From what I have seen, they are very reliable spawners and it is not hard to find larvae amongst the plankton after the spawning takes place. The bottleneck appears to be whether or not they survive the window where they settle out in the littoral zone and operate much like Bluegill during the first summer of life. It seems to me they have to reach a larger size than Bluegill before odds greatly increase a given fish will recruit into the fishable population. I am betting the cover plants or other structure provides near open water the crappie feed is key. And LMB must of the size that targets the YOY and even age-1 crappie must not be too abundant. The BG are simply more resilient in the face of the predation and may also benefit from the extended breeding season.

Aquaculture
Cooperative Research / Extension
Lincoln University of Missouri