Addtionally your thermometer seems to be off about 4 few degrees. Very doubtful your water is 39 just under the ice and 41 in deep water. Water is densest at 39 which would mean your 39 degree water should be deeper than your 41 degree water. If you subtract about 4 degrees from both readings that should be correct.

Have access to a fish finder? If you can't catch fish but mark fish that would tell you they are there. Also if they are not that far off the bottom they should be fine. However if they are up high that could mean depleted oxygen in the deeper water.

If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.