Yellowstone Cutthroat Trout

 

Yellowstone cutthroat trout—native to Yellowstone—are a keystone species that many species of birds and mammals rely on as an energy source.

NPS/Jay Fleming

 

Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri) are the most widespread native trout in the park and were the dominant fish species here prior to the early 1900s. They are an important species in Yellowstone National Park, upon which many other species depend. They provide an important source of food for an estimated 16 species of birds, and mammals including bears, river otters, and mink.

Genetically pure Yellowstone cutthroat trout (YCT) populations have declined throughout their natural range in the Intermountain West, succumbing to competition with and predation by nonnative fish species, a loss of genetic integrity through hybridization, habitat degradation, and angling harvest. Many of the remaining genetically pure YCT are found within the park. State and federal wildlife agencies classify YCT as a sensitive species. However, the US Fish and Wildlife Service concluded that YCT does not warrant listing as a threatened species under the Endangered Species Act.

 

Description

• Red slash along jaw and spots common to all cutthroat varieties.
• Body mostly yellow-brown with darker olive or gray hues on the back, lighter yellow on sides.
• Highly variable black spotting pattern, but few to no spots on the head.

Distribution

• Native to the Yellowstone River, Snake River, and Falls River drainages.
• Require cold, clean water in streams or lakes.

Behavior

• Spawn in rivers or streams in late April through mid-July.
• Most important foods are aquatic insects—mayflies, stoneflies, caddisflies, etc.—and other small aquatic animals, plus terrestrial insects that fall into the water. Leeches, amphipods, worms, and small aquatic invertebrates such as water fleas and copepods are important foods in Yellowstone Lake.
• Also eat smaller fish, fish eggs, small rodents, frogs, algae and other plants, and plankton.

 

Population

The Yellowstone cutthroat trout population in the Yellowstone Lake ecosystem was abundant in the early-1980s, when the average number of YCT caught at survey sites was more than 45 fish per 100 meters of net. Invasive lake trout caused a dramatic decline in YCT to only 20 fish per 100 meters of net in the early 2000s. NPS gillnetting has since reduced the predatory lake trout and allowed YCT abundance to increase. The average number of YCT caught at survey sites has been more than 30 fish per 100 meters during 2014 to 2022. Although YCT abundance is still below pre-lake trout levels, the fish are much greater in size. An adult YCT now weighs twice what one did in the past, probably because of reduced competition with others.

Two-thirds of the streams that were part of the species’ native habitat outside the Yellowstone Lake watershed still contain genetically pure YCT; in other streams, they have hybridized with rainbow trout.

 

History

Yellowstone Lake and the Yellowstone River together contain the largest inland population of cutthroat trout in the world. While the Yellowstone cutthroat trout is historically a Pacific drainage species, it has naturally traveled across the Continental Divide into the Atlantic drainage. One possible such passage in the Yellowstone area is Two Ocean Pass, south of the park in the Teton Wilderness.

The variety of habitats resulted in the evolution of various life history types among Yellowstone cutthroat trout. Some populations live and spawn within a single stream or river (fluvial), some live in a stream and move into a tributary to spawn (fluvial-adfluvial), some live in a lake and spawn in a tributary (lacustrine- adfluvial), and still others live in a lake and spawn in an outlet stream (allacustrine). Life history diversity within an ecosystem helps protect a population from being lost in a single extreme natural event.

Habitat remains pristine within Yellowstone National Park, but nonnative fish species pose a serious threat to native fish. In Yellowstone Lake, lake trout are a major predator of cutthroat trout. In other waters, brown, brook, and rainbow trout all compete with cutthroat trout for food and habitat. Rainbow trout pose the additional threat of hybridizing with cutthroat trout. Because of the lack of barriers in the lower reaches of most drainages, nonnative fish have been dispersing upstream and have replaced, or threaten to replace, cutthroat trout.

 

Duration:

7 minutes, 35 seconds

Journey through Yellowstone's aquatic ecosystems.

 

Cutthroat x Rainbow Trout Hybrids

In waters where rainbow trout have been introduced, there has been a serious degradation of the cutthroat trout population through interbreeding.

Presently, hybridized cutthroat trout exist throughout the Bechler, Falls, Gallatin, Gardner, and Lamar river drainages, and the Yellowstone River below the Upper Falls. Hybrids will have characteristics consistent with both species, often making identification difficult.

 

Restoration

The objectives of Yellowstone’s Native Fish Conservation Plan (2010) include recovery of YCT abundance in the lake to that documented in the late 1990s, maintaining access for spawning YCT in at least 45 of Yellowstone Lake’s 59 historical spawning tributaries, and maintaining or restoring genetically pure YCT in the current extent of streams occupied by pure or hybrid YCT.

Lamar River

Because no barriers to upstream fish migration exist in the mainstem Lamar River, descendants of rainbow trout stocked in the 1930s have spread to many locations across the watershed and hybridized with cutthroat trout. Genetic analysis indicates that cutthroat trout in the headwater reaches of the Lamar River remain genetically unaltered.

To protect the remaining Yellowstone cutthroat trout, the NPS has implemented a selective removal approach. A mandatory kill fishing regulation on all rainbow trout caught upstream of the Lamar River bridge was instituted in 2014. Currently regulations state that all nonnative fish and identifiable cutthroat x rainbow trout hybrids upstream of Knowles Falls must be killed. Selective removal by electrofishing has been conducted annually through the Lamar Valley since 2013. In 2019, 7% of fish sampled during electrofishing surveys upstream of the Lamar River Canyon were classified as rainbow or hybrid trout. This low percentage is a stark contrast to work conducted downstream of the Canyon.

In 2015, 136 fish were sampled downstream of the Lamar River bridge. Based on field identification, 48% were Yellowstone cutthroat trout, 19% were rainbow trout, and 31% were hybrids. The majority of these fish were tagged with radio transmitters or passive integrated transponder (PIT) tags as part of an ongoing research project to determine if Yellowstone cutthroat, rainbow, and hybrid trout are using the same areas to spawn and spawn timing and to inform management actions.

Slough Creek

In Slough Creek, rainbow-cutthroat trout hybrids have been found with increasing frequency over the past decade. Unlike the Lamar River, Slough Creek is smaller, and a barrier to upstream fish movement has been constructed. With a barrier in place and rainbow trout no longer allowed passage into the system, existing rainbow and hybrid trout can be effectively managed with angling and electrofishing removal.

Soda Butte Creek

Brook trout became established in Soda Butte Creek outside of the park boundary and spread downstream into park waters in the early 2000s. Initially, brook trout were isolated in headwater reaches by a chemical barrier created by mine contamination upstream of Cooke City, Montana. When the mine tailings were capped and water quality improved,, brook trout passed downstream and began to negatively impact the cutthroat trout.

For nearly two decades, interagency electrofishing surveys were enough to keep brook trout populations low, but did not prevent range expansion. Over time, brook trout spread downstream and became a threat to the Lamar River. In addition, rainbow trout hybridization continued to be identified in cutthroat trout upstream of Ice Box Canyon.

In 2013, Ice Box Falls was modified to be a complete barrier to upstream fish movement, preventing further rainbow trout introgression. Rotenone, a fish toxin, was then used to remove all nonnative fish from the system. Nearly 450 brook trout were removed during the chemical treatment in 2015. Only two brook trout were collected from Soda Butte Creek during a second treatment in 2016. From 2017 through 2021, eDNA sampling as well as electrofishing surveys found no evidence of brook trout in the system. This is a good indication that a complete kill was achieved in the drainage. However, in 2022, following historic flooding in the system, brook trout were discovered.

Electrofishing and eDNA surveys found brook trout from the Northeast Entrance downstream to the second road bridge within the park. NPS, USFS, and MTFWP fisheries biologists are working together to determine the extent and abundance of the population, where the brook trout may have come from, and the best actions to remove them from the system.

Elk Creek Complex

There is a natural cascade barrier in Elk Creek just upstream from its confluence with the Yellowstone River. The cascade prevented fish from naturally populating the system, so the Elk, Lost, and Yancey creeks complex of streams (Elk Creek Complex) was fishless when first stocked with cutthroat trout in the early 1920s. In 1942, the streams were stocked with brook trout, eventually resulting in the complete loss of cutthroat trout.

To restore YCT to the system, the Elk Creek Complex was treated with rotenone annually from 2012 to 2014 to remove the brook trout population. Once clear of brook trout, reintroduction of native Yellowstone cutthroat trout began. Antelope and Pebble creeks provided fish for restocking in October 2015. Additional stocking took place in 2016 and 2017. Natural reproduction was also documented in 2017 during electrofishing surveys. Semi-annual surveys of the Elk Creek Complex show that YCT are well established in the system and continue to naturally reproduce. No brook trout have been detected since the 2014 rotenone treatment.

 

Resources

Baril, L.M., D.W. Smith, T. Drummer, and T.M. Koel. 2013. Implications of cutthroat trout declines for breeding ospreys and bald eagles at Yellowstone Lake. Journal of Raptor Research 47(3): 234–245.

Bigelow, P.E., T.M. Koel, D. Mahony, B. Ertel, B. Rowdon, and S.T. Olliff. 2003. Protection of native Yellowstone cutthroat trout in Yellowstone Lake, Yellowstone National Park, Wyoming, Edited by US Department of the Interior, National Park Service. Fort Collins, CO: National Park Service, Water Resources Division.

Gresswell, R.E. and J.D. Varley. 1988. Effects of a century of human influence on the cutthroat trout of Yellowstone Lake. In R.E. Gresswell, ed., Status and management of interior stocks of cutthroat trout, 45–52. Vol. Symposium 4. American Fisheries Society.

Gresswell, R.E., W.J. Liss, and G.L. Larson. 1994. Lifehistory organization of Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri) in Yellowstone Lake. Canadian Journal of Fisheries and Aquatic Sciences 51(S1):298–309.

Gresswell, R.E. 1995. Yellowstone cutthroat trout. In M. K. Young, ed., Conservation assessment for inland cutthroat trout, 36–54. Fort Collins, CO: US Forest Service, Rocky Mountain Forest and Range Experiment Station.

Heckmann, R. 1994. Cutthroats and parasites: Yellowstone Lake’s complex community of fish and companion organisms. Yellowstone Science 2(3).

Kerkvliet, J., C. Nowell, and S. Lowe. The economic value of a predator: Yellowstone trout. In A. P. Curlee, A. Gillesberg and D. Casey, ed., Greater Yellowstone predators: Ecology and conservation in a changing landscape: Proceedings of the third biennial conference on the Greater Yellowstone Ecosystem, 143–150. Yellowstone National Park, WY: Northern Rockies Conservation Cooperative and Yellowstone National Park.

Koel, T.M., P.E. Bigelow, P.D. Doepke, B.D. Ertel, and D.L. Mahony. 2005. Nonnative lake trout result in Yellowstone cutthroat trout decline and impacts to bears and anglers. Fisheries 30(11):10–19.

Koel, T.M., P.E. Bigelow, P.D. Doepke, B.D. Ertel, and D.L. Mahoney. 2006. Conserving Yellowstone cutthroat trout for the future of the Greater Yellowstone Ecosystem: Yellowstone’s Aquatic Sciences Program. Yellowstone Science 14(2).

Koel, T.M., D.L. Mahony, K.L. Kinnan, C. Rasmussen, C.J. Hudson, S. Murcia, and B.L. Kerans. 2006. Myxobolus cerebralis in native cutthroat trout of the Yellowstone Lake ecosystem. Journal of Aquatic Animal Health 18(3):157–175.

May, B.E., W. Urie, and B.B. Shepard. 2003. Range-wide status of Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri): 2001, Edited by US Forest Service, Montana Fish, Wildlife and Parks, Montana Cooperative Fishery Research Unit. Bozeman, MT.

National Park Service, Yellowstone National Park. 2010. Native Fish Conservation Plan / Environmental Assessment, Edited by Department of the Interior. Yellowstone Center for Resources.

Reinhart, D.P., S.T. Olliff, and K.A. Gunther. Managing bears and developments on cutthroat spawning streams in Yellowstone National Park. In A.P. Curlee, A. Gillesberg and D. Casey, ed., Greater Yellowstone predators: Ecology and conservation in a changing landscape: Proceedings of the third biennial conference on the Greater Yellowstone Ecosystem, 161–169. Yellowstone National Park, WY: Northern Rockies Conservation Cooperative and Yellowstone National Park.

Varley, J.D. and P. Schullery. 1995. The Yellowstone Lake crisis: Confronting a lake trout invasion: a report to the director of the National Park Service. Yellowstone National Park, WY: National Park Service, Yellowstone Center for Resources.

Yellowstone Center for Resources. 2009. Yellowstone cutthroat trout: Conserving a heritage population in Yellowstone Lake, YCR-2009-02. Mammoth Hot Springs, WY: National Park Service.