From anecdotes to evidence: Environmental DNA detection of Arctic charr (Salvelinus alpinus L.) at the southern limit of its circumpolar range.

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The urgency of rapid species monitoring is at an all-time high due to the increasing threat of climate change to global ecosystems, in particular freshwater habitats. Fish such as Arctic charr, Salvelinus alpinus, are particularly vulnerable to increasing water temperatures and changes in land use due to their dependence on cold waters and confinement to lacustrine environments. Nonetheless, current monitoring practices, relying on physical capture of organisms, are hindered by resource constraints, desire to manage habitats for recreational fishing, and restricted access to sites. Here we applied a targeted environmental DNA (eDNA) assay in Northwest Scotland to circumvent these limitations and update existing knowledge of Arctic charr habitats, including in locations previously only supported by anecdotal knowledge. Arctic charr eDNA was detected in 10 out of the 16 sites sampled. Additionally, shore and outflow sampling successfully detected Arctic charr eDNA during spawning season, providing a viable sampling strategy where boat access may be limited. These data enabled Arctic charr distribution records to be updated and demonstrated the effectiveness of eDNA as a method for monitoring a vulnerable salmonid in a rapidly changing landscape.