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Digging
the Nest Salmon nests are
called redds. They are dug feverishly
in the stream and riverbeds by the
female, who, having established
her territory, faces upstream, turns
on her side and begins scooping
out gravel using sweeping movements
of her tail. Redds can be up to
60 centimetres long and up to 15
centimetres deep, depending on the
size of the species. Many salmon
dig multiple nests. While the female
digs, male partners keep intruders
at bay, though nest-building females
can be similarly ferocious. Gravel
size and quality is a key factor
in determining egg survival.
Spawning
With mouths agape, both male and
female salmon position themselves
vertically above the redd. Males
compete aggressively with one another
for spawning privileges, with larger
males dominating. Simultaneously,
the female releases her eggs (up
to 15,000 for the largest species),
the male releases his sperm or milt
and fertilization takes place. In
some cases, two or three males join
one female in the release. Females
then cover the nest with gravel,
which protects the eggs but allows
circulation of water. Most salmon,
battered and weakened by the upstream
run, lacking in food energy, and
experiencing rapid glandular aging,
die within days of spawning (semelparity).
A few species (Atlantic salmon,
steelhead trout, cutthroat trout)
survive to repeat the spawning cycle
at least once. Spawn survivors are
known as kelts.
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