Several final products have been submitted to U.S. Fish and Wildlife Service in addition to this final report: the Master’s thesis (Mueller 2013) “Effects of temperature, salinity, and suspended solids on the early life history stages of Arkansas River shiner”; and the publication “Sampling efficiency of the Moore egg collector” (available at DOI:10.1080/02755947.2012.741557) by Worthington et al. (2013). These products present completed results for portions of the two major objectives and will not be repeated here. Results from the remaining portions are presented in this report: 1) determine the landscape-level effects on the probability of Arkansas River shiner presence, and 2) assess egg transport related to channel geomorphology.
Objective 1: Conservation efforts for threatened or endangered species are challenging because the multi-scale factors that relate to their decline or inhibit their recovery are often unknown. To further exacerbate matters, the perceptions associated with the mechanisms of species decline are often viewed myopically rather than across the entire species range. We used over 80 years of fish presence data collected from the Great Plains and associated ecoregions of the USA, to investigate the relative influence of changing environmental factors on the historic and current truncated distributions of Arkansas River shiner Notropis girardi. Arkansas River shiner represents a threatened reproductive ecotype considered especially well-adapted to the harsh environmental extremes of the Great Plains. Historic (n = 163 records) and current (n = 47 records) species distribution models were constructed using a vector-based approach in MaxEnt by splitting the available data at a time when Arkansas River shiner dramatically declined. Discharge and stream order were significant predictors in both models, however the shape of the relationship between the predictors and species presence varied between time periods. Drift distance (river fragment length available for ichthyoplankton downstream drift before meeting a barrier) was a more important predictor in the current model and indicated river segments 375-780 km had the highest probability of species presence. Performance for the historic and current models was appropriate; however forecasting and backcasting to alternative time periods suggested less predictive accuracy than when using standard validation techniques. Our results identify fragments that could be considered refuges for endemic plains fish species and we highlight significant environmental factors that are reasonable targets to address recovery. Our results also emphasize the need for development of ecologically-significant metrics.
Objective 2: Habitat fragmentation and flow regulation are significant factors related to the decline and extinction of freshwater biota. Pelagic broadcast-spawning cyprinids represent a threatened guild of fishes that require moving water and some length of stream to complete their life cycle. However, it is unknown how discharge and habitat features interact at multiple spatial scales to alter the transport of semi-buoyant fish eggs. Our objective was to assess the relationship between downstream drift of semi-buoyant egg surrogates (beads) and discharge and habitat complexity. We released a known quantity of beads at seven locations on the North Canadian and Canadian rivers. Habitat complexity was assessed by calculating width: depth ratios at each site, and several habitat metrics determined from aerial photographs analysis. We quantified the capture of beads in two or three egg collectors at each site. Median time of egg capture was significantly and negatively related to site discharge. Extent of the sampling period at each site was significantly and negatively related to site discharge and habitat patch dispersion. Our results highlight the role of discharge in driving transport times but also the dispersion of habitat patches across the landscape. Higher dispersion of habitat patches related to increased retention of beads within the river. The management implications are important given the high demands for water and the importance of drift for many threatened Great Plains species. These results could be used to target restoration activities or prioritize water use to create and maintain habitat complexity within large, fragmented river systems.
