National Carp Control Plan released, but questions remain
After seven years, researchers have recommended harvesting the pest fish ahead of any virus release in the Lower Murray.
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More research, consultation and heavy fishing will be needed before any carp virus can be released into the River Murray, researchers have found.
Seven years after the National Carp Control Plan was trumpeted as part of the solution to the Murray-Darling Basin’s environmental problems, the plan itself was finally released last Thursday.
As instructed by the federal government at the time, it focused heavily on one method of removing the pest fish from the river system: releasing a deadly virus.
However, it stopped short of recommending that course of action.
Instead, it proposed:
- Establishing a task force to keep looking at the issue
- More research on topics including cross-species infection, where and when carp were at their thickest, and whether the virus would work in the slightly more saline Lower Lakes
- Making plans to protect the Coorong and Lower Lakes environment
- Continuing to engage with locals in river communities
Researchers found that a cyprinid herpesvirus would not be a “silver bullet”, but would reduce the river’s carp population by 40 to 60 per cent.
However, harvesting – fishing – would first be needed to reduce carp numbers in areas where their population was densest, such as the Lower Murray and Lower Lakes.
The virus would not infect humans, and was not likely to infect other species; but all the rotting fish would make water quality and bacterial infections such as botulism a problem, and again the Lower Murray would cop the worst of it.
After all, there were likely about one million tonnes of carp in the river system, including up to four tonnes per hectare in the areas closest to Murray Bridge.
If decision-makers did decide to release the virus, how would it be done?
It would be best to time the release during spring in a drier-than-usual year, when there would be fewer carp and when those remaining would more likely be closer together.
The virus would first be released in northern New South Wales, not in the Murraylands as previously suggested.
The carp in a given area would die over the course of four to eight weeks, and their carcasses would need to be either flushed downstream or collected, mechanically or by hand.
The cost of such a project would run into the hundreds of millions of dollars.
But it might, ultimately, be feasible – or at least, “no results have emerged to clearly indicate that further consideration of the virus as a bio-control agent should cease”.
Despite all the noise made about the National Carp Control Plan over the years, it was published last week without any fanfare: no announcement from the federal Agriculture, Forestries and Fishery Minister, just a short statement on the departmental website.
The department emphasised that the plan had not yet been considered by state or federal governments.
It would be up to those governments to decide what – if anything – to do next.
