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An Eye on Walleye

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Avista fisheries technician Tim Tholl with a walleye captured during a fall gillnetting survey in Noxon Reservoir (courtesy of Jon Hanson with MFWP) Avista fisheries technician Tim Tholl with a walleye captured during a fall gillnetting survey in Noxon Reservoir (courtesy of Jon Hanson with MFWP)

Lake Pend Oreille is also noted as the home of the preferred perch of the Pacific Northwest

In the Lower Clark Fork River, the non-native but much-loved walleye (Sander vitreus) are building their forces. In Noxon Reservoir, evidence has recently been collected to suggest that the species are now naturally reproducing.

Walleye are in the perch family, of which there are over 140 species in North America alone; even given the broad family selection though, anglers notoriously adore the walleye. A wide-ranging species, walleye are found in diverse habitats spanning across the continent. They prefer clear to slightly turbid, or murky, waters. They are most abundant in large, shallow and turbid lakes.

The color of walleye varies depending on habitat; they are often paler with less obvious black markings in turbid waters, and more strikingly marked in clearer water. They range from olive to dark green on their backs, with golden yellow sides and a white spot on the bottom edge of the caudal, or tail, fin. They have sharp canine teeth, good for feeding upon suitably-sized fish.

Walleye begin the courtship process right when the ice is breaking apart and melting; they are social creatures that engage in group sex. Prior to spawning, the chase is very involved and effort-laden. There is much circular swimming, pushing, and fin erection.

By spring or early summer, they are ready for the job. Spawners take to shallow waters at night with one large female and two smaller males or two medium-sized females with multiple males. The spawning group rushes upward into shallow waters where the females flip on their sides and release eggs—the maximum number of eggs released by one female is over 600,000. The males, for their part, simultaneously discharge milt, or sperm, upon the eggs, completing the reproductive process. Most females release the bulk of their eggs in a single night. Though the process seems promiscuous in nature, the group approach is utilized to produce more genetic diversity in the young.

"Females generally produce about 25,000 eggs per pound of their weight so a
ten pound female can produce 250,000 eggs," remarks Montana Fish, Wildlife, and Parks biologist Jon Hanson.

The fertilized eggs are heavy and sink to the bottom where they fall into crevices and holes, where they stick to stones and debris. From here on out, the eggs are on their own. The eggs hatch in 12 to 18 days; 10 to 15 days after hatching, the young that survive disperse into the upper levels of deeper water. The young feed on plankton and insect larvae for most of the first year. After that, they shift towards small fish before preying upon larger ones as adults. The mortality on walleye in the egg and fry stages is quite severe.

Unsurprisingly, females grow quicker than males. They prefer, for the most part, consorting in discrete schools, but maintain separate spawning grounds and summer territories. New evidence suggests that walleye can and do utilize the same spawning grounds year-to-year.

"This is our third year of a three year telemetry study of walleye in Noxon Reservoir and preliminary results show that walleye are returning to the same spawning area when water flow conditions are similar from year to year," says Hanson. However, one year when spring water flow was rather high all of our tagged walleye went to different, more suitable locations."

The current telemetry study MFWP are doing is to try and determine habitat
preferences, movement patterns and distribution, with a focus on potential spawning locations, reports Hanson. He says they are seeing fairly predictable movement of tagged walleye with fish staying lower in the reservoir near the Trout Creek area during the winter and summer, and then moving up reservoir in the spring, where they are spawning within the first couple miles below Thompson Falls Dam. "This is pretty typical movement for walleye that are found within reservoirs," he says.

Currently in Noxon Reservoir, where they were likely illegally introduced multiple times in the 1990s but first caught by MFWP in 1994, there are good numbers of prey fish like yellow perch and northern pike minnow (squawfish). Whether or not the prey population will be able to sustain the voracious appetite of the walleye is unknown. "We’re not sure whether the prey base will withstand a lot of predators out there," says Hanson. "At some point the walleyes will likely start stunting and they’re fairly prone to doing that."

Noxon Reservoir is known for its exceptional smallmouth and largemouth bass fisheries, with numerous bass tournaments held annually, April through September. Although bass are not native to Montana, they’re established and managed for anglers. According to Hanson, the walleye will prey on these fish along with their food base, so the number and growth of bass will likely go down to some degree. Trout are likely to get hit hard too, as walleye and trout often end up competing for the same habitat in reservoirs. With the federally listed (as threatened) bull trout and the native westslope cutthroat trout, the habitat competition is of concern.

The walleye get their name from a special layer in the retina of the eye that is super-sensitive to light. This is why their feeding is restricted to twilight or dark periods. In turbid waters, where the light is not as much of an issue, the walleye are more active during the day.

The predominant predator of walleye is the northern pike (Esox lucius). Most walleye are caught by still fishing with live minnows or earth worms as bait, or with artificial lures such as spinners, spoons, plugs, and jigs. Drifting or trolling appears to be the most effective way to seek out schools of walleye. Twilight periods are best for obvious reasons. Though walleye are not known to be magnificent fighters, they are said to be a steady battler that bore to the bottom, and very, very tasty.

Other places in Montana, like Fort Peck and Canyon Ferry have numerous walleye, and have gained support all over the country. Walleye fishing is a big business in the angling world, and thousands of dollars are spent chasing them.

"The average angler has a hard time catching [walleye] on a consistent basis," says Hanson. "A walleye pro’s boat looks like a battleship with all the gear and electronics on it."

MFWP do raise some walleye in their Fort Peck Hatchery and plant them in places east of the divide. Walleye are certainly appropriate in some locations, Hanson says, and the agency supports those programs with walleye stocking and active management. Walleye are being caught downstream in Lake Pend Oreille now too, which is a growing concern in regard to impacts to the food chain and the entire ecosystem.

Hanson says that most people he talks to are initially excited about the prospect of walleye, but after they get the full story of what it could mean for the current fish that inhabit Noxon and Cabinet Gorge, they tend to get rather concerned. "Remember," Hanson says, "for every new species introduced something else has to give."

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Author info

Kate Wilson Kate Wilson was a Project Journalist for Avista's Clark Fork Project. She has been interested in environmental issues since she was a youngster.

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