To help prevent new and emerging invasive problems, governments put systems in place to ensure that ‘high risk’ species – those that could readily establish and become pests in the wild – are not imported into Australia.

The Australian Government’s Chief Environmental Biosecurity Officer is currently planning the implementation of an interim priority pest list referred to as the ‘National Priority List of Exotic Environmental Pests, Weeds and Diseases’ (EEPL), which focuses on exotic pests, weeds and diseases that are not established in Australia and that pose the highest risk to our environment and public spaces. The EEPL contains species from a broad range of organisms including the vertebrates listed here. It will be used to direct and coordinate activities that help prevent the entry, establishment and spread of exotic pests, weeds and diseases in Australia.

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Information about the top six listed vertebrate pest threats are displayed below.

Asian black-spined toad (Duttaphrynus melanostictus)

Asian Black Spined toad by Bernard Dupont

A stocky, poisonous large toad that is highly adapted to many climates and environments, including brackish water. The Asian black-spined toad (ABST) is widespread throughout south-east Asia, being native to north Pakistan, Singapore and parts of Indonesia. It has now established in the rest of Indonesia, Papua New Guinea, Andaman and Nicobar Islands, East Timor, and Madagascar.

The impacts of ABST are thought to be comparable to the cane toad (Rhinella marina) (Christy & Kirkpatrick 2017a). However, ABST can tolerate a wider range of climates, so it could impact over much of Australia, including high conservation habitats in temperate areas. ABST could significantly reduce Australian biodiversity by outcompeting and displacing native species, and transmitting diseases. It outcompetes native amphibians by feeding on a wide range of native insects, and also feeds on the eggs and juveniles of other amphibians. It has glands that secrete toxins that can poison native species that predate on it, such as quolls. The parasites and diseases that this toad carries, could further reduce populations of native species (Rahman et al. 2008). Chytrid is present in Australia; however, it is thought that ABST could increase the risk of chytrid infections in frogs (Christy & Kirkpatrick 2017a). In terms of social impacts, this poisonous toad would be a nuisance to and cause harm to people and pets (USFWS 2018d), and their presence would be damaging to important iconic, cultural and heritage regions, for example Kakadu National Park.

ABST has entered Australia on a number of occasions, but has been eradicated each time. This species has been an accidental stowaway in luggage, ships, machinery, and shipping containers from south-east Asia (Tingley et al. 2017; NSW DPI 2018a; DPIRD 2017). This species looks like other toad species when juvenile and have varied colourations as an adult, so it could be difficult to detect in the wild.

Boa constrictor (Boa constrictor)

Boa Constrictor by Flávio Eiró

A large non-venomous, nocturnal, heavy-bodied predatory snake that occupies a wide range of warm environments such as forests, grasslands, farmland and suburban areas. It can live both on land and in trees. It is native to most of temperate and tropical South America, but has been introduced to south-east Asia, USA, Puerto Rico, Mexico and Aruba.

If established in Australia, the boa constrictor could negatively impact on biodiversity by preying on our native fauna, especially as it does not have any known predators in Australia. The boa predates heavily on a broad range of native species, such as birds, bats, amphibians, small mammals, lizards and other snakes, as well as eggs (Ernst & Ernst 2003; Greene 1983; Quick et al. 2005; Reed & Rodda 2009; GISD 2019c). Boas will compete with larger snakes, such as native pythons. Boas may impact on the health of our native fauna, as they are known to host parasites and diseases such as paramyxovirus and inclusion body disease (IBD) of pythons (Reed & Rodda 2009; Henderson 2011; DPIPWE 2011). It can also be a threat to people, particularly children, as well as pets.

The boa has been introduced to many countries via the pet trade, and has been intentionally or unintentionally released into the wild. Illegal trade is one of the most likely pathways of entry into Australia. It could also enter as a stowaway (Christy & Kirkpatrick 2017b; DPIPWE 2011; Reed & Rodda 2009). Given that this species is nocturnal, secretive, and similar looking to native pythons, it may be difficult to detect if introduced. It has proven to be difficult to eradicate from areas where it has established (Henderson, Bomford & Cassey 2004; Christy & Kirkpatrick 2017b; DPIPWE 2011; Reed & Rodda 2009).

Climbing perch (Anabas testudineus)

A small hardy freshwater fish that lives in canals, lakes, ponds and swamps. It is highly adaptable to different environments and can tolerate freshwater and brackish water. It is native to India and China, and has established in Indonesia, Papua New Guinea and the Torres Strait islands.

Where it has been introduced, it has had negative impacts on the environment by outnumbering and outcompeting native fish species, often becoming the dominant species. It reduces overall biodiversity by competition, predation, and modifying the habitat through increased water turbidity (East & Micke 2008; Miller et al. 1995; Storey et al. 2002). It consumes aquatic plants, shrimps, snails, worms, insects and small fishes, which can reduce overall species diversity in waterbodies (Hitchcock 2006). Native species that could potentially predate on the climbing perch could be impacted, as it can inflate its body to block the airways of predators thus killing them. In terms of social impacts, this species could reduce the diversity of native fish for recreational fisheries and could harm pets if ingested (East & Micke 2008; Hitchcock 2008).

This species could be introduced to Australia as a stowaway aboard local fishing vessels, through discarded bycatch, or illegal trade for food or aquariums (East & Micke 2008). Climbing perch are highly resilient and mobile, as the species is able to survive for up to 6 days out of water and can use its fins to walk from one water source to another. The combination of broad tolerances, adaptability and competitive behaviours would enable this species to establish and spread widely within Australia (Hitchcock 2008). This fish has proved difficult to eradicate where it has invaded.

Corn snake (Pantherophis guttatus)

A small species of rat snake that inhabits a range of environments including grasslands, forest, farmland and semi-urban areas. It is native to southern North America and has invaded the Cayman Islands, Virgin Islands and the Bahamas.
The corn snake is an emerging invasive species worldwide. Its impacts on the environment include competition with and predation on native snakes and prey. This snake is a generalist predator that could have significant impacts on native rodents, nesting birds, amphibians and lizards if it establishes in Australia (Lever 2003; Kraus 2009; Meshaka Jr 2011; Xiao et al. 2004). Other impacts include being a host for exotic pests and diseases that could further threaten native hosts (e.g. Ehrlichia ruminantium tick; cryptosporidiosis disease).

The most likely pathways of entry of corn snakes into Australia are through illegal trade or as a stowaway. The corn snake has been intercepted at the Australian border on several occasions, and this appears to be on the rise. The corn snake is popular in the illegal pet trade industry, with high numbers predicted to be in captivity in Australia. It has also been intentionally or unintentionally released into the wild (Henderson, Bomford & Cassey 2011; Csurhes & Fisher 2016). This species can climb trees and shelter under rocks, which makes it difficult to detect. This snake has a broad diet, breeds rapidly and is long-lived, which contribute to its high risk of establishment and spread (Csurhes & Fisher 2016; de Magalhaes & Costa 2009; Ernst & Ernst 2003).

Red-eared slider turtle (Trachemys scripta elegans)

Red eared slider turtle

A medium-sized freshwater turtle that is highly adaptable and lives in a broad range of habitats including swamps, lakes, ponds and rivers, as well as brackish water. It is native to the Midwestern states of the USA and north-eastern Mexico, and is now feral on every continent except Antarctica.

The red-eared slider turtle is an opportunistic omnivore, which consumes a broad range of plants and animals, including algae, pond grasses, fish eggs, snails, fly larvae, insects, crustaceans, small fish and small aquatic snakes. If it were to establish in Australia, this species could compete with native turtles for food, nesting and basking sites. Vulnerable or endangered species of native turtles would be most at risk, which include Western Swamp tortoise, Mary River turtle, Bell’s Saw-Shelled Turtle, Gulf Snapping Turtle; Brisbane River Turtle and Krefft’s Turtle (Cann 1998; Kirkpatrick, Page & Massam 2007). The red-eared slider turtle could impact nesting birds using the same bank environment. It is also known to transmit diseases to other native species as well as humans or domestic pets (e.g. being a reservoir for salmonella bacteria).

The red-eared slider turtle has been very popular in the pet trade since the 1970s, and has been intentionally and unintentionally released into the wild on numerous occasions (Kirkpatrick, Page & Massam 2007). Illegal trade is the major pathway of its entry into Australia. It has been reported to be localised in some states in Australia. The species is long-lived, breeds rapidly, and has a broad environmental range, so it has a high risk of establishment and spread throughout Australia.

Silver carp (Hypophthalmichthys molitrix)

A freshwater carp that resides in lakes and ponds, but requires moving water to spawn. Its native range includes China and eastern Siberia. It has been introduced and/or spread by interconnected waterways to 88 countries around the world (in Africa, the Americas and Europe; also Fiji, New Zealand, and Papua New Guinea).
Silver carp poses a large threat to Australia’s environment as it can consume large quantities of phytoplankton, thus competing with and depleting native diversity, particularly that of similar types of fish and other phytoplankton feeders.

This species could lead to shifts in food webs if stable populations were to establish in the wild. If phytoplankton is scarce, this species would consume zooplankton, substantially reducing their biomass (Spataru & Gophen 1985). There would also be considerable losses in macro-invertebrates and benthic aquatic plants in Australian waterbodies. This species can also transport diseases to new areas, such as Salmonella typhimurium (GISD 2019d). When startled, this heavy-bodied fish can jump 2 m into the air, which could cause injuries to recreational fishers and other boat- or water-users (Chapman 2004, CABI 2018n; Fulton & Hall 2014).
This species has been introduced to many countries in the world for aquaculture purposes as well as for controlling excessive growth of phytoplankton in natural waters (Elvira 2001).

Pathways to Australia would include accidental stowaway, illegal smuggling as food, or escape from confinement, especially during a flooding event. This species is also often released into the wild for cultural/religious practices. It has a wide temperature and salinity tolerance, so it would be able to establish across much of Australia (Nico, Fuller & Li 2018; GISD 2019d). It is an efficient breeder, and can spread rapidly through connected waterways, which would be a major threat if it enters the Murray Darling Basin.