All About This Favorite Fish

The Growth Rate Chart: Comparison of average mean back-calculated length at each age for walleyes in South Dakota and Minnesota. Age Determination: Scale reading has been the traditional method for determining the age of fish and the average growth rate of populations. The assumption is that scales grow proportionately with fish length. And this relationship usually holds true. During periods of slow or no growth, as in winter, rings, called circuli, are narrowly spaced. Fast growth brings widely spaced circuli. Year marks or annuli show rather clearly under magnification, and measurements from the central focus to succeeding annuli provide the fish’s growth history. Scales of slow-growing fish or fish from consistently warm climates may not reveal true age. For these fish, otoliths (ear bones) are more accurate. But they must be removed from the skull and usually sectioned, a more difficult process than scale reading.

From 50,000 to over 600,000 eggs are produced by a 12-pound-class fish. Eggs hatch in 12 to 18 days at usual postspawn water temperatures if environmental conditions are favorable. Studies of walleye recruitment (annual production of young fish) often show 10- to 50-fold annual fluctuations. Strong year classes can support a walleye fishery for several years, but when several weak year classes follow, catch rates dip dramatically, once older fish are harvested or die of natural causes.

Factors that affect hatching success and survival of young walleyes include water quality, river flows, wave action, excessive turbulence, siltation, spring water temperatures, availability of zooplankton and small fish to feed young walleyes, abundance of predators on young walleyes (including cannibalism), and competition for food. Studies suggest that the number of adult spawners has little effect on success of a year class, compared to the many environmental factors.

Growth and Abundance

Walleyes grow fast for the first 3 or 4 years of life, with average size reflecting length of growing season or latitude, body of water productivity, and abundance of forage. Females live longer than males and grow faster, particularly after they reach maturity.

Within a body of water, growth rates of year classes may vary considerably due to climatic conditions and abundance of prey. Walleyes in southeastern reservoirs grow fastest, with some young fish approaching 12 inches at age 1. The average for Minnesota walleyes, however, is 12 inches at age 3, while in South Dakota, they average 15 inches at that age.

In infertile northern waters, older walleyes may grow negligibly from year to year, so a 20-year-old fish may not be huge. In Montana’s Frenchman Reservoir, old walleyes may actually shrink from year to year, apparently due to limited forage.

Walleye density also varies greatly among lakes and reservoirs. Stable populations in northern waters may contain from 5 to 10 pounds of adult walleyes per acre. Highest abundance on record was at Storm Lake in Iowa, where in the 1940s, biologists estimated a biomass of 33 pounds of walleyes per acre. Walleyes thrive in mesotrophic waters where productivity at all levels of the food web is lower than in eutrophic (fertile) waters.

Prey

Walleyes are opportunistic predators, consuming locally abundant fish and invertebrates that are reasonably nutritious, and catchable. During the mayfly hatch, walleyes seem to subsist on these small insects until this food source has flown away to mate and die. On many Minnesota lakes, fishing success may be more closely related to the abundance of yellow perch than to the abundance of walleyes. When small perch are dense, walleyes focus so closely on them that presentations of minnows, leeches, crawlers, or crankbaits receive little attention.

In Lake Erie and other populations of the Great Lakes, walleyes take advantage of seasonal and annual peaks in young gizzard shad, alewives, spottail and emerald shiners, white perch, and rainbow smelt. Research studies on walleye prey preference have suggested that walleyes prefer slender-bodied spineless prey but can thrive on far spinier meals. In prairie lakes of the Midwest, walleyes rely on warm-water gamefish like bluegills, crappies, and bullheads.

Walleyes browse along weededges, sometimes suspending to feed on schools of small panfish. During lower light levels of dawn and dusk or after dark, walleyes move onto shallow flats where they feed heavily. In all waters, peak walleye feeding occurs at dawn and dusk, a pattern termed “crepuscular.”

This feeding cycle lets walleyes feed when their sensory systems offer them an advantage over their prey species. Even at air temperatures of -30°F in the dimly lit waters of a lake covered by two feet of ice and a layer of snow, evening brings a flurry of feeding.