Westslope Cutthroat Trout get their name from the distinctive red slash that occurs just below the lower jaw (on both sides). Cutthroat Trout have small irregular-shaped spots along their back and on their fins. Adults typically exhibit bright yellow, orange and/or red colours along their belly area, especially among males during the spawning season. Most often they are silver with yellow, green, blue or brown colouration on their back; these colour traits can differ depending on the colour of the water or substrate. Cutthroat in more turbid (dirtier, cloudy) water, or in glacially fed streams with steeper slopes (gradients), tend to be paler in colour, with fewer but larger spots and narrower body types. Whereas, Cutthroat in clearer streams with shallower slopes tend to have more spotting, as well as having a more round-shaped body profile. At maturity, the Cutthroat reaches between 15cm-56cm in length and can weigh just over 100 g and up to 3 kg.
Westslope Cutthroat Trout live in a variety of different stream conditions throughout the year. These conditions range from heavily glacial water systems, to clear, stable, spring-fed streams. They require cold, clean water, and varied forms of cover, such as undercut banks, boulders, logs, pool-riffle habitat and/or aquatic or riparian vegetation. In winter they prefer deeper pools with low flow currents where ice cannot form. Many populations of Cutthroat are isolated from one another by natural barriers and watershed divisions. Westslope Cutthroat Trout tend to inhabit cooler, less productive waters than other closely related Trout species. Adult Cutthroat tend to occupy the best available habitat, such as deep pools where there is ample cover. Young, Juvenile Cutthroat, on the other hand, are usually forced to feed in shallower pools or riffles. Spawning habitat usually occurs in shallower, low-gradient streams that have a gravel substrate. When the water temperature reaches about 7-10 degrees Celsius, the Westslope Cutthroat will migrate to their spawning habitat. Cover near spawning habitat is important for the adult fish to hold up in before they begin spawning, in addition to escaping predators.
Cutthroat Trout reproduce in the Spring, when the water temperature reaches above 10 degrees Celsius and water streams are flowing more rapidly. Female Cutthroat prefer clear, cool water and clean gravel substrates as their nesting site. Once the preferred site is located, the female Cutthroat bury their eggs (“redd”), but not until after excavating a small, cavernous nest with their tail. She will generally lay between 200-4400 eggs at one time. The eggs normally hatch within a month of fertilization by the male, and the young generally spend another 2 weeks in the gravel absorbing their yolk-sac before emerging from their nest. The newborn Cutthroat usually remain in their native stream or spawning grounds for 1-2 years before migrating to a low energy habitat, with low water velocity and appropriate cover from predators. They typically require about 3-5 years to reach maturity, they live to an average age of about 12 years, and have been recorded as living to as much as 20 years old.
Like most trout, the Westslope Cutthroat Trout are an opportunistic forager that—without much competition from other species—will feed on the most readily available food sources. In general, they feed on aquatic insects and often depend on drifting aquatic insect larvae as an easy and desirable food source. Cutthroat tend to feed near dawn and dusk which corresponds to a larger density of insects and larvae drifting downstream. As the Cutthroat Trout grow into maturity, their diet becomes more diverse and they’re known to eat small fish or even small mammals if they present a convenient option.
Historically, the largest limiting factor for the Westslope Cutthroat has been its inter-breeding with Rainbow Trout and Brook Trout. Additionally, they are a species with a diverse diet and are considered an opportunistic forager, making them, amongst other things, very vulnerable to anglers of all skill levels. They are intolerant of high water temperatures (exceeding 20 degrees Celsius) and to low oxygen levels.