Prosopium williamsoni

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General Information
Common Name: 
Mountain whitefish

Conservation Status in California: Class 3, Near threatened (Moyle et al. 2011).
Mountain whitefish are locally abundant although their overall abundance and distribution are probably much less than they were historically. Because of poor knowledge of their actual numbers, mountain whitefish should be treated as a declining species unless evidence indicates otherwise

Life History: 

Life History: Mountain whitefish are usually observed in loose shoals of 5–20 fish, close to the bottom. As their subterminal mouths and body shape suggest, they are bottom-oriented predators on aquatic insects (Moyle 2002). Small juveniles feed on small chironomid midge, blackfly, and mayfly larvae but their diet becomes more diverse with size. Adults feed on mayfly, caddisfly, and stonefly larvae during summer (Ellison 1980). In Lake Tahoe they consume snails, a variety of insect larvae, crayfish, and amphipods (Miller 1951). Most feeding takes place at dusk or after dark. However, they will feed during the day on drifting invertebrates, including terrestrial insects (Moyle 2002).
According to Moyle (2002), “Growth is highly variable, depending on habitat, food availability, and temperature. Growth of fish from a small alpine lake (Upper Twin, Mono County) was… 11 cm SL at the end of year 1, 13.5 cm at year 2, 15 cm at year 3, 17 cm at year 4, and 20 cm at year 5. Fish from rivers at lower elevations seem to be 25–30 percent larger at any given age after the first year. Young reared in tributaries to Lake Tahoe were largest in the Truckee River (8.6 cm FL at 10 months) and smallest (7.3–7.8 cm) in small tributaries (Miller 1951). Large individuals (25–50 cm SL) are probably 5–10 years old …The largest seems to be one measuring 51 cm FL and weighing 2.9 kg from Lake Tahoe.” Rogers et al. (1996) have developed a standard length-weight relationship for mountain whitefish, based on data from 36 populations throughout their range.
“Spawning takes place in October through early December at water temperatures of 1–11°C (usually 2–6°C)…. Spawning is preceded in streams by upstream or downstream movements to suitable spawning areas, possibly as the result of homing to historical spawning grounds. Movement is often associated with a fairly rapid drop in water temperature. From lakes, whitefish migrate into tributaries to spawn, but some spawning may take place in shallow waters as well… Whitefish do not dig redds but scatter eggs over gravel and rocks, where they sink into interstices. The eggs are not adhesive. Little is known about spawning behavior, but they seem to spawn at dusk or at night, in groups of more than 20 fish. They become mature in their second through fourth year, although the exact timing depends on sex and size. Each female produces an average of 5,000 eggs, but fecundity varies with size, from 770 to over 24,000... The embryos hatch in 6–10 weeks (or longer, depending on temperatures) in early spring. Newly hatched fish are carried downstream into shallow (5¬–20 cm) backwaters, where they spend their first few weeks. As fry grow larger, they gradually move into deeper and faster water, usually in areas with rock or boulder bottoms. Fry from lake populations move into the lake fairly soon after hatching and seek out deep cover, such as beds of aquatic plants (Moyle 2002).”

Habitat Requirements: 

Habitat Requirements: Mountain whitefish in California inhabit clear, cold rivers and lakes at elevations of 1,400–2,300 m. In streams, they are generally associated with large pools Environmental tolerances of mountain whitefish in California are poorly understood but generally they are found in waters with summer temperatures


Distribution: Mountain whitefish are found in western North America, from California to Alaska. They are distributed throughout the Columbia River watershed (including Wyoming, Montana, Oregon, Washington, Idaho, British Columbia, and Alberta), the upper reaches of the Missouri and Colorado Rivers, the Bonneville drainage, and the Mackenzie and Hudson Bay drainages in the Arctic. In California and Nevada, they are present in the Truckee, Carson, and Walker River drainages on the east side of the Sierra Nevada. Their range includes both lakes (e.g., Tahoe) and streams. Curiously, they are absent from Susan River and from Eagle Lake, Lassen Co.

Abundance Trends: 

Trends in Abundance: According to Moyle (2002), “Mountain whitefish are still common in their limited California range, but their populations are fragmented. There is no question that they are less abundant than they were in the 19th century, when they were harvested in large numbers by Native Americans and then commercially harvested in Lake Tahoe. There are still runs in tributaries to Lake Tahoe, but they are relatively small and poorly documented. Whitefish apparently were already reduced in numbers by the 1950s. They still seem to be fairly common in low-gradient reaches of the Truckee, East Fork Carson, East and West Walker, and Little Walker Rivers. Small populations are still found in Little Truckee River, Independence Lake, and some small streams, such as Wolf and Markleeville Creeks, tributaries to the East Carson River. Their populations in Sierra Nevada rivers and tributaries have been fragmented by dams and reservoirs, and whitefish are generally scarce in reservoirs. A severe decline in the abundance of whitefish in Sagehen and Prosser Creeks followed the construction of Stampede and Prosser Reservoirs, respectively.” These observations all suggest that mountain whitefish are less abundant and less widely distributed in California than they once were, although they continue to be common enough in the Truckee, Carson, and Walker Rivers so that they can support recreational fisheries. At present, both California and Nevada allow 10 whitefish per day to be taken by anglers.
Overall, there is no evidence in that whitefish populations have declined significantly in last 5-10 years but no agency is monitoring populations. Present numbers of whitefish in most of their habitats are likely only a small fraction of their historic numbers, when they were frequently harvested from the rivers and lakes of the eastern Sierra.


Description: Mountain whitefish are silvery, large-scaled (74-90 on lateral line) salmonids, with a conspicuous adipose fin, a small ventral mouth, a short dorsal fin (12–13 rays), a more or less cylindrical body, and a forked tail. Gill rakers are short (19¬–26 on the first gill arch) with small teeth. They have 11-13 anal fin rays, 10-12 pelvic fin rays (with a conspicuous axillary process at the base), and 14-18 pectoral fin rays. The body is silvery and olive green to dusky on the back, and scales on the back are often outlined in dark pigment. Breeding males develop distinct tubercles on the head and sides. Juveniles are pencil-thin and silvery with 7–11 dark, oval parr marks.