|Fish survey results|
Carp spread to upper MacKenzie River
...but Mt William and Salt creeks clear
Fish surveys have found carp in the upper MacKenzie River for the first time since Wimmera Catchment Management Authority started surveys in 2005.
But an inaugural CMA survey of upper Mt William Creek and Salt Creek, which flow into Lake Lonsdale near Stawell, failed to find any carp. This gives researchers confidence there are no carp in this section of the Wimmera River system or the lake.
The annual surveys establish and monitor the condition of fish communities, including the ratio of indigenous to exotic fish and threats to indigenous fish.
Wimmera CMA water monitoring officer Mark Toomey said locals reported seeing carp in the MacKenzie River after the January 2011 floods. The main aim of the latest survey was to investigate then quantify the extent to which carp had spread into this part of the river since the floods.
“We’ve sampled this section of the river twice since 2005 and have never caught carp. Locals say they hadn’t seen carp here since before we started surveying but during our latest two days of surveys at four sites we found 182 carp ranging from 180 to 480 millimetres long,” he said.
Mr Toomey said the CMA did not have specific options for controlling carp in the Wimmera River system but would use survey results for future planning while continuing to investigate all options to reduce their presence.
“The MacKenzie River is a high value area for indigenous fish and is one area of focus for our environmental water release program, so our first step was to see how abundant the carp were. They increase competition for resources, degrade vegetation habitat and are therefore a threat to native fish.”
Mr Toomey said the Mt William Creek and Salt Creek surveys yielded good numbers of indigenous and native fish such as mountain galaxia, common galaxias and southern pygmy perch. They said exotic fish weren’t overly abundant but included redfin and goldfish.
It was the first time the CMA had surveyed the upper Mt William Creek system.
“There was a concern that carp may have been detected but fortunately the sampling confirmed that carp were not present,” he said. “Researchers did find feral goldfish which are technically a member of the carp family and are sometimes confused with carp, however, they are less harmful to the river system.”
Mr Toomey said the absence of carp was a real bonus for the Wimmera River system.
“Upstream of Lake Lonsdale the flow of Mt William Creek is mostly unimpeded by weirs, dams or water diversions,” he said. “This means the water regime is near to being natural, which is a positive for the native fish because they have adapted to this and they complete stages of their life cycle in response to seasonal flows.”
Mr Toomey said an unfortunate finding was the evidence of illegal fishing activities in Mt William Creek. Researchers removed homemade drum nets and opera house nets from the creek at two locations.
In other Mt William Creek results, researchers discovered a 1.8-kilogram, adult short-finned eel – a rare find in a closed river catchment because the eels breed in the sea. The Wimmera River is the largest river system in Victoria that doesn’t flow into the sea.
“The eel may have arrived from an illegal angler translocation, a short wriggle overland from the Wannon River catchment or via water transfer from the Glenelg River system,” Mr Toomey said. “Eels can live 20 years before they need to return to the sea to breed so this fish may have been around in the system for quite some time.”