A Salmon's Life Cycle

The salmon life cycle begins as an egg buried in loose gravel in a cool stream with lots of oxygen. When the salmon first hatch they are called alevins. They wait in the gravel until they finish the last of their yolk then hurry to the surface for a quick gulp of air to fill their swim bladders.

The little salmon, now called fry, are whisked downstream with the current towards the ocean. Some species hang out in their native streams for months or even years, hiding in snags and other slack waters and feeding. Others ride the current to estuaries where they will wait while their bodies go through necessary changes for life in the salty oceans.

As the young fry near the estuary they become smolts. Their scales grow, they become more silvery to help blend into the ocean environment. The smolts feed like mad in the estuary, trying to become as big as they can before braving the treacherous waters of the Pacific ocean.

Salmon at sea might migrate thousands of miles or they may stay right off the coast. They may spend anywhere between 2 and 8 years feeding in the ocean before returning to their native rivers and streams to spawn. Their homing abilities are legendary and not entirely understood.

On the way back salmon make another stop in coastal estuaries. Like last time, their bodies go through chemical changes so they can survive in the freshwater of their home streams. This time they also stop eating and adopt their flashier, spawning colors. Males may get hooked beaks and humped backs. The journey home is a daunting one, only the strongest will survive to reproduce.

Those salmon who make it will go through the final task of their lives. The females will build gravel nests with their tails called redds. and the males will fight for the opportunity to fertilize the females eggs. Although some steelhead and cutthroat will live to spawn again, most anadromous salmon will die after spawning. Their bodies feed the stream environment.

Perils of the journey
The journey to and from the spawning grounds is dangerous indeed.

Not even the egg is safe. Some predators prefer eggs because they are high energy sources of food. Careless hikers, unleashed dogs and other disturbances can destroy redds and either crush eggs or loose them to drift downstream. too much erosion can cause silt to smother the redds and suffocate the eggs. Streamside vegetation and responsible forestry can help reduce this hazard.

When the fry emerge from the gravel they are very vulnerable to predators. They are small and need to learn very quickly how to hide. Predators are natural but around dams predators gather to await salmon fry that are spilled over the top or rocketed through bypasses. Young salmon must also be wary of dam turbines, and irrigation water diversions. When the plant life along the streamside is removed the temperatures in the stream increase, the flow is reduced and their are fewer insects to eat. Pollution from cities and farms also takes its toll.

At sea, adult salmon must deal with not only the larger oceanic predators like sharks and killer whales but also with commercial fisheries.

And the trip back upstream can be even more dangerous. Adults have to face natural predators like bear and eagles plus both commercial and recreational fishers. Dams bar the path of migrating salmon. Those who make it up the fish ladders may become confused or even sick in the warmer slack waters above the dam. Pollution, erosion and water diversions play key roles in preventing adults from successfully spawning by destroying good salmon spawning habitat.