Theme 3: Human Impacts on Catchments

Topic: Exotic Pests

What is an exotic pest?

Like an exotic plant, an exotic pest is an animal or fish that has been introduced to the local environment. The pest may have come from overseas or even another part of Australia. Feral animals found in this State include rabbits, goats, pigs, feral cats, foxes, black rats, brown rats, house mice and the camels. Feral bird species include Blackbirds, Starlings, Sparrows, Goldfinches, Mallards, Spotted Turtledoves and Rock Pigeons.

Characteristics of a pest

Characteristics common to feral animals include:

• broad, general diet that allows animals to switch between different types of food, depending on availability
• minimal requirement for water, ie. they obtain moisture from their diet
• being indigenous to a country with a similar climate
• a high rate of reproduction
• having become a pest in another country outside its home range, and
• having no or very few predators.

The threat to local biodiversity

The International Convention on Biodiversity and World Conservation Union has, in the last decade, identified exotic pests as the second greatest threat to biodiversity after habitat loss. Australia alone has seen 27 bird species, 25 mammals, 2 reptiles and 1 amphibian successfully establish themselves. Fortunately, so far, only a handful of these animals have caused serious impact.

Australia's unique fauna has evolved in isolation, without competition from animals from other continents for thousands of years. This lack of competition has resulted in animal and plant communities being very susceptible to the impacts of invasion. Humans are almost entirely responsible for the transcontinental movement of animals. Some were brought here as livestock (goats and pigs), pets (cats and dogs), transport (camels and horses), biological controls (Cane Toads) or just to make Australia feel a bit more like home (rabbits and foxes). Somewhere along the line they have managed to escape human control and live on their own in the natural environment.

Exotic pests in the water

It is not only the land which has suffered the ravages of feral animals, but also our creeks and rivers. Prior to European settlement, local South Australian rivers were well stocked with a diverse species of native fish. Native fish species included Murray Cod, River Black Fish, Southern Pygmy Perch, Congoli, Flathead Gudgeon, Galaxias and many more.

Most of the native fish species are quite small and were not particularly sporting to catch or that great to eat compared to their European counterparts. So, to address those two issues, Brown Trout, Rainbow Trout, Redfin, Mosquito Fish and European Carp were introduced into local waterways. Of these introduced species, Trout and Redfin are the most voracious predators, happily eating their own young or any other small fish they happen upon when hungry.

Mosquito Fish or Gambusia, a native to Mexico, are about the same size as most native fish but far more aggressive and attack the native fish, often maiming them and making them easy prey for Trout and Redfin. Redfin also carry disease that can be lethal to native fish.

Most South Australians are aware of the harm caused by the European Carp. Adult Carp are herbivorous, feeding on plant matter buried in the sediment on the bottom of creeks and rivers. They feed by sucking mud in through their mouths and filtering out edible matter, pushing the mud out across their gill rakers. This method of feeding causes turbid conditions which cannot be tolerated by many other species. This mud filtering process also prevents the growth of aquatic plants as they are unable to anchor in the constantly disturbed sediment.

Student Activity Ideas

• Students to research one of the feral animals or fish found in the local area. They should investigate the following. Where the animal is from? Why was it introduced to Australia? How long it has been in Australia? Is it a pest in other countries? What makes it a pest species? What impact does this species have on the local environment?
• There are many animals that are considered extremely high risk that are not allowed into Australia unless they are kept in high security enclosures of zoos. These include Hamsters and Dwarf Meercats. Despite this, people are always trying to bring exotic animals into Australia as pets, both legally and illegally. Discuss with students the issues that make an animal a threat to Australia. How might the Animal and Plant Control Board decide which animals are allowed into Australia?

Enquiry Learning

• How has the introduction of animals and fish from other parts of Australia and from around the world impacted on the local environment?
• Why can some exotic animals, that originated from other parts of Australia or from overseas, do so well in some environments, despite not being native to the area?
• Why and how do exotic animals get transported from one area to another?

Internet Resources

Type	Description	Resources Covering the Topic
Easy	Good overview of key trends in invasive species in South Australia.	SA Department of Environment and Heritage www.environment.sa.gov.au/reporting/ biodiversity/introduced.html
	Pest animal proliferation. Summary of issues.	Landcare Victoria www.netc.net.au/enviro/fguide/ pestanimal.html
	Exotic Animals in NSW.	NSW NPWS - Exotic Animals www.nationalparks.nsw.gov.au/ npws.nsf/Content/Pest+animals
	Threats to National Parks: Pest animals. Brief overview of issues in NSW National Parks.	NSW National Parks and Wildlife www.npws.nsw.gov.au/help/ takecare.htm#1pest
	Feral Animal control in Australia. PDF download.	Onkaparinga Catchment Water Management Board www.onkaparinga.net/education/ downloads/folder_4/ 6_18.pdf
More Comprehensive	Invasive species - feral animals in Australia. An in-depth look at some invasive species, such as rabbits, foxes, cats, pigs etc. Discusses the damage they do to the environment.	Environment Australia Biodiversity www.ea.gov.au/biodiversity/ invasive/pests/index.html
	Background to threats to biodiversity around the world.	Species Survival Commission www.iucn.org/themes/ssc/pubs/policy/ invasivesEng.htm#BACKGROUND
	Introduced wild animals in Australia. Descriptions of a wide range of pest animals in Australia, how they were introduced and the damage they do.	Australian National University rubens.anu.edu.au/student.projects/ rabbits/wildanim.html
	Marine Invaders. Comprehensive review of the main issues.	WA Government Fisheries www.wa.gov.au/westfish/hab/broc/ marineinvader/miintro.html
	Feral Animal control in Australia. PDF download.	Onkaparinga Catchment Water Management Board www.onkaparinga.net/education/ downloads/folder_4/ 6_18.pdf
More Complex	The threat of non-indigenous species across the US. Thorough and comprehensive examination of the processes of invasion.	US Geological Survey biology.usgs.gov/s+t/SNT/noframe/ ns112.htm

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