If Mother Nature were to explain the term "instinctive behavior," she would probably use migratory fish as an example of instinct in its most concentrated form. Several species of migratory fish, particularly the anadromous species, have such strong, instinctive patterns that their actions defy human understanding.

Anadromous fish are hatched in fresh water but spend a large part of their lives in the ocean before returning to fresh water to reproduce. These ocean travelers spend one to five years in the ocean before returning to their stream of origin. Enroute they face obstacles and dangers that seem insurmountable, and sometimes are. But as long as anadromous fish survive, they obey their instinctive urge to reproduce and continue their species.

During the ocean phase of their life cycle, anadromous fish enjoy a growth rate and vitality that freshwater members of the same species could never hope to achieve. The vast ocean food chain provides food supplies virtually guaranteed to help them gain weight quickly - provided, of course, they can stay on the diner's side of the food chain! Killer whales, seals, porpoises, sea lions, sharks, other fish and the nets and hooks of humans tend to make the anadromous traveler's stay in the ocean a very dangerous one.

As adults, the salmon return to fresh water to spawn. Some, such as chinook salmon in Idaho, migrate more than 900 miles to their spawning grounds. Most return to the stream of their birth, although there is some straying. Straying ensures that salmon will colonize new areas if their old streams get destroyed by natural disasters. For example, when the 1980 eruption of Mount St. Helens destroyed spawning habitat in the Toutle River in Washington, scientists observed the salmon spawning elsewhere.

The life cycles of anadromous fish are fascinating! Click here for a more complete discussion of the Umpqua Basin salmon life cycles.

Pat Wray. Oregon's Migratory Fish. Oregon Department of Fish and Wildlife. 1989.