as Woolnorth, West and South West, Central Highlands, Tasmanian Midlands, D'Entrecasteaux, Freycinet, Ben Lomond and the Furneaux Peninsula (Internal linkDEWR None). Feral cats were successfully eradicated on Macquarie Island by 2000.

Predation by cats is listed nationally as a Key Threatening Process under the Commonwealth External link: LegislationEndangered Species Protection Act 1992. The Australian Government Threat Abatement Plan for Predation by Feral Cats, 1999 that identifies research, management and other actions needed to control cats is currently under review. Tasmania has no specific legislation to control cats although the External link: LegislationNature Conservation Act 2002 defines 'cat' as a member of the species (Felis catus), the External link: LegislationAnimal Welfare Act 1993 refers to them in respect to the welfare of animals, and the External link: LegislationCrown Lands Act 1976 prohibits them to be abandoned in public reserves. Therefore, government officers or members of the public do not have the 'authority' to take action. However, local councils are increasingly implementing a range of voluntary measures to control both domestic and feral cats.

Rabbits and rodents

Rabbits, rats and mice are significant environmental pests in Tasmania. They are distributed throughout the State and were most likely introduced by the first European settlers. In particular, three species of rodent have been introduced to Tasmania: the brown rat (Rattus norvegicu), black rat (Rattus rattus) and the house mouse (Mus musculus).

In particular, rabbits in the family Leporidae are classified as 'vermin' under the Tasmanian External link: LegislationVermin Control Act 2000. Under this Act, landholders are required to 'suppress and destroy' any wild rabbit on their property. With respect to rabbits, they have been successfully eradicated on Partridge Island located at the south-western tip of Bruny Island (Internal linkDPIWE 2005). Hares, while not classified as vermin under this Act, have no legal status and can be hunted under the same conditions that apply for rabbits.

There is evidence to suggest that rabbit numbers in Tasmania have decreased in recent years, possibly due to the introduction of Myxomatosis and Rabbit Haemorrhagic Disease (RHD, or Rabbit Calicivirus as it is more commonly known), and the drought conditions (particularly in the Tasmanian Midlands) resulting in less food sources being available. More information on rabbits and hares are detailed in the Internal linkAnimal Pests and Diseases Indicator.

European rabbits (Oryctolagus cuniculussci) were introduced to Macquarie Island in the 1870s, while black rats and the house mouse were first recorded on the island in the 1890s. Rabbits and rodents are the only remaining animal pests following the successful eradication of feral cats by 2000.

Macquarie Island a subantarctic island approximately 34 km long and 5.5 km wide at its broadest point that is located about 1,500 km to the southeast of Tasmania. The Macquarie Island Nature Reserve includes Macquarie Island, Bishop and Clerk Islets, Judge and Clerk Islets, all adjacent offshore islands, rocks and reefs, and the surrounding seas extending to the limit of state waters to three nautical miles (Internal linkPWS 2006).

Macquarie Island Nature Reserve has been established to protect the natural values of Macquarie Island and its surrounding offshore islands and is well recognised for its conservation, geological, ecological and scientific values. It is a World Heritage Area, a Biosphere Reserve, and is listed on the Register of the National Estate. The Macquarie Island Nature Reserve is adjacent to the Australian Government Macquarie Island Marine Park, which is the second largest marine protected area in the world. It is part of Tasmania and managed by the Parks and Wildlife Service (PWS) of the Department of Environment, Parks, Heritage and the Arts (DEPHA). Further information on Macquarie Island Nature Reserve and World Heritage Area can be accessed through the DEPHA website.

Macquarie Island is protected because it is home for up to four million seabirds, 850,000 pairs of royal penguins and 100,000 seals. However, these threatened and protected species are being severely impacted upon by environmental animal pests. In particular, there has been a dramatic increase in rabbit numbers on Macquarie Island since 2001, with some commentators estimating that numbers have increased from approximately 10,000 in the 1980s to more than 100,000 in 2007, devastating the grasses that provided shelter for nesting birds (Internal linkDTAE 2008). This increase has been attributed to a combination of factors that include the eradication of cats prior to 2000.

Rabbit numbers were estimated to be higher in the 1960s when cats were present. In particular, they have increased dramatically since the late 1990s (Internal linkDPIWE 2005). Increasing rabbit numbers generally, was the reason for introducing Myxomatosis in 1979, although the island's rabbit population has since developed resistance to the myxoma virus over recent years. In particular, rabbit breeding has significantly increased on the island from producing a single successful litter per year to producing two to three litters per year. Breeding success has been attributed to changing climatic conditions and the burrows are no longer flooded regularly as they were in the past. It is also suspected that a series of warmer and drier winters in recent years have contributed to higher survival rates of rabbit kittens.

Rabbit damage on Macquarie Island has resulted in serious vegetation degradation and is impacting on burrowing seabirds that require vegetation cover around their breeding habitat. More recently, landslides in the rugged terrain have at partially been caused by rabbit grazing have caused the deaths of penguins and damage to visitor infrastructure.

Rodents are also having a significant impact on Macquarie Island. In particular, rats are known to eat the eggs and chicks of burrowing petrel species and mice are more recently recorded as having eaten albatross chicks. With tussocks providing the highest vegetation, all bird species must breed on, or in, the ground where they are easily found by rats and mice.

Pigs

Feral pigs (Sus scrofa) are not recorded as being present in Tasmania. However, pigs became feral on Flinders Island situated at the eastern end of Bass Strait in the 1800s after being released by sealers and following the ship wreck of the City of Foo Chow in 1877 (Internal linkCopson 2001). This original stock has since been supplemented by pigs that were accidentally or intentionally released in the 1970s. Their main distribution covers the Strzelecki National Park area located in the southwest corner of the island, and through the wetlands along the east coast. During very wet seasons, feral pigs have been sighted throughout the island (Wayne Dick pers. comm.). On the east coast, feral pigs are found in the wetland sites recorded in A Directory of Important Wetlands of Australia (Internal linkANCA 1996), of which two are listed on the Register of the National Estate – which are also listed as international Ramsar sites.

It is believed that the populations of feral pigs in the Strzelecki National Park and those found in wetlands along the east coast of Flinders Island could be separate populations, as extensive land clearing for agriculture has effectively isolated the two populations from each other (Internal linkDPIWE 2000).

Feral pigs are environmental and agricultural pests on Flinders Island. They can cause damage to the environment through wallowing, rooting for food and selective feeding. They compete with native animals for food, destroy habitat for native plants and animals and can spread environmental weeds. Many native plants and several native animals threatened by feral pigs are listed under the Tasmanian Threatened Species Protection Act 1995 under the Tasmanian External link: LegislationThreatened Species Protection Act 1995 and the Commonwealth External link: LegislationEndangered Species Protection Act 1992 (EPBC Act).

For example, feral pigs impact endanger heathlands, valuable wetlands, estuarine marshes and relict Oyster Bay pine (Callitris rhomboidea) scrub-woodland communities that are of considerable conservation significance. They also impact upon the rare New Holland mouse (Psuedomys novaehollandiae) and burrowing crayfish species, by uprooting the moss beds and root mats in which they live. They can also destroy entire populations of ground orchids through feeding activity. In addition, it is thought that feral pigs have contributed to the spread of the cinnamon fungus (Phytophthora cinnamomi) on Flinders Island when they have passed through contaminated areas and transporting the spores into previously uncontaminated areas.

It is difficult to estimate the current number of feral pigs on Flinders Island because they are elusive animals and are rarely sighted. It was conservatively estimated that 1,000 feral pigs were present on the island in 2001, with at least this number remaining in April 2008 (Wayne Dick pers. comm.). Refer to the Internal linkIntroduced Species on Offshore Islands Indicator for further information on introduced animals to offshore islands.

Goats

Feral goats (Capra hircus) probably built up in the 1980s in Tasmania from the offspring of haphazard escapes and releases from private properties (Internal linkDPIWE 2003). Feral goats can become environmental pests because they invade bush and browse a wide variety of native and introduced plants. In addition, feral goats do not need to locate near water sources because vegetation in Tasmania has a high enough water content to meet their needs. They also can breed quickly and crossbred varieties are common in the State. Young animals are weaned within months and can breed from six months of age. Consequently, a feral goat herd can double in size in a couple of years, further increasing their threat to ecosystems.

These animals have been found across a wide range of habitats in Tasmania, ranging from agricultural areas to native vegetation communities, from sea level to the Central Plateau, from rainforest to alpine vegetation, and both within and outside the WWHA. Overcoming the problem of feral goats in Tasmania depends on owners of domestic goats keeping their stock inside fences, and disposing of unwanted animals responsibly.

At the beginning of 2008, no feral goat herds were known to exist in the wider Tasmanian landscape. However, it is possible that goats may be present on Courts Island and Swan Island.

Fallow deer

Fallow deer (Dama dama) have established wild populations in five of six Australian states, with the largest population found in Tasmania (Internal linkWebley et al. 2006). This species was first imported into the State in 1836. Currently, it is estimated that there are approximately 20,000 animals roughly bounded by a line from Launceston to Derwent Bridge to Pontville to the east-coast to St. Helens and back to Launceston (Internal linkDPIW 2008).

The Midlands Highway appears to be a geographical divide in the State for fallow deer, with those to 'the east of the Highway predominately having red coat colour, while those to the west predominately having black coat colour' (Internal linkWebley et al. 2006). There are also three distinct genetic wild populations here that cluster into two groups – the Lake Echo and Connorville deer cluster in central Tasmania and the Benham population near Avoca. Generally, these animals preferentially reside in woody vegetated slopes and gullies during the day, with some animals moving into cleared areas at night. More information on fallow deer is detailed in the Internal linkAnimal Pests and Diseases Indicator.

Fallow deer compete with native herbivores for food and graze on threatened plant species. For example, in the Great Lake area on Tasmania's Central Plateau, grazing and browsing by this species is contributing to low seed establishment of the endangered Miena cider gum (Eucalyptus gunnii spp. divaricata) (Internal linkThreatened Species Network 2006). The Miena cider gum is only known from a 40 by 40 kilometre area from west of Miena to Interlaken.

Bees and wasps

Non-native bees and wasps are significant environment threats in Tasmania. They have extended their ranges and are now widespread and common throughout the State. Not only are they found in areas of human disturbance, they are also found on our pristine offshore islands, the WWHA and remote areas of the West Coast. For example, the large earth bumblebee (Bombus terrestris) now inundates DeWitt Island and the European wasp (Vespula germanica) is found on many remote Tasmanian islands including Mewstone Island. Both these islands are located near Maatsuyker Island in the WWHA and ought to offer high protection to native species given that they have been designated with the highest reserve status in Tasmania.

In Australia there are about 2000 species of native bees. Only 10 of these are social bees with a queen, drones and workers (like honeybees) and they live in colonies in places such as hollow trees. Other native bees are solitary and do not have a social colony structure. Solitary bees do not store excess honey in their nests, although they play an important role as pollinators of native species. In times of food scarcity introduced honeybees and bumblebees can out-compete native bees.

See the Internal linkIntroduced Species on Offshore Islands Indicator for further information on introduced animals to offshore islands. Interestingly, the 2005 data presented in this indicator does not include introduced invertebrates such as bees and wasps. This is partly because little research has been undertaken to determine the impacts of invertebrate species on the Tasmanian environment, but also because bee and wasp introductions to offshore islands is a more recent observation.

Bees

Although commercial honeybees (Apis spp.) are the most important pollinator of crops and are essential for the production of honey, they have also been shown to 'decrease available nectar and pollen in leatherwood forests and in some areas may cause a decline in the abundance of native insects' (Internal linkMallick 2001 Driessen et al. in Internal linkTSN 2005).

Honey production

Honey productioninternal SOE link to larger image

Notes: Tasmanian native bees include reed bees (Exoneura and Braunsapis), resin bees (Megachile, formerly in genus Chalicodoma), leafcutter bees (Megachile), homalictus bees (Homalictus) and masked bees (Amphylaeus, Hylaeus and Meroglossa).

Source: Internal linkForestry Tasmania 2008

Commercial honeybees are potentially threatened by an overseas parasite, the Varroa mite (Varroa destructor). This mite weakens and kills honeybee colonies and can also transmit several honey bee viruses (Internal linkKnoxfield 2007). To date, this parasite has not been introduced into Australia, although if it were to become established on the mainland or in Tasmania it would be a major problem. Varroa mites are a major problem in Europe, Asia and the Americas and were discovered in New Zealand in 2000 (Internal linkDAFF 2008). Where found, they cause immense impact on honeybee populations and the apiary industry, with significant control costs and losses of bees. Given that honeybees in Tasmania are potentially threatened by Varroa mites, it is vital that we understand how our own native bees pollinate our plants and ensure their populations are not impacted by this environmental pest, or other pests and diseases.

The large earth bumblebee has been present in Tasmania since 1992, when it was discovered in a wide variety of native vegetation types within three kilometres of Hobart (Internal linkHingston 2006). There has been disagreement surrounding the distribution of the large earth bumblebee in Tasmania and its capacity to become feral and invade Tasmanian native vegetation (Internal linkHingston 2006). One survey conducted in 1999 found that the distribution of the bumblebee radiated from Hobart where human settlement had occurred. Since this time, other surveys have found that the bumblebee is now found in all of Tasmania's major native vegetation types from sea level to above 1,250 metres.

It was also generally thought that this species preferred to feed on plants that have been introduced and rarely on native vegetation. Nonetheless, the bumblebee has been found to feed extensively on native vegetation in Tasmania both within and outside national parks and the WWHA (Internal linkHingston 2007). Despite this species feeding largely on introduced plants, the bumblebee could still seriously impact native plants and the animals that feed upon them because pollination services supplied by this species may result in weed plant species producing more seeds, becoming more invasive and out competing native plants. In particular, bumblebees compete with the endangered Tasmanian swift parrot (Lathamus discolor) for nectar. By increasingly invading native vegetation, bumblebees could also affect seed pollination in native plants.

Little is known about the impact of the large earth bumblebee on native species or ecosystems although it is thought they could potentially:

  • compete with native animals for nectar and/or pollen of native vegetation;
  • reduce seed production and/or altered gene flow in native vegetation;
  • increase seed production in introduced weed species.

The effectiveness of the large earth bumblebee as a pollinator in the horticultural industry, and particularly of greenhouse tomatoes, as resulted in some industry members supporting its introduction to mainland Australia. However, concern about the potential for the establishment of this species in the wild and its impact on native plants and animals on mainland Australia has led to it being listed as a threatening process in Victoria and New South Wales (Internal linkHingston 2007).

Wasps

Two species of the exotic wasp genus (Vespula) occur in Tasmania (Internal linkDPIW 2008). The European or German wasp was first found in Hobart in 1959 and has since spread throughout the State. The English or common wasp (Vespula vulgaris) was first discovered in 1995 and is restricted to south-eastern Tasmania. The two species are visually very similar, although the European wasp is more common and widespread in the state.

The impacts of wasps on native species and ecosystems are largely unknown. However, wasps are considered environmental pests because they can enter native beehives in search of food, and persistent attacks may weaken the hives. They are also a nuisance in public areas and are highly attracted to ripe fruit, sweet-drink residues and meat.

In particular, European wasps have spread dramatically in recent years and are now widespread and common. They are currently accelerating their establishment to the east of Tasmania (perhaps doubling their numbers) and have established a population in the west and WWHA.

Not only do European wasps compete with native bees, they also predate on other native animals, especially invertebrates such as the vulnerable Ptunarra brown butterfly (Oreixenica ptunarra) and mussels. They are also predating on native tadpoles. Once European wasps have eaten easily available food sources, it is possible that it can become a predator. In environments like the WWHA, this species may compete meat eating native animals such as the endangered wedge-tailed eagle (Aquila audax fleayi).

Other invertebrates

Two new invertebrate pests have become established in Tasmania since 2001, although they do not threaten native species. The lettuce aphid (Nasonovia ribes-nigi) is a pest of lettuce crops. This species blew into Tasmania on wind from New Zealand in 2004, quickly established widely across the State, and in the following two years spread to most mainland states. It is no longer under quarantine control in most of Australia. The elm leaf beetle (Pyrrhalta luteola) is a pest of amenity trees (elms in gardens and parks). This species was first detected in Victoria in 1989 and was not recorded in Tasmania until 2002. In Victoria, this species is beyond eradication and simply another pest that local councils and gardeners need to cope with. In Tasmania, it has been largely restricted to the Launceston area. However, more recently it has been recorded in Evandale and at Glenorchy in Hobart.

It is not known if these invertebrate pests will impact native species or ecosystems in the State. This level of uncertainty is not uncommon, and little is known about the environmental impacts of all non-native invertebrate species on the Tasmanian environment. Some commentators point out that research directed towards understanding the environmental impacts of non-native invertebrates will only be undertaken after they impact upon the agricultural sector and Tasmania's economic base.

Water-based animals

Introduced fish found in inland waters can also be pest animals and cause environmental harm. Pest fish management in Tasmania covers the management, monitoring and control of identified pest fish species, particularly those species listed as controlled fish under the External link: LegislationInland Fisheries Act 1995. These include European carp (Cyprinus carpio) all species of mainland yabbies (Cherax spp.) and Eastern gambusia (Gambusia holbrooki). In Tasmania, you are not permitted to possess these fish or release them into any inland water in Tasmania, including an aquarium.

In addition, goldfish (Carassius auratus), Redfin perch (Perca fluviatilis) and Tench (Tinca tinca) have become 'acclimatised' in Tasmanian waterways, and although not identified as controlled fish, they are regarded as undesirable pests. The Inland Fisheries Service has little control over reducing populations of these species. However, preventing their spread is considered a high priority because they can compete with native fish species for habitat and food, have the potential to spread fish diseases and parasites, and in the case of Redfin perch, are capable of forming large unmanageable populations.

Brown trout (Salmo trutta) also impact native fresh water species such as fish, frogs and zooplankton. This species is widespread throughout Tasmania and was first introduced in 1864 to stock the recreational fishery. Brown trout can also live at sea and have been able to migrate around the coast to otherwise inaccessible waterways (Jackson in Internal linkTSN 2005). It is believed that the impacts of this highly predatory species on native freshwater species are significant, although poorly understood. Brown trout can also potentially spread fish diseases and parasites that could affect other native species. The Inland Fisheries Service continues to manage the brown trout as a recreational fishery, although it does not stock natural waterways that do not already contain the species.

Carp

The introduction of European carp (Cyprinus carpio) into Tasmania could potentially result in significant impacts on our native fish species and inland fishery. The ornamental Koi strain of carp have probably been present in Tasmania since the turn of the century, although they do not appear to have established wild fish populations (Internal linkIFS 2004). Carp of the vigorous Boolarra strain were then discovered in the northwest region of Tasmania in 1975 and again in 1980 (Internal linkIFS 2007) and they were eradicated using the fish poison rotenone. European carp infestations were discovered in February 1995 in Lake Crescent and then in the interconnecting Lake Sorell (Internal linkIFS 2008). If carp were to become established in wild fish populations the species could cause the following impacts:

  • competitive interactions with native fish species;
  • destruction of fragile aquatic macrophytes (water plants);
  • increase in water turbidity;
  • damage to stream beds and irrigation channels;
  • nutrient enrichment of waterways leading to algal blooms; and
  • introduction of new parasites and diseases to desirable fish species.

The European carp is listed as a controlled fish under the Tasmanian External link: LegislationInland Fisheries Act 1995 and a noxious fish under the External link: LegislationLiving Marine Resources Management Act 1995.

A total of 10,531 were removed from Lake Crescent and Lake Sorell from February 2005 to February 2008 by officers from the Carp Management Program. For the 2006/07 season, a total of five carp were caught in Lake Crescent (2 females) and 81 carp were caught in Lake Sorell (57 females) (Internal linkIFS 2007). All carp removed from the lakes were eradicated. Carp removal from Lake Crescent and Lake Sorell is detailed in the Internal linkAnimal Pests and Diseases Indicator.

Yabby

Although all species of mainland yabbies (Cherax) spp. are listed as controlled fish, the only species found in Tasmania is the variety known as (Cherax destructor). They have possibly been present in Tasmania since 1968 when they were introduced for human consumption at Hawley on the northwest coast, but were detected in greater numbers by the Inland Fisheries Service in the late-1970s (Jackson in Internal linkTSN 2005). This species was first released in Tasmania's midlands, and has subsequently been transported to farm dams and waterways around the State. Yabbies are a threat to native animals because they can tolerate poor water quality, their burrowing behaviour disturbs habitat for native species and they can potentially out-compete the vulnerable giant freshwater crayfish (Astacopsis gouldi).

Eastern gambusia

Eastern gambusia (Gambusia holbrooki) are small fish that were first discovered in Tasmania in 1993 in a farm dam near the Tamar River (Jackson in Internal linkTSN 2005). Currently, there are several self-sustaining populations in the upper reaches of the Tamar estuary in the north of the State. The largest population is found in the Tamar Island Wetland Reserve Conservation Area where there is unrestricted access to the main estuary. Given this species large reproductive capacity, high tolerance to a wide range of environmental conditions and aggressive egg-eating and fin-nipping behaviour, it has the ability to compete native with fish and frogs for habitat and food.

The most common method of dispersal of Eastern gambusia is intentional or accidental human translocation, particularly when they adhere to footwear or gear. They can also be spread by flood events or can adhere to the feathers of wetland birds that migrate to other locations.

Broader concerns

The common starling (Sturnus vulgaris) has spread throughout Tasmania. Fewer birds are found in the southwest of the State although their impacts are of particular concern at Birches Inlet on Macquarie Harbour and at Melaleuca to the south. Common starlings are also found on Tasmania's offshore islands such as Gull Island located at the eastern end of Bass Strait south of Cape Barren Island. In these remote locations, they tend to favour coastal areas with sea cliffs. As an environmental pest, this species is largely overlooked because the general public has become accustomed to 'seeing' these birds in the landscape. However, common starlings impact native bird species because they compete with native birds for food, destroy their habitat and steal nest sites. For example, at Melaleuca common starlings have been known to peck to death the critically endangered orange-bellied parrot (Neophema chrysogaster) and steal their nests. There is currently no management of common starling populations in Tasmania (Glenn Atkinson, pers. comm.). However, this species has been identified as a Priority 1 species for future monitoring by DPIW (Internal linkDriessen and Hocking 2008).

The rainbow lorikeet (Trichoglossus haematodus) has also become established with flocks of up to 30 individuals being recorded in the Taroona and Blackmans Bay area south of Hobart and near Ulverstone in the north of the State. Their establishment in the State is possibly because environmental conditions have become more amenable to the species (Eric Woehler pers. comm.). However, their impact on native species and ecosystems has yet to be evaluated although they are known to compete with the endangered Tasmanian swift parrot (Lathamus discolor).

The superb lyrebird (Menura novaehollandiae) was introduced to the Hastings and Mt Field areas during the 1930s and 1940s primarily because of concerns about the threat of foxes to this species on the Australian mainland. However there are concerns that this bird may be reducing the cover of ferns and saplings in wet forests during their search for food in the litter layer and causing impacts to other native species found in these vegetation communities (Internal linkTanner 2000; Driessen et al. in Internal linkTSN 2005). The superb lyrebird is currently a protected species under the External link: LegislationNature Conservation Act 2002.

The common Indian myna bird (Acridotheres tristis) is fast becoming one of Australia's most problematic environmental pests. First introduced to Australia to control insect pests, the arrival of this bird in a region has resulted in devastating consequences to native bird populations and horticulture, particularly the soft-fruit industry (Internal linkABC 2003). This bird has been inadvertently transported into Tasmania via ferries or freight cargo and has been found near the Devonport port area and near the Launceston Airport. There are currently no known sightings of the common Indian myna bird in Tasmania although it is significant threat.

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