Causes of mortality of Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) smolts in a restored river and its estuary

During October 2000 to August 2002, the River Skjern Nature Project was implemented by removing dykes and re‐meandering 20.5 km of the lower canalized river. As a consequence the length of the river stretch increased to 23 km. A lake of 250 ha developed in the river valley 5 km upstream from the river mouth because of subsiding soils caused by reclamation and drainage since the 1960s. Using radiotelemetry, the mortality of wild Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) smolts in the River Skjern and its estuary was investigated prior to and after the implementation of the project. Altogether, 77 Atlantic salmon and 66 brown trout smolts were caught, tagged and released in the river upstream of the restoration project during the spring of 2000 and 2002. The in‐river smolt mortality was more than double in 2002 for both Atlantic salmon and brown trout compared with 2000. This was primarily due to bird predation in 2002 which was not observed in 2000. The in‐river bird predation in 2002 was mediated by the new lake, which quickly became an important bird rest area. Estuarine mortality mainly caused by cormorants (Phalacrocorax carbo sinensis) differed significantly between species, but was high for both Atlantic salmon (39%) and brown trout (12%) in both years of investigation. The aggregated smolt mortality in the river and in the estuary (48%) may threaten an indigenous self‐sustaining Atlantic salmon population in the River Skjern. When planning river restoration projects, caution should be used, especially where permanently flooded floodplains (lakes) develop due to subsiding soil. In situations where rivers pass directly through newly developed lakes, migratory species such as Atlantic salmon and brown trout may be severely affected due to increased exposure to predation from predatory fish and birds. Copyright © 2006 John Wiley & Sons, Ltd.     

Migratory patterns and return to the catch site of adult brown trout (Salmo trutta L.) in a regulated river

The spawning migration and local homing of adult brown trout was analysed using radio telemetry in a regulated river in central Norway. Twenty‐eight large (37–64 cm) brown trout (Salmo trutta L.) were tracked before, during and after spawning in the River Nea, a watercourse with several obstructions, including an outlet tunnel from a power station and a regulated stretch (26 km) with 45 weirs. Two major patterns of spawning migration were found: (1) about half (n = 16; 57%) of the trout moved very little and remained in the deeper pools of the river from June until November; (2) about half (n = 12; 43%) of the trout migrated relatively long distances (12.5–28 km) up the river prior to the spawning period where they stayed in the outlets of small tributaries, or in rapids on the main river during the spawning period. We assume that these trout belong to a population of lake‐run migratory trout using the River Nea for spawning. There was no significant difference in body length of migratory and stationary brown trout and no significant difference in total distance moved by migratory males (30.5 km, n = 6) and females (20.5 km, n = 6, p > 0.05). Among migratory trout, we found no correlation between body length and migrated distance. Of the 12 migratory trout, nine undertook fast upward migration in periods of high water flow (> 100 m³/s). They passed the outlet tunnel from the power station and negotiated two to 35 weirs before reaching their main reproduction areas. Three trout crossed several weirs when the discharge was low (10–40 m³/s). When there was low discharge, fish remained at the outlet tunnel for up to four weeks and showed a high level of activity. Postspawning downstream migration started between 25 September and 25 October. Most migratory trout (n = 9) wintered in pools on the lower part of the river or in weir basins; only two trout descended to the lake (Selbusjøen) in late autumn. Copyright © 2004 John Wiley & Sons, Ltd.     

Habitat suitability curves for brown trout (Salmo trutta fario L.) in the River Adda,Northern Italy: comparing univariate and multivariate approaches

Habitat suitability of brown trout (Salmo trutta fario) was studied in the upper portion of the Adda River, Northern Italy. Measurements were made for 528 individuals distributed in two life‐stage classes, adult and juvenile, based on body length. In order to provide basic biological information for the physical habitat simulation (PHABSIM) system of the instream flow incremental methodology (IFIM) in the Italian regulated rivers, habitat suitability curves (HSCs) have been developed with respect to several microhabitat riverine parameters. Initially, current velocity, water depth, substrate class size and cover were analysed with an univariate approach, then bivariate habitat suitability models were developed from depth and velocity data. The comparison of experimental univariate HSCs with those from the literature outlined some differences that can essentially be explained by characteristics of the investigated river, confirming the necessity of using site‐specific curves in relation to each experimental study area. To compare the univariate and bivariate approaches, the weighted usable area (WUA)–discharge relationships were calculated using both types of HSCs. Response curves obtained from the two approaches turned out to be quite different. In PHABSIM habitat modelling, HSCs univariate functions need to be aggregated to produce the WUA–discharge relationship. A multiplicative criterion is generally used for the combined suitability factor; by means of this aggregation criterion all variables have equal weight. According to bivariate models, depth is much more important than velocity in defining habitat suitability requirements. Copyright © 2001 John Wiley & Sons, Ltd.     

Urbanization in a great plains river: Effects on fishes and food webs

Spatial variation of habitat and food web structure of the fish community was investigated at three reaches in the Kansas River, USA to determine if δ¹³C variability and δ¹⁵N values differ longitudinally and are related to urbanization and instream habitat. Fish and macroinvertebrates were collected at three river reaches in the Kansas River classified as the less urbanized reach (no urban in riparian zone; 40% grass islands and sand bars, braided channel), intermediate (14% riparian zone as urban; 22% grass islands and sand bars) and urbanized (59% of riparian zone as urban; 6% grass islands and sand bars, highly channelized) reaches in June 2006. The less urbanized reach had higher variability in δ¹³C than the intermediate and urbanized reaches, suggesting fish from these reaches utilized a variety of carbon sources. The δ¹⁵N also indicated that omnivorous and detritivorous fish species tended to consume prey at higher trophic levels in the less urbanized reach. Channelization and reduction of habitat related to urbanization may be linked to homogenization of instream habitat, which was related to river food webs. Published in 2009 by John Wiley & Sons, Ltd.     

Changes to the trophic structure of a desert fish community following river regulation and species turnover: Implications for an endangered top predator

A poor understanding of factors leading to species decline can result in inefficient or ineffective species restoration. Endangered Colorado pikeminnow (Ptychocheilus lucius) was nearly extirpated from the San Juan River, NM, USA and recent efforts to reestablish the species via hatchery augmentation of juveniles has yet to reach the target number of adults in the system. To assess how changes to the river's food web could be limiting reestablishment of this top predator, we used stable isotope (δ¹³C and δ¹⁵N) signatures of the fish community pre- (museum specimens) and post river regulation with coincident extirpations and invasions. Following river regulation, four of five community-wide trophic structure metrics that quantify overall resource use were reduced and species turnover likely had little effect per se. For species sampled in both time periods, shared trophic resources generally increased (mean niche overlap = +35.7%). Additionally, Colorado pikeminnow experienced the largest decrease in niche breadth (−72%) and diet mixing models suggested a shift from piscivory towards insectivory in contemporary collections. Our results suggest an overall reduction in basal resource availability after river regulation. We propose increased reliance on similar resources may be limiting fish prey for Colorado pikeminnow, ultimately contributing to the slow and limited reestablishment in the San Juan River. This study adds to the growing body of knowledge provided by museum specimens and stable isotope analyses to identify food-web dynamics that are a departure from historical conditions, which can provide novel information critical to imperiled species management in modified systems.     

Use of native macrophytes for recovery of the habitat structure and complexity of a lowland stream affected by river engineering works: Implications for management

Macrophytes were transplanted into a lowland stream affected by river engineering works. The aim was to analyse the feasibility of their reintroduction and potential to be used for the recovery of the structure and complexity of the lotic habitat. Macrophytes contribute heterogeneity to streams, modify the current velocity, affect sediment and nutrients dynamics, and provide a substrate for epiphytic biofilm. We transplanted specimens of Ludwigia peploides, Gymnocoronis spilanthoides, and Egeria densa into a stream located in the Pampean plain (Buenos Aires, Argentina). The growth and coverage of the transplanted macrophytes and the changes in the structure of the epiphytic biofilm were assessed. The results show that specimens of G. spilanthoides were negatively affected by the transplant and new conditions, E. densa decreased its coverage after the transplant, and L. peploides endured the transplant and adapted to the dredging site with successful establishment and expansion. There were no significant differences between the biofilm developed in L. peploides and G. spilanthoides. Additionally, the biofilm had similar features between the transplanted macrophytes and those from a site with no dredging. Considering this result, the selection between these macrophytes in relation to biofilm production is indifferent. However, as L. peploides adapts better to the new conditions generated by the river engineering works, its use in the rehabilitation project is recommended. Moreover, it is important to consider the ability of different species of macrophytes to survive the transplant and grow under new environmental conditions in order to include them in rehabilitation projects.     

Dynamics of discharge,sediment transport,heavy metal pollution and Sábalo (Prochilodus lineatus) catches in the lower Pilcomayo river (Bolivia)

The Pilcomayo river is one of the few intact natural river systems left on the South American continent. The high, largely natural, sediment loads of the river have led to the development of an alluvial fan system, which is still active. The river is currently retracting due to siltation of its bed, and in the near future the river is likely to abruptly change its course. There is a large difference in discharge between the wet and dry seasons. Pollution of the transported sediments by heavy metals from the mining district of Potosí is largely prevented by dilution of the toxic mining sludges with clean sediments derived from natural erosion processes. The Sábalo (Prochilodus lineatus) is a migrating fish which is very important for commercial fishing. The Sábalo grows up in the floodplains in the lower reaches of the river and starts its upstream migration at the end of the rainy season to spawn in the Andean foothill at the beginning of the next rainy season. Pollution does not seem to affect fish catches. Sábalo catches in a given year, however, do appear to depend strongly on the mean discharge in the three preceding years. Annual discharge is strongly influenced by the El Niño–Southern Oscillation (ENSO) phenomenon. Copyright © 2002 John Wiley & Sons, Ltd.     

Effect of a vertical half cylinder on swimming of silver carp,Hypophthalmichthys molitrix: Implications for microhabitat restoration and fishway design

In recent years, the relationship between hydraulics associated with the substrate and fish swimming behaviour has become increasingly important to the design of microhabitat around substrates for river restoration. To better understand the hydraulics associated with substrate on fish swimming, we studied the effects of a vertical half cylinder (hereafter, cylinder) on the critical swimming speed of juvenile silver carp (Hypophthalmichthys molitrix). Absolute and relative critical swimming speeds of fish in the flow field of the cylinder were significantly increased compared with those swimming in free flow. In addition, the amplitude of fish head and tail oscillations were significantly greater in flows created by the half cylinder. This study highlights the importance of roughness elements in stream microhabitat restoration and, possibly, for fishway design.     

Regulated Rivers: Research & Management,Volume 17 Issue 4/5 ‘Understanding natural patterns and processes in river corridors as the basis for effective river restoration’ by J.V. Ward,K. Tockner,U. Uehlinger and F. Malard.

The incorrect version of this article was published previously. Please find the correct version, which retains the original pagination, on the next page. The publisher wishes to apologise for this mistake Running water ecology is a young science, the conceptual foundations of which were derived largely from research conducted in Europe and North America. However, virtually all European river corridors were substantially regulated well before the science of river ecology developed. While regulation of North American river systems occurred later than in European systems, river ecology also developed later. Therefore, there is a general impression of rivers as being much less heterogeneous and much more stable than they actually are in the natural state. The thesis of this paper is that established research and management concepts may fail to fully recognize the crucial roles of habitat heterogeneity and fluvial dynamics owing to a lack of fundamental knowledge of the structural and functional features of morphologically intact river corridors. Until quite recently, most concepts in river ecology were based on the implicit assumption that rivers are stable, single‐thread channels isolated from adjacent floodplains. Unfortunately, many rivers are in just such a state, but it should be recognized that this is not the natural condition. This incomplete understanding constrains scientific advances in river ecology and renders management and restoration initiatives less effective. Examples are given of the high level of spatio‐temporal heterogeneity that may be attained in rivers where natural processes still operate on a large scale. The objective of this paper is to promulgate a broader and more integrative understanding of natural processes in river corridors as a necessary prelude to effective river conservation and management. Copyright © 2001 John Wiley & Sons, Ltd.     

Long‐term changes in macroinvertebrate communities of a heavy metal polluted stream: the river Nent (Cumbria,UK) after 28 years

The macroinvertebrate fauna of the river Nent, a heavy metal polluted upland stream in northern England, first surveyed in 1976, was re‐examined in 2004 to assess long‐term changes in relation to activities in the catchment which have included, a river restoration project, works associated with the development of a mine heritage site and the removal of a chicken farm and more effective organic pollution control measures. The degree of change between years in total abundance, numbers of taxa and community composition varied considerably between sites. Two tributary sites showed marked changes between years due to a reduction in acidity in one and changed substratum in the other but in the main river no significant difference in total taxa and total abundance was observed between years, although seasonal differences were significant. Multivariate community analyses grouped 1976 samples with those taken in 2004 but revealed a clear separation between upper and lower Nent sites. This observed difference may be related to increased algal cover in the lower sites in conjunction with geomorphological features of the lower Nent. Environmental assessment methodology River Invertebrate Prediction and Classification System (RIVPACS) identified ‘sensitive’ faunal groups and indicated that the extensive impact of zinc pollution in the main river has remained practically the same between 1976 and 2004. This persistence of community structure despite the heavily disturbed nature of the river is attributed to relative constancy in instream habitat conditions. The recent activities in the catchment have had little effect on the overall controllers of faunal communities in this system, zinc concentrations and geomorphological characteristics of the stream. However, further disturbances involving movement of spoil heaps and channel alterations in the upper catchment may increase both sediment and heavy metal loadings to the river. Copyright © 2007 John Wiley & Sons, Ltd.