Distribution, Ecological Niche, Movement, and Home Range of the Sickle Darter (Percina williamsi) in the Upper Tennessee River Basin.

The Sickle Darter (Percina williamsi) is a rare and imperiled species that is endemic to the upper Tennessee River basin. Over the last ~50 years it has declined across much of its range, and as a result it has been petitioned for federal listing under the Endangered species Act. This species has been relatively understudied, and important questions remain to be addressed: 1.) What is the current distribution of the Sickle darter and how has it varied spatiotemporally? 2.) What is the ecological niche of the Sickle Darter? and 3.) What is the movement capability of the Sickle Darter and what is its home range? To address these questions, a total of 154 Sickle Darters were observed at 15 sites throughout the upper Tennessee River Basin. Sickle Darters were observed in the Little River, Emory River, and Middle Fork Holston River sub-basins. A total of 133 unique historical occurrences were used for the spatiotemporal analyses. Sickle Darters have declined in 8 out of 10 historically occupied sub-basins. Our best model for the whole distribution suggests that habitat fragmentation (due to damming) and temperature (likely due to climate change) have had adverse effects on Sickle Darter populations across this species’ distribution. The accuracy of the whole basin model was evaluated with 70% of the testing area under the curve metric, which was high (0.85), and correctly predicted the presences used to test the model. The most important variable contributing to this model was stream order (48.2%). The ecological niche models varied from the whole basin to the sub-basin scale in terms of their accuracy and variable importance, but they were similar in accurately predicting the area of suitable habitat for the Sickle Darter. Best sub-sets regressions modeling suggest that Sickle Darter movement is significantly related to discharge (m³/sec) at multiple temporal levels. Home range for each individual varied in size. Median home range size was 157.5 m² and median degree of overlap for estimated home range was 23.3 %. The data outlined in this study provide information to inform conservations for this species to ensure that it is preserved for future generations.

Revised draft