Australia doesn’t have the best history when it comes to invasive species. One such animal is the European carp, which has spread throughout much of Australia’s waterways. Now, in an unlikely alliance, both conservationists and fishermen are calling for approval to be granted for a “koi herpes virus” to be released. Highly specific to the European carp, the virus affects the skin and kidneys, disrupting the fish’s water balance. After about seven days of infection, during which they pass the virus on to other carp, the fish start to show symptoms and die within 24 hours.
The worry, however, is that the virus could have unintended consequences. This is why the Commonwealth Scientific and Industrial Research Organisation has spent the last eight years testing the virus in a secure facility on a whole magnitude of species, from amphibians and birds to other native fish species. They now claim that they are happy that the virus will not be able to cross the species barrier.
Carp removal is currently reliant on techniques like this, such as netting. Melbourne Water/Flickr CC BY-NC-ND 2.0
The carp's highly invasive nature in non-native habitats is mainly due to its behavior. The fish are known to sit at the bottom of waterways and weave though the sediment, eating any plants and other food they might come across. This dramatically alters the environment, preventing the growth of native aquatic vegetation while also removing the habitat in which native fish species normally breed. This, combined with their fast reproductive rates, has meant they are often compared to rabbits, which also plague Australia.
The Murray-Darling river basin in south eastern Australia has been particularly hard hit by the carp. By some counts, it’s estimated that the invasive fish make up an astonishing 80 percent of all fish biomass. At a single location on the Murray River, where there is a barrier to stop the carp from traveling upstream, around 140,000 tonnes (154,000 tons) of carp were caught and removed over the course of one year. The pace at which they breed means that it is almost impossible to fish them all out at current levels. It is hoped that if the virus is introduced, it will reduce the number of carp to more manageable levels, where other methods such as netting might then be able to remove those left behind.
But as mentioned, Australia doesn't exactly have a great track record when it comes to using biological control for pests. One of the most high-profile examples of when this tactic can go wrong is from when the country decided to introduce cane toads in order to control the cane beetle that had been chomping its way through the nation’s sugar crop. Unfortunately, while the toads did feed on the beetles, they also turned out to be highly toxic to the majority of Australia’s native wildlife and have now spread right across the country. It is for good reasons such as these that officials are reluctant to potentially repeat the same mistake again.