A decade ago, biologists involved in walleye management convened at the annual meeting of the North Central Division of the American Fisheries Society (AFS) to discuss the latest research findings and to plan strategies for improving and maintaining walleye populations across North America.

That symposium, sponsored by the Walleye Technical Committee of AFS and held in Minneapolis, focused on evaluations of stocking efforts; walleye genetics and their importance to stocking efforts; and investigations of the attitudes of walleye anglers concerning walleye management, conservation, and fishing quality. Studies published from that meeting advanced the art and science of walleye management over the last decade.

The latest walleye scientific conclave, held this past December, again in Minnesota, the walleye capital, was arranged by the Walleye Technical Committee. This meeting focused on the recruitment process, long a puzzle in the walleye world; investigations of how harvest regulations can improve fishing; and developments in walleye stocking.

Recruitment

Biologists use the term recruitment for the process by which young walleyes join the fishery. In most cases, studies investigate survival during the first summer or first complete year, when most variation in production and survival seems to occur. Recruitment eventually shows up in the catch as strong or weak year classes that affect the quality of walleye fishing for years.

Walleye recruitment varies greatly from year to year, influenced by many factors including weather, adult numbers, prey availability for young walleyes, the abundance of predators like yellow perch and older walleyes, and stocking. At the symposium, Dennis Schupp of the Minnesota DNR used his extensive file of lakes and fish survey data to note important trends in the recruitment process.

The two weakest year classes of walleyes produced since the late 1970s occurred in 1992 and 1993. Those years were plagued by unusually cold temperatures, caused at least in part by the eruption of Mount Pinatubo in the Phillipines during the previous summer.

Resulting ash shaded the sun worldwide and reduced June temperatures in Minnesota lakes by an average of 3.5 degrees. Analysis of data showed that June temperatures are positively correlated to walleye recruitment. The gradual warming over the last 20 years has resulted in an annual increase in walleye abundance of over 3 percent per year.

John Pitlo of the Iowa DNR, a researcher involved with the Mississippi River, also noted the importance of warm weather for production of sauger. He found that warm temperatures during the first two weeks of April led to abundant young walleyes and sauger in fall. The strongest year classes throughout many navigational pools of the river were produced in 1994 and 1997.

A team of researchers from Michigan State University and the Ohio DNR studied the world’s largest naturally reproducing walleye population, in Lake Erie. They found that the great variation in year-class strength seems due to the availability of good habitat in near-shore waters that function as walleye nurseries. In particular, hatchling walleyes need abundant zooplankton and warm water to quickly begin growing. Fast early growth improves survival.

The team also found that the walleye larvae fared best when they inhabited shallow, rather murky water. While water temperatures have been generally higher in recent years, concern is felt about declines in zooplankton and increases in water clarity, both attributable to the zebra mussel.

In contrast to the positive picture on the Mississippi River, Lake Erie, and Minnesota lakes, Dave Fielder of the Michigan DNR reported the loss of traditional spawning reefs in Saginaw Bay of Lake Huron. Underwater cameras showed that silt covered most inshore reefs, reducing their value as spawning sites. To buoy the fishery, the DNR has stocked the bay since the 1980s and, indeed, Fielder’s study found that the large walleye population is dependent on stocking, though wild fish also are produced in tributary rivers that have remained suitable for spawning.