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Photo by Tom Pettengill
Photo Copyright Tom Pettengill
Bonneville Cutthroat Trout
Oncorhynchus clarkii utah
NatureServe conservation status
Global (G-rank): G4T4
State (S-rank): S4
- Reason: Although the species is moderately widespread in western Utah, many populations have been reduced in size and extent from historical levels and continue to be affected by population fragmentation and nonnative gamefish populations.
External links
General information
The Bonneville cutthroat trout, Oncorhynchus clarkii utah, is a race, or subspecies, of the cutthroat trout native to the Bonneville Basin of Utah, Wyoming, Idaho, and Nevada. Pure Bonneville cutthroat trout are rare throughout their historic range, but several Utah populations exist, including populations in Bear Lake and Strawberry Reservoir. Major threats to the Bonneville cutthroat trout include habitat loss/alteration, predation by and competition with nonnative fishes, and hybridization with nonnative fishes, such as the rainbow trout.
Bonneville cutthroat trout primarily eat insects, but large individuals also eat fishes. Like other cutthroat trout, the subspecies spawns in streams over gravel substrate in the spring. The Bonneville cutthroat trout can be found in a number of habitat types, ranging from high-elevation mountain streams and lakes to low-elevation grassland streams. In all of these habitat types, however, the Bonneville cutthroat trout requires a functional stream riparian zone, which provides structure, cover, shade, and bank stability.
Species range
This subspecies occurs in streams and lakes of the Bonneville Basin and in a few headwater streams of the Virgin River drainage in the Pine Valley Mountains. Most populations are found in the headwater streams and high-elevation river reaches of drainages entering the Basin at its eastern and southeastern edge, and several small populations occur in perennial streams in the Deep Creek Mountains along the western boundary of the Basin (see, e.g., Holden et al. 1974, Hickman and Duff 1978, Behnke 1992, Schmidt et al. 1995, Sigler and Sigler 1996, Lentsch et al. 2000, USFWS 2001).
Habitat
This subspecies occurs in large lakes (both deep and shallow), rivers, and streams in Utah (Schmidt et al. 1995). Schmidt et al. (1995) noted: "Many remnant populations were confined to tiny headwater streams above natural barriers which prevented contamination by nonnative trout . . .."
Food habits
Eats mainly aquatic insects and terrestrial insects that fall into the water, and fishes; incidence of fishes in the diet increases with size. In Bear Lake, trout of 30 cm or longer preyed largely on fishes (e.g., Bear Lake sculpin and Bear Lake cisco). See Kershner (1995) for further details.
Ecology
Bear River group is the only form of this subspecies able to persist in their native waters with introduced non-native trout (Behnke 1992, Idaho DF&G 1994). Sculpins appear to be a minor predator (Kershner 1995). May compete with syntopic fishes (e.g., mountain whitefish) for invertebrate prey (Kershner 1995). There is concern that whirling disease may spread throughout the Bear River system (Kershner 1995).
Reproductive characteristics
Spawns in spring (April-June) at water temperatures of about 4-10 C; sexually mature in 2-3 years in several areas (Spahr et al. 1991, Kershner 1995). In the Bear Lake population, over 90% of the spawners were 6-11 years old; repeat spawning was rare; when stocked in new waters, Bear Lake cutthroat may mature earlier (modal age of 4-6 years) (Nielson and Lentsch, cited by Behnke 1992). Fry typically emerge in mid- to late summer. Growth rates generally are low in small headwaters.
Threats or limiting factors
Hybridization with nonnative rainbow trout (O. mykiss) and Yellowstone cutthroat trout (O. c. bouvieri) has resulted in the genetic swamping of some populations and remains a threat to those that remain. Nonnative populations of these and other game fishes may also threaten some populations through competitive exclusion. Habitat destruction and degradation are important threats in most areas. Of particular importance are habitat alterations that result in the fragmentation of populations. In many areas, small population sizes in stream reaches isolated by dams are subject to the deleterious genetic effects of inbreeding.
References
- Biotics Database. 2005. Utah Division of Wildlife Resources, NatureServe, and the network of Natural Heritage Programs and Conservation Data Centers.
- Sigler, W. F. and J. W. Sigler. 1996. Fishes of Utah[:] a natural history. University of Utah Press. Salt Lake City. 375 pp.
