Environmental DNA dispersal from Atlantic salmon farms

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.