The silver bullet that was to be the koi herpes virus to control carp numbers in the Murray is becoming increasingly tarnished.
And even if it does get released on an industrial scale, the virus may still be several years away.
It is news that has deflated some of the river’s most dedicated enthusiasts – the fishing fraternity.
It has also made major stakeholders such as the catchment management authorities wonder what comes next.
The National Carp Control Plan was completed by the Fisheries Research Development Corporation late last year but ongoing research has cast doubt about how the virus could impact native fish species.
State and federal agriculture ministers will receive new research recommendations from the Agriculture Department’s environment and invasivese committee in July.
According to Australian chief environmental biosecurity officer Bertie Hennecke there are still a lot of issues unsolved, such as the impact on town water, stock and domestic consumption and irrigation, along with cultural and recreational considerations as well as the clean-up of dead fish biomass.
Irymple-based OzFish senior program manager Braeden Lampard said carp are one of the worst introduced pest species in Australia and have significant social, environmental, and economic impacts.
Introduced to Australia more than 100 years ago, carp have become the most dominant large-bodied fish in the Murray-Darling Basin, making up as much as 80-90 per cent of fish biomass.
Carp have major negative impacts on water quality and the amenity value of our freshwater environments.
“The OzFish stance for the carp herpes virus is yes, let’s put it in (and OzFish will help), but it’s only going to be effective for just a few years,” Mr Lampard says.
“So, we really need to make sure there is a raft of supplementary habitat rehabilitation measures put in place (such as fish screens, fishways, re-snagging and recreational fisher capacity) for it to have any value in the long term,” he said.
“OzFish is working alongside local, state, and federal government agencies to undertake isolated carp control methods – to date we have run more than 30 catch a carp fishing events with each removing hundreds of carp.
“OzFish has submitted a project proposal to work alongside Indigenous owners across NSW to undertake large-scale carp removal events. We will hear the outcome of this proposal in the coming months.”
At its most recent event – four hours at King’s Billabong last month – about 200 fishers landed more than 200kg of carp – one man alone caught 80.
Mr Lampard said he understands some of the major issues between the virus and the waterways is the clean-up of dead fish and the release of the virus into a water supply used for everything from drinking water to irrigation.
He said with the bulk of carp deaths expected very early after the virus is released, the potential clean-up would be overwhelming.
“However, something is going to have to be done because they simply do so much damage,” he said.
Mr Hennecke said even if a decision is made to introduce the virus, with so many affected jurisdictions with a say, and Environment Protection and Biodiversity Act requirements to be met, an actual release is “probably two to three years away at least”.
The new paper being delivered next month “is mainly around further consideration of impact on native species and also looking at cost-benefit analysis to update that and some other elements”.
Modelling, done as part of the federal government’s investigation, estimated the virus would kill 60 per cent of the carp in basin waterways and cut fish densities well below the damaging threshold of 100kg/ha.
“I think their comment on effectiveness was that it was not going to be a silver bullet; that it would have to be used in conjunction with other management strategies,” he said.
However, Dr Hennecke also said the taskforce found some other control tools “need to have further consideration to improve them”.
Researchers have $3.68 million remaining from a $15 million funding envelope to complete the trouble-plagued, years-long project.
In the meantime, OzFish will push ahead with its programs, including its upcoming installation of ‘fish motels’ in partnership with BFC and the Mildura RSL Angling Club.
Mr Lampard describes the motels as complex installations designed to protect smaller fish, such as the Murray Hardyhead, as they grow out and breed. The will start installing them next month.
Mildura RSL Angling Club president Garry Hodson agrees carp are a big problem that is getting even bigger.
Mr Hodson said since the flood, carp numbers have taken a sharp rise – adding even when there is blackwater in creeks, tributaries and billabongs, the carp are able to break surface and breathe the air, which native fish cannot do.
It will kill the Murray cod and the perch but not the carp.
“I recall the Kerang Lakes being drained years ago, and the piles of dead carp rotting, stinking out the area until some were removed and the lakes refilled,” Mr Hodson said. “But you can’t empty the Murray.
“The other day I was out fishing and while I did catch my limit of five perch, I also caught 30 carp, they’ll take your bait, they’re such a pest.
“And we’re not talking small fish, I’ve caught them up to 75cm and a lot of them, they grow into very big fish.”
Mr Hodson said club members have been running working bees with OzFish to build the fish motels, and they’ll help out again next month.
He said while he missed the most recent catch a carp event, he has taken part in previous ones.
“We have always been keen on putting fingerlings into the river but the carp tend to clean them up,” he explains.
“And with the floods, in the creeks, we had a lot of blackwater, and even in the shallow stretches you could see the young carp on the surface, breathing air, but none of our good fish.”
