Biologists know a fair amount about walleye movement, and they’ve got the spawning migrations especially well pinned down. They’ve tracked ’eyes in the winter in reservoirs at the southern edge of the species’ range, but winter location and movement have been largely overlooked in the heart of walleye country. Thanks to recent efforts by Iowa Department of Natural Resources’ John Pitlo and his successor Mike Steuck, however, we now know more than ever.
The scene is Pool 13 of the Mississippi River. Pitlo had been tracking walleyes for several years and was quite familiar with their habitat preferences—the ’eyes hung out around wing dams and channel closing structures in winter.
To keep the navigation channel open, however, the U.S. Army Corps of Engineers had installed new wing dams in an area frequented in the past by Pitlo’s radio-tagged walleyes. The biologists were concerned about how the habitat alterations would affect the fish.
Pitlo and Steuck had another concern. Walleyes are highly selective in choosing spawning sites, and they return to the same ones each year. Pool 13 walleyes were known to spawn in areas of cobble, gravel and mussel-shell bottom at four sites in the upper end of the pool.
Although spawning and recruitment of walleyes in Pool 13 is guided by nature and fairly stable, the known spawning habitat was limited. And limited spawning habitat presents a precarious situation in a dynamic system like the Mississippi River.
Biologists found walleyes spawning in vegetated areas in the middle and lower portions of pools 4 and 8 upriver, which begged the question: Might there be additional, undocumented spawning areas in the lower section of Pool 13?
To answer the biologists’ questions, 15 4- to 7-pound walleyes were collected in the lower part of Pool 13 each October from 1998 to the present, implanted with radio transmitters, and tracked through the spawning season. The fish remained in the lower pool through winter, then migrated 20 to 24 miles upstream to the known spawning areas in the upper reaches of the pool.
Most fish made the upstream migration during February and March, either moving directly to the known spawning sites or staging in channel border or backwater areas. By April the fish had returned to the lower part of the pool.
The bad news—the walleyes radio-tagged in the lower pool failed to lead the biologists to any new spawning areas. Apparently Pool 13 walleyes all spawn at the previously identified upstream spawning sites at Mill Creek, Pleasant Creek, Sand Prairie and the Lock and Dam 12 tailwaters.
The good news—the new wing dams installed by the Corps of Engineers did not adversely impact the fish’s use of historic habitat. In fact, they actually added habitat. Walleyes began to use the new wing dams soon after rock placement was completed and scour holes began to develop below them.
High-Dollar Fish Finders
Over the years numerous anglers have commented that they wished they could track walleyes. Believe me, it’s not as exciting as it seems. But the extensive work in Pool 13 provides some information about walleye whereabouts. According to Steuck, most ’eyes spend the winter around deep water near wing dams—not in the deepest water, but on the breaks.
Despite the 32-degree water, the walleyes remained active and moved around the dams. When the water warmed to 39 to 40 degrees, walleyes headed upriver to the spawning sites. After spawning, they finned their way directly back to their summer homes.
Dr. Hal Schramm is a biologist with the U.S. Geological Survey, Mississippi Cooperative Fish and Wildlife Research Unit, and professor of Wildlife and Fisheries at Mississippi State University.