A new study by Minnesota DNR biologists Steven DeLain, Christopher Dawald, and Nicole Ward looked closely at the diets of bluegill and yellow perch in three Mississippi River backwater lakes—Big, Peterson, and Robinson—in Lower Pool 4, just downstream of Lake Pepin.
Over the last two decades, this part of the river has shifted toward clearer, plant-filled waters, which helped yellow perch thrive alongside the long-established bluegill population. But as both species expanded in these shallow, vegetated areas, scientists began to wonder: were they competing for food—or even eating one another?
Between spring 2018 and winter 2019, researchers examined what both species were eating across the seasons. The findings paint a fascinating picture of seasonal coexistence and winter conflict:
Spring through fall, bluegill and perch shared much of the same diet—mostly insects, snails, and small crustaceans—showing that both are flexible, generalist feeders that can live side by side without strong competition.
Winter was different. As food became scarce under the ice, large perch began feeding almost entirely on small, young-of-year bluegill. Nearly 97% of the fish in perch stomachs were baby bluegill, revealing a clear predator–prey link between perch and bluegill in the Mississippi River’s Pool 4 backwaters.
Though these fish have been well studied in lakes, this work provides one of the first modern looks at how two of our most familiar sport fish interact in the Mississippi’s backwaters. It also underscores how seasonal changes—especially winter conditions—can reshape the balance of fish communities.
For conservationists and anglers alike, these findings are a reminder that managing for healthy fish populations isn’t just about numbers—it’s about the river’s rhythm. When water clarity, vegetation, and the places fish rely on in winter shift, so do the relationships that sustain the system. Knowing when and how those shifts occur is what allows us to protect the natural balance that makes the backwaters thrive.
Read the full study here.