California Golden Trout: Can Their Warming Streams Handle Other Stressors?

The California golden trout (CGT) Oncorhynchus mykiss aguabonita is at risk from warm stream temperatures and now faces further stress from climate warming. Their native habitat includes stream areas impacted by cattle grazing so some areas have reduced streamside vegetation and widened channels with shallow stream depths that contribute to warmer water temperatures. Climate change will further compromise CGT and their habitat because warmer water temperatures are predicted under most warming scenarios. I have initiated a spatially explicit analysis of stream temperatures and shade throughout CGT habitat. Results from 2008 to 2013 indicate that stream temperatures reached 26^oC in degraded areas.  These high temperatures are reportedly lethal for salmonids but work is needed to determine CGT temperature thresholds. Moreover, CGT streams have extremely low in-stream shade (<10%), high diel range of temperatures (+ 15^oC) and extended periods (55 days) where daily highs exceed 20^oC. In its current condition, CGT habitat does not have the capacity to keep the streams cool and are not resilient to future increases in water temperatures from climate warming. Thus, restoration plans must find ways to cool streams and should carefully consider the future feasibility of manageable stressors that also contribute to stream warming (e.g. cattle grazing).