I was wondering what the typical behavior is of salmon and steelhead that are transplanted into other rivers, like the Boise River? What happens to their homing instinct, and do they typically continue to move upstream or do they go downstream or stay in the same location confused?
We don't have great information on this, but we do have some idea about how these fish typically move. IDFG has tagged some of the steelhead and salmon that have been released into the Boise River. By keeping track of where tagged fish are released, and where they were caught by anglers, we can get some idea of the movement patterns. Most of the salmon and steelhead released tend to move upstream after a day or two of being stocked, so they tend to spread out if they were caught immediately. Some anglers claim to have found Boise River steelhead in odd places like irrigation return drains that connect to the Boise River, and even as far downstream as Star or Middleton. This suggests there are some steelhead turn around and try to "leave" the river, but most seem to stay and move upstream. In some years, anglers have reported catching steelhead as late as March, showing that some spend the entire winter before being caught. However, this is not typical and most steelhead are caught within a month of being transferred to the Boise River.
Best of luck if you head out on the river!