Myocastor coypus is a mammal designated as invasive alien species. Intrusion prevention and control of this species is desired from both ecological conservation and river management. In this study, we determined the distribution of this species by using eDNA analysis in broad area of Yamaguchi prefecture and we estimated the potential habitat by using GIS and maximum entropy modeling （Maxent）. These results showed that the distribution of M. coypus has already expanded in wide areas in Yamaguchi prefecture and there is a risk of invasion and colonization in the middle and lower stream of the rivers regardless of watershed characteristics.

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The purpose of this study was assess the ability of frogs to escape from agricultural concrete channels. The escape capabilities of four frog species from vertical concrete wall surfaces of different abrasive characteristics (＂abration degrees＂) were examined in a laboratory. The arithmetical mean roughness index (Ra) was used as a criterion for measuring the abration degree of the wall surfaces. Walls with Ra values of 0.23, 0.28, 0.55, and 1.23 were used for laboratory tests. More than 7.5％ of the individuals (comprising the Indian rice frog, Fejervarya kawamurai and the black spotted pond frog, Pelophylax nigromaculatus) escaped from the four experimental devices. The wrinkled frog, Glandirana rugosa escaped from the three experimental devices of abration degree values of Ra 0.28, 0.55, and 1.23. The daruma pond frog, Pelophylax porosa brevipodus only escaped from the device of abrasion degree value of Ra 1.23 at low rate (12.5％ of the individuals). We proposed that P. porosus brevipodus should be regarded as an indicator for frog escape tendencies from concrete channels. If such a standard is adopted, it will be necessary to take coutermesasures in channel walls with Ra vaule 1.23. These criteria would be applicable to drainage basins with orthogonal walls or a type of channel in which channel branches project from the sides of the stream (referred to as Water Channel Fabricated I.). Because, every species showed a preference for routes containing ＂corners＂(i.e., ＂surface where two walls come together at an angle＂) it was assumed that climbing would be very difficult in a channel with a flat wall surface. These results suggested that measures should to be taken to create escapable conditions in such channels.

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We surveyed fish communities and environmental characteristics above and below the weir set in the lowest reaches of each four rivers in northern region of Ibaraki Prefecture in August of 2014. Of 16 fish species captured, seven were diadromous fishes, seven were freshwater fishes, and two were peripheral fish species. Diversity index (H') of fishes above weirs was significantly lower than those of below weirs in case for total fishes and diadromous fishes. The best model of GLM based on AIC indicated that presence of weir had a negative significant effect on diversity index in case for total fishes and diadromous fishes. The parameters (slope of standardized partial regression coefficient) incorporated with best GLM model to account for population number of diadromous fish species are: water depths (+) , current velocities (-) , height of weir (-) , and area of study site as an offset for Plecoglossus altivelis altivelis; presence of weir (+) , water depths (+) , and height of weir (-) for Gymnogobius petschiliensis; presence of weir (-) , water depths (+) , and current velocities (+) for Rhinogobius nagoyae; presence of weir (-) , current velocities (-) , height of weir (+) , and area of study site as an offset for Cottus reinii. Bray-Curtis dissimilarity index (BC_d) of fish species composition between any possible combinations of study sites positively correlated with Euclidian distance based on two environmental characteristics (mean water depths and current velocities) in case for total fishes and diadromous fishes, and Pearson?s correlation coefficient was highly significant for diadromous fishes. These results suggest that remarkable decline in diversity and population number of diadromous fishes above weirs would stem from not only inhibition of upstream migration by weirs, but also weir-induced anthropogenic modification of instream habitat features for diadromous fishes.

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[in Japanese]

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In eutrophied lakes, water pollution and degradation of biodiversity are caused by the overgrowth of lotus (Nelumbo nucifera). For this reason, lotus management activities, such as mowing, have been conducted in several lakes. To develop an effective method to control lotus plants, the influence of mowing on their survival was evaluated in a test pond adjacent to Lake Izunuma-Uchinuma in Japan. Leaves of twenty-two ramets of lotuses, each with 2-36 leaves, were cut at 40 cm under the water surface. Of these leaf-bearingramets of lotuses, eight (36.4%) were dead. The mean number of leaves of the dead lotus ramets before cutting (4.5±0.8 leaves) was less than half the number of leaves of the surviving lotus ramets (11.9±2.8 leaves). However, cutting the leaves of 11 ramets oflotuses prevented the growth of new leaves on the water surface within three days, after which all lotuses died regardless of the number of leaves the ramets had before cutting. These results suggest that the emergence of leaves is an important factor determininglotus survival. Therefore, it is suggested that repeatedly cutting lotus ramets when they have fewer leaves is an effective method to control lotus plants.

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Vertical distribution of masu salmon, Oncorhynchus masou masou, during high flow was investigated by using the archival tags in a large pool (ca. 70 m long, ca. 150 m wide and Max. 13.7 m depth) just below the Jin-san Dam in the Jinzu River in 2009. The masu salmon, resided in the surface layer （ca. 1.0 m below the surface） under low flow conditions, moved to a deeper layer while repeating up-and-down movement with the increase in flow. It is supposed that the masu salmon took refuge in the middle layer （2-4 m）of weak current near the river bank aside to avoid surface and bottom of center layers (5-14 m) of rapid current when the flow has increased to the maximum level. And the masu salmon moved to a shallower layer again while repeating up-and-down movement with the decrease in flow. After the flow came to an ordinary level, masu salmon returned back to the surface layer. These results suggest that deep pools, having a variety of spaces ideal for creating weak currents, play an important role as refuge in case of high flow.

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A simple method was developed to estimate longitudinal profiles of ordinary water level using existing gauging station data and its estimation accuracy was verified by comparison with observed values for the Shonai River, Japan. First in this new method, a longitudinal profile of ＂reference riverbed elevation＂ is created using riverbed elevation data, periodically measured by the river manager. Second, the longitudinal profile of ordinary water level is estimated using the reference riverbed elevation and gauging station water levels. Overall, the estimation accuracy of our method was high. Our new estimations showed higher accuracy than the linear interpolations in the all river segment types (M, 1, 2-1, and 2-2). Our new estimations showed higher accuracy than the uniform flow estimations with simplified roughness coefficients and slopes in the 2-1 and 2-2 segments, and showed similar accuracy to the uniform flow estimations in the M and 1 segments.

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