Yes, speculation for sure. And we may never know the true cause. But if we can find a few areas to improve our methods, systems, etc., then I think it is a step in the right direction. I know I learn a lot from the ideas others are throwing out there. As stated above, we (me anyway) are always learning something new.All these theories are really interesting. Guessing, I'd tend to agree. Just don't forget that new predator fish is also a variable... aggression or disease are still in play.