Freshwater degradation as a potential extinction factor of the Japanese river otters

Exploring the causes of species extirpation can provide insights into mitigating the ongoing extinction. The Japanese otter Lutra lutra whiteleyi had extincted around 1970s, but their extinction causes remain unknown. To elucidate the ecological relationship among their foraging ecology, habitat degradation, and the extinction, we assessed dependency of Japanese otters on marine- or freshwater-derived resources using sulfur stable isotopes ( δ ³⁴ S: ³⁴ S/ ³² S) of the museum specimens which were collected on the brink of extinction. Our results clearly showed that the otters strongly depended on marine-derived resources, indicating anthropogenic activities led to depletion of freshwater prey and a potential extinction factor of the last population of otters in Japan. Protecting freshwater habitats was crucial for preventing otter extinction in Japan, and for safeguarding the extant otter species.