A Game and Fish estimate of a walleye population of about 2,000 in Buffalo Bill Reservoir means the invasive species may be possible to contain in order to sustain the health of the cutthroat trout fishery.

“I’m cautiously optimistic we can suppress the walleye population in Buffalo Bill,” said Cody region fisheries biologist Jason Burckhardt.

The department, aided by graduate students, has been studying the scenario at the reservoir 10 miles west of Cody.

While a very popular fish for anglers elsewhere in the United States, walleye are an invasive species in Buffalo Bill and the implications of their presence threaten the native trout.

Walleye were discovered in Buffalo Bill in 2008. It is not certain how they appeared, but there has been speculation fishermen who migrated from the Midwest and missed going after them illegally introduced the fish.

Once it was realized the walleye were present and had the potential to devour the smallest trout in great numbers, Game and Fish implemented policies to attack them.

Over the years, policy shifted from encouraging anglers to keep every walleye caught to mandating that. Walleye was even removed from the list of game fish. That meant there is no regulation requiring they be eaten and a fisherman “could kill it and throw it in the garbage can,” Burckhardt said.

Also, as part of the recent studies, a reward was offered to those who caught and kept walleye and reported them to Game and Fish.

Burckhardt said the caught  fish helped the agency reach its population estimate.

“We didn’t really have an idea how many were out there,” Burckhardt said.

He also estimated there are between 50,000 and 100,000 trout (cutthroat, rainbow, lake and hybrids) in Buffalo Bill, so the apparent ratio is encouraging.

“Two thousand isn’t that many fish in the grand scheme,” Burckhardt said of the walleye.

Some 800 of those 2,000 were removed from Buffalo Bill this spring, tilting the odds even more in favor of the trout.

Initially, Game and Fish greeted the news of walleye in Buffalo  Bill with alarm. The trout travel up the North Fork of the Shoshone River and its tributaries to spawn. The area is a renowned fishery.

Walleye had the capability of decimating the trout and the fishery, so Game and Fish declared war.

“Efforts are currently underway to ensure the sustainability of this incredible trout fishery for future generations,” the department declared in its June 2017 newsletter.

Part of charting the future of the trout in the reservoir revolves around the mortality of the walleye. The biggest threat to trout is when they swim to tributaries to spawn.

“They’re going to be vulnerable to predation,” Burckhardt said.

If trout make it to a year or year-and-a-half old they can probably avoid being eaten because they will have outgrown the walleye’s target size. That’s a spurt to perhaps eight or nine inches long.

Cody residents are familiar with the ongoing battle by the National Park Service to eradicate lake trout from Yellowstone Lake. That invasive species was overpowering the cutthroat trout.

Several years of effort and millions of dollars have been invested with hundreds of thousands of lake trout being removed from the lake each year.

In Yellowstone Lake, the invasive species basically outnumbered the native species. That is not so in Buffalo Bill Reservoir.

It is nearly impossible to eliminate an invasive species in a sizeable body of water. Game and Fish has a few advantages in this case, being able to borrow successful techniques from the Yellowstone Lake experience, and dealing with what appear to be a limited number of walleye.

“I think the trout population has a fighting chance,” Burckhardt said. “It’s better than saying the toothpaste is out of the tube, let’s just let the walleye take over.”

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