In general, salmon
and steelhead have similar life cycles. The following diagram represents
the life cycle of chum salmon. It can be viewed as an example of the life
cycle of other salmon species and also for steelhead with the exception
that steelhead may repeat the cycle and return to spawn again. During
the freshwater spawning and rearing phase of the salmon and steelhead
life cycles there are periods of time when caution must be used when recreating
in or near the water. See the chart below to identify general timing when
activities may impact salmon and steelhead spawning grounds.
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/fishing/salmon/species.html.
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
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.
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.
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.
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
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.
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.
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.
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
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.
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.