I have heard the same question regarding catching catfish in deeper water water. some guys use a plastic hypodermic needle, more or less a "worm puffer" needle, and suck the air out of the fishes swim bladder. I sometimes fish in holes in the river nearing 50 ft deep but for cats the trick is to bring them up slowly, a few feet at a time then let them swim around some then reel up a few more feet and so on. when they get up to around 10-15 feet deep they start burping bubbles out, this is the air sack decompressing air. I don't know if this would work for crappies or not, but my catfish almost always take right off when I release them. the ones that don't get released into grease...