Using fish hard-part microchemistry and genetics to quantify population impacts of low-use lock-and-dam structures on the Alabama River

Abstract

Objective: We used two approaches, fish hard-part microchemistry and genetics, to quantify effects of low-use lock-and-dam structures on riverine fish movement. Each approach varied in temporal scope, with microchemistry addressing effects within a lifetime and genetics addressing effects across generations. Methods: Water samples and individuals of two species (Paddlefish Polyodon spathula and Smallmouth Buffalo Ictiobus bubalus) were collected from four river sections that were separated by three low-use lock-and-dam structures on the Alabama River. Quarterly water samples were collected from 15 sites during 2017–2018, and concentrations of Sr, Ba, Mn, Mg, and Ca were quantified using mass spectrometry. Result: Water elemental signatures were spatially variable but temporally consistent. The Sr:Ca ratios in fish hard parts differed significantly among river sections for both species. Additionally, discriminant function analyses classified fish to their river capture section with accuracy between 55% and 74% for Paddlefish (errors nearly always assigned individuals to adjacent river sections) and 37–47% for Smallmouth Buffalo. Population genetic analyses included fish from each river section, as well as from Alabama River tributaries and a neighboring watershed. Genotyping-by-sequence techniques identified 1,889 and 3,737 single nucleotide polymorphisms postfiltering in Paddlefish and Smallmouth Buffalo, respectively, which we used to estimate population diversity indices and conduct differentiation analyses. Analysis of molecular variance, discriminant analysis of principal components, Bayesian clustering, and pairwise comparisons of FST values indicated no strong evidence for genetic divergence in either species among river sections. Conclusion: Within-lifespan results based on hard-part microchemistry suggested a potential for population isolation. However, longer-term genetic effects were not apparent, possibly because the life span of these large and relatively long-lived species means that few generations have passed since dam construction, and there could be sufficient mixing or population connectivity to prevent genetic divergence across river sections, particularly at the most downstream structure.