Aquatic Invaders - Introduced species are a threat to our aquatic biodiversity
Yabbies, red-fin, carp, goldfish, mosquito fish, tilapia, guppies and swordtails - our rivers, lakes and dams don't need them!
Select from the 9 species illustrated below for more details.
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The natural inland waterways of Western Australia are a valuable part of our environment, and in good condition support a unique ecology, and many rare and vulnerable native fish, crustaceans and other aquatic lifeforms.
These systems are under intense pressure due to changes in environmental conditions, declining rainfall, human land use in their catchments, and other activities.
All our unique native fishes are found nowhere else in the world. Our galaxiid minnows can trace their ancestry back many millions of years, while our crustaceans such as marron, gilgies and koonacs have developed in response to the often harsh and changing conditions typical of Western Australian freshwater systems.
All these aquatic creatures are an important part of Western Australia's biodiversity, and we have a duty to protect them and their habitats for future generations.
A major threat to these native fish communities is the introduction and spread of some exotic species, many of which are aggressive and can breed rapidly in the right circumstances.
Fishes such as cichlids and swordtails directly displace native species by outcompeting them for habitat and food, and eating them and their offspring.
They also indirectly deconstruct native freshwater ecologies, by disrupting the foodchain, eating a wide range of insects and crustaceans, and creating physical conditions not favourable for native aquatic life.
Once introduced into natural waterways, fish that become feral and breed in the wild are almost impossible to completely eradicate, but it is possible to control their numbers and impact on native species.
The challenge we face as a community is to work out the best way of protecting our natural waterways important to native fishes from further pressures.
What can be done?
Eradicating feral aquatic species once they establish breeding populations is very difficult. Common methods of control for severe infestations may include using a series of small underwater explosions that creates a “shock wave” through the water body, or the application of various chemicals that kill fish (piscicides).
Recreating natural habitats, replanting streamside vegetation to improve habitat structure, and reducing water flow rates is an effective longer term strategy, as long as feral fish numbers are controlled by either trapping, fishing or other methods including egg-trapping.
Regular monitoring and continuing care are an important part of any control program, and success often depends on the amount of community support there is for restoration and management work.
What are the side effects?
All feral fish control methods affect other aquatic creatures. Chemicals that kill fish may also affect invertebrates of many kinds, and can affect reptiles and other aquatic lifeforms. However, these chemicals break down and become neutral within a few days, and there is no known residual effect.
A key to successful control is to ensure that sufficient native species are removed from the control area for later restocking, or that there are nearby breeding populations which can naturally repopulate the area.
What are the benefits?
Uncontrolled feral fish populations can have a devastating effect on native freshwater ecologies. Protecting Western Australia's biodiversity and natural ecosystems is an important part of the State's sustainability strategy.
Not only native freshwater species benefit from control programs for feral fish. Local communities can also develop their understanding and appreciation of WA's biodiversity, and help conserve a valuable resource for science and education as well.
What can you do?
- Never, ever release introduced species into our waterways or dams. Design or locate aquaria and ornamental ponds so they can't escape. Take unwanted aquatic animals back to suppliers or dispose of them humanely (refrigerate the fish in water, and when the fish stops moving put the bag into the freezer overnight – endorsed by the RSPCA WA Inc).
- Consider stocking native species for mosquito control.
- if you catch any of the introduced species in this brochure, don't return them to the water. Eat them or dispose of them humanely.
- Be aware of your surroundings. Report the presence of freshwater pest species to the Department of Fisheries using the FISHWATCH service on 1800 815 507. This helps us track infestation and control the problem. Some dams and waterways are being cleared of introduced species and restocked with natives and it is important to monitor them.
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