Oncorhynchus clarkii (Richardson, 1836): cutthroat trout

Biological Description

Body elongate and typically trout-like, rounded, and slightly compressed; scales cycloid, small to medium in size, 140-230 in the lateral line. Head conical, moderate to short; eye moderate; snout rounded, occasionally slightly pointed; mouth terminal, rather large; small sharp teeth on jaws, vomer, tongue, and median basibranchial plate between the lower end of the gill arches; gill rakers 14-22, usually 7 on the upper limb and 11 or 12 on the lower limb. Dorsal fin rays 8-11; anal fin rays 10 or 11; caudal fin slightly forked. Color highly variable, often differs between watersheds; normally greenish-blue to steel gray on back and upper side, yellowish-green to copper color on lower side, and sometimes silvery on belly. Black spots on back and side and more concentrated posterior to the dorsal fin. Spots on dorsal, adipose, and caudal fins; anal and paired fins without spots; red dash on each side of jaw along dentary; young with 9 or 10 oval parr marks on lateral line.

The cutthroat is distinguished from other trouts by a variety of characteristics. The maxillary of the cutthroat usually extends beyond the posterior margin of the eye in fish longer than 4 inches. In addition, this species has basibranchial or hyoid teeth behind the tongue between the second gill clefts. The rainbow trout differs in having a maxillary that usually does not extend beyond the posterior margin of the eyes (except in fish longer than about 20 inches), and in lacking the basibranchial teeth. The cutthroat trout usually has 10 (range, 8-11) rays in the dorsal fin and typically 9 in the pelvic fin, and red-orange "slash marks" on the underside of the lower jaw. The cutthroat trout has 140-230 scales in the lateral line; the rainbow trout has fewer than 150.

Life History

Spawning occurs in the spring, normally in April and May, depending on water temperatures. Egg production of females ranges from about 250 to 2,100 eggs depending on the length of the fish and the stream. The spawning act of the cutthroat follows the pattern of other trouts except that the densities of spawning fish are lower and spawning occurs in much smaller streams. The female digs a nest in the gravel of a riffle in the presence of a male. Digging and spawning alternate as she works her way upstream. A typical redd in a natural stream is two feet long and one and a half feet wide; the redd is in seven inches of water in a riffle, with the eggs five to seven inches under coarse gravel about the size of a walnut (pea-sized at the level where the eggs are laid). Most cutthroat fry emerge from the gravel by mid-April, but the time of emergence varies depending on the spawning date and the water temperature. There is normally a fairly heavy post-spawning mortality of adults. Cutthroat and rainbow spawn at about the same time and place, and considerable hybridization results when rainbows are stocked in streams with native cutthroat present.

The age and growth of cutthroat is quite variable and is reflected in the quality of habitat and with the race. The Snake River cutthroat race often grows to five and six pounds in weight while the westslope cutthroat seldom exceeds two pounds in weight. Snake River cutthroat normally spawn at three and four years of age, however, the westslope variety is usually five years of age at time of spawning.

Geographic Distribution

The cutthroat trout is native to all of the major river drainages in western North America. There are a number of different subspecies recognized, four of which are found in Idaho. The Yellowstone cutthroat occurs in southeastern Idaho in streams tributary to the Snake River above Shoshone Falls. It is the subspecies found in Henrys Lake and has been widely stocked in Idaho waters. The fine-spotted Snake River cutthroat is an undescribed subspecies inhabiting the South Fork of the Snake River from Palisades Reservoir, Idaho up to Jackson Lake, Wyoming. Recently, the Bonneville cutthroat was found in Idaho. It is found in the upper reaches of tributaries to the Bear River in southeastern Idaho. The fourth subspecies is the westslope cutthroat which is found in the Salmon River drainage and the major river systems north of the Salmon River. The native range of the species also extends from Alaska to Southern California. It was also native in the intermountain area to headwaters of the Missouri, Platte, Colorado, and Rio Grande drainages. Originally it was abundant in many streams of the state, but with the advance of civilization, the change in habitat of various streams, and the introduction of other species of non-native salmonids (mainly rainbow trout and brook trout), its range has been greatly reduced.

Habits and Habitats

Cutthroat trout inhabit both lakes and streams where water is clear and cool, preferably under 60° F.

Diet

Feeding habits of the cutthroat are similar to the other trouts and the diet consists primarily of aquatic and terrestrial insects. Fish form a sizable portion of the diet of the larger fish in the Snake River system. Other foods include crayfish, terrestrial arthropods, salamanders, salmonid and sculpin eggs, and sculpins. These food items indicate that cutthroat are opportunistic feeders.

Idaho Conservation Status

Idaho Native or Import

Native.

Comments

The popularity of cutthroat trout with the angling public is equal to that of the rainbow. The quality of flesh is excellent when taken from clear, cool water. The Idaho Department of Fish and Game operates a spawning station on Henrys Lake and 10 to 12 million eggs are taken annually and distributed to other Southern Idaho fish hatcheries. Formally it was distributed in many of the waters of northern Idaho but its success in northern waters has been below the desired level. This and a desire to retain the gene composition of the westslope variety has greatly reduced the transfer of eggs from Henrys Lake to northern fish hatcheries. Attempts are presently underway to establish a brood stock of westslope cutthroat in one of the northern lakes.

The westslope cutthroat trout has been designated as the state fish of Idaho.

Credits

Simpson and Wallace 1982.Wydoski and Whitney 1979. Image Copyright Joseph Tomelleri. Used by permission.

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