Newly developed ad hoc molecular assays shows how eDNA can witness and anticipate the monk seal recolonization of central Mediterranean

The monk seal, the most endangered pinniped worldwide and the only one found in the Mediterranean, has suffered a drastic decline in the last few decades. Nowadays molecular techniques allow to detect minute amounts of DNA released in the environment (eDNA) by any organism. We present three qPCR-assays targeting the monk seal mitogenome. The assays were soundly tested on an extensive/diversified sample set (n=73), including positive controls from Madeira breeding population and two opportunistic Mediterranean eDNA-sample collections (offshore/coastal) from on-going projects. Monk seal DNA was detected in 47.2% and 66.7% of the samples collected in the Tyrrhenian from a ferry platform (2018-2019) and in the Pelagie archipelago (2020) respectively, anticipating (up to 2 year) visual observations occurred subsequently in proximity of the sampled areas. In the Tyrrhenian, detection occurrence increased between 2018 and 2019. Monk seal DNA recoveries were commoner in night-time ferry-samples, suggesting nocturnal predatory activity in pelagic waters. The proposed technique provides a non-invasive and yet highly-sensitive tool for defining the monk seal actual range, its recovery rate and pinpoint coastal/offshore localities where prioritizing conservation.