Pacific salmon commence their existence in the gravel beds of freshwater rivers and streams. The female deposits her eggs, which are then fertilized by the male. Upon hatching, the tiny, vulnerable creatures are known as alevin, remaining hidden within the gravel, sustained by the yolk sac attached to their bodies. As they grow, they develop into fry, emerging from the gravel to seek sustenance in the stream. Many species, such as coho and Chinook, spend a year or more in freshwater, developing distinctive vertical stripes called parr marks for camouflage. Before migrating to the ocean, they undergo a crucial physiological transformation called smoltification, adapting their bodies to tolerate saltwater.

Once smolts, young salmon embark on an arduous journey to the vast expanses of the Pacific Ocean. Their time at sea is characterized by extensive foraging and rapid growth. They travel thousands of kilometers, navigating ocean currents and evading predators. During this period, which can last from one to five years depending on the species, salmon feed voraciously on smaller fish, crustaceans, and squid, accumulating the energy reserves necessary for their eventual return. They mature sexually, developing the biological imperative to reproduce, which triggers their homeward migration.

Driven by an instinctual urge, adult salmon cease feeding and begin their epic migration back to their natal freshwater streams. This upstream journey is fraught with challenges, including waterfalls, rapids, and predators. During this period, remarkable physical changes occur: their bodies darken, males often develop a pronounced humped back and hooked jaw (kype), and their digestive systems begin to atrophy. Once they reach their spawning grounds, females dig nests (redds) to deposit their eggs, which are then fertilized. Exhausted and depleted of all energy, the salmon die shortly after spawning, their decaying bodies providing vital nutrients for the ecosystem.

Pacific salmon hold immense economic and cultural value across the regions they inhabit. Commercial fisheries, both wild-capture and, controversially, aquaculture, represent a significant industry, providing employment and food security. Sport fishing tourism attracts enthusiasts globally, contributing to local economies. Furthermore, salmon are fundamental to the traditional diets, spiritual beliefs, and artistic expressions of numerous Indigenous peoples along the Pacific coast, embodying a central role in their heritage and way of life. The sustainable management of salmon populations is thus critical for ecological balance and human well-being.

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