Sakhalin taimen (Parahucho perryi) is one of the largest freshwater fishes in Japan and critically endangered in the world. They are known to be not only a keystone species in the river ecosystem, but also an iconic species for local societies and anglers. Some of them are trying hard to conserve them locally, but it is necessary to understand their distribution and biomass in large scales to make it efficient at the species level.
Environmental DNA (eDNA) technique was first reported to estimate the distribution of alien species in the wild from environment water samples about 10 years ago. Because eDNA detection is based on environmental samples (water, soil, air, etc.), sampling efforts can be reduced drastically. In addition, it is especially useful for rare species due to its strong sensitivity.
In this study, we applied the eDNA technique to answer the following question: where and how many are Sakhalin taimen in Hokkaido now? We collected eDNA samples from 130 rivers and estimated presence/absence and biomass of them using a species-specific, quantitative eDNA detection system. We discuss an applicability and an efficiency of this technique for monitoring of endangered species in general.