The mountain whitefish boasts a unique combination of characteristics, resembling cyprinids in body shape but distinguished by the presence of both the adipose fin and axillary process of salmonids. Its slender and nearly cylindrical body is typically silver with a dusky olive-green shade dorsally. Notably, the scales exhibit pigmented borders, particularly well-defined on the posterior end. With a forked homocercal tail, a short head housing a small mouth, and fins characterized by a specific number of rays, the mountain whitefish can reach impressive sizes of up to 70 centimeters (28 inches) in length and a weight of 2.9 kilograms (6.4 lb).
Understanding the life history of the mountain whitefish is crucial to appreciate its ecological significance. The spawning season of this species occurs between October and early December when water temperatures range from 2 to 6 degrees Celsius. During this period, mountain whitefish gather in large schools and migrate to areas with coarse gravels or cobbles, usually found in shallow sections of small tributaries or along lakeshores. The non-adhesive eggs are scattered along the substrate, undergoing a slow developmental process over the winter, typically lasting 6 to 10 weeks. Hatching takes place in the early spring, generally in March. Females, which can produce up to 4,000 eggs annually, reach reproductive maturity around three years of age. In the wild, mountain whitefish usually live for 7 to 9 years.
Mountain whitefish are demersal feeders, employing their pectoral and tail fins to stir up the substrate and expose a variety of prey. Their diet primarily consists of insect larvae and other invertebrates such as snails, crayfish, and amphipods. They are most active during the evening but will also consume drifting prey throughout the day. While feeding, mountain whitefish tend to stay in the lower strata of streams, although they may rise to the surface to prey on hatching insects, including mayflies. Additionally, the fry of mountain whitefish serve as a common food source for other trout species, underscoring their ecological importance within freshwater ecosystems.
Habitat: Mountain whitefish are commonly found in mountain streams and lakes, exhibiting a preference for clear, cold water and large deep pools with a minimum depth of one meter. Notably, the population residing in Lake Tahoe tends to inhabit deeper water just above the lake bottom, showcasing their adaptability to specific environmental conditions.
Range: This resilient species occupies a vast range across the western half of North America. Its distribution extends from the Mackenzie River in Canada, encompassing the Hudson Bay, Columbia River, upper Missouri River, and upper Colorado River drainages. The mountain whitefish's ability to thrive in diverse habitats contributes to its widespread presence throughout this region.
Migration: Mountain whitefish are non-anadromous, spending the majority of their lives in freshwater ecosystems. While limited information is available on their migration patterns, there is evidence suggesting that they migrate for spawning purposes and in response to temperature fluctuations. For instance, in the Methow River, a tributary of the Columbia River, mountain whitefish have been observed migrating to larger bodies of water due to shallower tributary water temperatures. Furthermore, these fish have been known to spend winters in the Columbia River, which offers more suitable habitats. In line with other anadromous salmonid species, mountain whitefish in the Methow River exhibit an annual return to their birth streams for spawning.
Accurate understanding of mountain whitefish life history strategies plays a crucial role in conservation and management efforts. By comprehending their growth patterns, age structure, and age at maturity, biologists can make informed decisions regarding harvesting limitations and release practices. Determining the age of mountain whitefish involves counting annuli (growth rings) in fish scales, pectoral fin rays, and otoliths (ear bones). These data provide valuable insights into population dynamics and contribute to the preservation of healthy mountain whitefish populations.
Despite historical misconceptions and challenges, the mountain whitefish holds a secure conservation status. In many large intermountain Western rivers, they represent the sole native salmonid species. For instance, in the Snake River Basin in Idaho, mountain whitefish abundance reaches impressive levels, with a count of 1,257 individuals per 100 meters. It is crucial to dispel the notion of mountain whitefish as "trash fish" and acknowledge their significance within the ecosystem. By recognizing the importance of maintaining healthy populations, we can ensure the prosperity of not only mountain whitefish but also the environments they inhabit. As a valuable indicator species, the well-being of mountain whitefish can serve as a barometer for the overall environmental health.