California Golden Trout and Climate Change: Will Their Stream Habitat be Resilient to Increased Water Temperatures?

The California golden trout (CGT), Oncorhynchus mykiss aguabonita, is one of the few native high-elevation fishes in the Sierra Nevada. They are already in trouble because of exotic trout, genetic introgression, and degraded habitat, and now face further stress from climate warming. Their native habitat on the Kern Plateau meadows, primarily within the Golden Trout Wilderness (GTW), currently includes stream areas impacted by cattle grazing. As a result, some areas have reduced streamside vegetation (willows or sedge) and widened channels with shallow stream depths that often lead to warmer water temperatures. Climate change will further compromise CGT and their habitat in stream areas still being grazed, because the warmer water temperatures predicted under most warming scenarios could increase to lethal levels. One important management response to climate warming will be to ensure that habitats are more resilient to predicted changes in water temperature, flow, and snow pack. I have initiated a study to determine the climate change resiliency of golden trout habitat by conducting a spatially explicit analysis of stream temperatures in restored and degraded sections of meadows in the GTW.  Preliminary data from 2008 to 2010 indicate that stream temperatures often reached 25^oC in degraded areas.  These high temperatures are reportedly lethal for salmonids, but may affect CGT in more subtle ways such as growth, condition, or long-term survival. Moreover, CGT experienced an extremely high diel range of temperatures (+ 15^oC) which will further stress trout. In the Sierra Nevada Mountains (California, USA), there is great opportunity to increase resiliency of high elevation aquatic habitats because most of it is within federally designated Wilderness set aside by U.S. Congress to “to preserve its natural conditions and which generally appears to have been affected primarily by forces of nature” (Kloepfer et al. 1994).  Indeed, most of the CGT habitat is within the Golden Trout Wilderness; hence, there is the opportunity to reduce or eliminate activities that reduce the resiliency to increased climate warming. While Wilderness status typically prohibits logging, roads, and mechanized equipment, it does allow cattle grazing, that often impacts stream habitat and increases water temperatures.  To provide more resiliency of important habitat for aquatic species, Wilderness areas could be used as refuges, i.e., the freshwater version of marine preserves. In these preserves, managers could eliminate or minimize activities that are currently allowed, such as cattle grazing, but are lowering the resiliency of freshwater habitats to increased warming.