The invasive Prussian carp continues to spread through the South Saskatchewan River basin and researchers want to learn more about this aquatic invader with a field program around Lake Diefenbaker this summer.
The field program is carried out by the Department of Biology at the University of Regina. The program started in 2018, but it was interrupted last year due to the COVID-19 pandemic.
“The last time we've actually been in the field in a major way would be 2019, and the outcome of that was that the Prussian carp are distributed pretty much from the Alberta border throughout the South Saskatchewan River and Lake Diefenbaker,” Prof. Christopher Somers said.
He is an applied ecologist and head of the Somers Lab in the Department of Biology at the University of Regina.
“The reports in general over the time we've been studying indicate that the fish are expanding, but we did not get any major expanding reports last season,” he said.
There have been reports of Prussian carp well beyond Lake Diefenbaker in the South Saskatchewan River system and it is already past the Saskatoon weir.
“They are already confirmed as far north as Saskatoon,” he said. “So they are out of Lake Diefenbaker and substantially downstream off to that northeast direction.”
The big question is if Prussian carp, an invasive species from Asia, can still be stopped or whether it will simply continue to spread down waterways.
“We don't know,” he said. “It is unlikely that we'll be able to present any sort of barrier that they won't be able to cross, but at some point we hope that they hit either an environmental barrier or a predator population, you know a healthy predatory fish population that maybe will slow them down. At this point, I think we have missed the opportunity or maybe we never had the opportunity to eradicate them. It's more about damage control now.”
The next major downstream barrier for these fish will be the dam structures in the Saskatchewan River at Codette Lake and Tobin Lake.
“Those are obviously some of the province's premier walleye fisheries, and so it would be maybe a bad scenario if these invasive fish were to get into those bodies of water,” he said.
Prussian carp is a very competitive species and their potential impact on fisheries and native fish species is therefore a concern.
“These guys compete with basically everybody,” he said. “So they are extremely prolific and they're very, very opportunistic. They eat essentially everything and they spawn up to four or five times per season. It's really a matter of them taking over resources in a body of water and becoming super abundant and crowding out the other species. … These guys are just so good at eating and reproducing that they basically outcompete the other fish.”
The Prussian carp presents a real challenge for various reasons. They are considered to be a generalist species that can eat a wide range of food options. They can survive in a large variety of environmental and water conditions. They can reproduce at a prolific rate by spawning three to four times a year. Females can lay up to 200,000 eggs per spawn and they are able to reproduce without males through a technique called gynogenesis.
“Part of their reproductive strategy is that they actually can have all-female populations that don't require males of their own species,” he explained. “They can use the sperm from other fish to stimulate the development of an unfertilized egg, which creates clones of the females, and so you have these clonal populations that are able to get established and to reproduce from very, very small numbers of female colonists arriving at a new site and starting a new population.”
Attempts to implement management approaches to limit or slow down the spread of Prussian carp has been unsuccessful. The goal of this field program is therefore to learn as much as possible about this fish.
“These fish do well in shallow, productive systems and what we are hopeful for in Saskatchewan is that because our lakes tend to be deeper, especially those as you go further north, that maybe these guys won't be able to get that stranglehold on these systems and so maybe there'll be some natural resistance that will help, but most of the management approaches have failed to have a significant impact on their populations once they become in that invasive, kind of explosive growth phase.”
According to Prof. Somers there are still many gaps in the information available about Prussian carp, and his team hopes to find answers through the field program.
“We would like to know some basic things about how old they get, how quickly they grow, how quickly they reach an age of maturity where they can spawn, and we want to be able to confirm what type of mating system they're actually using, how often are they using that gynogenesis, are they actually using all the reproduction in some circumstance,” he said. “So just fundamental aspects of their biology and very importantly, we're trying to determine more about their diet and what native species are immediately at risk of direct competition with them for food.”
This year’s field program started in May and eastern Lake Diefenbaker is the focal area for sampling by the fieldwork team.
“This year we're hoping to learn more about the particular parts of Lake Diefenbaker and the South Saskatchewan River that have large and established populations that are reproducing, and specifically we're interested in when reproduction is happening and where it is happening, because that is a potential target for management down the road,” he said. “We have a crew of students in the field that are doing index netting on a variety of places on Lake Diefenbaker on a daily basis and their job is strictly to look for Prussian carp and to see when juvenile fish start to emerge to confirm where reproduction is happening.”
Jayme Menard, a M.Sc. student at the University of Regina, is participating in the field program. She is studying the ecology of Prussian carp. Her research is focused on the timing and location of reproduction, as well as the genetic mating system of this invasive fish. She is also investigating the age structure in newly established populations of Prussian carp in Saskatchewan waterways.
“Where they are reproducing with a donor, we need to identify which donor that is and what time they're spawning, because right now we have a lot of unanswered questions, such as even where to find them,” she said.
She is out in the field every day to set nets and to look for potential areas where Prussian carp may occur, based on the information they have about their preferred habitat.
“So far we've had some relatively good success,” she said. “We've got a couple, which is more than we can say for previous years, and to do that we set nets overnight and then we also pull a net through the water.”
The information collected from anglers, landowners and other people have been invaluable to help the researchers to identify potential areas to find Prussian carp.
“For the most part we're staying in pretty shallow end coulees,” she said. “We've had a citizen science reporting system going on since 2018 and most of our sites are places where we've received a citizen science report saying that they've seen or they've caught Prussian carp in that area. So we're staying back in the coulees by the Gardiner and the Qu'Appelle Dam this year in areas that citizen scientists have reported seeing them in previous years.”
Field team members have been dealing with a variety of weather conditions since the field program started in May, and another challenge has been the changing water levels in Lake Diefenbaker.
“The water is slowly coming up and so the areas that we can go into that we can reach in our waders and do our near shore sampling are slowly getting smaller and smaller, because the water is going a little big higher than where we can go in the water,” she explained.
They will have to adjust their approach as water levels change, because the Prussian carp seem to move upstream into the creek area as the water comes up.
“We'll still be able to set them in certain areas, but we'll have to avoid other areas because it's too steep,” Menard said.
They already had some success in identifying potential spawn areas, based on citizen science reports about a lot of Prussian carp in shallows and their splashing behaviour.
“Those areas also we have found juveniles and we believe juveniles probably won't swim very far from where they're born,” she said. “And so for the most part we're focusing on Coteau Bay for looking at spawning areas and what kind of environment they use to spawn.”
Anglers are requested to assist this field program by reporting sightings of suspected Prussian carp and to submit carcasses for research purposes. Prof. Somers said they are easy to identify compared to most native fish.
“They kind of looks like a flattened football,” he noted. “They're very flat and tall kind of body shape and they have very large scales. They're quite distinctive from other species, and their mouth is not downturned. The other species that have large scales like that in Saskatchewan tend to have a downturned sucker type mouth. A Prussian carp's mouth is much more like that of a yellow perch. It's straight at the end of it's face and it's not that sort of bottom feeding mouth that we're used to from other sucker type fish.”
Anglers can submit reports by sending an e-mail to: firstname.lastname@example.org; and they are requested to include a photograph. The first 10 anglers to catch Prussian carp in Saskatchewan and submit the carcasses to the field program will qualify to receive a $100 Cabelas gift card.