LANDER -- Somebody has introduced walleye into Buffalo Bill Reservoir west of Cody, and the Game and Fish Department is offering a reward of up to $10,000 for information leading to the apprehension of the person or persons who "bucketed" the fish in, said Steve Yekel, Cody region fisheries supervisor.

It's too early to tell how extensive the walleye population is in the reservoir, Yekel said, but if it takes hold, it could potentially devastate the best trout fishery in the Cody area.

"It is extremely disturbing news for us," Yekel said. "This is a highly successful trout fishery, it has a lot of fishing opportunities for folks, and we hate to see that diminished by an act of this type."

Walleye are large ambush predators, not native to Wyoming, that subsist on other fish, according to Chris Hunt, a spokesman for Trout Unlimited.

"That's really unfortunate that somebody felt the need to introduce walleyes," Hunt said. "The Shoshone is one of the last 'big water' habitats for Yellowstone cutthroat."

One of the major concerns about this illegal walleye introduction, Yekel said, is that the fish will add to the struggles of the Yellowstone cutthroat trout in the North and South Fork Shoshone Rivers, Yekel said.

"The Yellowstone cutthroat has been petitioned for listing as a threatened or endangered species on two occasions now," Yekel said. "In this particular drainage, we're trying to protect the Yellowstone trout."

Yellowstone cutthroat as a species now lives in only 43 percent of its traditional range, Yekel said, and in the North Fork Shoshone, the species is further compromised by cross-breeding with rainbow trout, and it is being out-competed at times by other species.

The Yellowstone cutthroat is already being hunted in the area by lake trout, or mackinaw, Yekel said, and adding another predator could be disastrous.

"This is essentially another whammy on the cutthroat population," he said. "Walleye are a top predator, and in most cases, where walleye have been introduced into Wyoming waters that contain trout, the walleye have flourished and the trout and trout fishing have suffered."

Nellie Williams, spokeswoman for Wyoming Trout Unlimited, expressed disappointment about the news. Her group has put a lot of time, resources and energy into helping the native cutthroat populations throughout the state, she said, especially in the Cody area.

"All of our work to restore habitat and protect the Yellowstone cutthroat populations, and enhancing the big trout fishery in the Cody area, especially the Shoshone River, is important from (Trout Unlimited's) perspective," Williams said. "We really hate to see the walleye that were introduced into the Buffalo Bill Reservoir work against all of the great work of our volunteers on the ground."

Really a big deal?

Not everybody with a stake in the Buffalo Bill trout fishery, however, is worried about the walleye.

Todd Miller, an avid fisherman and manager of Rocky Mountain Discount Sports in Cody -- who fishes the North Fork regularly -- said he hadn't heard about the presence of walleye in the reservoir before Monday.

But even if the reports turn out to be true, he said it wouldn't be anything to fret about, in his opinion. And it certainly wouldn't ruin the fishery, Miller argues.

"I lived in Montana for 10 years, and all the lakes around Helena had trout and walleye in them, and they have for years and years," Miller said. "They said the same thing out there, too, but it just doesn't happen. Predator fish can do just fine in a lake with game fish. Game fish eat fish, too. It certainly isn't anything I'd worry about."

Boysen Reservoir is also "full of walleyes," he said, and it's still full of trout.

"Trout fishing is great in Boysen," Miller said.

And just because a fishery increases from one large predator to two, it doesn't mean the predatory impact on a given species, such as cutthroat, has doubled, Miller argues.

"Those walleyes will eat the little mackinaw, too," he said. "That's just what fish do. Fish eat other fish."

But Yekel said it's not always illuminating to compare one reservoir to another.

"In some of these reservoirs, we manage around the walleye by stocking larger trout," Yekel said. "That's exactly what they do in Boysen: They've had to go to a larger trout."

The North Fork Shoshone and the Buffalo Bill Reservoir, however, is managed as a "wild" fishery, and the success of the population is not bolstered by stocking of fish, he said.

"We stocked for many years Yellowstone cutthroat, but with no success," he said. "So stocking larger trout is not something we feel is going to be very successful."

The effect the walleye will ultimately have on the trout population of Buffalo Bill Reservoir is uncertain, he said. If walleye numbers are low, they probably won't do much harm to the fishery, but since there is ample walleye spawning habitat available, it's likely the population could take off, he said.

"We're trying to determine right not how extensive the walleye are out there," Yekel said. "Any information folks can give us about where they're catching them, what size, what they're catching them on, will help us determine how extensive the population is, or whether this is a one-time illegal bucket stocking by a misinformed person."

Contact Chris Merrill at (307) 267-6722 or chris.merrill@trib.com