Environmental DNA dispersal from Atlantic salmon farms
Dylan Shea, L. Neil Frazer, Kiran Wadhawan, Andrew W. Bateman, Shaorong Li, Kristina M. Miller, Steven M. Short, Martin Krkošek
Abstract
The spatial spread of genetic material is fundamental to analyses of invasive species, species dispersal, and disease surveillance. Using a quantitative environmental DNA methodology, we assessed spatial variation in Atlantic salmon ( Salmo salar) eDNA concentration, originating from four active salmon farms, along ∼55 km of narrow channels in British Columbia, Canada. We evaluated eDNA from 36 and 47 seawater samples collected at 2 and 8 m depths, respectively, at 0.3–3 km intervals along the channels. We fitted a Laplace dispersal kernel to eDNA data separately for 2 and 8 m depths. The model estimates that 95% of eDNA spread at 2 m depth was within 1.6 km upstream and 3.2 km downstream from farms relative to a prevailing current, and this was expanded at 8 m (1.8 km upstream; 3.7 km downstream). Our modeling results were robust to multiple sources of simulated uncertainty associated with sampling regime and variable eDNA shedding rates. Our results provide a benchmark for the spatial spread of biological material such as pathogens or eDNA from invasive or imperilled species in a coastal marine context. This work has implications for the interpretation of eDNA data for species surveillance and predicting disease spread.