The salmon fish species, the best source of omega 3 fatty acids for man, has a very interesting life cycle. Adult fish spend most of their lives in the open seas and the Pacific and Atlantic oceans. Upon maturity, they experience this deep nature call to go back to their birth grounds to lay eggs. They swim thousands of miles, mostly upstream, and overcome prey such as bears, birds, foxes, and humans, to go back to the very place where their own lives started. In most cases they go back to the very stream where they were born, sometimes meters from the exact point. And the big question is, how do they manage to do this?
The odds:
The odds of the salmon being able to trace back their original breeding grounds is quite rare. That is why the sight of salmon fish making their way back to their birth grounds every fall makes for quite a celebrated fete of nature full of tourists and biologists who are in awe of what the salmon managed to do.
Prey aside, overcoming strong water currents and swimming uphill, sometimes even jumping over waterfalls is unbelievable. And then you have the vast ocean space which occupies thousands of square miles and the salmon are able to swim out of that huge maze and travel back home. The odds of the salmon making this journey is possibly one of the most unbelievable achievements in nature.
How they manage to do it:
It is believed that the salmon are able to make their way back home thanks to their strong sense of smell. Apparently, salmon use their olfactory senses to trace back the streams where they first lived for months. Most do this every four years in the Pacific north-west rivers. The clean, cold, high-oxygen waters provide just the right environment for their eggs to survive and breed the next generation of salmon.
For one of the 7 species of the Pacific salmon, the sockeye salmon, they are able to detect magnetic fields and this acts as a sort of natural GPS tracking system that enables them to travel in the right direction and to know if they have arrived at the spot they are looking for. That is how in Canada’s Fraser River, millions of them come back each year, as many as 19 million in some cases.
The spawning process
At the near end of the journey they stop eating and their skin turns red. They find a shallow location that’s best for egg-laying and bury about 4000 eggs under gravel. Males protect the eggs until the females die. And then the males too follow suit. After about 4 months the salmon eggs hatch and they spend months in the rivers before heading out to sea.
The salmon migration supports lots of life in Alaska. It feeds bears, other predators, and humans before winter comes in. However, toxins in the oceans pose grave risk to these fish. Also, high temperatures in the water due to global warming affects them and causes death often.
For more info about salmons press here.