City targets invasive fish
By Lethbridge Herald on September 6, 2023.
Dead goldfish and minnows are seen lying near the shore of Chinook Lake in the Uplands subdivision Wednesday after the water was treated with rotenone.
Herald photo by Al BeeberAl Beeber – LETHBRIDGE HERALD – abeeber@lethbridgeherald.com
A program to eradicate invasive species of fish out of an Uplands lake was expected to see between 50,000 and 80,000 koi and goldfish killed this week.
City crews on Tuesday began efforts to remove the invasive species out of both Chinook Lake in the Uplands and the Elma Groves storm pond at the edge of the Legacy Ridge subdivision.
After water levels were lowered in both water bodies, rotenone treatment was started. Rotenone is a naturally occurring substance that only harms gilled species, not humans, wildlife or pets so only fish will be die after the treatment, said Jackie Cardinal of the City of Lethbridge.
Chinook Lake park was closed to the public with fencing around its entire perimeter while the public was advised to stay away from the Elma Groves pond.
Those two water bodies were the only ones being treated with rotenone by the City this year.
Last year, a similar initiative in the Copperwood subdivision at Firefly pond resulted in 87,000 koi and goldfish being removed. Those fish are considered aquatic invasive species in Alberta which threaten and disrupt natural ecosystems, negatively impacting biodiversity, says the City.
Dead fish are hauled to the landfill and covered with soil.
Cardinal, the Parks Natural Resources co-ordinator for the City, said the rotenone works by blocking the oxygen intake of fish. Once the rotenone begins working, fish can die in about 30 minutes.
Some fish that were retrieved last year were 15 inches in length and weighed as much as five pounds.
Because of their hard scaly bodies, goldfish and carp aren’t particularly digestible to predators such as pike and walleye.
On Wednesday, it appeared there were far fewer fish in Chinook lake than anticipated. A smattering of small goldfish and minnows had washed up against the northeast shore of the scenic lake overnight, far fewer than the numbers seen at Firefly last September.
Kirby England, a wildlife biologist and wetland ecologist who teaches in the school of Environmental Sciences at Lethbridge College, had students primarily in the Natural Resource Compliance program volunteering to get some work-integrated learning experience and hands-on time identifying the fish and doing other things.
“It’s part of their requirement to do some volunteer work, it’s part of their program so they get that time in and they also get some real good hands-on opportunity,” said England.
The biologist said expectations were that the Chinook Lake would have somewhat near the same density of fish as in Firefly pond last year so he lined up a half dozen students every days over coming days but he said he probably wouldn’t need them.
He said Elma Groves behind the new northside bark park could be a different story.
Many city water bodies are fed by storm water but also by irrigation districts, said England, with some drawing from the river and other natural sources so some native fish wash in, he said.
A yellow perch was seen in Chinook on Tuesday, along with white and long-nose suckers which, like the perch, are native fish.
England said it’s important for the City to eradicate invasive species because water will get back to the Oldman river eventually.
“You can’t have these invasive species moving from your infrastructure out into public waterways.”
Storm ponds are ideal places for invasive species to thrive because they have no natural predators. Conditions are ideal for fish that like high nutrients, high water temperatures and can live in lower oxygen content water than a lot of native fish can, England said.
Invasive species while feeding do a lot of grubbing in roots so more thinly rooted submerged plants and semi-aquatic plants can be disturbed, said England.
“The big thing, of course, is they’re creating a ton of nutrients and waste which then plants and algae and other bodies will take up and grow quickly. But then they die and that creates those anoxic conditions. Then you get that second big algal bloom,” added England.
An anoxic water environment is one which doesn’t contain dissolved oxygen.
“Eventually those algae die and then they start being decomposed” and that eats up all the oxygen in a pond, he added.
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So only fish will be die…..hmm, this is award winning journalism?