There are seven species of Pacific salmonoids--five salmon and two trout. The five species of salmon are sockeye, chum, pink, chinook and coho. Only the later two species--chinook and coho--are sport fish, though chinook has many restrictions in fresh water. The two species of trout are cutthroat and steelhead, both of which are important game fish.
As sexually mature adults, the seven species of salmonids return to their birth stream to spawn. Within days of spawning the five species of salmon die, while cutthroat and steelhead trout may return to saltwater and live to spawn again.
Female salmonoids deposit between 2,000 and 4,500 orange red eggs in gravel nests or reeds scooped out of the stream bottom. A large number of eggs is essential, since many biological and environmental factors affect egg survival. Ducks, freshwater fish and a bird known as a dipper eat salmonoid eggs during and after the fish have spawned.
Besides natural predators, eggs are sensitive to mechanical shock and bruising for about four weeks after fertilization. Construction projects, clear-cut logging and agriculture all contribute greatly to floods and erosion, thus choking off the oxygen supply necessary for egg development.
After salmonoids have hatched as alevins, they remain buried under the gravel until their yellow yolk sacs are almost completely absorbed. From the thousands of eggs deposited by a single female, approximately 10 to 15 percent of them hatch to produce alevins that emerge as salmon fry. They have numerous enemies, including freshwater fish, birds, garter snakes, mink and otter. In addition, high water temperature and pollution also affect fry survival.
Depending on the species and hazards, only 10 to 30 percent of salmon fry survive to smolt stage. Sockeye females, for example, deposit about 3,000 eggs.
Of these, 450 will emerge as fry and swim to a nearby lake. Of this number, only about 100 smolts will survive to migrate downstream. . . |
