The objective of this study is to understand the characteristics of fish assemblages in the boat slips of two fishing ports. We obtained fish samples from 39 sites, including two fishing ports on the 150-km coastline of northwestern Kyushu, Japan. Cluster analyses and nonparametric multiple comparison reveal that the boat slips contain many species of immature fish in large numbers. In contrast, they contain adult fish of far fewer species in smaller numbers. Therefore, we conclude that the boat slips potentially serve an ecological function as nursery grounds for immature fish. On the other hand, they may be unsuitable for sustaining adult fish.

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River environments must be managed appropriately if we are to take a strategic approach to river rehabilitation. For appropriate management we often need to use river environmental information that was collected a long time ago. There is an increasing need for support systems to help us use this information, but most of the acquisition and recording of environmental information still depend on analog data or qualitative information, including photographs, maps, or the memories of elderly long-term inhabitants of the area. Meanwhile, the development of electronic information-gathering techniques has progressed rapidly in recent years. Environmental information is now being acquired digitally - for example, by the use of GPS to take positional information on living organisms or laser profiling to gather terrain information. We used both analog and digital data to establish a connection between environmental conditions - especially hydrological ones - and the presence of the native damselfly Mortonagrion hirosei Asahina and various plants. We found that the bulk of the larvae (57%) were present at points with cumulative inundation times of 1 to 500h, 1% to 9% inundation probabilities, and a Y. P. range of 0.2 to 0.6 m. Our results suggested that the best landform conditions for the exit of many larvae were based on the connectivity of water and soil flow with soil deposits by plants. Interestingly, the optimum ecological performance of the larvae differed from that of the population of the common reed Phragmites australis. In planning to manage river environments, if we can utilize both analog data and digital GIS data appropriately then we will be able to predict adequately the influences on river ecosystems and apply this information to monitoring after river rehabilitation.

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A simple model forecasting benthic community structure in estuarine tidal flats based on physical characteristics of sediment was proposed in this study. Monitoring data of the investigations conducted by Tokushima Prefecture in the Yoshino River was used to develop the present simple model. Physical characteristics of sediment such as particle size and difference in elevation were selected as the major factors forecasting benthic community structure. Relationships between physical characteristics of sediment and benthic community structure from the data for 5 years seemed to be enough for developing the simple model. Silt-clay content of sediment and difference in elevation could be classified into 5 to 6 groups in the present simple model. Those groups were also characterized by several specific benthic species. It meant that benthic community corresponded to sediment characteristics in the tidal flat. The integrated prediction accuracy of the model was 71 % at the maximum. It needed to compile for the monitoring data to develop the simple model at least 2 years judged from prediction accuracy.

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Water chemistry deterioration has become increasingly evident at mire pools with agricultural development occurring in pool catchment areas. Improvement of hydrochemical conditions is urgently necessary for the conservation of such mire pools' ecosystems. We investigated the hydrological and chemical budgets of Lake Miyajimanuma, a Ramsar Convention wetland, which is surrounded by paddy fields in Ishikari Peatland, northern Japan, during its ice-free period in 2007-2008. Surface water inflow and outflow via ditches dominate its hydrological budget, respectively constituting 88 % of total input and 78 % of total output. Similarly, chemical budgets including Ca²⁺, total nitrogen, and total phosphorus were dominated by ditch inflow and outflow. Chemical constituents of the ditch inflow were derived from mineral-rich and nutrient-rich river water supplied to paddy fields as irrigation water. Therefore, the input fluxes of Ca²⁺, total nitrogen, and total phosphorus were much greater than those of a pristine mire pool. Increased input fluxes of chemical constituents induced by irrigation changed the hydrological and chemical budgets of mire pools, which degraded the water chemistry through eutrophication and other processes.

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Microhabitat distribution of the Japanese mitten crab Eriocheir japonica was surveyed in May in the lower river reaches of Fukuoka Prefecture. Quadrat samples (50 cm X 50 cm) and environmental factors were measured at 24 and 36 points along the river course for nearly 50 m at 2 sites (Research 1), and at 75 points within 3 X 25 compartments separated by 1 m across and along the river course (Research 2). Carapace width (CW, mm) and crab density per stone relative to the stone coverage area (cm²) were investigated in October (Research 3). Crabs mostly with 4-10 mm CW exhibited aggregated distribution. In Research 2, crabs preferred a rapid environment (1-20 crabs / 0.25 m²) with shallow depth, high current velocity, and large grain size (5-15 cm deep, 40-70 cm / sec, and 4-50 mm [gravel] to 250-500 mm [large rock]) instead of a pool environment (0-5 crabs / 0.25 m²; 20-40 cm deep, 0-20 cm / sec, and < 0.125 mm [mud] to 0.125-1 mm [fine sand]). Crabs also preferred high stone coverage areas. However, high crab density (10-25 crabs / 0.25 m²) was found around the upper rapid and the lower pool boundaries, caused by positive rheotaxis and high locomotive activity of juvenile crabs. Thus, a natural river environment with repeated rapid-pool units is an important microhabitat for mitten crabs. There was no significant relationship between stone coverage area and CW, but crab density was positively correlated with stone coverage area. This suggested that gaps beneath large stones were utilized by a large number of crabs regardless of their size, and they opportunistically use the stones in the river. River-crossing structures such as weirs may facilitate aggregation of mitten crabs, but mitigation may be possible by increasing stone coverage in the pool area riverbeds.

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We examined spawning preference of the Arctic lamprey Lethenteron japonicum in order to establish an effective conservation measures for the critically endangered natural populations. Investigations were carried out in the Oshirarika River. The spatial distribution of spawning site was monitored by DGPS and environmental variables (current velocity, substrate composition and water depth) were measured at each spawning redds in 2005, 2006 and 2009. The generalized additive models (GAM) were employed to extract a determinant variable for presence / absence of spawning redds. The spawning redds were made at water depths between 35 and 60 cm, and current velocity between 25 and 70 cm/s, with cobbles of 10 cm in diameter according to field observation. Spatial distribution of spawning redds differed by each research year, but they tent to show aggregate distribution. Water depths were a significant factor to determine the location of spawning redds throughout the three years, but current velocity was the only significant in 2006. The GAM analysis demonstrated that critical environmental factors influencing on spawning redds of L.japonicum was water depth, especially with 35-50 cm depth. Since water level of Oshirarika River decreases rapidly from May to July after snow-melt (decreasing 25 cm in two weeks). Our results suggest an adaptive behavior that L.japonicum selects to spawn in medium water depth in order to prevent the depth of fertilized eggs by dry during water discharge decreasing periods.

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[in Japanese]

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[in Japanese]

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[in Japanese]

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To assess a fish habitat in a mountain stream, accurate estimation of the pool size is critical. We estimated the surface area (SA) and relative water volume (RWV) of pools by using photographs and simple field surveys. The utility of this method was validated by comparing the estimates with those obtained by conventional cross-sectional survey. Twenty-four pools (long axis: 1-7 m) in a step-pool channel with a slope of around 20 % were surveyed. Each pool was photographed using a digital camera affixed to the head of a 5-m-long staff. The deepest point of each pool was found and its depth measured. For each pool, the SA was estimated by analyzing the photograph and the RWV was estimated as the product of the SA and its maximum depth (photographic method). In addition, the SA and water volume (WV) of the pools were estimated by cross-sectional survey using four transects, each with five depth measurement points. A nearly proportional relationship was observed between the SA estimated by the two methods and between the RWV estimated by the photographic method and the WV estimated by cross-sectional survey. The effort per pool required for implementing the photographic method in the field was less than one-third or one-fourth of that required when using cross-sectional survey. In addition, the cover area available to the fish in a pool could be accurately measured by analyzing the photographs. Therefore, our proposed photographic method is useful for assessing the size of pools inhabited by fish in steep mountain streams.

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Although submerged vegetation is considered to be the most suitable refuge against predators and forms foraging habitats for small fishes, submerged plants are often scarce or lacking in turbid eutrophic lakes. To evaluate the emergent vegetation as refuge areas against predators and as foraging habitats for small fishes, we described the fauna and abundance of the fish community in Zizania latifolia and Typha angustifolia beds in a eutrophic shallow lake, Lake Teganuma, in Japan. Trophic status of fishes was estimated with carbon and nitrogen stable isotope ratios.The stems of Z.latifolia occupied an area more than two times larger than that of T.angustifolia. Fishes caught in both beds were all omnivores. Biomass of small fishes was comparatively larger in the Z. latifolia bed than in the T. angustifolia bed especially in June when juvenile fishes were found in both vegetations. The difference in fish habitation in Z. latifolia and T. angustifolia beds suggests that further studies are needed to assess the effect of plantation of emergent vegetation on the fish community.

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Spatial structures of 7 types of aquatic habitat at the reach scale were delineated using a high precision Global Position System (GPS) in 3 dam-impacted and 6 reference riverrine reaches in Miyagi Prefecture, Japan. Taxonomic and functional compositions of quantitative benthic invertebrate samples were also investigated. Out of the three dams, two indicated decreased levels of habitat diversity indexes (S, H', α, and E) at the outlet reaches due to reduced sediment supply and reduced hydraulic variation through dam-operation; but one dam connected to meandering outlet reach did not. Percentage of total area of lentic habitats (i.e., backwater and isolated pool) at the dam-impacted reaches (mean = 1.5 %) was significantly lower than reference reaches (mean = 5.5 %). The taxon richness, abundance of swimmers, predators, attachers and crawlers increased with the percentage of lentic habitat area (P < 0.05, n = 9), which suggests that lentic habitats contribute to maintain species diversity and the functional groups at the reach scale. Our data indicated a high application potential of the GPS-based evaluation of habitat structure for biodiversity conservation in rivers.

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