Invasive Prussian carp made its way upstream in creek to Swift Current

The invasive Prussian carp has been making its way up the Swift Current Creek and the latest sampling results indicate it has reached the city of Swift Current.

The Swift Current Creek Watershed Stewards (SCCWS) collected environmental DNA (EDNA) at several sites along the creek during the summer of 2023 and announced the findings in its March 2024 newsletter.

“I think we’re generally not surprised other than the results that we’ve seen within the city of Swift Current, because we’ve known for a while that there’s a very good chance the Prussian carp were going to keep moving upstream and moving farther within the creek,” SCCWS Executive Director Kevin Steinley said.

The EDNA sampling was done for a second year in 2023. The SCCWS used the same technology, which has been applied by scientists for biodiversity monitoring in recent years, to do sampling in 2022.

The EDNA sampling in 2022 was done at 10 sites across the Swift Current Creek and Rush Lake Creek watersheds. Those results indicated that EDNA for Prussian carp were present at three sample sites 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.

The SCCWS decided to focus the 2023 sampling on five sites. Samples were again taken at the three sites north of the city. There was also a sample site within the city and another one south of the city.

“Our main goal was to refine the areas where Prussian carp are in the creek,” he said. “We were focusing more on the area where we found it in 2022 in that stretch from north of the city to the South Saskatchewan River and then within the city and south of the city.”

Samples at the five sites were taken at three different times during the summer in June, July and August. The 2023 results showed a strong presence of Prussian carp EDNA at the three sampling sites north of the city. There was no Prussian carp EDNA recorded at the site just south of the city.

However, sampling results for the site within the city varied over the three months. There was no Prussian carp EDNA present in June, but the July samples showed some presence. The August samples indicated a presence of Prussian carp at the site in the city at a higher level than what was detected at the sites north of Swift Current.

“This is an indication that possibly they moved in and got caught within shallow pools within the creek during the summer and then through their spawning their numbers increased,” he said. “It could be that and it could just be that the water was so low that their concentration was higher too. It does show that they’re there and then any numbers that possibly were increasing were through spawning at that site through the summer.”

Prussian carp will swim upstream to look for places to spawn. A possible explanation for their presence at the sampling site within the city is that the higher water levels during the spring flooding in 2023 assisted them to move further upstream.

“This was an explanation that we got from people with experience with Prussian carp and invasive species,” Steinley said. “The flooding gave them a good vector to move easier upstream within the creek.”

The ability of Prussian carp to move further upstream in the creek will probably be limited by the weir at the City of Swift Current water treatment plant.

“The weir is probably a physical barrier,” he said. “That’s why we wanted to check south of the city. It’s something definitely to keep an eye on is to see if they do breach that barrier, but at this point I’m not sure if they can.”

The EDNA sampling at the five locations along the Swift Current Creek also provided data about the presence of other fish species.

“It tested for all types of aquatic wildlife EDNA,” he noted. “Our main goal was to refine the areas where Prussian carp are in the creek, but the side benefit is that we’ve got a really good report and understanding on other fish species within this area of the creek.”

The results of the EDNA sampling indicate a diversity of fish species in the creek and the presence of Prussian carp has not yet resulted in a negative impact.

The SCCWS is not planning to do further EDNA sampling along this section of the creek, partly because it is expensive. The Saskatchewan Fish and Wildlife Development Fund provided funding for the sampling in 2023. Steinley said the next step is to verify sampling results through the use of other methods.

“I think we’ve done as much as we can with that type of sampling,” he noted. “We’re going to be looking for funding and opportunities to do netting of fish in some of these locations to catch live fish to do population counts and identification to verify the results of the EDNA.” 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 reproduce very rapidly and they are considered to be a generalist species that can eat a wide range of food options.