Cynthia R. Johnson, age 11, of Gary, Indiana, for her question:

When is the salmon egg laying season?

The bears of the Northwest expect the salmon runs to start soon after the end of their winter hibernation. In early spring, schools of the mature adult fish enter the rivers and swim upstream to their ancestral nesting grounds. In most species, the major egg laying season is in the spring and a smaller upstream migration also occurs in the fall. However, migrations may occur at unexpected times during the summer. Some of the deep ocean species travel 2,000 miles and their amazing journeys may be delayed by unscheduled events.

The eggs are strewn and fertilized in gravelly streams of shallow cool water. Depending on the species, the youngsters spend a few months or several years in their fresh water streams    and six months to several years in the salty sea. When food is plentiful and ocean conditions are suitable, most salmon reach maturity and start their migrations in time to lay their eggs in the spring. But various things can change these plans, which may explain why small migrations return later in the summer and fall.