Carp-ocalypse now

Mike Mosedale, Minnesota Reformer
July 5, 2023, 

Silver carp jumping in the Fox River in northern Illinois. (Ryan Hagerty/USFW)

As he dipped a net into a big cylindrical tub in the dimly lit fish laboratory at the University of Minnesota’s Hodson Hall, Dr. Peter Sorensen scooped a half dozen small silvery fish and gazed at the wiggling, bug-eyed creatures with a look of benevolence.

“I don’t hate them, I really don’t,” said Sorensen. “It’s not their fault they’re here.”

Sorensen, a longtime researcher and professor at the university’s Department of Fisheries, Wildlife and Conservation Biology, restricts the diet of his captives to stunt their growth. If he didn’t, he explained, the fingerling-size fish would already weigh 10 or 15 pounds — an unwieldy size for lab experiments.

The fish in question — silver carp — have occupied Sorensen’s professional attention for over a decade. It’s an outgrowth of rising concerns that the highly invasive species is inexorably moving up the Mississippi River from Iowa.

While the fishes’ northward march has been slowed by the existence of barriers in the river — the locks and dams that enable navigation — the carp can pass through spillway gates during times of high water, as well as the lock chambers during normal operations.

In 2012, lawmakers in St. Paul responded to the looming crisis and funded a new entity at the University of Minnesota, the Minnesota Aquatic Invasive Species Research Center. Sorensen, who had developed an expertise in the control of two other harmful invasive fish, the common carp and sea lamprey, was tapped as its first director.

Sorenson didn’t last long in the leadership post — “I’m a scientist, not a manager,” he said — but he has continued his research in the field of invasive carp, a catch-all term that describes silver carp, the closely related bighead carp, grass carp and black carp. His cluttered office is adorned with a trio of taxidermied silver, bighead and common carp.

In the course of his investigations, Sorensen has developed respect for the silver carp. For one thing, he notes, they are far more elusive than our native fish, with a wariness that makes them difficult to capture. “They are smart, skittish fish. They hear you coming. Traditional fishing gear doesn’t work very well. These are not walleyes,” he said, adding with a laugh: “Honestly, our native fish are pretty stupid.”

Silver carp are also not fish anyone, least of all a fisheries scientist like Sorensen, wants to see in Minnesota’s lakes and rivers.

“They have no ecological value, they take food from other fish, and they destroy water quality,” Sorensen said flatly. “They are just bad news.”

The other ‘silver tsunami’

Silver and bighead carp escaped into the Mississippi River in the 1970s after they were originally imported from Asia to Arkansas to control algal blooms in fish farms and sewage ponds (and widely touted as a green alternative to common chemical treatments).

In the years since, they have relentlessly expanded their range. Along the way, the fish — voracious, fast growing filter feeders that hoover up the phytoplankton and plankton that is base of the food chain — have devastated native fisheries. In some stretches of the Illinois River, silvers and bigheads account for as much as 90% of the fish biomass.

It’s not just anglers and fish biologists who are disturbed by this development. Silver carp, which can reach weights in excess of 90 pounds, have a strange habit of leaping high out of the water when startled. This has created a new hazard in many lakes and rivers, as schools of leaping carp, triggered by the sound of motors, occasionally collide with and injure people in passing boats.

The unusual behavior has given rise to some novel fishing tactics. To kill silver carp, some people deliberately drive through pods and, when the fish leap from the water, they shoot them with bow and arrow. The made-for-YouTube spectacle serves as a gruesome comedic counterpoint to the dire environmental calamity the fish represent.

In Minnesota, the first documented bighead was netted in Lake St. Croix, a wide spot in the St. Croix River in 1996. The first silver was discovered in the Mississippi near the Iowa border in 2008. In the years since, the fish — especially the silvers — have been spotted with increasing frequency in Minnesota waters, including in the Mississippi River in St. Paul.

While the appearance of the occasional stray is not necessarily worrisome, evidence that fish are here in substantial numbers is; that’s because both silvers and bigheads are wildly prolific spawners.

“At some point, they will reproduce. And if they start to reproduce, I don’t see any hope,” Sorensen said. “The females can produce a million eggs. They are moving upstream. If they reproduce, it will destroy half the fish in the river.”

That’s why Sorensen has focused his research on technologies that can stop — or at least slow — the carps’ upriver passage. The approach that he has long endorsed is called a bio-acoustic fish fence. The BAFF, as it is commonly referred to, combines strobing lights with underwater audio speakers and a curtain of bubbles.

While it sounds like a Rube Goldberg device (or an underwater disco), Sorensen said the BAFF, manufactured by a British company called Fish Guidance Systems, has been shown to be remarkably effective at repelling silver and bighead carp. Under laboratory conditions, Sorensen found that the BAFF deterred 90% of fish from passing the gauntlet. Real world experiments have been similarly encouraging. (Sorensen served as a co-leader of an ongoing BAFF demonstration project in Kentucky, where the device has been placed in a lock in highly infested waters).

Sorensen pointed out that he has published two peer-reviewed scientific papers that validate the efficacy of the approach. Long ago, he came to the conclusion that he knew the ideal spot to install a BAFF to best protect Minnesota waters: Lock and Dam #5, just upriver from Winona.

Frustration at the Legislature

Over his years working on the carp problem, Sorensen has become a regular figure at the Capitol, where he has testified in support of funding for carp research. In more recent years, he has repeatedly advocated for the construction of a BAFF in the lock at Winona.

“I think I’ve tried to get it funded five or six times now. I’ve lost count,” Sorensen said. “By 2015, when we were first looking at this, it was very clear to me that Lock #5 was the best spot.” In part, that’s because the spillway gates at the dam — the easiest means for fish to move upriver — are rarely open.

As part of his research, Sorensen has implanted receivers in common carp in the waters below the lock. Not once in two years of data collection has he recorded an upriver passage through the spillway. To the south, he said, the dams and spillways are “like Swiss cheese.” To his thinking, that makes clear that a deterrent in Lock # 5 is the best — and maybe last — bet to hold the fish back.

If reproducing populations of silver carp become established upriver of Winona, it would expose some of Minnesota’s most iconic waters to ecological catastrophe. The fish would almost certainly prosper in Lake Pepin, the nutrient-rich 22-mile long wide spot in the Mississippi south of Red Wing. The St. Croix River below the dam at Taylors Falls and the Minnesota River could easily be overrun soon afterwards.

In March, Sorensen appeared before the Senate’s Environment, Climate and Legacy Committee to testify in support of $17 million appropriation to fund the BAFF, along with monies for contracted netting operations and further research that the DNR sought.

Despite past failures at the Legislature, Sorensen was optimistic. Among other things, he came armed with a freshly completed 128-page feasibility study from Barr Engineering Company, which endorsed Lock #5 as the most suitable site for the BAFF.

According to the company’s analysis, a BAFF could be installed at a cost between $8.2 and $16.5 million, depending on whether the state chose to purchase or rent. Combined with other measures, including netting of fish below the lock, Barr endorsed Sorenesen’s findings that the BAFF could prevent the upstream passage of 99% of carp.

This year’s legislative push was spearheaded by the group Friends of the Mississippi River, with support from a bevy of other conservation organizations operating under the banner of the Stop Carp Coalition. It had the full-throated support of several lawmakers, including chief author, Sen. John Hoffman, DFL-Champlin. “This proposal is the only plan we have,” Hoffman told fellow lawmakers. If the fish begin to reproduce upriver from Winona, Hoffman warned, the state would likely be forced to spend millions on netting programs every year.

In one notable regard, the timing of the Senate hearing could not have been better. In past years, experts like Sorensen had cautioned that the carp were on their way. But on the very day of the hearing, the DNR announced that a commercial crew had just netted 30 silver carp just below Lock #5. It was the largest single capture of the fish that far north on the Mississippi.

In her testimony, Colleen O’Connor Toberman of Friends of the Mississippi highlighted the significance of that event. She also pointed to a political reality of the moment: With the state coffers awash in a record $17 billion surplus, there would probably be no better opportunity to fund a BAFF than 2023. “We will invest now or we will pay more later,” she told lawmakers.

Despite the prevailing enthusiasm for the BAFF, one key voice was conspicuous in its silence: the Department of Natural Resources. In testimony that day, Heidi Wolf, the supervisor of the DNR’s invasive species unit, touted the agency’s emphasis on carp capture and research. She also told lawmakers that the agency was ramping up plans to commence “a structured decision making” process, which would bring key stakeholders, including the U.S. Army Corps of Engineers, DNR and the state of Wisconsin, together to settle on the best path forward.

Wolf did not expressly oppose the BAFF proposal but did not endorse it either. And she offered what seemed to be a measure of reassurance to senators anxious to get moving: There is no evidence, she said, that silver or bighead carp are successfully reproducing in Minnesota. (In Sorensen’s view, the absence of evidence of reproduction does not mean much, given the difficulty of sampling a big, fast flowing river like the Mississippi).

Still, both Sorensen and Toberman left the hearing convinced that there was a good chance the BAFF funding would be included in the committee’s big budget bill. They were wrong.

Due diligence or undue delay?

A few days later, when the language of the Senate’s environmental spending bill was unveiled, Whitney Clark, the executive director of Friends of the Mississippi, was “shocked” to see the BAFF money stripped out, with just $1.7 million left for more research, more targeted netting and, possibly, a study of potential modifications to the operation of the spillway at Lock #5.

After consulting with FMR’s lobbyist, as well as the chair of the Senate environment committee, Sen. Foung Hawj, DFL-St Paul, Clark concluded that the BAFF funding had been excised at the behest of DNR Assistant Commissioner Bob Meier. “Bob Meier went to Sen. Hawj and told him it was unworkable, that there would be cost overruns, and they had big questions about the viability, efficacy, and ongoing costs,” Clark said.

Clark felt sandbagged. Through the fall and winter, FMR had consulted regularly with the DNR about the bill. Before that, the group had repeatedly prodded the DNR to update its 2011 carp action plan (a process that is now underway). While the BAFF wasn’t included in the agency’s budget proposal, Clark said Meier and others in the agency seemed encouraging in the discussions. “I wanted it to be a collaborative effort,” said Clark. “I thought we were in a really good place.”

Reached for comment, Meier eschewed the notion that he single-handedly tanked the BAFF funding. That said, Meier contended that there are too many lingering questions to proceed with the BAFF before getting answers. “We were just concerned about putting the cart before the horse,” he said.

Some of the hurdles are jurisdictional. Lock #5 is federal property, he noted, which raises the question of whether it makes sense for the state to own and operate equipment. He believes the Army Corps of Engineers is more suited to the task. Further, Meier said the costs of the maintenance and operations remain uncertain. He also questioned whether the BAFF could withstand flood conditions and what, if any, effect it might have on native fish.

As part of the DNR’s structured decision-making process, which kicked off this June, Meier expects to have more answers by the end of the year. If there is a consensus among the agencies and stakeholders, he said, the Legislature could come up with the money for the BAFF. Twenty million dollars may be a lot of money, he noted, but it is less daunting against the backdrop of a $72 billion state budget

“If it’s important enough to do, and it makes sense, I don’t see that being a real excuse,” Meier said. As to the criticisms he has received from Sorensen and Clark, Meier was unruffled. “I don’t take those things personally,” he said. “I do my job and I do what’s best for the state of Minnesota.”

Asked whether the BAFF would have been funded had the DNR offered institutional support, Hawj was diplomatic. “I don’t want to be absolute on that,” he said of the agency’s role. “They’re not against it, but they want to have a good foundation for support.”

That said, Hawj insisted that the BAFF will be one of his priorities moving into the next session, adding: “I trust Dr. Sorensen’s research.”

For his part, Sorensen is unlikely to have much involvement in the fight over the BAFF going forward. At 68, he is moving into phased retirement. If the DNR funds the spillway study, he may go on emeritus status and work on that piece of the puzzle. But he has little appetite for further tracking the upriver spread of silver carp — a prospect he finds depressing.

In the months since the BAFF proposal died at the Legislature, Sorensen had visited Lock #5 regularly to track the movements of common carp that he has tagged with receivers. On several occasions, he said, silver carp were conspicuous in their presence, leaping out of the water.

By mid-June, Sorensen had an undergraduate disassembling his lab at Hodson Hall as he readied himself for a vacation at his off-the-grid summer home in British Columbia. He was not inclined to offer the DNR the benefit of the doubt, referring to the lack of urgency at the agency as “dereliction” and “ineptitude.”

In the course of his long career, Sorensen has worked on an array of vexing issues involving invasive fish, from the control of sea lamprey in the Great Lakes to the control of common carp in Tasmania. Many of those experiences were validating, as various state, federal and other government agencies coordinated to take swift action. “You’re not seeing any of that here,” he said. “It’s embarrassing.”

While no solutions are perfect, Sorensen said, aggressive action can bear results. After the sea lamprey devastated populations of lake trout, scientists have managed to curtail their numbers, and the trout have largely rebounded, even though the lamprey have not been completely eliminated.

Sorensen said that the level of collaboration to achieve such goals — and the willingness to take decisive, if imperfect action — has been missing since the alarms were sounded over the invasion of silver carp in Minnesota. In 2005, when the carp were beginning to appear in large numbers below a Mississippi River dam in Keokuk, Iowa, the DNR’s now-retired invasive species coordinator broached the idea of installing a BAFF at the dam there. Nothing came of it.

While no single approach is likely to be 100% effective in stopping the movement of the silver carp, in Sorensen’s view, that’s no excuse for not trying the best available option and buying time.

“My analogy is, if you are in a boat and it’s sinking because there is a hole and you don’t have a perfect plug but you have an old T-shirt, you stuff that old T-shirt in the hole. You fix the hole. Then maybe you go on Amazon and get a better plug,” Sorensen said. “I don’t know why that isn’t intuitive.”

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