Yellowstone National Park's “Other” Native Fish

When fly fishers think of Yellowstone national park they often conjure images of native Yellowstone cutthroat trout. But both westslope cutthroat trout and fluvial (river-dwelling) Arctic grayling are native to some park waters. It’s been seven years since Yellowstone National Park’s fisheries biologists began implementing their plan to eliminate nonnative rainbow trout, brook trout, and adfluvial (lake-dwelling) Arctic grayling from the upper Gibbon River and its headwater lakes—Grebe, Wolf, and Ice lakes. This is part of an ambitious project to restore westslope cutthroat trout and fluvial grayling to at least 20 percent of their historic range.

The intention is to create a survival zone for native fish in the face of a warming climate and dramatic population declines caused by the introduction of rainbow trout, which were first planted in the watershed more than 140 years ago. Though most public reactions to the plan were overwhelmingly supportive, some fly fishers were against it, accusing Yellowstone’s fisheries biologists of “playing God” by deciding which fish species got to thrive and which were slated to be eliminated.

But neither the scope of the project nor a few negative reactions would deter Yellowstone’s lead fisheries biologist, Dr. Todd Koel, or biologist Andi Puchany from following their mandate to preserve and enhance Yellowstone’s native fish. Puchany has a special affinity for Grebe Lake: In 2015, years before it would become part of her job, she caught her first fly-rod fish from Grebe Lake on a $30 Cabela’s outfit. She had no idea at the time that one day she would become a steward of the Gibbon River and Grebe, Wolf, and Ice lakes, and instrumental in reshaping their futures.

Fish Removal and Restoration

The upper Gibbon received Yellowstone’s first-ever planting of nonnative rainbow trout in 1880. The stretch above the Gibbon’s Virginia Cascade had historically been fishless—as were Grebe, Wolf, and Ice lakes—when Europeans arrived in North America. But those rainbows from 1880 didn’t stay where they were stocked. The fish quickly spread throughout the watershed, outcompeting and interbreeding with the natives downstream, pushing them to extirpation. Yellowstone’s 2010 Yellowstone Native Fish Plan, created by Todd Koel, designated this area for native fish restoration. Its lower reaches include waterfalls that stop nonnative fish from encroaching upon the recovery zone, creating a protected area where the native trout can potentially flourish.

A project of this size is a monumental undertaking: More than 20 fisheries staff were involved, sometimes working 16-hour days. Permits had to be obtained. All the water in the entire system, from tributary streams to small spring seeps, had to be mapped to determine the amount of rotenone to use to remove the nonnative fish. Rotenone is a natural compound made from plant roots that kills gill-breathing organisms. As it was being deployed in August and September of 2017, the rotenone was continuously monitored by fisheries staff who hiked into the backcountry for this sole purpose.

Helicopters delivered the rotenone, as well as the potassium permanganate that deactivates it. Helicopters also delivered thousands of pounds of gear, including the boats used in the work.

The project couldn’t begin until autumn to allow time for the lakes’ trumpeter swan signets to fledge, so, of course, it snowed, making the potentially dangerous work even more so. Native fish fingerlings had to be stocked in the lakes a few weeks after the treatment. It was important to do this quickly so the loons would have something to eat when they returned in the spring.

Rotenone is controversial in fly-fishing circles. Some anglers believe that rotenone destroys all aquatic insects—it does not. The insects bury themselves in the substrate and other areas to avoid it. Sure, some die. But there has to be a functioning food base when fish are added to the system. If the rotenone had really destroyed the entire aquatic insect population, the westslope and grayling fingerlings that were introduced after treatment would not have been able to survive without something to eat. And they have survived. I asked Todd if native fisheries can be restored without using rotenone.

“No,” he said. “The use of rotenone is the only way to completely eradicate nonnative species to give native fish a chance.”

In the summer of 2024, Todd and Andi asked me (the coordinator of the Yellowstone Fly Fishing Volunteer Program) to use our program to sample these waters, all of which are accessible from Yellowstone’s Norris Canyon Road. Our goal was to help formulate a population estimate to see how the fish are faring. I worked with Puchany to schedule two three-night, four-day camping trips on Grebe Lake. One day, in each of those weeks, we hiked to Wolf Lake to fish.

The YFFVP also conducted two sampling days on the Gibbon River, in its Virginia Meadows section. All these efforts included mark-and-recapture events, where the fish we caught with our fly rods received individually numbered Floy tags inserted alongside their dorsal fins. By comparing the number of tagged and untagged fish to the numbers caught previously, biologists are able to determine the approximate number of fish in a population. Tagged fish are also reported by other anglers in the park, augmenting the data.

Grebe & Wolf Lakes

Our camping trips to Grebe and Wolf lakes began with Koel, Puchany, several fishery techs, and YFFVP members meeting at the Grebe Lake trailhead with Yellowstone National Park packers and their horses and mules. The animals carried all our camping gear and supplies to our campsite on the north side of Grebe Lake. The trail is 3 miles long, but it’s flat and easy to navigate—I’ve actually fished Grebe Lake by hiking in and out the same day. The trail to Wolf Lake is right on the edge of our campsite. It’s a 1.25-mile hike to the Gibbon River, which flows out of Grebe Lake, and you follow it to Wolf Lake.

On our first day at Grebe, it took about five minutes to catch our first westslope cutthroat while we were waiting for the packers to arrive with our gear. I fished a size 12 tan Chubby with a Perdigon dropper. A small trout mouthed the Chubby on my first two casts but didn’t fully inhale it, so I didn’t hook the fish. I decided to strip the dry across the surface, hoping to provoke a more aggressive strike that would (hopefully) help the fish get the fly into its mouth. This tactic worked and became our primary method for catching fish for the next two weeks.

The reason stripping dry flies like Chubbies works so well on Grebe, Wolf, and Ice lakes is due to their prolific populations of Traveling Sedges. These large—sizes 8 or 10—tan-bodied, mottled-wing caddisflies rise to the surface to emerge. Once they do, they begin running quickly across the water in hopes of reaching the grass along the shoreline. Drawn to the commotion, trout and grayling aggressively hunt the naturals. These giant caddis are joined by several mayfly species (including large numbers of Callibaetis), other caddis

species, leeches, and enormous populations of dragonflies and damselflies. These lakes are fish food factories, even after the rotenone treatments.

During our two four-day trips to Grebe and Wolf, our combined crew caught 683 fat and healthy westslope cutthroats and Arctic grayling. That’s an amazing number, since these were not full fishing days due to the time it takes to hike to the fishing spots, set up and take down camp, retrieve drinking water, and prepare food. Overall, we caught larger fish in Grebe Lake, westslopes up to 19 inches and grayling to 16 inches. But we caught more fish from Wolf. These two lakes now provide some of the best fly fishing for native species in all of Yellowstone. In addition to the great fishing, the project has also produced something miraculous: In the spring of 2024, Arctic grayling fry were found in Grebe’s inlet stream—the grayling are spawning and producing viable offspring. It’s exceedingly rare to find fluvial Arctic grayling spawning successfully in the wild in the Lower 48.

Ice Lake

Ice Lake is smaller than both Grebe and Wolf. It’s also the easiest to reach, requiring a flat, half-mile hike from the trailhead to the lake. This makes it very popular with tourists who walk in to view the lake’s wildlife. The lake is like a giant puddle; most of its water arrives from springtime snowmelt runoff. Ice Lake doesn’t have an obvious outlet stream, and the only surface water flowing into it most of the year is from tiny spring seeps that do not support spawning sites. Some fish species are able to spawn in lakes and ponds without river or creek tributaries. But westslope cutthroat trout and fluvial Arctic grayling cannot.

Unlike Grebe and Wolf lakes, in Ice Lake the park decided to place only Arctic grayling; it’s possible that grayling introduction efforts could be more successful if the fish are given time to gain a foothold before westslope cutthroats are added. Ice Lake held only a handful of very large rainbow trout when it received its rotenone treatment, and no cutthroats or grayling were found.

That fact made for a particularly memorable fishing day during the 2023 Yellowstone Fly Fishing Volunteer Program. One of our volunteers hooked a fish with a black Woolly Bugger, and as he brought it closer to the bank, a great mystery was revealed: The fish wasn’t a grayling—it was a large westslope cutthroat trout. Todd and Andi were as surprised and perplexed as I was when I reported the catch that night. How did it get there? During several more YFFVP Ice Lake sampling sessions in 2023 and 2024, we didn’t catch another westslope—then we did.

After a slow morning on the north side of Ice Lake, I decided to move the volunteers to the lake’s southern shore. I often avoid this area because the water is filled with downed timber, which makes wading very difficult. I was fishing a black Micro-bugger streamer around some submerged wood when the first fish ate my fly. It was a small westslope. The volunteers and I proceeded to hook nine more that day, deepening the mystery of how these fish came to live in Ice Lake.

Koel and Puchany’s current hypothesis is that during heavy runoff, Ice Lake overflows, creating a temporary channel that runs through the forest, briefly connecting the lake to the Gibbon River. The westslope cutthroats are swimming among the rocks, bushes, grass, and trees, and into Ice Lake. Amazing! There are plans to investigate this possibility in 2025.

Ice Lake fishes similarly to Grebe and Wolf, and it contains the same prolific aquatic insects. But my most effective tactic here is to fish size 14, black or olive Micro-buggers with either an intermediate or a floating fly line combined with a 9-foot 3X leader. (This also works well on Grebe and Wolf.) If I’m using the floating line, I add a BB size nontoxic split-shot to the leader about a foot above my streamer.

I then roll cast the rig into the drop-offs, and along the sunken trees that are clearly visible from shore. I count down to let the fly sink before I begin to strip. My initial cast is usually held for a five-second sink, and if nothing eats my streamer, I keep adding a few seconds before I begin stripping, until I catch fish. The grayling will sometimes take the fly while I’m counting down its descent, on the drop, but most often they eat when the fly is stripped. It’s vital to strip-strike by pulling on the fly line to set the hook rather than raising the rod tip, or you’ll miss the fish.

Upper Gibbon River

Upon Puchany’s request, the Yellowstone Fly Fishing Volunteer Program visited the Gibbon River in Virginia Meadows twice in 2024. During both outings, six anglers fished for approximately six hours. We caught exactly 62 fish each time, mostly westslopes, but approximately 9 percent of our fish were grayling. I implanted a single Floy tag alongside each fish’s dorsal fin during our first outing, but no fish were tagged during our second visit. Puchany had also been tagging fish in this section with her electrofishing crew.

After an initial tagging event occurs, there’s a mathematical equation (N=MC/R) to determine a fish population estimate during subsequent events by comparing the number of recaptured fish to those without tags. I’ll save you from the math lesson and just report our findings: The total estimated fish population in the Gibbon’s Virginia Meadows section, according to the YFFVP’s angling work, is 1,280 westslope cutthroat trout and grayling. This number is similar to estimates derived from the electrofishing-only events. That’s really cool, and it demonstrates one important way that fly fishing can contribute to the park’s fisheries data and help in effective conservation measures.

Fly fishing the upper Gibbon is not difficult. The fish are generally small, about 4 to 11 inches, though larger fish may be found around spawning time. But be aware that the park doesn’t open to fishing until late May—after the fish have spawned—to protect them. The adult fish seem to leave this area to spend most of their lives in the lower portions of the Gibbon, below Virginia Cascade, where they grow to much larger sizes. Fish can navigate downstream, through the cascade, but they are unable to swim back above it.

This creates a continuous supply of westslope cutthroats and Arctic grayling from the upper Gibbon, which filter downstream into the Madison River drainage, where they are also native. The upper Gibbon is nursery water, and the young fish greedily inhale most attractor-

style and terrestrial-imitating dry flies. Leader length and tippet size really don’t matter. The most important factor for hooking fish is using flies that are small enough to get into their mouths. Size 14 hooks will work, but size 16 and smaller drys are better choices. Some people may wonder why anglers would care to pursue small trout and grayling. But these fish are the wild, spawned-in-the-Gibbon, native descendants of Todd and Andi’s efforts. They are a beautiful illustration, by every definition, of a successful project.

Fisheries biologists are often accused of playing God when they attempt to correct the errors of the past by removing nonnative fish to secure a place for native species. But gods don’t make mistakes, so they don’t have to fix them. To recognize and repair an error, especially an error that you didn’t commit, isn’t god-like. It’s human, perhaps one of humanity’s finest traits.

Koel and Puchany’s work is a gift, both to Yellowstone’s imperiled native fish and to future generations of anglers who will now have the chance to catch them in the watersheds in which they belong. Andi told me, “People travel from all over the world to catch native fish in the park. Many birds and other animals rely on them for food. Native fish make the ecosystem whole.” So does the work of Yellowstone’s fisheries biologists. Native westslope cutthroat trout can now be found in 21 percent of their historic waters.

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Paul Weamer is the author of Favorite Flies for Yellowstone National Park (Stackpole Books, 2022) and Dry Fly Strategies (Stackpole Books, 2021). He is a program coordinator with the Institute on Ecosystems at Montana State University and runs the Yellowstone Fly Fishing Volunteer Program. His previous story for Fly Fisherman was “Science in the Thorofare: Researching Cutthroat Trout in the Most Remote Area of the Lower 48” in the Feb.-Mar. 2024 issue.

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