The battle against Carp: will the virus work?

On this episode of OzCast, Dr Martin Mallen-Cooper re-joins the show to look below the surface at one of the most topical questions circulating our inland fishing communities – should Australia release the Carp herpes virus (cyprinid herpesvirus 3)?  

Martin, who has spent decades looking into the health of our freshwater rivers in Australia, sets the record straight on how the carp virus would work if released and offers his expert opinion on which direction the Australian government should take.

Dr Martin Mallen-Cooper is a highly respected river ecologist. He was born in 1958, in Sydney and grew up with a strong love for the ocean, rivers, and fishing, which led him to pursue a career in aquatic sciences. Dr Mallen-Cooper received his undergraduate degree in Environmental Science from the University of Technology Sydney in 1980, where he developed a passion for freshwater ecosystems. He worked as an environmental consultant and then joined NSW Fisheries in 1984 to research the design of fishways (structures to get migratory fish past dams and weirs), which became the subject of his PhD.  

Martin is the first to concede that no freshwater fish ecologist in Australia can actively study the health and solutions for our native fish, without understanding the detrimental effect European carp have. First brought to Australia in the late 1800s, Carp cause their main environmental impacts through their feeding habits. As adults, they usually feed on the bottom of rivers and ponds. They feed by sucking soft sediment into their mouths, where food items are separated and retained, and the sediments are ejected back into the water.  

Martin explains that when carp are present in high densities, the resultant suspended sediment can bring on more problems, including deterioration of water quality and increased nutrient levels, reduced light penetration resulting in reduced plant growth, invertebrates and fish eggs and clogging of gills of other fish species.  Carp feeding can result in fewer aquatic plants: carp will graze on plants directly and uproot plants during feeding and are also effective grazers of surface films on plants and rocks. 

Throughout the episode, Martin explains that various bio-control mechanisms have been implemented over the decades, with limited success – which has led Australia to now consider a more extreme measure in the Carp herpes virus.  In breaking down how the virus would work; Martin distils a common misconception about introducing viruses in aquatic environments. He explains that the virus would effectively ‘knock down’ carp numbers for a short period, which would allow native fish numbers to survive. After this period, the carp numbers would bounce back, with native fish having a stronger foothold in the environment allowing them to compete with the carp. Martin believes Australia would have a 3–5-year window to act on a number of issues to see this virus work effectively.  

When asked whether a virus like this should be a concern for native species in the river, like Murray Cod and Golden Perch, Martin explained the virus is already naturally occurring in carp around the world and only impacts carp  

An important issue to consider, according to Martin, is the control mechanisms for the dead carp which would inundate our river systems in the years preceding the release of the virus. Just as we experienced with the Menindee fish kills in 2018 and 2023, dead fish raise community concerns around water quality, drinking suitability and aesthetics of our rivers and towns.  Dealing with the dead fish is an important cog in deciding whether the virus is released - but overall the science looks positive.  

In an interesting development, Martin uncovers the notion that the carp virus might very well get to Australian rivers anyway, through natural causes or through it being unintendedly introduced. In Martin's opinion, Australia needs to be ready for it regardless. 

Join us as we take a look below the surface at whether the carp virus should be released into Australian waterways and when.