How the Salmon Spawn Works

Silver salmon of western North America.
Glenn Oliver/Visuals Unlimited/Getty Images

Silver salmon of western North America.


­Many of us have grown up watch­ing nature shows that pres­ent dramatic footage of large salmon swimming and leaping heroically upstream to spawn. For many, that image is a last act of the salmon -- and not just because a bear got to the leaping fish.

Where does spawning fit into the salmon's life cycle? For most species, spawning is the final act before dying. Eggs are deposited in a redd, or gravel nest, that the female salmon has made. The embryos hatch, becoming alevins, or yolk-sac fry, and live off the yolk-sack on their undersides. When they have completely absorbed the yolk-sack, they begin to search for food as fry. After growing in freshwater, ­the juvenile salmon, known as smolts, change physically to adapt to saltwater. They lose the spotted coloring that allowed them to be hidden in a stream and become silvery to blend into the ocean. Once in the ocean, they feed and become full adults.

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A few species can spawn more than once in a lifetime. Most, however, die within a week of spawning, completely worn out from their migration and spawning efforts. Their decomposing bodies provide food for other species during the winter and help fertilize the streams.

To everything there is a season, so let's find out more about salmon seasons. Just when do the salmon spawn?