Population Size And Habitat Association Of Etheostoma Nebra, The Buck Darter, Using Abundance Modeling In The Buck Creek System, Cumberland River Drainage, Kentucky

Etheostoma nebra (Buck Darter) is a recently described fish species confined to the Buck Creek system, Cumberland River drainage, Kentucky. A 2010-2012 survey of Buck Creek by Kentucky Department of Fish and Wildlife Resources personnel observed E. nebra at 2 of 47 historical sites. Within the entire system, individuals were found only in Flat Lick Creek around the confluence of two spring-fed tributaries, Big Spring Branch and Stewart Branch. The objectives of this study were to: (1) determine population size, demographics, and habitat association of E. nebra in Big Spring Branch and Stewart Branch, (2) evaluate habitat conditions both within extant range and historical range, (3) complete fish surveys within the species\u27 historical range, and (4) monitor and compare water quality at extant and historical localities within the system. Totals of 75 and 86 individuals of E. nebra were captured in Big Spring Branch and Stewart Branch, respectively; however, no individuals were observed in Buck Creek or other tributaries. In both extant populations, average total Length of males exceeded that of females (TLmales = 63.5 mm, TLfemales = 54.5 mm). Using N -Mixture models to predict abundance based on measured habitat variables and to account for imperfect detection, the total population in both streams was estimated to consist of approximately 17,000 individuals. Analyses of the two occupied streams yielded higher abundance estimates of E. nebra in Big Spring Branch. Important habitat variables associated with their abundance included a mixture of substrate size classes resulting in habitat complexity. Pebble and cobble showed positive relationships with predictions of increased E. nebra abundance. Comparison of occupied and unoccupied plots within Big Spring Branch and Stewart Branch showed significant differences in most of the habitat variables (i.e. maximum depth, average depth, median substrate type, and presence of canopy). However, when unoccupied plots from historical streams were added and compared to occupied plots, few habitat variables showed significant differences. This indicated that unoccupied plots at historical streams had similar habitat conditions compared to occupied plots of Stewart and Big Spring Branch, and thus, habitat conditions were most likely not contributing to the disappearance of E. nebra at these streams. Average conductivity was higher in occupied streams than historical streams across seasons (Occupied: 342 μS/cm, Unoccupied: 146 μS/cm). Additionally, with more springs present, occupied streams exhibited warmer average winter temperatures and lower average summer temperatures than unoccupied streams (Range of monthly temperatures, Occupied: 11.6- 20.6 ℃, Unoccupied: 9.2- 23.9 ℃). Spawning activity of E. nebra was observed through July, and lower summer water temperatures could be a contributing factor to the species\u27 persistence in these two streams. These results will aid cooperating natural resource agencies in making decisions toward management and conservation of this imperiled species