Salmon and steelhead are anadromous fish. This means that they move from a freshwater environment to a saltwater environment and back again. Salmon and steelhead spawn in a freshwater environment. Adult salmon die after spawning but steelhead may make the cycle of live from freshwater to saltwater and back again more than once. The eggs incubate in the gravel of streams or lakes. The fry emerge and rear in the freshwater habitat or descend quickly back to the marine environment where they mature to adults.

Those anadromous species that rear for an extended period of time in freshwater also migrate downstream at some point to the ocean where they grow and mature into adults. Salmon and steelhead spend various amounts of time in the ocean until they reach maturity and then begin the return to their natal freshwater spawning grounds to begin the cycle again.

During the freshwater phase of their life cycle anadromous fish need certain habitat requirements. These include adequate stream flow that are not too excessive that they cause blocks to migration or the disruption or removal of eggs from the gravel after spawning occurs.

They also need cool, well-oxygenated water for successful incubation of the eggs in the gravel and the rearing period of juveniles in the stream. Streambed gravel must be clean with little sediment that may cause problems during spawning, incubation or rearing. There needs to be in-stream structural diversity that will provide pools, riffles, and hiding and resting cover for both adults and juveniles. There also needs to be access to and from the spawning grounds and to rearing areas for juveniles.

Each pacific salmon species and steelhead has their own life history and habitat requirements. For more information see the following link: http://wdfw.wa.gov/outreach/fishing/salmon.htm.

Adult Migration:

After two to four years or more, depending on the species, salmon and steelhead are ready to reproduce, or spawn and they begin the long and difficult migration to the spawning grounds. Each salmon or steelhead is seeking its home or parent stream. The ability of most salmon and steelhead to navigate accurately from the ocean to a particular spawning ground is amazing. At first, they use ocean currents, stars, and the earth's magnetic forces to find their way to their home stream. As they get closer, they use their sense of smell to find the exact place where they were hatched.

Some salmon and steelhead stray from their natal stream of origin. This may have some very positive effects on the survival of the species as a whole. Straying ensures that the salmon or steelhead stocks may survive even if some environmental or man-made disaster has threatened the spawning grounds where they were born. When the salmon enter the mouths of their rivers in order to begin their upstream journey they cease feeding and swim more or less in groups. The energy they need for migration and spawning is derived from fat stores accumulated while in the ocean. As the salmon begin their migration, they start to display some sexual dimorphic characteristics such as large humps and hooked jaws. Most species also exhibit radical color changes.

During this arduous migration they need access to the freshwater environment and to their natal spawning grounds. Obstructions that can impede their up-stream migration include falls, fast moving cascades or areas that do not have adequate flow, or any flow, to allow them to pass. Other barriers to up-stream migration include man-made structures (such as culverts) or harassment by humans (such as driving through spawning areas). In turn, they also need structural diversity in the stream channel to provide holding and resting areas as they make the long up-stream journey.

Good water quality is also important. Water temperature is important for several reasons. If the water in the stream is too warm or too cold, it can create a barrier to up-stream migration. This may result in total inaccessibility or delays in reaching the spawning grounds. Water temperature can also have an impact on the amount of oxygen in the water. High water temperature results in decreased dissolved oxygen. Fish need well-oxygenated water to survive and meet their physical needs for this difficult journey.

Spawning:

Salmon and steelhead have different requirements when choosing a spawning area. The female will select a site that has right substrate in both size and composition. There must also be good water quality, including dissolved oxygen content and water temperature.

The female utilizes her tail and body to dig a nest (redd) in the gravel. (See here for more detail on redds.) She will excavate a depression up to 18 inches deep, preferably in a riffle area where water will flow through the redd and provide oxygen to the eggs and carry off waste products. When the redd is completed, the female will lay her pea sized eggs into the depression while a male fertilizes them by covering them with a milky substance, called milt, that contains the sperm.

The female then covers the eggs when she digs a new redd upstream of the first nest. The gravel dislodged during the creation of this new nest moves downstream to create the cover for the previous nest. This process continues until up to several thousand eggs have been laid. The eggs stay in the nest all winter and hatch in the spring.

Pacific salmon die after spawning however steelhead can live to spawn again. The decomposing bodies for these dead fish provide nutrients to the stream for the production of food material for both aquatic and terrestrial animals.

Incubation

The eggs are laid in the fall and incubate over the winter. Over the winter months embryos develop within the eggs. The duration of the incubation period depends on water temperature and on the species. It is essential during this time that water flow and temperature are suitable. The period of greatest mortality in an anadromous fish’s life cycle is in the egg-to-fry stage. The embryos are very sensitive during the first two or three weeks of incubation, and any jostling or disturbance can kill them.

About a month after they have been deposited in the gravel, eyes begin to show on the eggs. This normally happens in late November or early December. In another 20 or so the eggs will begin to hatch. At this stage, of their life they are called alevin (a-le-vin).

The tiny alevins remain in the gravel living on the nutritious yolk sac on their undersides. The alevin do not need to eat while they are living off of their yolk sac. However, once the yolk sac is gone, they must find food quickly or they will starve.

Alevins

The alevins grow rapidly under the gravel for several months. The fish at this stage are totally protected from predators and other hazards. Good flow of pure water is critically important to their survival.

The alevin don't need to eat while they still have their yolk sac, but once they use that up, they need find food quickly. At this time the alevins will begin to swim up out of the gravel as fry and start feeding on aquatic insects.

Salmon and steelhead are most at home in water colder than 60 degrees F. Depending on the species and race of fish, temperatures of 65 to 70 degrees can be stressful or even lethal at this age.

Fry

Alevins lose their yolk sacs, and emerge from the gravel as fry. Under ideal conditions this upward journey presents no real problems. However, if the gravel is covered with silt or heavy debris, the young salmon and steelhead may actually need to tunnel out if possible.

The fry are about an inch (2.5 cm) long when they emerge and are free swimming. As fry, the young salmon and steelhead are striped (distinctive black vertical markings on their sides called parr marks) for camouflage but are still easy prey to predators like ducks, great blue herons, and larger fish. In the river, or a nearby lake, depending on the species, they feed and grow for periods ranging up to a year or more. Sockeye fry move into a lake for a year, although pink and chum fry swim directly to the sea. Coho remain in fresh water for an average of one year while Chinook usually have a freshwater residence time of between three months to a year.

It is during this time as fry that the salmon and steelhead imprint on their natal streams. Detecting odors and other stimuli from their surroundings prepares them for the eventual return to the spawning grounds.

Outmigration

When they are ready to migrate, begin the dangerous trip to the ocean, encountering predators, dams, and other obstacles along the way. For protection, they swim at night and hide during the day.

In the spring, during the season of freshets, the young salmon and steelhead move downstream to the sea. They are called fingerlings during this phase of their lives, and are up to four inches (10 cm) long.

For several weeks or months, the young salmon and steelhead stay in saltwater estuaries and bays where the river meets the ocean. They undergo a special process called smoltification (and are called smolts), in which their bodies change in many ways to tolerate living in salt water. Salt is very dehydrating, so their bodies must become able to drink the saltwater and get rid of the excess salts through special salt cells in the gills and mouth lining, and through changes in the kidney.

There is plenty of food in the estuary, and the salmon double or even triple their weight. Estuaries are the zones where fresh and saltwater mix. As a result there is a wealth of nutrients that support large populations of microscopic organisms. The peak of plankton production occurs during the time when salmon and steelhead juveniles migrate through this area.

The length of time spent in the estuary varies by species. Some species such as the pink salmon appear to pass through the estuary rapidly while Chinook salmon may spend months in the estuary.

Ocean Rearing

After out-migration immature salmon and steelhead spend from six-months to four to six years in the ocean depending on the species. They thrive on an abundant food supply including krill, squid, herring, anchovies, and other small fishes, which allow them to grow quickly into adults. They must also avoid predators such as tuna, seals, dolphins, sea lions and whales during this time of growth.

Salmon and steelhead make huge migrations during this time of growth traveling thousands of miles from their natal or home stream. The majority head north along the coast as far north as Alaska while others may head south as far as California. Some even remain in Puget Sound while they mature prior to returning to spawn.

Once they reach maturity they begin their long journey back to the stream and the spawning beds from which they originated. They are ready to spawn and start the cycle of life anew.

Additional Reading:

Spence, B. C., G. A. Lomnicky, R. M. Huges, and R. P. Novitzki. 1996. An ecosystem approach to salmonid conservation. TR-4501-96-6057. ManTech Environmental Research Services Corp., Corvallis, OR.

Knutson, K. L., and V. L. Naef. 1997. Management recommendations for Washington’s priority habitats: riparian. WA. Dept. of Fish and Wildlife, Olympia, WA. 181 pp.