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Carpageddon: what you need to know about the release of carp herpes in Australia

Carp are a major threat to Australia’s rivers. Melbourne Water/Flickr, CC BY-NC-ND

Yesterday’s announcement of funding for a National Carp Control Plan – including the release of the carp herpes virus – has generated a lot of interest in the media. I welcome plans to release the virus by the end of 2018. In January I wrote an article here explaining the concept and why I think it could work in Australia.

Since the announcement I’ve listened to discussions on radio and television highlighting the concerns of the public. I hope to address some of the confusion and set the record straight.

What will we do with piles of dead fish?

Among people who live near the Murray River or one of its tributaries, this is the main objection to the release of the virus. This in itself suggests that those close to the rivers understand the implications of carp being 80% of the biomass in the Murray Darling Basin. Many people have lived through black-water events (where oxygen levels drop resulting in large fish kills) and they know how unpleasant it is to have a lot of dead fish at one time.

Their concerns are justified. Fortunately, Science Minister Christopher Pyne is aware that hundreds of thousands, possibly millions of tonnes of dead carp will need to be cleaned up, and this will require community consultation and potential legislative changes. Pyne says we can use dead carp as fertiliser, as pet food or bury them in large graves. It is interesting to note that the fertiliser company Charlie Carp welcomes the move and may expand their business into South Australia so they can respond to large fish kills there.

The trick will be disposing of the fish quickly because after 48 hours they will begin to rot and will not be suitable for use. My reading of the announcement suggests that planning for this one time big carp kill will be a large part of the $15 million spent over the next two years.

How is the virus transmitted?

There were some giggles about how this virus is transmitted among fish, given that herpes is a sexually transmitted disease in humans. However, all the fish have to do is bump into one another to transmit the virus, and they can also be infected by the virus that lives in the water, although the virus will only survive for a few days outside of the body of a fish.

Once infected, any survivors will carry the carp-specific herpes virus for life. Stress can re-activate the virus, causing it to persist in the carp population and allowing it to spread rapidly under crowded conditions.

What a waste – we could have sold these fish overseas!

It is true that Australians resist eating carp due a perception that they are “junk” fish. Some say they have a muddy flavour, or that they are too bony. Neither of these issues stop people in Europe, the Middle East and Asia eating carp, where they are a common part of the diet.

There are two problems with the suggestion that we are missing a commercial opportunity here. The first is the economic viability of shipping fish to the other side of the world. We cannot get them there alive so we will need to freeze or can the carp, and once we’ve done that, consumers must pay enough to cover the processing and shipping.

I was on a committee with the NSW Department of Fisheries 15 years ago that was looking for markets for carp products. Enthusiastic investors with support from government could not find a way to make money with this export.

The second problem is that any industry relying on carp as a product will not remove carp from our rivers. Carp are causing enormous damage to the ecology of rivers and lakes across our continent and fishing alone will never remove enough of them to return those ecosystems to health.

But biological control never works, does it?

“Myxomatosis and cane toads – need I say more?” was a text to my local ABC radio station by someone concerned about the failure of biological control in the past. Yes, cane toads were a disastrous introduction to Australia and it is now clear that the problem was insufficient research prior to release. The carp herpes virus has been researched in Australian laboratories for 7 years so far. See my previous article for more on why this looks like a safe bio-control option.

Myxomatosis actually worked beautifully, killing 500 million rabbits in two years after the first release in 1950. Resistance did increase in the decades to follow and in 1996 another virus (calicivirus) was released to further reduce rabbit populations.

The rabbit plague of 1860 onward was the fastest spread of any mammal in the world. Rabbits had an enormous environmental and economic impact right across Australia, leading us to build the rabbit-proof fence. In 1887 the state of New South Wales was offering a reward of £25,000 for any successful method not previously known for exterminating rabbits. Although srabbits were useful for food in the depression and to make lots of hats, nobody wants to return to pre-myxomatosis times.

And no, we didn’t kill all the rabbits, just like we will not kill all the carp. However, a virus transmitted by water may be more effective as suggested by the government’s goal of a 95% carp reduction by 2045.

Carp are natural by now – our native fish rely on them for food

Australian native fish have been seriously impacted by carp. Many of them are visual predators, such as the magnificent Murray Cod. The turbidity created by carp reduces their ability to hunt and thrive, even though the high biomass of carp may give them plenty to eat.

The muddy river that runs through my home town is a hazard for swimmers and boaters because you can’t see the snags. This is due almost entirely to the presence of carp. None of us can remember when the Murray River ran clear and native fish were more common than introduced fish, but Senator Anne Ruston, Assistant Minister for Water Resources, recalls her mother and grandmother talking about being able to see the bottom of the river.

If you cannot imagine why anybody cares what type of fish are living in our rivers, remember that native Australian fish and plants are not adapted to the muddy rivers we have now. Let’s give them a chance to grow and thrive again in an environment more similar to the natural situation.

Sounds like a waste of money

Our Deputy Prime Minister Barnaby Joyce says that carp cost the economy up to $500 million per year. I don’t know how he got that figure but it may include the extra water treatment we need for river towns like mine and tourism losses due to reduced biodiversity and frequent algal blooms. Even if it is only half of that, spending $15 million to remove carp from the system seems like a sound investment.

The future of Australia’s waterways are at stake. Is there anything more precious than clean, fresh water?

The image on this article was corrected on May 6 2016. It previously incorrectly showed a different species of fish.

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