As a charter captain who often targets lake trout in the Keweenaw, I have a deep interest (pun intended) in data about them… where they go, what they like, where and how they spawn and their migration patterns. (I certainly have as much interest in salmon – coho and kings – as well as steel head, splake and browns, but that’s another subject)
One great resource for me has been a study put out by the GLIFWC (Great Lake Indian Fish and Wildlife Commission). I have printed the study and put it into a 3 ring binder and highlighted the areas of interest to me for later reference. I also have made a summary video on it: Video on Temperature and Depth study. In the study, there were 124 lake trout netted, tagged with sensors and released so that when sport fishermen caught them, the temperature and depth sensors from the fish were tabulated for our learning.
Of particular interest to me was the fact that it was proven you will rarely find a lake trout in water of 55 degrees or more, and they prefer temperatures of 51 or less. When they do go into warmer water, it’s only for short periods to feed, then back to the deeper,colder waters. (You can also get a free PDF download of the study here: Download of Study.
I’d also like to dispel a myth about Lake Superior: There is a perception that the lake never gets above 55, but I remember several years back, it was really warm and I measured with a temperature probe 110 feet below the surface (4 miles offshore) and read temps of 66 degrees! We knew we would not find a lake trout (or salmon) in that warm water, so we went out deeper to find fish. Check out this graph of 2016 and Average surface temps.