A Review on Eurasian Otters in Urban Areas: Principles for the Enhancement of Biodiversity

Eurasian otters, as apex predators in freshwater ecosystems, are crucial to maintaining nutrient cycling and habitat stability. Although Eurasian otters prefer unaltered natural habitats, their adaptive and opportunistic behavior allows them to occupy suboptimal environments, including urbanized areas. As urbanization increases, the pressure on apex carnivores like the Eurasian otter will continue to grow. To date, urban stream restoration plans have not used the Eurasian otter as a keystone species, but given their influence across the trophic levels, Eurasian otter-focused restoration plans could enhance otter populations and overall biodiversity in urban areas. Here, we lay out six principles designed as a template for enhancing urban habitats for Eurasian otters as well as biodiversity. The principles (enhancing habitat structure complexity, restoring natural riparian vegetation and habitats, safeguarding water quality, providing native prey species, reducing otter mortality, and promoting positive public perception) are essential for urban ecosystem regeneration focused on Eurasian otters. Although there have been no urban restoration projects specifically tailored toward Eurasian otters, initiatives based on similar principles have been effective in promoting biodiversity and otter presence. Overall, an urban habitat restoration plan focused on Eurasian otters will not just increase otter presence but biodiversity across all trophic levels.