Noxon Dam is run-of-the river, so walleyes have spilled into Idaho’s Lake Pend Oreille. Embraced by the Cabinet and Selkirk mountain ranges, the lake has a maximum depth of 1,158 feet (deeper than Loch Ness). It’s 43 miles long, 6 miles wide, and girdled by 111 miles of mostly wild shoreline.
Pend Oreille is now producing enormous walleyes of up to 16 pounds, and the fishery is being whooped up by anglers, guides, and the hook-and-bullet press. But the lake is the most important bull trout critical habitat in the United States. The walleyes are competing with bull trout and Kamloops rainbows for kokanee salmon; and the kokanees are a popular sportfish. So the Idaho Department of Fish and Game lets anglers kill as many walleyes as they want.
In 2018 the department started netting on an experimental basis to see if it could curb the growing population. “We have not yet started [aggressive] walleye suppression,” declares Idaho’s Andy Dux. “There are folks who oppose even this experimental work, but they’re a vocal minority. The majority of anglers are very supportive of us managing against walleye in interest of maintaining traditional fisheries.”
While current state and federal managers finally perceive the dangers of attempting to improve on nature by flinging around aliens, their predecessors in Idaho share responsibility with private bucket biologists for the woes of Pend Oreille and its tribs. A native suite of bull trout, westslope cutts, mountain whitefish, northern pike minnow, pygmy whitefish, peamouth chubs, redside shiners, largescale suckers, and longnose dace has been defiled with walleyes, Kamloops rainbows, brown trout, brook trout, kokanee salmon, northern pike, pumpkinseed sunfish, bluegill sunfish, largemouth bass, smallmouth bass, black crappies, yellow perch, lake whitefish, black bullheads, brown bullheads, even tench from Europe.
The two biggest disasters—lake trout and Mysis shrimp—were unleashed by managers in 1925 and 1966 respectively.
For a while, though, introduction of lake trout appeared to be brilliant management. By the early 21st century, the population had transformed from basically nonexistent to prolific, creating a popular trophy fishery.
The Mysis shrimp were supposed to improve the already booming fishery for alien kokanees, which in 1933 had washed down in a winter flood from Montana’s Flathead Lake, where they’d been introduced by managers in 1916.
Both kokanees and Mysis shrimp feed on zooplankton; and, while kokanees were known to thrive on Mysis shrimp in British Columbia’s shallow Kootenay Lake, they couldn’t catch many in Pend Oreille (or Flathead Lake, for that matter, where managers had also introduced Mysis shrimp). Kokanees are sight feeders, and by day the shrimp dropped down into the dark depths where the kokanees didn’t venture. At night, when the kokanees couldn’t see them, the shrimp moved up in the water column, gorging on and depleting the zooplankton that sustained the kokanees.
Meanwhile, the deep-dwelling lake trout chowed down on the shrimp, and the lakers’ population exploded. When the lake trout reached a certain size they switched their diet from shrimp to kokanees.
Lake trout have a tremendous advantage over Pend Oreille’s two native trout in that they spawn on reefs. So they don’t have to expose themselves to predation by running up tributaries. And unlike the fry of bull trout and westslope cutts, lake trout fry hatch into a shrimp smorgasbord and don’t have to run the predator gauntlet down to the lake.
In 1949 the lake produced a kokaneefattened, 32-pound bull trout, which still stands as the world record. But the alien lake trout depleted the alien kokanees that had sustained the native bull trout.
In the late 1960s the robust kokanee fishery started to fall apart. Some of the decline may have been attributable to dissolved gases from Cabinet Gorge and Noxon Dams. And lake drawdowns from operation of the Albeni Falls Dam definitely limited spawning by exposing gravel. Flooding in the mid-1990s accelerated the decline. But the kokanee fishery would have survived all that. What it could not survive was predation by lake trout.
So in 2006, in a move that made the current walleye war seem like a pillow fight, Idaho Fish and Game implemented suppression heavy for lake trout and Kamloops rainbows. It offered a $15 bounty for each fish head of either species presented by anglers, and it killed lake trout with gill nets.
“It was very controversial,” remarks Dux. “For a lot of folks, the idea of setting gill nets in the lake was not palatable. Even if we were successful, they were concerned about damage to other species. We had to clear that hurdle and assure them we could put a program together that would not be detrimental to other species. There were already enough large lake trout that they were generating lots of interest. And we told anglers that, for a period at least, we’d also have to reduce the kams [trophy fish that commonly attained 20 pounds] because kokanee were in such trouble that we needed to lower predation in general. Rainbow anglers were troubled by that.
That said, there was still a lot of support because people valued the traditional kokanee fishery, and many rainbow anglers understood that the traditional trophy rainbow fishery was made possible by the kokanees.”
At first the lake trout kill was unimpressive. But lake trout are aggregate spawners, and “Judas fish,” implanted with transmitters, told managers where the spawning reefs were.
In Yellowstone Lake, managers are recovering native Yellowstone cutts by suppressing alien lake trout. They’ve learned tactics from Idaho’s successful effort. In fact, Hickey Brothers Research, the commercial fishing company Idaho contracted to gillnet lake trout in Pend Oreille, now kills lake trout for the park.
So what does the future hold for the alien morass extant in the stillwaters of Montana and Idaho? Don’t look for lots of change in the Missouri system. The fishery for hatchery rainbows will continue to cost more money because of the need to stock bigger fish. But the fishing is excellent and will likely remain so.
Spotty evidence of dreissenid mussels in the Missouri system’s Tiber and Canyon Ferry Reservoirs (quagga or zebra; it’s unclear which) is an ill wind blowing a bit of good. The threat has inspired Montana to increase its boatcheck stations and fisheries enforcement. And with that effort, more people are getting the message about the dangers of alien introductions.
In Idaho’s beautiful and sprawling Lake Pend Oreille, the scene is much less scary than it might appear. While abundant, and in some cases providing great fishing, the northern pike, bass, perch, crappies, sunfish, bullheads, and tench are pretty much restricted to the shorelines and shallow north end of the lake. They’re not having a huge impact on native fish or rainbows; nor are lake whitefish, which may constitute Pend Oreille’s biggest biomass.
In feeder streams there’s hybridization between alien brook trout and native bull trout and between rainbows and native westslope cutts, but it doesn’t seem to be ecologically significant.
With suppression of lake trout and rainbows, kokanees have rebounded. Kokanee fishing was outlawed from 2000 until 2013, when the population was estimated at 1.4 million, higher than it had been in 17 years. So managers were able to allow a daily kokanee limit of 6 in 2013 and to increase that limit to 15 in 2014.
In 2012 Idaho ceased gillnetting Pend Oreille rainbows and removed the bounty on them. “We don’t have good estimates of current Kamloops abundance,” says Dux. “But we certainly have seen tremendous increase in growth rates as kokanee have increased. The rainbow fishery is as good as it’s been for decades. We’ve reduced lake trout by about two-thirds from when we started netting in 2006. And we’ve recently completed some modeling work to look at how we transition into more of a long-term maintenance program so we can start dialing back effort. That modeling has shown that if we keep our effort at a high level for ten more years, we will be in a position to reduce effort by about eighty percent.” The $15 bounty on lake trout will remain in effect indefinitely.
The most important news is that the lake’s bull trout are now thriving.
Has anything been learned by the American public about playing musical chairs with fish species? Perhaps.
On the other hand, walleyes are under threat in the heart of their natural U.S. range—from Vermont and New York through the Midwest. Among the aliens being illegally superimposed on their habitat, by bucket biologists seeking to correct what they perceive as divine error, is the zander—a larger relative of the walleye widely distributed across Eurasia as far north as Finland.
Other aliens merely compete with or prey on native walleyes—or both. But zanders are capable of hybridizing them into extirpation.
Walleye advocates agitating in the Rocky Mountain West would be well advised to shift their focus east.
Ted Williams’s environmental writings enjoy national acclaim, and keep the bad guys sometimes honest and looking over their shoulders.