By Matthew Liebenberg
Technology is helping the Swift Current Creek Watershed Stewards (SCCWS) to identify the potential presence of invasive Prussian carp in the aquatic ecosystem.
The results of the project have been released in a report titled Hunting for Prussian Carp in the Swift Current Creek and Rush Lake Creek Watersheds.
It was carried out with funding from the Saskatchewan Fish and Wildlife Development Fund. The fieldwork was done during the summer of 2022. It involved the collection of environmental DNA (eDNA) and water quality samples at several sites within the study area.
SCCWS Executive Director Kevin Steinley said stakeholder consultations in 2019 identified the impact of invasive species on watershed health as a priority area to focus on.
“Trying to address the issue of invasive species within the watershed is something they want us to do,” he mentioned. “So it’s important that we look to see if Prussian carp are here and where they are. There’s anecdotal evidence of them being in the creek and our 2017 monitoring project identified Prussian carp being in the creek between the city and the confluence of the South Saskatchewan River.”
A Prussian carp was found approximately 50 kilometres upstream of the Swift Current Creek’s confluence with the South Saskatchewan River in 2017. The SCCWS also received other reports about this invasive species in the creek and irrigation canals, which made it necessary to take a closer look at where they might occur.
Prussian carp spread from Alberta into Saskatchewan through the South Saskatchewan River system. It is very adaptable and its presence in a watershed is a concern for several reasons.
“They have the ability to reproduce very rapidly once they get in and they’re just sort of predatory,” he said. “They’ll eat just about anything. So they would change the ecosystem of the creek and reservoirs and lakes very quickly, and really just push out or diminish the number of native fish that are there and would have an impact on our recreational fishing within the watershed.”
The main challenge in locating Prussian carp is the size of the Swift Current Creek watershed. The creek is 302 kilometres long and the watershed’s total drainage area is 5,592 square kilometres. It therefore made sense to use eDNA sampling, which has been used increasingly for biodiversity monitoring in recent years.
“It came down to resources, money and staff,” he said about the decision to do eDNA sampling. “It was to use that sampling to prioritize areas for future study. It was cheaper to do it and less time consuming to send somebody out to take water samples and ship it to a lab than to get a crew together for a good chunk of the summer to go out to try and actually catch the Prussian carp. And we didn’t know where to go. Now that we have the data that we got, we can look at finding areas to go out and pinpoint areas.”
The eDNA and water quality samples were taken at 10 sites spread out across the Swift Current Creek and Rush Lake Creek watersheds. Site selection was based on strategic locations in the watershed, frequent use for recreational fishing, and accessibility for sample collection. Some locations have been used in the past for SCCWS monitoring projects and others were new sampling sites.
The sampling sites included Duncairn Dam, Lac Pelletier, a site upstream of the weir at the Swift Current water treatment plant, the site north of Swift Current where a Prussian carp was caught in 2017, Highfield Dam on Rush Lake Creek, and Herbert Reservoir.
Each of the 10 sites was visited three times during the summer of 2022 to collect eDNA and water quality samples. The eDNA samples were shipped to the NatureMetrics laboratory in Guelph, Ontario for testing and the water quality samples were sent to the Saskatchewan Research Council Environmental Analytical Laboratories in Saskatoon.
The water quality testing results were similar to those of previous SCCWS monitoring projects and there were no significant deviations from water quality parameters.
“With every project we do, we try to incorporate a water quality testing component to it to tie in with work done previously,” he said. “We found no change in the water quality from previous years. So nothing is jumping out at us in terms of water quality.”
Traces of eDNA from a variety of fish and animal species were recorded in the water samples taken for the eDNA laboratory tests.
In addition to different fish species at the sample sites, the tests from a few locations also found eDNA from dog, mink, rodents, muskrat and gophers.
The eDNA of about 20 different fish species were identified, including native fish species. These results indicate healthy populations of aquatic wildlife.
“It’s still very good,” he said. “The species that are important to the people who go out to those reservoirs and lakes to fish are still there in good numbers.”
The DNA profile of Prussian carp is very similar to goldfish. The sample results can therefore only indicate that Prussian carp or goldfish eDNA was present at three sample sites.
Steinley felt it is more likely this eDNA indicates the presence of Prussian carp, based on past anecdotal evidence and the fish caught in 2017.
“We know that they’re in the South Saskatchewan River and that they do have the ability to swim upstream,” he said.
At the same time these results serve as a useful reminder to watershed residents that they should not release goldfish or any other non-native fish into the creek. Goldfish can have a similar negative impact on ecosystems.
“They don’t really have any predators and they eat just about anything,” he said. “They’re an invasive species that can do damage. So they can do damage similar to what Prussian carp do.”
The eDNA for Prussian carp or goldfish were found at the three sample sites located north of Swift Current. One site is just north of the city and the second site is halfway between the city and where the creek enters the South Saskatchewan River. The third site is the last vehicle accessible spot along the Swift Current Creek before its confluence with the South Saskatchewan River.
“So they haven’t made it into some of the areas that are important to recreational fishing within the watershed,” he said. “We’re quite happy to see that Prussian carp is confined to one defined area within the creek and it’s not in Duncairn Dam or Lac Pelletier at this point. We want to keep it that way.”
The potential presence of Prussian carp in this section of the Swift Current Creek over a distance of approximately 50 kilometres between the three sampling sites indicates they are swimming upstream from the South Saskatchewan River. The weir at the Swift Current water treatment plant and the CPR weir are potential barriers to their migration further up the Swift Current Creek.
The project report recommends further testing in the creek area where the Prussian carp or goldfish eDNA were recorded. It also suggests the study area should be expanded to include the section of the creek up to the weir at the Swift Current water treatment plant and the monitoring should include netting of fish to confirm the presence of Prussian carp.
“We’re hoping to do something this summer, provided that there’s funding, to pinpoint within the study area where the Prussian carp are, how far they’ve gotten, as well as bring some netting to see if we do find any live, full grown or partially grown ones,” he said.
The detailed report for this project is available on the SCCWS website (www.sccws.com). Go to the projects tab and click on the link named Hunting for Prussian carp.