Assessing fish assemblage structure in St. Charles Creek, Idaho

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Kade A. Linder, Megan R. Heller, Kerri T. Vierling and Anne Yen, Department of Fish and Wildlife Sciences, University of Idaho, Moscow, ID, Kade A. Linder, DDCSP Collaborative, University of Idaho, Kade A. Linder, ESA Seeds Program, Michael C. Quist and Courtney J. Conway, U.S. Geological Survey, Idaho Cooperative Fish and Wildlife Research Unit, Moscow, ID

Background/Question/Methods
Fish populations can be indicators of a functioning stream system. Total number of individuals and species diversity are both important parameters that can depict the status of fish populations in a stream. St. Charles Creek is a tributary that flows into Bear Lake, a natural lake bisected by the Idaho-Utah border. St. Charles Creek is one of three tributaries that are important for several fishes, including the adfluvial population of native Bonneville Cutthroat Trout (Oncorhynchus clarkii utah). In this study, we measured fish species richness and fish abundance in varying sample reaches in St. Charles Creek. We tested the hypothesis that both fish species richness and fish abundance would decrease in St. Charles Creek as distance from Bear Lake increased. Gaining a better understanding of how fish populations change spatially throughout a watershed is important for management of fish species in spawning tributaries such as St. Charles Creek. We used a backpack electrofishing unit to sample fish, and sampling occurred during July and August in both 2019 and 2020. Electrofishing surveys were conducted in 33 sample reaches with varying distances from Bear Lake (2190 meters to 15520 meters). Data were analyzed using linear regression to analyze the relationship between our variables.
Results/Conclusions
Our results suggest that distance from Bear Lake had a relationship with both fish species richness and fish abundance. Fish species richness was negatively correlated with distance from Bear Lake (x= -0.0002, p= 0.009, r2= 0.2), as was fish abundance (x= -0.006, p= 0.06, r2= 0.1). These data support our hypotheses that fish species richness and abundance in St. Charles Creek declined with increased distance from Bear Lake. Although our results were promising, there are likely other parameters influencing fish populations than distance. Measuring other biotic and abiotic parameters would possibly give more insights regarding the factors influencing fish populations the most. By understanding where fish populations are thriving or struggling, managers and ecologists can develop specific frameworks for management at specific locations. More research would better identify which parameters in addition to distance from Bear Lake have significant effects on fish populations in streams.