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Fry and Parr live in riffle areas and rapids where
they fight to obtain territories that they protect from intruders. The
fast water brings them food and makes it difficult for predators to
see them in the froth. Territories provide shelter, and first crack
at food in the territory. In winter, parr bury themselves in the gravel
at the bottom of streams. Parr feed principally on insect larvae, and
insects that have fallen into the water. Very rarely they cannibalize
the eggs or fry of their own species. In freshwater, fry and parr try
to avoid being eaten by dragonfly larvae, crayfish and birds like mergansers
and kingfishers.
Smolts abandon their territories, form schools and
swim near the water’s surface, drifting downstream with the current
as they move out to sea. They can cover 20 km per day, easy. In the
river they will feed on insects, but at sea they begin to feed on zooplankton
(microscopic organisms on drifting plants) and small fish.
Smolt predators include cod, small sharks and birds.
Adult salmon are fish that swim in the open sea, cruising at depths
of less than 30 m. They feed on a variety of fish, including some that
are bioluminescent ("glow in the dark"). They will also eat
shrimp, and their flesh becomes pink or orange from these prey if they
eat a lot. Adult salmon are eaten in turn by seals, sharks, and perhaps
killer whales.
While in the ocean, salmon are sometimes infected
with small crablike parasites called sea lice. The sea lice feed on
the salmon’s skin and the skin’s mucous cover. The little
holes the sea lice chew in the skin can let bacteria and virus infect
the salmon. If salmon have a lot of sea lice, the lice can kill them.
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