Effects of catch-and-release angling on salmonids at elevated water temperatures. North American Journal of Fisheries Management 30:898–907

Abstract.—Few studies have assessed catch-and-release mortality of salmonids at water temperatures of 238C or above, despite predictions of warming stream temperatures due to climate change. The primary objective of this study was to measure the catch-and-release mortality of rainbow trout Oncorhynchus mykiss, brown trout Salmo trutta, and mountain whitefish Prosopium williamsoni in three water temperature treatments, namely, when daily maximum water temperatures were cool (,208C), warm (20–22.98C), and hot (238C). A secondary objective was to assess the catch-and-release mortality of salmonids angled in morning and evening within the water temperature treatments. These objectives were related to Montana Fish, Wildlife and Parks ’ drought fishing closure policy. Angling (fly-fishing only) occurred in the Gallatin and Smith rivers. All angled fish were confined to in-stream holding cages and monitored for mortality for 72 h. Mortality of rainbow trout peaked at 16 % in the Gallatin River and 9 % in the Smith River during the hot treatment. Mortality of brown trout was less than 5 % in all water temperature treatments in both rivers. Mountain whitefish mortality peaked at 28 % in the hot treatment in the Smith River. No mortality for any species occurred in either river when daily maximum water temperatures were less than 208C. Mortality of rainbow trout peaked at 16 % in the evening hot treatment in the Smith River. Mortality rates of brown trout and mountain whitefish were not related to time of day. The catch-and-release mortality rates presented her