Stream health, topography, and land use influences on the distribution of the Eurasian otter Lutra lutra in the Nakdong River basin, South Korea

In South Korea, Eurasian otter (Lutra lutra) habitat has increased since the 1990 s because of legal protection, forest development, and increased public awareness. Although otters have been detected throughout the country, a precise investigation of habitat conditions has not previously been undertaken. We hypothesized that higher values of stream health assessment programme (SHAP) indices would indicate better habitat for otters. Otter distribution based on spraint density was investigated along 600 m riverside transects at 250 sites in the Nakdong River basin. We defined four otter population categories (absent, rare, normal, and abundant) and compared the results with presence and absence data. Use of the four population categories provided more details about habitat conditions than presence and absence analysis. The highest spraint densities were found at higher altitudes, and densities declined in areas with high human density and urbanization. The benthic macro-invertebrate community index was highly positively related to the otter population indices. In terms of fish as prey items, the proportion of species tolerant to environmental change were negatively related to otter indices, otherwise number of species sensitive to environmental change positively related. Overall, stream health assessment indices provided the highest correlations with otter population numbers and distribution.