The significance of meandering channel to habitat diversity and fish assemblage: a case study in the Shibetsu River,northern Japan

This study examined the structure and function of habitats for fish, the contribution to fish populations, and the effects of channel modification on habitats and fish populations in the lowland meandering Shibetsu River, northern Japan. Electrofishing and environmental measurements were conducted in bank areas of habitats constituting natural meandering and modified reaches. All types of habitats in a meandering reach highly contributed to the fish population(s). In particular, the contributions of lateral and wood habitats to fish populations were generally high, despite the low spatial extent of these habitats. The modified reach was simplified and had fewer types of habitats with uniform currents, and there was a low abundance of most fish within these habitats. Abundance of each fish group (taxa) was negatively affected by the changes in the habitats and/or channel shortening (i.e., decrease in the absolute abundance of habitat) due to river modification, which was implemented during 1950–1978. This study suggests that the recovery of all the habitat types is important in meander restoration and that the changes in habitat types and abundance should be examined in monitoring meander restoration and channel shortening.     

Using macroinvertebrate species assemblages to identify river channel habitat units: an application of the functional habitats concept to a large,unpolluted Italian river (River Ticino,northern Italy)

The functional habitat concept was applied to a large Italian river for the first time. The characteristically wide range of hydraulic conditions present in this river (compared to previously-studied small, lowland, English rivers) were expected to be of central importance to biota and, therefore, to habitat definition. TWINSPAN analysis of the invertebrate assemblages sampled in the Ticino river identified five distinct habitats: two habitats in lotic areas (run-riffle and macrophytes in current), two along the river margins (with and without macrophytes) and one in backwater areas. These correspond to five of the functional habitats identified in U.K. lowland rivers. Each of these five functional habitats could be defined either in terms of hydraulics, substratum and/or presence/absence of macrophytes. Representative taxa are presented for each habitat and community structure discussed. Macrophyte and run-riffle habitats supported the most heterogeneous and abundant benthic fauna. No match was found between replicates grouped by invertebrate assemblage (the five functional habitats identified by TWINSPAN) and the grouping of the same replicates by PCA, carried out on the physical data matrix. While obvious velocity differences were found between the functional habitats, of particular note was the fact that the Froude number did not show any clear association with habitat type. In the future, improved river management will follow improved understanding of river habitats.     

Secondary and tertiary stress responses to BKME exposure in the St. Maurice River fish populations

In the St-Maurice River, Canada, white suckers (Catostomus commersoni) collected at two stationslocated downstream of a bleached kraft mill effluent(BKME) outfall exhibited increased muscle lipidconcentrations relative to upstream reference fish.White suckers collected in a physicochemicallycomparable but uncontaminated river, also demonstratedan increasing trend of lipid accumulation withdistance downstream. The similar general trends inboth rivers may result from a river continuum in whichincreasing loads of nutrients with distance downstreamincrease the energy available to fish.However, the general trends differed in two respects.The gradient of lipid accumulation in the St. MauriceR. was irregular, suggesting a sharply increasednutrient input by BKME. Secondly, in the referenceGatineau river, increased lipid reserves wereaccompanied by increased growth and reproductiveeffort relative to body size. In contrast, increasedgrowth rates in the contaminated St. Maurice River wereaccompanied by a reduced reproductive effort relativeto body size. The failure to translate increasedenergy intake, as indicated by increased musclelipids, into increased reproductive effort suggestsone or more components of BKME have a toxic effect.Accelerated river enrichment contributed by thedischarge of the bleached kraft effluent combined withthe natural river continuum made it difficult toisolate the reproductive effects related to effluentexposure.