Guns on board

Via Robert Farley, I learn that Rush Limbaugh is opposed to putting weapons on board merchant vessels to prevent piracy. And his reasoning -- that weapons make mutinies a lot more likely -- is totally sound.

Yet I remember a scene from "The Perfect Storm" in which the crew accidentally hooks a shark and brings it on deck. Coaxing a shark off the deck proves difficult, and since it's trying to eat everyone, George Clooney grabs a shotgun and pumps some daylight into the shark's tiny brain. That seemed like a good call to me. But is it common for small commercial fishing vessels to carry shotguns? I'd guess that the captains of such ships have to make a lot of unpleasant calls that put the other crew members in danger. Isn't an armed mutiny a possibility there, too?