Cooperative Fish and Wildlife Research Units Program: Tennessee
Education, Research and Technical Assistance for Managing Our Natural Resources

Potoka, K.M., C.P. Shea, and P.W. Bettoli. Multi-species occupancy modeling as a tool for evaluating the status and distribution of darters in the Elk River, Tennessee. Transactions of the American Fisheries Society 145:1100-1121.


Sixteen darter species, including the federally endangered Boulder Darter Etheostoma wapiti, are known to occur in the Elk River, a large, flow-regulated Tennessee River tributary in Tennessee and Alabama. Since the construction of Tims Ford Dam (TFD) in 1970, habitat modification caused by cold, hypolimnetic water releases and peak-demand hydropower generation have contributed to population declines and range reductions for numerous aquatic species in the mainstem Elk River. We developed multi-species occupancy models to determine the influence of site-, habitat-, and species-level characteristics on darter occurrence using presence-absence data for 15 species collected from 39 study reaches. Modeling results indicated that the large river obligate species, such as Boulder Darters, were 7.53 times more likely to occur for every 37 km increase in downstream from TFD. In contrast, small stream and cosmopolitan species were 2.04 and 1.82 times less likely, respectively, to occupy stream reaches for every 37 km downstream from TFD. The probability of occurrence for darter species also was strongly and negatively related to the absence of cobble and boulder substrates and the presence of high silt levels, particularly for species that require boulder substrates during spawning. Although total darter species richness was similar across all 39 sample sites, the composition of darter assemblages varied substantially among locations, presumably owing, in part, to species-specific habitat affinities and hydrothermal conditions. Results from this study provide a baseline for managers to assess future changes in the status and distribution of darter species following recent operational changes at TFD.