Abstract
The integration of environmental DNA (eDNA) within management strategies for lotic organisms requires translating eDNA detection and quantification data into inferences of the locations and abundances of target species. Understanding how eDNA is distributed in space and time within the complex environments of rivers and streams is a major factor in achieving this translation. Here we study bidimensional eDNA signals in streams to predict the position and abundance of Atlantic salmon (Salmo salar) juveniles. We use data from sentinel cages with a range of abundances (3–63 juveniles) that were deployed in three coastal streams in New Brunswick, Canada. We evaluate the spatial patterns of eDNA dispersal and determine the effect of discharge on the dilution rate of eDNA. Our results show that eDNA exhibits predictable plume dynamics downstream from sources, with eDNA being initially concentrated and transported in the midstream, but eventually accumulating in stream margins with time and distance. From these findings we developed a fish detection and distribution prediction model based on the eDNA ratio in midstream versus bankside sites for a variety of fish distribution scenarios. Finally, we advise that sampling midstream at every 400 m is sufficient to detect a single fish at low velocity, but sampling efforts need to be increased at higher water velocity (every 100 m in the systems surveyed in this study). Studying salmon eDNA spatio-temporal patterns in lotic environments is essential to developing strong quantitative population assessment models that successfully leverage eDNA as a tool to protect salmon populations.
Highlights
Recent advances in the collection and analysis of extra-organismal environmental DNA provide a novel indirect approach that can fill gaps in large-scale fish distribution assessments, complementing logistically difficult traditional methods
Environmental DNA has three hierarchical potential uses for broadly examining single species: (1) detection, determining the large-scale spatial distribution of a species; (2) quantification, determining the population size in a system based on the environmental DNA (eDNA) concentration or detection rates, and (3) quantitative distribution assessment, localizing high or low concentrations of organisms to particular geographic locations based on eDNA variability
In lotic habitats, fine-scale population quantification and quantitative distribution assessment are currently limited by our ability to translate eDNA distribution to upstream fish distributions. eDNA distribution is impacted by the physical properties of the stream, e.g., morphology and hydrodynamics (Dejean et al, 2011; Deiner and Altermatt, 2014; Jane et al, 2015)
Summary
Recent advances in the collection and analysis of extra-organismal environmental DNA (eDNA) provide a novel indirect approach that can fill gaps in large-scale fish distribution assessments, complementing logistically difficult traditional methods. Using eDNA to detect and quantify aquatic populations has the power to drastically improve our knowledge of the large- and fine-scale spatial distribution of animals (Lacoursière-Roussel et al, 2016a; Yates et al, 2019). In lotic habitats (rivers and streams), fine-scale population quantification and quantitative distribution assessment are currently limited by our ability to translate eDNA distribution to upstream fish distributions. Despite the advantages of lotic eDNA surveys over traditional electric and net surveys in terms of person-power, cost, and potential harm to study organisms, implementation for management could be substantially improved by better characterizing of lotic eDNA dynamics that influence eDNA-based detection, quantification, and distribution assessment of aquatic species
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