Development of Field-based Models of Suitable Thermal Regimes for Interior Columbia Basin Salmonids

primary objectives of this research included 1) develop models relating occurrence of two threatened inland salmonid fishes to stream temperature regimes; 2) develop a comprehensive protocol for sampling stream temperatures using digital data loggers. The two species of interest were bull trout (Salvelinus confluentus) and Lahontan cutthroat trout (Oncorhynchus clarki henshawi). The distribution of each species in relation to stream temperature regimes was modeled using a variety of approaches. The results of this work were related to thermal responses of each species in the laboratory. Together, these lines of evidence form a more rigorous basis for evaluating the biological requirements of each species, and for determining appropriate temperature criteria for water quality management. Given that water temperature is a critical concern in streams in the western United States, it is also important to provide guidance for monitoring stream temperatures. The recent widespread availability and use of digital temperature data loggers has resulted in a proliferation of data on stream temperatures. In many cases, our ability to carefully assure and document the quality and utility of the data has not tracked our capacity to collect temperature data. We anticipate three published products from this research. Two papers will focus on the relationships between the distribution of bull trout and Lahontan cutthroat trout in relation to different measures of maximum annual temperatures. A third paper will be a protocol for measuring and sampling stream temperatures using digital data loggers. The first two papers will be submitted to peer-reviewed journals, and the third will be published electronically as a Forest Service/Environmental Protection Agency report. Each section of this final report corresponds to these papers. These should be considered as early drafts of papers to be submitted for publication in the near future. Introduction Temperature plays a key role in determining the distribution of many aquatic organisms (Magnuson et al. 1979). Temperature has been a particular focus for salmonid fishes, due to their requirement for relatively cold water (Elliott 1981). Past research has linked salmonid distributions to several indicators of temperature, including elevation gradients associated with climate modeled (Meisner 1990) groundwater temperatures, and measured surface water temperatures (Eaton et al. 1995; Torgerson et al. 1999). While the latter most directly affect fish, detailed information on surface water temperatures is often limited or expensive to obtain, so alternative indicators (e.g., air temperature) may be more useful (e.g., Stoneman and Jones 1996). The utility of a …