Chinook (Oncorhynchus tshawytscha)

Spring run Chinook salmon in the Sierra Nevada

Threats

Chinook Central Valley spring-run chinook salmon were once legendary in the rivers and streams of the west slope of the Sierra Nevada. In 1999 it was listed as threatened with extinction under both the state and federal endangered species acts. Spring-run Chinook were historically the most abundant race in the Central Valley. Now only remnant runs remain. On the west slope of the Sierra Nevada runs still occur on Butte, Mill, Deer, and Antelope Creeks, flowing into the Sacramento River, and on portions of the Feather and Bear Rivers. According to fisheries experts, approximately 82 percent of the historical spawning and holding habitat is no longer available for Central Valley chinook salmon. Historically, dam building, gold rush era hydraulic mining and the impacts of pollutants from smelters, and water diversions of all kinds combined with over fishing contributed to the extirpation of the legendary runs of chinook salmon in the Sierra Nevada.

Habitat degradation is the number one source of ongoing risk to spring-run chinook salmon. The only remaining accessible habitat for spawning or juvenile rearing continues to be severely degraded by elevated water temperatures, agricultural and municipal diversions and returns, restricted and regulated flows, and entrainment of migrating fish into unscreened or poorly screened diversions. Dams and other water diversion for agriculture, flood control, domestic and hydropower purposes have greatly reduced or eliminated habitat. In the Sierra Nevada, heavy snow pack is necessary to provide sufficient cold water to provide suitable habitat for salmonids. With the termination of natural streamflows throughout most of the southern and central Sierra, salmon runs have been completely extirpated. In the Northern region, logging activities in the headwaters of Battle Creek, Butte, Mill, Deer, and Antelope Creeks are an additional source of threats to the survival of the species. Logging alters salmonid habitat through sedimentation and smothering of spawning grounds, loss of canopy, and increased stream temperatures, and from run-off of chemical herbicides used in plantation management. Diseases introduced from fish hatcheries are also a threat to survival.

Chinook eggs experience 8% mortality if water temperatures exceed 58 degrees F on average for more than 24 days. If the mean daily water temperature exceeds 62 degrees F for more for 7-12 days, the eggs would experience 100% mortality. Holding adult spring chinook are stressed at 61 to 66 degrees F (16-18 C) and retain little fecundity if exposed to temperatures greater than 66 F for long periods. The lethal temperature for adult spring run is 80 degrees F.

The homing fidelity of salmon has resulted in distinct populations distributed among watersheds. Environmental risks (eg., from landslides or floods) must vary between streams in order to ensure survival of populations. Survival also requires migratory connections among the watersheds to allow for periodic genetic exchange and alternate spawning sites in the case that natal streams are inaccessible due to natural events or human caused events. Preservation of streams with sufficient natural features to maintain cold temperatures is imperative for the survival of the species under predicted global warming scenarios.

Habitat and Life History

Adults migrate from a marine environment into the freshwater streams and rivers of their birth in order to mate (called anadromy). They spawn only once and then die (called semelparity). Each spawning migration is called a "run." Juvenile chinook may spend from 3 months to 2 years in freshwater before migrating to estuarine areas as smolts and then into the ocean to feed and mature. They prefer streams that are deeper and larger than those used by other Pacific salmon species.

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 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.

Chinook salmon are very similar to coho salmon in appearance while at sea (blue-green back with silver flanks), except for their large size, small black spots on both lobes of the tail, and black pigment along the base of the teeth.

Chinook salmon are easily the largest of any salmon, with adults often exceeding 40 pounds (18 kg); individuals over 120 pounds (54 kg) have been reported. Chinook mature at about 36 inches and 30 pounds. They are named after the Alaskan Russian native name for the fish.

They feed on terrestrial and aquatic insects, amphipods, and other crustaceans while young, and primarily on other fishes when older.

Conservation

In 2005, in accordance with the requirements of the Endangered Species Act, the National Marine Fisheries Service (NMFS) and the National Oceanic and Atmospheric Administration (NOAA) issued a final rule designating critical habitat for seven evolutionary significant units of Pacific salmon and steelhead in California. To qualify as a distinct population segment, a Pacific salmon or steelhead population must be substantially reproductively isolated from other conspecific populations and represent an important component in the evolutionary legacy of the biological species. A population meeting these criteria is considered an Evolutionary Significant Unit or ESU.

Critical habitat is defined as 1) specific areas within the geographical area occupied by the species at the time of listing under the ESA, on which are found those physical or biological features that are essential to the conservation of the listed species and that may require special management considerations or protection, and 2) specific areas outside the geographical area occupied by the species at the time of listing that are essential for the conservation of a listed species.

Critical habitat designations were made for 1,158 steam miles for Central Valley spring run Chinook, of which 12.1 percent occurs on Federal lands, and 84.5 percent occurs on private lands. Counties with critical habitat designation include: Tehama, Butte, Glenn, Shasta, Yolo, Sacramento, Solano, Colusa, Yuba, Sutter, Trinity, Alameda, San Joaquin, and Contra Costa.

In Tehama County, $42.75 million in funding has been awarded for implementing Phase 1 of the Battle Creek Salmon and Steelhead Restoration Project. The project is one of the largest cold water anadromous fish restoration efforts in North America. The stream with its two branches, the North Fork and the South Fork, has been designated as a prime recovery site for spring and winter-run Central Valley Chinook (winter-run is an endangered species currently limited to the Sacramento River because of dams on the upper Sacramento, Pit and McCloud Rivers) and steelhead, because of the stream's relatively clean water and cold temperature fed by numerous springs along its length. Current plans are now in place to remove one diversion dam, modify another, and install new fish screens and ladders that will hopefully ensure safe passage for the imperiled salmonids. Currently there are nine dam sites on Battle Creek. When the project is completed ultimately five dams will be dismantled, including the dam at Coleman Fish Hatchery which now holds the fish back. After the dam is removed, the salmon will return without impediment to Battle Creek for the first time since 1942.

Status

Spring run chinook were listed as threatened under the Endangered Species Act in 1999 and reaffirmed during review in 2005. Critical habitat designations for all listed Pacific salmonids occurring in California were also designated in 2005. The Federal Register documents can be accessed below, under Supporting Resources.