Its not suprizing that the carp population is so prolific in countries with a warm climate.
Carp were initially bred for food way back in the time of the Romans an were subsequently introduced into this country (UK) around the time that the Romans came over and settled.
The reason they were used for the table is several fold, ease of breeding, tolerance to unsatisfactory conditions, fast growth rates and large body mass.
As always once a species is introduced into an alien environment it will have some form of impact on the native species. In this case because the carp have been introduced into a warmer clime they are reproducing at an abnormal rate compared to their natural climate therefore creating problems to the native aquaculture and ecology.
Carp spawn in water temperatures exceeding 18oc and become prolific breeders at temperatures of 21oc+. When you think that a female can produce around 550,000 eggs per pound of body weight and the aelvin have a greater survival rate than most other species, its not suprizing that problems are then created.
As the battle then goes on for food within the waters, it then becomes a battle for survival which is again where the Carp's tolerance to poor conditions comes into play. As the native species find that the natural foodstock is depleting and the water quality due to higher levels of polutants due to excretions and insuficient oxygen rises, the inevitable happens and they become no more.
How would you get around this? The only option available is to effect a selective cull or removal. The second option in this case would be pointless because what would you do with the removed fish as no one wants them either.
It's just a shame that they can't be exported to third world countries for food rather than ploughed into the land as fetilizer but then again there is the cost to be weighed up.
Dave - you said " .... The only option available is to effect a selective cull or removal ... "
In this case (carp in OZ) and probably in many others there are other options. It was even mentioned in this article.
Clean up the water, improve the fishery in general, and the other species can bounce back until a reasonable balance is achieved.
We have carp in pretty much all our waters. We have lots of spring days when the water is well above 18. But the carp have not taken over. They are simply one species of fish the water holds.
For one thing, many pred species breed a little sooner than carp and have fingerlings swimming around when the carp do spawn. And happily eating carp eggs and carp hatchlings.
The whole "balance" thing works well. If you have enough preds, you don't have a problem with too much of any prey species. And the pred population (with the obvious exception of people) will be self limiting based on the availiblity of prey.
For instance, if you had more raptors in the wild I suspect your cormorant problem would go away. You would still have some cormorants but not the excess you have now that is causing such problems.