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Two key elements of pest fish management are:
Containment and exclusion are critical actions in a rapid response to new pest fish incursions and in the ongoing management of established pest fish populations. Effective containment and exclusion limits the scale of potential environmental, social and economic impacts and reduces the area of management, thus reducing associated costs and resources. Physical and behavioural barriers can be used for fish containment and exclusion and their use is often an integral part of pest fish eradication and control programs.
The best fish barriers are those that are highly effective but easy to use and quick to deploy
|Physical barriers||Barrier description|
|Flat panel screen||A mesh screen/s is inserted vertically into a slot in a solid supporting structure. Screens may be made of various materials such as stainless steel, aluminium or plastic, with a variety of mesh aperture sizes.|
|Wedge wire screen||Wedge-shaped stainless steel bars are set side by side (the broad side of the bars forms the screen surface) fixed to a support structure. Bars may be spaced closely to create a fine screen.|
|Rotating drum screen||A cylinder-shaped frame covered in a mesh screen is fixed to a structure and set perpendicular to the water flow, with the drum lying horizontally. A single drum or drums may be placed end to end as a set. The drums rotate continuously in the direction of the water flow.|
|Rotating travel screen||A mesh screen belt rotates vertically between two drums or rollers. The belt is made from flexible plastic perforated plates, wire or grid material.|
|Barrier nets and fences||Mesh nets, or other barriers such as shadecloth fencing or wire mesh are set to exclude fish from a specific area. Stacked sandbags may be used to create a barrier fence.|
|Floating curtains||Nylon strips or metal chains are suspended side by side from bridges or pontoons set perpendicular to the water flow.|
|Vertical drop||A water drop is created over a structure that is too high for fish to jump — this prevents fish swimming upstream to a new habitat or breeding ground.|
|Traps and cages||Designed to be set into fishways, wetland entrances, irrigation channels, or other narrow channels where fish movement is bottlenecked. (Refer to carp traps factsheet).|
|Sound3||The use of underwater sound as a repellant to carp. The three main systems use audible frequency, infrasound frequency or ultrasound frequency.|
|Light||Light barriers use lamps to attract or deter fish. Lamp types include strobe, mercury vapour, sodium, fluorescent or filament lights. Continuous light is considered more effective than discontinuous light.|
|Traditional electrical4||An electric field is generated by a vertical array of submerged electrodes set apart with alternating polarity (AC/DC electrical current).|
|Pulse–generated electrical||A series of pulse generators is used to apply short pulses of direct current through a parallel array of electrodes across a river bottom.|
|Air bubble curtain||A basic curtain is produced by pumping compressed air through a pipe with ejection nozzles or perforations. A bio-acoustic fish fence (BAFF) adds sound to an air bubble curtain to increase its effectiveness.|
|Water jet curtain||Similar to the air bubble curtain — pressurised water is pumped through the pipe instead of air.|
Fish barriers vary in design, effectiveness, cost, construction, maintenance needs and operational safety-related needs. Barriers may be permanent or temporary, installed on a seasonal basis or for a rapid response to a new pest fish incursion (refer to Rapid Response fact sheet). The best fish barriers are those that are highly effective but easy to use and quick to deploy. The selection of a barrier to contain or exclude pest fish at a given location will vary on a case-by-case basis. In all scenarios, successful pest fish containment and exclusion relies on:
Physical barriers are effective if they provide complete exclusion of pest fish, such as carp1, 2. Suitable for use in various water bodies, they can be used to isolate an infestation from the rest of the catchment. Some barriers are mobile and can be rapidly deployed. But some barriers can be expensive, their effectiveness may be limited in floods, they may need regular monitoring and maintenance, and they may affect all fish species present.
In Australia, the most common barriers installed for pest fish control are screens and cages.
Behavioural barriers use external stimuli such as sound, air or electrical currents3,4 to influence fish behavior. Behavioural barriers are often used when physical barriers are impractical because of, for example, excessive debris loading, location accessibility or cost considerations. Complete exclusion is unlikely to be achieved with most behavioural barriers.
Water-level management via dewatering or drawdown may also be used for pest fish containment or removal. Suitable in small, isolated water bodies or those with mechanisms for water level control, regular annual water drawdown regimes may be used to manage specific habitats of pest fish (eg to remove access to carp wetland breeding areas in spring).
The authors of these documents have taken care to validate the accuracy of the information at the time of writing. This information has been prepared with care but it is provided “as is”, without warranty of any kind, to the extent permitted by law. The views and opinions expressed in this publication are those of the authors and do not necessarily reflect those of the institutions the authors work for or those who funded the creation of this document.
Centre for Invasive Species Solutions, 2012. Containment as a method for tilapia control. Factsheet. PestSmart website. https://pestsmart.org.au/toolkit-resource/containment-as-a-method-for-tilapia-control accessed 29-01-2022