Ten Years of Mediterranean Monk Seal Stranding Records in Greece under the Microscope: What Do the Data Suggest?

This paper presents the results of an analysis of stranding events of the Mediterranean monk seal Monachus monachus over a decade. The analysis involved categorization according to the cause of stranding and seasonality, the identification of hotspot stranding areas and an assessment of possible correlations between stranding events and environmental/climatic patterns using time series analysis. Moreover, Generalized Additive Models (GAMs) were applied to explore the effects of the size of small-scale fishing grounds, the number of species sightings, and the occurrence of reproduction sites on "human-related" strandings. Finally, special focus was put on the central part of the eastern Ionian Sea for the assessment of stranding hotspot areas by means of the Multi-Criteria Decision Analysis (MCDA) approach, based on different kinds of spatial information such as anthropogenic pressures and the location of breeding sites and feeding grounds. Time series analysis results revealed that oscillation indices, during the first half of the year, and sea surface temperature (SST) in the Mediterranean from October to December were positively correlated with monk seal stranding events. GAMs underlined that areas combining extended small-scale fishery grounds and a higher number of sightings were more likely to cause more strandings. Regarding spatial analyses, the central Aegean Sea was highlighted as a hotspot for "human-related strandings", while the MCDA approach emphasized that the southern coasts of Cephalonia and the gulf between Lefkada and mainland Greece were susceptible to subadult strandings.

Monk seal faeces as a non-invasive technique to monitor the incidence of ingested microplastics and potential presence of plastic additives.

Anthropogenic debris, including plastics, has recently been identified as a major threat for marine mammals and the Marine Strategy Framework Directive aims to achieve the good environmental status of European waters by addressing among other criteria, the effects of marine litter on biota. This study implemented for the first time a non-invasive technique for collecting monk seal samples to assess microdebris ingestion in combination with identifying plastic additives and porphyrins biomarkers. A total of 12 samples of monk seal faeces were collected from marine caves in Zakynthos Island, Greece. A total of 166 microplastic particles were identified; 75 % of the particles were smaller than 3 mm. Nine phthalates and three porphyrins were detected. A strong correlation was found between the number of microplastics and the concentration of phthalates. The values of both phthalates and porphyrins were found lower than in other marine mammal tissues, suggesting that seals might not be impacted by them yet.

The antique genetic plight of the Mediterranean monk seal (Monachus monachus).

Disentangling the impact of Late Quaternary climate change from human activities can have crucial implications on the conservation of endangered species. We investigated the population genetics and demography of the Mediterranean monk seal (Monachus monachus), one of the world's most endangered marine mammals, through an unprecedented dataset encompassing historical (extinct) and extant populations from the eastern North Atlantic to the entire Mediterranean Basin. We show that Cabo Blanco (Western Sahara/Mauritania), Madeira, Western Mediterranean (historical range) and Eastern Mediterranean regions segregate into four populations. This structure is probably the consequence of recent drift, combined with long-term isolation by distance (R2 = 0.7), resulting from prevailing short-distance (less than 500 km) and infrequent long-distance dispersal (less than 1500 km). All populations (Madeira especially), show high levels of inbreeding and low levels of genetic diversity, seemingly declining since historical time, but surprisingly not being impacted by the 1997 massive die-off in Cabo Blanco. Approximate Bayesian Computation analyses support scenarios combining local extinctions and a major effective population size decline in all populations during Antiquity. Our results suggest that the early densification of human populations around the Mediterranean Basin coupled with the development of seafaring techniques were the main drivers of the decline of Mediterranean monk seals.