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Few Lines of Defense for Asian Carp

May 26, 2014 By Erik Alfvin, Macalester College

Today Minnesota 2020 continues a series of columns focusing on agricultural and biodiversity issues. This is part of a continuing collaboration with Macalester College's Geography Department and its students.

Imagine that while waterskiing on a Minnesota lake one day, you suddenly come face to face with a 110-pound fish that has jumped out of the water. That seems to be the popular vision of the Asian Carp, a fish known to jump up to ten feet out of the water in the presence of motorboats. However, these fish also pose a serious threat to biodiversity that could be much more costly for the fishing industry.

The fish were originally introduced from China into ponds in the south to control plankton and aquatic species, and later escaped into rivers. Since they eat large amounts of plankton at the bottom of the food chain, they compete with other species for food and can drive their populations down. If they migrate into the Great Lakes they could easily become the dominant species and out compete native fish, greatly reducing the productivity of the fishing industry. The fish have also been moving north in the Mississippi River.

To combat this problem we will need to find a sustainable solution that does not end up creating additional problems.



Strategies have been put into place to stop, or at least slow the fishe's spread. As of now in Minnesota, DNA sampling shows that no Asian Carp exist below Lock and Dam No. 1 in the Mississippi River, but the fish are still prevalent in Iowa waters.

Preventative actions should still be taken in and around the Twin Cities given the ease of their spread. One method of prevention that the Wisconsin Department of Natural Resources takes is to check boats before they enter new water. They advise to drain all water tanks, as just a few carp could start a new population. Young Asian Carp can also resemble other species. The WDNR has therefore banned the collection of baitfish from the Mississippi River so fishermen do not mistakenly introduce them to lakes. The carp may not be brought in to markets or moved in live form. Other actions taken by the Minnesota DNR are to regulate the fish trade from other areas and to require commercial fisherman to document what they catch.

On a broader scale, the WDNR suggests that strengthening the natural habitat of the upper Mississippi River could alleviate the problem. A strong aquatic ecosystem could better deal with an invasive species than a weak one since the natural ecological balance would be harder to change. This strategy is promising in the sense that it does not introduce another foreign species to deal with the carp and helps the native species at the same time. If this were a viable option, it would have a small effect on the outside world and appears not to have any major consequences. However, it might not work. Asian Carp are not native so it will be hard to predict how they interact with the upper Mississippi River habitat. They may still easily dominate over native species and then we would be back to where we started.

One of the major prevention measures recently put in place to halt their spread is the electric barrier, consisting of electric cords that run under a portion of the river upstream of where the carp are thought to be. There is an adjustable DC current established across the river that is supposed to block any fish from moving upstream. One of the major barriers is in the Chicago Ship Canal, designed to be the “last line of defense” for blocking the fish from moving upstream into the Great Lakes. The problem with this method is that tests have shown that small schools of fish can still swim through the barrier even after increasing the voltage. Passing boats also create a lower electricity “wake” that can allow larger fish to swim through as well. No Asian Carp have been found to pass the barrier, but it is still an imperfect system. There is also the safety hazard of sparks igniting flammable material on boats passing through.

I suggest that the Wisconsin and Minnesota DNRs take a combination of the above-mentioned actions as soon as possible. The electric barriers may be a useful method after they are improved, but even still they should not be relied upon since they are not a long-term solution. Instead the barriers should be used to buy more time while we look into more sustainable solutions.

The idea of strengthening the natural ecosystems in the Mississippi River is an appealing idea, but it should not be relied upon until it has been tested. The DNR should conduct small-scale, controlled tests to see if this method really works since it is the most natural solution with the smallest effects on the outside world.

In the meantime, we need continued assessment of the problem – how far the fish have gotten in the waterways. We also need to continue fisherman and boater education efforts to prevent advertent advancement. The Asian Carp problem can be solved, but it will take a collaborative effort between groups that use and maintain the waterways.

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