Citizen science indicates significant range recovery and defines new conservation priorities for Earth's most endangered pinniped in Greece

Abstract

Conservation actions for endangered species often require detailed data over large temporal and spatial scales, which are usually hard to obtain from traditional scientific surveys that operate at localized scales. In contrast to the terrestrial conservation world where citizen science has become nowadays a highly relevant and useful tool to overcome such difficulties, Marine Citizen Science is still highly underrepresented. Using a dataset of 20 years of citizen science data and appropriate statistical modelling, we developed a methodological approach to monitor the presence of the endangered, notoriously elusive Mediterranean monk seal Monachus monachus. We used sighting data collected in Greece from 2000 to 2020 and fitted dynamic occupancy models that allow inferring range dynamics whilst accounting for species imperfect detectability to estimate species occupancy. The occurrence of Mediterranean monk seals of all age categories combined, and pups separately, increased during the study period. Mediterranean monk seal occurrence increased also spatially: the distribution of the species in Greece increased by approximately 12.5% for seals of all age categories and by approximately 185% for monk seal pups. Most of this distribution (i.e. 67 and 72% of the distribution of seals of all age categories and of pups, respectively) was located within the boundaries of the network of protected areas in the country. These results indicate a significant range recovery of the Mediterranean monk seal in Greece over the last two decades and facilitate the prioritization of conservation actions for the species in the country. We demonstrate how occupancy modelling and citizen science can be used to evaluate the distribution of an endangered species and become a highly relevant and reliable tool in marine mammal conservation. We advocate the increased use of citizen science in the conservation of the Mediterranean monk seal in the eastern Mediterranean Sea.