Matt Barwick, National Coordinator, National Carp Control Plan 

An undated copy of correspondence from a UK researcher to an Australian Senator raising concerns about the possible use of Cyprinid herpesvirus 3 (CyHV-3, hereafter ‘the carp virus’) as a biological control agent for Carp in Australian waters has been circulated on social media.

I would like to directly address concerns raised, on behalf of the National Carp Control Plan (NCCP).

The current stage of the NCCP is a planning process led by the Fisheries Research and Development Corporation (FRDC) on behalf of the Australian Government to investigate the most appropriate options for an integrated program of carp control, with the potential release of the carp virus a key focus amid a complementary suite of measures.

Australian Governments will make a decision regarding whether to release the carp virus based on extensive scientific research funded under the NCCP to determine whether it can be done safely and effectively.

The NCCP is bringing together world-class social scientists, economists, biologists, water-quality experts, veterinarians and risk assessment specialists to investigate the challenges, risks, costs, opportunities and potential benefits of carp biocontrol.

Our extensive research program into the potential release of the carp virus includes inter alia:

  • Completion of trials testing susceptibility of non-target species to the carp virus.
  • Assessment of the social, economic, and ecological risks posed by carp biocontrol.
  • Investigation of water quality impacts including anoxia and blue-green algal blooms following major carp mortalities.
  • Development of strategies for cleaning up dead carp.
  • Exploring feasibility of secondary carp control approaches.
  • Assessing productive uses for harvested dead carp.

For more detail on these, and other projects please visit the research projects page.

The correspondence raises some particular concerns including species specificity, the impact of dead carp and secondary infections. Please find below a summary of work currently being undertaken by the NCCP in relation to these matters:

CyHV-3 species specificity

Twenty-two non-target species have now been tested for susceptibility to the carp virus in Australia, adding to a significant global body of work demonstrating the virus’s specificity to carp. I note that the authors cite Grimmett et al. (2006), who reported CyHV-3 replication in cultured cell lines of fathead minnow (Pimephales promelas) as evidence of this species being susceptible to infection. Grimmett et al. (2006) were seeking to identify the virus responsible for a mass carp mortality in the Chadakoin River, New York. Their study was not designed to test P. promelas susceptibility to CyHV-3, nor do they claim to have done so.

Assumption of a simple ‘single-outbreak’ epidemiology

The correspondence suggests that “the NCCP may be expecting a simple mass carp mortality…”. Those working on the NCCP do not assume a simplistic outcome from virus release. The NCCP’s entire research and planning process is based on recognition of the complexity of CyHV-3’s epidemiology, and challenges associated with continental biocontrol.

Research under the NCCP to estimate carp biomass in Australian waterways will provide data essential for understanding the carp virus’s epidemiology in Australian environments. This carp biomass estimation research will improve understanding of carp density in the various habitats throughout the species’ Australian distribution, and will critically inform epidemiological modelling to accurately and usefully inform decision-making and planning.

If carp biocontrol does proceed in Australia, knowledge derived from epidemiological modelling will inform development of virus release and clean-up strategies.

The impact of dead carp on other fish species and wildlife

Understanding and mitigating risks to water quality (and hence to other species and ecosystems) posed by possible major carp mortalities is central to the NCCP research program. Independent university researchers are currently investigating the effects of decaying carp on water quality parameters, and the potential for short-term release of nutrients resulting from carp kill events to trigger cyanobacterial (blue-green algae) blooms. This work augments detailed studies underway by NCCP researchers to explore water quality responses to carp mortality.

Research to investigate appropriate water treatment responses to carp mortalities is continuing. More broadly, the NCCP risk assessment project is taking a systematic approach to identifying risks to Matters of National Environmental Significance (MNES) as part of the NCCP’s stringent approval process under the Environmental Protection and Biodiversity Conservation Act 1999. This suite of projects aims to quantify the potential impacts of major carp kills on water quality and specific ecosystem components.

A second set of projects addresses the logistical and practical elements of clean-up. These projects include a global scan and review of fish-kill clean-up approaches, including reference to direct and extensive fish-kill clean-up experience in other countries, and work to explore engineering solutions that could enhance clean-up efficiency.

Risk of secondary infections

The letter raises the prospect of secondary infections by pathogenic bacteria living on decaying carp bodies. This is an important point, requiring careful consideration. Risks associated with harmful bacteria are being assessed through research underway at the University of Technology Sydney. This research includes quantification of bacterial loads under varying densities of decaying carp, while the NCCP risk assessment will ensure that this risk is considered as part of legislative approval processes.

I would again like stress that that no decision has been made at this time on deployment of a biocontrol agent for the control of carp in Australia. However, earlier small-scale studies have demonstrated that significant ecological benefits can result when carp numbers and impacts are able to be reduced. That means carp control on a continental scale is worth considering carefully. And only methods such as biocontrol – which can operate over significant geographic extents, are likely to be effective over the million square kilometres that carp now affect in Australia. Once complete, the NCCP will help answer the question, once and for all, “How could we as the Australian community successfully tackle the challenge presented by carp and their ecological impacts?”

The National Carp Control Plan is coordinating the detailed research, planning, and community consultation necessary to assess the risks and determine whether virus release is viable.

Read a more detailed version of this response.