The Chinook salmon (Oncorhynchus tshawytscha) is the largest and most valuable species of Pacific salmon. Its common name is derived from the Chinookan peoples. Other vernacular names for the species include king salmon, quinnat salmon, tsumen, spring salmon, blackmouth, and tyee salmon. The scientific species name is based on the Russian common name chavycha (чавыча).
Chinook are anadromous fish native to the North Pacific Ocean and the river systems of western North America, ranging from California to Alaska, as well as Asian rivers ranging from northern Japan to the Palyavaam River in Arctic northeast Siberia. They have been introduced to other parts of the world, including New Zealand and Patagonia. Introduced Chinook salmon are thriving in Lake Michigan and Michigan's western rivers. A large Chinook is a prized and sought-after catch for a sporting angler. The flesh of the salmon is also highly valued for its nutritional content, which includes high levels of important omega-3 fatty acids. Some populations are endangered; however, many are healthy. The Chinook salmon has not been assessed for the IUCN Red List. According to NOAA, the Chinook salmon population along the California coast is declining from factors such as overfishing, loss of freshwater and estuarine habitat, hydropower development, poor ocean conditions, and hatchery practices.
Distribution
thumb|right|A male Chinook in his spawning phase
Natural range
Historically, the native distribution of Chinook salmon in North America ranged from the Ventura River in California in the south to Kotzebue Sound in Alaska in the north. Recent studies have shown that Chinook salmon are historically native to the Guadalupe River watershed in California, the southernmost major metropolitan area hosting salmon runs in the United States. Populations have disappeared from large areas where they once flourished, however, or shrunk by as much as 40 percent. In some regions, their inland range has been cut off, mainly by dams and habitat alterations: in Southern California, in some areas east of the Coast Ranges of California and Oregon, and in large areas in the Snake River and upper Columbia River drainage basins.
In the western Pacific, the distribution ranges from northern Japan (Hokkaido) in the south to the Arctic Ocean as far as the East Siberian Sea and Palyavaam River in the north. Nevertheless, they are consistently present and the distribution is well known only in Kamchatka. Elsewhere, information is scarce, but they have a patchy presence in the Anadyr River basin and parts of the Chukchi Peninsula. Also, in parts of the northern Magadan Oblast near the Shelikhov Gulf and Penzhina Bay, stocks might persist but remain poorly studied. In the 1960s, alewives constituted 90% of the biota in these lakes. Coho salmon had been introduced the year before, and the program was successful. Chinook and Coho salmon thrived on the alewives and spawned in the lakes' tributaries. After this success, Chinook were introduced into the other Great Lakes, where sport fishermen prize them for their aggressive behaviour on the hook. Despite a consistent program of release, the chinook has not established itself as a natively reproducing species in the Great Lakes. While limited natural reproduction occurs in the wild, the continued presence of the fish is depended on yearly stocking.
The species has also established itself in Patagonian waters in South America, where both introduced and escaped hatchery fish have colonized rivers and established stable spawning runs. Chinook salmon have been found spawning in headwater reaches of the Rio Santa Cruz, apparently having migrated over from the ocean. The population is thought to be derived from a single stocking of juveniles in the lower river around 1930.
Sporadic efforts to introduce the fish to New Zealand waters in the late 19th century were largely failures and led to no evident establishments. Initially ova were imported from the Baird hatchery of the McCloud River in California. Further efforts in the early 20th century were more successful and subsequently led to the establishment of spawning runs in the rivers of Canterbury and North Otago: Rangitata River, the Ōpihi River, the Ashburton River, the Rakaia River, the Waimakariri River, the Hurunui River, and the Waiau Uwha River. The success of the latter introductions is thought to be partly attributable to the use of ova from autumn-run populations as opposed to ova from spring-run populations used in the first attempts. Adult fish typically range in size from , but may be up to in length; they average , but may reach . The meat can be either pink or white, depending on what the salmon have been feeding on.
Chinook salmon are the largest of the Pacific salmon. In the Kenai River of Alaska, mature Chinook averaged . The current sport-caught world record, , was caught on May 17, 1985, in the Kenai River. The commercial catch world record is caught near Rivers Inlet, British Columbia, in the late 1970s.
Life cycle
thumb|Fertilized Chinook eggs
Chinook, like many other species of salmon, are considered euryhaline, and thus live in both saltwater and freshwater environments throughout their life. Once hatching, salmon spend one to eight years in the ocean (averaging from three to four years) before returning to their home rivers to spawn. The salmon undergo radical morphological changes as they prepare for the spawning event ahead. Salmon lose the silvery blue they had as ocean fish, and their color darkens, sometimes with a radical change in hue. Salmon are sexually dimorphic, and the male salmon develop canine-like teeth, and their jaws develop a pronounced curve or hook called a "kype". Studies have shown that larger and more dominant male salmon have a reproductive advantage as female Chinook are often more aggressive toward smaller males.
Chinook spawn in larger and deeper waters than other salmon species and can be found on the spawning redds (nests) from September to December. The female salmon may lay her eggs in four to five nesting pockets within a redd. After laying eggs, females guard the redd from four to 25 days before dying, while males seek additional mates. Chinook eggs hatch 90 to 150 days after deposition, depending upon water temperature. Egg deposits are timed to ensure the young salmon fry emerge during an appropriate season for survival and growth. Fry and parr (young fish) usually stay in fresh water for 12 to 18 months before traveling downstream to estuaries, where they remain as smolts for several months. Some Chinook return to fresh water one or two years earlier than their counterparts and are referred to as "jack" salmon. "Jack" salmon are typically less than long but are sexually mature.
The Yukon River has the longest freshwater migration route of any salmon, over from its mouth in the Bering Sea to spawning grounds upstream of Whitehorse, Yukon. Since Chinook rely on fat reserves for energy upon re-entering fresh water, commercial fish caught here are highly prized for their unusually high levels of heart-healthy omega-3 fatty acids. However, the high costs of harvest and transport from this rural area limits its affordability. The highest elevation Chinook spawn is in the Middle Fork and Upper Salmon River in Idaho. These fish travel over in elevation, and over , in their migration through eight dams and reservoirs on the Columbia and Lower Snake Rivers.
Chinook eat amphipods and other crustaceans and insects while young, and primarily other fish when older. Young salmon feed in streambeds for a short period until they are strong enough to journey out to the ocean and acquire more food. Chinook juveniles divide into two types: ocean-type and stream-type. Ocean-type Chinook migrate to salt water in their first year. Stream-type salmon spend one full year in fresh water before migrating to the ocean. After a few years in the ocean, adult salmon, then large enough to escape most predators, return to their natal streambeds to mate. Chinook can have extended lifespans, in which some fish spend one to five years in the ocean, reaching age eight. More northerly populations tend to have longer lives.
thumb|upright=1.14|right|Chinook salmon school
Salmon need suitable spawning habitat. Clean, cool, oxygenated, sediment-free fresh water is essential for egg development. Chinook use larger sediment (gravel) sizes for spawning than other Pacific salmon. Riparian vegetation and woody debris help juvenile salmon by providing cover and maintaining low water temperatures.
Chinook also need healthy ocean habitats. Juvenile salmon grow in clean, productive estuarine environments and gain the energy for migration. Later, they change physiologically to live in salt water. They rely on eelgrass and seaweeds for camouflage (protection from predators), shelter, and foraging habitat as they make their way to the open ocean. Adult fish need a rich, open ocean habitat to acquire the strength needed to travel back upstream, escape predators, and reproduce before dying. In his book King of Fish, David Montgomery writes, "The reserves of fish at sea are important to restocking rivers disturbed by natural catastrophes." Thus, it is vitally important for the fish to reach the oceans to grow into healthy adult fish to sustain the species without being impeded by man-made structures such as dams.
The bodies of water for salmon habitat must be clean and oxygenated. One sign of high productivity and growth rate in the oceans is the level of algae. Increased algal levels lead to higher levels of carbon dioxide in the water, which transfers into living organisms, fostering underwater plants and small organisms, which salmon eat. Algae can filter high levels of toxins and pollutants. Thus, it is essential for algae and other water-filtering agents not to be destroyed in the oceans because they contribute to the well-being of the food chain.
thumb|upright=1.14|left|Chinook salmon moving upstream
With some populations endangered, precautions are necessary to prevent overfishing and habitat destruction, including appropriate management of hydroelectric and irrigation projects. If too few fish remain because of fishing and land management practices, salmon have more difficulty reproducing. When one of these factors is compromised, affected stock can decline. One Seattle Times article states, "Pacific salmon have disappeared from 40 percent of their historic range outside Alaska," and concludes it is imperative for people to realize the needs of salmon and try not to contribute to destructive practices that harm salmon runs.
Fishing industry
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Wild capture
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