Impact of riverine habitat structure and season on sprainting behavior of the Eurasian otter (Lutra lutra) along an urban stream

Background Although the Eurasian otter ( Lutra lutra ) is highly sensitive to urbanization, its occurrence in urban areas has recently increased. Few studies have examined the sprainting behavior of urban otters in response to environmental conditions. We aimed to determine which environmental factors best explain otter sprainting behavior and quantify seasonal shifts in their spatial distribution. Accordingly, we conducted seasonal otter spraint surveys along the Gwangju Stream, an urban stream in South Korea, over 2020–2021, and used spraint marking intensity indicators (spraint and latrine site counts) to test two hypotheses: (1) riverine habitat structure accounts for a larger proportion of variance in sprainting behavior than human population size, land use, and water quality, and (2) the spatial distribution of sprainting behavior becomes more uneven among survey sites during autumn and winter than during spring and summer. To test our first hypothesis, we selected a refined set of variables related to riverine habitat structure, human population size and land use, and water quality to perform variance partitioning. Subsequently, we evaluated eight candidate negative binomial generalized linear models, including a temporal baseline model, in terms of the best fit. We tested the second hypothesis using seasonal sprainting patterns and coefficients of variation. Results Riverine habitat structure made a substantially larger contribution to explaining sprainting behavior than human population size and land use or water quality. Models incorporating riverine habitat structure provided the best fit for both spraint intensity indicators. Artificial structures had positive effects on both spraint sites and latrines, while water areas and gravel pits were positively associated with spraint sites. In contrast, human population size and water depth had negative effects on latrines. Seasonal coefficients of variation suggested that sprainting behavior tended to become more spatially uneven among survey sites during autumn and winter. Conclusion While mitigating basic water quality and human population and land use pressures is required for otter occurrence, suitable riverine habitat structure is the primary driver facilitating successful coexistence in urban streams. Identifying seasonal constraints on habitat use provides crucial insights for developing site-specific conservation strategies for urban otter populations.