Hi Larry welcome to the forum. I think its the location of the fish more than tactics. My reasoning for this is that I've been getting bass from this spot, an area about the size of 2 pool tables, since July. In the last 2 weeks its switched over from bass to perch while the same fly was used. The fly was a grizzly brown bead head wooly bugger fished deep on a dead drift. Whenever the line stops moving or twitches I tighten the line to see if its a fish. Its interesting to note that I haven't caught anything of decent size at this spot on the surface. I think the bass are still in the general area but havent found the new location.