Carp herpes virus could cause secondary infections such as botulism, risking public health, says Coorong ecologist Faith Coleman

The release of a carp herpes virus into the River Murray could prove more damaging than the carp themselves, a leading ecologist says.

Faith Coleman lives in the Coorong district, where she can be close to the estuary she has spent years studying, and was recognised last year as one of the unsung heroes of South Australian science.

Ms Coleman said she based her opinion of the carp virus on evidence, and would gladly support it if all her concerns were addressed.

But those concerns were many.

Chief was her worry that the carp could not be cleaned up quickly enough to prevent environmental devastation.

The bodies of infected fish would be covered in holes, leading them to decay more quickly and, in turn, making outbreaks of secondary infections such as botulism – which is highly toxic to livestock, native animals and humans – more likely.

If tonnes of fish were left lying around after such an outbreak, they would inevitably be eaten by birds and the infections would spread.

The presence of dead carp in such numbers was also likely to remove oxygen from the water, she said, which would likely kill all the other fish in the system.

The effect would be most pronounced in the Lower Lakes and Coorong, below Lock One, where carp were likely to be densest and water flows were most sluggish.

Higher volumes of water would flush the dead carp out of the Murray Mouth, but then there were more problems.

Because it thrived in warm temperatures, the virus was unlikely to be released in winter, when the extra water might be available; and even if water could be found, many of the dead fish could conceivably flow into the Coorong rather than out into the sea.

Finally, after the initial carp kill, Ms Coleman foresaw more risks: the possibility of herpes-resistant carp, more mass kills every couple of years, or another pest species filling the gap in the ecosystem.

"By the time 10 years had passed, unless other methods of control were introduced like fishing or carp traps, I'd be expecting they'd need to be releasing another virus," she said.

She expected it would take the basin environment up to 30 years to recover.

So she urged patience.

"It has taken the carp 50 years to get this far," she said.

"They are bad, they need removing.

"It might take 20 or 30 years to remove them (without a virus).

"It might cost more, and would definitely take more political will, but perhaps that is what we need to do."

The Lincolnshire letter

Ms Coleman's comments came amid a social media storm created by the circulation of a letter from another scientist, British acquatic pathobiologist Paula Reynolds, to an Australian Senator.

In the so-called "Lincolnshire letter", Ms Reynolds expresses concerns about the potential for the virus to jump between species, to be spread by species that could not be infected, and for the initial mass kill to threaten livestock and clean-up workers with infections such as botulism, E coli and aeromonas.

"All attempts to control the virus (in the UK) have proven futile, with many new strains emerging over time," she said.

"Based on our long experience, we advise against the plan to release this virus into the rivers and waterways of Australia.

"I do not consider it safe, or indeed ethical."

She suggested international experts had reached a consensus that the virus was unsafe, and that their opinions needed to be more widely reported in Australia.

Mr Barwick responded to the Lincolnshire letter with a post on the National Carp Control Plan (NCCP) website last week.

He said claims that the virus could jump between species were unproven.

Research was continuing into the likelihood of secondary infections; the impact of dead carp on other species; and the density of carp in the Murray-Darling Basin, which would help establish whether more than one mass kills was likely.

"I would again like (to) stress that no decision has been made at this time on deployment of a biocontol agent for the control of carp in Australia," he said.

"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.

"Only methods such as biocontrol ... are likely to be effective over the million square kilometres that carp now affect in Australia."

The first draft of the National Carp Control Plan is due to be published in July.

The public will be consulted about it during the second half of the year, and the results of NCCP research will be incorporated into a final version of the plan before it is presented to governments for a decision in December.

Fairfax Media sought comment from Biosecurity SA for this story, but was directed to contact the NCCP.