There are reasons why animals migrate. One of the reasons are to avoid winter and for reproduction, and this is one of the reasons why migration of birds happens. Do the birds migratory happen to all species of the birds?
Another animal that migrates is salmon. This migration becomes an animal culture. Speaking of animal culture, what is animal culture? Get to know about it on here.
Every year, salmon migrate from the Pacific Ocean or the Atlantic Ocean to the rivers where they are born. If calculated, the journey made by salmon can reach more than 1,000 kilometers.
Many scientists say that the salmon migration is the heaviest migration in the animal kingdom. So, the questions are, why do salmon migrate? How do salmon find their way home?
Why Salmon Migrate
Salmon is a fish from the family Salmonidae. In general, salmon is an anadromous species, which is a species of fish that spends its life growing up in the sea and moving or looking for fresh water to spawn or lay eggs. It said that salmon always returns to where it was born to breed. Hence, they migrate.
Salmon are born in rivers and live there until they are juvenile. After that, salmon will migrate to the sea. During its life at sea, salmon prey on shrimp, crabs, and other marine invertebrates, saving their energy for a long migration, and will temporarily fast while in the river.
Salmon only rely on fat reserves in the body when they are fasting. Female salmon can produce eggs seven times before they run out of eggs in their ovaries. Therefore, salmon can die of exhaustion after laying eggs.
Salmon eggs are placed under the gravel in cold water with a good flow for oxygen supply. Most of the salmon die immediately after spawning; only about 15% can return to the downstream (sea).
How Salmon Migrate
It is not easy for salmon to migrate. To survive during migration, salmon swim at speeds of around 30 km/h, so they have a jumping power as high as 3-3.5 m.
Salmon begin to swim quickly into the river against the current. This time the task is heavier. In the previous trip, they could easily pass the waterfall, thanks to the help of the river’s flow. This time, the salmon must climb the waterfall.
What salmon do to climb a waterfall is jumping up to the river to reach where it was hatched. During this journey, salmon may have to swim through shallow water, which makes its fins appear above the surface of the water. This shallow water is filled with birds and various other wild predators.
Bears are also included in a predator for salmon, but surprisingly, they eat something else too. Check out this observation of bear’s life (proving they are not monsters, they eat berries too).
The difficulties salmon must overcome are not limited here. Salmon hatched from eggs in a tributary, in the interior. To reach that place, salmon must take the right path when the river branches. Salmon did not make any mistakes in dealing with this choice. They always follow the correct river.
There are various studies conducted to understand how salmon migrate. The distance that salmon must travel to reach its destination is often 1,500 kilometers (930 miles), which means it requires months of travel.
There are so many obstacles that must be overcome these fish along the way. First, they have to find the river where these fish swim downstream during their first trip that boils down to the sea. Based on this, salmon determine their route back.
Scientists are still researching how salmon find their way home. According to some researchers, salmon travel long distances with the help of Earth’s magnetic field. Salmon uses a magnetic field as ocean navigation when returning to the river to breed.
United States scientists say the memory of the magnetic field when first entering sea waters will help these salmon find their way back to the river. Data collected in Current Biology provides direct evidence that salmon use geomagnetic signals in their migration. Other marine animals such as turtles and seals also use a similar mechanism to find their way home.
One hypothesis, known as natal homing, shows that salmon uses chemical mechanisms in their bodies and geomagnetic cues to find their way home. To test this theory, researchers studied fish data for 56 years that recorded the return of salmon to the Fraser River in British Columbia.
The endangered sea turtles species, sea lions, and other fish such as eels, tuna, and sturgeon have the same migration strategy.
How salmon remember the magnetic traces of their origin at birth is not yet known. However, scientists believe the change from freshwater to salt has triggered a neurological process. The memory also helps salmon find their way to the mouth of the original river.