Platypus (Ornithorhynchus anatinus) occurrence in the catchments of the outer local government areas (LGAs) of Sydney, Australia. An investigation using environmental DNA (eDNA) and community reporting

Platypuses (Ornithorhynchus anatinus) have historically occupied streams throughout the outer Sydney Basin, Australia, but no recent systematic assessment of their distribution has been undertaken. From June 2020 to May 2024, platypus presence was surveyed using environmental DNA (eDNA) analysis at 222 sites, across 10 local government areas (LGAs) in the Hawkesbury-Nepean and Georges River catchments. New South Wales (NSW) BioNet database records, community sightings and mark-recapture surveys were also reported. Platypus DNA was detected at 39% of sites across the Hawkesbury-Nepean catchment but were lowest in Georges River catchment (16.3%). The outer more rural LGAs – Wingecarribee (42.9%), Camden (41.6%), Wollondilly (40.5%) and Blue Mountains (38.5%) – had the highest detection. These findings confirm persistent platypus occupation of waterways across outer Sydney, although the detection data suggest most populations are probably small and vulnerable to the discussed environmental pressures. Some sites recorded no eDNA detections but verified sightings or captures were recorded at these sites, highlighting the limitations of eDNA as a standalone monitoring method. Integration of eDNA sampling, community reports and live-capture data provides a more robust research approach, underscoring the necessity for multi-faceted monitoring to gain better understanding of platypus occurrence, especially considering the need for targeted conservation efforts in areas of increased environmental disturbance, including urbanisation.