Chinook salmon

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 60 cm (24 in) long but are sexually mature.

The Yukon River has the longest freshwater migration route of any salmon, over 3,000 km (1,900 mi) 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 2,100 m (7,000 ft) in elevation, and over 1,400 km (900 mi), 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.

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.

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.

In the Pacific Northwest, the summer runs of especially large Chinook once common (before dams and overfishing led to declines) were known as June hogs.

A Chinook's birthplace and later evolution can be tracked by looking at its otolith (ear) bone. The bone can record the chemical composition of the water the fish had lived in, just as a tree's growth rings provide hints about dry and wet years. The bone is built with the chemical signature of the environment that hosted the fish. Researchers were able to tell where different individuals of Chinook were born and lived in the first year of their lives. Testing was done by measuring the strontium in the bones. Strontium can accurately show researchers the exact location and time of a fish swimming in a river.