Abstract
The monk seal is the most endangered pinniped worldwide and the only one found in the Mediterranean, where its distribution and abundance have suffered a drastic decline in the last few decades. The limited understanding of the population demographics and conservation status of this species are due to both its rarity and evasiveness, with records biased towards occasional, mostly coastal, encounters. Current molecular techniques allow us to detect DNA traces released into the environment (eDNA) by any organism. We have developed three species-specific qPCR-assays targeting the 12S/16S rRNA mitogenome regions of the monk seal. The assays have been tested extensively on a comprehensive and diverse set of samples (n = 73), including positive controls from a breeding population in Madeira collected during their peak abundance, and two opportunistic collections of Mediterranean eDNA samples (offshore/coastal) from on-going projects. Monk seal DNA was detected in 47.2% of the samples collected from a ferry platform in the Tyrrhenian (2018–2019) and in 66.7% of those obtained in the Pelagie archipelago in the Strait of Sicily (2020). These findings anticipated subsequent visual observations in the proximity of these sampling areas by up to 2 years. At the Tyrrhenian site, monk seal detection increased between 2018 and 2019. The demonstrated approach provides a non-invasive and highly sensitive tool for defining the monk seal actual distribution and home range -enabling monitoring also in nocturnal hours-, for assessing its recovery rate and pinpointing coastal/offshore sites where prioritizing conservation, research, citizen-science, and educational opportunities.
Highlights
The Mediterranean monk seal (Monachus monachus) is the only pinniped permanently resident in the Mediterranean basin
The 12SrDNA and 16SrDNA fragments targeted by the three primer sets -MarVer1, MarVer2 and MarVer3- were all highly polymorphic, as evident when aligning the homologous regions in two sister species of the Mediterranean (Monachus monachus) and the Hawaiian (Neomonachus schauinslandi) monk seals (GenBankANs NC_044972 and NC_008421 respectively)
At each of the three MarVer loci (Valsecchi et al 2020), one Monachus monachus specific primer site was identified that fulfilled the specificity criteria established for the target species (Table 2)
Summary
The Mediterranean monk seal (Monachus monachus) is the only pinniped permanently resident in the Mediterranean basin. Mediterranean monk seals were commonly found throughout the Mediterranean, Marmara and Black Seas, stretching out into the Atlantic Ocean along the West African coast as far south as Cap Blanc, as well as around Cape Verde, Canary, Madeira and Azores Islands. The current distribution of the Mediterranean monk seal is still only partially defined, relying on opportunistic data from sporadic (mostly coastal) sightings, some of which remain unverified. Little is known about the foraging areas and social interactions, or their actual distribution in the non-breeding season. This kind of information is difficult to retrieve as monk seals are often elusive and hard-to-study in offshore waters and/or during the night
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