Man, i would go and type up a debate for treble hooks, but in reality... If you really look at the deitails... It depends on how hungry the fish is and your "hooksetting" has a major role in fish mortality. You should, as a fisherman be able to set the hook at the right time and hook the trout in any part of the mouth. GUTHOOKING is possible to avoid when u set the hook at the right time, but then again.... it comes back to how hungry the fish is!! If the fish is hungry enough that fish will swallow whatever presentation you throw at them. Most simple thing you can do... if u guthook/gillhook more then 1 fish in one trip, is to chance ur dang hooksize until you are consistantly hooking them in the lip.
Not trying to hurt any feelings or send any hard feelings towards other fisherman... But if you are are good enough at removing hooks... most of your hooked fish, that hook really shouldnt be that hard to get out in the first place! Also... when a trout swallows a treble, there is always a puzzle to getting them out with out doing any harm to the fish, if you are in no hurry... that hook should come out fine!! Take your time and be gentle with removing hoks from fish. Simple as that. If a fish dies from your hooks... what r u gunna do? nothing cuz its already gunna die. It's the world and sport that we live in!! All this is debatable, and every hook/lure/fly will have some type of side affect on trout/salmon/steelhead. It's all just the commen sence of the fisherperson to be honest. Sorry... i kinda went on a rant. but i am done noww.