Much of it is very dependant on local conditions and species of trout.
Often Rainbows stocked will migrate downstream. They had that trouble when stocking the Grand River in Ontario. The rainbows headed downstream as far as the waters allowed (lake Erie). Browns on the other-hand stayed as residents within 25km of where they were stocked. In other situations (the next river to the east) the browns move into Lake Ontario.

Brook trout will generally stay put unless there is a reason to move. The coaster brookies of Lake Superior are a great example of this. Although genetically the same as the resident populations, some of the brookies decide to move downstream an grow in the lakes. The theory is that the brookies reach a threshold in the streams where the stream cannot support the population anymore. Instead of over-populating and stunting the brookies growth, many just move downstream.

All trout will move during spawning (spring or fall) to find the best suitable habitat. For lakers it means looking for the rocky shoals. For Rainbow/steelhead it means moving upstream to smaller "nursery waters". For brookies it means finding cold water upwellings. they may go back to where they were stocked or they may find some place better along the way.

Chars,
Paul


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Paul H.
"Whiskey is for drinking; Water is for Fighting over."
http://www.flymph.com/