Salvelinus confluentus

Resident adults are 15-30 cm in length whereas migratory adults commonly exceed 60 cm (see Rieman and McIntyre 1993).

Habitat includes the bottom of deep pools in cold rivers and large tributary streams, often in moderate to fast currents with temperatures of 45-50 F; also large coldwater lakes and reservoirs. In the contiguous U.S., now extirpated in most large rivers that historically were inhabited; confined mostly to headwater streams. Conditions that favor the persistence of populations include stable channel, relatively stable stream flow, low levels of fine substrate sediments, high stream channel complexity with various cover types, temperatures not exceeding about 15 C, and the presence of suitable corridors for movement between suitable winter and summer habitats and for genetic exchange among populations (Rieman and McIntyre 1993).

Migratory forms live in tributary streams for up to several years before migrating downstream into a larger river or lake, where they spend several years before returning to tributaries to spawn (Rieman and McIntyre 1993). Some or most juveniles move to larger rivers or to a lake by mid-summer, while others stay in spawning areas for 2-4 years (Spahr et al. 1991). Adults return to river or lake after spawning in small streams. May move to lower reaches of mainstream river for winter. Resident populations often occur in small headwater streams where they spend their entire lives (see Rieman and McIntyre 1993). In lakes, inhabits all depths in fall, winter, and spring; moves to cooler, deeper water for summer.

Spawning usually occurs in gravel riffles of small tributary streams, including lake inlet streams. Spawning sites often are associated with springs (Rieman and McIntyre 1993). According to California Department of Fish and Game (1990), spawning requires a large volume of cold water. Optimum temperatures for incubation are about 2-4 C (see Rieman and McIntyre 1993). Constructs spawning redd. Young are closely associated with stream channel substrates (Rieman and McIntyre 1993). Areas with large woody debris and rubble substrate are important as juvenile rearing habitat (Spahr et al. 1991).

Resident and migratory form live together but whether they represent a single population or separate populations is unknown (Rieman and McIntyre 1993).

Vigorous populations may require abundant fish forage (Rieman and McIntyre 1993).

Available information indicates that bull trout and other native fishes use different resources, reducing direct competition (Rieman and McIntyre 1993).

Spawns in late summer or fall, with falling temperatures between 5 C and 9 C. Eggs hatch in late winter or early spring. Fry emerge from gravel in April or May. Most information indicates that sexual maturity is attained in 5-7 years (also reported as 4-5 years). May spawn each year or in alternate years. Spawning populations may comprise four or more year classes, though one or two year classes may dominate. See Rieman and McIntyre (1993).