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Molecular methods, including those for environmental DNA (eDNA), provide essential information for biological and conservation sciences. Molecular measurements are often performed in the laboratory, which limits their scope, especially for rapid on‐site analysis. eDNA methods for species detection provide essential information for the management and conservation of species and communities in various environments. We have developed an innovative novel method for on‐site eDNA measurements using an ultrarapid mobile PCR platform. We tested the ability of our method to detect the distribution of silver carp, Hypophthalmichthys molitrix, in rivers and lakes. Our method reduced the measurement time to 30 min and provided high detectability of aquatic organisms compared to national observation surveys that use multiple fishing nets and laboratory extraction/detection using a benchtop qPCR platform. Our on‐site eDNA method can be immediately applied to various taxa and environments. [ABSTRACT FROM AUTHOR]

The signal crayfish, Pacifastacus leniusculus , is non-native to Japan, and its invasion may have contributed to the habitat loss of the endemic Japanese crayfish, Cambaroides japonicus. We assessed the distribution of the signal crayfish and the Japanese crayfish in small streams that flow into Lake Akan (Hokkaido, Japan), which the signal crayfish inhabits. We conducted this survey with 2 methods: analysis of environmental DNA (eDNA) and hand capture. Of the 17 streams we surveyed, we detected signal crayfish DNA in 16 streams and Japanese crayfish DNA in 9 streams. In contrast, with our hand-capture survey of the same 17 streams, we found signal crayfish in 9 streams and Japanese crayfish in 4 streams. These results suggest that the signal crayfish may have invaded almost all the small streams with culverts around Lake Akan. The presence of signal crayfish was also confirmed on the upstream side of a 69-cm-high road-crossing culvert. There were only 2 culverts above which the absence of signal crayfish was supported by eDNA analysis, suggesting that culverts have limited effectiveness against signal crayfish invasion in our study site. Active species-specific removal projects may be an effective management option to minimize the negative impacts of signal crayfish where they are already present. eDNA has great potential as a cost-effective tool to monitor crayfish range expansion. [ABSTRACT FROM AUTHOR]