Sander vitreus

Geographic Range

Walleyes are native to freshwater rivers and lakes of the northern United States and Canada. Their native range makes a lopsided triangle with the southernmost point on the Gulf of Mexico border between Mississippi and Alabama, extending upwards (bound on both sides by the Appalachian and Rocky Mountains) towards the northernmost border between the provinces of Yukon and the Northwest Territories, then back along the southern edge of the Hudson Bay, peaking again at the Atlantic Coast, just north of Quebec City. They stay safely inland aside from river deltas and away from the salt waters of the coast. Their range has expanded somewhat over the years by introducing them to various parts of North American, especially the United States, where they have greatly expanded their range via human means to include large chunks of the Northeast, from southeast Maine down to Virginia, passing lightly through North Carolina to establish a firm hold on inland South Carolina and Georgia. Their introduced range is equally vast in the western United States, although much more spread out, and includes large parts of nearly all the western and southwestern states, branching off very slightly into southern British Columbia. As a cool-water species, their natural habitat is greatly skewed towards the northern United States and much of Canada. Their success in their introduced ranges likely depends in part on latitude and elevation. Predictions on the effects of climate change on walleye populations suggest the more southern ranges will become less habitable and the northern walleye populations will become dominant.

• Biogeographic Regions
• nearctic nearctic
  • introduced introduced
  • native native

Habitat

Walleyes are believed to have evolved in the North American river systems, and moved only recently (in evolutionary terms) into lake environments. For this reason, many of the physical requirements that characterize optimal walleye habitat have qualities that closely resemble rivers, especially those areas of rivers that form slow-moving pools such as oxbows, sloughs, and embayment habitats. While walleyes live in both rivers and lakes in the middle and northern end of their range, they live almost exclusively in rivers farther south. Walleyes prefer shallow to moderately deep locations with extensive shallow areas and shoreline. They live mainly in the littoral and sublittoral layers of lakes (although they make short, daily migrations to the pelagic layer), moving deeper into the sublittoral layers during the daylight hours in keeping with their nocturnal lifestyles. These fish prefer murky water, with less than 2 meters of light penetration. By day, walleyes rest on their preferred substrate, sand and large gravel, with plenty of submerged vegetation in a moderate current. Walleyes tend to do well in large shallow lakes with plenty of littoral and sublittoral zones and minimal seasonal stratification. These fish can still be found in many river systems, but their presence has declined in these habitats, likely due to the increased eutrophication of North American rivers.

As a cool water species, the climate of a location is important to the well being of walleyes. The eggs have been shown to be particularly resilient to fluctuating temperatures, and are able to survive rapid temperature changes of up to 20 to 21°C (68 to 70°F) in laboratory settings with no discernable increase in mortality, although it did result in an increase in abnormal fry. Temperature first affects walleye reproduction at the spawning stage, with optimum egg fertilization temperatures around 6 to 12°C (42 to 53°F), optimal egg incubation temperatures around 9 to 15°C (48 to 59°F), and the optimal hatching temperature is around 15°C. Temperature affects growth rates by regulating the metabolism, food conversion ability, and the ability to secure food. Their preferred temperature for maximum growth is between 20 to 24°C (68 to 75°F). This temperature may be higher for juveniles, to between 27 to 31°C (80 to 88°F). As much as 21% of walleye recruitment is positively correlated with spring water temperatures, making temperature an extremely important factor in early development and growth. Dissolved Oxygen (DO) concentrations for walleye embryos is above 5 to 6 mg/L, although this number is linked to temperature, since increased temperature can increase both metabolic functions in fish as well as decrease the solubility of oxygen. Walleyes do relatively well with DO fluctuations, they may survive for extended periods with only 3 mg/L of DO, and shorter periods with even less. However, walleyes are more sensitive than many other species of fish towards very high oxygen levels. They experienced a sudden die off due to “Gas-Bubble Disease” in a Wisconsin lake when the water became supersaturated with DO. Walleyes prefer pH levels between 6.0 to 9.0. Lower, more acidic levels substantially decrease survival and reproductive success. Due to their ability to withstand relatively low dissolved oxygen levels, walleyes have been able to survive under fairly harsh conditions. However, their eggs are more susceptible to negative environmental conditions. In addition to sulfides and ammonia, research indicates that certain levels of heavy metals and salinity can also affect walleye survival, reproduction, and behavioral patterns.

Walleyes survival and reproduction, like most riverine species, has been directly impacted in many instances by the creation of dams along their native waterways. Dams can disrupt their migrations by either blocking access to native spawning areas or by flooding these areas beyond their usefulness for spawning. Unlike some species, however, their reactions have been mixed. There are certainly examples of unsuitable or contaminated reservoirs preventing successful walleye population numbers, so long as all the conditions for survival and reproduction are present, walleyes have adapted very successfully to life in reservoirs, as well as extensions of their range due to human introductions.

• Habitat Regions
• temperate temperate
• polar polar
• freshwater freshwater

• Aquatic Biomes
• lakes and ponds
• rivers and streams

Physical Description

Walleyes are relatively small for predatory fish, reaching an average adult size of 350mm among males and 450mm among females. Walleyes are darkly colored on top, with colors ranging from brown, to olive, to dark yellow with a paler underside, ranging from white to pale yellow. Walleyes have silvery eyes that have a reflective underlayer, which causes it to reflect in the dark. Their mouths contain a series of very sharp teeth, specialized for a piscivorous lifestyle. Some sexual dimorphism exists within this species in that females grow consistently larger than males.

• Other Physical Features
• ectothermic ectothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• female larger

Development

Like many fish, walleyes begin their development as an egg and progress into the larval and juvenile stages, before becoming an adult. Individual female walleyes release tens of thousands to hundreds of thousands of eggs during each spawning period. These eggs are roughly 2mm in diameter on average. The eggs begin their life cycle coated in an adhesive for sometimes several hours, which is believed to increase the fertilization rate. Once fertilized, the egg hardens, losing its adhesiveness and floats into safer protective substrate where, with proper protection, temperature, and oxygen, it eventually hatches. Despite hatching, larvae are still considered embryos due to their underdeveloped fins and fin rays. These begin to develop when the larvae reach approximately 10mm in length (they range from 6 to 9mm at hatching), with full ossification at 18mm. Because they are still underdeveloped (which includes an underdeveloped swim bladder, inhibiting their buoyancy), the larvae continue to sit on the substrate and are subject to their location’s current, being swept away (if the spawning site was well chosen) into nursery habitats. Due to the small size of the egg, larvae have very little yolk to consume upon hatching and must begin feeding immediately on various zooplankton and chironomids . Prey density can play a large role in survival at this early stage, as does predator density, since both walleye eggs and larvae are common sources of food for larger fish. Indeed, very few walleye make it to 1 year of age. Survival rate estimates of larval walleye are in the order of 0.01%, due mainly to lack of fertilization of eggs, starvation upon hatching, and predation. Upon surviving their first year, however, walleye growth is rapid. Both male and female walleyes grow at the same rate prior to this time, but upon reaching the juvenile life stage, growth rates can begin to differ, depending on growth rates in a particular location. Walleyes in the southern part of their range, for instance, grow more quickly in general than walleyes in the north, with female walleyes growing larger than males. Because adulthood is determined mostly by size, the juvenile stage can last anywhere from two to eight years, depending on geographic location and food availability. Average length at adulthood (defined as reaching sexual maturity) is considered 350mm for males and 450mm for females although this varies between individuals. As this size difference indicates, males typically reach sexual maturity before females.

Reproduction

Walleyes are promiscuous: females and males spawn with multiple partners with no indication of lasting relationships. Mating takes place in a marshland. Male walleyes frequent the spawning marshland for several weeks, however, female walleyes go only to spawn, which lasts approximately one day. Neither sex displays territorial behavior during this time.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

Walleye spawning occurs once annually in early spring. Spawning behavior is temperature dependent, with spawning occurring at 5°C (41°F). With the extensive range of this species, the exact dates vary according to climatic conditions. Walleyes display homing behavior, returning to the same site again and again to spawn. Female and male walleyes reach sexual maturity at different ages and sizes. Female walleyes ultimately release tens of thousands to hundreds of thousands of eggs in a single spawning session, which is itself broken up into approximately five minute egg release intervals for the duration of spawning.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• fertilization fertilization
  • external external
• broadcast (group) spawning
• oviparous oviparous

There is no evidence of parental care of any kind taking place among walleyes.

• Parental Investment
• no parental involvement

Lifespan/Longevity

Interestingly, the maximum age and mortality rate are strongly correlated with the growth rate of walleyes. Walleyes that grow bigger faster tend to have shorter lifespans than walleyes that grow more slowly. While the maximum lifespan of fast-growing southern walleyes is 3 to 4 years, northern walleye have been known to live as long as 20 years, or possibly up to 30 years. Due to their enormous size and variability of their range, walleye mortality rates are very difficult to estimate, making averages and ranges nearly meaningless. For example, natural mortality rates for lakes and rivers sampled in North America range from 3 to 81%, an enormous difference which means little for walleye populations in general. In addition, walleyes are a popular sport fish, meaning that mortality rates must take into account both natural deaths and exploitation numbers. Total mortality annual rates ranged from 13 to 84% across 14 different lakes and rivers in North America, most commonly falling between 40% and 55%.

Behavior

Once walleyes reach a certain size (between 51 and 100mm), they begin displaying more demersal behavior, tending towards deeper, cooler, darker depths during the daylight hours. This corresponds to certain developmental milestones, including changes in the retina that allow walleyes to see more clearly in dim light. Walleyes are nocturnal predators with a high visual acuity beyond the abilities of many other visual fish predators, although they seem to have sacrificed lateral line sensitivity relative to these other species in exchange for the ability. If ideal depths are not available, walleyes have been known to seek out dense vegetation or other physical cover during the daylight hours to reduce their light exposure. Walleyes are more active at dusk and dawn.

• Key Behaviors
• natatorial natatorial
• nocturnal nocturnal
• motile motile

Home Range

Walleye behavior tends to vary with age as well as lake versus river lifestyles. Due to their limited development upon hatching, larval walleyes in rivers are found in all depths, from the surface to near the stream bottom, likely influenced more by current than any other considerations. In contrast, lake walleye larvae tend to live a more pelagic lifestyle (sticking to deeper parts of the lake) although they, too, have been found in multiple locations. As walleyes grow more developed and assume more control over their movement, they display shoaling behavior with fish of their same size (though not always of their same species). Walleyes do not show territorial behavior, however, these fish do seem to maintain general home ranges when they are not in their spawning grounds. These home ranges vary based on the individual, as well as whether they inhabit a lake or river, individuals inhabiting rivers typically have a smaller home range size than those in lakes. Home range sizes do not appear to vary based on gender. In one study, walleyes in the New River, Virginia, maintained a median home range size of 4.7 km, although they moved frequently from week to week.

Communication and Perception

Although walleyes are a shoaling species, which means they move together in a loose congregation in open waters, there is little evidence of advanced communication systems between members. Walleyes are not territorial, nor do they keep mates or invest time in offspring. The only example of observed communicative movements by walleyes is during mating, when male walleyes bump against the females and, when she is ready to spawn, the female signals so by turning on her side.

• Communication Channels
• visual visual

• Perception Channels
• visual visual
• tactile tactile
• chemical chemical

Food Habits

While walleye eggs and larvae tend to be a frequent source of food for a large variety of fishes, adult walleyes sit at the top of the food chain in many systems. Walleyes become piscivorous early in life, feeding on the larvae of other fish as soon as they get big enough. Adult walleyes feed on a large variety of other fish species, including yellow perch , gizzard shads , emerald shiners , spottail shiners , and numerous other species, depending on what is available in a given ecosystem. These fish have also been documented consuming smaller conspecifics. In situations in which fish species are not readily available, walleyes may also eat certain types of invertebrates.

• Primary Diet
• carnivore carnivore
  • piscivore piscivore
  • insectivore insectivore

• Animal Foods
• fish
• insects

Predation

Walleyes are generally top predators in their habitat; however, this high place in the food chain is not universal. Because walleyes do not get overly large on average compared to other predator species, they, too, can become prey in certain ecological foodwebs. Walleyes have fallen victim to species such as largemouth bass , smallmouth bass , muskellunges , yellow perch , and other walleyes. Non-fish predators such as cormorants have also been known to eat subadult walleyes. In general, however, walleyes usually become prey in the early years of their development. Before reaching adult status, walleye eggs, larvae, and juveniles can form a regular food source for fish species of many sizes and varieties, including not only other piscivorous fish such as white perch , stonecats , and white suckers , but also planktivores such as black crappies , white crappies , and alewives . In one Kansas reservoir, white crappie population numbers were inversely correlated with walleye abundance, meaning this early predation can have a very real effect on the predator’s longer term success. The enormous number of eggs and larvae produced by each female, as well as the temperature requirements for spawning, which is much colder than many fish species prefer, are both likely adaptations to egg and larval predation.

Ecosystem Roles

As top predators, walleyes have a profound role in the ecosystem, which is also multifaceted and complex. Like most predator/prey relationships, the abundance of walleyes and their preferred prey species are highly interrelated. An increase in adult walleyes can lead to a decrease in their prey. However, despite adult walleyes being at the top of their food chain, their larvae, eggs, and sometimes juveniles remain near the bottom. For this reason, the predator/prey relationship becomes more dynamic, as increases in species such as yellow perch , can adversely affect walleye populations as fewer and fewer larvae make it to adult status. Yellow perch are the preferred prey of adult walleyes in many circumstances. Since yellow perch feed heavily on juvenile walleyes, a focus on yellow perch as a prey species actually aids in juvenile survival. This relationship extends beyond the survival of these two species. It has, in some instances, dramatically increased the importance of the role that yellow perch play in the ecosystem as a whole. If yellow perch populations begin to decrease, walleyes must turn to other species for food (something they do with little hesitation) causing a ripple effect across the ecosystem as prey from various ecological niches begin to decrease in numbers.

Economic Importance for Humans: Positive

Walleyes are one of the most popular sports fishes in North America. The species is prized by Canadian, American, and Native American fisheries alike and has a substantial national and international legal framework surrounding their capture. Fishing ranges from subsistence to recreational to commercial with millions of kilograms harvested annually. Surprisingly, recreational fishing has proven the most lucrative investment in walleye fishing. While Canada’s commercial walleye fisheries on Lake Erie and various other Canadian lakes total around CAN$60 million annually, the walleye recreational fishing industry in Lake Erie alone total around $600 million annually. Due to their extensive range, walleye fishing is popular throughout the United States and Canada. In addition to lake and river populations, walleyes also constitute the base of a thriving aquaculture business, a practice used primarily for stocking, rather than as a food provider.

• Positive Impacts
• food food
• controls pest population

Economic Importance for Humans: Negative

There are no known negative effects of walleyes on humans.

Conservation Status

Due to their immense popularity, walleyes are the subject of intense scrutiny and study. Management systems of walleye stocks range from simple to extremely complex, usually operating under the assumption that stock exploitation plays a leading role in fish populations (as opposed to other factors, such as habitat and food availability) and manages accordingly. These regulations are most regularly in the form of bag or length limits. There is evidence that these efforts can and have been effective in helping overexploited walleye populations to recover. A potential walleye subspecies, blue pike , were once endemic to Lake Erie and Lake Ontario, but are now believed to be extinct. Blue pike were smaller than walleyes and preferred to inhabit greater depths than walleyes. Although no blue pike are now known to exist, tissue studies show no discernible genetic difference between the species. Blue pike might have been a sympatric morph or species pair with walleyes. If this were the case, anthropogenic habitat changes could have lead to blue pike and walleye habitat crossover, causing blue pike to be genetically mixed back into the walleye gene pool. Another genetic quirk of walleyes is their ability to hybridize with saugers to form a fish known as a "saugeye". This hybridization can occur naturally, although this is rare, as their mating seasons rarely overlap. This mix is bred artificially as a stock species, as saugeyes tolerate warmer, more eutrophic waters than walleyes and have a faster growth rate than both species. The hybrid's ability to breed with saugers and walleyes may have the potential to break down the genetic barrier between the species should they be present in large enough numbers in the same area. It has been argued that even stocking saugeyes in lakes separate from both species has the potential to contaminate this genetic line, as high rains and flooding could result in a mixing of the species.

Other Comments

There has been some debate as to the appropriate taxonomy of walleyes. Since the early 1800’s, walleyes were known as Stizostedion vitreum and their taxonomic movement to Sander vitreus is a recent change. The International Commission of Zoological Nomenclature has declared Sander vitreus the official scientific name of the species, although the debate continues, with some scientists claiming that the commission’s rules were not correctly followed when the name was established. Searches for research on walleyes reveal a great deal of research listed under both names.

Additional Links

Encyclopedia of Life

BioKIDS Critter Catalog

Contributors

Betsy Riley (author), University of Michigan-Ann Arbor, Jeff Schaeffer (editor), University of Michigan-Ann Arbor, Lauren Sallan (editor), University of Michigan-Ann Arbor, Leila Siciliano Martina (editor), Texas State University.

References

Auer, N., M. Auer. 1990. Chemical Suitability of Substrates for Walleye Egg Development in the Lower Fox River, Wisconsin. Transactions of the American Fisheries Society , 119:5: 871-876.

Barton, B., T. Barry. 2011. Reproduction and Environmental Biology. Pp. 1-34 in Biology, Management, and Culture of Walleye and Sauger . Bethesda, MD: American Fisheries Society.

Becker, G. 1983. Fishes of Wisconsin . Madison, WI: University of Wisconsin Press. Accessed October 09, 2013 at http://digital.library.wisc.edu/1711.dl/EcoNatRes.FishesWI .

Billington, N., C. Wilson, B. Sloss. 2011. Distribution and Population Genetics of Walleye and Sauger. Pp. 1-28 in Biology, Management, and Culture of Walleye and Sauger . Bethesda, MD: American Fisheries Society.

Bozek, M., D. Baccante, N. Lester. 2011. Walleye and Sauger Life History. Pp. 1-70 in Biology, Management, and Culture of Walleye and Sauger . Bethesda, MD: American Fisheries Society.

Bozek, M., T. Haxton, J. Raabe. 2011. Walleye and Sauger Habitat. Pp. 133-197 in Biology, Management, and Culture of Walleye and Sauger . Bethesda, MD: American Fisheries Society.

Bruner, J. 2011. A Phylogenetic Analysis of Percidae Using Osteology. Pp. 1-80 in Biology, Management, and Culture of Walleye and Sauger . Bethesda, MD: American Fisheries Society.

Hasnain, S., C. Minns, B. Shuter. 2010. Key Ecological Temperature Metrics for Canadian Freshwater Fishes. Climate Change Research Report , 17: 1-51.

Kitchell, J., M. Johnson, C. Minns, K. Loftus, L. Greig, C. Olver. 1977. Percid Habitat: The River Analogy. Journal of the Fisheries Research Board of Canada , 34: 1936-1940.

Madenjian, C., J. Tyson, R. Knight, M. Kershner, M. Hansen. 1996. First-year Growth, Recruitment, and Maturity of Walleyes in Western Lake Erie. Transactions of the American Fisheries Society , 125: 821-830.

Moore, A. 2011. Manipulation of Fertilization Procedures to Improve Hatchery Walleye Egg Fertility and Survival. North American Journal of Aquaculture , 65:1: 56-59.

Nate, N., M. Hansen, L. Rudstam, R. Knight, S. Newman. 2011. Population and Community Dynamics of Walleye. Pp. 1-56 in Biology, Management, and Culture of Walleye and Sauger . Bethesda, MD: American Fisheries Society.

Ohio Department of Natural Resources, 2013. "A to Z Species Guide: Fish: Walleye." (On-line). ODNR Division of Wildlife. Accessed October 09, 2013 at http://www.dnr.state.oh.us/tabid/6781/Default.aspx .

Palmer, G., B. Murphy, E. Hallerman. 2005. Movements of Walleyes in Claytor Lake and the Upper New River, Virginia, Indicate Distinct Lake and River Populations. North American Journal of Fisheries Management , 25: 1448-1455.

Pauley, G., R. Nakatani. 1967. Histopathology of 'Gas-Bubble" Disease in Salmon Fingerlings. Journal of the Fisheries Research Board of Canada , 24(4): 867-871.

Quist, M., C. Guy, J. Stephen. 2003. Recruitment dynamics of walleyes ( Stizostedion vitreum ) in Kansas reservoirs: generalities with natural systems and effects of a centrarchid predator. Canadian Journal of Fisheries and Aquatic Sciences , 60: 830-839.

Schmalz, P., A. Fayram, D. Isermann, S. Newman. 2011. Harvest and Exploitation. Pp. 1-28 in Biology, Management, and Culture of Walleye and Sauger . Bethesda, MD: American Fisheries Society.

United States Environmental Protection Agency. Spatial Distribution and Temperature Selection of Fish near the Thermal Outfall of a Power Plant during Fall, Winter and Spring. 600/3-80-008. Duluth, MN: University of Minnesota. 1980.