Stream temperature rise and future stocked-trout management in North Carolina

Objective: Climate warming disproportionately threatens coldwater fishes and presents an immediate challenge for fisheries managers near the southern extent of coldwater sport fish distribution. In North Carolina, some recreational angling opportunities targeting Brook Trout Salvelinus fontinalis, Brown Trout Salmo trutta, and Rainbow Trout Oncorhynchus mykiss are sustained mainly by fall and spring stockings in waters where summer temperatures are marginal for trout. The future of these seasonal fisheries is uncertain, and managers may need to consider management changes to ensure the long-term viability of stocking programs. Methods: We used a Bayesian hierarchical model to analyze a 33-year stream temperature data set collected at 183 reaches during individual stocking events to characterize warming trends and inform management decisions. Results: Warming trends varied among stream reaches, with a mean annual warming rate of 0.05°C. We forecasted future thermal exceedance probabilities based on the observed trends; mean July temperatures would more likely (>50% chance) exceed a thermal threshold (21.1°C) and become too warm for trout survival at many reaches by 2050. Conclusions: Spatially varying warming trends emphasize the importance of reach-specific management to maintain or alter current practices due to warming. Overall, fisheries managers will need such thermal resolution to minimize adverse thermal effects on waters supporting these popular, recreational fisheries.