The Westslope cutthroat trout (Oncorhynchus lewisi)Page, Lawrence M.; Bemis, Katherine E.; Espinosa-Pérez, Héctor S.; Findley, Lloyd T.; Gilbert, Carter R.; Hartel, Karsten E.; Lea, Robert N.; Mandrak, Nicholas E.; Neighbors, Margaret A. (2023). Common and scientific names of fishes from the United States, Canada, and Mexico. Special publication (Eighth ed.). Bethesda: American Fisheries Society. . is a freshwater salmonid in the cutthroat trout complex. The nominate subspecies, also known as the Missouri River cutthroat trout, is Oncorhynchus lewisi lewisi. The Westslope cutthroat trout is the Montana state fish.1-1-507. State fish , Montana Code, accessed 23 April 2009. The Westslope cutthroat trout is a species of concern in Montana and British Columbia ranges and is considered threatened in its native range in Alberta.
Taxonomy The scientific name of the Westslope cutthroat trout is Oncorhynchus lewisi,Trotter, P., P. Bisson, B. Roper, L. Schultz, C. Ferraris, G.R. Smith and R.F. Stearley. 2018. A special workshop on the taxonomy and evolutionary biology of cutthroat trout. Pages 1–31 in Trotter P, Bisson P, Schultz L, Roper B (editors). Cutthroat Trout: Evolutionary Biology and Taxonomy. Special Publication 36, American Fisheries Society, Bethesda, Maryland.Love Stowell; Metcalf; Markle; Stearly (2018), Trotter; Bisson; Shultz; Roper (eds.), "Species Conceptualization and Delimitation: A Framework for the Taxonomic Revision of Cutthroat Trout", Cutthroat Trout: Evolutionary Biology and Taxonomy, American Fisheries Society, , , retrieved 2024-08-13 as it was first described in the journals of explorer William Clark from specimens obtained during the Lewis and Clark Expedition from the Missouri River near Great Falls, Montana. Cutthroat trout were given the name Salmo clarki in honor of William Clark, who co-led the expedition of 1804–1806. One of Lewis and Clark's missions was to describe the flora and fauna encountered during the expedition. The type specimen of S. clarki was described by naturalist John Richardson in 1836 from a tributary of the lower Columbia River, identified as the "Katpootl", which was perhaps the Lewis River as there was a Multnomah village of similar name at the confluence. This type specimen was most likely the coastal cutthroat subspecies. In 1853, naturalist George Suckley while working for the Pacific Railroad Survey led by Isaac Stevens collected specimens of Westslope cutthroat trout by fly fishing below the Great Falls on the Missouri River. In 1856, he described the trout as Salar lewisi to honor explorer Meriwether Lewis. In David Starr Jordan and Barton Warren Evermann's A Check-list of the Fishes and Fishlike Vertebrates of North and Middle America (1896), the name Salmo mykiss lewisi was given to Yellowstone trout or cut-throat trout and included a reference to specimens collected from the Missouri River by George Suckley. In 1898, Jordan and Evermann changed the name of cutthroat trout to Salmo clarki. Salmo clarki lewisi persisted as the subspecies name for both the Yellowstone cutthroat and Westslope cutthroat trout until 1971 when fisheries biologist Robert J. Behnke gave the name Salmo clarki bouvieri to the Yellowstone cutthroat with Salmo clarki lewisi reserved for the Westslope cutthroat trout.
In 1989, morphological and genetic studies indicated trout of the Pacific basin were genetically closer to Pacific salmon (Oncorhynchus species) than to the Salmos–brown trout (S. trutta) or Atlantic salmon (S. salar) of the Atlantic basin. Thus, in 1989, taxonomic authorities moved the rainbow, cutthroat and other Pacific basin trout into the genus Oncorhynchus.
This single species (O. clarkii) classification is now changed.Schultz; Thompson; Cathcart; Williams (2018), Trotter; Bisson; Shultz; Roper (eds.), "Where the Rubber Meets the Road: Further Research Needs and Implications for Cutthroat Trout Management", Cutthroat Trout: Evolutionary Biology and Taxonomy, American Fisheries Society, , , retrieved 2024-08-21 Genetic, taxonomic, and geologic studiesLink; Keeley (2018), Trotter; Bisson; Shultz; Roper (eds.), "Geologic Constraints on Snake-Columbia River Drainage Changes and the Associated Evolutionary Diversification of Cutthroat Trout over the Past 17 Million Years", Cutthroat Trout: Evolutionary Biology and Taxonomy, American Fisheries Society, , , retrieved 2024-08-13Smith; Stearly (2018), Trotter; Bisson; Shultz; Roper (eds.), "The Fossil Record of Cutthroat Trout: Implications for Evolution and Conservation", Cutthroat Trout: Evolutionary Biology and Taxonomy, American Fisheries Society, have determined that cutthroat trout should be divided into four distinct species, with each having multiple subspecies corresponding to the evolutionary lineagesThorgaard; Brunelli; Smith; Johnson (2018), Trotter; Bisson; Shultz; Roper (eds.), "Y Chromosome Marker Evolution in Cutthroat Trout", Cutthroat Trout: Evolutionary Biology and Taxonomy, American Fisheries Society, , , retrieved 2024-08-13 found within major river basins, except for the Coastal cutthroat trout.Shiozawa, D. K., R. P. Evans, D. D. Houston, and P. J. Unmack. 2018. Geographic variation, isolation, and evolution of Cutthroat Trout with comments on future directions for management and research. Pages 129–172 in P. Trotter, P. Bisson, L. Schultz, and B. Roper, editors. Cutthroat Trout: evolutionary biology and taxonomy. American Fisheries Society, Special Publication 36, Bethesda, Maryland.
Subspecies Common nameScientific nameRangeImageMissouri River cutthroat troutO. lewisi lewisiNative to the Missouri River drainage from the Judith River upstream to the headwaters. Captain Meriwether Lewis of the Lewis and Clark Expedition described trout caught near the Great Falls of the Missouri River in Montana on June 13th, 1805.Trotter, P., P. Bisson, B. Roper, L. Schultz, C. Ferraris, G.R. Smith and R.F. Stearley. 2018. A special workshop on the taxonomy and evolutionary biology of cutthroat trout. Pages 1–31 in Trotter P, Bisson P, Schultz L, Roper B (editors). Cutthroat Trout: Evolutionary Biology and Taxonomy. Special Publication 36, American Fisheries Society, Bethesda, Maryland.Young, M.K., K.S. McKelvey, T. Jennings, K. Carter, R. Cronn, E.R. Keeley, J.L. Loxterman, K.L. Pilgrim and M.K. Schwartz. 2018. The phylogeography of westslope cutthroat trout. Pages 261–301 in Trotter P, Bisson P, Schultz L, Roper B (editors). Cutthroat Trout: Evolutionary Biology and Taxonomy. Special Publication 36, American Fisheries Society, Bethesda, Maryland.Neoboreal cutthroat troutO. lewisi ssp.Largest native range of all Westslope Cutthroat, and are native to parts of the upper Columbia, Fraser and Saskatchewan watersheds in Washington, Idaho, Montana, British Columbia, and Alberta. Several disjunct populations in British Columbia that were initially classified as a distinct subspecies the Alpine Cutthroat,Dymond, JR. 1931. Description of two new forms of British Columbia Trout. Contributions to Canadian Biology and Fisheries 6(1): 391–395. but based on taxonomic characteristics and genetics these populations clearly align with the Neoboreal Cutthroat.Behnke, Robert J. Native Trout of Western North America. American Fisheries Society, 1992 p. 65.Coeur d’ Alene cutthroat troutO. lewisi ssp.Native to the Coeur d’ Alene River drainage in Northern Idaho.St. Joe cutthroat troutO. lewisi ssp.Native the St. Joe watershed of the Idaho panhandle. Neoboreal subspecies inhabit the lower reaches of the Coeur d’Alene and St. Joe watersheds. It remains uncertain what factors distinguish them from the St. Joe Westslope Cutthroat or whether these Neoboreal fish are native to these watersheds.North Fork Clearwater cutthroat troutO. lewisi ssp.Native to the North Fork Clearwater River and its tributaries including Kelly Creek in Idaho.Clearwater Headwater cutthroat troutO. lewisi ssp.Restricted to the upper Selway River upstream of Selway Falls and the South Fork Clearwater approximately upstream of the Crooked River. The exact boundary is currently not known.Clearwater-Eastern Cascades cutthroat troutO. lewisi ssp.Native to the mainstem Clearwater River, Locsha, and lower Selway Rivers in Idaho, as well as the Eastern Cascade Mountains from the Methow River to the Yakima River in Washington State.Trotter, P., B. McMillan, N. Gayeski, P. Spruell and M. Cook. 2001. Genetic and phenotypic catalog of native resident trout of the interior Columbia River Basin: populations in the Wenatchee, Entiat, Lake Chelan, and Methow River drainages. Bonneville Power Administration, Portland, OR.Salmon River cutthroat troutO. lewisi ssp.Native to the Salmon River watershed in central Idaho.Shepard, B. B., B. E. May, and W. Urie. 2005. Status and conservation of Westslope Cutthroat Trout within the western United States. North American Journal of Fisheries Management 25: 1426–1440.John Day cutthroat troutO. lewisi ssp.Native to about 220 miles (355 km) of 41 tributaries to the John Day River watershed in Oregon. Has the smallest and southern-most range of all Westslope Cutthroat.Howell, P, P. Spruell and R. Leary. 2003. Information regarding the origin and genetic characteristics of westslope cutthroat trout in Oregon and Central Washington. United States Forest Service. La Grande, Oregon. 18p.
Description The fish has teeth under its tongue, on the roof of the mouth, and in the front of the mouth.Trotter, Patrick C. (2008). Cutthroat: Native Trout of the West (2nd ed.). Berkeley, CA: University of California Press. p. 16. . Westslope cutthroat are common in both headwaters lake and stream environments. Like most other cutthroat trout, they are opportunistic feeders with diverse diets, and as their size increases, so does their food. Some of their primary forage, frequently imitated by fly fishers, include macroinvertebrates such as caddisflies, stoneflies, mayflies and aquatic dipterans (including midges and craneflies) in adult, larval, and pupal stages. They will also prey on ants, beetles, spiders, grasshoppers and crickets, and aquatic items including crayfish, freshwater molluscs, fish eggs, shrimp and other crustaceans, and other fish. Generally, they adjust their diet and feeding behavior due to factors such as food availability, habitat, age, and size.Behnke, R.J. 1992. Native trout of western North America. American Fisheries Society, Monograph 6, Bethesda, Maryland.Leeseberg, C. A., and E. R. Keeley. 2014. Prey size, prey abundance, and temperature as correlates of growth in stream populations of Cutthroat Trout. Environmental Biology of Fishes 97:599–614. The average length of the fish is about 12–15 inches (300-400 mm) and rarely exceeds .Behnke, R. J. 1988. Phylogeny and classification of Cutthroat Trout. Pages 1–7 in R. E. Gresswell, editor. Status and management of interior stocks of Cutthroat Trout. American Fisheries Society, Symposium 4, Bethesda, Maryland. The skin has small dark freckle-like spots clustered towards the tail, and is mostly orange-hued. They can be distinguished from rainbow trout by the red, pink, or orange marking beneath the jaw (hence the name "cutthroat").
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