Evidence of Recent Climate Change within the Historic Range of Rio Grande Cutthroat Trout: Implications for Management and Future Persistence

Evidence of anthropogenically influenced climate change has motivated natural resource managers to incorporate adaptive measures to minimize risks to sensitive and threatened species. Detecting trends in climate variables (i.e., air temperature and hydrology) can serve as a valuable management tool for protecting vulnerable species by increasing our understanding of localized conditions and trends. The Rio Grande cutthroat trout Oncorhynchus clarkii virginalis has suffered a severe decline in its historical distribution, with the majority of current populations persisting in isolated headwater streams. To evaluate recent climate change within the subspecies' historical range, we examined trends in average air temperatures, biologically important hydrological variables (timing of snowmelt and seasonal flows), and the April 1 snow water equivalent over the last 45 years (1963-2007). While rates of change in all three metrics were variable across sites, rangewide patterns were evident. Across the subspecies' historical range, average annual air temperatures increased (0.29 degrees C per decade) and the timing of snowmelt shifted 10.6 d earlier in the year (2.3 d/decade). Flows increased during biologically important periods, including winter (January 1-March 31; 6.6% increase per decade), prespawning (April 1-May 14; 6.9% increase per decade), and spawning (May 15-June 15; 4.2% increase per decade) and decreased in summer (June 16-September 15; 1.9% decrease per decade). Evidence of decreasing April 1 snow water equivalent (5.3% per decade) was also observed. While the impacts of these changes at the population level are equivocal, it is likely that negative effects would influence the subspecies by altering its distribution, decreasing available habitat, and altering the timing of important life history components. Continued monitoring and proactive management will be required to increase the resiliency of remaining populations to ensure long-term persistence and protection in a changing climate.