Evaluation of eDNA as a technique to monitor freshwater fish in southwestern Australia

Our goal was to evaluate eDNA as a monitoring tool for freshwater fish and specifically the use of passive eDNA collection. We had two aims: (1) to determine the effectiveness of active and passive eDNA sampling compared to a conventional technique (fyke netting) to quantify a freshwater fish assemblage in a riverine environment, and (2) to investigate the sampling effort (i.e., replicate number) required to optimize detection of individual species as well as the entire fish assemblage (i.e., species richness). We used a hierarchical multispecies N-mixture model that disentangles the processes of abundance and detection to evaluate the performance of the different sampling methods and to determine the sampling effort required to accurately detect species and describe site-level species richness. This study is one of the few to trial a passive approach to eDNA collection in freshwater. Our findings will assist the advancement and adoption of eDNA monitoring in freshwater ecosystems.