Scott:
Metabolism drops with water temp, and appetite with it to a degree. IIRC for LMB metabolism is cut in half for each 8 degree drop in temp; assuming a similar drop for BG (a fellow Centrarchid), metabolism is (theoretically) 1/32 as much at 44 deg compared to 84 deg in Summer.
Biting rates don't drop that much, IMO, but vary considerably depending on the weather. You can still get some decent fishing periods in late Fall, like when you have a couple warm, sunny days after a cold spell.
YP being a cool water species stay more active in Fall/Winter temperatures. Some of the YP experts can probably provide tips for fishing them successfully in cold, or even hard, water.