Within a river rehabilitation context, this action involves reducing or eradicating populations of invasive aquatic animals. Preventative action that avoids the introduction or spread of invasive aquatic animals is widely acknowledged as a more cost-effective approach than controlling established populations and should be pursued in the first instance to control invasive aquatic animals at a state or regional level. Preventative action depends primarily on the effectiveness of biosecurity legislation, monitoring, public education and behaviour.
Most invasive aquatic species in Queensland are fish. These include introduced species from outside Australia (e.g. carp, tilapia) but also native species translocated beyond their natural range (e.g. sleepy cod, striped grunter, red claw crayfish). Another example of an introduced invasive animal in Queensland is the cane toad.
Exotic invasive aquatic species often proliferate in degraded habitat conditions. Control of aquatic weeds been found to reduce the abundance of exotic pest fish species. The figure shows comparison of proportion of Plague Minnow Gambusia holbrooki to total abundance before and after weed mat removal at Payard's lagoon in SheepStation Creek. Data shown are the mean abundance estimates from nine push net samples from each of nine surveys.
Image by Perna, 2009
A range of strategies and methods can be pursued to reduce invasive aquatic animal populations. They include:
direct harvesting/capture or lethal controls
alteration of environmental conditions to reduce suitability for the invasive species
exclusion from breeding areas or other use of barriers (e.g. screening irrigation water transfers)
increasing predation or competition pressure
use of specific pathogens or bio-controls
community education programs.
Examples of complete eradication of invasive aquatic species populations in Queensland are rare and have only occurred when there has been early detection of small founder populations. Gains obtained by direct harvesting and lethal control are seldom sustained where the targeted species has a high reproductive capacity. Such methods can produce useful outcomes if applied strategically. Rehabilitation of degraded habitat conditions and native predator populations has been shown to provide sustained outcomes for a number of invasive fish species.
Invasive aquatic animal control is a relevant management action for any aquatic ecosystem rehabilitation objective that seeks to improve the native biodiversity of a river system or address habitat conditions potentially impacted by invasive aquatic animals.
Potential benefits from this intervention:
Support higher levels of native biodiversity in the absence of competitive pressures and site environmental impacts associated with introduced aquatic species.
Invasive aquatic animal control programs (e.g. toad muster, carp fish outs) provide opportunities to engage community in site rehabilitation objectives and environmental education.
Provide justification for environmental works (e.g. weed control, riparian revegetation) which have broader environmental benefits.
Justify access to biosecurity funding program support.
Potential negative implications from this intervention:
Control methods (e.g. electrofishing, screening) can impact non-target species.
High levels of resources for outcomes that may not be sustainable in the longer term.
Negative public sentiment if control is not sustained.
The removal of large numbers of pest animals may result in a rapid change in ecosystem processes. For example, Tilapia consume algae and their removal may result in algal blooms.
Intervention considerations:
Seek appropriate specialist advice and check legal obligations (e.g. permits).
Consider size, distribution and reproductive capacity of targeted invasive species versus effectiveness of proposed control mechanisms/methods.
Assess the impact of invasive species relative to other degradation drivers and resource commitment required to address invasive animal control versus other degradation drivers (i.e. return on effort invested analysis).
Determine location of refugial areas that are free of pests as well as pest refugia (where pests find refuge during control efforts).
Will the removal of dominant aquatic pest species impact the population of introduced species present at the site that have not yet generated significant impacts (i.e. sleeper species)?
Consider inter-site quarantine opportunities and lines of control within the surrounding catchment.
Ethical considerations and obligations associated with some forms of aquatic pest removal.
Safety of volunteers and employees including seasonal exposures (e.g. heat) and high risk areas (e.g. crocodile presence in waterways).
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Additional information
Publications:
Molloy, K.L. and Henderson, W.R. (Eds). 2006. Science of Cane Toad Invasion and Control. Proceedings of the Invasive Animals CRC/CSIRO/Qld NRM&W Cane Toad Workshop, June 2006, Brisbane. Invasive Animals Cooperative Research Centre, Canberra.
Perna C, Cappo MC, Burrows D and Pusey B. 2009. Floodplain degradation and restoration in northern Queensland: the response of the alien fish pest, Gambusia holbrooki. Ecological Management and Restoration. 10: 241-243.
WetlandCare Australia. 2008. Wetland Rehabilitation Guidelines for the Great Barrier Reef catchment. Compiled for Department of the Environment, Water, Heritage and the Arts.
Department of Environment, Science and Innovation, Queensland (2022) Aquatic fauna pest control, WetlandInfo website, accessed 16 April 2025. Available at: https://wetlandinfo.des.qld.gov.au/wetlands/management/rehabilitation/rehab-process/step-4/intervention-options/aquatic-pest-control-mod.html
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— Department of the Environment, Tourism, Science and Innovation
