Calgary is developing a five-year plan to control invasive fish in the city’s storm ponds, including a population of Prussian carp reported in the northwest community of Evanston. The city says the fish have been reported in several ponds, most recently in a storm pond at the southern end of Evanston, near Beddington Trail and Stoney Trail N.W. Rather than deal with the Evanston pond in isolation, the city is working on a broader strategy for invasive fish in storm ponds across Calgary. The five-year management and control plan will cover multiple locations, with details expected in the fourth quarter of this year. Nicole Sparks, manager of stormwater operations and water services with the City of Calgary, says the city does not know exactly how many of its more than 300 storm ponds contain invasive fish. “We are aware that it is, I would say, probably a fairly widespread problem – but we don’t have an exact number.” The city is working with a consultant to determine which ponds should receive the most attention and what measures should be used. “The intent of that plan is to identify which ponds are of highest priority, which actions we should take to control this problem and how we’re going to go about doing that,” Sparks said. ‘Fairly substantial problem’ Prussian carp and goldfish are related species and are the predominant invasive species found in Calgary storm ponds. Megan Evans, executive director of the Alberta Invasive Species Council, says the problem extends well beyond the city. “It’s a fairly substantial problem in Alberta, and the problem continues to grow with these invasive fish.” Prussian carp have been found in the North Saskatchewan, Red Deer, Rosebud, Oldman, Bow and South Saskatchewan river systems, according to Evans. One reason they are so difficult to control is how quickly they can reproduce. “A female can spawn up to three times per year – 400,000 eggs per spawning event – and they don’t even need a male Prussian carp to reproduce.” Evans said. “They can utilize the sperm from other fish species to activate their eggs, resulting in all-female clones.” Both Prussian carp and goldfish are non-native species that can reproduce quickly after becoming established. Then they compete with native fish for food and habitat and potentially spread disease. Evans said Prussian carp are omnivores, can survive in poor water quality and low-oxygen conditions and disturb sediment while feeding, increasing the turbidity of the water. “There’s only so much food and habitat to go around,” Evans said. “We know when we have a quick reproducer that can thrive in a wide variety of environmental conditions that they will generally do a pretty good job of out-competing native species.” ‘Unfortunately thriving’ The concern is not limited to what happens inside the ponds. Calgary has more than 350 storm ponds, which are designed to collect runoff, reduce the risk of flooding and allow sediment and pollutants to settle before water eventually makes its way back into the river system. The city says invasive fish in those ponds can potentially spread through the drainage system and into local waterways. Prussian carp have already been found in Alberta’s Bow River watershed. The city says preventing populations living in its stormwater system from spreading into rivers remains a priority. Sparks says the potential for invasive fish to move from storm ponds into natural waterways is a major concern. “They can withstand quite difficult conditions. Many of our fish would not survive in a storm pond like native fish, but these fish are able to survive over winter with low oxygen – and they are unfortunately thriving in some of the ponds,” Sparks said. “They’re a problem in our ponds to begin with, but they will be a much larger problem for Albertans and Calgarians if they make their way into the natural waterways.” Evans says the fish can move through connected waterways, but their presence in isolated ponds points to another means of spreading them: people. “We know that Prussian carp and goldfish will move themselves through moving water, obviously, like all fish, but they make jumps sometimes,” Evans said. She pointed to Prussian carp appearing in the North Saskatchewan watershed after previously being found farther south. Evans says finding Prussian carp in ponds cut off from other waterways indicates people are moving the fish, although exactly why they are doing it is less certain. “We are making some assumptions surrounding the motivations for that, but they are… Prussian carp particularly are a desirable species for consumption for certain folks,” Evans said. ‘The size of dinner plates’ Goldfish present a different problem. Evans says there are more than 100 known goldfish infestations across Alberta, a number she says continues to grow. Goldfish released into the wild can also become much larger than the small fish commonly kept as pets. “They will grow to be quite large – about the size of dinner plates,” Evans said. Evans says people may release unwanted goldfish believing it is a humane alternative to killing them, but a few goldfish can eventually produce tens of thousands, which may have to be destroyed to eradicate an infestation. Calgary has previously resorted to draining storm ponds in an effort to control invasive fish. Earlier this year, the city drained a storm pond in Tuscany after finding large numbers of Prussian carp and goldfish. The work began in January and involved lowering the water level and exposing the pond bottom to winter temperatures. The goal was to kill as many of the invasive fish as possible before allowing runoff to eventually refill the pond. The city has used a similar approach elsewhere. A storm pond in Royal Oak was previously drained after Prussian carp and goldfish were discovered there. The city says its response to invasive fish can also include physically removing them and monitoring affected ponds. Hefty fines Introducing fish into a Calgary storm pond is illegal. Anyone caught stocking or releasing fish into one can face a $3,000 fine under the city’s stormwater bylaw. Fishing in storm ponds is also prohibited. The provincial penalty for releasing fish illegally is substantially higher. “In Alberta, it’s illegal to release aquarium plants and pets into the wild, and it can come with a big fine – over $100,000 and or a year in prison – if you are caught releasing your plants or pets or live fish into a water body other than the one where it was caught,” Evans said. She says enforcement can be difficult because releasing a fish takes only seconds. “It’s very hard; it’s unlikely and it’s challenging to come across somebody when that’s happening – but the consequences of that, obviously, will just mount over time as those populations grow.” The city advises people with unwanted aquarium fish to return them to a pet store or find another home for them rather than releasing them into the environment. Anyone who sees fish in a Calgary storm pond is asked to contact 311 so the city can investigate. Evans says preventing new infestations ultimately depends heavily on people changing their behaviour. The city is expected to provide more details later this year on how it intends to deal with existing invasive fish populations and reduce the risk of them spreading through Calgary’s waterways.
