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Salmon stop eating when they return to fresh water,
in preparation for spawning which occurs in the autumn. During their
upstream migration they can jump waterfalls up to 12 ft (3.5 m) in height.
Their scales and mucous-covered skin help protect them from scratches
if they hit rocks.
As spawning time approaches, the fish begin to move
out onto the spawning grounds. Big adult male salmon, which are called
cockfish, develop a "kype" in their jaw, which is a large
hook with sharp teeth. They slash each other with these kypes in fights
among themselves to determine who will spawn with the females. The female
fish, which are called hens, then decide whether or not they like the
winners of the fights. If a hen accepts a winner’s advances, she
will begin to build a nest for her eggs in the stream bottom.
The nest is called a redd, and the female digs it
into fist-sized gravel with powerful beats of her strong tail. When
the nest is ready, both the male and female shed their eggs and sperm
into it. Sometimes some of the small male parr manage to mature, and
they sneak up on a pair of spawning adults and dart into the nest when
the big male is not looking. They add their sperm to the nest and can
fertilize some of the eggs. These small males are called precocious
parr.
When she’s done, the hen salmon will cover the eggs with gravel
to keep them from washing away while they are incubating. This also
protects the eggs from hungry fish and other predators that would quickly
eat anything that was not covered up.
The eggs are round, orange or pink, and about 5
mm in diameter. They take about 180 days to hatch. A hen usually lays
about 600 eggs for every pound (450 g) she weighs. Of every 6000 eggs
laid, only about two survive to return as adult salmon.
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