ROBERT SIEGEL, host:

Fish that have the potential to devastate the Great Lakes ecosystem may be just a few miles from Lake Michigan. Two carp species from Asia � the silver and the bighead � are invasive fish with huge appetites, and if they enter the Great Lakes, they could overwhelm the native fish.

In order to halt their migration, the U.S. Army Corps of Engineers built an underwater electric fence on a canal 20 miles south of Lake Michigan. But now tests have indicated that Asian carp have gotten close to the lake despite that.

David Lodge performed those tests. He's director of the Center for Aquatic Conservation at the University of Notre Dame.

Welcome to the program, and tell us what your sampling found.

Professor DAVID LODGE (Director, Center for Aquatic Conservation, University of Notre Dame): Well, what we found is that, surprisingly, the carp seem to be much closer to Lake Michigan than anyone previously thought.

Using a new approach to measuring what we call Environmental DNA in the water, we've detected the presence of carp or at least their DNA in places much closer to Lake Michigan than the traditional tools had told us.

SIEGEL: You're saying you haven't actually found a carp there but you have found the DNA of these species.

Prof. LODGE: That's right. I think you can think of this e-DNA, as we call it, as the equivalent for environmental protection of, say, using DNA in crime fighting to detect whether a suspect was at the crime scene. So, we don't actually have a body, but we have DNA.

SIEGEL: Well, what would happen if there, indeed, were many bodies of these carp species in the lake?

Prof. LODGE: We can't, of course, know what impact they'd have in the Great Lakes with certainty. But there's lots of reasons to think that they would be highly damaging. We can look, for example, to what happened in the Mississippi River and the Illinois rivers where these fish now often constitute up to 90 percent or more of what fishermen catch, where commercial fisheries have been almost destroyed with this very abundant fish that has very low commercial value.

In addition, the silver carp, especially, have this unusual habit of jumping high out of the water and they've harmed many people. They're like living missiles. And because they reach weights of up to 80 to 100 pounds, a fast-moving boat and a person sitting in it collides with such a fish is likely to come out much worse for the wear.

SIEGEL: Wow. They actually are a hazard, you're saying, in the water.

Prof. LODGE: They are a very serious hazard for boaters.

SIEGEL: Now, the carp - these Asian carp - as they get closer to the Great Lakes are coming up river. How did they get there in the first place?

Prof. LODGE: Well, they were first brought to control nuisance algae and other nuisance organisms in aqua culture ponds, where the primary goal was to produce other fish. But like all sorts of other organisms introduced for fisheries and for pets and for horticulture, these fishes escaped and they have found the environment of the Midwest - the Mississippi River Basin - very much to their liking.

SIEGEL: Professor Lodge, I've heard of the idea of possibly poisoning the Asian carp somehow in the water. Is that an option?

Prof. LODGE: There is a plan to poison a five- or six-mile reach of the canal in order to reduce the populations immediately below the electric barrier. That plan was developed before our latest results, which suggests that the carp are above the barrier. It nevertheless remains important to conduct that poisoning, and to realize that just because there may be some carp above the barrier that the game is not over. It's not time to give up.

There are lots of examples of invasions that while may initially look successful, may fail or certainly could be made to fail with effective management. We shouldn't give up at this point.

SIEGEL: That's David Lodge who is director of the Center for Aquatic Conservation at the University of Notre Dame.

Professor Lodge, thank you very much.

Prof. LODGE: Thank you.

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