I just got back from a week long fishing trip in northern Ontario Canada. Four guys fishing at least 6 hrs a day. We only caught WE,NP and SMB. Seems it is possible to have a mainly predator population. Only crayfish and young of other predators in the stomachs of the fish we cleaned. Put our minnow trap out in various areas, no minnows caught, only leeches and a couple of crayfish.
