Chinook Salmon

Oncorhynchus tshawytscha

Description

The chinook salmon, also known as the king salmon, is the largest species of salmon in the world. Large individuals can reach a weight exceeding 50 lbs (23 kg) and a body length of more than 58 in (147 cm). One individual caught in Alaska weighed an enormous 126 lbs (57 kg). Adults have a silvery body marked with irregular black spots on the back, on both lobes of the caudal (or tail) fin, and on the dorsal (top) and adipose (top back) fins. Chinook salmon have 10 to 14 major dorsal fin rays, 14-19 anal fin rays, 14-19 pectoral fin rays, and 10 to 11 pelvic fin rays. The gill rakers are rough and widely spaced, with six to 10 rakers on the lower half of the first gill arch. Reproductive adults are uniformly olive brown to dark maroon in color, but males are darker than females and have a hooked upper jaw and an arched back.

Behavior

The chinook salmon is an anadromous species of fish, meaning it spends most of its adult life at sea, but migrates to breed in freshwater rivers and streams. The eggs are laid in clean, well-aerated gravel beds, where they hatch and the fry (or alevins) live for about one month. Juveniles then emerge and feed on aquatic invertebrates for an additional eight to 12 weeks until reaching 3-4 in (7-10 cm) fork length. The juveniles then undergo a metamorphic change known as smolting, which is necessary for undertaking the transition from freshwater to saltwater habitats. The transformed stage, known as smolts, then migrate down tributaries and to the river estuary, where they enter the marine environment. Adult chinook salmon live at sea for two to four years before returning to their birth river to spawn. The adults are exhausted by the breeding effort and die soon afterward. However, the particulars of behavior and life history vary significantly in different parts of the range of the chinook salmon. Some species run up-river in the autumn, and others in the winter or springtime. For example, winter-run chinook salmon that spawn on the Sacramento River ascend the river between December and May. The run consists of mostly three-year-old fish along with smaller numbers of two-and four-year-old individuals. In the late spring and summer each female excavates a gravel nest, known as a redd, in water 9-42 in (23-107 cm) deep. The redd is an approximately 1 ft-deep (30 cm) depression dug by the female turning on its side and rapidly flexing its tail to dislodge gravel, which settles slightly downstream. The female then extrudes eggs into the depression; these are fertilized by one or more attending males. The female then moves slightly upstream and excavates another redd, with the dislodged gravel covering the eggs in the first depression. This process continues until all of the eggs of the female, usually numbering 4,000-5,000, have been deposited and fertilized. Both males and females die after spawning; the females usually remain on the redd, while the males move downstream. Newly hatched alevins emerge from the eggs after about four months. They remain buried in the gravel for another one to four months, nourished by their yolk sac. The salmon fry spend only a short time in their rearing areas before beginning their out-migration to the ocean, passing through the river's estuary between December and April.

Habitat

Chinook salmon need streams or rivers with a clean gravel bottom and an adequate flow of well-oxygenated water to aerate their eggs and alevins. The water temperature must be cooler than about 56°F (13°C) for eggs to hatch. Adults live in the open ocean, in cool temperate and boreal habitats.

Distribution

The general distribution of the chinook salmon is western North America and northeastern Asia. In western North America it occurs from the Ventura River in California, and north to Point Hope, Alaska, and the Mackenzie River area in Canada. In northeastern Asia it occurs from Hokkaido, Japan, to the Anadyr River, Russia. Adults occur in waters of the northern Pacific Ocean. Within this broad range, the chinook salmon can be divided into numerous distinct breeding stocks, or evolutionarily significant units, including the ones considered in this entry on endangered and threatened populations of the United States.

Threats

The chinook salmon has suffered large population declines throughout most of its range. Much of its breeding habitat has been degraded or destroyed by siltation and warm-water conditions associated with forestry practices in the watershed of the river or stream. In other cases habitat damage has been caused by nearby urbanization, industrialization, mining activities, road building, or agricultural practices (including pesticide use). Many historical breeding habitats are now inaccessible to migratory fish because of the construction of impassable hydroelectric dams or other kinds of impoundments. In addition, most stocks of pelagic and migrating fish are being harvested excessively, resulting in decreasing populations of breeding adults. Juvenile salmon are threatened by various factors, including predatory fish species (especially in estuarine habitats), diversion into irrigation projects that draw water from rearing rivers or streams, and mortality caused by water-intake pipes and turbines of hydroelectric facilities.

Conservation and Recovery

The U. S. Fish and Wildlife Service, National Marine Fisheries Service, state agencies, and other organizations are undertaking various actions on behalf of populations of chinook salmon. Similar actions are being undertaken to enhance breeding populations in other countries, including Canada, Japan, and Russia. Management practices include actions undertaken to improve spawning habitat (for example, by providing clean gravel), mitigation of obstructions associated with dams and impoundments (for example, by constructing fish ladders; in some cases, dams are being removed to restore migratory runs), or by relaxing the fishing pressure. In addition, many agencies are attempting to enhance the reproductive efforts of wild fish by rearing eggs and alevins in hatcheries, later releasing the finger-lings in suitable habitat to fend for themselves. In some areas, these actions are helping to maintain or increase the numbers of wild chinook salmon. In many other areas, however, overfishing and habitat damage (the latter often associated with forestry operations) are continuing to have severe effects on the species and its populations continue to decline.

Contacts

U. S. Fish and Wildlife Service
Boise Ecological Services Field Office
4696 Overland Road, Room 576
Boise, Idaho 83705
Telephone: (208) 334-1931
Fax: (208) 334-9493

U. S. Fish and Wildlife Service
Division of Endangered Species
4401 North Fairfax Drive
Arlington, Virginia 22203
Telephone: (703) 358-2171

National Marine Fisheries Service
Protected Resources Division
525 N.E. Oregon Street, Suite 500
Portland, Oregon 97232
Telephone: (503) 231-2005

National Marine Fisheries Service
Office of Protected Resources
1315 East West Highway
Silver Spring, Maryland 20910
Telephone: (301) 713-1401

References

National Marine Fisheries Service. 1992. "Endangered and Threatened Species; Threatened Status for Snake River Spring/Summer Chinook Salmon, Threatened Status for Snake River Fall Chinook Salmon." Federal Register 57 (78):14653-14663.

National Oceanic and Atmospheric Administration.1999. "Designated Critical Habitat: Revision of Critical Habitat for Snake River Spring/Summer Chinook Salmon." Federal Register 64 (55):57339-57403.

National Oceanic and Atmospheric Administration.1999. "Endangered and Threatened Species: Regulations Consolidation; Final Rule." Federal Register 64 (55):14051-14077.

National Oceanic and Atmospheric Administration.2000. "Designated Critical Habitat: Critical Habitat for 19 Evolutionarily Significant Units of Salmon and Steelhead in Washington, Oregon, Idaho, and California." Federal Register 65:7764-7787.

U. S. Fish and Wildlife Service. 1999. "Endangered and Threatened Wildlife and Plants; Determination of Threatened Status for Two Chinook Salmon Evolutionarily Significant Units (ESUs) in California." Federal Register 64 (249):72960-72961.

U. S. Fish and Wildlife Service. 1999. "Endangered and Threatened Wildlife and Plants: Listing of Nine Evolutionarily Significant Units of Chinook Salmon, Chum Salmon, Sockeye Salmon, and Steelhead." Federal Register 64 (147):41835-41839.

Waples, R., R. P. Jone, Jr., B. R. Beckman, and G. A.Swan. 1991. NOAA Technical Memorandum NMFS F/NWC-201. Status Review for Snake River Fall Chinook Salmon. National Marine Fisheries Service, 73 pp.