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

A precise framework of species occurrence and distribution trends is crucial for conservation measures. Traditional survey methods are often labour-intensive and time-consuming, and they can be ineffective in detecting the presence of rare and elusive taxa, especially in harsh environments. The effectiveness and feasibility of an environmental DNA (eDNA)-based approach was tested to detect the occurrence of the semiaquatic Eurasian otter (Lutra lutra) in six rivers in the Trans-Himalaya, comparing the results with those obtained from a traditional field survey. Water samples were collected and filtered on-site at 15 locations, from 2,660 to 3,819 m a.s.l. Otter scats were actively searched for at the same locations in a 900 m buffer along the river bank. Fifteen environmental parameters were recorded at each sampling site. After eDNA extraction and target quantitative realt-time polymerase chain reaction (qPCR) assay, statistical analyses were run to explore the relationship between environmental factors and the presence/absence of otters at each site. Otter DNA was found at 73% of sites, whereas traditional field survey results showed that 53% of sites were positive for otters. Results from principal component analysis showed that the sites avoided by otters, as measured through eDNA, were clearly segregated along PC1 and PC2, with both axes explaining 57% of the cumulative variance. The best-performing generalized linear model suggested that the occurrence of otter eDNA was influenced by channel width, surface velocity, nitrate level, total dissolved solids, and average water depth. The results of this study highlight that, compared with traditional field surveys, eDNA-based methods increased the detection of positive sites by 20%, thus demonstrating their reliability for monitoring the presence of otters in the study area and providing new insights into the ecology of this species in the Indian Trans-Himalaya.