Natives feast on noxious species

Catch results at Horsham Fishing Competition have revealed a surprising downturn in carp domination of the Wimmera River in the region’s capital.

Regional catchment leader David Brennan said the size, number and types of fish caught in the contest had again provided important and encouraging information about river characteristics and health.

He said a combination of everything from predation to managing water flows and levels and other environmental factors were obviously playing a role in influencing carp numbers.

“We were certainly surprised by the size of carp caught. There were some mighty big fish and several weighing over a kilogram,” he said.

“But what was pleasing was that there were very few juvenile carp caught.

“We also had very large predatory yellowbelly, the winner weighing in at more than 4.5 kilograms and one of the largest we have ever seen caught in the river.

“This is a good indicator that native fish populations are healthy and surviving.

“We can confidently make the assumption on the evidence we’ve seen that the level of predation of native fish on carp, along with other management techniques, are helping supress carp numbers.”

Mr Brennan, Wimmera Catchment Management Authority chief executive, said the observation was significant because one large adult female carp was capable of producing millions of eggs.

“What we’ve seen is that something is keeping this in check and it’s a fair assumption that this involves predation from other species. But it might also be about controlling water levels in weir pools,” he said.

Mr Brennan said the number of native target species caught in the river also reflected that they were adapting well to Wimmera conditions.

“Catfish numbers were perhaps down on previous years, but their capture is often reflective of weather conditions and can be a bit hit and miss,” he said.

Wimmera River populations of native yellowbelly, also known as golden perch or callop, silver perch and Murray cod are in most cases the result of release programs.

These species usually need conditions that occur in the Murray-darling system, such as summer floods and warm water, to breed naturally.

Nest-building and relatively rare eel-tailed catfish, although also native to the Murray-darling, are an exception and have successfully established a resilient breeding population in the Wimmera River.

Researchers have used Wimmera River catfish, which have a strong genetic background and reputation for devouring carp eggs, for breeding programs in other parts of the state.