Spatial and temporal patterns of occurrence of the vulnerable Mediterranean monk seal in the Tyrrhenian Sea via seawater eDNA

The Mediterranean monk seal ( Monachus monachus ), one of the world’s most endangered pinnipeds and the only seal endemic to the Mediterranean, was historically widespread in the Tyrrhenian Sea but declined sharply in the 20th century due to habitat loss and human disturbance (direct killing and fish bycatch). Despite recent increases in opportunistic sightings, evidence based on reliable scientific methods remains scarce, highlighting the urgency of adopting more effective and systematic monitoring approaches. Here, using a species-specific eDNA qPCR assay, we analysed 288 seawater samples collected between September 2023 and June 2025 at 22 sites across the central and southern Tyrrhenian Sea. Monk seal DNA was detected in 7.6% of samples, with positive detections strongly clustered in the Tuscan and Pontine Archipelagos. Detection frequencies differed significantly among sectors and showed seasonal peaks in spring and autumn, while remaining low in summer. Spatial patterns were significantly associated with insular environments characterized by suitable cave habitats and lower anthropogenic pressure. Our results provide the first molecular confirmation of monk seal presence in the Pontine Archipelago, and support the hypothesis of a renewed use of parts of the species’ historical range. Overall, this study highlights the importance of insular habitats for monk seal persistence in the Tyrrhenian Sea and underscores the value of eDNA-based monitoring for guiding conservation strategies for rare and elusive marine mammals.