Shiro Sagawa

We studied the habitat status of fishes in a Tanaka retention pond (TRP) , which was expected to become a foraging site for oriental storks (Ciconia boyciana) in Japan. By comparing the distribution of a fish community in a lateral drainage channel (LDC) of a paddy field before (December 2018) and after (November and December 2019) flooding by Typhoon No. 19 (Hagibis) , we examined the problems and future policy considerations for fish habitats in the TRP during periods of normal water level. Before flooding, the numbers of taxa and individuals in the LDC were small, and some study sites were no fish. In the LDC, most fish species that have been observed in the main drainage channel (MDC) during the same season were not captured. After flooding, the number of fish taxa and individuals increased significantly in the LDC compared to those before flooding, and some fish species such as the Gnathopogon elongatus elongatus and the Oryzias sp., which were not observed before Hagibis, were captured. In addition, oriental weather loaches (Misgurnus anguillicaudatus) were captured from LDCs that were completely dry before the flood. According to the paddy field survey in May 2019 (before flooding) , only Misgurnus dabryanus, the invasive loach species, were observed to breed in the study paddy fields during the cropping season. Breeding abundance may have been impacted by low continuity to the LDC during baseflow conditions, as many fish species could not migrate to paddy fields during the cropping season nor overwinter sufficiently in the LDC during the non-cropping season. For improving the function of the TRP as a breeding and wintering habitat for fish during baseflow conditions, gaps between the MDC and the LDC and between the LDC and paddy fields must be connected, and a wintering habitat for fish must be secured by actively preserving the channel sections with soft mud and connecting them with the inter-levee floodplain water bodies. However, since these restorations may expand the distribution range of invasive species, our goal should be to conserve the continuity of healthy water bodies.

In Toyooka City, Hyogo Prefecture, fallow-field biotopes (hereinafter FFB) have been produced by flooding fallow fields throughout the year to maintain habitats for various aquatic plants and animals, including feeding habitats for the oriental stork Ciconia boyciana. In this study, specifically, we clarified the poorly understood habitat status of Odonata larvae, aquatic Hemiptera, aquatic Coleoptera, and frogs at the FFB. The effects of the FFB on the conservation of local aquatic animal communities were also evaluated by comparing habitat statuses in the FFB with those in the surrounding paddy fields and multitopes (i.e., earth ditches laid alongside the paddy fields). Results showed that many Odonata larvae inhabiting an irrigation pond were found in the FFB, while several peaks in the annual polyploidy of Odonata taxa were also observed. For many species of aquatic Coleoptera, larvae were less abundant in the FFB than in the surrounding paddy fields and side ditches; however, the number of adult taxa increased rapidly after August. In addition, the regal pond cruiser Epophthalmia elegans elegans, water stick-insect Ranatra chinensis, and diving beetle Eretes griseus were captured in the deep waterbody of the FFB in autumn. These results suggest that the FFB serves as a refuge and habitat in the nonbreeding season, and as a wintering site for a variety of aquatic insects; however, its function as a breeding site may not be as important as that of the paddy fields and multitopes, especially for aquatic Coleoptera. Nevertheless, the FFB is an important breeding site for some aquatic animals including the Japanese brown frog Rana japonica and annual polyphagous Odonata taxa. Overall, this study suggests that the coexistence of various water bodies, such as temporary paddy fields and side ditches, with year-round flooded biotopes effectively conserves the diversity of aquatic insects and frogs in the study region.

<p> An oriental white stork (Ciconia boyciana), which had been rescued after hatching in a nest on an electric pole in Shimane Prefecture, was released after hand rearing at Hyogo Park of the Oriental White Stork. However, the bird was found dead after 27 days in Tottori Prefecture. Necropsy revealed three pieces of foam rubber (840 mm in total length) in the bird's gizzard. This finding suggested that the bird was weakened and died because of the lack of digestion and absorption of food owing to the accidental ingestion of foam rubber. This is the first report of accidental ingestion of an artificial material causing death in the reintroduced population of oriental white storks in Japan.</p>

<p>To conserve paddy field fish communities and the foraging habitats of Oriental White Storks Ciconia boyciana, a wetland area connecting the Kamatani River to a fallow field biotope (paddy area) was created by means of fishways and a permanent deep water area within the biotope in Toyooka City, central Japan. This ecological network had the following positive effects on paddy field fish species: 1) Gnathopogon elongatus elongatus became more abundant in the upstream habitat following restoration; 2) G. elongatus elongatus and Carassius spp. reproduced for the first time in the biotope after restoration; 3) C. spp. and Misgurnus anguillicaudatus utilized the fishway to swim up to the biotope; 4) current-year juvenile G. elongatus elongatus, C. spp., and M. anguillicaudatus grew in the biotope, and 5) adults and juveniles overwintered in the biotope, and Oryzias sakaizumii especially assembled within the deep water area. After restoration, storks regularly visited the biotope to forage. Additionally, one pair nested near the biotope and fledged five young during the 2016–2017 breeding seasons. The young birds and their parents continued to forage frequently in the biotope. Thus, our results indicate that ecological networks for paddy field fish communities contribute greatly to the foraging and breeding habitats of reintroduced storks.</p>

<p>We investigated the number of individuals and biomass of aquatic animals as prey for the Oriental White Stork Ciconia boyciana in winter paddy fields in Tobadani, Wakasa Town, Fukui Prefecture. Analysis of the prey biomass revealed that the red swamp crayfish Procambarus clarkii was most abundant, followed by the oriental weather loach Misgurnus anguillicaudatus and Odonata larvae. It is known that storks generally prey on these taxa. Aquatic prey animals were more abundant in plowed paddy fields with a rough surface than in plowed fields with smooth surfaces or in unplowed fields. The results suggest that the temporary puddles made when plowing boggy paddy fields provide suitable habitats for these aquatic animals.</p>

This study examined freshwater mussel habitats in excavated flood-channels with reference to initial ground heights and years elapsed since the excavations in the lowland Ibi River in order to facilitate efficient management of inter-levee floodplains using flood- channel excavation work. Mussels were captured in ponds at excavation sites with different ground heights and at different years since the excavations. Time-series data of cumulative sediment depth and the amount of ponds in the sites were also obtained. In the sites with lower excavation heights （but higher than drought water level）, mussel abundance and the proportion of the pond occupied by the mussels were higher, and sediment depths and deposition rates were lower. Mussel abundance and the amount of ponds increased and then decreased with peaks of 5 and 6-9 years after the excavations, respectively, in the context of continuing sedimentation. These results suggest that flood-channel excavations should be strategically implemented so that low excavation sites with 5-9 years elapsed since excavation are always present somewhere in a target river segment.

The fish fauna of River Kamatani, a tributary of River Maruyama drainage system, was surveyed in June and August 2014. Twenty-two fish species/subspecies, belonging to six fish families, were caught at four stations. The oriental white stork favors a foraging habitat with high biodiversity and rich food. Crucian carp, Carassius spp., was identified as a valuable prey for the oriental white stork. The fish community structure differed between the middle and upper reaches of River Kamatani. Biodiversity was higher in the lower reaches than in the upper reaches of the river. To increase the fish population in River Kamatani, it is necessary to maintain the continuity of the river in terms of fish migration.

<p>Since 2005, Oriental white storks Ciconia boyciana have been continuously reintroduced by Hyogo Park of the Oriental White Stork (HPOWS) in the Toyooka Basin, Japan. However, most of them remain strongly dependent on hand-feeding in HPOWS after release because they can thereby obtain highly nutritious fish (Trachurus japonicus, Oncorhynchus mykiss, etc.). In contrast, a few storks are independent of hand-feeding, preying on various animal species (such as fish, frogs, insects, crustaceans) in the Toyooka Basin. However, this information on the foraging of reintroduced storks is on the basis of behavioural observations, but their trophic levels and food habits are unclear. Stable isotope analysis can be useful for estimating feeding habits. Therefore, we analysed carbon and nitrogen stable isotope ratios (δ¹³C and δ¹⁵N) in feeding-dependent storks (FDS) and -independent storks (IS), and then compared these values with those of captive-bred storks (CBS). The stable isotopic analysis showed that the levels of δ¹³C and δ¹⁵N were in the fol lowing order: CBS ＞ FDS ＞ IS. Our results suggest that the trophic level of storks rises upon strong dependence on hand-feeding; the provision of highly nutritious fish via hand-feeding thus has a major impact on the feeding habits of wild storks.</p>

Wando and tamari are water bodies in the floodplain of a river and play an important role in maintaining valuable ecosystems. There are over 100 wando and tamari in the middle and lower basin of the Kiso River. An Acheilognathus longipinnis, Itasenpara Bitterling, which is designated as an endangered species, has been identified in these areas. The habitat of these valuable wando and tamari species is endangered by the development of large land plants around these reservoirs caused by river dredging for flood protection. Therefore, it is essential to collect detailed data about the habitat, hydraulic water flow, physical structures and landscape in order to preserve this species, but so far little attention has been given to water quality. The purpose of our research was to classify the water quality of wando and tamari water, especially ions, and to determine the water type based on its origin. Samples were collected at 10 wando sites and 15 tamari sites from August 2011 to February 2013 along the Kiso River. As our analysis by trilinear diagram shows, the waters of wando and tamari almost all belong to the category of Type I (Ca-HCO3), which forms in shallow aquifers. The two reservoirs that do not belong to Type I are presumably contaminated by drainage water from human activities.

We examined fish community structures in floodplain backwaters in the Kiso River, Central Japan, in an uncommon drought year. Nine floodplain backwaters with varying levels of flood inundation frequency were surveyed for winter fish communities, and measured for local environmental variables in summer and winter periods. The winter fish community was better represented, with less diverse and physiologically tolerant species in backwaters with a decreasing flood pulse frequency. The temporal frequency of hypoxic conditions (dissolved oxygen of <2 mg l(-1)) and chlorophyll a in summer explained the heterogeneity of the fish community along the gradient of inundation frequency, while no variables measured in winter had an explanatory power. These results suggest that drought-induced, infrequent flood pulses in the autumn-winter period limited the dispersal opportunity of fishes, and thus maintained community structures selected by summer limiting factors until the survey took place in winter. Future comparisons of our data with those in non-drought years would provide important implications to the sustainable management of floodplains for wintering fishes against the increasing probability of future flow regime changes.

To infer the population genetic structure and genetic diversity of Itasenpara bitterling (Acheilognathus longipinnis), a cyprinid species endemic to Japan and distributed in only three specific regions, we investigated mitochondrial DNA variation. The distribution of the haplotypes among the three regions showed distinct geographic structure, and no common haplotypes were observed among regions. Analysis of molecular variance revealed a significant proportion of the genetic variance was partitioned among regions (93.1 %, P < 0.001), and pairwise estimates of D-A and I broken vertical bar(ST) between regions also revealed strong population structure. Given the strong genetic structure and low genetic diversity within regions, we strongly suggest that each region should be treated as a separate unit in any conservation program and any inter-regional translocations should be avoided.

We tested the hypothesis that globally imperiled freshwater mussels (Order: Unionoida) can be used as an indicator of fish communities in lowland aquatic systems for relatively small geographic areas (i.e., &lt;100 km(2)). The survey was conducted in 13 reaches within a network of agricultural drainage channels and in 9 floodplain backwaters in Central Japan. In each site, the fish community was examined on four seasonal occasions (spring to early summer, mid-summer, fall to early winter, and winter) and related to the mussel community. Total abundance, taxon richness, and diversity index were used to characterize fish communities. Mussel community variables predicted some aspects of fish communities, but such patterns were seasonally limited. In both systems, mussel community variables had no predictive power for the total abundance of fishes. In drainage channels, taxon richness of mussels was a good predictor of all fish community variables except for total abundance in early summer. In winter, mussel abundance predicted well the taxon richness of the fish community, while taxon richness predicted the diversity index of the fish community. In backwaters, mussel abundance was a good predictor of fish community variables except total abundance in mid-summer. A relatively minor portion (&lt;23%) of fish-mussel relationships was attributable to direct commensalism between mussels and bitterlings. A conceptual framework was provided to help identify the mechanisms behind fish-mussel relationships. Our findings validated the use of mussels as an indicator of high-quality summer rearing habitats in backwaters and wintering and reproduction habitats of fishes in drainage channels. (C) 2012 Elsevier Ltd. All rights reserved.

1. Understanding mechanisms behind the distribution of organisms along a gradient of hydrological connectivity is crucial for sustainable management of riverfloodplain systems. We tested the hypothesis that frequency of flood pulses exerts a direct influence on the distribution of freshwater mussels (Unionoida) by creating a local environment that limits their fitness. 2. Multiscale habitat analyses combined with transplant-rearing experiments were carried out with a focus on abundance, presence/absence, survival rates and growth rates of mussels. Sixty-nine floodplain waterbodies (FWBs) were surveyed within a 15-km lowland segment of the Kiso River in Japan. 3. The abundance of mussels significantly increased with increased frequency of inundation associated with flood pulses at the among-FWB scale, while the probability of occurrence of mussels was negatively predicted by the amount of benthic organic matter at the within-FWB scale. 4. Field-rearing experiments showed that survival rates were low and growth rates nearly zero in infrequently inundated FWBs (these FWBs had no naturally occurring resident mussels). In such FWBs, hypoxia (DO < 2 mg L-1) was frequently observed near the bottom when temperature was optimal for mussel growth (>15 degrees C). 5. These findings demonstrated that flood pulse frequency was the most important factor in determining mussel distribution in FWBs because it directly limits mussels fitness by mediating local environmental factors, possibly dissolved oxygen (DO) levels. Successful restoration efforts for mussel habitat conservation should focus on processes that lead to improved local conditions.

This study tested the applicability of airborne scanning laser altimetry (LiDAR) for characterizing surface connectivity of floodplain water bodies by comparing it with in situ measurements of water levels, and examined whether LiDAR derived data accurately predicted the occurrence of globally imperilled unionid mussels. We intensively examined 10 isolated and 3 connected floodplain water bodies (IWBs and CWBs, respectively) located within a 15-km lowland segment of the Kiso River in Japan. Using a digital elevation model (DEM) of floodplain ground surface, which is derived from LiDAR, and water surface DEM, which is obtained from records of water level fluctuations, the frequency of surface connectivity between IWBs and the main channel (inundation frequency) was calculated. Inundation frequency of IWBs was also measured in situ using water level and temperature probes. Also, the occurrence of mussels in CWBs and IWBs were examined. LiDAR derived data well predicted in situ derived one with a high level of accuracy (r2&gt;0.77), validating the LiDAR-based approach. Some errors existed in the predictive model, indicating that the applicability of LiDAR data is limited by its spatial resolution and snapshot nature. The occurrence of mussels was positively explained by an increasing level of inundation frequency, and the high accuracies of empirical models were validated using data for other 67 water bodies within the study segment. This study overall demonstrated a high potential of LiDAR data for efficiently monitoring hydrological and biological conditions of floodplain water bodies in the Kiso River and beyond. Copyright (C) 2010 John Wiley & Sons, Ltd.

The microhabitat characteristics of the Tokyo bitterling, Tanakia tanago, designated a natural monument of Japan, were investigated in its natural habitat. To elucidate the habitat requirements of juvenile bitterling, we analyzed the relationships between the occurrence (presence/absence) of juveniles and microhabitat variables using a generalized linear mixed model (GLMM). The model showed that the occurrence of juveniles was positively correlated with the presence of underwater cover and the number of bitterling eggs deposited in adjacent mussels, and negatively correlated with current velocity. When the habitat was evaluated using this model, it predicted that the occurrence probability of juveniles was low in the upper reach of the canal. Therefore, the upper reach habitat was restored (i.e., the bottom was excavated, stakes were installed, and mussels were introduced) after considering the habitat requirements of juveniles. To assess the effect of these restorations, we compared the occurrence of juveniles between restored and control (non-restored) stations. Over the duration of the observations, 99 and 41 juveniles were found at restored and control stations, respectively; 71 % of the total number of juveniles was observed in the restored sections. These results suggest that the restoration scheme could increase suitable habitat for juvenile bitterling. Assuming that the juveniles observed in the upper reach of the canal survive and breed, the size of this population should increase. The habitat-requirement model constructed in this study should be applicable for maintenance and reconstruction of habitats of this species.

We examined use of small perennial agricultural canals by fish according to seasons and life stages and habitat characteristics in 4 regions, southern Gifu, central Japan, in irrigation (June and August) and non-irrigation (September and February) periods. Seasonal changes in the number and size composition of six dominant fish species showed that the canals function as habitat for growing and overwintering. Total abundance of all fish species was higher in earth canals, which had natural bed materials, than in concrete canals in all study periods other than August. Fish diversity was higher in earth canals than in concrete canals only in winter (February) . Abundance of each of most dominant fish species was positively related to the bed materials, such as silt, sand, or gravel, in warmer seasons (from June to September) . In winter, that was primarily explained by cover ratio or water depth. In addition, we found close positive relationship between bitterling and mussel abundance in three study periods including spawning and other seasons. These habitat characteristics according to the study periods were satisfied in earth canals. Our findings suggest that a set of natural bed materials and covers, such as bank vegetation and undercut bank, is important when canals are considered as fish habitat throughout irrigation and nonirrigation periods including winter. Therefore, the bank-lined canal with natural bed should be adopted for canal construction and modification, although unlined earth canal is ideal. If the canal bed is necessarily lined, the hydrological conditions that allow sediment deposition should be ensured.