The crappie are moving shallow b/c they know the days are getting longer which tiggers them to start feeding so they can make it through the spawn b/c it takes a lot of energy and work. I always look for the magic water temp. which is 62 but some of the larger females will lay at 58 so you got to be a little early or you will miss the big girls. But, moon phase, water conditions, etc can also play a role in their spawn. Thats my two cents worth.