Opti has it right, much more bycatch with Hybrids, they are generally mixed in fairly well with warmwater species. If you fish a little deeper, in colder water, there are more pure breed Stripers caught. 3'-5' deeper can make all the difference in which you catch. Many times in the Summer Hybrids will be in great condition, and the Stripers will be snakes, mostly head and little body mass. I try not to target them in when they are in that condition.
In the headwaters of lakes where there is no clear thermocline, they can be just about any depth, especially in low light conditions. The Stripers caught here seem to be feeding much better as well, not nearly as skinny.