Plan to Reduce Australian Carp Numbers Using a Virus Bound to Fail, Study Shows

(CN) — A multifaceted plan to reduce the numbers of invasive common carp in Australia by introducing a virus into the population is “dead in the water” and should be abandoned, according to an analysis of the strategy released Thursday by England-based researchers.

Carp now make up the vast majority of the biomass in Australian waterways after initially being introduced to the continent in the 1800s.

Since that introduction, carp have caused massive ecological damage in Australia, in part by uprooting vegetation at the base of rivers where their activity also increases sediment in the water.

The rapid growth of carp populations worldwide is tied to the fish’s popularity in fish farming operations and recreational angling. That growth has also undercut the health and productivity of other species worldwide.

Australian government scientists are seeking approval of their $15 million plan to release the koi herpesvirus into the continent's largest freshwater supply in order to kill the non-native carp population. 

British-based researchers from the University of Exeter and the University of East Anglia examined the plan and shared their findings Thursday in the Journal of Applied Ecology.

Jackie Lighten of the University of Exeter said in a statement released with the study that the plan to spark a KHV outbreak in waterways should be dropped.

Even if the plan succeeds in depleting a high percentage of the carp population, introducing a foreign pathogen into a fragile ecosystem could have negative effects on native species in waterways, Lighten said.

“Viral biocontrol is highly questionable and, as our study shows, it is unlikely to reduce carp numbers in the long term,” Lighten said.

Lighten and colleagues found that the Australian common carp would eventually evolve resistance to the KHV virus and quickly recover from any population decline.

“Releasing KHV carries significant risks to human and ecosystem health, which likely outweigh the benefits, and we have previously urged further detailed research to avoid an unnecessary ecological catastrophe,” Lighten said. “Based on our findings, we believe the plan to control Australia's carp with KHV is dead in the water.”

The KHV strain has been used to kill millions of carp worldwide and first appeared in European aquaculture and fish farming facilities in the late 1990s, according to the study titled "Genetic variation in resistance and high fecundity impede viral biocontrol of invasive fish."

Computer simulation modelling was used in the study to determine the effectiveness of using KHV, with researchers noting the virus resistance that already resides in the global carp population.

Katie Mintram of the University of Exeter said in the statement modelling allowed researchers to assess the risks and likely outcomes of releasing KHV into the ecosystem. 

“We built a simulation model which allowed us to examine realistic interactions among carp, virus and disease resistance, to estimate how long it would take carp populations to recover even if 95% of them were wiped out,” Mintram said. “We show that the biological characteristics of the carp, including their rapid breeding rates, allow infected populations to recover rapidly with individuals that are KHV resistant.”

Lighten previously presented at the Australian Senate arguing that the nation’s National Carp Control Program wasn’t rooted in a comprehensive examination of all conditions. 

Cock van Oosterhout of the University of East Anglia said in the statement that NCCP officials failed to take into account researchers findings, which are rooted in the strongest disease projection models.   

“The modelling strategy that we took is a very powerful way to assess how disease can spread among individuals within a population,” said Van Oosterhout. “It's an ‘individual based model,’ which is similar to those used by scientists around the world to understand and prevent the spread of Covid-19. Also, they didn't model the impact of disease resistance, which is crucial in understanding the epidemiology of infectious disease.”

Researchers recommend the Australian government invest in restoring native plant ecosystems, which would reduce habitat for carp.

Another recommendation is to invest in habitat restoration and reviving the health of Australian water systems, such as by reducing the volume of water extracted from the Murray-Darling Basin, researchers said.

“We recommend that the Australian government takes bold steps to significantly improve the health of its waterways, rather than releasing a potentially catastrophic virus into its ecosystems,” Lighten said. “Freshwater is in desperate shortage in large parts of Australia, so the first step must be to reduce the amount of water extracted for thirsty crops such as cotton.”

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