A routine pest-control survey on Perth's Swan Coastal Plain has turned up a monster. Researchers from Murdoch University's Centre for Sustainable Aquatic Ecosystems have pulled an 11.9kg European carp from Careniup Reserve in Gwelup, believed to be one of the largest carp ever recorded in Western Australia.
The fish stretched 823mm and, when examined, was found to be a female carrying more than three million eggs — a single illustration of why the introduced species is so hard to control once it takes hold in an urban wetland.
Research assistant Cindy Palermo was aboard the electrofishing boat when the carp surfaced. "When the fish was stunned by the electrofishing boat, I couldn't believe the size of its head sticking out of the water," she said.
The sheer bulk of the fish made landing it a two-person job. "It was so heavy that it took two of us to bring it onboard the boat," Palermo said.
The capture came as part of the WA Urban Carp and Goldfish Roundup, a long-term program targeting feral fish in the wetlands and drains that thread through Perth's northern suburbs. Far from a one-off, the survey is the opening chapter of a sustained effort to measure — and then knock down — carp numbers across the metropolitan area.
"We have an ambitious program operating over the next 3 years over 21 different waterbodies where we plan to demonstrate the benefits of ongoing pest fish control programs on the health of urban wetlands on the Swan Coastal Plain," Palermo said.
For anglers, the giant carp is a useful reminder of what is lurking in waters many drive past without a second glance. European carp are a declared pest across much of southern Australia. They root through soft sediment as they feed, muddying the water, tearing up aquatic plants and out-competing native fish for food and space. A single large female, like the Careniup specimen and its three million eggs, can seed an entire system.
That destructive feeding is exactly why fisheries managers urge recreational fishers never to return a captured carp to the water. In Western Australia, as in other states, carp caught by anglers should be humanely dispatched rather than released — and certainly never moved between waterways, a practice that has helped the species spread.
The Careniup catch also shows the scale of the problem hiding in plain sight. Urban wetlands like those on the Swan Coastal Plain are prized for birdlife, native fish and water quality, yet they are precisely the kind of warm, nutrient-rich, slow-moving water in which carp thrive. Electrofishing surveys give researchers a snapshot of just how dense those populations have become.
With 21 waterbodies on the program's list and three years to run, the Murdoch team is betting that consistent, repeated removal will let native species and aquatic plants recover. The 11.9kg female is a striking headline, but the real measure of success will be the thousands of smaller carp the roundup takes out of circulation before they ever grow that big — or spawn the next generation.