It is very true that once the water warms and the spawning is complete, that <large> smallies, in a large reservoir or lake, do move deep. The reason for this is food. They follow the primary forage in the system, such as alewives, smelt or perch. I search deep water structures (25' - 40') and only look for large bait balls. Once I find them, I anchor and work the area, using a drop shot, Senko, or swimbaits. This approach works well for me.
If you find bait, on a deep ridge or hump, you can be sure they are moving. This is critical to know for your mind-set. Trying to follow moving bait around with your trolling motor puts you at a distinct disadvantage. First of all, you are bombarding the bait - and bass - with your electronic signals. Trust me, it's conditioned reflex for the bass to stop feeding. Not good. Secondly, you may be fishing between the schools of bait a higher percentage of your time and not ever know it!
In a situation where the bait is running freely along deep water structures, it's a much better approach for you to anchor and let the fish come to you. JMO.