Walleye are showing up in Idaho rivers where they don’t belong, and the Idaho Department of Fish and Game (IDFG) wants anglers to keep and cook the non-native invaders rather than throw them back. The once-walleye-free stretches include portions of the Snake River and the Salmon River—both of which host endangered anadromous fish like salmon and steelhead.

Walleye are established in the Lower Snake and the Columbia River Basin in Washington due to illegal introduction some 80 years ago. The Upper Snake was consideed walleye free, until recent years when the fish started clearing Lower Granite Dam—the last of eight major dams salmon must navigate before entering Idaho on their way home from the Pacific Ocean through Oregon and Washington.

Walleye are apex predators, and they could pose a grave threat to Idaho’s already declining population of native salmon and steelhead, according to the IDFG. Annual data collected at Lower Granite Dam shows that the first walleyes began appearing in 2016. In 2022 IDFG reported a total of 74 walleyes removed from the area below the dam. But what’s removed is only a small portion of what actually comes through. IDFG estimates that nearly 300 walleye entered Idaho waters last year, making it as far as 80 miles up the Salmon River. 

“Many more walleye migrate up the fish ladder than are trapped because the trap operates periodically and most smaller fish (less than 12 inches) are too small to be trapped,” the agency wrote in a recent press release about the walleye invasion. “This is not good news for people trying to manage for salmon and steelhead and those hoping to catch them in the future.”

To reign in the expansion, the department isn’t just asking anglers to keep, kill, and cook their walleye, but to report back about where they caught them and what methods they used. “As walleye grow, they will include many other fish species on top of salmonids in their diet,” the press release states. “Walleye only add to the many difficulties that salmon and steelhead face.”

According to the Idaho Statesman, walleye are stocked in Idaho but not in the places where the fish are now starting to appear. The department suspects that warming water temperatures could aid in the spread of the population. The prolific invader can lay up to 300,000 eggs a year and eat 2.5 young salmon per day.

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Washington state offers a bounty on pikeminnow in the Columbia and Snake because they too prey on salmon, but a program is not established for walleye. Pikeminnow payout in Washington is $6 per fish up to 25 fish, $8 per fish up to 200 fish, and $10 per fish for those who manage to net 200 or more. The highest annual angler bounty on record is $119,341 for 14,109 northern pikeminnow. In the last decade more than 5 million pikeminnow have been removed from Washington waters to help native salmon and steelhead.