Dead or alive — Old empty shells do not prompt false‐positive results in environmental DNA surveys targeting the freshwater pearl mussel ( <scp> <i>Margaritifera margaritifera</i> </scp> L.)

Environmental DNA (eDNA) from water samples is increasingly used to detect the presence and distribution of species in aquatic ecosystems. However, before implementing eDNA monitoring programmes, various species-specific sampling or analytical issues remain be resolved order minimize frequencies false-positive -negative results. For example, empty shells freshwater pearl mussels (Margaritifera margaritifera) contain extractable (chemical extraction ground-up shells) suggesting a risk at stream sites with extinct populations but shell material remaining. The aim this study was investigate whether naturally degrading M. margaritifera can cause signals samples. Water were collected outdoor channels (in Lemming, Denmark) living (density ~10 individuals m−2) during 3-week experimental period. Living Hemgravs Sweden transported Denmark according permissions granted by Swedish Danish authorities. All containing negative for indicating that traces are most likely originate located upstream site. consistently positive except one sample (interpreted as false negative). shows reflect individuals. Consequently, we suggest should locate remaining population fragments deep turbulent streams, providing platform faster more efficient decision making when launching investigative mitigation initiatives.