Playing “hide and seek” with the Mediterranean monk seal: a citizen science dataset reveals its distribution from molecular traces (eDNA)

Abstract

Animal conservation relies on assessing the distribution and habitat use of species, but for endangered/elusive animals this can prove difficult. The Monk Seal, Monachus monachus, is one of the world's most endangered species of pinniped, and the only one endemic to the Mediterranean Sea. During recent decades, direct observations have been few and scattered, making it difficult to determine its distribution away from the Aegean Sea (core distribution area of the post-decline relict population). This study relies on environmental DNA (eDNA) analysis to detect the presence of the Monk Seal in 135 samples collected in 120 locations of the central/western Mediterranean Sea, spanning about 1500 km longitudinally and 1000 km latitudinally. A recently described species-specific qPCR assay was used on marine-water samples, mostly collected during 2021 by a Citizen Science (CS) project. Positive detections occurred throughout the longitudinal range, including the westernmost surveyed area (Balearic archipelago). The distribution of the positive detections indicated six “hotspots”, mostly overlapping with historical Monk Seal sites, suggesting that habitat-specific characteristics play a fundamental role. We applied single-season occupancy models to correct for detection probability and to assess the importance of site-specific characteristics. The distance from small islets and protected (or access-restricted) areas was correlated negatively with the detection probability. This novel molecular approach, applied here for the first time in an extensive CS study, proved its potential as a tool for monitoring the distribution of this endangered/elusive species.

Environmental DNA revealed high accuracy in detection of the Eurasian otter in Himalaya

“…eDNA studies rely on DNA fragments released in the environment (soil, water, air) from faeces, mucus, skin cells, or other sources of organism DNA to infer the presence of a target species (Taberlet et al, 2012;Harrison, Sunday & Rogers, 2019;Prié et al, 2020;Pascher, Švara & Jungmeier, 2022). The application of molecular-based techniques targeting eDNA has proven to be particularly useful for detecting rare and elusive species in aquatic environments (Hinlo et al, 2018;Valsecchi et al, 2022;Valsecchi et al, 2023), including the Eurasian otter (Lutra lutra) (Jamwal et al, 2021). However, the efficiency of eDNA approaches for the detection of otters has not yet been tested in areas where the species is rare and occurs in extreme conditions, such as Himalayan rivers.…”

Environmental DNA reveals fine scale spatial and temporal variation of prey species for marine mammals in a Scottish marine protected area

“…eDNA can expand the spatiotemporal scope of marine mammal monitoring where visual or acoustic monitoring are infeasible, i.e., at night or in adverse weather conditions and for cetaceans that vocalise infrequently or have unknown vocalisations (Baumgartner et al, 2019;Valsecchi et al, 2021). To date, single species eDNA approaches have improved our understanding of several rare or threatened species, i.e., dwarf sperm whales (Kogia sima) and Mediterranean monk seals (Monachus monachus) (Juhel et al, 2021;Valsecchi et al, 2023), and species that are challenging to detect with conventional survey techniques, i.e., beaked whales Hooker et al, 2019). They have also provided insights into population genetics, with important management consequences (Parsons et al, 2018).…”

“…To date, single species eDNA approaches have improved our understanding of several rare or threatened species, i.e. , dwarf sperm whales ( Kogia sima ) and Mediterranean monk seals ( Monachus monachus ) (Juhel et al, 2021; Valsecchi et al, 2023), and species that are challenging to detect with conventional survey techniques, i.e. , beaked whales (Boldrocchi et al, 2023; Hooker et al, 2019).…”

Surface-sourced eDNA to track deep-diver cetaceans: the study case of Cuvier’s beaked whale (Ziphius cavirostris) at Caprera Canyon and surrounding areas (Western Mediterranean Sea)

“…The identification of areas critical for species survival is essential for effective wildlife conservation, particularly when focusing on species of concern (Ambal et al, 2012; Stokes et al, 2015; Valsecchi et al, 2023). Threatened marine vertebrates are challenging to study as they are often rare or elusive, resulting in insufficient knowledge on their occurrence and distribution, which impedes management and limits effective conservation (Boldrocchi and Storai, 2021; Kiszka et al, 2007; Smith et al, 2021).…”