Riparian habitat quality and seasonality drives spatiotemporal habitat ecology of sympatric Asian otters in southern Western Ghats

Introduction Riparian habitats in the Western Ghats are vital semi-terrestrial zones playing multi-functional roles in the conservation of freshwater species. In dynamic ecosystems, we have scant knowledge on the interactive role of season and local riparian habitat conditions in driving spatiotemporal habitat use of sympatric semi-aquatic mustelids. Methodology We conducted seasonal monitoring of 169-196 riverine segments (250 m) in 2020 and 2021 to measure the sign encounter rates of Asian small-clawed otter (SCL) and smooth-coated otter (SCO) and recorded 29 riparian habitat variables. Results Our self-organizing map algorithm characterized alarge multivariate habitat data into six habitat clusters representing a gradient of riparian habitat conditions. The random forest (RF) algorithm identified forest cover, water quality, and substratum as influential factors in high quality habitat. The low-quality habitat with low sign encounter rates or no evidence of otters had anthropized stream buffers, with high proportion of agriculture, weed cover and anthropogenic disturbance as influential factors predicted by the RF algorithm. SCO distribution was restricted to the higher-order streams in close proximity to hydro-power dams. SCL had a comparatively larger spatial distribution in the lower-order streams. Our study shows that rainfall plays a significant role in enhancing the hydrological flow in non-perennial streams and also improves the water quality parameters and the riparian habitat conditions. We found highly variable encounter rates of both species across seasons and habitat quality gradients, however, overall, their mean encounter rates increased with the habitat quality gradient. Discussion Our findings showed that relating otter sign encounter rates with fine-scale riparian habitat quality was a useful and practical approach to monitor the sensitivity of sympatric semi-aquatic mustelids towards habitat conditions and simultaneously monitor the riparian ecosystem health, across seasons and years. The long-term persistence of sympatric Asian otters in the Bhavani-Noyyal river basin would depend on the availability of high-quality riparian habitat patches. Our findings emphasize the need to develop comprehensive riparian habitat management plans in the southern Western Ghats which involves restoration of fragmented riparian zones and maintenance of riparian habitat heterogeneity to facilitate freshwater connectivity and movements of sympatric otters.