Nah mang, dog fish are pretty well known and common. A lot of people in Europe eat them and they are actually a pretty important commercial fishery.
Reference: http://en.wikipedia.org/wiki/Spiny_dogfish.
Plus if you have ever fished in coastal waters anywhere except the tropics you have either had them steal your bait, break your line, steal half the fish you are reeling in... or like me, reel one in only to have the fucker stab the fuck out of your hand as youre trying to be the nice guy and put him back.
Back on topic, the crab pot sounds like a great idea.