We carried out an ecological and civil-engineering study on nest site selection of the three sympatric species of plovers, Charadrius dubius, C. placidus and C. alexandrinus on a flood-bed of the Kizu-river flowing through Kyoto Prefecture, Japan. The viewpoint of hydro-physics and animal ecology are applied and substrate size-sorting during the annual flood plays an important role here. We divided substrate size class around the plover nest site into six categories. C. alexandrinus, which generally nest on seacoast, significantly preferred fine texture “sand.” C. placidus and C. dubius significantly preferred larger texture “pebbles.” C. placidus tended to nest on larger substrate than C. dubius, although this difference was not significant. We discuss the physical mechanism driving the substrate distribution pattern on the sandbar, and suggest that flood-out is necessary for forming and maintaining the breeding habitat and coexistence of the three species of plovers.

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The environmental factors influencing the abundance of fluvial larvae of the lamprey Lethenteron japonicum was studied in a tributary of the Ishikari River, central Hokkaido, Japan. We also conducted their food requirements by laboratory rearing experiment. The abundance of larvae and environmental parameters (Water temperature, Water depth, Water velocity, pH, Dissolved oxygen, Conductivity, Turbidity, Substrate hardness) were measured in one-meter-square quadrats. The larvae were captured using an electro-fisher and separated into two size classes (1-5 cm and 5-15 cm). The relationships between abundance and environmental factors were analyzed using generalized linear mixed models for each size class. The environmental factors that predicted the patterns of abundance of the two sizes of larvae differed for each size class. The abundance of larvae in the large size class was positively correlated with substrate hardness and dissolved organic matter (DOM), while that of the small size class was positively associated with substrate hardness, substrate composition (Silt), and current velocity. Sub-yearling larvae were also collected and reared for two months in the laboratory to observe their feeding preference by adding different foods. Their food uptake ratio was determined using stable isotope analysis. By the rearing experiment, the larvae which were given fallen leaves had significantly greater increases in wet mass and body length, as compared to the larvae which were given algae. The stable isotope analysis indicated that the larvae can take up nutrients from fallen leaves. We concluded that lamprey larvae change their habitat requirements with growth stage, and fine substrate containing fine organic matter is a significant microhabitat for fluvial larvae lamprey.

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Reintroduction of endangered or extinct species is becoming major restration activities for conservation of biodiversity and ecosystems. The crested ibis (Nipponia nippon), once extinct in Japan, was released into natural environment on Sado Island, Japan, in September 2008. Since orthopteran insects are thought to be one of the major prey for the crested ibis, it is important to clarify the factors influencing the distribution and abundance of orthopterans. We investigated abundance of five orthopterans (Oxya yezoensis, Atractomorpha lata, Conocephalus maculatus, Ruspolia lineosa and Teleogryllus emma) on Sado Island in September 2008. Local-scale environmental factors including grass-height and land-use type (arable or fallow) were recorded in the field. Landscape-scale factors such as proportion of paddy fields and total length of forest edge in the buffer circle surrounding the paddy fields were extracted using GIS. Various sizes of buffer circles were generated around each paddy to identify appropriate spatial scales. Model selection was performed with a generalized linear model using the AIC to find the best model for accounting for the abundance or the probability of occurrence of these species. Landscape factors were important for all species except A. lata. The proportion of paddy fields had a significant positive effect on the abundance of O. yezoensis which was conspicuously dominant. The interaction between the proportion of paddy fields and the length of forest edge had a significant effect on C. maculatus and T. emma. At the local scale, intermediate grass-height enhanced the abundance of O. yezoensis and C. maculatus and the occurrence of R. lineosa, and fallow fields were the suitable habitats for T. emma. Our results suggest that maintaining lowland paddy fields containing fallows and reducing the frequency of mowing surrounding paddy fields are effective for increasing the orthopteran abundance and diversity in the paddy-dominated ecosystems.

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We examined spawning condition of the Ryukyu-ayu Plecoglossus altivelis ryukyuensis which is endangered through habitat destruction and decreasing population size and harbored in the Amami-oshima Island in order to contribute to making an effective conservation program. Investigations were carried out in the Yakugachi River which provides the largest habitat for the subspecies, and their eggs attached to substrates occurred only in a reach at 2.4 km away from the river mouth. The principal component analysis which was conducted for environmental variables including water depth, flow velocity, substrate size and silt sedimentation drew the property of spawning site on a transitional zone between riffle and run. The logistic regression analysis conducted for the environmental variables around the spawning site factored out the substratum adhesion as a determinant variable to explain presence/absence of spawning ground. A lot of net-spinning caddis larvae were observed in the spawning site of the Ryukyu-ayu, which has a potential to prevent the fish from spawning because of their substratum adhesion. As for water depth and flow velocity no other reaches within the Yakugachi River satisfied the preferable conditions for spawning, and likewise spawning sites were not realized in the neighboring small stream, the Yanma River, in which the Ryukyu-ayu sometimes establishes inconsistent population. The Yakugachi River population of the Ryukyu-ayu has a role to be a donor within a meta-population structure and therefore should be given priority of conservation. In conclusion, the restoration of spawning site is effective to avoid the risk of local extinction. Cultivation of streambed by handworks using shovels and hoes is practical and recommended from the view point of cost performance.

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We tracked eight matured chum salmons (Oncorhynchus keta) using acoustic and radio telemetry to understand their upriver migration around ca. 120 to 180 km site starting from the mouth of the Ishikari River in autumn 2002-2004. This study area was divided into the natural levee area, the gorge area, and the basin area including the past major spawning sites until ca. 1940s. Three tagged fish reached to the basin area, and two fish reached to the natural levee area. The maximum duration of the upstream migrationwas 17 days, and the maximum migration distance was 56 km. Mean migration speed in the basin area was 6.6 km/day, where the staying behavior was frequently observed, was approximately three times slower than those of the natural levee area (19.5 km/day) and the gorge area (14.8 km/day). The basin area had better conditions of substrates, depth, flow velocity and subsurface flows for O. keta spawning than the other areas. In addition, groundwater upwelling for egg survival and hatching occurs adequately in the basin area. Their migration patterns reflected geographical differences among three areas. Therefore, the observed slower migration in the basin area was probably due to their pre-spawning behaviors including searching for spawning sites and mates. The faster migration in the natural levee area and gorge areas was due to utilization of these areas as corridors.

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[in Japanese]

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[in Japanese]

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