Along the winding banks of North Indian rivers, the smooth-coated otter (Lutrogale perspicillata) acts as an inconspicuous guardian of freshwater ecosystem health. As an apex predator, it regulates fish populations and serves as a living indicator of water purity and biodiversity. However, expanding settlements, dams, and pollution are gradually displacing these vulnerable mammals from their usual habitats.
An eight-year study covering 7680 kilometers of rivers in the Ganges basin found that only 0,26 percent of the area—about 2138 square kilometers out of more than 800 thousand—remains highly suitable for the species. Another 1,65 percent (13 300 square kilometers) is classified as moderately suitable. The rest of the basin appears already unsuitable for stable populations.
The scientists used ensemble ecological modeling, combining data from 267 encounter points with six algorithms and 26 environmental variables. Key factors turned out to be proximity to protected areas, stable water bodies, and small daily temperature fluctuations. Beyond two and a half kilometers from the riverbed or a one-kilometer buffer around reserves, suitability drops sharply.
The largest share of optimal sites was found in Uttarakhand—2,43 percent. The left-bank tributaries in the Terai region near Rajaji, Corbett, Dudhwa, and Valmiki form the core of the remaining range. In densely populated and altered areas of West Bengal, Chhattisgarh, and Delhi, no highly suitable sites were identified at all.
Interestingly, some artificial reservoirs, such as Gandhi Sagar and Rana Pratap Sagar, also showed high suitability due to permanent water and limited human access. Meanwhile, about 21 percent of suitable sites lie outside official protected areas, where otters are threatened by sand mining, agriculture, and discharges.
Mapping allows focusing efforts on the most valuable sites instead of spreading resources across the entire basin. Protecting these areas supports not only otters but also water purity and fish stocks that local communities depend on.
Preserving even small key river sections helps maintain the balance of entire freshwater systems.
