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Knowing your enemy is important to any defence strategy, including the management of invasive fish species. Analysis of the biology of the species is therefore an essential part of an integrated pest management plan.
A lot is known about the biology and population structure of carp in Australia1, 2 and certain stages in its life cycle are regarded as weaknesses that present opportunities for management. This factsheet explains these weaknesses and the implications for managing carp.
Carp spawn (lay eggs) when water temperatures reach about 17oC, which is usually in spring. They prefer shallow, vegetated areas usually less than 1 m deep. The eggs are sticky and are usually attached to vegetation. They hatch within 3–8 days, after which the juvenile (larval) carp move passively downstream with high water levels. Early growth usually takes place in stream backwaters or in lake marshes.
Research by the Invasive Animals CRC has shown that most successful carp spawning in the Murray–Darling Basin (MDB) takes place in only a few localised areas. It is likely that more than 80% of carp in the basin come from a small number of key nursery areas. These include major wetland areas such as the Macquarie Marshes, the Namoi and Gwydir wetlands and the Barmah–Millewa Forest.
Mass movements of any species usually mean that they will be concentrated at some point at a particular time. The fact that there are only a few preferred spawning sites of carp means that the carp will make mass migrations to these sites. In Australia, carp are known to:
Once they arrive at their preferred spawning location, large numbers of carp usually spawn at the same time.
These spawning aggregations are often quite vigorous and visible. Adult carp are also known to form winter aggregations in specific areas in lakes and probably also in large rivers. The locations of these aggregations are quite predictable and are probably related to slight variations in water temperature.
Juvenile carp will also form large aggregations. These tend to happen below stream barriers in autumn, and are probably related to their dispersal from the juvenile growth habitat.
Carp appear to move very little in streams for most of the year, suggesting that their feeding habitat is located nearby. By contrast, carp living in lakes are known to move considerable distances when feeding. Some patterns are evident in this movement, with large, easily visible aggregations of carp feeding in shallow areas.
Population genetics: Even though some of the carp strains were introduced to Australia more than 100 years ago there is still evidence of genetic isolation in the population structure of carp within Australia.
Carp are usually only available as prey for Australian native fishes and birds in the first 12 months of their life, as they grow quite rapidly. For the early part of this growth, their preferred habitat is vegetated marsh areas in lakes or river backwaters.
Most control strategies are more effective if applied at particular stages in the life cycle of the target pest species, or at specific times of the year, or at certain places where the pest is found.
Specific carp vulnerabilities have been analysed by the IA CRC6. The implications for carp management are that control strategies need not be implemented across thousands of kilometres of river basin. They also do not need to be carried out all year round.
Control strategies related to spawning migrations and spawning sites could focus on targeting:
Control strategies related to other aggregations of carp could focus on:
Knowledge of the genetic structure of carp populations in Australia can be used to:
Knowledge of the predators of carp, and their capabilities to reduce carp populations could also potentially be used, where suitable.
Not all of these strategies will work at any one site, and their use will depend on the nature of the particular site and how it is used by carp. A combination of strategies is likely to offer the best chance of success.
1. Koehn J, Brumley A and Gehrke P (2000). Managing the Impacts of Carp. Bureau of Rural Sciences, Canberra.
2. Brown P, Sivakumaran KP, Stoessel D, Giles A, Green C and Walker T (2003). Carp Population Biology in Victoria. Report 56, Marine and Freshwater Resources Institute, Department of Primary Industries, Victoria.
3. PestSmart Case Study: Carp spawning hotspots. PestSmart publication. Invasive Animals Cooperative Research Centre, Canberra.
4. Brown P and Gilligan D (2014). Optimising an integrated pest management strategy for a spatially structured population of common carp (Cyprinus carpio) using metapopulation modelling. Marine & Freshwater Research
5. PestSmart case study: Native fish predators as a biological control method for carp. PestSmart publication. Invasive Animals Cooperative Research Centre, Canberra.
6. Gehrig S and Thwaites L (2012). Exploitable Biological Vulnerabilities of Common Carp. PestSmart Toolkit publication, Invasive Animals Cooperative Research Centre, Canberra.
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, 2014. Carp weaknesses & vulnerabilities. Factsheet. PestSmart website. https://pestsmart.org.au/toolkit-resource/carp-weaknesses-vulnerabilities accessed 29-09-2020