as stated the black seem to like rock when its available , this is why so many are found on bridge columns .
there is a small plankton creature that is consumed by them during certain months of the year that are on rocks and concrete .
its only a quarter of an inch long and thus the need for a micro bait .....
i know of a few locations where large boulders are off in deep water and they seem to frequent them often .
one thing for certain ,the spot you are hitting has a ton of black crappie in it ,and some of them are quite large for our neck of the woods , 2lb plus range ....
you might try looking a bit shallower ,8 to 10 foot of water real soon , the blacks will be in a pre spawn pattern sometime in late Feb. i would tend to think in that lake,when your water temp rises 10 degrees from its low ,you best go prowl some shallower rocky water early in the morning after about 2 or 3 days of real hot sunshine .....western rocky shore lines close to the deep water channel bro .....the more sunshine exposure on the them rocks the better .
if you find a good spot watch over your shoulder , the crowd down that way will beat your spot to death if they see you on fish and thats a fact !