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Invasive Walleye Moving Higher into Snake River Basin, Threatening Juvenile Salmon, Steelhead, Lamprey by Staff Columbia Basin Bulletin, March 22, 2024

Walleye can eat an average of 2.5 salmon and steelhead smolts per day in the spring.

Walleye, an invasive species with a reputation for a voracious appetite, has moved down the Columbia River from Lake Roosevelt and are now being counted in increasing numbers upstream of Lower Granite Dam on the Snake River, according to a report by the Idaho Department of Fish and Game.

The numbers of Walleye trapped and counted at Lower Granite have increased from two in 2016 to 154 in 2023, and that could be a threat to juvenile salmon and steelhead, some listed under the federal Endangered Species Act, in tributaries where they rear, according to a report by Marika Dobos, Fisheries Staff Biologist at IDFG. She gave her report to the Northwest Power and Conservation Council's Fish and Wildlife Committee March 12.

The growing number of walleye reported as trapped and counted at Lower Granite Dam does not account for all of the fish suspected to have slipped past the dam. For example, in 2021, the count at the trap was 75 fish, but the number of walleye counted at the U.S. Army Corps of Engineer's counting window at the dam was 1,877 (April -- October). However, the number trapped is indicative of the threat to juvenile fish rearing in the mainstem Snake River and tributaries upstream of the dam, including the Salmon River. A walleye was caught in that river by an angler as far upstream as Riggins, 80 miles upstream of the Salmon River confluence with the Snake, Dobos said.

"This expansion of walleye is a concerning issue that poses greater predation risk to wild and hatchery stocks of juvenile anadromous salmon, steelhead and lamprey that use the overlapping habitat for rearing and emigration," noted a March 5 Council memorandum (www.nwcouncil.org/calendar/council-meeting-2024-03-12/).

Juvenile salmonids in Idaho rivers and streams are already affected through predation by native and non-native birds and fishes, and as more walleye continue to move and colonize upstream of Lower Granite, predation rates will continue to rise, IDFG reported in 2022.

In its Fish and Wildlife Program Addendum, the Council identified three predation management issues -- Northern pike, pinniped and avian predation -- but has yet to include walleye on that list, "but their predation threat to juvenile salmonids is increasing as populations expand into additional habitat in the Snake River," the memo says.

According to Dobos, walleye can eat an average of 2.5 salmon and steelhead smolts per day in the spring, and that walleye and other non-native predators could be eating up to 17 percent of certain populations of juvenile emigrants (research by Harnish et al. 2014).

During spring months (May through June), she said, 60 percent of a walleye's diet can be made up of juvenile salmon and steelhead. That's compared to a diet of 90 percent salmonids by northern pikeminnow and 10 percent salmonids by smallmouth bass.

A report last year by the Independent Scientific Review Panel of the Bonneville Power Administration's pikeminnow rewards program, which resulted in a harvest of 140,000 pikeminnow at a cost of nearly $1.4 million in 2022, questioned whether the reduction of pikeminnow due to the rewards program is resulting in an increase of other piscivorous predators, such as smallmouth bass and walleye.

The walleye native range is the Midwest U.S. and in the Appalachian Mountains, but they were likely introduced to Lake Roosevelt and Banks Lake in the 1940s, Dobos said. By the 1990s they were noted in angler surveys in the lower Columbia River and first seen in the lower Snake River at about the same time.

There was a notable increase in the number of walleye in the Snake seen in angler surveys between 2010 and 2018, but not upstream of Lower Granite Dam. It is thought the first walleye migrated upstream of the dam around 2016.

Walleye are considered a cool-water species and, although adaptable, populations in their native range in the Midwest are declining due to warming water, according to a study recently published in the journal Limnology and Oceanography Letters.

Males mature at two years of age, females at four years, and a 20-year-old walleye can weigh as much as 20 pounds, Dobo said. The range in size of the 154 walleye trapped at Lower Granite in 2023 was 10 to 26 inches.

Noting that a 12-inch female can produce 30,000 eggs per year and a 10-pound female can produce 250,000 eggs per year, Dobos said walleye are both "egg producing machines" and "fish eating machines."

She explained the walleye's predation threat has several layers:

• The extent of their invasion upstream of Lower Granite Dam overlaps with important rearing habitat;
• There is also an overlap with fall Chinook salmon hatchery releases;
• An established walleye population and further expansion into areas above the dam would likely lower the survival of wild salmon and steelhead.

"Walleye have responded and capitalized on that food source, especially in tailraces of dams where the density of juveniles is high," Dobo said. "When walleye are allowed access to migration corridors where juvenile salmon are present, they will colonize."

In addition, angler support for walleye fisheries is "loud and boisterous." Walleye are classified as a game species in Oregon, Washington and Idaho, although none of the three states have a size or bag limit on the fish in the Snake River or downstream of Lake Roosevelt on the Columbia River.

A non-native piscivore work group is working on predation issues by invasive fish species. In her presentation Dobo said their goal is to "implement research and management actions with a goal to reduce, minimize, and prevent piscine predation-related mortality from introduced non-native fishes on anadromous species within the Columbia River basin."

The workgroup is made up of representatives of Confederated Tribes of the Umatilla Indian Reservation, Idaho Department of Fish and Game, Nez Perce Tribe, Oregon Department of Fish and Wildlife, US Geological Survey, Washington Department of Fish and Wildlife and NOAA Fisheries, Northwest Fisheries Science Center.

For solutions, the group is proposing:

• Encourage reporting and harvesting of Walleye -- Get the word out!
• Learn more about walleye, such as:
  • Where and how successful are they moving upstream of dams?
  • Where do they spawn?
  • Are they naturally recruiting above Lower Granite Dam?
  • What are abundances and angler harvest?
• Consider what methods of suppression can be effective
• Consider modifications that could limit passage at dams
• Consider policy changes that can be useful

Related Pages:
'Not Good for Salmon and Steelhead': Smolt-Eating Walleye Worry Fishery Managers by Eric Barker, Spokesman-Review, 8/30/23
Increasing Number of Predatory Walleye Logged at Lower Granite Dam by Nolan Smith, Big Country News, 6/29/15
WDFW Removes Bag Limits for Bass, Walleye, Catfish on Columbia River, Tributaries to Protect Salmon by Staff, Columbia Basin Bulletin, 3/4/16
New Rules Mean More Walleye, Fewer Sturgeon for Washington Anglers by Eric Barker, The Bend Bulletin, 3/13/13
It's Official: Bag Limits Off in WA for Columbia/Snake Bass, Walleye, Channel Catfish by Staff, Columbia Basin Bulletin, 3/3/13
Bass, Walleye Pose Substantial Threat To Salmonids by Staff, Columbia Basin Bulletin, 3/6/9
Pikeminnow Season Catch Up; Data Confirms Snake Walleye Increase by Andy Walgamott, Northwest Sportsman, 10/13/22

Columbia River Area Show Slow Fishing with a Few Sturgeon and Walleye Appearing in Catches by Mark Yuasa, Seattle Times, 2/13/17
Columbia River Reports on Skinny Side Due to Bad Weather Except for Good Walleye Action by Mark Yuasa, Seattle Times, 12/15/16
Columbia River Area Producing Decent Steelhead and Walleye Fishing by Mark Yuasa, Seattle Times, 12/2/16
Fair Catches for Coho, Walleye and Steelhead in Pockets of Columbia River System by Mark Yuasa, Seattle Times, 11/17/16
Walleye in Columbia River Mainstem is Only Viable Fishing Choice by Mark Yuasa, Seattle Times, 10/27/16
Autumn Fishing Choices Plenty Along Columbia River for Salmon, Steelhead and Walleye by Mark Yuasa, Seattle Times, 9/29/16
Columbia River Region Offers Fall Fishing for Chinook, Steelhead and Walleye by Mark Yuasa, Seattle Times, 10/18/12
OR Fish & Wildlife Fishing Reports Show Fall Options to Catch Walleye and Chinook by Mark Yuasa, Seattle Times, 10/3/12
Fall Chinook, Summer Steelhead & Walleye Among the Best Columbia River Fishing Bets by Mark Yuasa, Seattle Times, 8/29/12
Columbia River Full of Fishing Fun for Fall Chinook, Steelhead and Walleye by Mark Yuasa, Seattle Times, 8/1/12
Steelhead and Walleye Among the Top Picks in Columbia River Region by Mark Yuasa, Seattle Times, 2/22/12
Walleye & Bass are Good Fishing Alternative Along with Some Steelhead by Mark Yuasa, Seattle Times, 4/26/11