Five types of salmon migrate from the ocean to the freshwater creeks, lakes, streams and rivers in the Pacific Northwest every year to spawn and eventually die– the Chinook (also called King for its size), Coho (or Silver), Pink ( or humpback), Sockeye (or Red ) and Chum (or dog salmon).
The Chinook is by far the largest salmon. Its average size is 3 feet and weighs 30 pounds, although it can grow to as big as 5 feet and 130 pounds. The most colorful is the Sockeye, with its bright red body.
From September to November but often as early as June, the salmon swim from the Pacific Ocean back to their birthplace in the freshwaters of the Pacific Northwest, and especially in Washington and Canada, to nest and spawn. This could be a short journey or a long arduous one from the ocean, as they swim against the current to get ‘home’. Along the journey, they have to dodge predators, and often have to overcome obstacles such as strong currents and even waterfalls. Hence, only the fittest make it back to the spawning grounds.
Scientists believe that salmon returning to their natal place are guided by magnetic fields and their very acute sense of smell. This sense of smell, stored in the memory of their brain, is said to be a thousand times better than dogs and lead them to return to the exact river or creek or lake where they were born. In normal times, this sense of smell helps the salmon detect predators.
Generally, the Chinook and sockeye salmon gives birth when it is 3-5 years old, but the smaller Coho will return after 2-3 years.
The best areas to spawn are in gravel beds and where there is the right amount of water flow to oxygenate the eggs without washing them out of the gravel.
Each pregnant female salmon carries about 2,000 to 10,000 eggs in her belly. The large number of eggs is a form of insurance to ensure that at least some of the eggs survive the many perils they encounter from the moment they are laid in the nests. For one, after the eggs are laid, the male salmon has to coat the eggs with a protective layer of sperm within 45 seconds for fertilization to take place. The pair moves upstream and repeats the process until they are done, usually over a day or two.
These salmon die very soon after giving birth, including the male salmon. Their carcasses add minerals and nutrients back into the water, nourishing the waters that were once their home, and feed wildlife such as ducks, eagles and bears. The magical cycle and rhythm of life.
In the 2-3 months that they return to spawn, the salmons don’t eat, leaving more space for the eggs and sperm. Instead, the salmon rely on the stored fats accumulated during their time in the ocean. It is during this time that they become mushy in texture and loose their flavor. Some succumbed to infections. Most of the wild-caught salmon we eat are from the oceans, when they have the best flavor and texture before they swim upstream.
The fertilized eggs, if they escape the sharp eyes of birds and waterfowls nearby, hatch in three to four months. Baby salmon eat insects in their stream. Each species spends a different amount of time in the stream as a baby. Also, each stream is a little different.
All baby salmon eventually migrate downstream to the ocean. Hence, there are two salmon runs here in the Pacific Northwest. In fall, you see the adult salmon swimming upstream to spawn. In early spring or late winter, you get the young salmons swimming downstream from their birthplace to start their adult life in the ocean.
A new life cycle has begun.
Citations
Everything Nature 
Great post on the wonders of salmon migration and reproduction
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Very interesting and knowledgeable to learn about life cycle of wild salmon. Y
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