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

Fifteen darter species are known to occur in the Elk River, Tennessee, including the Boulder Darter (Etheostoma wapiti), a federally endangered species that is currently restricted to 100 km of the mainstem Elk River and two of its tributaries. Since the construction of Tims Ford Dam in 1970, coldwater releases and altered flow regimes have resulted in substantial habitat modification that has reduced the range of Boulder Darters throughout the Elk River. In 2007, the Tennessee Valley Authority implemented an adaptive management process at Tims Ford Dam to determine the optimal combination of spilling, sluicing, and hydroelectric generation that would: (1) promote the persistence of Boulder Darters throughout the mainstem Elk River, (2) allow for continued hydropower generation, and (3) maintain conditions suitable for the existing tailwater trout fishery. Recently implemented operational modifications also are anticipated to improve spawning and rearing conditions for E. wapiti and provide an additional 50 km for potential recolonization. To assess the current status of darter species in the Elk River, a multi-species occupancy models that accounts for incomplete detection was constructed to determine the influence of several environmental factors on the occurrence of 15 darter species in the Elk River. Thirty-nine sites were surveyed using a combination of backpack electrofishing and seining and presence-absence data were used to estimate detection and occupancy probabilities for each of the 15 darter species native to the Elk River. Occupancy modeling indicated that darter species occupancy was strongly and negatively related to the absence of cobble substrates and high levels of silt. The probability of occurrence for large river obligates such as boulder darters was strongly and positively related to distance downstream from Tims Ford Dam. Results from this study provide a baseline for TVA and USFWS biologists to assess future changes in the status and distribution of Boulder Darters following operational changes at Tims Ford Dam that will be driven by a Structured Decision Making model currently being developed.