On the west coast of North America, California streams support the southern-most Chinook Salmon runs. Chinook Salmon in California display a wide array of life history patterns that allow them to take advantage of the diverse and variable riverine and ocean environments. Chinook Salmon are “anadromous” fish, migrating upstream as adults to spawn in freshwater streams, and migrating as juveniles downstream to grow and mature in the ocean. The time spent in the ocean and freshwater varies greatly among the various runs. Chinook have been classified into six major groups, or Evolutionarily Significant Units (ESUs) by NOAA Fisheries.
The Fisheries Branch Anadromous Assessment Unit compiles annual population estimates of Chinook Salmon, Oncorhynchus tshawytscha. Estimates are based on counts of fish entering hatcheries and migrating past dams, carcass surveys, live fish counts, creel census data, and ground and aerial redd counts.
Southern Oregon and Northern California Coastal Chinook Salmon
The Southern Oregon and Northern California Coastal Chinook Salmon ESU includes fall-run Chinook Salmon in coastal streams from Cape Blanco in Oregon south to the Klamath River. Southern Oregon and Northern California Coastal Chinook Salmon were proposed for federal listing in 1999, but listing was determined to be "not warranted".
California Coastal Chinook
The California Coastal Chinook Salmon ESU includes all natural spawning populations of Chinook Salmon from rivers and streams south of the Klamath River to the Russian River.
Due to concern over depressed population sizes relative to historical abundance, California Coastal Chinook Salmon was federally listed as threatened in 1999.
Upper Klamath - Trinity River Chinook Salmon
Within the Upper Klamath - Trinity River ESU, fall and spring Chinook Salmon spawn and rear in the Trinity River and in the Klamath River. In the Trinity River, Chinook Salmon spawn in the mainstem (with their upstream distribution limited by Lewiston Dam), the north and south forks, Hayfork Creek, New River, and Canyon Creek. In the Klamath River, Chinook Salmon once ascended into Upper Klamath Lake, Oregon, to spawn in the major tributaries to the lake (Williamson, Sprague, and Wood Rivers), but access to this region was blocked by Copco Dam, built in 1917. Today Chinook Salmon are known to spawn in the mainstem Klamath River, Bogus Creek, Shasta River, Scott River, Indian Creek, Elk Creek, Clear Creek, Salmon River, Bluff Creek, Blue Creek, and the lower reaches of some of the other smaller tributaries to the mainstem river.
The Upper Klamath - Trinity River Chinook Salmon ESU was proposed for federal listing in 1998, but listing was determined to be "not warranted".
Central Valley Fall and late-fall-run Chinook Salmon
Four distinct runs of Chinook Salmon spawn in the Sacramento-San Joaquin River system, named for the season when the majority of the run enters freshwater as adults. Fall-run Chinook Salmon migrate upstream as adults from July through December and spawn from early October through late December. The timing of runs varies from stream to stream. Late-fall-run Chinook Salmon migrate into the rivers from mid-October through December and spawn from January through mid-April. The majority of young salmon of these races migrate to the ocean during the first few months following emergence, although some may remain in freshwater and migrate as yearlings.
Fall-run Chinook Salmon are currently the most abundant of the Central Valley races, contributing to large commercial and recreational fisheries in the ocean and popular sport fisheries in the freshwater streams. Fall-run Chinook Salmon are raised at five major Central Valley hatcheries which release more than 32 million smolts each year. Due to concerns over population size and hatchery influence, Central Valley fall and late-fall-run Chinook Salmon are a Species of Concern under the federal Endangered Species Act.
Central Valley spring-run Chinook Salmon
Four distinct runs of Chinook Salmon spawn in the Sacramento-San Joaquin River system, named for the season when the majority of the run enters freshwater as adults. Spring-run Chinook Salmon enter the Sacramento River from late March through September. Adults hold in cool water habitats through the summer, then spawn in the fall from mid-August through early October. Spring run juveniles migrate soon after emergence as young-of-the-year, or remain in freshwater and migrate as yearlings.
Spring-run Chinook Salmon were historically the most abundant race in the Central Valley. Now only remnant runs remain in Butte, Mill, Deer, Antelope, and Beegum Creeks, tributaries to the Sacramento River. In the mainstem Sacramento River and the Feather River, early-running Chinook Salmon occur, but significant hybridization with fall run has occurred. The Status Review of Spring-Run Chinook Salmon in Sacramento River Drainage (PDF) was prepared in 1998. Due to the small number of non-hybridized populations remaining and low population sizes, Central Valley spring-run Chinook Salmon were listed as threatened under both the state and federal endangered species acts in 1999.
Annual reports to the Fish and Game Commission on Central Valley spring-run Chinook:
Sacramento River winter-run Chinook Salmon
Four distinct runs of Chinook salmon spawn in the Sacramento-San Joaquin River system, named for the season when the majority of the run enters freshwater as adults. Adult Sacramento River (SR) winter-run Chinook Salmon pass under the Golden Gate Bridge from November through May, and pass into the Sacramento River from December through early August. SR winter-run Chinook Salmon spawn in the upper mainstem Sacramento River from mid-April through August. Fry and smolts emigrate downstream from July through March through the Sacramento River, reaching the Delta from September through June.
Two biennial reports to the Fish and Game Commission on winter-run Chinook Salmon:
Historically, winter-run Chinook Salmon spawned in the upper reaches of Sacramento River tributaries, including the McCloud, Pit, and Little Sacramento Rivers. Shasta and Keswick dams now block access to the historic spawning areas. Winter-run Chinook, however, were able to take advantage of cool summer water releases downstream of Keswick Dam. In the 1940’s and 1950’s the population recovered. However, beginning in 1970, the population experienced a dramatic decline — a low of approximately 200 spawners by the 1980’s. The run was classified as endangered under the state California Endangered Species Act in 1989, and as endangered under the federal Endangered Species Act in 1994.