The cutthroat trout (Oncorhynchus clarkii) is a fish species of the family Salmonidae native to cold-water tributaries of the Pacific Ocean, Rocky Mountains, and Great Basin in North America. As a member of the genus Oncorhynchus, it is one of the Pacific trout, a group that includes the widely distributed rainbow trout. Cutthroat trout are popular gamefish, especially among anglers who enjoy fly fishing. The common name "cutthroat" refers to the distinctive red coloration on the underside of the lower jaw. The specific name clarkii was given to honor explorer William Clark, coleader of the Lewis and Clark Expedition.
Cutthroat trout usually inhabit and spawn in small to moderately large, clear, well-oxygenated, shallow rivers with gravel bottoms. They reproduce in clear, cold, moderately deep lakes. They are native to the alluvial or freestone streams that are typical tributaries of the rivers of the Pacific Basin, Great Basin and Rocky Mountains. Cutthroat trout spawn in the spring and may inadvertently but naturally hybridize with rainbow trout, producing fertile cutbows. Some populations of the coastal cutthroat trout (O. c. clarkii) are semi-anadromous.
Several subspecies of cutthroat trout are currently listed as threatened in their native ranges due to habitat loss and the introduction of non-native species. Two subspecies, O. c. alvordensis and O. c. macdonaldi, are considered extinct. Cutthroat trout are raised in hatcheries to restore populations in their native range, as well as stock non-native lake environments to support angling. The cutthroat trout type species and several subspecies are the official state fish of seven western U.S. states.
The cutthroat trout is the state fish of Idaho, Montana and Wyoming, while particular subspecies of cutthroat are the state fish of Colorado, Nevada, New Mexico and Utah.
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InsectivoresAn insectivore is a carnivorous plant or animal that eats insects. An alternative term is entomophage, which also refers to the human practice of e...
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CarnivoreA carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of a...
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PiscivoresA piscivore is a carnivorous animal that eats primarily fish. Piscivorous is equivalent to the Greek-derived word ichthyophagous. Fish were the die...
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OviparousOviparous animals are female animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive...
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PolygynyPolygyny is a mating system in which one male lives and mates with multiple females but each female only mates with a single male.
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starts withThroughout their native and introduced ranges, cutthroat trout vary widely in size, coloration and habitat selection. Their coloration can range from golden to gray to green on the back. Cutthroat trout can generally be distinguished from rainbow trout by the presence of basibranchial teeth at the base of tongue and a maxillary that extends beyond the posterior edge of the eye. Depending on subspecies, strain and habitat, most have distinctive red, pink, or orange linear marks along the underside of their mandibles in the lower folds of the gill plates. These markings are responsible for the common name "cutthroat", first given to the trout by outdoor writer Charles Hallock in an 1884 article in The American Angler. These markings are not unique to the species. Some coastal rainbow trout (Oncorhynchus mykiss irideus) and Columbia River redband trout (O. m. gairdneri) populations also display reddish or pink throat markings.
At maturity, different populations and subspecies of cutthroat trout can range from 6 to 40 inches (15 to 102 cm) in length, depending on habitat and food availability. Sea-run forms of coastal cutthroat trout average 2 to 5 pounds (0.9 to 2.3 kg). The length and weights of mature inland forms vary widely depending on their particular environment and availability of food. Stream-resident fish are much smaller, 0.4 to 3.2 ounces (11 to 91 g), while lacustrine populations have attained weights ranging from 12 to 17 lb (5.4 to 7.7 kg) in ideal conditions. The largest cutthroat trout subspecies is the Lahontan cutthroat trout (O. c. henshawi). These fish average 8 to 9 in (20 to 23 cm) in small streams and 8 to 22 in (20 to 56 cm) in larger rivers and lakes. In ideal environments, the Lahontan cutthroat trout attains typical weights of 0.25 to 8 lb (0.11 to 3.63 kg). The world record cutthroat trout is a Lahontan at 39 in (99 cm) and 41 lb (19 kg).
Cutthroat trout are native to western North America and have evolved through geographic isolation into 14 subspecies, each native to a different major drainage basin. Native cutthroat trout species are found along the Pacific Northwest coast from Alaska through British Columbia into northern California, in the Cascade Range, the Great Basin and throughout the Rocky Mountains including southern Alberta. Some coastal populations of the coastal cutthroat trout (O. c. clarkii) are semi-anadromous, spending a few months in marine environments to feed as adults and returning to fresh water from fall through early spring to feed on insects and spawn. Cutthroat trout have the second-largest historic native range of North American trout; the lake trout (Salvelinus namaycush) having the largest. Ranges of some subspecies, particularly the westslope cutthroat trout (O. c. lewisi), have been reduced to less than 10 percent of their historic range due to habitat loss and introduction of non-native species.
Although members of Oncorhynchus, the Pacific trout/salmon species, three subspecies—the westslope (O. c. lewisi), the greenback (O. c. stomias) and Yellowstone cutthroat trout (O. c. bouvierii)—evolved populations east of the Continental Divide in the upper Missouri River basin, upper Arkansas and Platte River basins and upper Yellowstone River basin, each which drain into the Atlantic basin via the Mississippi River (in 2005, researchers published a report stating that a natural distribution of (O. mykiss), the Conchos trout, is also located in an Atlantic basin drainage). Scientists believe that the climatic and geologic conditions 3-5 million years ago allowed cutthroat trout from the Snake River to migrate over the divide into the Yellowstone plateau via Two Ocean Pass. There is also evidence that Yellowstone Lake once drained south into the Snake River drainage. Evidence suggests that the westslope cutthroat trout was able to establish populations east of the divide via Summit Lake at Marias Pass which at one time connected the Flathead River drainage with the upper Missouri River drainage. Scientists speculate that there are several mountain passes associated with the headwaters of the Colorado River drainage and Arkansas/Platte River drainages that would have allowed migration of cutthroat trout east of the divide.
Cutthroat trout have been introduced into non-native waters outside their historic native range, but not to the extent of the rainbow trout (O. mykiss). Within the native range of the Yellowstone cutthroat trout, U.S. Fisheries Bureau and National Park Service authorities introduced Yellowstone cutthroat trout into many fishless lakes in Yellowstone National Park. Cutthroat trout were introduced into Lake Michigan tributaries in the 1890s and sporadically in the early 20th century, but never established wild populations. A population of Yellowstone cutthroat trout purportedly has been established in Lake Huron. Although cutthroat trout are not native to Arizona, they are routinely introduced by the Arizona Game and Fish Department into high mountain lakes in the White Mountains in the northeastern region of that state.
Cutthroat trout require cold, clear, well-oxygenated, shallow rivers with gravel bottoms or cold, moderately deep lakes. Healthy stream-side vegetation that reduces siltation is typical of healthy cutthroat trout habitat and beaver ponds may provide refuge during periods of drought and over winter. Most populations stay in fresh water throughout their lives and are known as nonmigratory, stream-resident or riverine populations. The coastal cutthroat trout (O. c. clarkii) is the only cutthroat trout subspecies to coevolve through its entire range with the coastal rainbow trout (O. m. irideus). Portions of the westslope cutthroat trout's (O. c. lewisi) range overlap with the Columbia River redband trout (O. m. gairdneri), but the majority of its native range is in headwater tributary streams above major waterfalls and other barriers to upstream migration. At least three subspecies are confined to isolated basins in the Great Basin and can tolerate saline or alkaline water.
Cutthroat trout are opportunistic feeders. Stream-resident cutthroat trout primarily feed on larval, pupal and adult forms of aquatic insects (typically caddisflies, stoneflies, mayflies and aquatic dipterans), and adult forms of terrestrial insects (typically ants, beetles, grasshoppers and crickets) that fall into the water, fish eggs, small fish, along with crayfish, shrimp and other crustaceans. As they grow the proportion of fish consumed increases in most populations. In saltwater estuaries and along beaches, Coastal cutthroat trout feed on small fish such as sculpins, sand lance, salmon fry and herring. They also consume shrimp, small squid and krill. In fresh water, they consume the same diet as stream resident trout—aquatic insects and crustaceans, amphibians, earthworms, small fish and fish eggs. Within the range of the bull trout (Salvelinus confluentus) the cutthroat trout is a forage fish for the piscivorous bull trout.
Cutthroat trout usually inhabit and spawn in small to moderately large, clear, well-oxygenated, shallow rivers with gravel bottoms. They are native to the alluvial or freestone streams typical of tributaries of the Pacific Basin, Great Basin and Rocky Mountains. They spawn in the spring, as early as February in coastal rivers and as late as July in high mountain lakes and streams. Spawning begins when water temperatures reach 43 to 46 °F (6 to 8 °C). Cutthroat trout construct a redd in the stream gravel to lay eggs. The female selects the site for and excavates the redd. Females, depending on size, lay between 200 and 4,400 eggs. Eggs are fertilized with milt (sperm) by an attending male. Eggs hatch into alevins or sac fry in about a month and spend two weeks in the gravel while they absorb their yolk sack before emerging. After emergence, fry begin feeding on zooplankton. Juvenile cutthroat trout typically mature in three to five years. Lake-resident cutthroat trout are usually found in moderately deep, cool lakes with adequate shallows and vegetation for good food production. Lake populations generally require access to gravel-bottomed streams to be self-sustaining, but occasionally spawn on shallow gravel beds with good water circulation.
Cutthroat trout naturally interbreed with the closely related rainbow trout, producing fertile hybrids commonly called "cutbows". This hybrid generally bears similar coloration and overall appearance to the cutthroat trout, usually retaining the characteristic orange-red slash. Cutbow hybrids often pose a taxonomic difficulty when trying to distinguish any given specimen as a rainbow or cutthroat trout. In addition, cutthroat trout may hybridize with O. gilae, the Gila trout and O. apache, the Apache trout in regions where their ranges overlap.
The historic native range of cutthroat trout has been reduced by overfishing, urbanization and habitat loss due to mining, livestock grazing and logging. Population densities have been reduced and in some cases populations have disappeared though competition with non-native brook, brown, lake and rainbow trout, kokanee salmon, lake whitefish and mysis shrimp which were introduced in the late 19th and early 20th centuries. Scientists believe the westslope cutthroat trout will eventually be extirpated from the large lakes in Western Montana due to the trophic cascades resulting from lake trout and mysis shrimp introductions. The most serious current threats to several subspecies are interspecific breeding with introduced rainbow trout, creating hybrid cutbows, and intraspecific breeding with other introduced cutthroat trout subspecies. In the Greater Yellowstone Ecosystem, the presence of lake trout (Salvelinus namaycush) in Yellowstone Lake in Yellowstone National Park has caused a serious decline in Yellowstone cutthroat trout (O. c. bouvierii). Outbreaks of whirling disease in major spawning tributaries within the native ranges have also caused declines. Most subspecies of cutthroat trout are highly susceptible to whirling disease, although the Snake River fine-spotted cutthroat trout (O. c. behnkei) appears to be resistant to the parasite.
