We investigated the growth potential of the freshwater plant Vallisneria asiatica Miki in Lake Togo-ike, a brackish lake that was shown to have reduced biodiversity in a study focusing on salinity and light, which are important aspects of the growing environment for aquatic plants. Based on the results of a one-year salinity study that began in April 2016, it was revealed that growth was possible at 6.98 PSU, which exceeds the previously reported upper limit of salinity. Furthermore, based on the average annual transparency in Lake Togo-ike in 2016, it was estimated that Vallisneria asiatica Miki can grow at water depths of up to 1.5 m. With these conditions, areas of Lake Togo-ike that are suitable for the growth of Vallisneria asiatica Miki were extracted from a salinity distribution map and a topographic map of the lake bottom. The northeastern and western inlets, which satisfied both conditions, were selected as areas with high growth potential. It was suggested that these areas, which have both low salinity and a shallow water depth throughout the year, would be important sites for the conservation of this species.

The habitat environment over winter for the female signal crayfish carried eggs with radio transmitters was investigated by using a mark-recapture method in a small river on Bihoro, Hokkaido. This kind of information could make increasing the efficiency of the disinfestation of the invaded signal crayfish if the female carried eggs gathered over winter and disinfested intensively. At the same time, we developed the method to identify the area of the radio source by piloting the drone with a radio receiver over the river, i.e., drone telemetry. Three crayfishes with radio transmitters were released in October 2017, and the habitats over winter for all three crayfishes were pinpointed and recaptured in December 2017. All crayfishes were found in the soil under 60-90 cm away 1-2 m from the riverbank in meandering sections. The environment of habitat over winter was considered to spread throughout the flood channel such inter meandering section. Therefore, it seemed to be practically impossible that we would capture the female lobsters carried eggs in winter, intensively. On the other hand, certain methods of the radio wave source with a drone been shown that there were also effective in soil and water, were expected future applications.

In the northern snowy region of Japan, chloride deicers, which are mainly composed of NaCl, are widely used to prevent road surfaces from freezing. Large amounts of the scattered chlorides accumulate at snow disposal sites and flow into streams with snowmelt runoff. Here, we studied how the snowmelt runoff affects stream water quality and organisms in Sapporo, Japan. We measured water quality at the outlet of snow disposal and adjacent stream, both at upstream （control） and downstream （impact） reaches of the outlet, for several sites. We also collected benthic algae and macroinvertebrates at both stream reaches. The results showed that the concentrations of Na^＋ and Cl^－ in runoff water were 2-9 times higher than those in stream water during the early snowmelt period （March）. Additionally, the concentrations of both ions in the stream water were higher in impact reaches than in control reaches, although the differences were relatively low （average ± S.D.＝1.56 ±1.27 mg L^－1 for Na^＋ and 3.05 ± 2.74 mg L^－1 for Cl^－）. For instream organisms, abundance of Trichoptera, total abundance of EPT （Ephemeroptera, Plecoptera, Trichoptera） and relative abundance of EPT to total macroinvertebrates were lower in impact reaches than in control reaches and decreased over the snowmelt period. To conserve stream ecosystems, we need to mitigate the impacts on stream water quality and organisms by preventing direct inflow of snowmelt runoff water.

The purpose of this study was to describe the particle size composition of spawning gravel of ayu （Plecoglossus altivelis） in 10 rivers flowing into Lake Biwa. We sampled surface gravel of their spawning ground （loose-stone riffles） near the mouth （＜2 km from the mouth） of each river, and examined particle size distribution of the gravel. The average and median values of the particle size ranged from 5.2 to 28.4 mm and 4.8 to 28.1 mm, respectively, with the percentage of particles ＜32 mm being 57-100%. These results were generally consistent with previous reports on characteristics of spawning habitat of ayu. However, the particle size in five study rivers on the eastern side of the lake was larger, which may be related with recent concern that spawning habitat of ayu is degrading in those rivers.

We investigated a river section where spring water can be seen, the Katsura-gawa River of the Yodo-gawa River System (Kameoka-si, Kyoto-fu) and the Kuto-gawa River of the Kishida-gawa River System (Shin-onsen-cho, Mikata-gun, Hyogo-ken), as survey targets. Visible light and thermal infrared ortho-mosaic images were obtained using UAV （Unmanned Aerial Vehicles）. Based on the results of the field survey and visual interpretation of the ortho-mosaic images, we determined the distribution of aquatic plants. The thermal infrared ortho-mosaic images with high spatial resolution enabled us to determine the distribution of water surface temperatures. The distribution of water surface temperatures was spatially heterogeneous. Analysis of the relationship between the water surface temperature and the distribution of aquatic plants revealed that the water surface temperature of the distribution patch was significantly higher for alien species than for native species. In addition, the water surface temperature of the distribution patch was found to be significantly lower for endangered species, such as Sparganium japonicum and Ranunculus nipponicus than for other species. Application of thermal infrared ortho-mosaic images to the analysis of river ecosystems, as well as aquatic plants, is a potential method of revealing new relationships between organisms and water temperature. This study presents the possibility of applying thermal infrared ortho-mosaic images acquired by UAV to river ecosystem analysis.

The life cycle of the Tokyo Daruma pond frog (Pelophylax porosus porosus) has been comprehensively studied over time; however, there is still disagreement regarding its hibernation behavior. Here, we investigated the hibernation sites of the frog using passive integrated transponder (PIT) tagging, which is a radio-frequency identification tag technology. First, we examined the suitability of PIT tagging for this species by (1) determining the effect of the tags on frogs and (2) testing our ability to locate tagged frogs hibernating underground. We performed controlled laboratory experiments to compare survival rates between tagged and untagged frogs and found no effect on survival rate or body weight. Next, using an HPR Plus reader and BP Plus portable antenna, we determined that the maximum depth at which the PIT tags (BIO12B) could be detected underground was 20 cm. In addition, we used the PIT tag system to detect hibernating individuals in paddy fields and found that (1) the main hibernation site of the Tokyo Daruma pond frog is cultivated fields, and (2) the frogs hibernate at a depth of approximately 18 cm underground. This investigation was a case study, and further analysis is required to determine hibernation sites for this species.