While I don't doubt that braided line could do damage to fish, I have been witness to the same sort of thing with mono as well. This summer I got taken down some rapids by a fish and when I brought it in I noticed that the fish had a deep laceration along it's tail, as if someone had slit it cleanly with a knife - I know it was fresh because blood was pumping out while it was in the water. So I'm convinced that the line got wrapped around it during the fight. Fortunately that was a hatchery fish. By the way, I was using straight 8# UG, tough stuff is all I got to say.