Paradigm versus paradox on the prairie: testing competing stream fish movement frameworks using an imperiled Great Plains minnow

Background: Movement information can improve conservation of imperiled species, yet movement is not quantified for many organisms in need of conservation. Prairie chub (Macrhybopsis australis) is a regionally endemic freshwater fish with unquantified movement ecology and currently considered for listing under the Endangered Species Act. The purpose of this study was to test competing ecological theories for prairie chub movement, including the colonization cycle hypothesis (CCH) that posits adults must make upstream movements to compensate for downstream drift at early life stages, and the restricted movement paradigm (RMP) that describes populations as heterogeneous mixes of mostly stationary and few mobile fish. Methods: We tagged prairie chub with visible implant elastomer during the summer (May–August) of 2019 and 2020 to estimate net distance moved (m) and movement rate (m/d). We tested the hypotheses that observed prairie chub movement would be greater than expected under the RMP and that prairie chub movement would be biased in an upstream direction as predicted by the CCH. Results: We tagged 5771 prairie chub and recaptured 213 individuals across 2019 and 2020. The stationary and mobile components of the prairie chub population moved an order of magnitude further and faster than expected under the RMP during both years. However, we found only limited evidence of upstream bias in adult prairie chub movement as would be expected under the CCH. Conclusions: Our findings are partly inconsistent with the RMP and the CCH, and instead closely follow the drift paradox (DP), in which upstream populations persist despite presumed downstream drift during early life stages and in the apparent absence of upstream bias in recolonization. Previous mathematical solutions to the DP suggest organisms that experience drift maintain upstream populations through either minimization of drift periods such that small amounts of upstream movement are needed to counter the effects of advection or increasing dispersal regardless of directionality. We conclude that the resolution to the DP for prairie chub is an increase in total dispersal and our results provide insight into the spatial scales at which prairie chub conservation and management may need to operate to maintain broad-scale habitat connectivity

Groundwater declines are linked to changes in Great Plains stream fish assemblages

Groundwater pumping for agriculture is a major driver causing declines of global freshwater ecosystems, yet the ecological consequences for stream fish assemblages are rarely quantified. We combined retrospective (1950–2010) and prospective (2011–2060) modeling approaches within a multiscale framework to predict change in Great Plains stream fish assemblages associated with groundwater pumping from the United States High Plains Aquifer. We modeled the relationship between the length of stream receiving water from the High Plains Aquifer and the occurrence of fishes characteristic of small and large streams in the western Great Plains at a regional scale and for six subwatersheds nested within the region. Water development at the regional scale was associated with construction of 154 barriers that fragment stream habitats, increased depth to groundwater and loss of 558 km of stream, and transformation of fish assemblage structure from dominance by large-stream to small-stream fishes. Scaling down to subwatersheds revealed consistent transformations in fish assemblage structure among western subwatersheds with increasing depths to groundwater. Although transformations occurred in the absence of barriers, barriers along mainstem rivers isolate depauperate western fish assemblages from relatively intact eastern fish assemblages. Projections to 2060 indicate loss of an additional 286 km of stream across the region, as well as continued replacement of largestream fishes by small-stream fishes where groundwater pumping has increased depth to groundwater. Our work illustrates the shrinking of streams and homogenization of Great Plains stream fish assemblages related to groundwater pumping, and we predict similar transformations worldwide where local and regional aquifer depletions occur

Appendix C. A table summarizing data for sampling sites in each dendritic ecological network, listing connectivity status, species richness, and stream widths.

A table summarizing data for sampling sites in each dendritic ecological network, listing connectivity status, species richness, and stream widths

Appendix B. A figure showing 12 Great Plains, USA, dendritic ecological networks with locations of perched road crossings and fish collections as well as Dendritic Connectivity Index values for each network.

A figure showing 12 Great Plains, USA, dendritic ecological networks with locations of perched road crossings and fish collections as well as Dendritic Connectivity Index values for each network

Appendix A. A figure illustrating the relative frequency of stream orders and distribution of road crossings within the USGS eight-digit hydrologic unit codes for four streams in Kansas, USA.

A figure illustrating the relative frequency of stream orders and distribution of road crossings within the USGS eight-digit hydrologic unit codes for four streams in Kansas, USA

First record of the Conchos Shiner Cyprinella panarcys (Hubbs & Miller, 1978) from the mainstem of the Rio Grande along the USA–Mexico border

Cyprinella panarcys is considered to be endemic to the upper Río Conchos drainage of Mexico. A single individual of C. panarcys was collected from the Rio Grande along the USA–Mexico international border (Presidio Co., Texas) in April 2018. This is the first record of C. panarcys from outside of the Río Conchos and the first record from the USA. A brief description of the external morphology of the individual collected is provided along with an updated distribution map for the species