As hopeless as the contest seems, there is no search involved that we know of. The salmon find their particular, "door" easily, and sail into the estuary they left some years before. In a reverse process they pause long enough to condition themselves to the freshwater and then, as if on some vital time table, thunder onward for the moment of spawning.
In between the estuary and the spawning place a salmon might be confronted with many life threatening barriers. The wrenching, repeated leaps up a dam's, "steps" leaves many torn and battered at the bottom. their particular stream may not even be where it was when they left. It may have been diverted by, or for, a commercial undertaking. (Although this isn't apt to happen much as many individuals and agencies have taken a stand in protecting the fate of the salmon.) Worse yet, the waterway may not be there at all...only a bog of mud where over-logging has been done.
Happily, there are always those fish who win the prize, those who reach the pinnacle of a salmon's life. There time has been spent in adding assets, swirling in deadly beauty and guided by a Creator-driven purpose.
A worn-out mother salmon prepares a gravel nest--called a "redd"--and one or more large males join her and ferilize each group of eggs she deposits. When spawning is finished the gentle water laps a sandbar; the sunset blazes one last time, and the adult Oncorhyncus close their eyes.
In 60 days the eggs will hatch and the story repeats.
There really IS no place like home.
Note* This was written with no claim to a scientific background, however the facts are correct as far as I know them, and the salmon are amazing.
What a Creator we have.