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.

Stocking

Walleye stocking is big business across the Midwest, and anglers sometimes see this as a sure cure for slow fishing. Unfortunately, increasing walleye populations is not as easy as pouring more fish into a lake. As with recruitment in natural populations, many factors affect the survival, growth, and eventual contribution to the fishery of stocked fish.

Over the years, biologists have assessed differences in stocking fry—recent hatchlings less than an inch long—and larger fingerlings. Lately, studies also have compared the success of stocking small fingerlings (two inches or so) with larger fingerlings (up to four inches). Because walleye stocking is expensive in terms of manpower, equipment, and hatchery maintenance, agencies seek the most cost-effective stocking procedures that produce good fishing.

Recent breakthroughs in marking small fish have enabled many comparative studies, and biologists from five states reported these study findings at the walleye symposium. Biologists in South Dakota and Nebraska used oxytetracycline to mark young walleyes, immersing them in a bath of the antibiotic.

This treatment creates a fluorescent ring on otoliths and other bones. Dave Lucchesi of the South Dakota Game, Fish and Parks Department reported that in small South Dakota lakes, stocked fry strongly contributed to the population of young walleyes when sampled that fall. Fingerling stocking also increased walleye numbers, but not as dramatically as the stocking of tiny fry.

Daryl Bauer of the Nebraska Game and Parks Commission evaluated walleye stockings in 18 reservoirs throughout the state. In five of eighteen waters, stocking fingerlings maintained the fishery, with over 75 percent of year-class strength resulting from stocked fish. In five other reservoirs, however, where walleye populations were maintained by natural reproduction, stocking contributed far less to adult abundance. Also, Bauer noted that abundant larger gizzard shad tended to suppress walleye recruitment. Water releases from reservoirs also reduced recruitment, as stocked fish migrated through the dam to downstream impoundments.

At Rathbun Lake in Iowa, Larry Mitzner faced the daunting task of tripling the number of walleyes over 18 inches in the population. He evaluated stockings of fry and fingerlings raised both extensively (allowed to grow in ponds) and intensively (housed in hatchery raceways). Fry stocking at Rathbun seemed to be a boom or bust scenario, as some of the largest year classes (1985, 1986, 1993, 1995, 1997, and 1998) were based on fry stocking. Stocking fry at a rate or 2,000 to 3,000 per acre in spring yielded averages of 9 to 27 fingerling fish per acre in October.

Intensively raised fingerlings survived twice as well as those raised in ponds. Mitzner also compared results of stocking fingerlings in the fall and in the following spring, when they were almost a year old. In three of five years, fingerling walleyes stocked in spring survived better, but fall stocking was superior in the other two years. By 1992, the goal of tripling the population was met.

A cooperative study in five lakes in Illinois examined the survival and contribution to the fishery of three size classes of fish—fry, small fingerlings, and large fingerlings. In these waters, small fingerlings generally provided the best results, though some variation was seen among waters and various years. Fry and small fingerlings grew faster than large fingerlings in their first and second years. As a result, the researchers recommended that Illinois stocking protocols plant small fingerlings wherever they may be needed.

Dennis Schupp again took the stage to report his findings on stocking results in Minnesota. His results reflected those in Iowa, as fry stocking showed the ability to provide exceptional fishing, but was not consistently successful. Fingerling stocking tended to provide more stable fisheries. Stocking of any sort had a greater chance of success in lakes of fewer than 1,000 acres.

Schupp also noted that fry stocking tended to work best in lakes with higher total alkalinity, possibly because alkalinity tends to be higher in more fertile waters. Also, in moderately turbid waters, abundant black crappies spelled doom for stocked fry.

In a different line of investigation, James Schneider of the Michigan DNR reported results of an experiment designed to improve stunted bluegill lakes by stocking large walleye fingerlings, in conjunction with catch-and-release regulations, and reduction of bluegill numbers with the toxicant antimycin. He found that stocking large fingerling walleyes helped reduce the density of small bluegills, thereby allowing the production of more acceptable-size fish. Catch-and-release regulations, in conjunction with bluegill reductions, also worked well.

Regulations

Of course, once walleyes have reached catchable size, anglers rush to harvest them. Walleye length-limit regulations have been studied for years, with variable results and little similarity among bodies of water or regions. The rise in walleye popularity in Alberta led to drastic declines in fish populations in these northern fisheries, characterized by slow growth and low productivity.

Strict harvest regulations, such as 20-inch minimum-length limits, were enacted in the 1990s to preserve populations, but biologists feared that illegal harvest could render the regulations useless. A study from 1991 to 1999 found that indeed anglers either were ignorant of regulations or chose to ignore them, as legally protected walleyes comprised 19 percent of the harvest. Biologist Michael Sullivan also found that more walleyes were illegally kept when anglers didn’t catch many.

Illegal harvest apparently wasn’t a problem at Lake Francis Case, where a seasonal length limit of 14 inches (April through June) was enacted in 1990, along with a reduction in daily bag and possession limit from 6 and 12 to 4 and 8 walleyes. Cliff Stone of the South Dakota Game, Fish and Parks called the regulation a success, which was enhanced by excellent walleye recruitment through the 1990s, following high inflows in the Missouri River.

Last year, the regulation was tweaked with a 15-inch minimum and a restriction to just one walleye over 18 inches in order to maintain the excellent walleye fishing. Also, the duration of the length limit was extended from 3 to 10 months (September through June).

In the most southerly walleye fishery in the United States, Texas researchers reported that a 16-inch minimum-length limit at Meredith Reservoir was successful in increasing walleye abundance, though it has been altered to allow anglers to harvest two walleyes under 16 inches per day. The change was enacted to prevent stockpiling of fish just below the legal size, since growth is fast in Texas, but fish don’t grow as large as in more northern regions, because they don’t live as long.

Saugeye Studies

Kay Hill of the Iowa DNR reported on comparisons of stocking walleyes and saugeye into two Iowa lakes. In this case, fish were freeze-branded for identification. One notable finding was that young saugeye are more vulnerable to night electrofishing than walleyes, potentially biasing electrofishing evaluations of stocking success.

Walleyes and hybrids stocked in June at two inches showed generally equivalent survival into fall. Saugeyes grew faster than walleyes during their first summer, while growth rates of older saugeyes and walleyes were similar. Total mortality of the two groups was similar in one lake but slightly higher for saugeyes in the other lake.

Anglers also harvested saugeyes at a slightly higher rate. Hill recommended that future stocking be with walleyes rather than saugeye, based on production costs that averaged 70 percent greater for saugeye. At angler harvest, saugeyes were 50 percent more expensive to stock than walleyes.

These oral presentations at the Midwest Fish and Wildlife Conference will be the basis of a series of papers to be published in the North American Journal of Fisheries Management, a key scientific outlet for the American Fisheries Society. Anglers can expect ever better management of walleye populations and a better understanding of the biology of the species.