Everyone’s seen photos or video of high-flying silver carp in the Illinois and lower Mississippi rivers, endangering boaters and water skiers as the huge fish jump from the water and crash back to the surface.
Until this year, the antics of those fish were mostly a source of amusement for Minnesotans, something that only happened far downriver.
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| Acrobatic silver carp in the Illinois River Photo: Kevin Irons, Illinois Department of Natural Resources |
Then, in mid-April a commercial fishing crew caught a bighead carp, one of four invasive Asian carp species that have been slowly migrating north over about the last 30 years, in the St. Croix River. The 27-pound fish was caught near Prescott, Wis., where the St. Croix flows into the Mississippi.
It wasn’t the first Asian carp caught in the upper Mississippi or the St. Croix – in fact, it was the 10th caught since 1996 – but the catch came as the Minnesota Department of Natural Resources and the National Park Services were starting to get serious about fighting the spread of the carp.
Asian carp are an ominous threat to native fish and waterfowl because they out-compete the native species for food and habitat, consuming up to 10 percent of their body weight in in phytoplankton and zooplankton each day. In the Illinois River, Asian carp now account for 80 percent or more of the fish biomass.
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| Tim Schlagenhaft |
In July, the Minnesota Legislature approved Gov. Mark Dayton’s request to spend $16 million to upgrade the Coon Rapids Dam to try to stop Asian carp from making their way up the Mississippi into the lakes of Central Minnesota.
And in August, the DNR and the National Park Service announced the results of DNA testing aimed at determining whether the Asian carp were present further up the St. Croix and in the Mississippi near the Twin Cities.
Twenty-two of 50 water samples drawn from the St. Croix below the Taylors Falls dam contained DNA identified with silver carp. No Asian carp DNA was found in 50 samples taken from the Mississippi below the Ford Dam in St. Paul.
The presence of silver carp DNA did not prove the fish are present in the St. Croix. And the absence of carp DNA in the Mississippi did not prove they are not there.
An intensive nine-day effort by the DNR in late August to catch a silver carp in the St. Croix failed to yield a single fish. But DNR officials say they believe, based on the DNA testing, that silver carp are present in the St. Croix and perhaps in the Mississippi – but not yet in significant numbers.
“We think that maybe we’ve got a population that still is very low, is controllable,” said DNR Commissioner Tom Landwehr.
In two interviews, before and after the DNA evidence of silver carp was found, the Freshwater Society interviewed Tim Schlagenhaft, the DNR’s point person in the campaign against Asian carp. A transcript of those interviews, combined and edited for brevity, follows:
How big a problem do Asian carp pose for Minnesota lakes and streams?
They eat plankton and large quantities of plankton, which forms the basis of the food chain. Everything dependent upon that could potentially be affected if the numbers of those carp increase, and they are large fish so they can have a big impact on the ecosystem.
Are Asian carp potentially a much greater problem than the threat posed by zebra mussels or purple loosestrife or milfoil or any of the other invasives we have seen so far?
They are a different type of problem, I think all of the invasives have their own unique situations where they create problems, but these pose a direct threat to those fish that eat plankton, so the fisheries resources have a potentially great impact.
Where they have established reproducing populations further south on the river have they been the biggest problem the fisheries have ever seen there?
In places like the Illinois River: yes. If you look at the extensive effort that’s being put in now by the federal government and the state of Illinois, they have had a huge impact and are costing a lot of time and energy to combat them.
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| Al Stevens and Guy Schmidt of the Minnesota DNR search for Asian carp in the St. Croix River near Prescott, Wis. |
Yes, the Mississippi is a huge system with the locks and dams and it still floods. Preventing the movement of these fish upstream is going to be almost impossible up to the Twin Cities, where you start to have dams that are constructed in a different way. It is going to be really hard to stop them and we are going to have to look at ways to mitigate and slow them down if they do arrive here. I do believe that they can jeopardize long-term sustainability.
So do you think we are destined to have reproducing populations of Asian carp below the Twin Cities?
“Destined” is kind of a tough word there, but the climate we have here is similar to their native range. There are no barriers that are going to 100 percent stop their migration, so there is no reason to believe that they’re going to not get here.
Is there any evidence that they are becoming less of a threat as they move upstream?
No, they just aren’t upstream in the numbers as they are downstream.
How big a factor are the Mississippi River dams in slowing the migration of the carp?
Well, from Lock and Dam 2 in Hastings downstream, these dams operate to maintain high enough water levels for commercial navigation. When flows get high, they pull the gates out of the water.
Bighead and silvers are strong swimmers and it’s been documented that that’s when they move, when the flows are high during a flood situation. So the dams maybe slow them down, but the dams are not a long-term barrier to Asian carp.
Talk about the options for halting the spread of these fish. First the non-controversial ones, then the controversial ones, like closing the lock at the St. Anthony Falls dam?
Everyone’s pretty much in support of addressing this problem. The reality is there isn’t a lot that we can do. One of the things we’re trying to accelerate is more information about a bubble sound barrier at the mouth of the St. Croix because that site is real confined at Prescott. It’s got potentially a physical arrangement there that would allow a barrier to be put in place. We’ve made it clear that any barrier will not be 100 percent effective. It’s not a long-term solution. There are other control methods on which they are doing research. For example, something they call a bio-bullet, where’s it’s able to deliver a toxin that is eaten by a fish, and the enzymes in the Asian carp would release the toxin. But it wouldn’t be released in other species. If we can somehow slow the fish down and concentrate them at some kind of a barrier, and then apply those kinds of technologies, once they are developed, then we have a better chance of controlling them.
The controversial issue is related to the potential lock closure at Upper St. Anthony Falls. There are two dams in Minnesota, Upper St. Anthony Falls and the Ford Dam, that are high-head dams, and the only way the fish can get through is to lock through when there is navigation traffic there.
The Corps of Engineers has made it clear they don’t have the authority to do that. It would take Congressional action. The DNR position is that, from the point of preventing the carp getting into Central Minnesota and some of the tributaries – up into places like Mille Lacs – having that be a permanent fish barrier is probably our best way to prevent their movement.
Where does the Coon Rapids Dam come in?
Repairs that have been proposed to the Coon Rapids dam would help decrease the chance of fish movement. But the Coon Rapids dam would not be a 100 percent effective barrier.
Do you have any plans for keeping them out of the Minnesota River? A 2007 DNR report said preventing the introduction of Asian carp into Minnesota was a “daunting challenge and unlikely to be successful over the long term.” The same report said Asian carp have the potential to “cause extensive and irreversible changes to the aquatic environment…jeopardizing the long-term sustainability of native aquatic species.” Is that still your assessment today?
That would be very difficult. The Minnesota has a very large broad flood plain and any kind of technology barriers would be very difficult to install. (In a subsequent interview, Schlagenhaft said flood control barriers that contain the river’s channel at Mankato might allow some deterrent to be installed there.)
Is the DNR on record or in favor of closing the St. Anthony Falls lock permanently?
The DNR is in favor of having a permanent, 100 percent effective, barrier. If you can do that and still allow for navigation, with some kind of technology in the lock that allows navigation, then that’s OK, but we are in favor of a 100 percent effective barrier.
This year, the Legislature finally adopted a significant package of anti-invasive species laws – most of them aimed at zebra mussels. I think some Minnesotans think the DNR and the Legislature didn’t get serious about fighting zebra mussels until it was too late for lakes like Minnetonka and Gull and Pelican. Have we all waited too long to take strong measures against Asian Carp?
We’ve been taking measures against Asian carp for quite a while now, at least ten years, where we have addressed the transport of fish. We have done a lot with what you have to do with your bait. We also looked at alternative technologies, further downriver, that were never funded and would have had to have been federal projects. So we have been doing a lot, and I hope it’s not too late. Now we are getting more aggressive with a specific action plan. And the technologies being developed now give us some tools that didn’t exist ten years ago.
Anything else?
Just that to implement our plan is going to require resources. The alternative technology barriers will be expensive. Even a feasibility study to look at permanent closures is expensive and takes time. We want the federal government to recognize that the upper Mississippi River is an important system. We have a huge tourism industry; we have great recreational fisheries that are in jeopardy. So we should be putting federal resources into everything we can.