Fjord
Photo: Frank Martin Ingilæ
For salmon, the fjord is not the most important habitat
Norway has many fjords that are several hundred meters deep. Juvenile salmon on their way to the sea and adult salmon returning to the river where they were born only use the top few meters. The water here is often brackish. This means that it is less salty than the water in the sea, and more salty than fresh water. The water temperature and salt content of the water can vary from year to year and from fjord to fjord. The surface water in the fjords is fairly similar throughout the year - if we compare with the conditions in the watercourses.
To eat or be eaten
The young salmon (smolt) migrate in the spring, with camouflage that is adapted to life in the sea. They have dark backs and shiny bellies - almost like a herring. The dark back makes it difficult for fish-eating birds to see them as they swim across deep, dark fjords. The light-colored belly and sides camouflage it against predatory fish that come from below and look up at the light-colored water surface.
The smolts only spend a few days in the fjord. They swim purposefully out to the open sea. The most important food for smolts in the fjord is fish fry. Adult salmon on their way to their natal river to spawn rarely stop to eat in the fjord.
Rapid growth in aquaculture
The fish farms along the coast have a thousand times more fish than we have wild salmon. The parasite salmon lice likes that. Salmon lice are transmitted from farmed salmon to wild salmon and can damage and kill smolts on their way out to sea.
Salmon are particularly protected in some rivers and fjords
The Norwegian Parliament has given wild salmon special protection in 29 fjords. We call these national salmon fjords, and salmon farming is not permitted here. Tanafjorden and Namsenfjorden are two such national salmon fjords. You can read more about national salmon streams and fjords here.
Water is slightly salty
Water consists of a small amount of salt (NaCl) in addition to molecules composed of two hydrogen atoms and one oxygen atom. The proportion of salt can vary from less than 0.5% (fresh water) to 3.5% (seawater). Salt makes water heavier.
On the surface of the fjord there is often a thin layer of water with little salt. It is a mixture of sea water and fresh water. We call this water brackish water. Further down, there is "pure" seawater.
Top: adult female with egg strings. In the middle: adult female without egg strings. Bottom: young louse. Photo: Thomas Bjørkan, Norwegian Aquaculture Center, Brønnøy.
salmon lice
Salmon lice are crustaceans that live on salmonids (salmon, trout and char). It does not thrive in fresh water and therefore falls off the salmon in the river. If the salmon in the river have salmon lice, it indicates that they have recently arrived from the sea. Laboratory experiments show that salmon lice can survive on fish for up to 14 days in fresh water.
The smolts swim together
When the salmon fry have lost their parr marks and become smoltified, they become silvery. The smolts often gather in a shoal and swim together with other smolts out of the river, through the fjord and into the sea.