Depending on the species, life for a newly hatched salmon, called a fry, begins in a headwater stream or mainstem river, or at the interface of a coastal estuary and freshwater stream. Each female salmon lays hundreds to thousands of eggs in the gravel, where the eggs develop after the male salmon fertilize them.
Beyond the newly hatched stage, young salmon are called juveniles. They may live in fresh water a few weeks or up to two or more years. Juvenile salmon ready to migrate to the ocean are called smolts. They make this journey mostly during the spring and summer. Ocean-bound juveniles may spend days, weeks or even months in estuaries feeding and adjusting their body chemistry before they enter the ocean, depending on the species and population.
Once in the ocean, salmon stay there one to five years, depending on the species. During this time, they eat small fish and tiny animals called zooplankton. Some salmon travel thousands of miles out into the North Pacific. Others remain relatively close to shore.
As adults, the salmon return to fresh water to spawn. Some, such as chinook salmon in Idaho, migrate more than 900 miles to their spawning grounds. Most return to the stream of their birth, although there is some straying. Straying ensures that salmon will colonize new areas if their old streams get destroyed by natural disasters. For example, when the Mount St. Helens 1980 eruption destroyed spawning habitat in the Toutle River in Washington, scientists observed the salmon spawning elsewhere. With the exception of steelhead and sea-run cutthroat, salmon die after spawning.