Watch a video of silver carp leaping out of the water in a frenzy — sometimes landing in watercraft or injuring boaters — and it’s easy to see why the recent discovery of the fish in the St. Croix has many in the river valley worried.
"It does concern me," said Cliff Lewis, general manager of the Bayport Marina. "If we ended up like the Illinois River, it would be very difficult for all our boaters. It would just ruin boating on the St. Croix River."
Last week the Minnesota DNR confirmed the first capture of the invasive silver carp on the St. Croix River, near the Mississippi. A commercial angler caught the carp near Prescott, Wis., during proactive monitoring in partnership with the DNR. The fish was 33 inches long and weighed 13 pounds.
"This news is disappointing but not unexpected," said DNR invasive fish coordinator Nick Frohnauer. "The silver carp was captured within viewing distance of the St. Croix’s confluence with the Mississippi River. In 2014, two silver carp were found in the Mississippi only a short distance upstream from where the St. Croix and Mississippi meet."
This year one bighead carp was also caught on the St. Croix, in the same location as the silver carp. Bighead carp are another invasive species that had previously been found in the St. Croix. According to the Minnesota Aquatic Invasive Species Research Center at the University of Minnesota, at least 15 individual bighead carp have been caught in the St. Croix since 1996.
In late May and early June of 2015, a total of six bighead carp were caught near the Allen S. King plant in Oak Park Heights, the farthest north carp had been detected on the river. Frohnauer said follow-up sampling near the power plant so far hasn’t found any more carp, but there may be something about the output of the plant that attracts the fish at a certain time of year.
The good news is the DNR so far has no evidence of reproduction or an established population of either bighead or silver carp in the St. Croix.
"The location where the carp were captured is a well-known over-wintering area for several species of fish," Frohnauer said of the most recent catch. "At this time, it is hard to predict if these individuals would have moved further upstream the St. Croix River, or back into the Mississippi River when water temperatures warm up in the spring."
Immediate follow-up sampling near Prescott was not possible, the DNR said, because colder weather led to the river icing up. When weather permits, the DNR will work with commercial anglers to survey for additional carp near Prescott, and will continue sampling near the King plant. A commercial angler netting under the ice near the Bayport Marina early this year did not catch any invasive carp.
Native to Asia, bighead and silver carp were imported to the southern U.S. in the 1970s to remove algae from catfish farms and wastewater treatment plants, according to the Minnesota Aquatic Invasive Species Research Center (MAISRC). When severe flooding caused farm ponds to overflow, the carp escaped into local waterways.
Carp have become well established in the Mississippi River south of Minnesota, as well as other rivers, such as the Illinois River. They make up 75 percent of the biomass in portions of those rivers. The nearest known reproducing population is in Iowa.
These species feed voraciously on plankton, often out-competing native organisms for food and disrupting the food chain and entire ecosystems. They also reproduce quickly, with female bigheads producing up to a million eggs each year, and female silver carp laying up to two million, according to MAISRC.
Bighead carp can reach 51 inches long and weigh up to 110 pounds, while silver carp can be 39 inches and weigh more than 75 pounds.
Although carp have severely disrupted some ecosystems, Frohnauer said it’s possible that in Minnesota the Mississippi and other rivers will be more resistant, because there are healthy native communities of fish and other marine life.
"As you move upstream, the [Mississippi] river changes," he said. "Strong native communities are probably affecting the rate of expansion. ... It’s harder for [invasive fish] to find that niche or get a hold in the ecosystem if you’ve got strong native species there."
Efforts to stop carp
In Minnesota perhaps the most noticeable attempt to halt the spread of Asian carp was the closure of the Upper St. Anthony Falls lock on the Mississippi River in 2015. But the Minnesota DNR has been working to slow the spread of invasive carp since the early 2000s.
A Minnesota Invasive Carp Action Plan was created in 2011 and updated in 2014.
In 2012, the state Legislature funded the creation of the Aquatic Invasive Species Cooperative Research Center at the University of Minnesota.
The research center is looking for ways to prevent the spread of carp, as well as other invasive species.
For example, the center has been studying how to tweak the flow of water through locks to make it more difficult for carp to pass.
It has also installed speakers at Lock 8, on the Mississippi south of LaCrosse, near the Iowa border. Because carp have a better sense of hearing than most native fish, researchers believe playing sound underwater can keep the carp out of the lock, deterring their spread upstream.
The Minnesota DNR is an active partner in the Upper Mississippi River invasive carp workgroup, which seeks to limit the impact of invasive carp. The group includes representatives from Minnesota, Wisconsin, Iowa, Illinois, Missouri and several federal agencies.
In addition, the DNR leads a sampling program to monitor population expansion, population changes and impacts of management actions.
Frohnauer said the public can help by reporting sightings, as well.
"We always ask the public to keep an eye out, whether one’s caught or they suspect they have seen one," he said.
The DNR says invasive carp captures must be reported immediately by calling 651-587-2781 or emailing firstname.lastname@example.org. If you catch a carp, the DNR says to take a photo and transport it to the nearest fisheries office or make arrangements for it to be picked up by a DNR official.
Many in the St. Croix Valley are concerned by the capture of a silver carp in the St. Croix.
"As both a resident and local elected official of Bayport, I was extremely alarmed to hear about the recent silver carp captured near the St. Croix and Mississippi River confluence," Bayport Mayor Susan St. Ores said. "I am very passionate about protecting the St. Croix River and preventing degradation caused by aquatic invasive species. I acknowledge the ongoing deterrent testing and monitoring programs currently underway, but feel additional effort should be made to prevent the spread of invasive carp."
Elected officials aren’t the only ones worried.
"I would hate to see large populations make their way north on the St. Croix," said Angelique Dahlberg, invasive species coordinator for the St. Croix River Association. "I think it would really change our experience on the St. Croix, and I hope that never happens."
Last year the St. Croix River Association completed a strategic plan for addressing invasive species — such as carp, zebra mussels and Eurasian milfoil — in the St. Croix and its watershed. The goal was to help coordinate efforts among various partners in the region, and provide additional resources where possible. Preventing the spread of bighead and silver carp was identified as a high priority for the region.
"People take care of the things that they value," Dahlberg said. "If the silver carp population were to grow and people didn’t enjoy their time on the river as much or it was dangerous, my fear is that people would stop coming to the St. Croix as much."
In a region that attracts significant tourism and river-related recreation, that could have economic consequences.
Hudson resident Ron Smith operates a fishing guide business between Stillwater and Prescott, Wis.
"My biggest concern is whether they can spawn up here or not," he said.
Smith is more concerned about the jumping silver carp than bighead.
"That’d be a problem for me if I’m guiding — I run up and down the river a lot," he said. "You see the videos of people running boats on the rivers down south. You see people wearing helmets and stuff."
"We don’t know what to expect," said Cliff Lewis of the Bayport Marina. "We have to protect the waterway."
He hopes educating the public about the problem will help build support around efforts to curb the threat.
Dahlberg, too, hopes public awareness will help galvanize further action.
"We stand a lot to lose," she said. "Maybe this will get people moving. That would be the most exciting outcome."
The public is welcome to attend an invasive carp stakeholder forum Wednesday, March 29, at the Minnesota Valley National Wildlife Refuge visitor center in Bloomington from 9 a.m. to 12:30 p.m. For more information about the forum, contact Nick Frohnauer, DNR invasive fish coordinator, 651-259-5670, email@example.com.
The DNR also has information on invasive carp at mndnr.gov/invasivecarp.
Contact Jonathan Young at firstname.lastname@example.org