The carp problem
Carp (Cyprinus carpio) have been in Australia for over 100 years and are now established in all states and territories, except the Northern Territory. Carp impacts cost Australia about $500 million every year.
Carp completely dominate freshwater fish communities in southeastern Australia – in many areas they comprise over 80% of fish biomass, exceeding 350 kilograms per hectare in some parts of the Murray-Darling Basin.
Carp impacts are felt environmentally, economically and socially. They affect water quality, native fish, fishing and irrigation.
The key impacts of carp are as follows:
- Carp are ‘ecosystem engineers’ – modifying waterways as they suck up mud. They stir up silt and muddy the water, blocking sunlight to aquatic vegetation, and impacting plankton, aquatic invertebrates, waterbirds, and native fish.
- Carp are 'water wreckers' – their feeding activity lowers water quality and increases nutrient levels. They also impact zooplankton, which normally feed on microscopic planktonic algae. When combined, these factors can cause blue-green algal blooms that impact recreational use of waterways (i.e., swimming, skiing etc.).
- Carp are 'resource hogs' – they take valuable food away from native fish. This particularly impacts smaller native fish species, but also larger species higher up the food chain. Some native species, like Murray cod, eat small carp, but this is not their natural food source.
- Carp are 'trash fish' – getting in the way of natives. People go fishing to spend time with friends, get outdoors and maybe catch a few fish. Catching carp can be fun, but most anglers want to catch natives. Carp currently undermine the recreational fishing industry, worth billions of dollars.
- Carp are 'pump blockers' – they get into irrigation infrastructure and block pumps. This causes significant expense, through downtime and maintenance costs, for agricultural businesses.
Before and after carp removal, showing the effects on water clarity. Images: Iain Ellis.
The image above shows the benefits of removing carp from an area. This wetland dried out, carp were prevented from returning using a screen and the system filled again naturally. The improved water clarity is clear to see.
Carp have been identified as a priority pest species, both in Australia and internationally. The International Union for Conservation of Nature has named carp one of the world’s most invasive fish species.
A recent national survey reported that the public perceive carp as the fourth most significant vertebrate pest in Australia (after cane toads, feral cats and rabbits). For at least the last two decades, there has been a shared desire among natural resource management agencies and communities for control programs to reduce these impacts.
Australia is working hard to rehabilitate rivers and wetlands. Significant investment, in fishways, environmental watering and other measures, is being compromised by carp.
It’s time to get carp out of the way, so our native fish have a chance to compete.