An undergraduate student's inventory of shoreline fishes in the Middle Mississippi River shows a marked shift in fish populations in just the past 20 years.

Diane Zeman, a senior in zoology, won a 2003 Undergraduate Research Award to conduct the study, carried out at three locations near Grand Tower, Ill. Zeman's work repeated a 1983 master's thesis project by SIUC student Michael Klutho that was one of the few studies to look at fish populations along the shores and in the backwaters of the Middle Mississippi (the stretch between the Missouri River at St. Louis and the Ohio River at Cairo). Most fisheries research focuses on commercial and sport fish living in the main river channel.

"Shoreline fish are a whole different fauna," Zeman says. "It's important to look at them too" to monitor ecosystem changes.

With guidance from zoology professor Brooks Burr, Zeman used seines to collect fish every two weeks from March through November 2003. She recorded data on species; water temperature, flow, and stage; time of day; and habitat type. Then she compared her findings with Klutho's.

Fish species specialized for muddy backwaters are disappearing from this stretch of the river, she found, and carnivorous fish species that locate their prey by sight are increasing.

Those changes are due largely to changing conditions far upstream. Decades of dam building on the Missouri River has caused sediment to settle out into reservoirs rather than be carried downstream. Hence the Middle Mississippi, which gets much of its sediment load from the Missouri, is less turbid than it used to be.

On the plus side, the fish communities Zeman sampled were more abundant and diverse than in 1983. She turned up more than four times as many fish as Klutho did, and also more species (53 versus 46). Several species have extended their ranges into the Middle Mississippi because the water is clearer, she says.

Two of the new species, however, were Asian carp--introduced exotics. "Unfortunately, they're here to stay," Zeman says. And several native fish species seem to have disappeared from the Middle Mississippi, including two types of chub common 20 years ago.

The bottom line? Human activities can cause big changes in river ecosystems--whether for better or for worse--in a surprisingly short amount of time. Studies like Zeman's, which help us understand these changes, are important for planners and conservationists.

"Humans have more of an impact on river systems than most other things do," she says. "It's not always detrimental. But it's important that we preserve our freshwater resources, and fish are good indicators of water quality."

--by Marilyn Davis, ed.