Zeigler, M.P., A.S. Todd, and C.A. Caldwell. 2012. Evidence of recent climate change within the historic range of Rio Grande cutthroat trout: Implications for management and future persistence. Transactions of the American Fisheries Society 141:1045-1059
Overwhelming 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, hydrology, precipitation) can serve as a valuable tool for managers working to protect vulnerable species by increasing our understanding of localized conditions and trends. The Rio Grande cutthroat trout Oncorhynchus clarki virginalis has suffered a severe decline in its historic distribution, with the majority of current populations persisting in isolated headwater streams. To evaluate recent climate change within the subspecies’ historic range, trends in average air temperatures, biologically-important hydrological variables (timing of snowmelt, seasonal flows), and April 1st snow water equivalent over the last 45 years (1963 - 2007) were examined. While rates of change in all three metrics were variable across sites, range-wide patterns were evident. Across the subspecies historic range average annual air temperatures increased (range-wide increase of 0.29°C per decade) and the timing of snowmelt shifted to earlier in the year (range-wide change of 10.6 days earlier). Flows increased during biologically-important periods, such as winter (January 1st - March 31st), pre-spawning (April 1st - May 14th), and spawning periods (May 15th - June 15th), and decreased in the summer (June 16th - September 15th). Evidence of decreasing April 1st snow water equivalent (range-wide decrease of 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 insure their long term persistence and protection from the negative effects of a climate change.