Chelsea Greening and her boyfriend, Landon Polk, are avid bow hunters who have utilized their skills to capture fish at the Boundary Dam Reservoir.
But they never imagined that their capture of two large fish would be beneficial for the dam.
Greening and Polk have used their specially-equipped bows to shoot fish, particularly large carp, at lakes throughout Saskatchewan and Manitoba.
“You just hook the bow up with fishing equipment,” said Greening. “It's a different arrow with a string attached to it, and the reel is actually attached to the bow, so that you can catch carp fish.”
While at Boundary Dam's hot water return area earlier this year, they spotted a few large fish that they thought were carp. They used their bow to shoot one of them.
“They were very different from what we'd ever seen,” said Greening.
A photo was sent to a conservation officer, who forwarded the picture to Saskatchewan Fisheries. The fish was confirmed to be a koi.
Polk has since captured a second koi fish.
Koi are not native to Boundary Dam, or any other lakes in Saskatchewan. So they pose a threat to other living organisms in the reservoir.
They stir up the bottom of the reservoir, making the water murky, which increases nutrient levels and algae concentrations, and contributes to erosion.
“They also feed on and remove aquatic plants,” Greening said. “They prey on invertebrates, native fish and their eggs, causing a competition for the native species.”
The koi will need to be removed from the lake before they cause great harm to native organisms, she said.
“We consider it to be doing a favour,” said Greening. “They're not supposed to be in that lake, and they're a threat to the other organisms in that lake.”
Each of the koi that Polk captured weighed 25 to 30 pounds, Greening said. The first one was caught in early May, just after the start of fishing season, and the other one was snared in early June.
“At first, when we were first seeing them, there was eight or so grouped together, but we would see up to 30 of them,” said Greening. “And now, as the water has warmed up throughout the whole lake, they have started to disburse, and you only see one or two around where the hot water return is.”
Polk has continued to hunt the fish, but hasn't had any luck capturing them in the last couple of weeks. Greening said they don't know of anyone else who has snagged a koi.
Jennifer Merkowsky, an area fisheries biologist with the Saskatchewan Ministry of the Environment, said that the koi are an ornamental variety of common carp that have been bred for their vivid colours.
"They're actually native to Asia, but people in the aquarium trade sell them in Saskatchewan for people to put into their aquariums and their ponds," said Merkowsky.
Saskatchewan Environment doesn't know for certain how the koi wound up in Boundary Dam, but they suspect that the fish were released from an outside source.
They don't have any other reports of koi being in other lakes or rivers in the province.
Merkowsky said Saskatchewan Environment is encouraging anglers to capture the fish, and remove them from the reservoir.
"Right now there is no feasible method for eradicating the koi from Boundary Dam," said Merkowsky. "The predators would certainly include anglers, but also fish-eating birds such as herons, or other wildlife such as raccoons."
Young koi would also provide a food supply for game fish, she said, but not once they grow up.
The bow hunting employed by Polk and Greening is the best way to try to catch the koi, Merkowsky said, because carp are traditionally bow-fished.
"I'm not sure that a line-and-lure would be effective," she said.
Merkowsky said that aquarium pets, plants and water should never be released into lakes, rivers and wetlands, because of the potential impact that it could have on Saskatchewan's native species.