Autumnwatch

Where do the young Salmon return to as they do not know where they came from being hatched in a bowl in a laboratory?

I'm under the impression that they try to return to the hatchery itself. I visited a salmon hatchery in British Columbia when I was younger, and they told us that they had to make the outlet pipe a steeper gradient as at the lower gradient the salmon could make it back into the hatchery itself. Now it is steeper, the salmon try to get up the pipe until the last minute, then go and spawn in the adjacent river.