Why do salmon return to the place they were born to spawn?

Question

Why do salmon return to the stream they were born in to spawn? What is the survival value in doing this? Why don't they just stay in the ocean?

So many die or get eaten by predators on their way upstream that it seems like salmon that spawn in the ocean would have a better chance of having more offspring. So why did evolution give them the instinct to return upstream?

Answer 1

It will remain one of nature's great mysteries. However, there are large families of bears that depend on the annual migration of these fish to survive and breed. Just like crocodiles, people (African bushmen) and wolves depend on the annual migration of Wildebeest and Caribou for vital food supply. Cicadas hatch at the same time after being underground for 17 years and provide a bonanza for the forest inhabitants.

Nature works in ways to benefit the entire ecosystem. So, not all animal behaviors can be tracked to evolutionary motives. Despite the natural carnage, salmon never became an endangered species. They are such prodigious breeders that there is plenty to go around for the predators and they are still a successful species.    

Answer 2

Salmon return to the same place to breed because it has survival value. Ergo: I hatched there and survived therefor my offspring can do the same. It is programmed into them by evolution. However salmon are become scarcer and scarcer. Many fishing industries rely on catching them as they enter the estuary and they are netted. Its somewhat different with North American species (Sockey). They die after having mated and spawned. European salmon which at one time populated every stream and river are extinct in some areas. They are still to be found in the Hampshire Avon and Stour. In Scotland they are still reasonably common but the giant salmon of yesteryear are gone. It was not unusual to catch them weighing over 50lbs but such is the pressure of mainly man to catch and eat them they are sadly vanishing. Many industries have sprung up to farm them artificially keeping them in enclosures rather than allowing them to migrate and eat their fill in the Atlantic. This has caused problems because for one thing keeping them in close proximity allows lice to flourish on their skins with adverse effects on their health. Their is a corresponding influx of salmon in the Pacific but these are slightly different to the European.

They make the arduous journey upstream to spawn because the river habitat provides a safer nursery for the young fry and the running water over the eggs carries oxygen. The head of the river is usually free from polution with clear water and they do not return to the ocean until they have increased enough in size and speed to be able to elude predators.

Answer 3

They know for a fact that its a good place for there eggs to mature, (because there alive and well). The oceans has far more predetors than a stream. As for why did evolution give them the instinct to return upstream. Evolution is a process. They have been going upstream to lay there eggs for longer than humans have been around. It just works for them.