European carp

The common carp, Cyprinus carpio, is a large freshwater fish well  known in Australia as a significant pest of inland waterways. In 2000-2001, recreational anglers across Australia caught more carp than any other freshwater fish and it was also a major component of commercial–scale fish catches in Victoria.

While fishing (commercial or recreational) is not an effective means of carp control in itself, it can be a valuable component of an  integrated carp management program.

Localised, ad hoc or one-off carp removal events (eg. carp fishing competitions) are popular in many parts of Queensland, New South Wales, the Australian Capital Territory and Victoria. Commercial carp fishing occurs in Victoria, South Australia and (irregularly) in New South Wales.

Commercial fishing may help to keep carp numbers under control, especially when repeated over a period of time, and when areas such as carp breeding ‘hotspots’ are targeted. However, under normal circumstances only a proportion of the carp population is removed with each attempt, and because carp have a very high population recovery rate, numbers can quickly return to their original levels.

Current approaches

Carp closeup. Image by Marc Ainsworth

To help combat the impacts and spread of carp, some community groups have organised ‘fish-out’ events. Carp musters can be used as an opportunity to remove carp from a localised area and are a fun way of increasing community awareness. However, the impact on carp numbers in the long term is minimal. Musters can be good fundraising events for river rehabilitation projects or restocking of native species. Normal fishing rules apply to these events.

Harvested carp should be killed humanely and may be eaten but cannot be sold, unless the carp are taken by a commercial fisher who then sells them. Alternatively, the caught fish may be used by a carp processing company. For smaller quantities, options include eating, using as pet food, or composting.

Unfortunately, carp are so widespread and abundant in Australia that most state and territory fisheries agencies do not have the resources to send staff to remove carp from local sites on request, even when conditions appear favourable for carp removal (eg when large numbers are aggregating below a river barrier).

Commercial harvesting has the potential to quickly remove large quantities of carp in specific locations and can affect the carp population if it is sustained. However, sustained fishing usually takes populations to a point where it is not economically viable to continue fishing because of low market prices and high costs of fishing. Market returns will justify harvesters’ efforts only under specific conditions (eg high carp numbers, proximity to markets and minimal fishing obstructions such as snags). Public authorities or private businesses may contract endorsed commercial fishers to remove carp from a water body that they manage, as a fee-for-service contract.

The main fishing techniques used by state and territory fisheries agencies and commercial fishers include:

An electric field is generated between anodes and cathodes placed in the water. The current causes muscle contraction and temporary paralysis, and most fish will float to the surface where they can be netted. Stunned fish usually recover quickly when the power is switched off. Unfortunately, fish in deep water are not often captured. Different electrofishing methods (eg backpack, bank-mounted and boat, including electroseining) are used depending on local site conditions.

Electrofishing operations in the Lachlan River catchment,
NSW. Image: NSW Fisheries

Netting methods:

• Fyke nets — collapsible, cone-shaped trap nets, held open by hoops. Leader net panels or wings guide fish towards the trap entrance. Due to their size and placement in shallow locations, fyke nets are effective for catching smaller carp.
• Pound nets — fish traps that have net guide walls leading fish into aggregation chambers. These are usually set in shallow water.
• Gill nets — mesh net panels held vertically in the water to entangle fish. The net has a rope along the top with floats attached and another rope along the bottom with weights attached. The mesh of a gill net is uniform in size and shape and the netting is large enough for a fish to fit its head through, but not its body.
• Seine nets — long, small mesh nets that hang vertically in the water with floats along the top and weights along the bottom. They are typically used to surround fish in an area and pulled through the water to land the fish on shore. Seine netting is very effective but limited to areas that are snag free. Also known as hauling.

Hauling a small seine net through the shallow end of a lagoon. Image: Queensland Department of Employment, Economic Development and Innovation

Trapping methods:

• Bait traps — an effective means of trapping small fish, including carp. They are useful for targeting juvenile carp at breeding hotspots.
• Hopper traps — an automated feed dispenser, or hopper, is situated with a net or series of nets, attracting carp into a trap. Alternatively, a hormone-induced sexually mature carp can be  used as ‘bait’ during the breeding season to lure other carp for trapping and capture.
• Migratory traps — barrier traps that make use of the movement of fish. The installation of fish traps at fishways allows for sorting of the catch and removal of carp.

These techniques generally require specialised training, skills and equipment or present a risk to native fish and other aquatic animals. In public waters such as rivers, lakes or impoundments the use of nets by anyone other than appropriately licensed commercial fishers is illegal and significant penalties apply. It is also illegal to possess commercial nets in, on, or adjacent to public waters.

Hand-hauled drag nets may be used in a private water body (eg a farm dam) to catch carp in New South Wales and Queensland (refer to state fishing regulations). However, trying to remove carp in this way can be labour intensive and difficult and will not eliminate carp altogether. Periodic removal will assist in keeping carp numbers low. Fishing methods will be more effective if the carp can be aggregated in a small area before trying to catch them.

Other information:

Small-mesh fyke nets, large-mesh fyke nets, pound nets and electroseining were compared for the number of carp harvested per day, capture efficiency, cost of purchase and operation, ease of use, suitability for use in a range of different aquatic environments, and incidence of bycatch and injury to native fish.

Small-mesh fyke nets caught the most carp from the widest range of size classes, were the easiest to use, only resulted in a low level of potential injury to native fish and were the second most cost-effective gear type (large-mesh fyke nets were cheaper).

The Invasive Animals Cooperative Research Centre (IA CRC) project Carp control in the Logan-Albert Rivers catchment showed that a range of commonly used, generally low-cost fisheries techniques can be used to catch carp. The IA CRC PestSmart publication Effectiveness of Carp Removal Techniques: Options for Local Governments and Community Groups concluded that no single technique was appropriate in every scenario and recommended a combination of techniques be used in an integrated approach.

Electrofishing followed by hopper trapping was found to be the most efficient technique for catching carp; these two methods could also be used simultaneously to increase the number of carp caught per unit of effort. Seine netting was another highly effective technique, but only suitable in a limited number of areas. Similar research found hauling to be the most effective method of carp removal, but only in suitable locations. Electrofishing was highly effective in all habitat types, with minimal by-catch.

Research findings and implications for pest fish management

For now, it is not feasible to eradicate carp from large areas using fishing methods. However, at smaller scale sites considered to be of significance, fishing techniques can be used for carp removal, and radio-tagging techniques can be used to target aggregations of carp.

The best value for management actions will be achieved by well-timed (eg in warmer months, particularly before the carp spawning season), periodic removal of carp. This is especially the case in high-value wetlands or where carp reinvasion can be managed through the use of exclusion screens. To consistently achieve lasting benefits, a strategic and ongoing control plan is needed.

Further information:

1. Koehn J, Brumley A and Gehrke P (2000). Managing the Impacts of Carp. Bureau of Rural Sciences, Canberra.
2. Carp Fishing Competitions. PestSmart Toolkit case study.
3. Norris A (2011). The Role of Fishing Competitions in Pest Fish Management. PestSmart Toolkit publication.
4. Carp Spawning Hotspots. PestSmart Toolkit case study.
5. The Importance of Public Consultation for Pest Fish Management. PestSmart Toolkit factsheet.
6. West P, Brown A and Hall K (2007). Review of Alien Fish Monitoring Techniques, Indicators and Protocols:
   Implications for National Monitoring of Australia’s Inland River Systems. Invasive Animals Cooperative Research Centre, Canberra.
7. Chemical Attractants. PestSmart Toolkit factsheet.
8. Radio Tracking. PestSmart Toolkit factsheet.
9. Containment as a Method for Pest Fish Control. PestSmart Toolkit factsheet.

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.