A Distribution Survey for Otters Along a River in Central Bhutan
Abstract: We report the findings of a survey for otters along a major river in central Bhutan. The river bears various names in different stretches along its run, including Mochhu, Phochhu, Punatsangchhu and Sunkosh. We report: 1) the distribution and density of otter sign, including tracks, scats, latrines and dens, 2) the correlation between sign abundance and vegetation and substrate characteristics, and 3) the correlation of otter sign with human disturbance. Five of the six 5.5 km transects sampled were positive for otter sign. The one transect with no otter sign was the site of a recent severe flood event. Linear sign density was 9.4 sign km-1 along one bank of the river, with a mean of 45% of two sample rounds positive for presence of otter sign in sample plots. The Kamichhu site possessed the highest percentage of positive plots at 95%, and the Sunkosh site the lowest at 35%. The number of otter sign was positively correlated with bankside vegetation and with sandy beaches with large boulders. Human disturbance also influenced the density of otter sign, with proximity of settlements, represented by the presence of footpaths, grazing and trash, apparently deterring otter presence. Three species of otters likely occupy the rivers of Bhutan (Lutrogale perspillata, Lutra lutra, and Aonyx cinereus) but since altitudinal niche partitioning by these species is not understood in the study area, we make no attempt to predict distribution by species. Only one otter species, a smooth-coated otter (L. perspicillata) was directly sighted.