I don't consider myself to be an expert, but here's my belief. Large lakers feed on large forage. In lakes that have both smelt and cisco/whitefish, the smaller lake trout will feed on the smelt and the larger trout on the cisco/whitefish. I have seen Lake Trout with 21 inch ciscos in them. I believe that the lakers reach a certain size (@ 24 - 26 inches IMO) where they start focusing on the larger bait. In one lake I fish, some people catch the cisco and use them for bait, dead or alive. They are pretty successful at hooking the larger lakers.