I love fishing for whitefish. They are great sportfish and great tablefare.
Tips? Can’t offer much except for some personal insights. You were doing the right things in the right spots IMO. Whitefish love the deep mud and seem to slowly patrol along deep edges in search of forage or just seeking comfort. Whitefish are weird though, compared to more familiar gamefish. I’ve fished for them in Northern MN pretty extensively using Livescope both in the summer and on ice. I’ve seen big schools of them slowly swim by my presentation and do absolutely nothing. Then, for whatever reason, one will just decide to swim over and eat. Doesn’t seem to matter what presentation is used – and we’ve tried lots. The fish decide when they will light you up. The vast majority will reject your offering. When they decide to eat, just about anything they can fit in their mouth is going to get bit. Day in and day out though, we’ve found a small gold slender spoon tipped with a pink Gulp crappie nibble or plastic larvae to be about as good as anything.
What do they feed on? We’ve kept a number of whitties for the table over the years and always make a point to check stomach contents. All but one have been full of mayfly larvae. One that we caught on early ice was full of fish eggs, presumably cisco eggs. Interestingly, mayfly larvae imitation lures haven’t been ‘the deal’ when it comes to getting more bites. Small shiny flutter spoons have outproduced them consistently.
I’ve not fished whitties anywhere besides a large shield lake in northern MN. So, these observations may be unique to that fishery. Hope this helps in some way though.