Trapping minnows thru the ice

[NitroChukar]

I have been trapping a 4 acre shallow mud pond that is about 4 ft deep max.  First ice the trapping was good. The last week I haven't caught one fathead. For a while traps suspended just under the ice where doing well. If I placed the traps on the bottom, the minnows would die if I didn't check them every day.  Any idea what is killing them? I thought it might be a lack of oxygen. Also, any suggestions where to look for the minnows as they have seemed to disappear? There is no inlet or outlet to the pond.

[gaspumper]

There i a certain time they will not go into traps.Up to a week ago we got a gal.plus per trap,last week we were lucky to get 10 minnows per trap,we pulled all our traps for a while.

[NitroChukar]

Any idea what causes the change? You would think they would be active all winter long. I'm wondering if they haven't moved and we just haven't figured out where the are hiding out. Thanks