INTRODUCTION
The Mediterranean monk seal (Monachus monachus ) is the only
pinniped historically and permanently present in the Mediterranean
basin. Originally Mediterranean monk seals were found regularly
throughout the Mediterranean, Marmara and Black Seas, along the West
African coast to as far south as Cap Blanc, and in Cape Verde, Canary,
Madeira and Azores Islands. In the 20th century, the
species was drastically reduced, primarily by fishermen, over most of
its range, leading to severe bottleneck and inbreeding depression
signatures in the refugial populations in eastern Mediterranean (Stoffelet al. , 2018; Karamanlidis et al. , 2021). However, in the
last decade, occasional sightings on Italian coastal waters have been
recorded (Figure S1 in Supporting Information).
The Mediterranean monk seal current distribution is only partially known
with most available data retrieved from sites where adult females are
known to return every year to reproduce. Thanks to the predictability of
these events, some of the delivery caves are monitored year-round using
camera-trap (e.g. Martinez-Jauregui et al ., 2012), allowing us to
learn much about mother/pup relation. Yet, the home ranges of these
marine mammals are wide, as adult individuals are known to be able to
cover several tens of kilometers per day (Adamantopoulou et al .,
2011), and little is known about milling and foraging areas and which is
the actual distributional range during the non-breeding season. This
kind of information is difficult to retrieve as monk seals are often
elusive. The recently become available possibility to molecularly
monitor the presence of any target species through the analysis of
traces of its DNA released in the environment (eDNA) provides a precious
and absolutely non-invasive means by which unveiling and oversee the
Mediterranean monk seal population.
In this letter we desire to make available a triple set of
species-specific molecular assays able to detect the presence of
residual Mediterranean monk seal DNA both from soil and water
environmental matrices. The developed assays were validated both in
silico and in the wet lab on a wide range of DNA templates, including
tissue (n=3) and residual (n=12) extracts and marine eDNA samples
(n=58). The overall sample (n=73) was split into 7 categories: 3
positive and 2 negative controls and 2 sets (offshore/coastal) of marine
eDNA samples. Our results show that 1) the assays are successful in
identifying the smallest amount of monk seal eDNA (up to
5.7*10-8 mg/L); 2) the screening on both Mediterranean
marine eDNA sample sets (from previous and ongoing studies) detected the
presence of monk seal in about 50% of the samples of either set, and
showed that eDNA analysis can anticipate the detection of the monk seal
presence in the study areas before human eye; 3) finally, the proposed
approach can potentially unveil still unknown aspects of the biology of
this charismatic marine mammal species, by allowing its identification
in inaccessible contexts (i.e. offshore waters and during night-time).