Living here on Oahu, Hawaii I can't comment on the cold/warm water theory. But, I can add some fuel to the current/surge theory mentioned. Here in Hawaii it is a recognized fact that the bluefin trevally that thrive in the reef/surge areas are very much stronger than GT of equal sizes. Granted, the bluefin trevally only grow to 25lb max but............pound for pound, they will kick the GT's butt in it's quest for freedom.