Impacts of sediment deposition on stream fishes in the Dan and Roanoke River basins

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fine sediment , stream fish , environmental science
Hirschler, Mallory
Excess fine sediment is a leading cause of impairment to river biota worldwide and greater understanding of how instream fine sediment influences fish occurrence is needed. Understanding the relationship between species traits and their habitat has been recognized as a valuable tool to help predict lotic species’ distribution. Traits that influence the presence and absence of a species will change along environmental gradients, making traits vulnerable to habitat degradation, like sediment loading. This study aims to examine how fish species occurrences (presence or absence) vary across a gradient of fine sediment and if traits can predict which species’ occupancies are more sensitive to sediment. We sampled riffle-run transects (2-4 times each) in 29 reaches selected to represent a gradient of fine sediment conditions in the Piedmont region of North Carolina and Virginia. For the first section of this analysis, we categorized the observed species by their predicted sensitivity to sediment based upon their feeding and reproductive traits, then used binomial logistic regressions to predict each species’ occupancy based upon a suite of sediment metrics. Silt cover and embeddedness, commonly used fishery’s metrics, did not explain as much variability in occupancy as anticipated among the species and other metrics like stream size and upland watershed variables may be more important in explaining occupancy. More species’ occupancy significantly and negatively associated with embeddedness than silt cover, suggesting this form of sediment deposition could be more threatening to fish habitat. For some species, their association with these variables were context dependent on the stream’s benthic substrate size. Overall, our groupings of sediment sensitivity could likely be better developed to by considering more traits and providing a dynamic, as opposed to equal scoring, for the traits of a species. The second section of this study takes a heuristic approach to define species sensitivity to deposited sediment via functional traits related to feeding and reproduction based on prior studies for fish species, focusing on species in our study area. We then analyzed cooccurrence patterns between traits and two snapshot measurements of deposited sediment, silt cover and embeddedness and compared these results back to our literature-based trait scores of sediment sensitivity. We analyzed these relationships through canonical correspondence analysis (CCA) and Kendal-tau correlation analysis utilizing fish and habitat surveys. Our results indicate that feeding preference and spawning behavior may influence species responses to deposited sediment. Herbivory and nest association were negatively associated, whereas generalism, omnivory, piscivory, and open-water spawning was positively associated with the presence of deposited sediment. The research presented here provides insight into what species and what traits may be particularly sensitive to sediment.