Distribution analysis of the finless porpoises (Neophocaena sp.) and oceanic dolphins (Delphinidae) in the Korean Sea using environmental DNA

Environmental DNA (eDNA) serves as a non-invasive tool for monitoring the presence of specific organisms in challenging or hard-to-access areas. We attempted non-invasive monitoring of Korean cetacean species by extracting eDNA from the western and southern seas of the Republic of Korea, as well as around Jeju Island. In the present study, we focused on two representative cetaceans of the Korean Sea: the narrow-ridged finless porpoise (Neophocaena asiaeorientalis sunameri) and oceanic dolphins (Family Delphinidae). When selecting polymerase chain reaction primers, mitochondrial DNA (mtDNA) of N. asiaeorientalis and microsatellite Slo4 of oceanic dolphins were identified as the most effective gene sequences in high abundance in low concentration eDNA samples, using tissue samples for eDNA detection of the target species. A total of 139 samples were collected, and eDNA was detected from finless porpoises (Neophocaena sp.) in 94 samples (68%) and from oceanic dolphins in 50 samples (36%). Significantly, eDNA revealed the considerable presence of finless porpoise around Jeju Island, despite a lack of visual confirmation. In the Yellow Sea, eDNA primarily detected the presence of common dolphin (Delphinus delphis), orca (Orcinus orca), and Indo-Pacific bottlenose dolphin (Tursiops aduncus). Indo-Pacific bottlenose dolphins were identified along the coast of Jeju Island. The value of this research lies in being the first attempt to explore cetacean eDNA across various species in Korea. Further cetacean eDNA research should focus on developing metabarcoding primers capable of detecting a greater variety of cetacean species and primers for detecting specific porpoise species. This study will serve as a valuable reference for future studies.