Like many Australians, fishing was a big part of my childhood, and I have two vivid memories from my first fishing trip to the Murray River at about five years of age. I remember being so excited at the possibility of catching a Murray cod…I was entranced by the size and power of this giant enigmatic native and wanted in! My first memory from that trip was of sitting on a bank of this wide, lazy river under a big old red gum, and wondering why the water was so muddy…there had been no rain recently. I assumed that maybe our big rivers had always been muddy, for reasons I didn’t understand.
My second clear memory from the trip was later that afternoon when, after a long wait, my rod buckled and I felt the weight and tail beat of a big fish. Excitedly I shouted “It’s a cod! I’ve got a cod!”, and my family came down from the campsite to watch the tussle. After some time the big fish came to the surface and rolled in the muddy water, flashing golden in the sunlight. I remember my stomach lurching and a feeling of disgust and embarrassment washing over me. It wasn’t a cod at all…It was a stinking carp.
Reflecting on childhood memories
I’ve reflected back on that day many times since. Mostly because I’m intrigued by my strong response on seeing that fish, before I think I even knew what a carp was. It’s like I was hardwired to dislike the whiskered, golden invader. I also reflect on my assumption that our big rivers were always muddy, because I now know that our big rivers aren’t naturally turbid systems – they used to flow deep and clear. Older farmers have since shared stories with me of being able to walk the river bank and spot cod sitting on snags in 6 feet of water, and being able to spear crayfish, such was the water clarity. I, and those I work with, believe our big rivers can be clear again, but for this to happen, we must take action on carp.
Carp among the most disliked invasive pests
It turns out I’m not alone when it comes to a sense of disdain for this piscatorial pest. In fact, according to a recent survey it’s a bit of a national hobby. The Australian community rank carp among the top four most disliked and significant invasive species in Australia, along with cane toads, rabbits and feral pigs. So why the national repulsion?
There are probably a few reasons. Firstly, there are just so many of them! A single female carp can carry over 1 million eggs, and under the right conditions a small number of fish can result in a dense infestation. Unfortunately that’s exactly what you can see today throughout much of our largest river system – the Murray-Darling Basin (MDB). Carp currently make up more than 80 per cent of the fish biomass throughout the MDB, and up to 93 per cent in some places. Carp impact on the health of our waterways too; they can shape their surrounding ecosystem, changing it in ways to suit themselves, and disadvantage our native species. They do this primarily through the way they feed: they are largely bottom feeders, and so mooch around taking big mouthfuls of mud, eating the invertebrates hiding in amongst it, and then spit the mud back out. In this way, they contribute to the muddy condition of our rivers which, in turn, degrades the health of aquatic vegetation by reducing the light penetrating down to the riverbed. This then influences the types and abundances of invertebrates that are present.
Social and economic impacts
The ecological impacts of carp translate into social and economic impacts too. One report estimated the economic cost of having carp in our waterways at around $500 million per year. Much of this impact was due to the fact that carp reduce the quality of recreational fishing opportunities, which is a huge economic driver for rural and regional communities in the MDB. In fact, there are places where recreational fishers rarely go any more because all they are likely to catch is carp.
Carp herpes virus
Fortunately, the CSIRO have been researching a potential tool for the biological control of carp over the last eight years, with funding through the the Invasive Animals Cooperative Research Centre (CRC), and the results are promising. Their research shows that a naturally occurring virus called Cyprinid herpesvirus 3 (more commonly known as the carp herpes virus) has the key characteristics of a good biological control agent: it is extremely effective in killing the target species (carp), and it doesn’t affect other species. Most importantly, international experience has demonstrated that it is safe for humans too.
Public interest in carp herpes virus
The level of public interest on this issue became apparent in January 2016, when over 250 media outlets, as far afield as the United States and China ran stories on the potential to control carp in Australia through biocontrol, which resulted in over six million tweets on this topic over a two-week period. It seems the collective imagination of the Australian public was activated by the potential to address issues caused by the worst freshwater pest species our nation has seen.
Still much to be done
Though biocontrol gives new hope to those wishing to see carp disappear from our waterways, and last year’s announcement of federal investment will provide significant assistance at the perfect time, it is important to recognise there is much yet to do.
First, there is a need to complete a detailed legislative approval process, which will take up to two years. There is also a need to complete a thorough risk assessment and undertake public consultation on this issue to ensure the views of the Australian community are well understood. There is a need to undertake monitoring activities before and after release of the virus, so we can document how our aquatic systems and fisheries respond to carp reduction and, of course, there is a need to implement an effective clean-up program to remove dead carp from our waterways and ensure native species and water quality is protected.