The Westslope Cutthroat Trout (Alberta Population) a Species at Risk

This species has been identified as Threatened by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). It is currently being considered for listing under the federal Species at Risk Act (SARA). Protection is afforded through the federal Fisheries Act. If listed under the Species at Risk Act (SARA), it will be afforded additional protection. Under the SARA, a recovery strategy must be developed for this species.

General Description

Oncorhynchus clarkii lewisi

© FisheyeguyPhotography.com

The Westslope Cutthroat Trout (Oncorhynchus clarkii lewisi) is a subspecies of the Cutthroat Trout (Oncorhynchus clarkii). This subspecies has been further divided into two populations, the Alberta and British Columbia populations. The Westslope Cutthroat Trout is a member of the Salmonidae family and has the following characteristics:

• Streamlined body shape;
• Generally trout-like in appearance with small, irregularly shaped dark spots, which form an arc from the anal fin to the pectoral fin;
• Series of small basibranchial teeth at the back of the throat;
• Colouration ranges from silver to yellow green with red on the front and sides of the head;
• Spawning fish often develop a bright red colouration over the entire body; and
• Typically small in size at 150 to 230 mm (28 to 142 g); larger individuals rarely exceed 460 mm (1400 g).

Distribution

The Westslope Cutthroat Trout has a disjunct distribution on both sides of the Rocky Mountains. In the United States, it occurs in drainages in Montana, Idaho, Washington, Oregon and Wyoming. In Canada, it is restricted to the upper Kootenay, upper Columbia and South Thompson drainages in British Columbia. The native Alberta population occurs in the Bow and Oldman drainages of the South Saskatchewan River. Although it has been recorded in the Milk River (upper Missouri River drainage), its current status there is unknown. The Westslope Cutthroat Trout has also been widely introduced in many naturally fishless lakes and rivers.

Westslope Cutthroat Trout Distribution

Habitat and Life History

Westslope Cutthroat Trout are found in a wide range of habitats but do best in cold, clean, moving water with various forms of cover such as undercut banks, pool-riffle habitat and riparian vegetation. Spawning generally takes place in small natal streams in redds on bottoms of fine gravel. It occurs between May and August (depending on the location) at water depths of 20 to 50 cm and at 6o to 17oC. Eggs incubate for six to seven weeks and once hatched, alevins remain in the gravel until their yolk sacs are absorbed. Young-of-the-year fry disperse to shallow riffles or backwater habitat. Juveniles may reside in natal streams from one to four years. Following spawning, older fish may or may not need to move to summer habitat for feeding. In late summer and early fall, fish migrate to suitable overwintering habitat.

Diet

The diet of this fish consists of aquatic and terrestrial insects, crustaceans and small fish.

Threats

The greatest threats to the Westslope Cutthroat Trout in Alberta include habitat loss, overharvesting and the introduction of non-native species. Habitat degradation and loss due to timber extraction, mining and hydroelectric developments have been directly responsible for loss of habitat and the decline of several populations. In addition, the resulting network of roads impacts remote, small streams and leads to greater off-road vehicular traffic. This further degrades sensitive habitat and increases angling pressure on this already popular sportfish. Stocking of non-native species may lead to displacement, replacement and/or hybridization of native Westslope Cutthroat Trout populations.

Similar Species

Cutthroat Trout generally tend to have a larger mouth than the Rainbow Trout (O. mykiss) with a longer maxillary. Hybridization with Rainbow Trout usually leads to alternate spotting patterns including spots on the top of the head and back body.

Text Sources: COSEWIC Status Report 2005.

For more information, visit the SARA Registry Website at www.SARAregistry.gc.ca.