1. There is growing international concern about declines in populations of anguillid eels, resulting in their inclusion in the International Union for the Conservation of Nature (IUCN) Red List of Threatened Species. Monitoring the population dynamics of these species is often challenging, however, owing to their broad distributions and complex, catadromous life histories.2. Whether environmental DNA (eDNA) analysis could be used to monitor the spatial distribution of anguillid eels in rivers was investigated by conducting basin-scale surveys of Japanese eels, Anguilla japonica Temminck & Schlegel, 1846, in 10 rivers in Japan, and comparing the results obtained using eDNA analysis with the results obtained using the electrofishing method. Moreover, the relationship between the eDNA concentration and the abundance and biomass of Japanese eels was examined.3. The eDNA of Japanese eels was detected at 56 (91.8%) of the 61 study sites from which individuals were collected by electrofishing, and at an additional 35 sites where individuals were not directly collected. This indicates that eDNA analysis has a greater sensitivity for detecting the presence of eels, making it a powerful tool for monitoring the spatial distribution of anguillid eels in rivers. 4. A significant, but weak, positive relationship between the eDNA concentration and the abundance and biomass of Japanese eels was also found, suggesting that eDNA analysis may be useful for estimating the abundance and biomass of anguillid eels in rivers. 5. This is the first study to demonstrate the potential usefulness of eDNA analysis for estimating the spatial distribution, abundance, and biomass of Japanese eels in rivers. eDNA analysis will allow anguillid eel populations to be monitored over large spatial and temporal scales using a consistent protocol, with reduced time and effort compared with conventional techniques, providing invaluable information for managing populations of these endangered species.

Silver nanoclusters have attracted scientific interest due to their properties and applications. However, practical synthetic methods to access these materials are still limited mainly due to the low stability. Here, we report a controlled assembly strategy for fabricating atomically precise silver nanoclusters using polyoxometalates (POMs) as structure-directing as well as functionalizing units. A trefoil-propeller-shaped {Ag27}17+ nanocluster was synthesized by assembling reactive nanoclusters supported by open-Dawson-type POMs [Si2W18O66]16–. The {Ag27}17+ nanocluster possessed 10 delocalized valence electrons and showed unprecedented ultrastability in solutions. The cluster showed unique {Ag27}-to-POM charge transfer bands in the visible light region.

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Japanese eels (Anguilla japonica) perform large-scale oceanic migrations between their spawning ground and growth habitats in continental waters during life history.However, between these migrations, they spend most of time in growth habitats such as rivers. To investigate the diel and seasonal activities, homing behaviour and home range of yellow-phase Japanese eels in the lower reach of the Tone River, we tracked them throughout a year using a fine-scale positioning system (VPS) based on acoustic telemetry. The tracked eels were generally nocturnal, but not exclusively. They were mainly mobile from spring to autumn, with little or no activity observed during winter.A transport-release experiment showed that most eels returned to their original capture area within 13 days after release. The eels had very small home ranges (mean ± S D = 0.085 ± 0.068 km 2 ), core areas (0.014 ± 0.014 km 2 ) and linear home ranges (744 ± 268 m). They also tended to be distributed on one particular side of the river (right or left bank) and in one particular shore type (revetment or vegetation), rarely moving from one to the other. This study provides evidence for nocturnal, dormancy, homing behaviours, limited habitat use and small home range size in Japanese eels.The eels clearly showed strong fidelity to a "familiar" site, which contrasts with the long distances travelled during upstream and downstream migration phases in the river, and during spawning migrations in the ocean. K E Y W O R D Sacoustic telemetry, Anguilla japonica, dormancy, home range, homing behaviour, VR2WPositioning System