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Effects of Asian carp on rivers hard to find

(MCT) — Asian carp have gotten much bad publicity, as well they should. They’re poster fish for what’s wrong with America’s import laws – or lack of them – regarding how species of plants and animals are brought here from overseas.

Too many examples exist. The anglers who enjoy the Illinois River know that too well. Species like round gobies and zebra mussels came to the Great Lakes by way of the ballast tanks on oceangoing cargo ships. They then made their way down the Illinois River. Asian carp — a term lumping several invasive species of fish together — were brought here to clean domestic catfish ponds and for food. They escaped into the Mississippi River when the ponds were overwhelmed by flooding, and they have been migrating upstream ever since. Millions are being spent to keep them from reaching Lake Michigan.

The problem is the fish eat massive amounts of plankton, the single-celled animals that are the base of the river’s food chain. That means they compete with every small fish of any species. They also reproduce by the thousands. Unlike many fish species, they can reproduce twice or even three times a year. They are now a major part of the load on the rivers’ ecosystem.

Silver carp, one of the Asian species, have a nasty habit of jumping from the water by the hundreds at passing boats. If you’ve ever seen a video of their aerial act, you’ll never forget the sight. They wind up inside the boats. Folks downstream near the confluence of the Illinois and Mississippi rivers have what they call a redneck fishing derby every year. No fishing rods are allowed. They can only motor back and forth. They weigh in the many pounds of fish that land on their decks.

The carp were expected to create problems with the rivers’ game species, bass, walleye, sauger, catfish, white bass and crappie because of competition for food. For one, scientists thought they might see a decline in the number of small game fish surviving due to a lack of plankton. They also wondered if we might see a crash in the population of shad, a small fish that provides the bulk of food for larger game fish. Shad feed on plankton, too.

But so far no evidence of strain on the river’s fish species has materialized, according to Gary Lutterbie, who retired at the end of 2011 from the Illinois Department of Natural Resources, where he was streams biologist in charge of a section of the Illinois River.

Anglers complain the sauger are smaller than in past years. But Lutterbie said surveys show the sauger have had a couple of outstanding reproduction years. They’re so plentiful they’re competing with each other. The fact so many are surviving through their first year to reach that 14-inch legal mark shows ample food is available, he said. He thinks larger fish are still present but they don’t get a chance to strike a bait before quicker, smaller ones beat them to it.

As for shad, eagle lovers feared the primary fish eaten by the birds were declining, and scientists wondered the same thing for a few years. But shad numbers seem to be rebounding, too. As Lutterbie said, cycles in fish populations are the “nature of the beast.”

Asians have been in the Mississippi River and its tributaries for more than 20 years.

“But I don’t think anybody can point to one thing and say the Asians are affecting any species. We have just not seen it. You have to scratch your head and say ‘how can this be,’ there are so many of them. … But if the silvers didn’t jump, if you didn’t see them, no one would care,” Lutterbie said.

Lutterbie said the next threat are quagga mussels. Like zebra mussels, they are good reproducers and filter feeders. Plankton is their main diet. They were first identified in the Great Lakes in 1989. Now, they are “all over the bottom,” Lutterbie said. Like zebra mussels, quagga mussels came from the Ukraine in the ballast of oceangoing vessels.

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