We examined utility of hydraulic flow patterns, subcritical flow, supercritical flow and hydraulic jump for the classification of benthic macroinvertebrates habitats. The measurement of hydraulic parameters and quantitative sampling of benthic macroinvertebrates on stones were conducted in the step-pool reaches of Gunbetsu River in Hokkaido, Japan. Velocities near stone surface differed among the three flow patterns. The abundance of benthic macroinvertebrates on stones was significantly explained with the flow patterns for 75% of dominant species, including mayflies and a caddisfly. The hydraulic flow pattern better explained the abundance on stones for many species than maximum and minimum velocities near stone surface. Our results indicate that the classification of hydraulic flow patterns is useful to understand of macroinverterbrates habitats in step-pool streams.

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The purpose of this study is to verify the validity of the habitat assessment based on physical environments using biological community data in middle reaches of the Shibetsu River, eastern Hokkaido, Japan. We surveyed biological assemblages (fish, benthic invertebrates, terrestrial plants and birds) at 16 sites in the study reaches and examined relationships between the physical assessment results (DDR: the degree of departure in physical conditions from reference sites) and biological data: 1) abundance or diversity of species that are typical in pristine environment of the study reaches and 2) community compositions. The community compositions were analyzed by the Detrended Correspondence Analysis (DCA) ordination. Abundances of the typical fish and plant species were high in the sites that were evaluated as ‘good’ by the physical habitat assessment, whereas they were low in those as ‘degraded’. The first axis of DCA showed a gradient in species composition reflecting anthropogenic influences and correlated with DDR and many physical variables in fish, benthic invertebrate and terrestrial plant communities. The main DCA axes showed no relationship with DDR and few relationships with physical variables in bird communities. Our results showed that the habitat assessment method using the degree of departure in physical conditions from reference sites was an effective tool for comprehensive river habitat assessment.

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The material cycling in the Yoshino River with many dams was investigated on the basis of measuring bio-elemental concentrations, carbon and nitrogen stable isotope ratios. In the main river, there were not large differences in water quality between the upstream and just the downstream of these dams. The nitrogen concentration increased in the middle to the downstream of the main river, where human activity in the river basin increased. δ¹⁵N of the river sediment also increased with the increase of the nitrogen concentration. These results indicated that the nitrogen loading by the human activity in the river basin was the main cause to increase the nitrogen concentration in river water. But, organic substance in the river sediment did not increase, and therefore the material load by the human activity did not accumulate in the river. However, judging from high δ¹⁵N, it seemed that the nitrogen load to the Yoshino River was close to an upper limit of its ecosystem capacity. On the other hand, in the downstream of the Dozan river where its main stream was dammed up by a series of dams, the concentration of organic substance, δ¹³C and δ¹⁵N were high, and therefore the progress in eutrophication was found in the river bed. The water resource exploited by these dams is usually sent to the next basin and the downstream of the Dozan River has only a small amount of water flow, and it may have promoted its eutrophication by increasing the concentration of organic matter and nitrogen.

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[in Japanese]

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We developed habitat evaluation models for raccoon dogs (Nyctereutes procyonoides) using radio-tracking data and applied the multivariate models for impact assessment of a dam construction in Northern Tochigi, Japan. Raccoon dogs are common species and have been ignored in impact assessments as they were thought to be able to move to suitable habitat near construction sites. We found that raccoon dogs may suffer from both decreased suitable habitat and losing its connectivity after construction. Such models enable to detect habitat deterioration and fragmentation areas quantitatively with visualization, and such information can be used for effective conservation planning.

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[in Japanese]

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Bluegill sunfish Lepomis macrochirus is an alien species introduced from North America in 1960, and currently widespread over Japan. It is designated as an invasive fish by which many domestic aquatic animals are threatened. Every effort to exterminate the populations of L. macrochirus has been continued, since 1998, in Mizorogaike Pond at northern Kyoto City, where the whole biological community has been protected as a natural monument of Japan. Capturing individuals (since 1998) and destroying spawning redds (since 2002) greatly decreased the population size in the pond: the estimated population size in 2005 was about one tenth of 1998. In that regard, we evaluate the changes in genetic structure caused by this rapid reduction of population size by using microsatellite polymorphisms. A microsatellite BG6X locus has shown that the genetic structure of the Mizorogaike population of 2006 was in Hardy-Weinberg equilibrium, but that of 2007 deviated from the equilibrium. Also, allelic richness decreased in 2007. According to the size frequency distribution, the specimens from Mizorogaike in 2006 were expected to have been born in the years of 2003 or earlier, while those of Mizorogaike in 2007 were expected to have been born in 2003-2005 when the destruction of spawning redds had been successfully performed. The results suggest that the majority of the Mizorogaike population in 2007 were originated from the small number of spawning redds that were escaped from the population control, and it caused the deviation from Hardy-Weinberg equilibrium.

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