Every year, one of the most spectacular migrations occur along the Pacific Northwest coast. Millions of salmon from far across the ocean return to the streams where they were born. Not only is this a spectacular journey, but they’re extremely important as well, having the ability to shape entire ecosystems.
From The Salmon Society, a male Chinook Salmon swiming upstream
Every year, millions of salmon of breeding age make the journey from their ocean homes to the streams of where they were born along the Northern Pacific coast. Scientists are still unsure of how they find their way back to the streams in which they were born in. Though, they believe that the fish use their detection of magnetic fields to locate the streams, and then use their sense of smell to find their way to their spawning grounds upstream.
Their journey isn’t at all over once they reach the rivers. The salmon now have to battle the currents and swim upstream all the way to the exact spawning grounds to where themselves were born.
All their energy is devoted entirely to the run and their dramatic physical changes. Several species of salmon during the run transform, with the transformations in males being the most striking. The fish begin to lose their silvery blue colour as their colours darken. In some species, their hue changes completely. Notably, chinook salmon turn a dark red. Male salmon also grow canine-like teeth along with their jaws curving into hooks called kypes. Some species also develop large humped backs.
From Wikipedia, a regular male salmon (top) and a spawning male (bottom)
The swim upstream can be exhausting and dangerous. The fact that the fish don’t eat during the run doesn’t help very much either. Not only do the salmon have to swim hundreds of miles against the strong currents, but they may also have to get across waterfalls and rapids. In order to clear these obstacles, salmon have been recorded making vertical jumps as high as 12 feet (3.65 metres) into the air.
After several weeks of travelling and through all odds, the salmon make it to their destination. Their spawning grounds. There, the fish that make it mate and lay their eggs. That’s it. Their journey is finally over.
Once they've completed their great salmon run and successfully spawned, the exhausted fish never get to return to their ocean homes. Every single species of pacific salmon that make the migration, die after having completed it. It’s just a part of their life cycle. Once the eggs hatch, the countless baby salmon prepare to make their journey to the ocean, where they’ll live for a couple of years, before ultimately returning to take part in the salmon run again. The cycle continues anew.
Now, though, as the millions of salmon wash up dead along the riverbed, something extraordinary begins to happen
How it Affects Life on Land
The annual salmon run is a matter of reproduction and passing their genes onto the next generation,- for the salmon that is. But their migration has a much wider impact. Every year as millions of salmon return to their natal streams, they become prey for numerous species. Eagles, gulls, bears and even wolves gather to feast upon the salmon.
The salmon are keystone species, and their migration helps to bring nutrients from the ocean back to land. Their migration is perhaps the most remarkable case of interdependence in ecology.
Scavengers such as birds, foxes, bears, and the occasional wolf take the carcasses back into the forest. Once they’ve had their fill, the remains begin to decompose. As the salmon decompose, all those nutrients they gathered from the ocean get recycled. They get taken up by the surrounding soil, plants, fungi, and trees.
It’s safe to say that the long stretches of coastal temperate rainforests by the Pacific Northwest wouldn't be as rich and thriving as it is today if it weren’t for the salmon run.