Ictalurid populations in relation to the presence of a main-stem reservoirin a midwestern warmwater stream with emphasis on the threatened Neosho madtom

Ictalurid populations, including those of the Neosho madtom Noturus placidu s, have been monitored in the Neosho River basin since the U.S. Fish and Wi ldlife Sel vice listed the Neosho madtom as threatened in 1991. The Neosho madtom presently occurs only in the Neosho River basin, whose hydrologic re gime, physical habitat, and water quality have been altered by the construc tion and operation of reservoirs. Our objective was to assess changes in ic talurid densities, habitat, water quality, and hydrology in relation to the presence of a main-stern reservoir in the Neosho River basin. Study sites were characterized using habitat quality as measured by substrate size, wat er quality as measured by standard physicochemical measures, and indicators of hydrologic alteration (IHA) as calculated from stream gauge information from the U.S. Geological Survey. Site estimates of ictalurid densities wer e collected by the U.S. Fish and Wildlife Service annually from 1991 to 199 8, with the exception of 1993. Water quality and habitat measurements docum ented reduced turbidity and altered substrate composition in the Neosho Riv er basin below John Redmond Dam. The effects of the dam on flow were indica ted by changes in the short- and long-term minimum and maximum flows. Posit ive correlations between observed Neosho madtom densities and increases in minimum flow suggest that increased minimum flows could be used to enhance Neosho madtom populations. Positive correlations between Neosho madtom dens ities and increased flows in the winter and spring months as well as the da te of the l-d annual minimum flow indicate the potential importance of the timing of increased flows to Neosho madtoms. Because of the positive relati onships that we found between the densities of Neosho madtoms and those of channel catfish Ictalurus punctatus, stonecats Noturus flavus, and other ca tfishes, alterations in flow that benefit Neosho madtom populations will pr obably benefit other members of the benthic fish community of the Neosho Ri ver.