Despite of the importance of floodplain waterbodies for biodiversity and ecosystem services, human activities have degraded their quality as habitat for biological communities. Detailed understanding of life-history traits and population dynamics of organisms is crucial to the development and realization of effective management practices for the conservation of biodiversity. This study examined the distribution, reproductive traits, and host-fish utilizations of Unionoid mussels in floodplain waterbodies of the Ishikari River, northern Japan, and highlighted challenges in ecosystem management. Three target species exhibited the differences in habitat preferences, with Anemina arcaeformis（Heude, 1877）being disproportionately most abundant in marsh-type waterbodies. Two species, Sinanodonta lauta Martens, 1877 and Unio douglasiae nipponensis Martens, 1877, were gravid in summer（July and August）while A. arcaeformis was more gravid in fall and winter（October and November）. The low abundances of immature small individuals and the absence of parasitic attachments of mussel larvae to field-collected fish suggested the reduced levels of recent recruitments. The proliferations of invasive fish species such as Rhodeus ocellatus ocellatus, which comprised 30―70% of the total abundances of fish and were not suitable as host for the parasitic larvae of mussels, might be a possible cause of poor recruitment rates. Recognition of the diversity of waterbody types as a driver of species diversity, continued monitoring of population sizes and further elucidations of habitat quality as well as other aspects of life-history processes will contribute to improved ecosystem-based management of floodplain waterbodies in the Ishikari River.

The time-series change of the community structure of aquatic insects were investigated using environmental DNA（eDNA）metabarcoding analysis and a conventional Surber net sampling method. Field sampling was conducted from May to December in 2016 once per month at 2 sites located middle domain of the Hirose River and the Natori River in the Natori river basin, Miyagi prefecture, Japan. DNA extracted from river water samples were processed in metabarcoding targeting the cytochrome oxidase subunit 1 gene in mitochondrial DNA, and 8 taxonomic orders of aquatic insects（Ephemeroptera, Plecoptera, Trichoptera, Diptera, Coleoptera, Odonata, Hemiptera）were detected through bioinformatics process. Collected insects by a surber-net sampling were identified morphologically at family level to compare with eDNA outputs. As a result, the member of taxa in communities were mostly composed by Ephemeroptera and Diptera families and the trend of time-series change of taxa richness were consistent between two methods. Furthermore, the taxa that many individuals were collected by a surber-net sampling tended to obtain a large number of sequence reads in eDNA analysis. In addition, community structures by relative abundance from eDNA metabarcoding and the conventional method showed the same transition pattern after a flood disturbance, i.e. the ratio of swimmers increased immediatelyafter the disturbance and the ratio of crawlers increased later. Our results showed that eDNA metabarcoding targeting aquatic insects can describe the time-series transition of the community structure using relative abundance based on the number of sequence reads even though taxa members and taxa richness were not same with a conventional sampling method.C

In order to conserve disturbance-dependent species on the floodplain, it is neces sary to make a conservation plan based on knowledge on the patch dynamics of species and their habitats. Approximately 6.3 km of Honme River, the secondary tributary of the Katsura River in the Yodogawa River system, was investigated. Aerial images obtained us ing unmanned aerial vehicles from 2016 through 2019 were utilized. Interpretation of these images allowed us to document the distribution of Euphorbia adenochlora, the submerging areas during flood events, and the area of vegetation loss caused by cutting the grass and open burning. Using the spatial analysis function of GIS, we analyzed the relationship be tween E. adenochlora and these disturbance elements, aggregated patch area of E. adenochlora. The total patch area of E. adenochlora decreased from 285 m² in 2016 to 236 m² in 2018, but it increased to 298 m² in 2019, exceeding the 2016 value. The increase in the total patch size in 2019 is attributed to both development of new as well as expansion of existing patches. Based on the results of our 4-year survey, it can be stated that the population of E. adenochlora in Honme River is sustainable. However, the data suggest that decreases in patch area are dependent on the frequency and magnitude of flooding, a natural disturbance that was found to occur on a 3-year cycle, as well as the extent of artificial dis turbances such as cutting the grass and open burning. In particular, cutting the grass was noted to occur on a yearly basis in early July. Suitable ranges for E. adenochlora were determined from the analysis results of these three disturbance elements. Thus, this study clarifies the patch dynamics of E. adenochlora over a 4-year period.

To clarify the absorbing state of the yolk of larval ayu immediately after emerging from the spawning bed to surface water, the yolk-index of ayu larvae hatched in the natural and artificial spawning grounds in the Nahari, Monobe and Shimanto Rivers were observed. Although the larval ayu caught below the artificial spawning ground（pebbles took from the sandbar were laid）in the Monobe River were judged to be emerging from the spawning beds just before being caught, the ratio of the yolk-index 2 which considerably absorbed yolk was high from 45 to 74%. This fact means that there are many individuals which take several days to emerge from the spawning beds after hatching. In fact, larvae with the index of 1-2, which had progressed yolk absorption, were collected from the riverbed in the spawning ground. On the other hand, below the artificial spawning ground（pebbles after sieving to remove sands were laid）in Nahari River, if most of the larvae collected were judged to be emerging from the spawning ground, indexes 3 and 4（a large amount of yolk remained）occupied 75%, which was significantly different from the yolk index of larvae from natural spawning grounds. The yolk index of the larval ayu of the natu- ral spawning ground of Shimanto River, where the riverbed condition was＂soft bed＂with many gaps between pebbles, reached nearly 75 % of the whole by indexes 4 and 3. At the artificial spawning ground in the Nahari River, where sands were removed, the time from hatching to emerge to surface water was short. At the natural spawning grounds where the percentage of sands were slightly higher, many ayu larvae took a long time to emerge. Therefore, it was suggested that when the proportion of sands in the spawning ground was high, the interstitial space of pebbles was closed and the emerging of larvae to surface water was delayed.

The ecology of far eastern catfish Silurus asotus is poorly known particularly in the early life stage. Passive integrated transponder（PIT）tags have been a successful tool to evaluate the ecology of endangered fishes such as a far eastern catfish with relatively large bodies（TL＞ca. 20 cm）. However, there is no study applying the PIT technique to small individuals of far eastern catfish. Here I provide a case study applying 12-mm PIT tags to the juvenile of far eastern catfish. To evaluate the effects of the 12-mm PIT tags implantation on juvenile far eastern catfish, I compare growth and survival among three experimental groups; control, surgery with no tag, and surgery with tag. After the 24 days observation, neither expulsion of the PIT tag, nor death of fish is found in every tagged individual, as well as no significant difference in the growth among the three experimental groups. Subsequently, I explore the efficiency of the PIT technique by tracking and locating tagged individuals in a small river named Yagawa, Tochigi prefecture, central Japan. A total of 21 far eastern catfishes, which were caught in the Yagawa river, were released after being tagged by the 12-mm PIT tags in the abdomens. A portable waterproof antenna is used to locate the position of tagged fish in the study section. Although the detectable dis- tance in the field is no more than 50 cm, 12 individuals were successfully traced with the PIT signals. The longest trace record is up to 300 days after release accomplished by two individuals. All these results indicate that the PIT implantation technique and the tracking survey in the field are effective to collecting the ecological information of far eastern catfish including juveniles.

Flashboards are set in the water outlets of paddy fields to manage water depth of the fields. Fish can enter paddy fields through the water outlets of the fields when water overflows due to rainfall and continuous irrigation. However, these flashboards often block fish migration. Therefore, we devised four types of migrating boards, namely, flat type, V-shape type, 5 mm guiding wall type, and 20 mm guiding wall type. These migrating boards cover the top of the flashboard and connect the water surfaces of paddy fields and the top pools of fishways. Upward migration tests on Carassius spp., Gnathopogon elongatus elongatus, Misgurnus anguillicaudatus, and Oryzias spp. were conducted using these boards. The highest number of fish migrated when using the 20 mm guiding wall type board. A total of 374 times of migration were observed for three of the four species; that is, migration was not observed for Oryzias spp., which was found to be unable to migrate probably due to the too strong currents for the species in these set-ups. The 20 mm guiding wall type migration board enabled smaller-sized fish to swim just inside the guiding wall and larger-sized fish to swim at the center of the guiding wall. Based on these observations, we concluded that the 20 mm guiding wall-type migrating board is the most effective in promoting fish migration.

Nationwide information on the area, location, and utilization of the flood-control reservoirs throughout Japan was collected by literature and web surveys for building database including 143 facilities. Furthermore, this study discussed whether the location characteristics of the flood-control reservoirs contribute to conserve original wetland ecosystem or not. The number of the facilities was the largest in Saitama prefecture, 37 facilities. Most of the flood-control reservoirs were located at plain, old river channel, or back marsh in geological types. It was revealed that 64 facilities is used as urban park, 31 facilities as sports ground, 17 facilities as paddy field, and 91 facilities as other or vacant areas (water surface or grass land). Eighty-eight percent of the facilities examined included a nature observation area, paddy field, or vacant areas, suggesting that they could contribute to the conservation of wetland ecosystems.

Prior to excavation work for a river dam, the Japan Water Agency built a cofferdam in the Maefukase River where the dam was to be built, to divert the river course through a diversion tunnel, in April 2018. As part of the diversion work, a 4-day study was conducted to capture and relocate the indigenous Andrias japonicus. The study captured 36 larvae less than 3 years old, which were hard to find in previous studies. It was learned that the larvae live under large rocks with flat bottoms and no gaps that could serve as a way in or out, along the river bank where are found the exposed roots of reeds and bamboo grass, therefore they were relocated to a similar habitat. The larvae were captured when the water level in the river was low, which confirmed the importance of draining the water prior to conducting surveys.

On July 5, 2017, record heavy rains occurred in Asakura City in Fukuoka Prefecture and Hita City in Oita Prefecture, causing serious damage to 41 dead and missing persons. In the event of a disaster, the Ecology and Civil Engineering Society formed a disaster investigation team consisting of members from various fields, such as ecology, river engineering, and topography. The purpose of this study team are to (1) evaluate the impact of large-scale disasters on ecosystems and local communities, (2) make recommendations for sustainable and better restoration based on the results of field surveys and previous knowledge of the Japan Society for Applied Ecological Engineering, (3) obtain physical and biological information immediately after the disaster and contributing to future research. This report describes the summary of the survey results and the contents of the recommendations.

The purpose of this research is to describe and evaluate an example of the impact of large-scale disasters on a fish fauna of rivers. In the northern part of Kyushu from July 5th to 6th, 2017, a heavy rain fell steeply into a specific area. Especially in Asakura city, Fukuoka, Japan there was a recordable heavy rain which resulted in major damage to roads, buildings and rivers. From July to December 2017, we conducted capture survey at eight sites and environmental DNA (eDNA) metabarcoding at 18 sites in the middle reach tributaries of right bank of Chikugo River system in Kyushu, Japan. In the capture survey, four species 470 individuals were found from eight sites, although fish were not captured at three of those sites. In an eDNA analysis, 21 species were detected from 18 sites, however fish eDNA was not amplified at seven of those sites. The fish fauna of capture survey and eDNA analysis coincided at seven out of eight sites, which showed the high accuracy of fish fauna detection by eDNA analysis in this study. Our result confirmed that this heavy rainfall devastated blow to the fish fauna of the rivers.