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Only 2-10% of the eggs deposited in a gravel nest will survive to return to the spawning grounds as adults.
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Born in British Columbia’s cold coastal and interior rivers, wild salmon
swim to the open Pacific Ocean to mature and then return to their native waters
to spawn. An anadromous animal, the Pacific salmon breeds and spends varying
portions of its life in fresh water, then travels to the ocean to feed until
maturity. This is in contrast to palegic species which are born and live solely
in the sea.
As salmon migrate through the cool, pristine waters of the west coast, they
receive nourishment from their natural surroundings. During their time in the
ocean, sockeye, pink and chum salmon feed primarily on plankton and crustaceans
such as tiny shrimp, while chinook and coho salmon eat smaller fish.
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Click on diagram to see Life Cycle stages
| Eyed Eggs |
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Salmon are born in gravel beds in streams 10 to 700 miles (16 to 1200 km) from
the sea. Laid in the fall, the eggs incubate over the winter, frequently
under several feet (more than a metre) of snow and ice. Their pink eggs are
always covered from direct sunlight. About a month after they have been deposited
in the gravel, eyes begin to show. This normally happens in late November
or early December. It is essential during this time that water flow and temperature
are suitable. The period of greatest mortality in the salmon's life cycle
is in the egg-to-fry stage.
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| Hatched Alevins |
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In the late winter, the eggs hatch into alevins, tiny creatures with huge eyes
attached to bright orange sacs. They grow rapidly under the gravel for three
to four months. The orange yolk sacs contain a completely balanced diet of
protein, carbohydrates, vitamins and minerals. The vitelline vein, running
through the centre of the sac, picks up oxygen from the water. The fish at
this stage are totally protected from predators and other hazards. Good flow
of pure water is critically important to survival of alevins.
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| Newly Emerged Fry |
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Alevins lose their sacs, and emerge from the gravel as fry in May and June.
About an inch (2.5 cm) long, they are free swimming, and are easy prey for
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.) |
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| Fingerlings |
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In spring, during the season of freshets, they head downstream to the sea.
They are called fingerlings during this phase of their lives, and are up
to four inches (10 cm) long. In the sea they spend varying amounts of time
ranging up to five years, eating greedily and growing rapidly in the bountiful
ocean feeding grounds. In the early summer of their maturing year, they begin
to head back to their home streams. Scientists are uncertain as to how salmon
navigate back to their spawning grounds. (Current thinking ranges from theories
based on their highly developed sense of smell to an ability to work out
direction from the stars.) |
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| Adult Spawners |
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Salmon stop feeding as they enter fresh water, living on stored body fats.
They struggle for weeks against rapids, falls, obstructions in the form of
fallen logs and rocks until, bruised and travel-worn, they reach the placid
waters of the spawning river where they were born. Sockeye and chinooks are
the most hardy of the Pacific salmon family, travelling as far as 1,000 miles
(1,600 km) upstream to spawn. Chums, coho and pinks spawn closer to the sea.
With her tail the female digs a nest, or redd, in the gravel, hollowing out
a cavity up to 18 inches (45 cm) deep. She prefers a place in a riffle, where
the fast-running water will provide an ample supply of oxygen for the eggs.
When the nest is ready, which may be weeks after the spawner has reached the
gravelbeds, the female lays up to 8,000 eggs in the gravel. The male fertilizes
them by covering them with a milky substance known as milt. After fertilization,
the female covers the eggs with gravel, and remains on the redd until death
several days later. Pacific salmon, unlike Atlantic salmon, die once spawning
is complete.
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