Shiro Sagawa

Bitterling are fishes that use freshwater mussels for oviposition. The pattern of mussel utilization of an endangered bitterling species, Acheilognathus longipinnis, which spawned in autumn, was investigated in a lowland river. Six Unio douglasiae nipponensis (1.5% of total 388 individuals) hosted A. longipinnis embryos consistently in their outer gills, and they inhabited areas along the river bank where mussel density was relatively high on a less compacted mud substrate. Unexpectedly low rates of host utilization and the rare occurrence of juvenile (shell length, < 40 mm) hosts (< 0.8% of total individuals) suggest the need for greater attention to the conservation of A. longipinnis.

Despite the fact that flow and channel morphology are two critical factors that need to be taken into account when considering the conservation or restoration of river environments, there are no reports on the response of fish assemblages to changes involving both variables in combination. This study examined the response of fish assemblages to artificially induced changes in flow discharge in an experimental stream that had simple (a glide reach) and complex (pool-riffle reach) morphologies. When the flow of the glide reach was increased, the fish assemblage structure changed from one dominated by the demersal species Misgurnus anguillicaudatus and Cobitis sp. to one dominated by the water-column species Zacco platypus and Gnathopogon elongatus. In the pool-riffle reach, the fish assemblage structure changed from one dominated by Cobitis sp. and Z. platypus to one dominated by Plecoglossus altivelis altivelis. When the flow discharge was low, the fish assemblages of both reach types resembled each other in being dominated largely by demersal species, but when flow was increased these similarities faded and distinct assemblages emerged. In the glide reach, increasing the flow volume caused a linear increase in both water depth and velocity and a gradual increase in the diversity of water-column species, their relative abundance, and size. The number of Z. platypus increased fivefold whereas the number of M. anguillicaudatus decreased to less than a quarter of their original number. In the pool-riffle reach, the number of P. altivelis altivelis grew conspicuously although increased flow produced no clear increase in depth or velocity. Calculation of the availability of physical habitat environments suitable for Z. platypus and P. altivelis altivelis in each reach type indicated that preferable habitat for both species was more available in the glide reach. The lower abundance of P. altivelis altivelis in the glide reach was attributed to the relatively low availability of algal food resource due to the sand-predominated substrate whereas pebbles predominated in the pool-riffle reach providing good conditions for algal growth. Our findings suggest the need for a framework for considering environmental flow that takes into account variables such as channel morphology and food resource conditions. © 2007 International Consortium of Landscape and Ecological Engineering and Springer.

We examined electrofishing catchability of six most abundant fish species in experimental stream A in the Aqua Restoration Research Center in Gifu, Japan. The electrofishing catchability can be defined as the total catch obtained by electrofishing divided by the sum of catches obtained by electrofishing and by chasing into D-shaped nets. The six species were classified into high catchability species (more than 80% of the catch) (Plecoglossus altivelis altivelis, Misgurnus anguillicaudatus, and Cobitis sp.) and low catchability species (less than 80% of the catch) (Zacco platypus, Gnathopogon elongatus elongatus, and Rhinogobius sp.). Two age groups were confirmed in each of the low catchability species by estimation of the fish size (total length mm). Each peak of the first and the second age groups were positioned less and more than 40 mm, respectively. The catchability of the first age group of Z. platypus as a swimming fish was significantly lower than the second age group of the species. The catchability range of Rhinogobius sp., a benthic fish, was lower (24%-67%) than that of Z. platypus and G. elongatus elongatus values. Furthermore, the catchability of the second age group of Rhinogobius sp. was lower than that of Z. platypus. These results suggest that electrofishing alone is not a suitable capture method because its capture rates for small swimming fish < 40 mm and for all sizes of benthic fishes are low. Therefore, electrofishing should be used along with the D-shape nets and the small swimming fishes and benthic fishes should be chased into the nets. Additionally, we recommend that further studies are required to determine not only the catchability for each of these species but also to study damages by electrofishing to fish under various voltage, pulse, and environmental conditions.

We examined the habitat characteristics of larval Cyprinidae (larvae: < 13 mm in total length [TL], juveniles: 13-30 mm TL) at a base flow (0.1 m³s^-1) and under experimental flooding conditions (0.5 and 1.0 m³s^-1 discharge) in two zones (BRZ: Backwater Research Zone, IFRZ: Inundation Frequency Research Zone) of experimental stream B in the Aqua Restoration Research Center in Gifu, Japan. Although the two zones appear as a straight channel, the environmental characteristics of the BRZ, which had three backwaters, were more diverse than those of the IFRZ. In the base flow study, most larvae and juveniles were captured near the shore of the two zones (low abundances) and in the backwater areas of the BRZ (high abundances), where water velocity was slower (2 cm/sec) and there were more areas with high cover (larvae: 56%, juvenile: 44%). However, fish were absent in areas of high cover (> 78%), with a high water velocity (6.6 cm/sec). Sites in the BRZ where fish were present were separated into two different habitat types: 1) shallow, slow moving water and fine substrate on the backwater borders; 2) deep water in the open areas of backwaters. This result suggests habitat segregation of cyprinid species at early growth stages. Larvae congregated in the backwater areas during the experimental floods, whereas juveniles did not differ significantly in the periods before and after flooding. These results suggest that diversity of floodplain morphology should be preserved to maintain larval habitats not only at the base flow level but also under various flow regimes.

The effects of dam operations on river environment variables (water depth, current velocity, emergent plants, substrate composition, and channel morphology) and aquatic animals (fish and benthic macroinvertebrates) were examined over a four-year period using the BACI (Before, After, Control, Impact) design, before (1998) and after (1999-2001) regulation, at control (upstream) and impact (downstream) sites. The Takisato Dam is a 50-m vertical-face by 445-m-wide dam in the Sorachi River, Hokkaido, Japan. While there was a large fluctuation (20-80 m³/sec) in the diel discharge before dam operation, dam closure resulted in a low, uniform discharge (9 m³/sec) in the downstream reach, which resulted in low current velocities (from 0.87 m/sec to 0.17-0.42 m/sec) and affected sediment deposition, bar occurrence, pool-riffle sequence, spreading 0 m/sec shore area (0.7 to 21.5%), and emergent plant growth (length of area: 80.0 m to 243.1 m). These changes in the regulated downstream affected the ninespine stickleback (Pungitius pungitius), which became more abundant downstream (cumulative number for four seasons: 147 to 794 individuals), whereas the numbers of Siberian stone loach (Noemacheilus barbatulustoni) did not differ significantly between the periods before and after dam operation. The change in stickleback abundance was related to the establishment of emergent plants and spread of the slow shore area. The macroinvertebrate communities in the control reach upstream from the Takisato Dam remained taxonomically diverse during the study period, while the regulated reach downstream from the dam showed low diversity. However, the effects of the dam on macroinvertebrates differed among the study units (riffle, thalweg, shore). The conservation of taxonomic diversity in the downstream riffles might be due to maintenance of the area of this flow regime, due to the reduced flow width with the low water discharge and the occurrence of bars.

This study examined the effects of a concrete groundsill on the survival rate of fish falling off the groundsill. The survival of river sculpin (Cottus nozawae), Siberian stone loach (Noemacheilus barbatulus toni), and four age groups of 0+, 1+, 2+ and 3+ of rainbow trout (Oncorhynchus mykiss) in Shirigishimanai Stream, Hokkaido, Japan, was surveyed before improvement in November 2000. Immediately after the experiment, we observed the survival of the fish in a tank for 10 days. The survival analysis using the Kaplan-Meier method and Log-rank test showed that rainbow trout 0+ juveniles suffered seriously from falling off the groundsill (survival rate: 73%). After constructing a water cushion on the apron, the water on the apron became deeper (before: 11.3cm, after: 77.9cm) and the current velocity slower (before: 0.75 m/sec, after: 0.09 m/sec). We conducted a second survey after the construction using 0+ juvenile rainbow trout in November 2002. The improvement increased the survival of juvenile fish (survival rate: 95%). Our study suggests that the reduced height and the water cushion on the concrete apron should benefit juvenile salmonids during up- and downstream migration.

Habitat use and diet variation of immature (age 0⁺ and age ≧1⁺) Sakhalin taimen (Hucho perryi) during fall were studied in second- and third-order tributaries of A Stream, northern Hokkaido, Japan. Sakhalin taimen aged 0⁺ were most abundant near the shore of the second- order tributary, whereas those aged ≧1⁺ were most abundant in the thalweg of the third-order tributary. The size of the fish was positively correlated with water depth and cover patch size. The composition of the stomach content differed markedly between masu salmon (Oncorhynchus masou) and Sakhalin taimen. The former comprised terrestrial insects (IRI% = 66.8), whereas the latter comprised ephemeroptera (IRI% = 62.9). These results indicate that the masu salmon is a typical drift forager, whereas the Sakhalin taimen shows benthos foraging. Fish, particularly the Siberian stone loach (Noemacheilus barbatulus tori) and the Amur stickleback (Pungitius sinensis sinensis), constituted a fairly large part (IRI% = 30.6) of the diet of Sakhalin taimen aged ≧1⁺. Furthermore, those aged ≧1⁺ cannibalized individuals of their own species aged 0⁺. In order to preserve immature Sakhalin taimen, migration routes throughout the river system must be maintained and bank cover with a slow water velocity, undisturbed stream beds for benthic invertebrates and riparian forest for terrestrial insects are required.

We examined the selectivity of spawning habitat for shishamo smelt (Spirinchus lanceolatus) in December 2001 at pools and riffles of the Pon-warui stream, located in southern Hokkaido, Japan. We analyzed the sampling sites of fertilized shishamo smelt eggs in relation to environmental variables using princi-pal component analysis and ANOVA. The results showed that the eggs were dis-tributed to the pools with shallow (2-22cm), slow moving water (-0.07-0.10m/sec) and fine substrate (sand: particle size<2mm). The eggs are normally dis-persed downstream from the spawning ground (riffle or glide) by the stream cur-rent and should settle down against the bank of pools, highlighting the importance of preserving the pool-riffle sequence throughout the river system.

The summer habitat of adult Sakhalin taimen (Hucho perryi) was studied in a fourth-order tributary of the Teshio River, Hokkaido. Sakhalin taimen selected large pools with slow water velocity and canopy shade or cover (especially canopy shade). The maximum number of Sakhalin taimen observed in pools during three censuses was positively correlated with the percentage of canopy shade or cover, while the maximum body size was positively correlated with the bed area. The study section had a reach within some nature-oriented river works, but no taimen were found there, probably because of insufficient pool sizes and canopy shade or cover patch for this species. On the other hand, Sakhalin taimen in this study stream are known to spawn from May to June in first-, second- and third-order streams where meandering channels and riparian forests are well preserved. These results suggest the importance of preserving large deep pools with canopy shade or cover and allowing adult taimen to migrate upstream (first-, second- and third-order streams) and downstream (fourth-order streams) throughout the river system.

The objective of this study was to establish working hypotheses in order to improve the structure and function of river regulation works. We examined the choices for spawning grounds of rainbow smelt (Osmerus mordax eperlanus) and the characteristics of spring habitat of other fish species (especially, amphidromous fish). The survey was made from May to June 2000, in the Warui and Pon-warui streams, located in southern Hokkaido, Japan. We analyzed the density and mortality of the rainbow smelt egg, and fish density in relation to environmental variables. The results of the analyses showed that rainbow smelt spawning grounds are distributed from the downstream to the upstream reach, and mainly located downstream from the altered reaches. Other fish species had own habitat choices respectively (e.g. masu salmon Oncorhynchus masou selected pools with riparian forest cover), and a lot of amphidromous fish species also inhabit all reaches, however fish density declines with distance from the river mouth. Furthermore, rainbow smelt egg density and mortality were related to riparian forest cover. Without canopy cover (increased light levels) epilithic periphyton grows into a very thick covering, trapping fertilized rainbow smelt eggs as well as fine sediments on the streambed. Egg mortality was higher in the areas that had high epilithic periphyton biomass because of the thick deposition of fine sediment. Finally, two working hypotheses were presented for improvement of river regulation works. 1: Controlling the flow velocity over the altered section will facilitate upstream and downstream migration of fish populations, and will maintain the distribution of rainbow smelt spawning grounds and other fish species habitat downstream. 2: Replanting of riparian forests in the altered reaches will reduce egg mortality of rainbow smelt, and maintaining the meandering nature provided by geomorphic processes in the altered reaches will recreate habitats for masu salmon and other fish species.

The authors observed a white-spotted chaff Salvelinus leucomaenis redd in a small stream flowing into Lake Shikotsu, Hokkaido. The redd was located in the middle of a riffle with current velocity and average median gravel size being 0.4m/sec and 53mm, respectively. The spawning habitat of the white-spotted charr was different from that of Japanese charr, populations in mainland Japan, reported in the literature.

The distribution of Lacerta vivipara was investigated at fourteen sites on the Sarobetsu Wetlands from late July to late August, 1997-1998. A total of sixteen lizards were collected from eight sites of all. The mean number of collected lizards were 0.19 per 100 trap nights. They were randomly distributed in the Sarobetsu Wetlands. Sexual dimorphism was observed through the differences in tail width. They fed on small insects living in the grass and underground. Takdromus tachydromoides were collected with Lacerta vivipara at the same site.