RESEARCHERS `BUGGING' FISH TO TRACK RIVER MIGRATION PATTERNS

CARBONDALE, Ill. - This fall, scores of fish will swim the Mississippi River equipped with their own personal radios.

Don't look for waterproof Walkmans, however. The radios, each about the size of a quarter, are surgically implanted in the abdomens of the fish.

"Each one has its own signal, so when we start monitoring, we'll know which fish and which species we're looking at and where the fish is," said Robert J. Sheehan, a scientist in Southern Illinois University at Carbondale's Cooperative Fisheries Research Laboratory.

The radios, which also keep tabs on water temperatures, will assist SIUC researchers in a three-year project aimed at discovering habitat needs of such Mississippi River species as Northern pike and largemouth bass.

The scientists hope to learn whether older fish can tolerate winter's cold temperatures and strong currents better than younger ones. In addition, the researchers will track spring and fall migration patterns to see if fish prefer to spawn in protected backwaters.

A $712,000 grant from the Illinois Department of Conservation and the U.S. Fish and Wildlife Service underwrites the study, which focuses on Pools 13 and 14 near Savanna in Carroll County and a site near Alton in Madison County.

The project grew out of research that began in 1981 after thousands of dead and dying fish started showing up each spring in the water- cooling intakes at the Quad Cities nuclear power station in Cordova, north of Moline. Were the intakes sucking these fish to their doom, officials asked, and if so, why? Fish swim against currents, so they ought to be able to withstand the lesser pull of the intakes.

Zoology student Leo R. Bodensteiner undertook the puzzle as a topic for his Ph.D. degree. After ruling out disease and starvation as causes, he compared fish from a nearby lock and dam and with others from backwater areas. He found that only the backwater fish seemed robust and healthy.

He concluded that the warmer, gentler backwaters gave the fish a better shot at surviving the winter than did the river itself.

His study also turned up a surprise. Most of the fish in the power plant intakes were freshwater drum, a species important mainly to commercial fisherman. But the puny fish at the lock and dam included such sport fish as bluegill and channel catfish.

"This suggests that the requirement for specialized winter habitat is much broader than we first thought - it covers more species," Sheehan said.

That fact caught the interest of state and federal conservation folk particularly because many pools that once offered winter protection have filled in with silt.

"Rivers continuously destroy river habitat as they shift course, but at the same time that movement creates new habitat," Sheehan said. "What we have done with locks and dams and flood control and poor land- management practices has just about eliminated the process by which new habitat is created, but the process by which it is lost has continued."

Bodensteiner's findings led to a three-year study that helped researchers pinpoint which fish needed winter shelter and how to provide it. Of a half-dozen yearling gamefish species studied, only walleye pike were able to withstand the winter unaided. Crappie and catfish survived the cold temperatures, but exhausted themselves fatally fighting the stronger currents. Bluegill, green sunfish and bass needed protection from both temperature and currents.

SIUC researchers suggested dredging and stabilizing a series of pools with adjustable water levels in order to give the fish protection. Managers could close the pools periodically to ward off river silt.

The SIUC team has just finished a river renovation plan for Swan Lake near Alton, an area that has 15 percent of the Illinois River's natural backwaters.

"The U.S. Army Corps of Engineers is pretty pleased with how that went so they're starting to take what we worked out there and incorporate it into other plans," Sheehan said. "We're having some effect on what the rivers will be like in the long term, and that's one of the exciting parts of this work."