Meh? No comprende. I think it is good to warn people about the potential risk as temperatures rise, but not to overstate it either. Then it seems more like a scare tactic than reliable information, and you know how that has turned out for establishing other ethics. I usually know the first fish I catch how the water temperatures have effected them. If its fight is short, non-existent or weak, I become suspicious. It is no fun to catch lethargic fish, except maybe steelhead or salmon.
The upper lethal limit for brook, brown and rainbow are only a few degrees apart, I think 75-77 degrees or so. From what I have read, browns and rainbow are more or less equivalent, despite popular statements to the contrary. Of course, different local strains may make one superior to the other. Brookies are consistently reported lower, but by only a degree or so. Again, I imagine local variations occur.
The Upper Lethal Limit reflects the water temperature at which, if sustained for 24/48 hours (can't remember exact, but assume 24), the fish will die. At temperatures below that they certainly experience thermal stress. Their bodies are not designed to withstand heat even though they are cold-blooded. To protect the organs and other tissues, a chemical substance is released in the bloodstream. If sustained, this becomes lethal. I'm not sure if this is the same substance pcray expounds on, but you'll find the concept in the literature.
If you have the luxury, in any sense, to fish for trout only when there is little chance of incidental mortality, then asside from applying the most stringent landing and handling practices, never fish for trout above 70 or if the temperatures overnight do not drop into at least the mid-sixties. Beyond that is a matter of degrees until you hit the lethal limit, which depends upon no other factors, such as general trout health, dissolved oxygen, and fight and handling practices. Seen another way, the ULL can be effectively driven downward by any of these stressors.
