Nick -
The region's bull trout are interesting critters that exhibit complex behaviors that a driven by forage and habitat needs. As a result one may find different age classes and population segments behaving differently.

While without a doubt the bull trout life history switches noted earlier is in at least part drive by changes in food availability (either in in total or seasonally) there can be a habitat component as well. For example the river dwelling (fluvial life history) during much of their time in the river a tied to large pools (a home base if you will). As the quality or amount of that habitat changes (via floods?) one would expect to see the bull trout adapt.

Just another illustration of what makes the Skagit "trout" and the fishing for them so interesting.

Curt