Oncorhynchus tshawytscha

See Utter et al. (1989) for information on genetic differences among populations in the Pacific Northwest. In the Nanaimo River, British Columbia, within-stock variation in age of seaward migration of juveniles is a genetic adaptation to local rearing environments; fishes with different life histories had biochemical and morphological differences that were linked to increased fitness in different rearing habitats (see Nehlsen et al. 1991). Waples and Teel (1990) found substantial allele frequency changes over 2-4 years in hatchery, but not wild, populations along the Pacific coast of Oregon.

Has hybridized with pink salmon in the St. Marys River, Michigan (Rosenfield 1998).

Still widespread and locally numerous in large range in the North Pacific Ocean and associated streams; many stocks have been extirpated and many others have declined; habitat has been degraded by logging and other activities, and dams have impeded movements; releases of hatchery stock probably have masked declines/extirpations of some native stocks; see separate files for various chinook salmon populations.

Native range includes the Pacific Ocean and tributary drainages, in North America presently from the Sacramento-San Joaquin system (sometimes farther south) north to Point Hope, Alaska, and in northeastern Asia, from northern Japan to the Anadyr River. The species has been widely stocked elsewhere.

In the Columbia River basin, the Hanford Reach supports the largest population of fall chinook salmon; annual production is an estimated 20-25 million subyearling salmon (P. Hoffarth, Washington Department of Fish and Wildlife, unpublished data).

In a survey of populations in the contiguous U.S., Huntington et al. (1996) identified 32 healthy native stocks of fall chinook, all in Washington and Oregon, and 3 healthy native stocks of spring or summer chinook, all in Washington.

Initial cause of decline was adverse effects of logging, mining, irrigation withdrawals, and overfishing, then construction of hydroelectric dams blocked migrations and resulted in high mortality of smolts in turbines (Nehlsen et al. 1991, Williams et al. 1992). Spawning runs continue to be threatened by construction of dams and degradation of natural environment. Extinctions or large declines of some local native populations in recent decades may have been masked by releases of non-native hatchery stock (Williams et al. 1992).

Juveniles incur high mortality as they migrate through today's river systems and out to sea. Sources of mortality include hydroelectric turbines, mechanical bypass facilities (including transportation by barge or truck), and predation by non-native fishes. Gas bubble trauma (GBT)associated with total dissolved gas supersaturation (TDGS) at spillways also causes mortality and detrimental sublethal effects, but passage of juveniles through spillways may be the least damaging of the routes for juvenile passage at dams (Backman et al. 2002). In the Columbia River basin, adults were rarely observed with GBT, despite high TDGS levels (Backman and Evans 2002).

Concurrent with the construction of fish hatcheries, bacterial kidney disease became prevalent and may now play a significant role in mortality.

A change in climate, beginning around 1977, led to poor ocean survival.

See also threats comments for individual populations (ESUs).