You are mistaken if you think that migration is peculiar to birds. In fact, there are many migratory species on land and in sea. In this section, the adventure of salmon, a migratory fish species, will be examined.
Salmon are born into the world as they hatch from eggs the females of the species lay in the river. They grow and hunt in this place for several weeks after which they start to advance down the river. During this journey towards the sea, they encounter dams and polluted water, and try to avoid dangers such as bigger hunting fishes. Having overcome all these and reached the sea, they spend several years there. Once they mature enough to spawn, they swim back to the fresh water.
The point at which salmon aim to arrive is the place they were born. But make no mistake: it’s not a short distance. The distance that the fish needs to cover to get to the destination may sometimes be 1,500 km (930 miles), which means a demanding journey of months. There are many obstacles that the fish has to overcome during this journey.
The first, and maybe the most important problem that needs to be solved is to find where the river down which the fish swam during its first journey empties into the sea. Based on this, the fish will determine the return route to follow. Amazingly, none of the salmon makes a mistake and they all find the river right first time.