Monitoring reproductive migration is essential for the conservation of anadromous species. Shishamo smelt (Spirinchus lanceolatus) is endemic to Hokkaido, the northernmost large island in Japan. S. lanceolatus is an anadromous species that is known to migrate into rivers for a very short period in early winter. While this species has a special value for local fisheries, the catch amount has drastically declined in the last few decades. Information about S. lanceolatus reproductive migration dynamics is limited, which prevents them from being efficiently managed as a resource. In this study, we used environmental DNA (eDNA) methods as a noninvasive molecular tool for estimating presence/absence and abundance/biomass of S. lanceolatus during their migration into rivers. We developed a species‐specific qPCR system for S. lanceolatus, examining (a) temporal variation in S. lanceolatus eDNA concentrations compared with catch data gathered by traditional methods and (b) variability of migratory patterns among river systems. In a core river for their spawning migration, we consistently detected S. lanceolatus eDNA throughout the spawning season, and the temporal distribution of eDNA concentration was consistent with that of the number of migrating S. lanceolatus estimated by catch survey data. In addition, we were able to detect S. lanceolatus eDNA even from rivers without any official record of their migration. Among rivers with eDNA detection, the relative eDNA concentrations varied, indicating that the population biomass differs largely among the river populations. Our study suggests that eDNA detection systems are useful for tracking reproductive migration of S. lanceolatus at fine spatio‐temporal scales.
For protecting endangered species, precise understanding of their distribution is crucial. However, it is often very difficult to estimate at a large scale with conventional methods (e.g., casting nets or electrofishing for aquatic species) because of their low densities in the wild. Sakhalin taimen (Parahucho perryi) is one of the largest and most critically endangered freshwater salmonid fishes in the world. In this study, we applied an environmental DNA (eDNA) detection system for this species to 120 rivers in Hokkaido, the second largest main island of Japan. We successfully detected eDNA from Sakhalin taimen in seven rivers (5.8%). Although these rivers were widely distributed across the island, > 95% of the total amounts of eDNA were detected from region-A and-I, indicating that local populations in the other regions of Hokkaido are very small and on the brink of extinction. In addition, principal component analyses based on the eDNAbased estimation of Sakhalin taimen distribution and GIS revealed their distribution determinants including limited topographic relief of watershed as well as presence of wetlands and lagoons. Our results suggest that eDNA-based detection systems are an efficient means of monitoring the population status of endangered freshwater species at large scales.
Understanding the distribution of invasive species and their reproductive area is crucial for their managements after invasion. While catch and observation surveys are still embraced, environmental DNA (eDNA) has been increasingly utilized as an efficient tool for identifying these species in the wild. In this study, we developed a Bufo-specific eDNA assay for detecting an invasive, toxic, and terrestrial toad species Bufo japonicus formosus in Hokkaido, Japan, and applied it to their reproductive area at watershed scale. The eDNA assay was field-validated in ponds where B. japonicus were observed, as well as in rivers downstream of the reproductive ponds. Thus, the assay provided us an opportunity to screen watersheds that include their reproductive area by collecting downstream water samples. Applying it to the Ishikari river basin, the largest river basin in Hokkaido (c.a., 14,330 km2), we detected toad eDNA at 32 out of 73 sampling sites. They are composed of eleven sites with species observation records nearby (all the sites with observation records within a 500 m radius) and 21 sites without such records. And those eDNA detections were from twelve out of 31 river systems in the entire river basin. A Bayesian, multiscale occupancy model supported high eDNA detectability among those sites. These results suggest that the eDNA assay can efficiently estimate the presence of reproductive area of the terrestrial toad even from a distant downstream of the watershed, and that it provides a powerful means of detecting new reproductive area and monitoring further spread of invasive species.
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