Biology THE WORLD OF WALLEYES Steve Quinn August 23rd, 2012 | More From Steve Quinn Share0 Tweet Email Share on Facebook.Share on Twitter.Share on Google+The number of walleye anglers in the United States and Canada has increased dramatically over the last 20 years, from 5.2 million in 1980, to 5.8 million in 1990, to over 6 million in 1996. Anglers rate walleyes the most popular quarry in three states, second in four, and third in four more, indicating its broad appeal geographically. And in areas where bass, crappies, catfish, and stripers have had top billing since the first survey takers pounded on doors, walleyes are moving up the charts as anglers on the fringe of the walleye range discover this fish’s combination of large size, challenging behavior, and unsurpassed table excellence. Ichthyologists believe the ancestors of walleyes originated in Europe, moving across the Bering Sea land bridge to colonize North America, apparently during the Pliocene Epoch. The earliest fossils of walleyelike fish in North America date back to the late Pleistocene, less than a million years ago. Present distribution of walleyes and their closest cousin, the sauger, were established during the glacial retreat less than a million years ago. Ichthyologists originally noted two subspecies of walleye, the usual form, Stizostedion vitreum vitreum, and the blue pike, Stizostedion vitreum glaucum. Researchers generally believe that the blue pike is extinct, due to overfishing and habitat alteration, or has been absorbed into the gene pool of the walleye. Distribution Native range of walleye (Stizostedion vitreum) extended on the north from Great Bear Lake to James Bay and the Gulf of St. Lawrence, and south along the Allegheny Mountains to Georgia and into the Gulf Coast drainages of Alabama and Mississippi. Its western limit originally extended along a line from Arkansas north through the Dakotas. Stocking programs have extended the walleye’s range to Atlantic Coast drainages from Vermont to South Carolina, and westward throughout all western states except California, into British Columbia. Within these boundaries, naturally reproducing populations of walleyes generally occur in large lakes of moderate fertility (mesotrophic) or in large rivers. In the upper midwest and Canada, natural populations also inhabit smaller streams within the drainages of major walleye rivers. Populations of walleyes sustained by stocking thrive in smaller lakes and impoundments within their natural and expanded range. Spawning The Spawning Period begins the walleye year. In natural populations, success of the spawn affects fishing in future years. And walleye behavior in spring determines fishing patterns from ice-out until early summer. When water temperatures rise into the upper 30°F range, walleyes leave deep overwintering areas and move toward spawning sites. In lakes and reservoirs, they may migrate into tributaries while ice remains. In rivers, they spawn over rocky shoals or gravel bars, or migrate up tributaries to find suitable substrates and current. In either case, we call this prespawn movement the walleye “run.” Timing of the spawning run varies with latitude and local weather. Spawning as early as January has been reported in the Pearl River in Mississippi and as late as July in the Yukon and Northwest Territories. Male walleyes move to spawning grounds first and remain longer than females because they spawn with several females over a period of a week or two, while a female generally releases all her eggs in one night. Southern walleye populations spawn at somewhat higher temperatures and over longer periods. At the southern edge of the walleye range, biologists note that spawning peaks at water temperatures of around 50°F, and spawning activity lasts up to six weeks. In Minnesota, runs peak at water temperatures of around 42°F to 45°F and last about two weeks. Continued – click on page link below. 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. 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. 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. Continued – click on page link below. In many lakes in the northcentral and northeastern portions of the walleye range, yellow perch are the dominant prey once walleyes in their first year switch from invertebrates to a fish diet. Studies on Oneida Lake in New York indicate that perch are such important prey that they affect the strength of walleye year classes by buffering cannibalism. When young perch are abundant, walleyes selectively feed on them; when perch year classes are weak, walleyes cannibalize on each other, reducing year classes. 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. Various members of the minnow family, commonly called shiners, form huge schools; lack spines, speed, or other defenses; and inhabit almost every lake, river, and reservoir containing walleyes. The two most important shiner species are spottail shiners, which range from Georgia northwest into Saskatchewan, and emerald shiners, whose range overlaps that of the spottail but is absent from the Atlantic coast. Walleyes key on shiners, particularly in May and June when these species spawn on gravel shoals and near the mouths of feeder creeks. At this time of year, other prey aren’t so abundant in shallow hard-bottom areas. In northern lakes of moderate or low fertility, walleyes prey heavily on ciscoes, a small member of the whitefish family. Ciscoes, also called lake herring and tullibees, range from the upper Mississippi drainage and the Great Lakes basins north to Labrador and northwest to the MacKenzie River drainage. Ciscoes are coolwater fish, preferring temperatures below 60°F. Ciscoes school in open water, rising toward the surface at dusk to eat zooplankton and invertebrates. Walleyes near main-lake structure or suspended in the main basin approach these schools and feed heavily during the night. Anglers keying on this pattern make great catches from tough lakes by trolling after dark. In late fall when ciscoes spawn on reefs, walleyes again focus on them, producing great fishing for trophy-size walleyes for anglers who venture out in frigid conditions. Since smelt entered the Great Lakes, walleyes as well as salmon and trout have preyed on them. The success of this coldwater preyfish led to its stocking in other important walleye waters like lakes Oahe and Sakakawea. In these waters, spots where deep structure intercepts the preferred coolwater habitat of smelt, the best walleye fishing is in late spring and early summer. In Lake Erie and many reservoirs in the southern portion of the walleye range, gizzard shad are the principal walleye prey from early summer until fall. In most waters, schools of shad suspend in open water or graze along shallow flats, eating plankton and detritus from the bottom. Shad schools move with their food source, along with wind and current, and walleyes follow. Successful fishing in shad-laden waters depends on using sonar to locate prey and predators, and then longline trolling to place baits at the correct depth. Key on points, wind-blown flats, and other spots where walleyes may try to intercept shad schools. Water Quality Walleyes tolerate a wide range of environmental conditions, as indicated by their broad distribution and variety of habitat. They’re generally most abundant in medium to large lakes and river systems with cool temperatures, shallow to intermediate depths, extensive shorelines, slight turbidity, large expanses of clean rocky bottom, and medium fertility. Walleyes survive and grow in water from crystal clear to murky, but become most abundant in moderately turbid conditions. Peak feeding conditions occur in water with surface visibility (Secchi disc) between 3 and 6 feet. Activity decreases when visibility is less than 3 feet or more than 16. Continued – click on page link below. Walleye fry seek light until they’re 1 to 1.5 inches long, when they gradually become photonegative, seeking dim light during bright periods. During the day, adult walleyes often hold in cover and in deeper water during the brightest parts of the day. They frequently move inshore at night, feeding most actively during low-light hours. The pH of prime walleye waters ranges from 6.0 to 8.0. Walleyes seem to display no behavioral changes at pH levels within that range. Below 6.0, walleye spawning and recruitment often fail, while pH levels over 9.0 are unsuitable to most freshwater fish. Adult walleyes often inhabit areas with current, except during winter when they tend to avoid all but the slightest current. Walleyes can swim for only about 10 minutes in water flowing 2.5 feet per second. They seek current breaks to conserve energy, while remaining in range of potential prey. 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. Walleye larvae hatched in rivers rely on current to transport them downstream toward plankton-rich waters before their yolk sacs are absorbed (3 to 5 days). If current is absent, they starve. Fry don’t begin to feed, however, until water temperatures reach the upper 50°F range. Lab tests have shown that walleyes grow fastest at temperatures between 68°F and 75°F, avoiding water over 75°F. Growth of adults apparently stops below 53°F, and temperatures between 84°F and 95°F have proven fatal. Like most other freshwater fish, walleyes thrive in water containing at least 5 parts per million (ppm) of dissolved oxygen (DO). Adult fish can tolerate 2 ppm for short periods, while fry require 5 ppm. Senses Walleyes learn about their environment using the five senses we’re most familiar with (smell, taste, feel, hearing, and vision), plus an additional lateral line sense that receives low-frequency underwater vibrations. Sensory lobes compose a large portion of a walleye’s brain. Survival, growth, and reproduction depend on the function of these lobes. Smell and Taste: The senses of smell and taste are linked in humans, making it difficult to tell a bite of apple from a bite of potato without smelling them. For fish, these senses are linked even closer because both detect molecules of substances dissolved in water. This makes determining whether a behavior is due to smell or to taste difficult. Chemoreception in fish (including both smell and taste) is critical for finding prey, avoiding predators, locating fish of the same species, coordinating spawning time, and homing to residence areas or spawning sites. Sense of smell (olfaction) is primarily important for detecting distant substances, while for most fish, taste (gustation), determines the palatability of a substance once it’s taken into the mouth. Walleyes have paired “nares” located along the top of the head toward the upper jaw that sense molecules dissolved in water. As the fish swims or remains still in moving water, molecules pass through the nares and contact the olfactory organ, which includes the olfactory lobe. In addition, the nares contain tiny hairlike cilia that create water movement through the nares, even when a walleye is still. The olfactory organ contains folds, thought to enhance the sense of smell, since its surface contains receptor cells, and the number of receptor cells increases with the surface area of the olfactory organ. Walleyes have about 29 folds in their nares, a medium number between the channel catfish with 142 and members of the sunfish family with about 10. Continued – click on page link below. The most sensitive sniffer is the eel, capable of detecting amino acids in the range of a few parts per quadrillion. Although we know of no studies on the olfactory acuity of walleyes, it seems they probably can detect amino acids in a dilution of several parts per 10 million. That’s acute, for a part per million is about one ounce of a pure substance dissolved in enough water to fill 1,000 railroad tank cars. In hatchery tests, researchers lured young walleyes up one side of a y-shaped maze by dripping solutions of amino acids, including betaine into one side. Salt solutions also proved attractive. Other amino acids, fish mucus, and essences of walleye body parts were repulsive to the 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. It’s no surprise that walleyes smell well, for livebait often is the only answer to a tough bite and inactive fish. Sometimes the addition of a bit of crawler or minnow head provides a trigger that we surmise is due primarily to olfaction. For walleyes, the sense of taste spurs a decision to spit a bait or to swallow it. Here again, a jig tipped with a minnow passes the taste test more often than one tipped with a twister tail. Researchers at Berkley, Classic Manufacturing, Kodiak, and other companies that produce plastics impregnated with attractants hope to eventually synthesize a formula more appealing than natural prey to walleyes and other species. Certainly, plastics flavored with attractive amino acids, preyfish essences, and salt cause fish to hold them in their mouth and sometimes attempt to swallow them. Vision: Nighttime walleye fishing is a summertime tradition, but it’s also one of the best times to catch walleyes in winter, spring, and fall, particularly in clear lakes and reservoirs. Walleyes feed nocturnally because they see better at night than the prey they pursue. The only freshwater fish with better night vision is the walleye’s cousin, the sauger. The walleye’s eye is large, allowing the pupil, the light gathering part of the eye, to gather as much light as possible. No creature can see in complete darkness, but starlight provides enough light for walleyes and other nocturnal animals. The principal adaptation for night vision in nocturnal animals is the tapetum lucidum, a reflective layer on the retina that concentrates light after it enters the eye. Cats, raccoons, skunks, and deer in addition to walleyes, sauger, and some other fish have similar structures. Vision begins when light passes through the cornea and then the lens, which focuses the image as a camera lens does. Light then reaches two types of light-sensitive cells in the retina—rods and cones. Cone cells detect color when they’re exposed to daylight. Rod cells distinguish shades of gray and allow vision when sunlight isn’t present. Walleye and sauger eyes contain a larger proportion of rods than the eyes of perch, shiners, and other fish most active in daytime. The tapetum lucidum, a layer of guanine crystals, is located in the lower portion of the deepest layer of the retina. This physiology suggests that walleyes see lures and baits moving above them more clearly than those moving slightly below their level. And fishing experiences suggest that for the best response, lures should be set to run slightly above sonar images of fish. Luminous paint or strips of tape applied to a crankbait belly catch the fish’s eye. Share on Facebook.Share on Twitter.Share on Google+ Share0 Tweet Email Load Comments ( ) Don’t forget to sign up! 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