Walleyes are fairly 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, which helps them eat fish. Males and females can be told apart as females grow much larger than males. (Becker, 1983; Bozek, et al., 2011a; Ohio Department of Natural Resources, 2013)
Walleyes are native to freshwater rivers and lakes of the northern United States and Canada. Their range makes a lopsided triangle with the border between Mississippi and Alabama in the south, north to the border between the Canadian provinces of Yukon and the Northward territories, and bound to the east and west by the Appalachian and Rocky Mountains. This keeps them safely inland, away from salty coastal waters. Their range has become larger due to humans introducing them to new areas, especially in the United States. This new area includes large chunks of the Northeast, from southeast Maine down to Virginia, passing lightly through North Carolina into inland South Carolina and Georgia. This also includes large parts of nearly all the western and southwestern states, and part of southern British Columbia. As a cool-water species, their natural habitat is mostly found in the northern United States and Canada. (Billington, et al., 2011; Bozek, et al., 2011b)
Walleyes likely evolved in North American rivers and moved into lakes later. For this reason, preferred walleye habitats are similar to rivers with 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 mostly in rivers farther south. Walleyes prefer shallow to moderately deep areas; they mainly live in the areas near the lake shore, although they may sometimes travel further towards the bottom. These fish prefer murky waters with low light. By day, walleyes rest in areas with vegetation on sand and large gravel in moderate currents. These fish can still be found in many rivers, but their populations in these areas have declined. (Kitchell, et al., 1977)
As a cool water species, temperatures are important to the well being of walleyes. Their eggs are able to survive rapid temperature changes of up to 20 to 21°C (68 to 70°F). Temperature affects walleye spawning, the best egg fertilization temperatures are around 6 to 12°C (42 to 53°F), the best egg incubation temperatures are around 9 to 15°C (48 to 59°F), and the best hatching temperature is around 15°C. These fish prefer temperatures between 20 to 24°C (68 to 75°F) for maximum growth. This temperature may be higher for juveniles, to between 27 and 31°C (80 to 88°F). Walleyes are able to survive under fairly harsh conditions, although their eggs are more sensitive than fully grown adults. Certain levels of heavy metals and salt water can also affect walleye survival, reproduction, and behavior. (Auer and Auer, 1990; Becker, 1983; Bozek, et al., 2011b; Hasnain, et al., 2010; Kitchell, et al., 1977; Madenjian, et al., 1996; Pauley and Nakatani, 1967)
Like most fish living in rivers, walleye survival and reproduction has been directly impacted by the dams along their native waters. 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. So long as all the conditions for survival and reproduction are present, walleyes have adapted very successfully to life in reservoirs. (Bozek, et al., 2011b)
Like many fish, walleyes begin their development as an egg and progress into the larval and juvenile stages, before becoming an adult. Female walleyes release tens of thousands to hundreds of thousands of eggs during each spawning period. These eggs are about 2mm in diameter. For several hours after being released, the eggs are coated in an adhesive, which is believed to increase the fertilization rate. Once fertilized, the egg hardens, losing its adhesiveness and floats into safer areas 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 about 10mm in length (they range from 6 to 9mm at hatching), and are fully developed at 18mm. Because they are still underdeveloped, the larvae sit on the substrate and move based on the current, being swept away into nursery habitats. The larvae begin feeding immediately on zooplankton and chironomids. The amount of prey available plays a large role in their survival, as does the amount of predators, since walleye eggs and larvae are commonly eaten by larger fish. Very few walleye make it to 1 year of age. About 0.01% of larval walleyes survive their first year. If they do, their growth is rapid. Males and females grow at the same rate before this, but once they reach the juvenile stage, their growth rates can differ, depending on their location. Walleyes in the southern part of their range grow more quickly 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 the location and food availability. The average length at adulthood is about 350mm for males and 450mm for females although this varies. Males usually become sexually mature before females. (Bozek, et al., 2011a; Moore, 2011)
Male and female walleyes spawn with multiple partners with no lasting relationships. Mating takes place in a marshland. Male walleyes may spend several weeks in the spawning marshland, however, female walleyes go only to spawn, which lasts about one day. Neither males nor females display territorial behavior during this time. (Becker, 1983)
Walleyes spawn once a year in early spring. Spawning occurs at 5°C (41°F). With the large range of this species, the exact spawning dates vary by climate. Walleyes return to the same site again and again to spawn. Female and male walleyes reach sexual maturity at different ages and sizes. Female walleyes release tens of thousands to hundreds of thousands of eggs in a single spawning session, which is broken up into five minute egg release intervals. (Barton and Barry, 2011; Becker, 1983; Bozek, et al., 2011a)
There is no evidence of parental care of any kind taking place among walleyes. (Becker, 1983)
The lifespan and mortality rate of walleyes is strongly linked to their growth rate. 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 walleyes have been known to live as long as 20 years, or possibly up to 30 years. Due to these differences, and their large range it is very difficult to estimate their mortality rate. Walleyes are also popular sport fish, which means their mortality rate needs to take both natural and unnatural causes into account. Their yearly mortality rate ranged from 13 to 84% across 14 different lakes and rivers in North America, most commonly falling between 40% and 55%. (Bozek, et al., 2011b; Nate, et al., 2011)
Once walleyes reach a certain size (between 51 and 100mm), they begin spending more time towards deeper, cooler, darker depths during the day. This happens around the same time they develop changes in their retina, which allows walleyes to see more clearly in dim light. Due to their ability to see in low light, walleyes are able to hunt at night, although they have a less sensitive lateral line, which impacts their ability to sense movements in the water. If ideal depths are not available, walleyes may seek out dense vegetation or other cover during the daylight hours to reduce their light exposure. Walleyes are more active at dusk and dawn. (Bozek, et al., 2011b)
Walleye behavior varies with age as well whether they live in a lake or a river. Larval walleyes in rivers are found in all depths, from the surface to near the stream bottom, probably mostly due to the force of the current. In contrast, lake walleye larvae tend to live mostly in the deeper parts of the lake. As walleyes grow they develop more control over their movements. They move in groups with fish of their same size, although they are not always of the 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 live in a lake or river. Walleyes living in rivers usually have a smaller home range than those in lakes. Males and females tend to have the same home range size. 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. (Becker, 1983; Bozek, et al., 2011b; Palmer, et al., 2005)
Although walleyes move together in a loose group in open waters, there is little evidence of communication systems between members. Walleyes are not territorial, nor do they keep mates or invest time in offspring. One of the only examples of communication within the species happens during mating, when male walleyes bump against females and, when she is ready to spawn, the female signals so by turning on her side. (Becker, 1983)
Walleye eggs and larvae are often eaten by many fish species; however, adult walleyes sit at the top of the food chain in many systems. Walleyes begin eating other fish early in life. Adult walleyes feed on a large variety of fish species, including yellow perch, gizzard shads, emerald shiners, spottail shiners, and many other species, depending on what is available. These fish may also eat smaller members of their own species. When fish are not available to eat, walleyes may also eat certain types of invertebrates. (Nate, et al., 2011)
Because walleyes do not get overly large compared to other predator species, they, too, can become prey in certain foodwebs. Walleyes have been preyed on 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 becoming adults, walleye eggs, larvae, and juveniles may be the main food source for many different fish species 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 related to walleye populations, which means early predation can have a very real effects on the predator’s longer term success. The huge number of eggs and larvae produced by each female, as well as the temperature needed for spawning, which is much colder than many fish species prefer, likely helps eggs and larvae avoid predators. (Nate, et al., 2011; Quist, et al., 2003)
As top predators, walleyes have a large, complex role in the ecosystem. Like most predator/prey relationships, the population of walleyes and their prey are related. An increase in adult walleyes can lead to a decrease in their prey. Although adult walleyes are at the top of their food chain, their larvae, eggs, and juveniles are near the bottom. For this reason, increases in species such as yellow perch, can negatively affect walleye populations as fewer and fewer larvae make it to the adult stage. Yellow perch are the preferred prey of adult walleyes in many cases. Since yellow perch feed on juvenile walleyes, focusing on yellow perch as a prey species actually helps juvenile survival. This relationship does not just help these two species. If yellow perch populations begin to decrease, walleyes must eat other species, which causes a ripple effect across the ecosystem as other prey begin to decrease in numbers. (Nate, et al., 2011)
There are no known negative effects of walleyes on humans.
Walleyes are one of the most popular sports fishes in North America. There are regulations around catching these fish, this species is prized by Canadian, American, and Native American fisheries. These fish are captured for recreational and commercial purposes with millions of kilograms harvested annually. Recreational fishing of walleyes in Lake Erie alone makes about $600 million a year. Due to their large range, walleye fishing is popular throughout the United States and Canada. (Bozek, et al., 2011b; Schmalz, et al., 2011)
Due to their popularity, walleyes are often studied. There are regulations in place to help avoid over-fish this species such as bag or length limits. This may be helping in areas where they have been over-fished. Blue pike may have been a subspecies of walleyes found in Lake Erie and Lake Ontario, but they are now believed to be extinct. Blue pike were smaller than walleyes and lived in deeper waters. It is possible that blue pike and walleyes were separate species until humans introduced them into new habitats, which caused these species to interbreed. Walleyes also form hybrids with saugers to form a fish known as a "saugeye". This mix is bred as a stock species, as saugeyes tolerate warmer and more degraded habitats than walleyes and have a faster growth rate than both species. Currently, there is a concern that the interbreeding of these species and hybrids will mix until there are no walleyes or saugers left, only hybrids. (Billington, et al., 2011; Schmalz, et al., 2011)
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