I never really heard of anyone spearing blue crabs. The way I used to catch then is with a line attached to a raw chicken leg or other suitable bait. When one or more crabs are eating on it, you slowly draw in the line and nab them with a net. Or the more efficient method (but not as much fun) of using a crab trap.
Of course, I do remember the girl who used to cut my hair commenting that she would whack blue crabs with a two-by-four. That just seemed to be a rather unique way of collecting them, to me, anyway.
Blue crabs should be live when you steam them. Matter of fact, when it comes time for them to go into the pot, any that are dead are discarded.
Well, now I'm REALLY getting an appetite for crabs! But I guess I have to wait a couple of more weeks before I can get a batch of them.