Mozambique tilapia (Oreochromis mossambicus) is an invasive fish species, which was illegally introduced to Australia during the 1970s. Since its introduction, the species has spread throughout Queensland and is also found in Western Australia. This has occurred partly by natural dispersal and partly through people illegally moving fish between water courses.
In Australia, management options for tilapia have largely focused on public education campaigns and containment of existing populations. There have also been attempts to eradicate confined populations of tilapia using fish poisons (known as piscicides). These attempts have had mixed success, with reinfestation of water bodies occurring in some cases. However, when used under the right conditions, piscicides such as rotenone can be useful for stemming the spread of tilapia to new, unaffected catchments and watercourses.
In early 2009, Mozambique tilapia were seen for the first time near Bundaberg in central Queensland, by local water authority SunWater and members of the general public. Reports of sightings suggested that local farmers were cultivating tilapia in their farm dams for personal consumption. This practice is illegal in Queensland (Queensland Fisheries Act 1994), with heavy fines applicable for anyone found in possession of tilapia. A search warrant was issued for the suspected farms and the Bullyard area was extensively surveyed for tilapia. Significant numbers of tilapia were discovered in 18 farm dams across three properties. Individual tilapia were also found in an irrigation channel associated with these dams. A major concern was that, during periods of heavy rain, these dams overflow into the adjacent Bullyard Creek, a tributary of the Kolan River. These waterways were surveyed by electrofishing and netting, but evidence of tilapia was not found.
An eradication program using rotenone was designed to remove the contained populations of Mozambique tilapia and eliminate the spread of from the Bullyard area of central Queensland.
Partners and management
This eradication effort was managed by the Fisheries Queensland group of the Department of Agriculture, Fisheries and Forestry (DAFF) in cooperation with SunWater, Bundaberg Regional Council, the Local Marine Advisory Committee, local stocking and recreational fishing groups, the Burnett-Mary Regional Group (BMRG), Landcare, Oceanwatch, regional bait and tackle stores, Bundaberg Canegrowers Association, Queensland Parks and Wildlife Service, and affected landholders in the Bullyard area.
A risk management strategy was developed as a first priority to determine what action would be needed to control the tilapia infestation in the Bullyard area. This strategy was developed in consultation with a wide cross-section of skilled people, including those experienced in fisheries and pest fish management, fisheries regulation enforcement, media liaison, workplace health and safety and human resource management. The risk management process considered many factors, including:
- past experiences managing tilapia incursions using different options such as monitoring only, containment, population reduction, eradication and/or a combined approach
- potential socio-economic and environmental impacts of these different management options
- oportunities to set up partnerships with community groups and regional media outlets
- financial, logistic and geographic opportunities and constraints.
Pest fish eradications are generally very expensive, need a lot of preparation, and are usually only successful in small-scale situations and in shallow and closed waterbodies. The management group decided that eradication was the best option in this case, since the tilapia incursion was in a relatively small, contained environment and the water was not used for human consumption.
Onground operations involved:
- starting a register of personnel and resources offered by community groups and other government agencies
- seeking legal advice about the implications of declared pest fish incursions on private property (Note: at the time, the landowners were legally responsible for the eradication of pest fish species from their properties at their own cost)
- sending destruction orders to the owners of the affected farms (Section 108 under the Queensland Fisheries Act 1994)
- identifying experienced personnel, or those able to become trained and accredited in chemical application
- updating Fisheries Queensland personnel with the current operating conditions of the Australian Pesticides and Veterinary Medicines Authority’s (APVMA) ‘Minor use permit for rotenone’
organising timing and cost estimates for approved laboratory testing of water and soil samples
- calculating and ordering the amount of rotenone required (1.3–10.5 kg per dam)
- organising various logistical issues such as accommodation, meals, transport, equipment, dead tilapia disposal, exclusion of livestock and native fauna from the treated sites, backup irrigation supplies for landholders, post-eradication monitoring of dams and the future restocking of endemic fish species back into the treated dams.
Features of the program
To maximise the chances of success, strategies were developed to engage local government, water authorities, state government departments, industry groups and the local community. The aims of these strategies were to encourage all stakeholders to participate in ongoing surveillance, and emphasise the point that ‘pest fish are everyone’s problem’.
The pest fish issue was highlighted in media releases and in brochures distributed at field days, to local bait and tackle stores, schools, recreational anglers, and fish stocking groups. Fisheries Queensland gathered information about the presence of pest fish from these local groups, who were very passionate about pest fish incursions.
A total of 5900 Mozambique tilapia were eradicated from the 18 farm dams treated with rotenone. However, as would be expected with the use of a non-selective poison, large numbers of native fish were also killed. These included rainbow fish (Melanotaenia duboulayi), gudgeons (Hypseleotris spp. and Mogurnda adspersa), spangled perch (Leipotherapon unicolor), long-finned eels (Anguilla reinhardtii), dewfish (Tandanus tandanus), fly-speckled hardyhead (Craterocephalus stercusmuscarum), banded grunter (Amniataba percoides) and olive perchlet (Ambassis agassizii).
Post-eradication monitoring in November 2009 using boat electrofishing did not detect tilapia in any of the farm dams or in the adjacent irrigation channels. However, tilapia are now known to be present in other parts of the catchment.
- The use of education material and the media proved successful in keeping the community informed.
- Strategically targeting the farm dams succeeded in eradicating resident Mozambique tilapia from these waters.
- Tilapia do not appear to have colonised the nearby Bullyard Creek or the adjacent irrigation channel.
What didn’t work
- Feedback from landowners suggested that the information given to landholders on the likely effects of the fish poison rotenone was not comprehensive enough. Science-based literature detailing the impacts of the poison on the environment and on farming practices needs to be distributed well before eradication operations begin.
- The time needed to clean up the site was underestimated — it took about one week longer than expected. This was most likely due to cooler water temperatures that prevent the decomposition (and thus floating) of dead fish.
- Laboratory analysis of residual rotenone levels in dam water and surrounding soil returned inaccurate results in a poor timeframe. In future, the quality of laboratories needs to be verified in advance, to ensure timely and accurate results.
What was learnt
- Conflict with property owners during this exercise highlighted the importance of communication with all stakeholders. All parties involved need to understand their rights and responsibilities, and how resources and expenses will be shared.
- Detailed information about the chemicals involved and the application process needs to be given to the affected landholders, and their agreement sought before beginning on-ground activities.
- Landowners and the public need to be made aware of the limitations and benefits of planned eradication exercises or other proposed actions.
- Pre-eradication fish surveys do not always give a full picture of the extent of an infestation, so they are best considered as a rough guide.
- Unless the source and extent of an infestation is clear, localised eradication attempts can be high risk, expensive and potentially unsuccessful.
Mozambique tilapia were successfully eradicated from 18 farm dams near Bullyard in central Queensland using the fish poison rotenone. Post-eradication surveys of Bullyard Creek and nearby water storages have not located any tilapia, although they have since been found in other parts of the catchment. The source or sources of these new infestations remains unknown.
Where eradication works are to be done on private property, considerable effort should be put into engaging with landholders and developing ways to identify and prevent potential disputes before they arise.
|Author||Centre for Invasive Species Solutions|
|Publisher||Centre for Invasive Species Solutions|
|ISBN/ISSN||PestSmart code: TILCS1|
|Control method||Poison / Toxin|
|Documents||Case study: Eradication of Mozambique tilapia at Bullyard Creek, Qld [455 kb PDF]|