How deep is the creek where you catch them in winter? That may be the key. Most places I've seen and heard of will have the cats in the shallower tributaries during the spawn but in the winter they are found in the deeper holes of the river. Interesting that you appear to have the opposite situation. If your tributary is real deep, you may want to check out some of the smaller branches coming into that creek. That's one thing that makes the hunt so interesting. Same rules don't apply on all waters.