Isotopic Diet Analysis of the Japanese Water Shrew Chimarrogale platycephala to Estimate Their Feeding Habits and the Usefulness of Body Hair Samples

The water shrew Chimarrogale platycephala is an endangered species in Japan. Although immediate conservation actions are necessary, detailed information on this species is inadequate. We compared dietary trends obtained via C. platycephala digestive contents analysis with those through stable isotope analysis (delta C-13, delta N-15, %) of non-invasive body hair and invasive muscles to elucidate their diet and evaluate usefulness of the dietary stable isotope analysis. We captured 20 shrews from three streams in Aomori Prefecture from 2013 to 2016 barring snow accumulation seasons. The digestive contents analysis showed that water shrews mainly fed on aquatic insects, whereas freshwater crabs, fishes, and terrestrial insects were also observed as diets. delta C-13 values from the stable isotope analysis were not significantly different between muscles and body hair and indicated a primary diet of aquatic invertebrates and fishes. delta N-15 values were significantly lower in muscles and indicated a similar trophic position of water shrews to fishes. In the isotope mixing model, the contribution of terrestrial invertebrates was less than 0.35 except for two individuals that showed the highest terrestrial invertebrate ratio (> 0.5) and the lowest aquatic invertebrate ratio. This study also demonstrated that body hair from any part of the back was sufficiently useful for dietary stable isotope analysis.