Seasonal Changes in Instream Habitat Selection by Niangua Darters

Understanding temporal and spatial habitat relationships is important to the recovery of the federally threatened Niangua darter Etheostoma nianguae, and other imperiled freshwater fishes, in a changing landscape.  We evaluated microhabitat selection of adult Niangua darters at three Missouri Ozark stream reaches (mean= 503 m).  Each reach was snorkeled (mean= 2.9 m/min) to identify Niangua darter locations where we measured nine instream habitat variables believed to be important to Niangua darters.  These same variables were measured at three random locations within 100 m of each used location to represent available habitat.  We used an information theoretic framework to develop models representing hypotheses related to Niangua darter microhabitat selection.  We developed six models containing depth, velocity, substrate, embeddedness, distance to nearest cover, and cover size which we fit using discrete choice analysis.  The model containing depth and 60% velocity had the lowest AIC_c value with all other models having a ΔAIC_c >4.  During cooler months, adult Niangua darters selected deeper depths and slower velocities compared to warmer months.  Selection for shallower/intermediate depths and faster velocities during warmer months may optimize feeding opportunities whereas deeper depths and slower velocities may maximize energy conservation during cooler months.