10-20 years ago pre-dates my white bass infatuation, but I can certainly see a slow and steady decline since 2007 in the areas where I do the majority of my fishing.
Both in average size, and numbers being caught.
It isn't because of a lack of forage, I'm certain of that.
And I don't think it is because of over harvest, but I'm not ruling that out entirely.
For the most part I choose to blame Ameren, since they always seem to hose up what would otherwise be ultimate spawning conditions year after year.