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UPDATED: Invasive Smallmouth Bass Caught in Gardner River

The fish was landed just outside Yellowstone's boundary and is the furthest upstream in the Yellowstone River drainage that the species has ever been recorded.

UPDATED: Invasive Smallmouth Bass Caught in Gardner River

A smallmouth bass caught from the upper Yellowstone River drainage in 2020. The fish was harvested. (Photo courtesy of Brady Hughes)

UPDATED, 4-19-22: A mandatory catch, kill, and report regulation was adopted by the Montana FWP Fish & Game Commission for all smallmouth bass in the Yellowstone River from the Yellowstone National Park boundary to Springdale, using Montana’s Unauthorized Placement of Fish rule. This means that FWP believes the fish was illegally planted around the location it was landed, citing the distance from the previous upstream high-mark some 20 rivers miles upstream, and also that no environmental smallmouth bass DNA was found in the Yellowstone River between Emigrant and the Yellowstone Park boundary. The regulation is effective immediately. 

The commission also voted to amend the Shields River (a Yellowstone River tributary between Livingston and Springdale) mandatory catch, kill, and report regulation to include the entire river.

An angler caught and released a smallmouth bass from the mouth of the Gardner River, a Yellowstone River tributary, just outside of Yellowstone National Park’s boundary on February 19, according to an e-mail from Todd Koel, a Yellowstone Park supervisory fisheries biologist and the Park’s Native Fish Conservation Program Leader. The catch marks the furthest upstream that smallmouth bass have ever been found in the Yellowstone River drainage. Smallmouth bass (Micropterus dolomieu) typically require warmer water than the coldwater trout that are native to the area. 

The catch is a potential harbinger for the Park’s fisheries as the climate continues to warm and coldwater fisheries cease being suitable habitat for coldwater fish species such as trout and whitefish.

Koel said in the e-mail to local fisheries managers that the situation is a potential “nightmare” as smallmouth bass could potentially reach the Lamar River system, which is a true native cutthroat trout stronghold. 

"Smallmouth bass are an invasive predatory species that will threaten our wild and native trout populations if they become established in the upper Yellowstone River," Koel said in a statement. "Since anglers are highly effective at suppressing invasive fish in waters where they coexist with native species such as cutthroat trout, they will be required to kill and report any smallmouth bass caught in Yellowstone National Park when the fishing season opens Memorial Day weekend. Additionally, Yellowstone National Park and USGS biologists will be sampling the Gardner and Yellowstone rivers, upstream of where the invasive smallmouth bass was caught. Over the next few weeks, biologists will monitor these rivers closely to gauge the possible extent of the invasion. Our goal is to protect native fish populations and natural ecosystems. We will do everything in our power to prevent the establishment of smallmouth bass in the park and prevent them from preying on and displacing trout and other native fish.”

Smallmouth bass are a valuable and sporting gamefish in certain ecosystems, but are very dangerous to important cutthroat trout bastions like Yellowstone Park.

Potential Impacts on Yellowstone National Park Fisheries

It’s more bad news for Yellowstone fisheries, which have had their share of hardships over the past couple of decades. Lake trout have decimated one of the Yellowstone cutthroat’s last strongholds – Yellowstone Lake. Non-native ciscoes, a favorite forage fish of lake trout, were also recently found the massive high-country lake, likely the result of "bucket biology."

Knowles Falls on the Yellowstone River upstream of the Gardner acts as fish barrier that prevents non-native brown and rainbow trout from accessing the Lamar River drainage, keeping the cutthroat trout there relatively pure-strain (though rainbows from other Lamar tributaries have infiltrated in recent years). Koel, however, believes that these bass are likely to pass beyond Knowles Falls, which is more of a rocky cascade than a full-fledged waterfall. Smallmouth bass are different animals than trout, he said. 

“These guys are made to jump,” Koel said. “They’re incredibly athletic fish."

That, coupled with low- or high-water events that could affect the passibility of the falls, heightens the concerns that the bass could spread higher into the drainage. The Park Service has enhanced waterfalls in the past to act as more effective fish barriers (on Grayling Creek and on Soda Butte Creek) and will look into doing so at Knowles Falls on the Yellowstone as well, according to Koel.

The Lamar system has some of the Park’s coldest water which is not ideal for smallmouth, but there are thermal refuges created by hot-springs, geysers, and other geothermal features in the drainage that create “microhabitats” where the bass could take up residence. And average water temps are on the rise throughout the West, including in the Lamar watershed.


Subsequent testing of water samples from the Gardner River were negative for smallmouth bass DNA, which means there is not currently a reproducing population within Park boundaries (though an individual bass or two could easily move into the Gardner). 

Smallmouth bass and trout can coexist, but often as the result of supplemental trout stocking (which does not occur in Yellowstone or on Montana's rivers). Any reduction in Yellowstone's fragile native cutthroat trout population would be significant since Yellowstone cutthroat (Oncorhynchus clarkii bouvieri) have been reduced to about 5 percent of their original native range. Yellowstone fisheries managers have prioritized native fish for many years. 

And there are examples of smallmouth bass obliterating coldwater salmonid fisheries. The chinook salmon population in Oregon's Coquille River, for example, has fallen 99 percent in the ten years since smallmouth bass were first discovered there, according to an Oregon public radio story.

Yellowstone’s fishing season is currently closed, but a small section of the lower Gardner River around its mouth flows just outside of the Park’s boundary in Montana, where the fish was landed.

Smallmouth Bass in the Yellowstone River

Anglers have reported catching smallies in the upper Yellowstone River watershed as far south as what's known as the Fridley Channel just south of Emigrant, Montana, but the location where this bass was caught is approximately 20 river miles upstream of that previous high mark. Until a few years ago, these bass were believed to be relegated to the lower parts of the river, some 130 river miles downstream of Paradise Valley around Billings, where it transitions to a warm-water fishery. 

According to a Montana Fish Wildlife and Parks (FWP) news release: "Anglers have previously reported finding smallmouth bass in two locations on the upper Yellowstone River in the past seven years: Two smallmouth bass were caught at the Highway 89 bridge downstream of Livingston, and one near Emigrant ... FWP fisheries staff have not found smallmouth bass during yearly sampling efforts in the upper Yellowstone River."

The timing is particularly concerning since it was in the coldest part of the year. The water temperature in the Gardner should have been well below what smallies tolerate. A USGS streamflow gauge nearby on the Yellowstone River indicated that the temperature peaked at about 40 degrees on February 19 (and had been as low as 33 at times that month), making the find particularly puzzling since smallmouth bass typically do not live in water colder than 40 degrees.

Smallmouth Bass Caught in Gardner River
An angler fishes at the mouth of the Gardner River where it enters the Yellowstone River. The bass might have taken refuge here in the winter due to the warmer thermal-spring-influenced water of the Gardner. (Joshua Bergan photo)

"It is a concerning discovery," Morgan Jacobsen, spokesperson for FWP said. "There's a lot of things that we don't know at this point–one of those components is how this bass arrived at this location."

Montana FWP is reportedly preparing emergency regulations to address this discovery, which would have to go through the Fish and Wildlife Commission approval process. It would not be unprecedented to implement a mandatory-kill rule for smallmouth on the Yellowstone as this was done on the Shields River, a Yellowstone tributary, after a smallmouth bass was landed there in 2020. 

"In the mean time, we are asking anglers, if they catch smallmouth bass in the upper Yellowstone River, to remove them and document where they caught them, then provide those fish to Fish Wildlife and Parks so we can test them," Jacobsen said.

Smallmouth bass were stocked by FWP in the lower Yellowstone, Tongue, and Bighorn rivers (the latter two are tributaries to the lower Yellowstone) as recently as 1992.

Rick Wollum, a board member of the Joe Brooks Chapter of Trout Unlimited, instructor for Guiding for the Future, and the Retail Manager at Angler’s West Fly Shop in Emigrant, has fished the Yellowstone River for nearly 40 years and is quite concerned about smallmouth bass in the river.

“I am surprised (to hear that a smallmouth was caught that high in the system),” Wollum said. “To catch that fish on February 19 is pretty alarming.”

The influx of smallmouth bass, along with the proliferative kidney disease outbreak on mountain whitefish in 2016 and drastically increasing boat and river traffic could ultimately have extremely negative impacts on the river and valley. Wollum and others are doing their best to keep what’s happened on the upper Madison River, some 40 miles to the west, from happening in Paradise Valley.

“We’re doing a lot of work this summer on signage because we do see the impact of increased traffic,” Wollum said. “We’re pretty serious about doing everything we can to keep the Yellowstone pristine.”

Anglers are encouraged to harvest any smallmouth bass they catch in the upper Yellowstone River drainage, prior to any formal regulation mandating it. 

“Anglers are an amazing suppression tool,” Koel said. “We’ve done a lot in the Lamar to control rainbows and hybrids (cuttbow trout) with maintaining low prevalence of rainbow DNA up there.”

Problems Beyond the Trout

Loss of Yellowstone cutthroat trout is not the sole concern. This would be the only fish species in the Park whose diet includes birds, mammals (beyond mice), and reptiles. The greater ecosystem would be put at risk, beyond the lack of cutthroat as a food source for other animals.

Potential economic impacts would also likely accompany the decimation of the Yellowstone cutthroat fishery. This species of fish can only be caught in the Yellowstone River drainage and anglers come from all over the world to do so. Smallmouth bass are much more abundant and are available nationwide. Fishing is a nearly $1 billion industry in Montana. 

Joshua Bergan is Fly Fisherman's digital editor and author of the Flyfisher's Guide to Southwest Montana's Mountain Lakes.

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