Yellowstone Cutthroat Trout
Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri) are the most widespread native trout of the park and were the dominant fish species here prior to Euroamerican settlement. 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 20 species of birds, and mammals including bears, river otters, and mink.
Genetically pure Yellowstone cutthroat trout 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, predation, and angling harvest. Many of the remaining genetically pure Yellowstone cutthroat trout are found within the park. State and federal wildlife agencies classify Yellowstone cutthroat trout as a sensitive species. However, the US Fish and Wildlife Service does not warrant listing the Yellowstone cutthroat trout as a threatened species under the Endangered Species Act.
The Yellowstone cutthroat trout population in the Yellowstone Lake ecosystem has declined substantially since the mid-1980s. Lake-wide sampling began in 1968 and in 1984 the average number of Yellowstone cutthroat trout caught at survey sites reached a high of 19.1 per net.
Monitoring at Clear Creek, a Yellowstone Lake tributary, began in 1945. The number of Yellowstone cutthroat trout spawning there peaked at more than 70,000 in 1978 and fell to 538 by 2007. The decline is attributed to predation by nonnative lake trout, low water during drought years, and the nonnative parasite that causes whirling disease.
Two-thirds of the park streams that were part of the species’ native habitat outside the Yellowstone Lake watershed still contain genetically pure Yellowstone cutthroat trout; other streams have Yellowstone cutthroat trout hybridized with introduced rainbow trout.
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), and still others live in a lake and spawn in a tributary (lacustrine-adfluvial). 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. Brown, brook, and rainbow trout all compete with cutthroat trout for food and habitat. Rainbow trout also pose the additional threat of crossbreeding with cutthroat trout. Because of the lack of barriers in the lower reaches of the drainage, non-native fish have been dispersing upstream and have replaced, or threaten to replace, cutthroat trout.
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 59 Yellowstone Lake’s historical spawning tributaries, and maintaining or restoring genetically pure YCT in the current extent of streams occupied by pure or hybrid YCT.
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 and Slough Creek 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. Selective removal by electrofishing has been conducted annually through the Lamar Valley since 2013. To date, just 18 rainbow trout and hybrids have been removed from that area.
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 identify trout spawning locations.
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, a seasonal barrier exists, and a site has been identified to construct a complete barrier to upstream fish movement. 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 in the 1980s and spread downstream into park waters Initially, brook trout were isolated in headwater reaches by a chemical barrier created from the McClaren Mine tailings along the river upstream of Cooke City, Montana. When the tailings were removed, brook trout passed downstream and began to negatively impact the cutthroat trout. Mitigation of brook trout by annual interagency electrofishing surveys began in the 1990s, shortly after they were discovered. To date, no brook trout have been found in Soda Butte Creek downstream of Ice Box Falls.
For nearly two decades the interagency efforts were enough to prevent the brook trout from expanding in abundance but not in range. 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 Falls. It was determined that to entirely eliminate the threat of nonnative fish, the falls would need modification to be a complete barrier to upstream passage and a rotenone treatment of the entire system upstream of the falls would be necessary.
In 2013 Ice Box Falls was modified to be a complete barrier to upstream fish movement. 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 rotenone treatment in 2016. This is a good indication that a complete kill was achieved in the drainage. Monitoring will continue in 2017.
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, resulting in the complete loss of cutthroat trout.
The Elk Creek Complex was treated with rotenone annually from 2012 to 2014. Low numbers of brook trout remained in the system until 2015. Antelope Creek is the source of fish for stocking the Elk Creek Complex. Reintroduction of genetically pure Yellowstone cutthroat trout began in October 2015. Additional stocking took place in 2016.
Mottled sculpin live in shallow, cold water throughout Yellowstone except the Yellowstone River above Lower Falls and in Yellowstone Lake.
Yellowstone’s minnows are small fish living in a variety of habitats and eating a variety of foods.
Suckers are bottom-dwelling fish that use ridges on their jaws to scrape flora and fauna from rocks.
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