Traces in the water: eDNA reveals the return of the Eurasian otter Lutra lutra to central Italy

Genetic monitoring plays a crucial role in the conservation and management of recovering protected species. The analysis of species-specific DNA fragments in environmental samples (eDNA), such as from water or soil, facilitates the molecular detection of elusive species. The Eurasian otter Lutra lutra experienced a dramatic decline in Europe during the 20th century. Reintroduction efforts have recently led to population recoveries across many parts of Europe, but these populations are difficult to monitor. Recently, eDNA data provided evidence of the presence of the species in central Italy where it disappeared three decades ago. We performed an eDNA survey in rivers of central Italy where the species has not been recorded. Filtered water samples were collected at five streams and analyzed by real-time quantitative polymerase chain reaction (qPCR). eDNA monitoring revealed the presence of the Eurasian otter in all rivers, even though not in all sampling points, suggesting the need to update the Eurasian otter monitoring combining traditional and molecular tools.