They feed on mature sturgeon, beaver, or, sometimes, in the spring, moose calves learning to swim alongside mama.  Personally, I don't mess with them anymore... at least not since the incident.  If you happen to get one on the line, best to have a club handy (36" X 2", minimum) and pop them between the eyes; they generally release.  Keep your hands away from their teeth & dorsal barbs & you should be OK.  Heavy-duty leather gloves serve better than rubber.  If you hook a big one, cut your losses immediately by cutting the line.  Don't mess with it unless you are in a vessel larger than 20' & are reasonably close to shore.  Snap a picture, if you can.  They are almost as rare as Sasquatch.  If you are a masochist, bait your hook with beaver and troll that northern bay of Sturgeon Lake, not but 200 meters offshore from the portage into Ram Lake.

Good luck!

Jimbo   8-)