This chapter summarizes information on presence, absence, current status, and probable historical distribution of steelhead Oncorhynchus mykiss and stream-type (age-1 migrant) and ocean type (age-0 migrant) chinook salmon O. tshawytscha in the interior Columbia River basin and portions of the Klamath River basin. Data were compiled from existing sources and via surveys completed by more than 150 biologists working in the region.We developed models to quantitatively explore relationships among fish status and distribution, the biophysical environment, and land management.Biophysical setting was an important determinant of species distribution and habitat suitability.We applied model results to predict fish presence in unsampled areas and mapped expected distributions in more than 3,700 subwatersheds.Chinook salmon and steelhead are extirpated from more than 50% of their potential historical ranges. Most remaining populations are severely depressed; less than 2% of the watersheds in the current range were classified as supporting strong population of steelhead or stream-type chinook salmon.Wild, indigenous fish are rare: 22% of remaining steelhead stocks and less than 17% of chinook salmon stocks were judged to be genetically unaltered by hatchery-reared fish.Much of this historical production has been eliminated. However, a core for maintaining and rebuilding functional areas remains.Protection of core areas critical to stock persistence and restoration of a broader matrix of productive habitats will be necessary for productive and sustainable fisheries. This effort will require conservation and restoration of sufficient habitats to ensure the full expression of phenotypic and genotypic diversity in chinook salmon and steelhead.
Chapman estimated peak runs of Pacific salmon and steelhead in the Columbia River in the late 1800s were about 7.5 million fish. Estimates of annual chinook salmon returns prior to 1850 range from 3.4 to 6.4 million fish. Commercial harvest of chinook salmon in the mainstem Columbia River peaked in 1883 at 2.3 million fish and was about 1.3 million fish annually from 1890-1930. Steelhead have been reported in the commercial Columbia River catch since 1889 and 2.23 million kg of canned steelhead were produced in 1892. Estimates of steelhead runs were derived after Bonneville Dam was constructed, and, in 1940, 423,000 summer-run steelhead passed the dam. Returns of wild steelhead to the uppermost Snake River dam have declined from more than 80,000 in the 1960s to an estimated 7,900 in 1995. In the Snake River, an estimated 1,882 naturally produced stream-type chinook salmon reached Lower Granite Dam in 1994 compared to an estimated production of 1.5 million fish in the late 1880s. Redd counts in four tributaries to the Middle Fork Salmon River in central Idaho have declined from more than 2,000 redds in the late 1960s to 11 in 1995.
Steelhead formerly ascended the Snake River and spawned in reaches of Salmon Falls Creek, Nevada, more than 1,450 km from the ocean. Approximately 16,935 km of stream were accessible to steelhead in the Columbia River basin, including Canada
Steelhead were reported as present in about 33% of the subwatersheds within the potential range, with strong populations present in 1.9% of the current known range and <1% of the potential range.The distribution of steelhead was unknown or unclassified in 7% of the potential range (279 subwatersheds) and reported as present but of unknown status in another 289 subwatersheds.
Our results suggest that spawning and rearing areas for steelhead were likely to be found within specific ERUs (Ecological Reporting Units), in small to mid-size streams, in erosive land types and in steeper, higher elevation subwatersheds. Spawning and rearing occurred primarily on Forest Service Lands.
Steelhead were known or predicted to presently occur in 46% of their potential range and 23% of the subwatersheds in the study area. Despite their relatively broad distribution, very few strong steelhead populations exist and many populations have been influenced by non-indigenous forms. We estimated about 39% of the potential range still supports spawning and rearing, but only 2% of those subwatersheds were classified as supporting strong populations. Wild, indigenous steelhead, unaltered by hatchery stocks, are rare and present in 10% of the potential range and 22% of the current distribution.Remaining wild stocks are concentrated in reaches of the Salmon River in central Idaho and the John Day River basin in Oregon. Although few wild stocks were classified as strong, the only subwatersheds classified as strong were those sustaining wild stocks (6%). About 9% of strong populations were found in designated wilderness and 70% were found on Forest Service or BLM lands.
Chinook salmon were historically found in all accessible areas of the Snake River downstream from Shoshone Falls and in all accessible areas of the Columbia River downstream from Windermere Lake, British Columbia. Prior to overfishing and habitat alterations, migrating chinook salmon in the Columbia River formed a continuum from March to October with the largest part of the run likely consisting of summer chinook salmon. An estimated 16,935 km of stream were accessible to chinook salmon in the Columbia River basin in the U.S. and Canada.
Stream–type chinook salmon were reported as present in about 21% and ocean-type chinook salmon in about 25% of the subwatersheds within the potential range. Strong populations were judged to be present in<1% of the potential range of stream-type chinook salmon and in 4% of the potential range of ocean-type chinook salmon. Ocean-type chinook salmon remain in all ERUs in the potential range but are extirpated from more than 70% of the potential subwatersheds. We estimated that about 20% of the potential range still supports spawning and rearing areas for stream-type chinook salmon and 1.2% of those watersheds (0.2% of the potential range) were classified as supporting strong populations. The North Fork of the John Day River contains the only strong population of stream-type chinook salmon.
Like steelhead, many remaining chinook salmon populations have been influenced by hatchery-reared fish. Wild populations unaltered by hatchery stocks are rare and present in 4% of the potential range and 15% of the current range for stream-type chinook salmon and 5% of the potential range and 17% of the current range for ocean-type chinook salmon. With the exception of strong populations in the Hanford reach, the only subwatersheds classified as strong were those sustaining wild stocks. About 50% of stream-type chinook salmon were found in designated wilderness or National Park Service lands and 88% were found on Forest Service or BLM lands.
The status and distribution of chinook salmon and steelhead within the study area is very different than it was historically: we estimated that stream-type and ocean-type chinook salmon have been extirpated from more than 70% of their potential range and steelhead from 54% of their potential range. About 12,452 km of streams in the potential range in the Columbia River basin in the U.S. and Canada are no longer accessible to anadromous fish.
Populations in 99% of remaining spawning and rearing areas for stream-type chinook salmon, 76% of those for ocean-type chinook salmon, and 98% of those for steelhead were classified as depressed.
Extinctions and declining populations have resulted in lower diversity and total abundance of chinook salmon and steelhead.
The recent declines in Columbia River salmon and steelhead, for example, have likely been influenced by ocean conditions and a period of extended drought. Although environmental variability is a factor and may be the proximate cause of decline or extinction in some cases, the effects of human-caused disturbance appear to be far more important to the declines in abundance of chinook salmon and steelhead.
The number of subwatersheds where strong populations were know to be present included 8, 21, and 23 for stream-type chinook salmon, ocean-type chinook salmon and steelhead respectively.
Construction and operation of mainstem dams on the Columbia and Snake rivers is considered to be the major cause of recent declines of anadromous fish. Hydroelectric development changed Columbia and Snake river migration routes from mostly free flowing in 1938 to a series of dams and impoundments by 1975.
Smolt to adult return rates declined from more than 4% in 1968 to less than 1.5% from 1970-1974. In 1973 and 1977, low flows resulted in 95% of migrating smolts never reaching the ocean.Losses of mid- and upper-Columbia ocean-type chinook salmon were estimated to be about 5% per dam for adults and 18 to 23% per dam for juveniles.
More than 55 introduced fishes occur within the current range of salmon and steelhead.…non-natives may pose a greater risk to native species where habitat has been disturbed. Dams have created habitat that is suitable for a variety of native and non-native predators and potential competitors.
With few exceptions, most watersheds supporting chinook salmon and steelhead are also likely to be influenced by hatchery stocks. By the late 1960s hatchery production surpassed natural production in the Columbia River basin. Meanwhile, production of wild anadromous fish in the Columbia River basin has declined by about 95% from historical levels.
Byrne et al. (1992) suggested that (hatchery) supplementation of native stocks with hatchery fish have typically resulted in replacement, not enhancement of native fish.Most (107/121) of the healthy anadromous salmonid stocks identified…either have had no fish culture activities in the home watershed or have been exposed to little risk from stock transfers or interaction with hatchery fish.
Wild stocks appear to be rare. Biologists judged wild stocks of steelhead and stream- type and ocean-type chinook salmon unaltered by hatchery releases to be present in 10, 4, and 5% of the potential range, respectively.
Harvest has contributed to the decline of spring and summer chinook salmon in the study area since the late 1800s and to the decline of fall chinook salmon after 1920.Historical ocean and river harvest rates exceeded 80%.Although the harvest of wild stocks has been reduced, wild salmon and steelhead are killed during tribal fisheries, commercial salmon fisheries in the Columbia River and coastal marine waters, and in high seas driftnet fisheries.
We focused on identifying emphasis areas of two types: subwatersheds with designated strong populations and those retaining naturally reproducing populations of salmon and steelhead, including genetically intact populations.
…strong populations were rare or absent even in relatively undisturbed habitats in the Central Idaho Mountains ERU. Because salmon and steelhead have very few strongholds, subwatersheds supporting naturally reproducing populations and populations with high genetic integrity may represent the only areas available from which to anchor a conservation strategy.
The most productive, abundant, and diverse populations are likely to be the most resilient. Because native gene complexes likely offer the best resources for refounding extinct populations in similar environments, conservation of locally adapted and marginal populations will also be critical.
Federal land management will be crucial to the establishment of emphasis areas. Both steelhead (70%) and stream-type chinook salmon (88%) have most of their populations on federal land. The recovery of depressed populations will also depend on management of federal lands because 61% and 77% of depressed stream-type chinook salmon and steelhead populations, respectively, occupy federal land. In the short term, conservation and rehabilitation of habitats available to remaining populations will be key. Rehabilitation of depressed populations cannot rely on habitat improvements alone, but requires a concerted effort to address causes of mortality in all life stages including freshwater spawning, rearing, and overwintering, juvenile migration, ocean survival, and adult migration.
Healey and Prince (1995) report that genotypic variation maps mainly on the population scale whereas phenotypic variation maps strongly on the ecosystem and landscape scales.This suggests that local populations may have a much larger effect on phenotypic diversity than on overall genotypic diversity. The authors suggest that, because phenotypic diversity is a consequence of the genotype interacting with a particular environment, it is critical to preserve unique habitats and ensure their accessibility to Pacific salmon. The critical conservation unit, therefore, is the population within its habitat.
Conservation of salmon and steelhead populations will require the maintenance or rehabilitation of a network of well-connected, high-quality habitats that support the full expression of potential life histories and dispersal mechanisms, and the genotypic and phenotypic diversity necessary for long-term persistence and adaptation in a variable environment. Protection of stronghold emphasis areas will not be sufficient. Such reserves will never be large enough or sufficiently distributed to maintain biological diversity.