I have a ton of perch, and not one of them seems stupid enough to jump on a hook lately. I think they are a specific time of day fish, like just after the sun sets, or when you are trying to catch something else.
I doubt winter kill as they can survive very low O2 levels other fish cannot.
Try feeding them in the same place and same sun position every evening as the sun sets. They will hit surface feed once they are comfortable and then you can count them.
