Risk of morbidity and mortality to native trout on the Fort Hall Indian Reservation, Idaho, due to increased stream temperatures

Abstract

Climate change is now happening faster than ever. The Fort Hall Indian Reservation (FHIR), is located in Bingham, Power, Bannock, and Caribou Counties, Idaho. To estimate the quantitative risk of morbidity and mortality posed to Yellowstone Cutthroat Trout Oncorhynchus clarki bouvieri on the FHIR, stream temperatures, or at the very least, a robust estimate of stream temperatures, was needed. The first objective was to examine what stream temperature data were available. The second objective was to obtain elevation values for stream temperature monitoring sites within the FHIR. This helped in the third objective, which was to develop a regression model to predict stream temperatures. The fourth objective was to document thermal preferences of YCT. Cross-referencing thermal thresholds of YCT and stream temperatures allowed for the fifth and sixth objective, which was to create a deterministic and probabilistic risk assessment. The seventh objective was to map out the risk assessment and graphically display risk associated with each major stream reach within the FHIR. The results of this study indicate that a substantial amount of suitable YCT habitat within the FHIR will likely be lost due to increased stream temperatures, a direct result of global climate change. At this local scale the bulk of the habitat loss can be expected in the lower elevation areas of the FHIR. Mid to high elevation areas will also be negatively affected but not as much as the lower elevation areas. This effort led to the understanding that stream temperatures for the current time frame have been increasing as a result of climate change. With the projected increases in future July stream temperatures the optimal habitat for YCT will be significantly diminished as well. Therefore, this study may serve as a call to action to all interested parties within the FHIR, State of Idaho, and the Greater Yellowstone Ecosystem. With the gleaned information and understanding of how stream temperatures will put YCT at higher risk of temperature related morbidity and mortality, it is up to the risk managers of the greater FHIR and the FHIR to take whatever action they deem necessary in their unique environmental management responsibilities.