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". GPROTCOM: GTHREAT: GTHREATCOM: ~. Most in Glacier National Park and Bob Marshal Wilderness. B Hybridization appears to be a common problem where isolated or remnant resident populations overlap with introduced brook trout (spawning times and conditions are similar) . Hybrids are likely to be sterile and experience developmental problems. ^In Montana, introduced brook trout progressively depressed a bull trout population. Brook trout have been widely introduced and now occupy most basins inhabited by bull trout, though they often occupy different streams or stream reaches. See Rieman and McIntyre (1993). ^Introduced brown trout and rainbow trout have been associated with bull trout declines, apparently due to competitive interactions; lake trout may have a negative impact on bull trout, due to predation by lake trout on juvenile bull trout, probable competitive interactions, and increased harvest associated with increased fishng pressure for lake trout (see Rieman and McIntyre 1993). Lake trout can displace bull trout and may prevent bull trout from becoming established in certain low elevation lakes (Donald and Alger 1993). ^Threatened by activities that damage riparian areas and cause stream siltation; logging, road construction, mining, and overgrazing may be harmful to spawning habitat. Very sensitive and severely impacted by siltation of spawning streams. Timber harvest and associated activities may have negative impacts on stream channels through sedimentation and/or increasing flooding or scour events (Rieman and McIntyre 1993). Habitat fragmentation may be a problem, but it is unclear whether the fragmented distribution is natural due to specific habitat requirements or caused by human impacts (Rieman and McIntyre 1993). Some migratory populations have been virtually eliminated by water diversions or habitat disruption (e.g., in the Bitterroot basin) (Rieman and McIntyre 1993). Climate change (warming) is a potential threat because it would decrease the amount of suitable habitat (see Rieman and McIntyre 1993). ^Extirpation in California probably resulted from two factors: 1) interaction with the introduced brown trout, and 2) indirect effects resulting from the loss of the McCloud River spawning population of chinook salmon; loss of the massive influx of nutrients provided by dying salmon altered the character of the stream (Minckley and Deacon 1991). ^In the Klamath River basin, threatened by habitat degradation caused by livestock grazing, timber harvest, and water withdrawals; drought has aggravated the situation and existing land and water management and regulatory mechanisms have failed to protect populations and habitat; non-native brook trout also are a serious threat because of possible hybridization and competition; probably fewer than 5000 individuals remain in 7 fragmented populations (Fisheries Action News, Winter 1994). ' GFRAGIL: C GFRAGILCOM: Relatively tolerant of nondestructive intrusion. GOTHCONSID: Rank and Reasons: