Yoichi Kawaguchi

Longitudinal macroinvertebrate organization over contrasting discontinuities: effects of a dam and a tributary

Abstract Macroinvertebrate organization along a river was examined to relate biological responses to environmental changes observed across 2 discontinuities (a dam and a tributary). Benthic macroinvertebrates and a range of environmental variables were sampled from 4 study segments (above the dam, below the dam, below the tributary confluence, and in the tributary). Substrate was significantly coarser below than above the dam. In contrast, water-quality variables, such as water temperature and dissolved O2, changed little below the dam. The most striking discontinuity was substrate coarseness at the tributary confluence. Substrate below the confluence was finer than substrate below the dam and similar to the substrate above the dam. Macroinvertebrate organization differed across the 2 discontinuities. Assemblage composition above the dam was more similar to composition below the confluence than to composition below the dam. The longitudinal organization of the macroinvertebrates could be explained largely by changes in substrate characteristics and habitat preferences of the indicator species. The densities of drifting zooplankton and phytoplankton were higher below than above the dam and were higher below the dam than below the confluence. However, the density of drifting plankton did not differ between the reach immediately above the confluence and the reaches below the confluence. This result suggests that the decrease of zooplankton and phytoplankton occurred above the tributary, probably because of biological entrapment or passive deposition rather than the contribution of the tributary inflow. The dam and tributary caused contrasting discontinuities in macroinvertebrate organization. The tributary generally reversed the dam-related changes to the main stem habitat and the macroinvertebrate community. A key management implication of our study is that efforts to restore dam-related environmental impacts would be facilitated by understanding the role of tributaries downstream of the dam.

A review of the research on introduced freshwater fishes: New perspectives, the need for research, and management implications

Although freshwater fishes have a long history of human-induced introduction, recent globalization has accelerated worldwide introduction events even more, and those introduced fish species are now perceived to be a major threat to ecosystems. Over the last two decades, numerous studies have been published on introduced fish species; however, it has been challenging for researchers to understand the magnitude of the impact and the underlying mechanism of invasions. Recently, new perspectives in understanding invasive freshwater fish biology have been presented in a number of studies, which can be largely attributed to advances in analytical techniques and also to a growing need for proactive analysis in management strategies. The aim of this paper is to summarize new ecological perspectives, the need for research, and/or management implications with emphasis on technological advances in, for example, statistics, molecular analysis, modeling techniques, and landscape analysis addressed under the following five categories: introduction pathways, predicting spatial patterns, biotic homogenization, hybridization, and control and eradication. The conservation of native fish fauna and the management of introduced fish species will benefit from combining these new perspectives with fundamental studies such as those on life history and population biology.

River restoration for macroinvertebrate communities in lowland rivers: insights from restorations of the Shibetsu River, north Japan

Because of human impacts, lowland rivers are among the most degraded running water ecosystems, with their floodplains being the center of human activity. Recently, many programs to restore running water ecosystems have been undertaken using various methods in streams and rivers of North America, Europe, and Far East Asia. However, research and knowledge on the effects of river restoration in lowland rivers are limited around the world. The restoration project involving the first reconstruction of a meandering channel in Asia has been conducted in a lowland river section of the Shibetsu River, northern Japan. We review the geomorphologic and hydraulic characteristics of lowland rivers and their environments for macroinvertebrates and discuss approaches to restoring macroinvertebrate communities in lowland rivers, using insights from the restoration project in the Shibetsu River. It is concluded that the recovery of macroinvertebrate assemblages in channelized lowland rivers requires the implementation of restoration methods to create stable substrates.

Methods for and fish responses to channel remeandering and large wood structure placement in the Shibetsu River Restoration Project in northern Japan

The Shibetsu River Restoration Project intends to reestablish a historic meander pattern by connecting a 3.5-km channelized reach with a series of oxbow lakes that were previously isolated by channel straightening. Prior to full-scale construction, a remeandering experiment (pilot) was conducted upstream of the project segment to assess the methods for and ecological responses to channel remeandering. Large wood (LW) structures were also installed in the experimental remeandering reach. The channel remeandering project with LW placement in a large lowland river is the first undertaken in Asia, and it has rarely been undertaken elsewhere. In this report, we present an overview of the Shibetsu River Restoration Project and the methods for and fish responses to channel remeandering and LW placement in the experiment.

Effects of configuration of instream wood on autumn and winter habitat use by fish in a large remeandering reach

This study examined the effects of the configuration of wood structures on the use of local autumn and winter habitats by fish in a remeandering reach of a large lowland river. Fish diversity was higher at the simple wood-structure (SWS) and the log-jam (LJ) sites than at the no-wood (NW) sites during both seasons. In particular, the diversity at the LJ sites was higher than that at the SWS sites during the winter. The abundance of the four dominant fish species was generally higher at the LJ sites than at the NW sites during both seasons. The SWS and LJ sites were characterized by greater depths, finer bed materials, and more diverse flow conditions during the autumn. During the winter, the LJ sites were characterized by slower currents and finer bed materials. These habitat features satisfied the various habitat requirements of the fish observed in our study reach; during the autumn, areas with fast and slow currents were favorable for juvenile salmon, silt and sand bed materials for lamprey, and deep areas for one species of goby, while slow currents were critical in the winter for abovementioned fish species. Engineered log jams were also effective in supporting the colonization of fish during both seasons. These findings suggest that a larger and more complex wood structure, particularly log jams, plays important roles in creating local habitats suitable for various fish species during the autumn and winter and in preserving fish abundance and diversity in large lowland rivers.

19 Ecological responses to anthropogenic alterations of gravel-bed rivers in Japan, from floodplain river segments to the microhabitat scale: a review

Abstract We describe the relationship between disturbance regimes, the life history traits of aquatic and riparian organisms, and effects of human activity, using Japanese gravel-bed rivers in the Asia Monsoon Belt as an example. The consideration of various roles of disturbance in creating a spatial and temporal pattern of habitats is made hierarchically at three spatial scales. Segment scale is the largest, represented by a braided river landscape on an alluvial fan. Riparian tree species direct their life history strategies to survive in the shifting habitat dynamics. Reservoirs constructed at the fan apex regulate flood disturbances and seasonal flow variation, changing the dynamic state to a monotonous, static habitat structure. Intermediate reach-scale structures are represented by pool-riffle sequences, gravel bars, secondary and abandoned channels and oxbow lakes. We focused particularly on the lateral variation of the entire valley floor and its stream channel, which provide critical habitats for spawning, hatching, rearing, wintering, feeding and dwelling as well as flow refugia for fish and macroinvertebrates. Bed instability resulting from an increased tractive force due to channel straightening and its impact on macroinvertebrate communities is also discussed. Finally, the smallest scale is the microhabitat seen as the interstitial spaces in gravel beds used by salmonid and benthic fish for all or some of their life stages. Sediment control dams and gravel mining in rivers and floodplains is causing gravel-size sediment starvation, whereas the introduction of fine sediment is substantially increased following land-use development.

Thermal changes in the gastric evacuation rate of the freshwater sculpin Cottus nozawae Snyder

We experimentally measured thermal changes in the gastric evacuation rate (GER) of the freshwater sculpin Cottus nozawae Snyder under three water temperature regimes (2°, 7°, and 12°C). Laboratory experiments showed that the GER was accelerated with increasing water temperature. This result suggests that the daily food rations of fish are more likely to be underestimated at higher water temperatures if estimation is simply based on the stomach content weight alone. By comparing the GER for various fish species from subfrigid to temperate streams, we found a general pattern that the GER increases with water temperature, regardless of taxonomic group or foraging mode. However, the reaction norms of the GER against water temperature showed considerable interspecific variation. This means that stomach content weight is not comparable as a simple measure for determining the daily rations among fish species when water temperature regimes are different. To consider the temperature-dependent pattern of such a physiological phenomenon is important in understanding the feeding ecology of fishes and their roles in material cycles through food webs in aquatic ecosystems.

Stream Fish Habitat Science and Management in Japan: A Review

Japanese freshwater fish habitats can be generally categorized into 1) rivers and streams, 2) ponds and lakes, and 3) rice fields and small irrigation channels connecting them. Of these, reviewing studies on stream fish habitat is the primary objective of this paper. Streams in Japan have widely received severe habitat alterations through construction of artificial instream structures as well as modification of riparian vegetations. As a result, streamdwelling fishes that require natural flow regimes, substrates, and riparian vegetation have declined their populations in great deal in many parts of the country. Recent studies have found riparian forests control water temperature and provide woody debris creating cover structures for the stream fishes resulting in enhancing their carrying capacity. Differences in riparian vegetation types (forest versus grass) played an important role in determining the local distribution of salmonids. Also, experiments removing concrete-lined channel and installing log-drop structures demonstrated that such the treatment greatly improved fish habitat. As the general public became aware of the serious degradation of aquatic habitats, river management policy has gradually shifted to include conservation and improvement of river environment as habitat for wildlife during the last two decades. For fish migration, installation of fishway on dams has been prevailing, and research efforts have been made to design more effective fishway and passable weirs. In many cases, however, such restoration work lacks ecological data for assessment of their effectiveness. accumulated, a vital issue will be how it is accounted into actual management. Future studies on fish habitat should shift toward treating habitat network at larger spatial scales to seek better designs for distributing appropriate habitats over a whole catchment. Such studies should also include clarifying the habitat requirements of endangered species and effects of non-native on native species.

A study of seed dispersal by flood flow in an artificially restored floodplain

Riverine floodplains play many important roles in river ecosystems. However, many floodplains have suffered degradation or loss of ecological function due to excessive river improvements or through changes in agricultural systems. As a result, many floodplain restoration projects are being conducted worldwide. One of the many methods being implemented to restore floodplain vegetation is flood water seed dispersal. In this technique, precisely estimating the effect of seed dispersal by flood water is important in order to achieve successful floodplain revegetation. Here, we focus our attention on sediment transport by flood water into the Azamenose Swamp, a restored floodplain. We attempt to estimate the function of seed deposition in the restored floodplain and explain how the seeds are deposited in the floodplain by flood water. The result suggests that the restored floodplain functions as a more appropriate deposition site for seeds than the riverbanks of the main river. It was also found that the distance from the inflow site and the weight of the sediment were related to seed deposition.

APPLICATION OF MICRO-PIXE ANALYSIS FOR A MIGRATION HISTORY STUDY OF HUCHO PERRYI FOCUSED ON STRONTIUM DISTRIBUTION IN FISH SCALES

Sakhalin taimen, Hucho perryi, is one of the largest freshwater fish in Japan, where it is close to extinction because of indiscriminate fishing, water pollution, and river construction. Interpretable ecological information about the species, however, is scarce. We examined the migration history of H. perryi by analysis of strontium (Sr) content in fish scales using inductively coupled plasma mass spectrometry and Sr distributions associated with ridges (growth lines) in the scales, with micro-beam scanning PIXE (micro-PIXE) analyses. Sr levels in the scales of H. perryi collected along the Sarufutsu coast were higher than those of salmonid collected at Shumarinai, a freshwater lake. Micro-PIXE line analyses showed that the scale Sr values of the Shumarinai Lake samples remained consistently low from the edge toward the core of the scales. The Sr values from the Sarufutsu coast samples remained relatively high from the edge toward the core; Sr levels from second to fourth position from the edge were about ten times higher than the mean levels of Shumarinai Lake samples. These results suggested that H. perryi from the Sarufutsu Coast had experienced the marine environment.