A river restoration project has expanded the habitat of the critically endangered doring fiery redfin from 2 km to 10 km by removing invasive spotted bass from South Africa’s Breekkrans River.
An ambitious conservation project in South Africa has helped protect the critically endangered doring fiery redfin by removing invasive spotted bass from the Breekkrans River, giving native fish a greater chance of recovery.
The Breekkrans River Restoration Project is being carried out by the Freshwater Research Centre in collaboration with Cape Nature and the Fynbos Fish Trust. Since 2023, the team has worked during the Southern Hemisphere summer to eradicate invasive bass from the river and prevent them from returning.
Spotted bass were introduced into the river system in the late 1930s, primarily to support recreational fishing. However, the predatory fish began threatening native species, many of which grow to just 12 centimetres or less.
Before the eradication effort, the doring fiery redfin was restricted to a 2 kilometre stretch of the Breekkrans River that remained free of bass. The river supports the largest remaining population of the species, with an estimated few hundred adult fish. A separate population survives in another river but is present in very low numbers.
To remove the invasive predators, conservationists used nets, spear guns and electrofishing equipment across 8 kilometres of the upper Breekkrans River. They also constructed a fish barrier downstream to prevent bass from re-entering the restored section.
The initiative has expanded the doring fiery redfin’s habitat from 2 km to 10 km, significantly increasing the area available for the threatened species to survive and reproduce.
Researchers have also observed improvements among other native fish species. According to Cape Nature faunal ecologist Martine Jordaan, native fish populations have expanded their ranges following the removal of the predatory bass.
The project’s success demonstrates that mechanical removal methods can eliminate invasive fish from entire stretches of rivers under suitable conditions, allowing native populations to recover.
Conservationists believe the approach could provide a model for restoring other freshwater ecosystems in South Africa affected by invasive species. By removing introduced predators and preventing their return, similar projects could help protect vulnerable fish populations and improve freshwater biodiversity.