In general, where should I find Phoxinus spp. in the late fall/winter time? Are they found in the same streams where they are to be found in the spring or do they migrate to deeper water?

Northern redbellies and finescale dace found in bogs and similar nearby areas flock to any open water as soon as ice forms. You can literally catch them by the cooler full. I am not sure if southerns, and the other species with small ranges do the same, if there even is ice in those locations where the mountain and black (forgetting any? I am not a minnow guy ) are found.

In general, where should I find Phoxinus spp. in the late fall/winter time? Are they found in the same streams where they are to be found in the spring or do they migrate to deeper water?

Well... I suppose that depends on their access to deeper water. I've collected P oreas in high headwater brooks that seemed to be pretty remote from any really big water or significant depths. But a good quality creek of any size has pools in its course. So that is where I would look. It might also be that they would move downstream to the nearest area of larger stream order where a stable pool would be more likely to occur. Seems like Phoxinus are "locally common" in the sense that they are found in certain stream stretches and not in others. And they may be restricted to portions of drainages that are of adequate quality to support them and absent from the same drainage in unsuitable stretches. So, do they migrate? I think so, but maybe limited to certain suitable areas. Guess you'll just have to get out there and look for their winter hideouts!

Well, we were able to find P. oreas this past week. The stream was about 5m wide on average and the P. oreas were found in 1-4 foot deep pools. We weren't quite in the headwaters but close enough I suppose. There are some historical collection sites that we went by that were really small waters but flowed completely through private property.
Our biggest problem thusfar has been that most suitable locations are in private lands. This is at least the case for the streams within a 1.5 hour drive. Stronger populations are found 2+ hours from me.

Well, I collect Southern Redbellies from a stream on private property (My cousin). I have collected them in Mid-Dec. last year, and have found them in the same body of water they are in at summertime. Rarely will the creeks/streams freeze over down here, unless there is a long period of freezing temperatures. It may be different for northern redbellies. I find them in shallower spots of the stream. Hope this input helps.