Salmon are fantastical fish with complex, wondrous lives. They are anadromous, which means they are born in freshwater, migrate and spend most of their lives in salt water, and then return to freshwater to spawn. Their life cycle is truly extraordinary. It begins in the waters of a river and its tributaries or in a lake with an outlet river. Here, the adults mate and lay eggs—as many as three to five thousand of them. The female turns on her side and, by bending her body and striking with her tail, creates a depression in the gravel of the streambed. This spawning nest is called a redd. The female makes a series of redds and, in each, deposits a portion of her eggs, which are then fertilized by the male partner. After all the eggs have been deposited and fertilized, both female and male, with rare exception, age rapidly and die.
When the eggs hatch about four months later, the young fish, or alevins, consume their yolk sac, which takes four to six weeks, and then emerge from the redds. At this stage, they are called fry, and then later—a year after hatching—they are known as parr. The parr feed and grow in the stream until they are ready to begin their first migration down the tributaries to the river and finally out to sea. During this journey, the young fish undergo a complex set of physiological changes that prepares them for living in salt water. After these changes, they are referred to as smolts. Salmon live in the ocean from one to five years, eating—and being eaten—and growing until they reach sexual maturity. The returning adults undergo a reverse set of physiological changes, allowing them to migrate from salt water to freshwater. They regularly swim great distances to return to the river of their birth, where they spawn and then sometimes die, completing their life cycle.
What is it that directs salmon to travel from open ocean back to spawn and create the next generation in the same tributary or lake where they were hatched? Some scientists believe that salmon have a navigational sense similar to that of migratory birds. They also theorize that chemical imprinting during early development allows salmon to detect and home in on the unique chemical signature of not only the watercourse of their birth but also the very gravel bed in which they were conceived and from which they emerged to begin their lives. Understanding this life cycle, the interdependence of our environment, the rhythms of nature, and our need to preserve it informs us. We make choices about what we eat based on knowledge, respect, appreciation, and preservation.