Clint C. Muhlfeld
Montana Department of Fish, Wildlife & Parks
The Columbia River redband trout (Oncorhynchus mykiss gairdneri), a subspecies of rainbow trout (Oncorhynchus mykiss), is native to the Fraser and Columbia River drainages east of the Cascade Mountains to barrier falls on the Pend Oreille, Spokane, Snake and Kootenai rivers (Allendorf et al. 1980; Behnke 1992). Logging, mining, agriculture, grazing, dams, over harvest and hybridization and competition with other trout contributed to the decline of redband trout abundance, distribution and genetic diversity in the Columbia River Basin (Williams et al. 1989; Behnke 1992). Consequently, many populations are restricted to isolated headwater streams that may serve as refugia until effective conservation and rehabilitation strategies are implemented. Long-term persistence of these populations is threatened by loss of migratory life history forms and connectivity with other populations which is critical to maintaining genetic diversity and dispersal among populations (Rieman and McIntyre 1995).
In response to population declines, resident forms of redband trout are considered a species of special concern by the U.S. Fish and Wildlife Service, American Fisheries Society, and all states throughout their historic range (Idaho, Oregon, Washington, Nevada, California and Montana) and are classified as a sensitive species by the U.S. Forest Service and the BLM. Despite their broad distribution, few strong populations exist. Known or predicted secure populations inhabit 17 percent of the historic range and 24 percent of the present range (Lee et al. 1997). Furthermore, Lee et al. (1997) reported that only 30 percent of the watersheds supporting spawning and rearing populations were classified as strong populations. Consequently, populations in Oregon and California have been petitioned for listing under the Endangered Species Act (ESA). The California petition is currently under review and the 1999 petition to list the Great Basin redband trout in Oregon was deemed unwarranted at this time.
On April 4, 1994 the Biodiversity Legal Fund of Colorado and Mr. Donald Kern of Kalispell, Montana formally petitioned the United States Fish and Wildlife Service to consider the Kootenai River population of redband trout as an endangered species under the ESA. The 1994 petition to list this population under the ESA was dismissed due to lack of information. In 1993, the American Fisheries Society classified redband trout as a Class B species of special concern. A Class B species of special concern is defined as a species or subspecies that has “limited numbers and/or habitats in Montana; is fairly widespread and has fair numbers in North America as a whole; and elimination from Montana would be at least a moderate loss to the gene pool of the species or subspecies”(Holton 1980). A Class A species of special concern is defined as a species or subspecies that has “limited numbers and/or habitats both in Montana and elsewhere in North America and elimination from Montana would be a significant loss to the gene pool of the species or subspecies” (Holton 1980). Due to the imperiled status of redband trout in Montana and throughout their historic range, redband trout should be upgraded from a Class B to a Class A species of special concern in Montana.
The Columbia River redband trout is considered a subspecies of the rainbow trout Oncorhynchus mykiss evolutionary line (Behnke 1992). Ancestral redband trout probably reached the Sacramento-San Joaquin basin from the south during the second half of the Pleistocence Epoch and penetrated the Columbia, Fraser and Athabasca river basins between 30 and 50,000 years ago (Behnke 1992). Presently, rainbow trout classification recognizes a single species O. mykiss, yet in the past many species were recognized. Behnke (1992) separates rainbow trout into the following three separate evolutionary significant groups: 1) the redband trout of the Sacramento, Kern, and McCloud Rivers in California, 2) the redband trout of the Columbia and Fraser River basins located east of the Cascade Mountains to barrier falls on the Kootenai, Pend Oreille, Spokane, and Snake rivers and 3) coastal rainbow trout. Under this taxonomy, all redband trout of the Columbia and Fraser River basins are classified as O. mykiss gairdneri.
This subspecies is genetically and morphologically differentiated from coastal rainbow trout. Morphological characteristics of distinction include the presence of vestigial basibranchial teeth, larger spots, more elliptical parr marks, fewer pyloric caeca, yellow and orange tints on the body, a trace of a cutthroat mark, and light colored tips on dorsal, anal, and pelvic fins (Behnke 1992). However, genetic techniques (e.g. protein electrophoresis) provide the only method to correctly identify this subspecies as unique from other salmonids.
The Kootenai River drainage population of redband trout is Montana’s only native rainbow trout and represents the furthest inland penetration of redband trout in the Columbia River Basin. Until recently, the upper distribution of redband trout in the Columbia River Basin was believed to extend upstream to Kootenai Falls, which was considered a barrier falls located approximately 8 km east of Troy, Montana (Allendorf et al. 1980). Recent information suggests that the barrier was not Kootenai Falls, but existed in geologic time near the present day Libby Dam or Fisher River (Hensler et al. 1996). Presently, genetically pure populations of redband trout have been identified using starch gel electrophoresis in the following streams in the Kootenai River drainage in Montana: Callahan Creek, Basin Creek, the upper north (British Columbia) and east forks of the Yaak River, and upper Big Cherry Creek and Wolf Creek (Allendorf et al. 1980; Leary et al. 1991; Huston 1995; Hensler et al. 1996). Results of genetic surveys indicate that redband trout were native to low-gradient valley-bottom streams throughout the Kootenai River drainage but are presently restricted to headwater areas. Allendorf et al. (1980) concluded that redband trout is a native rainbow trout to the Kootenai River, Montana, and that “planting of hatchery rainbow trout has created a situation of tremendous genetic divergence among local populations” (e.g. hybridization). Perkinson (1993) hypothesized that of 300 km of habitat originally used by redband trout in Montana, only 100 km (33%) of their historic range is presently occupied by a stock that is at least 95% pure.
Redband trout inhabiting Callahan Creek and the upper Yaak River Drainage are isolated into two separate regions by Yaak River Falls, a falls-chute barrier located 4 km from the mouth of Callahan Creek and a barrier falls located in the lower East Fork of the Yaak River. These remnant populations, which are spatially fragmented and isolated from genetic exchange, represent the only known remaining sources of native redband trout capable of refounding their historic distribution in Montana downstream of Kootenai Falls.
Columbia River redband trout exhibit a wide variety of life history strategies. Anadromous stocks of redband (steelhead) trout historically migrated almost 1,600 km to the middle and upper Columbia River Drainage (Behnke 1992). Many of these stocks are now extinct due to dams impeding upstream migration. The gerrard strain of rainbow trout (kamloops) of Kootenay Lake, British Columbia, represents an adfluvial form which attains a large body size due to their piscivorous diet of kokanee salmon O. nerka and advanced size of sexual maturity. Kamloops redband trout reportedly spawn in Kootenai River tributaries in Montana downstream from Kootenai Falls (Huston 1995). Fluvial stocks occupy larger rivers and spawn in smaller tributaries. Resident forms inhabit smaller tributaries and headwater areas for their entire lives. The Kootenai River redband population in Montana supports subpopulations of the resident form (Muhlfeld 1999), although a migratory fluvial and/or adfluvial component may be undetectable due to hybridized populations inhabiting the lower portions of the drainage. Differentiation of redband trout life history forms (anadromous, adfluvial, fluvial, and resident) is undetectable using meristic counts, coloration patterns, and genetic markers (Behnke 1992). The inability to morphologically and genetically identify life history forms of Columbia River redband trout suggests that each population should be managed according to the geographic area or the site-specific life history strategy.
The seasonal habitat requirements of redband trout in the Kootenai River drainage in Montana were investigated in the Kootenai River drainage during 1997 and 1998 (Hensler and Muhlfeld 1999; Muhlfeld 1999; Muhlfeld et al. 2001 In-pressa; Muhlfeld et al. 2001 In-pressb). Summer results demonstrated that juvenile (36-125 mm) and adult (> 126 mm) redband trout prefer deep microhabitats (> 0.4 m) with low to moderate velocities (< 0.5 m/s) adjacent to the thalweg. Conversely, age-0 (< 35mm) redband trout select slow water (< 0.1 m/s) and shallow depths (< 0.2 m) located in lateral areas of the channel. Age-0, juvenile and adult redband trout strongly select pools and avoided riffles; runs were used generally as expected (based on availability) by juveniles and adults and more than expected by age-0 redband trout. At the macrohabitat scale, a multiple regression model indicated that low-gradient, mid-elevation reaches with an abundance of complex pools are critical areas for the production of redband trout. Mean reach densities ranged from 0.01-0.10 fish/m2. During the fall and winter period, adult redband trout occupied small home ranges and found suitable overwintering habitat in deep pools with extensive amounts of cover in headwater streams. In Basin Creek, adult redband trout commenced spawning (e.g. redd construction) during June as spring flows subsided following peak runoff. Redband trout generally selected redd sites in shallow pool tail-out areas (mean depth = 0.27 m; range: 0.20-0.46) with moderate water velocities (mean velocity = 0.50 m/s; range: 0.23-0.69 m/s) dominated by gravel substrate.
Land and water use practices, habitat loss, over harvest, hybridization and a geographical restricted range are leading factors contributing to the decline of redband trout abundance, distribution and genetic diversity in the Columbia River basin (Williams et al. 1989; Behnke 1992). Recent concern has arisen that the Kootenai River Basin redband trout population is at a high risk of extinction due to hybridization with introduced coastal rainbow trout, habitat fragmentation, and stream habitat degradation (Perkinson 1993; Muhlfeld 1999). Widespread introductions of non-native trout, primarily coastal rainbow trout and eastern brook trout (Salvelinus fontinalis), have lead to intensive competition, species replacement and hybridization. Stocking non-native fish above geologic barriers and in adjacent drainages poses a severe threat to the genetic purity and population persistence of isolated populations of redband trout. Habitat degradation has been primarily attributed to poor land management practices, construction of dams and diversions, and floodplain development. Land development activities such as road construction, logging and grazing can alter substrate composition and reduce the frequency and area of pools, which may have very deleterious effects to the abundance and distribution of redband trout.
Long-term conservation and management of this subspecies will require state and federal agencies to develop a comprehensive plan to protect and restore redband trout throughout their native range in Montana. One objective should be to develop a wild brood stock for reintroductions throughout the Kootenai River drainage. Montana Fish, Wildlife and Parks (MTFWP) is in the process of developing brood stocks that will be located at the Libby Field Station (M. Hensler, personal communication). Results of microsatellite analyses based on allozyme electrophoresis of several populations of redband trout in Montana and British Columbia indicate significant differences between watersheds and relatively small differences between populations within watersheds (Knudsen et al. In-prep). In order for reintroduction programs to be genetically rational, watershed-specific stocks are needed for successful recovery programs. Habitat surveys should be conducted to identify streams suitable for reintroductions of redband trout. However, re-introduction efforts should be implemented with caution because introduction of a species to any aquatic habitat requires many considerations because species interactions are complex and difficult to predict (Li and Moyle 1981). Maintaining channel complexity and quality pool habitat throughout their limited range is probably essential to the persistence of this subspecies in Montana. Habitat improvement and conservation efforts are scheduled for the foreseeable future by MTFWP and the U.S. Forest Service.
In summary, due to the imperiled status of redband trout in Montana and elsewhere throughout their historic range, the Montana Chapter of the American Fisheries should consider that the Kootenai River population of redband trout be upgraded from a Class B to a Class A species of special concern. Extirpation of redband trout in Montana would be a significant loss to the gene pool of the subspecies throughout the Columbia River Basin.
- Allendorf, F.W. , D.M. Esperlund, and D.T. Scow. 1980. Coexistence of native and introduced rainbow trout in the Kootenai River Drainage. Proceedings of the Montana Academy of Sciences 39:28-36.
- Behnke, R.J. 1992. Native trout of western North America. American Fisheries Society Monograph 6. Bethesda, Maryland.
- Hensler, M.E., J.E. Huston and G. K. Sage. 1996. A Genetic Survey of Lakes in the Cabinet Wilderness Area and Proposed Inland Rainbow Trout Recovery. Montana Fish Wildlife and Parks, Kalispell, Montana.
- Hensler, M.E., C.C. Muhlfeld. 1999. Spawning ecology of redband trout in Basin Creek, Montana. A Report to the Whirling Disease Foundation. Montana Fish, Wildlife and Parks, Bozeman, MT.
- Holton, G.H. 1980. Fishes of special concern. Montana Outdoors 11(1): 2-6.
- Huston, J.E. 1995. A Report on the Kootenai River Drainage Native Species Search. A Report to the U.S. Fish and Wildlife Service. Montana Fish, Wildlife and Parks, Kalispell, MT.
- Knudsen, K. C. Muhlfeld, K. Sage, and R. Leary. In-prep. Genetic differences among populations of redband trout in the Kootenai River drainage, Montana.Transactions of the American Fisheries Society.
- Leary, R.F, F.W. Allendorf, and K. G. Sage. 1991. Genetic analysis of trout populations in the Yaak River Drainage, Montana. Wild trout and salmon genetics laboratory report 91/3. University of Montana, Missoula.
- Lee, D.C., JR. Sedell, B.E. Reiman, R.F. Thurow, J.E. Williams. 1997. Broadscale assessment of aquatic species and habitats. In T.M. Quigley and S.J. Arbelbide, eds. An Assessment of Ecosystem Components in the Interior Columbia Basin and portions of the Klamath and Great Basins. U.S. Forest Service General Technical Report PNW-GTR, Portland, OR.
- Li, H.W. and P.B. Moyle. 1981. Ecological analysis of species introductions into aquatic systems. Transactions of the American Fisheries Society 110:772-782.
- Muhlfeld, C.C. 1999. Seasonal habitat use by redband trout (Oncorhynchus mykiss gairdneri) in the Kootenai River drainage, Montana. Master’s thesis. University of Idaho, Moscow, Idaho.
- Muhlfeld, C.C., D.H. Bennett, and B. Marotz. 2001-In pressa. Summer habitat use by redband trout in the Kootenai River drainage, Montana. North American Journal of Fisheries Management (February).
- Muhlfeld, C.C., D.H. Bennett, and B. Marotz. 2001-In pressb. Fall to winter movements and habitat use by redband trout in Montana. North American Journal of Fisheries Management (February).
- Perkinson, R.D. 1993. Presentation to the American Fisheries Society, Montana Chapter,17 February, 1993.
- Rieman, B.E., and J.D. McIntyre. 1995. Occurrence of bull trout in naturally fragmented habitat patches of varied size. Transactions of the American Fisheries Society 124:285-296.
- Williams, J.E., J.E Johnson, D.A. Hendrickson, S. Contreras-Balderas, J.D. Williams, M Avarro-Mendoza, D.E. McAllister, and J.E. Deacon. 1989. Fishes of North America endangered, threatened, or of special concern: 1989. Fisheries 14(6):2-20.