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Pelagic broadcast spawning cyprinids have declined throughout the North American Great Plains because of adverse habitat changes caused by river fragmentation and altered flow regimes. Despite losses elsewhere, a 218-river kilometer section of the South Canadian River maintains three of these imperiled species: Arkansas River Shiner, Peppered Chub and Plains Minnow. The objective of this study was to determine if species occupying the same river stretch and hence a shared environment, exhibit the same trajectory of genetic change and relative abundance over contemporary timescales. Genetic evaluation of these species is an essential precursor to conservation efforts that may include translocations and establishment of captive populations. Across the time series each species experienced substantial changes in abundance with Arkansas River Shiner consistently having the highest overall abundance. The abundance of Peppered Chub was uniformly lower but increased between 2012 and 2019, while Plains Minnow abundance declined from 2014 to 2019. Despite dramatic fluctuations in population size over the time-series, data from microsatellites and mitochondrial DNA demonstrated that the South Canadian River harbors genetically diverse populations of each of these species. With the Southwestern United States entering another period of exceptional drought, immediate intervention is necessary to ensure persistence of range restricted Arkansas River Shiner and Peppered Chub. Results of this study show that remnant populations provide a crucial resource for recovery efforts for these species. [ABSTRACT FROM AUTHOR]

The Rio Grande drainage of the southwestern United States and Mexico has undergone intense anthropogenic alteration by water diversions, extraction and associated habitat changes. These alterations have disproportionately impacted the pelagic broadcast spawning guild of minnows (pelagophils). Several Rio Grande endemic pelagophils, including the co-occurring Rio Grande Shiner (Notropis jemezanus) and Speckled Chub (Macrhybopsis aestivalis), have experienced dramatic recent range-wide declines yet have slipped under the radar of conservation efforts. The status of N. jemezanus and M. aestivalis in the Rio Grande and Pecos River was evaluated and standing genetic variation was characterized. Genetic evidence indicates that populations of both species found in the Rio Grande and Pecos River are genetically distinct. Additionally, 159 outlier loci were identified in M. aestivalis suggesting possible local adaptation in the Rio Grande and Pecos River populations. Though range-wide genetic data are limited, N. jemezanus populations in both rivers harbor considerable genetic diversity. Mitochondrial data from both taxa are consistent with a history of secondary contact between formerly isolated populations with deeply divergent haplotypes found within the Rio Grande and Pecos River populations of N. jemezanus and within the Rio Grande population of M. aestivalis. Extensive survey efforts in the lower Rio Grande and its tributaries in Texas document significant range contraction and near extirpation of N. jemezanus from this part of the basin; highlighting the need for immediate action to protect the species. [ABSTRACT FROM AUTHOR]

Biodiversity in stream networks is threatened globally by interactions between habitat fragmentation and altered hydrologic regimes. In the Great Plains of North America, stream networks are fragmented by >19 000 anthropogenic barriers, and flow regimes are altered by surface water retention and groundwater extraction. We documented the distribution of anthropogenic barriers and dry stream segments in five basins covering the central Great Plains to assess effects of broad-scale environmental change on stream fish community structure and distribution of reproductive guilds. We used an information-theoretic approach to rank competing models in which fragmentation, discharge magnitude, and percentage of time streams had zero flow (a measure of desiccation) were included to predict effects of environmental alterations on the distribution of fishes belonging to different reproductive guilds. Fragmentation caused by anthropogenic barriers was most common in the eastern Great Plains, but stream desiccation became more common to the west, where rivers are underlain by the depleted (i.e., extraction > recharge) High Plains Aquifer. Longitudinal gradients in fragmentation and desiccation contributed to spatial shifts in community structure from taxonomically and functionally diverse communities dominated by pelagic reproductive guilds where fragmentation and desiccation were least, to homogenized communities dominated by benthic guilds where fragmentation and desiccation were common. Modeling results revealed these shifts were primarily associated with decline of pelagic reproductive guilds, notably small-bodied pelagophilic and lithopelagophilic fishes that declined in association with decreased fragment length and increased number of days with zero flow. Graph theory combined with a barrier prioritization approach revealed specific fragments that could be reconnected to allow fishes within these guilds to colonize currently unoccupied fragments with the mitigation or removal of small dams (<10 m height). These findings are useful for natural resource managers charged with halting or reversing the prevailing pattern of declining fish diversity in the Great Plains. Our study represents one of the most comprehensive assessments of fish diversity responses to broad-scale environmental change in the Great Plains and provides a conservation strategy for addressing the simultaneous contributions of fragmentation and flow alteration to the global freshwater biodiversity crisis. [ABSTRACT FROM AUTHOR]