Upstream Salmon and Society in the Pacific Northwest (1996) / Chapter Skim
Currently Skimming:
2 Salmon Geography and Ecology
2 Salmon Geography and Ecology
Pages 28-45
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From page 28... ...
Salmon are parts of ecosystems that cover areas much larger than marked properties and government jurisdictions. Salmon generation times are usually 2-6 years, and interdecadal changes in climate influence salmon abundance and production.
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From page 29... ...
SALMON LIFE HISTORY AND DISTRIBUTION The life histories of Pacific anadromous salmon set the geographic stage for solutions to the problem of their decline. Their life histories have three characteristics anadromy, homing, and semelparity that are key to considering trends in abundance and factors responsible for salmon declines; these characteristics differ among species and individual runs.
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From page 30... ...
Second, coho and chinook usually rear in coastal waters, although some migrate to the open ocean as well. Third, steelhead migrate to the open ocean, butunlike pink, chum, and sockeye appear to migrate directly to open ocean as smelts and return directly to the vicinity of their river of origin, rather than migrating along the coast (Burgner et al.
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From page 31... ...
Winter steelhead, which are more prevalent in the lower reaches of rivers, enter freshwater in winter and spawn soon thereafter. Individual Species Distributions Pink Salmon Pink salmon, the most abundant anadromous salmon in North America, are relatively scarce in the Pacific Northwest (Heard 19911.
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From page 32... ...
Some populations migrate to offshore waters, but many remain relatively near the coast during their marine residence (Sandercock 19913. Coho are caught in commercial and recreational fisheries in waters off the coast and in Puget Sound and the Strait of Georgia.
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From page 33... ...
19933. PACIFIC NORTHWEST SALMON AREAS The region's political divisions do not correlate closely with the life history and distribution of anadromous Pacific salmon (see Chapter 4 for details of populations)
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From page 34... ...
Sacramento and San Francisco are the major urban centers in the Sacramento drainage. The Columbia River Basin differs from the Sacramento River Basin in that the largest urban area, Portland, is farther upstream, more than 185 km from the river mouth.
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From page 35... ...
Most salmon migrate along the North American coast, either north or south, to reach feeding areas, where they then follow major ocean currents while foraging (Pearcy 1992~. SALMON ECOLOGY IN RIVER BASINS To understand the ecology of anadromous Pacific salmon in freshwater, one must consider species interactions, complex adaptations of juveniles to stream habitat, and the influence of returning spawners on stream ecosystems.
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From page 36... ...
However, except in such large river basins as the Columbia, Chehalis, and Sacramento, the region's freshwater communities tend to contain few fish species. Typical Puget Sound and Pacific Coast streams might have two or three salmons (family Salmonidae)
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From page 37... ...
In small watersheds with dense forest canopies, much of the organic matter in streams originates in the surrounding forest, and the invertebrate communities are dominated by organisms specialized for processing wood and leaves (Gregory 19831. In larger watersheds, where streams are too wide to be completely shaded, or in small streams where the canopy has been removed, the food base of the aquatic community shifts to algae produced photosynthetically in the stream itself (Bilby and Bisson 1992~.
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From page 38... ...
When not eaten by wildlife, carcasses can be used through four pathways: autotrophic fixation by aquatic plants and subsequent transfer through periphyton-based food webs, heterotrophic fixation by bacteria and fungi and transfer through decomposer-based food webs, abiotic uptake by sorption within the stream substrate, and direct consumption of carcass tissues and remaining eggs by fish. Before they die, however, adult salmon can exert another important influence on the stream ecosystem by their digging activities.
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From page 39... ...
Interdecadal changes in the ocean environment especially in water temperature and currents and associated biological communities influence growth and survival rates and thus the return of adults (Francis and Sibley 1991, Beamish and Bouillon 1993, Francis and Hare 19941. Density-dependent effects-how salmon at sea are affected by the number of young salmon entering the ocean from their natal streams or hatcheriesmight be experienced during the ocean phase and could thwart attempts to supplement populations by stocking during periods of poor ocean conditions (R.
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From page 40... ...
Recognition of the interdecadal patterns enhances our knowledge of seasonal and interannual variations in the ocean environment (Wooster 19923. Interdecadal changes have influenced the migration routes of adult salmon returning to spawning streams and, more important, the physics and biology of the ocean (UNESCO 1992' related to salmon production.
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From page 41... ...
that the index and the catches of Pacific salmon were low at the turn of the centuryfurther evidence is needed to support their conclusion. The relation of both salmon catches and zooplankton abundance in the North Pacific Ocean to the Aleutian Low Pressure Index suggests that the interdecadal changes in salmon abundance are mediated via the food web.
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From page 42... ...
there are two mean states of winter atmospheric circulation in the North Pacific which relate to the intensity and location of the winter mean Aleutian Low .
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From page 43... ...
sockeye-salmon catches from 1920 to 1990, northern Gulf of Alaska pink-salmon catches from 1935to 1990, winter air temperatures at Kodiak Island, and the North Pacific index of the intensity of the Aleutian Low. Step changes were apparent in all four time series; in the air-temperature
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From page 44... ...
suggested that with the exception of Japanese chum salmon, hatcheries were not important contributors to the increase in salmon catches in the North Pacific during the 1970s and 1980s. In the Gulf of Alaska, increased hatchery production of pink salmon contributed to the increase in catches from the early to middle 1980s, but natural reproduction increased at the same time by a factor of 3 to 4.
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From page 45... ...
Interdecadal variations and the importance of the ocean phase should be incorporated into human thought, planning, and actions in response to the effects of and attempts to repair damage that occurred during the freshwater phases of the salmon lives. The possible overriding effects of interdecadal changes in ocean conditions on salmon, the results of freshwater salmon management, and the overwhelming focus of human attention on the more-visible freshwater phases of the salmon history combine to provide the key ingredients for surprises in the future.
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