Plan your trip around full moons and new moons. Fish spawn because of moon light and sun light volumes. Water temp has nothing to do with it. If every crappie had to have 65 degree water then the fish up north would never spawn. It's just like the rut for deer. The moon controls tides and many more things on this big ole rock. Not wanting to argue with anyone but its science.
I would concur, also would add, THEY DONT ALWAYS SPAWN SHALLOW. Last year I whacked them in 15 to 17 feet,and yes, they were spawning, males with milt and females full of eggs. Think of it this way, logically, there just isnt enough running linear feet of suitable banklines for them to all go shallow, plankton concentrations also have a large part in the area they spawn, and baitfish concentrations, where shad spawn is a great place to look. The bigger more mature fish spawn deeper as well. I start deeper and work shallow during spawn, I learned after fishing 140 miles of bankline and not catching one crappie one year.
If you asked me what the biggest secret of crappie spawn is, its that they wont spawn deep is a huge myth. Your brain will tell you, that your just not in the right 3 feet of water, so you go from spot to spot to spot, and dont catch squat, so you tell yourself, the temp must not be right. Many of the " legends" of crappie fishing just swore by that old temp myth, they were repeating what they had heard for so long, but it is simply not true. Start at 17 FOW fishing brush, rockpiles, stumps, ledges, ect, and work shallower from there. Ive caught crappie spawning as early as late february in central tx. if u do some recons, go before daybreak, and look for banklines with shad spawning, they usually spawn 6 to 8 weeks in spring, and sometimes in fall. right at daybreak, they stop, before daybreak, it looks and sounds like thousands of shrimp popping along the bank. try to find structure near the spawning bank. remember , everything is eating something else in a lake.