Globally, riverine fishes are affected by degradation of habitat, stream alterations, lost stream connectivity and introduction of non-native species. The plains topminnow Fundulus sciadicus, a small stream-dwelling fish, currently does not have a federal conservation status in the USA; however, anecdotal reports have suggested its decline for the last 20 yr. Our goals were to evaluate the validity of its reported decline and to determine the current range-wide status of this species. We identified 927 historical sites (1889−1999) of occurrence and compiled recent records or re-visited 667 sites (2000−2010). We found plains topminnow at 189 (28.0%) of these sites. Although Nebraska represented the center of distribution and included 66.7% of all historical sites, plains topminnow were only found at 34.4% of historical sites, with the largest declines observed in the Platte and Republican River drainages. Current sampling efforts in Colorado, Missouri, Oklahoma, South Dakota and Wyoming found similar declines. In Iowa and Kansas, plains topminnow was not found, whereas potential increases in distribution were observed in a single drainage in Minnesota and Wyoming. In addition to our sampling efforts, we repeatedly sampled 40 sites within Nebraska to determine detection probability. Detection probabilities for plains topminnow were consistent at 0.76 ± 0.05 (mean ± SE) among sites that were sampled with a single visit. Further research is needed on the species and the potential threats to its occupation of sites, as no singular cause for decline seems plausible. Observed threats include degradation and loss of habitat and shifts in species assemblages towards generalist non-native species
