Salmon

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

Perilous 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 they gather around dams 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.

For some populations, the little salmon, now called fry, are whisked downstream with the current towards the ocean. Others may hang out in their native streams for months or even years, hiding in snags and other slack waters and feeding. Sooner or later, they all ride the current to estuaries where they will wait while their bodies go through necessary changes for life in the salty oceans (see 'Striking a Balance' for more on this process).

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

Depending on species, salmon at sea may migrate thousands of miles, or they may stay right off the coast. They may spend anywhere between two and eight 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 the last time they were here, their bodies go through chemical changes so they can survive in the fresh water of their home streams. This time they also stop eating and adopt their flashier spawning colors. In some species, males get hooked beaks and humped backs. The journey home is a daunting one; only the strongest will survive to reproduce.

Those salmon that make it will go through the final task of their lives. The females will build gravel nests, called redds, with their tails, 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. Sound like a rough life? Try it on for size in our salmon activities.

At the Oregon Coast Aquarium
In our new At the Jetty exhibit we have two species of anadromous salmon: chinook and coho.

Chinook salmon
Oncorhynchus tshawytscha
Also known as: king salmon, blackmouth, chub salmon

The chinook or king salmon is the largest of all salmon species. Record chinook catches approach six feet. Juveniles are silvery or gold in color, with dark black spots on their backs. Some young chinook spend only a few months in the stream environment, some up to two years. Chinook seem to prefer deep, fast streams with large gravel. Adults are blue-green on the back and silvery on the sides. They may spend as many as eight years in the ocean before returning to spawn in the spring or fall. Adult spawners turn bright red on their sides and dark on their backs. Chinook are perhaps the most economically important and valuable of all salmon. They are highly prized by recreational, commercial and subsistence fishers alike.

ENDANGERED The National Marine Fisheries Service has recently listed four stocks of chinook salmon in the Pacific Northwest as either Threatened or Endangered. Judgment on four other stocks has been deferred until scientific disagreements have been resolved. These join three other stock of chinook already listed as Threatened or Endangered. (An Endangered species is considered in danger of becoming extinct throughout all or a significant portion of its range. A Threatened species is one that is likely to become endangered in the foreseeable future.)

Coho salmon
Oncorhynchus kisutch
Also known as: silver salmon, blueback salmon

Coho salmon spend a year or more in fresh water before going to sea. As juveniles they have distinctive vertical bars on their sides. Adults stay close to shore compared to some salmon species. As adults they are silvery, with dramatic blue backs. They will grow to lengths over three feet and are popular recreational catches. Spawners return in the late fall and winter after three years at sea sporting hooked beaks and deep red color. Immature "jack" salmon return a year early and are counted to estimate the size of the next year's spawning run.

THREATENED All Oregon coho salmon are considered Threatened by the National Marine Fisheries Service.