Fecal DNA metabarcoding reveals the winter diet of Eurasian otter (Lutra lutra) in Northeast China

As the top predator of freshwater ecosystems, the Eurasian otter (Lutra lutra) plays a vital role in maintaining food web structure and ecosystem stability. Understanding the dietary composition and dynamics of the Eurasian otter is crucial for comprehending its ecosystem function and interspecies interactions, providing vital information for determining conservation and management strategies. Currently, DNA metabarcoding technology has been extensively applied in dietary studies as a more effective and accurate method for identifying prey species. However, there remains an insufficient amount of research on otter diet using this technology, especially in Northeast China. In this study, we analyzed the vertebrate dietary composition and spatial variation of otters during the winter in Northeast China using DNA metabarcoding technology. We confirm 106 fecal samples belonging to Eurasian otter DNA from 118 putative otters fecal samples, and then performed polymerase chain reaction (PCR) amplifications using vertebrate universal primers with the otter blocking primer (OBS1) and the human blocking primer (HomoB) to the sequence. Subsequently, high-throughput sequencing was performed to analyze the dietary composition of Eurasian otter. We identified a total of 34 prey taxa, including 31 fish, 2 frog and 1bird. Our results showed that the winter diet of the Eurasian otter was dominated by fish (60.11 %), (e.g., Cottidae, Cyprinidae), followed by Ranidae (39.88 %). Furthermore, geographical variations in dietary preferences were observed. This study confirms that Eurasian otter is a generalist piscivorous predator, and that its diet could be related to the availability of resources in the habitat. This study enriches the information on the diet of Eurasian otter, and can be used to provide a reference for the development of effective conservation strategies. At the same time, it confirms the reliability of the fecal DNA metabarcoding technique for carnivore predation analysis, and provides a new perspective for the investigation and research of otters and other mammals.