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Study aims to control invasive fish in Calgary’s storm ponds

Invasive carp have become an issue affecting many regions of the world. Recently, goldfish (Carassius auratus) and Prussian carp (Carassius gibelio) have been introduced to North America. The City of Calgary is one of the first municipalities in North America to begin researching control and containment strategies for these invasive carp species.

The City of Calgary has identified invasive goldfish and Prussian carp in multiple stormwater ponds. Invasive carp escaping the stormwater ponds pose a risk to the downstream natural aquatic environment by competing with or displacing native species, impacting water quality, and spreading diseases. In addition, introducing invasive fish into a natural waterbody is illegal under provincial and federal legislation.

Invasive carp are highly adaptable, tolerant to poor water quality and habitat, grow rapidly, and reproduce early to maturity. They can travel between connected waterbodies and unconnected waterbodies during high flow events, resulting in population expansion over time. In addition, invasive carp eggs may be transferred between waterbodies in the digestive systems of water birds, and be deposited in new areas, spreading invasive species. People also contribute to spread of invasive fish, for example, by freeing unwanted pets, stocking ponds for recreational angling, or releasing fish as part of a prayer service.

To control and contain the spread of these invasive fish, the City of Calgary retained Associated to complete an identification and feasibility assessment of potential measures. The first part of the project involved a literature review to identify fish control or eradication solutions implemented in other jurisdictions, best practices implemented during other activities (e.g. instream construction) which could be adapted to stormwater ponds, potential new and innovative ideas which have not previously been used to address invasive fish, and the feasibility of implementing multiple measures concurrently.

Environmental Project Manager and Planning Lead, Dean Foster, says, "We completed a feasibility report for the City that recommended dewatering ponds and allowing ponds (and fish) to freeze over winter, as well as fish passage monitoring."

A pilot dewatering and freezing treatment program was completed on two stormwater ponds to evaluate their efficacy for fish control. We compared the presence of invasive carp pre-and-post treatment, and used dewatering and freezing as a treatment to eradicate invasive carp which appears to have potential; however, more results are needed to better understand the exact specifications required for success. The City plans to continue the fish population control and abundance program in 2024.

Fish passage monitoring was piloted at one outfall to inform future containment strategies and gain information about invasive carp movement, specifically eggs and larvae, out of the storm ponds and into natural waterbodies.

Associated is collaborating with the University of Alberta and Biologica Environmental Services to determine the best methodology to complete DNA testing on the preserved specimens and obtain specific information regarding invasive carp movement. The City, in partnership with Associated, plans to scale-up the fish passage monitoring program in 2024.

Lastly, eDNA sampling was conducted at all of the City’s stormwater ponds to detect and document the extent of invasive carp.

Our key personnel involved on the environmental component of this project include Dean Foster, Jessica Eaton, Carlo Gallotta, Krish Purohit, and Lee Hang-Liu.

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