Where are the fish?

Submitted photoIce fishermen pursue the elusive big one while on the river. 

A trail of auger holes in the ice maps the travels of hardy winter anglers that are in pursuit of that elusive big fish. Ice depth in the Mississippi River backwaters and tributaries determines how far winter anglers can safely travel to pursue their sport. 

January temperatures varied greatly that allowed both ice and boat fishing. So where do fish go in winter?

We are fortunate to have a premier Mississippi River fishery research facility nearby at the Iowa Department of Natural Resources Bellevue Fisheries Station located south of Bellevue. The research station has been mapping fish travels in summer and winter since the 1970s. Although personnel have changed over the years, the goal of improving fishing on the Upper Mississippi River has remained a priority. 

Kirk Hansen, a fisheries research biologist, provided insight into some of their projects.

“Since the 1980s, much research has gone into learning the habits and habitats of various fish species including walleye, sauger, largemouth bass, bluegill, crappie and northern pike,” Hansen said. “Radio transmitters have been attached or implanted into the fish and they are tracked to learn what habitats they use at different times of the year. When a fish is located, a suite of water quality measurements are taken including depth, flow, temperature and dissolved oxygen. Taking these measurements over several years from numerous fish has identified habitat preferences and defined general movement trends for different species.

“One such trend is the movement of bluegill, crappie and bass to specific areas during the winter. As the water temperatures cool below 50 degrees in the fall, these fish begin moving toward and into specific off-channel areas and backwater lakes to spend the winter. By the time ice forms, all the fish are in these areas. These areas have no water flow, depths of 3 feet or greater, water temperatures around 3 degrees above freezing (main channel water temperatures are around 32), and maintain good oxygen levels throughout the winter. These backwaters are no secret to local anglers and support ice fisheries throughout the winter. Top areas include Rock Creek in Pool 14 and Potter’s Marsh, Spring Lake, South Sabula Lake, and Brown’s Lake in Pool 13.”

Long periods of ice and snow cover are harsh on fish because they prevent the mixing of oxygen into the water column. Due to our current mild winter, the Mississippi River’s main channel, side channel and backwater areas have maintained good oxygen levels. This is in contrast to many years when low oxygen levels, especially in the shallow backwaters, cause fish to seek deeper water to survive.

Many backwaters in our area have a water depth of only a few feet. Ice and snow buildup have been minimal. Backwater ice depths have only been a few inches and the main channel has seen periods of ice cover and open water.

In a large system like the Mississippi River, the impact of a winter kill on the fishery resource is usually not significant. Some riverine species, such as gizzard shad, incur massive die-offs each year especially in young of the year and yearling fish. On smaller systems, such as inland lakes and ponds, a large percentage of many fish species may be killed during winter. In this case, fish stocking and a long period of population recovery may be needed.

The huge fluctuations in winter temperatures have been a roller coaster ride for winter anglers. Be aware of ice depth and especially underwater flows so that a tragic accident doesn’t prevent you from going home to your family tonight.

Ed Britton is a Wildlife Refuge Manager at the Upper Mississippi River National Wildlife and Fish Refuge and a volunteer at the Bickelhaupt Arboretum.

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