The effectiveness of construction of an artificial spawning channel to enhance white-spotted charr (Salvelinus leucomaenis) and masu salmon (Oncorhynchus masou masou) was examined in a channel (approximately 270 m long and 1 m wide) constructed below an erosion control dam, in the Gamata River, Jinzu River system, Gifu Prefecture from 2005 to 2007. Eight and 15 artificial spawning grounds were constructed in the channel in 2005 and 2006, respectively. As a result, multiple spawnings of the charr were observed at 4 of 8 grounds in 2005 and 8 of 15 grounds in 2006, respectively. The number of spawned eggs and the percentage of eyed eggs were 2503 and 90.0% in 2005. A lot of underyearling charr were observed in April of both 2006 and 2007. The growth, density, standing stock and survival rate of the underyearlings were studied from July to October in both years. The average fork length and body weight in October were 86.0 mm and 8.00 g for the 2005 year-class and 80.2 mm and 6.31 g for the 2006 year-class, respectively. The density and standing stock in October were 0.29 fish/m² and 2.32 g/m² for the 2005 year-class and 0.75 fish/m² and 4.73 g/m² for the 2006 year-class, respectively. The survival rate of the 2005 year-class was 3.2% from the spawned eggs to the underyearlings of October. The underyearlings were observed near the spawning redds in April, after that they dispersed throughout the channel. No spawning of masu salmon was observed throughout the channel in both years. The results suggest that the construction of artificial spawning channel is effective for the enhancement of white-spotted charr.

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Before the first infilling of Miharu Dam reservoir, a community of vulnerable species, Adonis ramose, was found in 1996 on a slope that was supposed to be submerged by the first filling of the dam reservoir. The main area of A. ramose community was in an area between the normal water level of the reservoir and surcharge water level. Elevation difference of two levels was 7 m. It was obvious that A. ramose community will be submerged in the reservoir during the first filling. For the conservation purpose, we transplanted the most of A. ramose individuals to another place before the first filling. However, for the examination purpose, we left a part of the community and tracked it. To examine the influence of the submergence, quadrates of the belt transect were set along the slope including both submerged area and non-submerged. We have specially focused on A. ramose individuals in the quadrates and tracked their growth for 12 years since 1996 of which 2 years are the pre-first filling and 10 years are the post-first filling respectively. 106 blooming individuals were observed in the pre-first filling period. In the first spring of post-first filling, no blooming individual was observed in the area once submerged and 3 individuals were observed in the area not submerged. However, the number of A. ramose recovered to 28 individuals in the 9th year of the post-first filling and to 46 individuals in the 10th year. Within the submerged area, no A. ramose individuals has been observed in the area which was submerged for more than 21 days, and we inferred that all individuals were dead or not germinated. Some individuals, which were submerged for less than 21 days, survived but did not bloom in the next year.

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The density and species composition of the propagule bank in lake-bottom sediment collected from 12 sites near the shore of Lake Kasumigaura, Japan, were analyzed using the seedling emergence method under wet and inundated conditions. In total, 92 species of macrophytes (vascular plants and charophytes), including 15 endangered or vulnerable plants and 15 native submerged plants that had disappeared from the aboveground vegetation of the lake, were recorded. The values of the Sørensen's quotient of similarity between the species composition in the propagule bank of each site and the aboveground vegetation remaining nearby the site were low (0-13%). Analyses of the factors affecting species richness of indigenous aquatic and helophytic plants revealed a significant negative effect of the average diameter of the sediment particle. The species richness and the propagule density of the indigenous submerged plants were significantly positively affected by the area of the submerged vegetation in 1970s. These results show that the location of past vegetation and particle size composition of sediments may provide clues to finding speciesrich and high-density propagule banks that are useful for restoration of lakeshore vegetation around a lake.

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A re-meandering project was implemented for the stream eco-system restoration of the Shibetsu River, Hokkaido Island, the northern part of Japan. It has been well known that the alteration of planview has an influence on stream structure such as pools and riffles, but there is only a little knowledge about changes in the energy flow of stream ecosystems. The present study evaluated the alteration of primary production rate brought by the re-meandering project comparing a re-meandering section with an upstream straight section. The single station diel O₂ curve method and the light and dark bottle method were applied for the measurement of primary production rate, and both methods indicated that primary production rate was higher in the re-meandering section than the straight section. The analysis of factors determining primary production rate showed that the standing crop of epilithic algae was lower in the straight section than the re-meandering section. The field observation gave the different view of lateral distribution of bedload transport between two sections: bedload transport in the straight section was considerably uniform across the channel, whereas it was heterogeneous and the transport was limited to the small area of the re-meandering section. Previous studies show that bedload distribution tends to be skewed in curved channels and the frequent collision of bedload particles with substrate leads to the standing crop reduction of epilithic algae. From these findings, we concluded that infrequent dislodgement of epilithic algae induced by the re-meandering treatment with small bedload area resulted to the high standing crop and it enhanced the primary production rate of the re-meandering section.

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[in Japanese]

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In March 2006, six spur dikes consisting of several sets of the wired boulders, were experimentally placed to restore gravelbed in a 50-m bedrock outcrop reach of the Makomanai River, central Hokkaido, northern Japan. The study purposes were to examine the influence of bedrock outcrop on summer habitats of wrinklehead sculpin (Cottus nozawae) and masu salmon (Oncorhynchus masou), and spawning habitat of masu salmon returning from ocean. The effects of spur dikes on habitat improvement were also examined. We set three sections representing gravelbed (reference), bedrock (control) and experiment (treatment), and investigated physical habitat variables, fish density and the number of masu salmon redd from July to October 2007. In the bedrock section, areal percentage of gravelbed was distinctly lower than that in the gravelbed section. Sculpin abundance and the number of redd were also lower in the bedrock section than in the gravelbed section. In the experiment section, abundance of small-sized sculpin (<90 mm) and the number of redd were similar to those in the gravelbed section, owing to an increase of gravel-pebble (2-64 mm) area in the experiment section facilitated by the spur dikes. Abundance of large-sized sculpin (≥90 mm) in the experiment section was lower than that in the gravelbed section because area of cobble-boulder (>64 mm) suitable for large-sized sculpin habitat did not significantly increase in the experiment section. These results suggested that the rehabilitation measures using the spur dikes foster the accumulation of medium-sized bed materials and accordingly improve fish habitat in bedrock rivers. Gravelbed is essential habitat component not only for anadromous fish but also for benthic fish at various stages of their life histories. We believe that restoration of sediment balance in a catchment is a fundamental measure to preserve gravel bed rivers.

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