Potential Influences of Climate Change on the Rio Grande Cutthroat Trout

Future climate predictions for the western United States surmise an increase in air temperature, decreases in mean annual precipitation, and decreases in snow season length and snow depth.  Regionally, these changes are likely to result in increased water temperatures, decreased stream baseflow, changes in hydrological cycles, and increases in extreme events.  Native salmonids will be confronted with changing conditions and stressors throughout their range that may include loss of thermally suitable habitat, increased intermittency of headwater stream reaches, and further population fragmentation.  One native salmonid receiving considerable attention is the Rio Grande cutthroat trout (RGCT, Oncorhynchus clarki virginalis) which occupies the southern-most range of cutthroat trout, with populations in the arid Rio Grande, Pecos, and Canadian drainage systems of New Mexico and southern Colorado.  RGCT distribution has shrunk to 12% of its historical range, and it was recently added to the candidate list under the Endangered Species Act.  The effects of climate change pose a substantial threat to the long term persistence, conservation and recovery of RGCT because of its limited range, fragmented populations, and southerly distribution.  Our objectives here were to (1) evaluate recent climate trends (last 40 years) throughout the historical and current range of RGCT by characterizing changes in air temperature, snow-water equivalent (SWE), and hydrological changes, (2) measure and evaluate the thermal and baseflow suitability of habitats within existing RGCT core conservation populations, and (3) use this information to predict the suitability of existing RGCT habitat under future climate scenarios.  Retrospective analysis of trends in climate data indicate an overall increase in air temperatures, decreases in April 1st SWE, and changing hydrology across the historic range of Rio Grande cutthroat trout.  Preliminary monitoring data from existing RGCT streams largely reveal small headwater streams with water temperatures cooler than thermal thresholds and with very low baseflow rates.