Fish Assemblages, Habitat, and Thermal Effects: Patterns of Mountain Sucker Distribution in the Black Hills

The conservation of native fishes requires knowledge of their population and community dynamics.  Although mountain sucker Catostomus platyrhynchus is stable across its range, regional trends indicate localized declines near the periphery, including the Black Hills of South Dakota.  Information on mountain sucker autecology and community dynamics is limited.  The objectives of this study were to 1) document historic changes in mountain sucker distribution, 2) evaluate the influence of physical and biological variables on distributional patterns in the Black Hills, and 3) assess their thermal tolerance.  Analyses of the past 50 years of stream survey data indicated declining mountain sucker catch per unit effort at three nested spatial scales (site, stream, and watershed), and mountain sucker appear to have been extirpated from several locations.  Models of mountain sucker presence and density as a function of landscape, habitat, and community factors indicated that suitable conservation areas would be streams that have low densities of introduced salmonids.  Mountain sucker have an intermediate thermal tolerance that is higher than co-occurring salmonids, but lower than that of three co-occurring cypriniforms.  With a balanced approach, stream fisheries management in the Black Hills for game and non-game objectives is possible.