A war is about to be declared on redfin in Lake Purrumbete after recent studies found growth rates of chinook salmon released into the fishery were noticeably stunted.
Lake Purrumbete Angling Club secretary Rob Hems said chinook salmon caught at Lake Purrumbete were about half the size of those caught at Lake Bullen Merri.
The chinook were released into both fisheries over the last two years but recent surveys show the ones coming out of Lake Bullen Merri weighed about 3kg compared to 1.5kg for those coming out of Lake Purrumbete.
“We know Lake Bullen Merri has a good food mass and believe the problem at Lake Purrumbete is due to the ever expanding redfin population,” Mr Hems said.
“The redfin population in Lake Purrumbete is enormous, you are more likely to catch a redfin than a trout whereas Lake Bullen Merri does not have any redfin at all.
“The redfin compete with the trout for the food mass.
“Most fish coming out of Lake Purrumbete are now noticeably stunted – trout, salmon and redfin.”
Mr Hems said unlike salmon and trout, redfin could breed in the freshwater lake.
Their eggs were also unpalatable to other fish, so they out-populate every other species.
The situation prompted the Lake Purrumbete Angling Club to secure a $5000 grant from the Recreation Fishing Licence Fund to investigate what could be done.
The club is now working closely with Fisheries Victoria staff to monitor the redfin situation and find a possible solution.
Mr Hems said the officers were asked to investigate how other fisheries interstate and overseas were dealing with the problem.
“They have been researching the redfin issue for awhile now and we hope to have a report in the coming months with a range of options for action,” he said.
Early control methods already discussed include the long-term netting of redfin, milking the females of their eggs or using hormones to render the males sterile.
“Lake Purrumbete is not the only lake in this situation,” Mr Hems said.
“If left unmanaged, lots of lakes will find themselves in the same situation.
“That’s why Fisheries Victoria is keen to help us find a solution, it could be something that is used to help other lakes as well.
“As a club we are confident the study will be the first step of a long-term solution.
“We’ll never get rid of them completely, but we hope to reduce their numbers substantially.”
Mr Hems said redfin first appeared in Lake Purrumbete in the 1970s and had been left uncontrolled ever since.
“We don’t know where they came from — someone could have used them for bait, they could have come up from the Curdies River in times of high rainfall, or they could have washed in from overflowing farm dams, we just don’t know,” he said.