Yellowstone’s wild trout populations still healthy after flooding
Yellowstone National Park and surrounding areas experienced record flooding in June. The once-in-a-thousand-year flood wreaked havoc on much of the park’s North Loop as the Yellowstone River reached historic levels, damaging roads and destroying bridges on its way through Paradise Valley and in front of the town of Livingston. Soda Butte Creek, the Lamar River and other iconic trout streams in the park also overshot their banks, causing some anglers to worry about the potential effects on wild trout populations.
Some two months later, the road connecting the north and northeast entrances to the park remains closed to private vehicles. Visitor numbers to Yellowstone are still down, and the National Park Service continues to assess the damage. But as the rivers tumbled in late summer, NPS workers can say with confidence that the June floods caused no long-term harm to native trout and grayling populations inside the Park.
Read more: Watch: Historic flood hits Yellowstone, spurs national park evacuation
According to Tood Koel, the park’s chief fisheries biologist, the only damage occurred on Slough Creek, a famous tributary of the Lamar River. And even then, he explains, the damage was minimal.
“We were very lucky,” says Koel. “The rain and flooding was very localized, so most of our projects were unaffected.”
Use natural and man-made barriers to separate natives from non-natives
For at least the past decade, the National Park Service has worked to restore and protect populations of Yellowstone cutthroat trout within park boundaries. They have also focused on restoring westslope cutthroat trout and arctic grayling, which are native to the park’s streams that form the upper reaches of the Missouri River.
The Yellowstone shadow is unique because it represents the southernmost native population in North America. Although these fish are rare today, they were so common in the Madison and Gallatin rivers when the park was first designated that early anglers believed their populations would never be depleted. About two decades after the first non-native trout were introduced to these rivers, all of the grayling was gone.
As part of the long-term effort to return grayling and cutthroat trout to their native waters, Koel’s team has installed artificial fish barriers throughout the park. One of these barriers is located at the lower end of Slough Creek, and it was placed there to prevent rainbow trout from encroaching upstream into the creek’s signature meadows. (Rainbows and Cutthroats can mingle on spawning nests, and the result is a fertile hybrid known as a “cutbow”.)
Koel says the main barrier held during the intense flooding that began June 12, but a diversion channel near the lower end of Slough Creek failed. Fortunately, Koel doesn’t believe that failure caused any rainbows to move upstream.
“There is still a very large barrier above this channel,” Koel said. “So the chances of anything coming up the creek were slim.”
Further south in the Gibbon River watershed, Koel’s team relies on two impassable natural barriers to keep non-native rainbow, speckled and brown trout from mixing with native species in the course. Upper Gibbon. These natural barriers are known as Little Gibbon Falls and Virginia Cascade.
While non-native trout have not been stocked in the park since 1958, the upper Gibbon above the falls has already been invaded by brook trout, which were first introduced in the late 1960s. 1800. Through a long and difficult process that involved the removal of all non-native trout and the repopulation of the natives, the upper course of the river is now the exclusive home of the west slope and grayling cutties. And due to the significant natural barriers that exist on the Gibbon, the June floods had no impact on this project.
As for the other major barriers in the national park, Koel says two other projects in the upper Missouri watershed were at issue when the flooding began. Specimen Creek, a tributary of the Gallatin River, now supports a reintroduced population of westslope cutthroat trout. These fish thrive above an artificial barrier several miles above the creek’s confluence with the Gallatin, and Koel says he was relieved to find that barrier still intact after the deluge.
He was equally relieved when he discovered that a barrier on Grayling Creek – which empties into the Madison shortly before it reaches Hebgen Lake – also survived the flood event. Above this barrier, the stream is still only home to cutthroat trout and grayling.
Net lake trout and make progress
The park’s most ambitious native trout restoration effort has taken place on Yellowstone Lake, which is the park’s largest lake. In the mid-2000s, biologists estimated that 90% of Yellowstone’s cutthroat trout of spawning age were extirpated by smuggling lake trout. This sowing probably took place around 1990.
These lake trout, native to the Great Lakes, literally ate the cutthroats out of the house and out of the house. The National Park Service and a host of conservation groups, including Yellowstone Forever, The Greater Yellowstone Coalition and local chapters of Trout Unlimited, have raised money to pay for lake trout filleting since the late 2000s. And this effort is laborious. For years, the Park Service has contracted with commercial gillnetters to remove hundreds of thousands of giant lake trout. Each year the gillnetters caught more and more lake trout, but the average size of the lakers kept decreasing.
This effort is now bearing fruit.
“We see the tracks that we saw before the lake trout took over,” Koel says of the cutthroat spawning migrations in the lake’s tributaries, particularly the upper reaches of the Yellowstone River that runs through the remote area of Thorofare, Wyoming. “There are giant cutthroats up there in the spring. It’s so good to see the effort working.
Today, the commercial gillnetters have disappeared, but the elimination of lakers continues. Using telemetry equipment and strategically placing gillnets throughout the lake, the park’s lake trout removal team managed to catch an estimated 300,000 sexually immature lake trout during 2021. Efforts are still ongoing. course this summer and will last until October.
“It really helps,” Koel says. “The lake is returning to balance and the future looks bright.”
The laker gillnet fishery will continue, but the future of the lake’s native cutthroats depends on a steady stream of funding to continue these removal efforts. And there is no guarantee that the funding will last forever.
Overall, however, Yellowstone’s native fish populations remain healthy, and the flood’s minor impact on the park’s fisheries restoration efforts amounts to a dodged bullet. As for Koel and his team?
“We’re full steam ahead,” he said. “We still have work to do, but we keep making progress.”
Chris Hunt is an award-winning journalist and the author of “Catching Yellowstone’s Wild Trout: A History and Guide to Fly Fishing.”