The sea
The Atlantic Ocean is huge! The journey from Norway to North America is more than 4000 kilometers long. The average depth is as much as 4000 meters. For us humans, the sea is deadly salty, but not for wild salmon. They eat themselves big there.
Wild salmon migrate in the sea for one to five years before returning to the river where they were born. The youngest are small and the oldest weigh more than 25 kg. The largest have large mouths and can eat large prey, such as adult herring. The smaller ones have small mouths and eat a lot of capelin and sandeel larvae. The abundance of prey in the sea is important for salmon. This means that both large and small wild salmon can eat what gives them the most energy. In winter, there is less prey for wild salmon in the surface layers. The salmon can then dive several hundred meters down in search of food.
Wild salmon is good food
A small wild salmon in the sea is an attractive prey for many. Many species of fish, seals, whales and birds like to eat wild salmon. That's why it's important to grow quickly and become too big to be eaten. Large wild salmon do not have many enemies, apart from seals and whales.
Wild salmon in the sea have camouflage. The light-colored belly and sides make the salmon difficult to see from below and up against the light-colored water surface. The dark back makes it difficult for fish-eating birds to see the wild salmon as it swims across deep, dark waters.
Warmest at the top and freezing at the bottom
Wild salmon in the sea experience spring, summer, fall and winter out there. The light varies greatly throughout the year, especially in the north. Surface water temperatures are slightly higher in summer and in southern parts of the North Atlantic. The Gulf Stream from the south brings some of the warm water all the way north to Svalbard. In the far north, ice-cold water flows from the Arctic Ocean. The area where the warm water from the Gulf Stream meets the cold ice water is known as the polar front. This is where there is extra food for wild salmon.
Down in the ocean depths, the water can be below 0 degrees. Seawater is salty and only freezes at -1.9 degrees. It is then heavier than warmer water and sinks into the dark depths.
Most salmon that go to sea never come back. The vast majority of those that survive only make this one journey. Some make two, and a few make three.
A female salmon from the Etne River in Western Norway did more. By studying a fish scale from the salmon, which they named Kaja, the researchers found out a lot about Kaja's life. She was hatched on a spring day in 2008 and went to sea for the first time on a spring day three years later. Kaja was nine years old when she died. By then she had been on five long ocean voyages. Scientists believe this is a world record.
Did you know that...
Seawater is toxic to us. If we drink seawater, our blood becomes so salty that our cells dry out. This causes us to die slowly but surely. Unlike us, wild salmon are able to get rid of the salt before their blood becomes too salty.
Salmon on the way home
Out in the big ocean, salmon don't have much to orient themselves by. When they start their journey home, they use their internal compass to find their way towards the coast. The researchers believe that the salmon use their sense of smell to find the right river.
This group is almost there. You can see that it's not that deep where they're swimming. In addition, you can see seaweed, which shows that they are still in the sea. You can also see some sea lice on the salmon. When the salmon reaches the river, the sea lice will die and fall off. Salmon lice cannot tolerate fresh water for very long.