LOP deep water bite over? Why?

It appears the bite at LOP is over. I don't understand why. The weather is still cold, and the water temp. has not risen at all and maybe even gone lower. Why then, do the fish seem to be either gone from the deep water or not biting? Seems like the colder it gets, the deeper they should go. My dad went today and there were only about 5 or 6 boats out, and he only caught one crappie. The last couple of trips we made, they seemed to be going downhill and by the mount of boats it seems to be over. Anyone with more experience know why that might be?
Curious,
JBJ

I'm just back from FL where the fish are starting to move shallow also. The length of days is one of the things that tells them what to do, and we are if February so it's getting close to that time.

Thanks for the response! I didn't realize day length made a difference but it makes sense. This is the coldest winter we've had here in probably over 25 years, and I figured they'd stay deep until the water began to warm, which it isn't. They certainly do know what's going on. There's other evidence the fish are trying to move here also (white bass moving).
Always learning,
JBJ