I love to fish the Great Lakes for spring salmon. This is when water temps. are generally cold, which is not a bad thing. If you find pockets of warmer water, even by a couple of degrees, you will probably find baitfish and salmon & trout feeding on them. This usually happens in water less than 60′ deep.
I rely heavily on my Raymarine HybridTouch to spot both baitfish, salmon & trout suspended near-shore and to know where the structure breaks are so I can head to them with the C-Map charts. In the above screen-grab you can see a large school of smaller baifish above. Normally fishing right in the baitfish school is not productive, but fishing away from them in the general are is.
In the screen-grab above, we were in much shallower water and the baitfish were larger. Usually larger baitfish means larger feeding gamefish.