Dynamics of Chinook Salmon Populations Within Idaho's Frank
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Dynamics of Chinook Salmon Populations Within Idaho’s Frank Church Wilderness: Implications for Persistence Russell F. Thurow Abstract—Research was begun in 1995 to describe factors influ- Since European settlement of the Snake and Columbia encing the spatial dynamics and persistence of federally listed river basins, a plethora of factors have contributed to de- chinook salmon within the Frank Church River of No Return clines in the distribution and abundance of chinook salmon. Wilderness. Results addressed two objectives: 1) description of These include blocked access to historical habitat, passage chinook salmon redd distributions, and 2) comparison of index and mortality at dams and obstructions, freshwater and estuar- total redd counts. Annual redd counts ranged from 20 to 661, and ies habitat degradation, overharvest, and interactions with 99% of redds were constructed in tributaries. Redds were observed hatchery-reared and nonnative fishes. Thurow and others at elevations between 1,140 and 2,070 m, with a majority (56%) (2000) reported that stream-type chinook salmon have >1,900 m. The distribution of redds deviated from a random pattern been extirpated from more than 70% of their potential and fluctuated with adult salmon numbers. At lower adult escape- historical range, and strong populations remain in 1.2% of ments, redds were clustered in specific areas of a few watersheds. At the current range in portions of the Columbia River and higher escapements, fish constructed additional redds near previ- Klamath River basins east of the Cascade Crest. An esti- ous clusters and also outside of clusters and in watersheds that were mated 12,452 km of potential historical habitat have previously not utilized. Index area counts averaged 63% of total been blocked and are no longer accessible to anadromous counts. fish in the Snake and Columbia river basins (Northwest Power Planning Council 1986). Nehlsen and others (1991) identified habitat loss or degradation as a major problem for 90% of the 195 at-risk salmon and steelhead stocks they The Columbia and Snake River basins historically sup- identified. ported large runs of chinook salmon (Oncorhynchus Although a variety of factors over many decades have tshawytscha). Estimates of annual chinook salmon returns influenced declines in Snake River anadromous fish, con- to the Columbia River prior to 1850 ranged to 6.4 million fish struction and operation of mainstem dams is considered the (Northwest Power Planning Council 1986). Despite several proximate cause of recent declines (Columbia Basin Fish decades of habitat alteration and commercial harvest by the and Wildlife Authority 1990). Smolt-to-adult return rates late 1880s, an estimated 1.5 million chinook salmon re- declined from more than 4% in 1968 (Raymond 1979) to less turned annually to the Snake River in that decade (Bevan than 0.5% in the 1990s (Marmorek and others 1998). As a and others 1994). Many native Americans depended on result of low flows in the migration corridor in 1973 and salmon as a subsistence and ceremonial resource (North- 1977, 95% of migrating smolts never reaching the ocean west Power Planning Council 1986). Since European (Raymond 1979). The influence of passage mortality was settlement, salmon and other anadromous species have further illustrated by Huntington and others (1996) and continued to influence social and economic systems (Thurow Lee and others (1997), who reported that no healthy or and others 2000). strong populations of anadromous fish were found in the Today, chinook salmon and other anadromous fishes central Idaho wilderness, even though it contains some of native to the Snake River are imperiled. All Snake River the Pacific Northwest’s highest quality spawning and rear- anadromous salmonids, including stream-type (spring and ing habitat. summer), and ocean-type (fall) chinook salmon, steelhead In response to declining populations and ESA require- (O. mykiss), and sockeye salmon (O. nerka), are listed as ments, agencies have adopted policies that attempt to con- threatened or endangered under the Endangered Species serve and restore remaining chinook salmon populations. Act of 1973 (ESA). Coho salmon (O. kisutch) have been These have included measures to maintain genetic integrity extirpated from the Snake River (Lee and others 1997). of remaining wild stocks, reduce passage mortality by im- Pacific lamprey (Lampetra tridentata) have declined dra- proving conditions in the migration corridor, reduce the matically. Harrison (1995) reported that in the 1960s nearly effects of exotics, restrict sport and commercial harvest, and 50,000 lamprey were counted at Ice Harbor Dam; less than adopt measures to conserve or restore remaining critical 400 were counted in 1994. habitat. The conventional approach to managing critical habitat focused on conserving or restoring the quality of In: McCool, Stephen F.; Cole, David N.; Borrie, William T.; O’Loughlin, remaining habitats–that is, conserving and restoring those Jennifer, comps. 2000. Wilderness science in a time of change conference— habitats considered necessary for chinook salmon to com- Volume 3: Wilderness as a place for scientific inquiry; 1999 May 23–27; plete their complex life cycle from an incubating egg to a Missoula, MT. Proceedings RMRS-P-15-VOL-3. Ogden, UT: U.S. Depart- ment of Agriculture, Forest Service, Rocky Mountain Research Station. mature fish depositing eggs in natal spawning areas. Russell F. Thurow is a Fisheries Research Biologist, U.S. Department of While conservation of the quality of critical habitats is Agriculture, Forest Service, Rocky Mountain Research Station, 316 E. essential, there is growing concern that the size and spacing Myrtle, Boise, Idaho 83702 U.S.A., e-mail: [email protected] USDA Forest Service Proceedings RMRS-P-15-VOL-3. 2000 143 of habitats also needs to be considered (Krohn 1992). Simberloff (1988) suggested that effective conservation may require maintaining or restoring a critical amount or mosaic of habitat, as well as habitat of certain quality. Recent papers support the hypothesis that conservation of declining salmonid stocks may require attention to spatial concepts (Frissell and others 1993; Rieman and McIntyre 1993). In an empirical study of larger scale processes, Rieman and McIntyre (1995) reported that habitat area influenced the distribution of disjunct populations of bull trout (Salvelinus confluentus) and suggested that larger-scale spatial pro- cesses may be important to salmonid persistence. The relevance of these concepts to declining populations of chinook salmon is unknown. In 1995, scientists at the Rocky Mountain Research Sta- tion initiated research to describe factors influencing the spatial dynamics of declining populations of chinook salmon. The central hypothesis states that habitat area, habitat quality, or habitat context (location in relation to other populations) influences the occurrence of spawning chinook salmon. If the hypothesis is true, recolonization and per- sistence of chinook salmon populations may be strongly influenced by the spatial geometry of remaining habitats. The hypothesis is being tested by describing the distribution of chinook salmon redds and potential spawning areas in a large, relatively undisturbed wilderness basin. Although a suite of objectives are being addressed, this paper reports results addressing two objectives: 1) describe the temporal and spatial distribution of chinook salmon redds and 2) com- pare index and non-index area redd counts. This research represents the first comprehensive survey of redds in the study area and provides information on the temporal and spatial dynamics of chinook salmon in a large wilderness watershed. In addition to addressing larger scale spatial questions about persistence, this research provides an estimate of the total number of redds constructed in the study area, enabling managers to estimate total adult Figure 1—Potential chinook salmon spawning tributaries in the Middle escapement. Fork Salmon River drainage, Idaho. Study Area _____________________ The Middle Fork Salmon River (MFSR), a National Wild the largest in the National Forest system. The Gospel Hump 2 and Scenic River, drains about 7,330 km of a remote area of and Selway-Bitterroot wilderness area border the FC- central Idaho. For most of its length, the river flows RONRW and together comprise nearly 1.6 million hectares through the Frank Church River of No Return Wilderness (US Forest Service 1998). In 1984, the current name was (FC-RONRW). The MFSR drainage provides critical habitat adopted in honor of the late Senator Frank Church’s efforts for six ESA listed species: bald eagle (Haliaeetus to secure wilderness designation. leucocephalus), peregrine falcon (Falco peregrines), grey Elevations range from >3,150 m in adjacent mountains to wolf (Canis lupus), chinook salmon, steelhead, and bull 1,550 m at the rivers’ confluence. The topography has high trout. From its origin at the confluence of Bear Valley and relief. The geology of the area is highly variable and domi- Marsh Creeks, the MFSR flows north-northwest for 171 km nated by Challis Volcanics (Eocene age) and intrusions of through the Salmon River mountains and joins the Salmon the Casto Pluton phase (Tertiary age) of the Idaho Batholith River 92 km downstream from Salmon, Idaho (fig. 1). Twelve (Minshall and others 1981). The climate is semiarid, with major streams and hundreds of smaller ones are tributary to most precipitation falling as snow. Climate varies markedly the river. Human access in the lower 156 km of the main with elevation; precipitation ranges from 38-50 cm in lower river and most tributaries is limited to a few airstrips, float valleys to 76-100 cm at higher elevations (Minshall and craft, or by trail. From 1930-1980, a majority of the region others 1981). Maximum daily air temperatures range from was managed in “Primitive Area” status (US Forest Service -30 to >33 °C. Vegetation also varies by elevation, with 1998). In 1980, the Central Idaho Wilderness Act estab- sagebrush (Artemsia sp), grasses and shrubs common in lished the 906,136 hectare wilderness that remains the lower elevations and on south-facing slopes.