UC Santa Barbara

Freshwater fishes face escalating pressures as a result of habitat alteration from global climate change paired with intensified land use by humans. Habitat fragmentation, disturbances like drought and wildfire, and water pollution all contribute to reductions in the quality and quantity of available freshwater fish habitat. When a fish species inhabits a broad geographic range, however, genetically distinct populations that experience vastly different conditions can exhibit variability in tolerance to stressors such as elevated temperature. Elucidating the distributions of such fishes and the extent of the ability of individual populations to tolerate or adapt to environmental stressors is essential for understanding their vulnerability to extirpation and/or extinction from climate change.

My PhD research makes use of environmental DNA (eDNA) and streamside physiology to assess the distribution and thermal tolerance, respectively, of fishes inhabiting streams in California and Oregon. Using eDNA analysis, observed differences in biodiversity between Southern California river basins were primarily attributed to the presence of exotic species. Using streamside physiology, thermal tolerance and vulnerability to warming differed between populations of an endangered salmonid, steelhead trout (Oncorhynchus mykiss). Populations with historically warmer environmental temperatures had higher thermal tolerance but were often living in temperatures closer to their upper thermal limits compared to those from cooler locations. This information allows managers to focus conservation efforts on areas that support native fish biodiversity and on specific populations of species of concern that are most vulnerable to extirpation.