Oops -- forgot the walleye part of the question.
Walleyes don't fit well into either mode. In the northern lakes where I now live, they often feed extensively on yellow perch, minnows, and even insects. They will feed extensivly on rocky bars or even in submergent vegetation or trees, when such habitats are present. We have other lakes in SD without much structure at all; in these lakes, the walleyes tend to roam a lot more. We used telemetry studies to see substantial differences in movement rates between lakes with complex bottoms vs. simple, bowl-shaped lakes.
When I worked in Kansas, where the primary prey source was young gizzard shad, the walleyes often could be found suspended in the water column, feeding on shad. I can remember fishing in one lake that had thermally stratified in the summer. We trolled with shad raps that ran just above the thermocline (temperature transition zone), and caught both walleyes and channel catfish! Obviously, everything "thinks" that channel catfish must be on the bottom. However, I've learned never to say never!
Dave
