Fish-fight revelations

Latest carp research suggests commercial fishing of the species would be an inadequate control method for the noxious fish across Australia.

Findings have found that commercial harvesting might instead help support biocontrol methods such as the release of a carp virus, being investigated as part of a National Carp Control Plan.

Professional harvesting of carp in inland waters has occurred across Australia for many years and has happened in the past in the Wimmera River.

Carp now make up a high percentage of the ‘biomass’ in many Wimmera waterways.

Associate Professor Paul Brown at La Trobe University in Mildura led the latest research in collaboration

with NSW Department of Primary Industries and Tasmania’s Inland Fisheries Service.

“We compared what we know about carp biology with the biology of fish stocks at risk of overfishing to see if we could overfish carp deliberately,” he said.

“We reviewed case studies where invasive fish species are managed by commercial fishing around the world. We identified what features were important for the success or failure in each case.”

The team then used the latest computer models of carp populations to simulate carp and commercial fishing activity typical of a known river catchment.

The modelling showed that unless commercial fishing removed substantial carp numbers of all sizes – including juveniles – it was impossible to effectively reduce carp populations.

The amount of carp that had to be fished from one Murray-darling River catchment – more than 1400 tonnes in the first five years of fishing – would overwhelm domestic markets.

Carp reserve

Findings also showed that if some carp were unavailable for commercial fishing, perhaps in inaccessible areas, they could act as a reserve to repopulate the fished areas.

Under these conditions, population eradication became impossible and population reduction was ineffective.

Carp are prolific breeders and highly adaptable, which means they can survive and flourish in a broad range of habitats. The research established these features meant Australia would need a permanent and much larger commercial carp industry to maintain lasting population control.

An up-scaled commercial fishery would need to fish hard in all areas, forever, to control carp in Australia and the type of commercial industry required would create a range of other environmental challenges.

The $10.2-million National Carp Control Plan aims to establish whether it is feasible to release the carp herpes virus and if so, what is the most effective way to release and manage the target-specific disease.

The investigation is due for Federal Government assessment in December.