Yellowstone’s Own Trout

The Yellowstone Cutthroat Trout (Oncorhynchus clarkii bouvieri), is the native trout of the Yellowstone River drainage of northwest Wyoming and southwest/south-central Montana. The YCT is one of nine or more subspecies of cutthroat trout native to the interior western United States. Other species include the Bonneville, Colorado River, Greenback, Lahontan, Paiute, Rio Grande and Westslope Cutthroat. 

The trout’s common name refers to the bright “cut-throat” orange-red slash beneath the jaws of the fish. The YCT commonly exhibits bright yellow, orange, and red colors and is generally distinguishable from other inland subspecies of cutthroat trout by the particular pattern of black spots that appear on the body. Its golden coloration and larger, more widely distributed spots distinguish it from the Westslope Cutthroat Trout (Oncorhynchus clarkii lewisi), the other native cutthroat subspecies in Montana and Yellowstone National Park. The scientific name of cutthroat honors Captain William Clark and the Westslope subspecies honors both Clark and Captain Merriweather Lewis, who first described the species during the Corps of Discovery expedition in 1805.

The fish measures from 6-20 inches in overall length, reaching maturity at 4-5 years of age. Spawning occurs in the Spring, between March and July, primarily in smaller tributary streams (like Big Creek) when water temperatures rise above 50°F. Fertilized YCT eggs are deposited in stream gravels where they incubate for several weeks, the actual period of time dependent upon water temperature. Several days after hatching from the egg, when about one inch long, the fry emerge from the gravel and disperse into the stream. The fry may grow to maturity in the spawning stream or they may move downstream and mature in larger rivers or lakes. YCT feed primarily on macroinvertebrates, particularly immature and mature forms of aquatic insects, terrestrial insects, and, in lakes, zooplankton. YCT are rarely pisciverous (habitually feeding on other fishes). Populations living their whole life in small tributary streams rarely live more than 3-5 years or attain a length of more than 9-10”. In Yellowstone Lake, cutthroat trout can reach eight or nine years of age and can grow to a length of about 21” and a weight of four pounds.

Other Gamefish Species

Anglers fishing Big Creek and the Yellowstone River will likely encounter four other salmonids, depending on the type of water fished: Brown, Rainbow, and Brook trout (all introduced trout species) and the Mountain whitefish.

Brown Trout (Salmo trutta) was introduced from northern Europe in the late 1700s (hence its common name “German brown”), and today it is considered the most valuable non-native fish in North America. The species name trutta is Latin for trout. It is a favored fish for stocking due to its higher tolerance for warmer waters than either brook or rainbow trout. In Big Creek, brown trout average 7-14 inches in total length, but can approach and exceed 20 inches. Breeding occurs in the fall and breeding males develop a long, hooked jaw and tend to brighten in overall coloration.

Rainbow Trout (Oncorhynchus mykiss) are members of the Pacific trout and salmon subgroup of the Salmonidae, which also includes the cutthroat trout. Originally native to the Pacific Northwest, the rainbow is the most widely introduced salmonid in the world (including the southern hemisphere where there were no native salmonids historically), and one of the top five most sought game fish in North America. The genus, Oncorhynchus, means "hooked snout" in reference to the distinctly hooked upper or lower jaw of mature males. The species name, mykiss, is vernacular from the Russian far east where the species was first described in the late 1700s. Rainbow trout prefer colder, highly oxygenated, fast-moving water. In Big Creek, fish typically range from 7-12 inches in total length with larger individuals in the 16-19-inch range. Rainbow trout breed in the spring.

Brook Trout (Salvelinus fontinalis), top image, a char native to eastern North American, frequents the upper headwaters of Big Creek and other tributaries, while Mountain Whitefish  (Prosopium williamsoni), bottom image, a species of whitefish native to the region, prefer the quieter and deeper waters of the Yellowstone River.

Conservation of Yellowstone Cutthroat

Yellowstone Cutthroat Trout are a Montana Fish of Special Concern, as much of their spawning habitat in tributaries of the upper Yellowstone River has been lost to irrigation withdrawals which de-water the streams before spawning and egg-incubation are completed in July and August. Mountain Sky Guest Ranch and neighboring Big Creek Ranch leases a portion of their water right on an annual basis to the State of Montana so help maintain optimal spawning and rearing habitat in Big Creek. In Yellowstone National Park, all cutthroat trout caught by anglers are to be released unharmed immediately. 

The YCT has been largely replaced throughout much of its historical range by introduced brown, rainbow, and brook trout. The notable exception is the Yellowstone River upstream of the Lower and Upper Falls in Yellowstone National Park. Here the YCT remain the dominant trout species and largely genetically pure due to the isolation provided by the falls, at least for the present. However, whirling disease and lake trout are two additional stressors.

Impacts from non-native trout takes two principle forms: competition and hybridization. Brown, brook, and rainbow trout can often outcompete YCT for available food and habitat, generally displacing YCT over time and space. The presence of lake trout (Salvelinus namaycush) in Yellowstone National Park is the result of the intentional stocking of the historically-fishless Lewis and Shoshone lakes in 1890. In the mid-1980s (or earlier, the actual timing is debated) lake trout were illegally dumped from Lewis Lake or elsewhere into Yellowstone Lake where, as top-level predators, they consume YCT. In the presence of lake trout, YCT declined significantly through 1990-2013, until lake trout control efforts begin to allow YCT population to rebuild.

Historical Footnote. Lake trout, once abundant throughout the Upper Great Lakes, were extirpated from much of their original range by the mid-20th century due to a combination of  factors including overfishing, predation by parasitic sea lamprey, and poor water quality.  In response, the U.S. Fish and Wildlife Service, Great Lakes states and tribes, and Canada worked to restore self-sustaining populations through stocking and other restoration activities. The principal source for genetically-similar lake trout used in the Great Lakes restocking effort was…. Lewis Lake in Yellowstone National Park, which were intentionally stocked with lake trout in 1889.

The rainbow also readily hybridizes with YCT, threatening to genetically swamp the YCT over time. In some environments, such as Henry’s Lake, at the headwaters of the Henry’s Fork of the Snake River, native cutthroat trout appear to have resisted replacement and hybridization. After some 100 years of coexistence between introduced rainbow trout and native cutthroat trout in the Yellowstone River downstream from Yellowstone National Park, however, the two species are in danger of melding into a single hybrid population.

Whirling disease has been documented to have caused major declines in Pelican Creek and downstream of Fishing Bridge in Yellowstone National Park.  Whirling disease is a parasitic infection caused by the non-native microscopic parasite, Myxobolus cerebralis. Its common name comes from the characteristic swimming behavior that results from the disease. Affected fish suffer reduced mobility and fertility, posing a risk to population health. It attacks juvenile trout and salmon. 

  

Fishing Big Creek

Much of Big Creek, immediately upstream of the Upper Ranch, runs through the Gallatin National Forest; the stretch downstream of the Hyalite Creek turn-off and the Sunnybrook Bridge is a Montana Fish Access Site. The remainder of the Big Creek is on Mountain Sky Guest Ranch. As it is a privilege to be able to fish Big Creek, Mountain Sky staff are requested to adhere to the following guidelines:

1.      All anglers must carry a valid Montana fishing license

2.      Fish barbless, it’s easier to take out of the fish and anglers alike. It also gives you a slightly better chance to retrieve from snags. To de-barb a hook, take a pair of hemostats and crimp the barb against the hook shaft.

3.      Carry a pair of hemostats to aid in hook recovery and de-barbing.

4.      Play all fish gently, but firmly, bringing to net as quickly as possible.

5.      Use a fine-mesh net and keep fish in water at all times (try to avoid lifting fish out of water).

6.      If taking a photo, get set up first (sunglasses off, facing light, hat brim lifted, etc.) before picking up the fish (wet hands, keep low to water, don’t squeeze).

7.      On release, face fish upstream in net, allowing them the choice to rest or swim off.

8.      If you hook a fish deeply and cannot easily remove with hemostats, cut tippet as close to hook as possible and release fish.

Montana fishing regulations require all cutthroat trout be released immediately. Anglers are allowed a daily limit of five “combined” trout (rainbow, brown) daily and in possession, of which only one may be over 18 inches in overall length. Mountain Sky staff are requested to practice catch and release, as a courtesy to our guests and overall fish conservation.

Reference: Trout and Salmon of North America, 2002, Robert Behnke. Illustrations by Joe Tomelleri.