The underside of a longnose skate. Don't know what kind it is specifically (and 200 pounds would be a really big one) but that family of beasts was my first thought too. And they do make good eating.
Reminds me of when I was working in the salmon cannery and I was so exhausted that when I came across an unusually mutilated salmon I convinced myself it had come across some very monstrous creature.
