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About SPU
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SPU & the Environment
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Salmon Friendly Seattle
The Life Cycle of Salmon
Although the life cycle of every salmon species is unique, there are important similaries across species. Here are the main stages.
Spawning Adult Salmon
Adult male and female salmon spawn together in gravel beds of rivers and streams. Using sweeping movements of her tail, the female salmon digs out a gravel nest, called a redd. The male fertilizes the eggs as the female deposits them. The female protects the redd for one to two weeks or as long as she is able before dying.
Fertilized Eggs
The fertilized eggs, or embryos, hatch and develop into alevins. As tiny alevins, they continue to live in the redd. Their food comes from a nutrient rich yolk sac attached to their undersides.
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Hatched Salmon
The freshly hatched salmon, or alevins, mature into fry. This occurs as the yolk sac is absorbed into the alevin’s body, and the alevin emerges from the redd. Once they become fry, they develop vertical bars called parr marks on their sides that help them remain camouflaged from predators. The parr marks last a few months to years, depending on the species of salmon. After a period of feeding and growth in freshwater, the fry begin migrating downstream towards the ocean.
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Frys Mature
The fry become smolts as they migrate downstream. Smolts undergo physiological changes that allow them to adapt to the saltwater conditions in the ocean. One of the most distinctive physical changes is the transformation from a brown color with stripes to a silvery color that serves as camouflage in the ocean environment.
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Smolts
The smolts grow to fully developed adult salmon as they continue their voyage to ocean habitat. Depending on the species, salmon will spend from one to five years in the ocean and travel thousands of miles before returning to their natal stream (the stream where they were hatched). Some fish stray to nearby rivers, colonizing new areas and replenishing weak populations.
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Adult Salmon
The adult salmon become spawners. Most salmon spawn only once during their lifetime and die within a week of spawning. The nutrients from their decomposing bodies help to fertilize the stream. Some steelhead and sea-run cutthroat trout can spawn more than once. After spawning, these adults, called kelts, migrate back to saltwater.
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