Australia has always been home to a large amount of native fish, however after European settlement in Victoria, ideas were hatched to turn the country more “European”, and hence the idea to bring a variety of European animals and fish came about. While most people are aware of foxes, rabbits and livestock, what many people who aren't involved in fishing don't realise is, in the vast majority of Australian waterways, there is by far the highest quantity of foreign species compared to native.
The problems began with the introduction of the redfin perch from Europe in 1850, and not long after the European fish known as Tench, a more predatory natured type of carp, was introduced. These two fish spread rapidly through the Murray darling river system, and caused a drop of around 50% of all native fish populations, before stabilising for over 100 years.
tench and redfin stabilised without doing irreversible damage to the
environment and native fish species, around 1960, people began to
notice European carp had appeared in a few waterways. By 1970, almost
every water body in the south of Australia was infested with carp,
with their numbers multiplying 10 fold every 10 years. Australia now
faces a European Carp invasive species crisis, the numbers are out of
control, even when European Carp harvesting occurs on the Murray
river between Victoria and New South Wales, this rarely has any
effect on their total numbers.
Another problem too is that the government once relied heavily upon recreational anglers to target and remove the species from the water, the only issue with that is Australians don't have a history of carp fishing like the Europeans do, Australia is more of a coastal fishing nation, and only targets edible species primarily. Since Australians rarely eat carp also, this means that the last thing most people want on their hook is a European Carp.
Fishermen however do enjoy fishing for tench and redfin, and both these species are edible, the good thing for anglers is that they can be caught using redfin fishing lures, while European carp will rarely attack a lure, the same can't be said for live bait such as worms. Native species in Australia also target fishing lures, so for most fishermen, catching a carp isn't a common occurrence unless using a live or dead bait, artificial baits and lures simply are not attractive to European carp, due to their instinctive feeding habits.
carp mostly feed by laying on the bottom of the water, sucking up the
dirt and debris on the bottom, where they find their food. Whether
that be baby yabbies (freshwater crayfish), baby freshwater shrimp,
freshwater snails, worms or vegetation. Their instinctive nature to
upturn the bottom of the waterways dislodges most plant life and also
strips the lower river bed layer of breeding ground for native fish
to reproduce. Already many freshwater snail species have perished
along with certain species of freshwater shrimp, relegated to the
extinction list, the Murray Cod and other Australian fish also find
it extremely difficult to reproduce when carp is the dominant species
in the waters.
The Australian government plans to tackle this issue by releasing what is known as the Carp Herpes Virus, this virus has been shown to affect no other creatures except carp, however the government has not yet mentioned how it will handle the biggest effect of releasing this virus, the cleanup.
Most European Carp can have up to 1 million young each breeding season, so by far the highest biomass in the rivers of South Eastern Australia are European Carp. When these fish die, they float to the top then begin to decompose, this releases toxic ammonia into the water, and if too many fish are decomposing at once, this toxic ammonia can take months to be broken down by bacteria in the water which feed off it, meaning that the country could end up with a few months of completely toxic and oxygen deprived waterways.
So will this solution kill off all the carp? Estimates state that around 90% will be killed off by releasing this virus. What we haven't been told is, if toxic ammonia is not controlled by immediately removing the dead carp from every inch of water around the country, will the native species even have any chance of survival?
Many fish keepers know the effects of ammonia, and it is common knowledge that the ideal level of ammonia in the water for fish to survive and be healthy is a level of absolute zero. Fish can handle up to a week of mild ammonia before it affects them, but if suddenly all the rivers biomass turns to ammonia, most anglers and scientists are beginning to agree that there is a high chance the release of this virus may do much more harm than good.
While the Australian Government and other agencies consult as to the effects of the release of this virus, we hope that they understand fully what they are doing, and the consequences that the country may face in terms of native species extinction, if this idea goes horribly wrong.