National Carp Control Plan questions answered at Mannum forum; virus would be released into lower River Murray first

The National Carp Control Plan will not be finished until December, but all the boxes are gradually being ticked.

The plan's coordinator, Matt Barwick, could not answer every question from the 80-strong crowd at a forum at Mannum on Monday night.

But he explained the progress that had so far been made on what he called "the best researched vertebrate bio-control project in the world".

The southern end of the River Murray, below Lock One, will be the first to be treated with a carp herpes virus if its release is approved by Australia's state and federal governments.

The release would take place in spring, summer or autumn, when water temperatures are most likely to fall within the ideal range: 18 to 28 degrees.

Individual carp infected with the virus would be released into the wetlands and shallows where the pest fish breed, the places they are most densely concentrated.

For about four days they would go about their lives as usual, digging up the river bed, displacing native plants and fish, clouding the water, making a nuisance of themselves.

Around the fifth day, most would develop sores; by day six, provided the conditions were right, more than 90 per cent would be dead.

Then the real work would begin.

The bodies of the thousands or millions of dead carp would begin to break down within two weeks – that would be the window for a clean-up.

Re-purposed commercial fishing equipment such as haul nets and trawls would be among the main methods used by an army of paid workers; trucks with huge vacuums could help.

In more sparsely populated areas, the carp would be left to break down and be eaten by other fish.

Would it stink?

Yes, Mr Barwick said, but so did the deaths of hundreds of millions of rabbits when myxomatosis was introduced in the 1950s.

Prior to that time, rabbit hunting had been Australia's biggest employer, but the public recognised that rabbit plagues were a problem worth solving.

"The benefits are certainly worth considering carefully," Mr Barwick said.

"We need to understand the risks; that's what the National Carp Control Plan is to do.

"At the end of this year, we have a decision to make about whether to do this."

By the evening's end, a majority of those present said most or all of their questions had been answered.

One resident of the shores of Lake Alexandrina recalled the clear-water days before the carp came, and expressed a sentiment applauded by the rest of the meeting.

"I don't care what the stink is, and I've got to live right by it," he said.

"Bring it on."

The carp problem

"I've spent my life studying native fish," Mr Barwick said.

"I love them.

"That's why I'm so interested in killing carp."

Carp were bottom-feeders, he said; they muddied the water, blocking light from native plants, they ate small creatures, and the nutrients they excreted helped algae grow.

He showed images from Lake Bonney, where a young girl caught 70 carp using a stick, and a channel in Victoria where the thrashing carp appeared thicker than water; he showed pictures of clearer water and wetlands teeming with life where carp had been removed.

It was hard to say exactly how many carp were in the river, he said: "it's like 'how many jelly beans are in the jelly bean jar?', except the jelly bean jar is southeastern Australia and the jelly beans are these fish".

But research had shown they made up between 80 and 93 per cent of fish by weight.

"It's disheartening to think of going through 93 kilograms of carp to get 7kg of native fish," he said.

At Echuca in the 1920s, the average recreational catch per hour was 18 to 22kg of native fish.

A single female carp could lay more than a million eggs, more than once per year.

Previous attempts

Since the 1960s, Mr Barwick said, Australians had tried commercial and recreational fishing, blocking off breeding grounds with screens, draining wetlands, harvesting carp using cages on weirs, synthesising pheromones to lure them into traps, using radio transmitters to trace populations, even tinkering with their genes to produce single-sex offspring.

It had not worked.

Fishing was not effective because it took out only about two per cent of the population, he said; even electro-fishing, running a current through the water, only captured about 15pc.

"Creating an income from catching carp and fixing the ecological devastation they cause are two different things," he said.

"It has been tried, seriously, and hasn't worked.

"But we're still looking at this because it may be part of a strategy moving forward."

The virus

Cyprinid herpesvirus three was discovered in Israel, Europe and North America in the 1990s and was now present in more than 30 countries, Mr Barwick said.

The relevant strain of the carp herpes virus is present in more than 30 countries.

The relevant strain of the carp herpes virus is present in more than 30 countries.

Strains one and two of the same virus were already present in Australian waterways.

Theoretically, if scientists could prove that the virus was unable to mutate enough to infect the carp's closest native relative – the catfish – all native fish should be safe.

But the CSIRO tested it on representatives of every fish family in the Murray anyway, plus a range of land animals, and found it to be safe.

"All living things mutate, that's evolution, but could this ever mutate in a way that affects native fish?" Mr Barwick asked.

"There's no evidence."

Even if the virus were approved for release, staggered across the Murray-Darling Basin over a couple of years, other methods would be needed to control carp after the initial wave of deaths.

Again, Mr Barwick compared carp to rabbits: what if scientists in the 1950s had planned to release myxomatosis, then the fleas which spread it further, then the calici virus, then begun ripping warrens, all within a few years?

What next?

A web of working groups and committees across state and federal governments, researchers from universities across the country, and volunteers on the ground across the nation are all working on the carp control plan.

A draft version will be completed by July and put through another round of public consultation between August and October.

Australia's state and federal agriculture ministers will decide whether to go ahead with the plan – and, if so, how to fund it – in December.

The decision will have to be unanimous – if one jurisdiction says no, it will not happen.