mortality rate on catch-and -release fishing

Your question is very broad and there are well over 100 papers out there on trout to draw on so generalizing is difficult.    Under most conditions,  Catch-and-release mortality or “hooking mortality” of trout is thought to be relatively low in most instances.   There are a number of summary papers out there but one of the most frequently cited suggests hooking mortality rates are around 4-6 % for flies and lures , respectively, to  somewhere around 25% for bait-caught resident trout.    However, some of the better studies that have not relied on caged trout have resulted in considerably lower loss rates than these averages.   For example on Yellowstone cutthroat in Yellowstone National Park, an “un-caged” estimate of hooking mortality was about 0.3% and in the case of wild, uncaged rainbow trout caught with bait and released, the estimate was 16%.   The estimate for bait fishing  in a steelhead or chinook stream are considered much lower (e.g.  5% or less for Steelhead).