Fish and fisheries of regulated rivers in the UK

This paper examines the historical and recent influences of river regulation on fish populations and fisheries in Britain. The construction of a series of canals and interconnecting waters during the 18th and 19th centuries facilitated the spread of some species between catchments. These slow-flowing habitats allowed many lowland species to thrive and this is reflected today in the fish community structure in some rivers. The problems of barriers to the movement of migratory species imposed by dams and weirs and the efficacy of compensation measures are discussed. The latter embrace fish passes, adult fish and smolt transport, and stocking. Potential problems for the future include the disruption of the homing of salmon to their natal rivers caused by transfers of water between catchments. River basin management in Britain attempts to reconcile the water resource requirements of fisheries with those of other water users. This can be seen in the practice of Regional Water Authorities to include ameliorative measures in many of their land drainage and flood prevention designs. However, more research is required on the long-term problems and benefits of these and other river regulation schemes on resident fish populations.     

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.     

Riverine characteristics dictate composition of fish assemblages and limit fisheries in reservoirs of the upper Paraná River basin

A qualitative comparative approach has been used to review whether fish assemblage characteristics, such as paucity of lacustrine‐adapted fish species, long food chains, and disproportionate number of piscivorous species, limit fishery yields in reservoirs of the Upper Paraná River basin. The paucity of lacustrine‐adapted species appears to limit fishery yields, but attempts to introduce lacustrine species have been generally unsuccessful. The food chains of species targeted by the fisheries are relatively long, but short food chains seem to be an adaptation of lacustrine species. Because reservoirs with many piscivorous species sustain high fishery yields elsewhere in the world, the hypothesis that an excessive number of piscivores limits yields is not supported. Instead, inadequacies of fish assemblages in reservoirs of the Upper Paraná River basin appear to be symptomatic of an unsuitable environment for lacustrine fish species. The physical characteristics of reservoirs in the Upper Paraná River basin, exacerbated by climatic patterns, may preclude the emergence of successful reservoir species from within the extant pool of riverine species. The resulting assemblages have characteristics that are neither riverine nor lacustrine, and are maladapted to support fisheries in the reservoirs. The introduction of lacustrine species is destined to failure because environmental characteristics are not lacustrine, except in reservoirs positioned high in the watershed, where increased retention times allow lacustrine conditions. Published in 2001 by John Wiley & Sons, Ltd.     

Guiding downstream migrating Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) of different life stages in a large river using bubbles

Salmonid repeat spawners are precious individuals for wild populations due to their high fecundity and previous spawning experience, making them important in environmental policy. However, repeat spawners rarely exist above hydropower dams in regulated rivers as the mortality of post-spawners (kelts) when passing through turbines during downstream migration is very high. To mitigate this problem, there are different technical solutions that potentially guide fish toward available fishways. Bubble barriers represent one alternative to costly physical guiding structures, but the efficiency of bubbles for guiding downstream migrating kelts has not been tested. In this study, we evaluate a 100 m long bubble barrier in guiding salmonids—both smolts and kelts—away from the main current and toward an alternative fishway in Ume River, a large regulated river in northern Sweden. We used both acoustic telemetry and sonar to measure the guiding effect of the bubble barrier for downstream migrating fish. We found that more than twice as many salmonids chose the alternative fishway when the bubble barrier was turned on. This was true both for smolts and kelts, suggesting that bubble barriers can be used to guide salmonids of different life stages in rivers with flow rates over 500 m³ s⁻¹. Indeed, our study indicates that bubble barriers are low-cost structures that could be rapidly applied in many regulated rivers to support salmonid migration.     

Migratory behaviour of adult fast-growing brown trout (Salmo trutta,L.) In relation to water flow in a regulated Norwegian river

The migration pattern of spawners of brown trout (Salmo trutta) in relation to water flow was analysed by radio-tracking in the regulated River Gudbrandsdalslågen, Norway. During the upstream spawning migration in the high flow period, trout (2–12 kg) were caught, tagged and released 15 km downstream of a fish ladder at the Hunderfossen waterfall. The released fish displayed a systematic and directional upstream movement to the outlet of the tunnel from the hydroelectricity plant. In autumn and winter there is a minimum water discharge of 20–2 m³/s on p.s. in the river between the dam and the outlet of the tunnel, which has a discharge of 200–300 m³/s. When the water flowing over the Hunderfossen dam decreased to 20 m³/s, the ascent of brown trout up the river stopped and fish periodically entered the power plant tunnel. To determine the flow necessary to attract fish into the spawning reach above the tunnel outlet, two experiments were undertaken using 12 and 17 radio-tagged trout. In the first experiment, 60 m³/s of water released for 24 h resulted in the migration of 50% of the trout up the river. The second experiment, releasing 60 m³/s for 24 h, followed by 30 m³/s for 24 h two days later, resulted in the migration of 60% of the trout. Only one fish ascended the river at a flow of 30 m³/s. It is recommended that a repeated release of water at 60 m³/s is made in periods of minimum water discharge to save the spawning migration. The results demonstrate the advantage of using radio-tracking in experiments dealing with fish migration in relation to water-flow management.     

Trends in interannual yield variation of reservoir fisheries in Bangladesh, with special reference to Indian major carps

Interannual variation in yield per species from a freshwater reservoir in Bangladesh was analysed by using long‐term landing data. Each species was categorized according to characteristics in interannual yield variation. The characteristics were defined with respect to size of the interannual variation in terms of absolute and relative variation around the mean yield and long‐term trends in catch levels. Annual variation was directly (t₁₈ = 7.84; P < 0.01) related to the yield and can serve as a good indication of the status of the fishery when catches are low. The target fish, Indian major carps (IMC) Labeo rohita, Labeo calbasu, Catla catla and Cirrhinus mrigala, showed large variation in annual yield. This might have occurred because of variation in annual recruitment. Illegal use of gears is mostly related to variation in year class strength, and is assumed to be the most important source of change of stock variation. An increase in catch rate was recorded for Corica soborna. Such a stable combination may only be possible for a certain period without a long‐term trend. Trends in the yield rate of the major fish category for three decades reveal a sharp decline in the catch of IMC. In contrast, small clupeid‐like C. soborna have the highest yield rate. Fishing gears can play a crucial role in this fishery. Fisheries managers must always be alert when issuing fishing licenses and on the control on gears. The conclusion is that the IMC fishery of Kaptai Reservoir is an overexploited fish stock. In this fishery, the same gears are usually employed indiscriminately for different species and size classes. To stabilize the fishery, the existing policy needs to be strengthened and more effectively implemented. Also, some fishing gears and traps need to be restricted. An effective stock protection policy is suggested. Further study on catch size of individual species is essential prior to the development and implementation of any management scheme.     

Estimating the sediment trap efficiency and lifespan of cascaded reservoirs in the Upper Yangtze River Basin,China

The cascaded reservoirs in the Upper Yangtze River Basin (UYRB) are subject to sediment inflow and deposition, resulting in reduction in their effective capacity. The sediment trap efficiency (TE) of the cascaded reservoirs was estimated using several empirical methods, and the factors affecting the TE also were analysed. A new empirical formula was obtained to calculate the TE of the small reservoirs (storage capacity C < 0.5 km³) in the UYRB. Further, four zones were partitioned to describe the relationship between the sediment trap effect and the service function of the reservoirs. The TEs of Xiluodu, Xiangjiaba and Ertan Reservoirs in the UYRB were investigated and compared between stand‐alone and combined operation modes, indicating the TE will be underestimated without considering the cumulative sediment trap of the cascaded reservoirs. Finally, the lifespan of the Xiluodu Reservoir, considering different water storage schemes and different capacity loss percentages, was estimated using the TE method and exhibited good agreement with the results calculated by the mathematical model. The derived TE calculation method under the combined operation of the cascaded reservoirs can be used to assess the sediment trap from the complex hydroelectric project system in the UYRB.     

Fish assemblages and biotic integrity of a highly modified floodplain river,the Upper Mississippi,and a large,relatively unimpacted tributary,the Lower Wisconsin

The Upper Mississippi River is a dynamic floodplain river that has been largely transformed by navigational levees and dams since the 1930s. The pools upstream of each dam are lake‐like and only about the upper third of each reach retains a riverine character. In contrast, the Wisconsin River is not managed for commercial navigation and today its lower 149 km represent one of the least‐degraded large river reaches in central North America. Riverine reaches in both the Mississippi and Wisconsin rivers have similar macro‐habitats including numerous islands, large side channels, and connected backwaters and floodplain lakes. In this study, shoreline electrofishing samples were collected during summer 2002 and 2003 to characterize resident fish assemblages. We compared fish species abundance, biomass, and biotic integrity along main and side channel borders between the Upper Mississippi River and the Lower Wisconsin River. We expected that, in the absence of environmental degradation, fish composition and structure would be similar between the Mississippi and Wisconsin rivers, and between channel types within each river. Nonmetric multidimensional scaling and redundancy analysis revealed that fish species in the Mississippi River, unlike in the Wisconsin River, were characteristic of non‐riverine habitats. We consider non‐riverine fish assemblages indicative of environmental impairment. The main and side channel sites in the Mississippi River had more variable fish assemblages than the Wisconsin River. Analyses of fish index of biotic integrity scores showed that environmental condition was excellent for both channel types in the Wisconsin River, whereas in the Mississippi River the side channel was rated good and the main channel only fair. We conclude that differences between the two rivers and between channel types of the Mississippi River are consistent with direct and indirect effects of navigation. This study demonstrates the utility of a fish index of biotic integrity, an inexpensive and rapid bioassessment tool, for detecting change in ecological health on one of the world's largest rivers. Copyright © 2006 John Wiley & Sons, Ltd.     

Monitoring of environmental flow outcomes in a large river basin: The Commonwealth Environmental Water Holder's long‐term intervention in the Murray–Darling Basin,Australia

The Murray–Darling Basin in south‐eastern Australia contains over 70,000 km² of wetlands and floodplains, many of which are in poor condition. In response, Australian governments have committed to a major restoration program, the Murray–Darling Basin Plan that includes management of 2,750 Gl of environmental water to protect and restore aquatic ecosystems. The restoration is being undertaken within an adaptive management framework that includes monitoring the outcomes of environmental flows in seven river valleys. This paper provides an overview of the 5‐year monitoring project and some preliminary results. Monitoring design considered the Basin Plan's environmental objectives, conceptual models of ecosystem responses to flow, and an outcomes framework linking flow responses to the environmental objectives. Monitoring indicators includes ecosystem type, vegetation, river metabolism, and fish. Responses are evaluated to identify the contribution of environmental flows to Basin Plan environmental objectives and continual improvements in management. The program is unique in that it seeks to monitor long‐term outcomes of environmental flows at the river basin scale. Despite many challenges, the monitoring has become a key part of the adaptive management of environmental flows in the Murray–Darling Basin.     

Hydrosedimentary classification of natural and engineered backwaters of a large river,the lower Rhône: possible applications for the maintenance of high fish biodiversity

At the end of the last century, the shorelines of the Lower River Rhône were embanked and submersible dikes were built in the main channel, delimiting dike fields. We compared the morphological, hydrological and sedimentary variables of nine dike fields, four sites in dead arms and one in the main channel, in order to describe the fluviosedimentary functioning and to produce a classification of these different natural and engineered backwaters. Within these ‘artificial floodplains’, the different types of backwaters and their long-term changes bear a strong similarity to those observed within a natural floodplain. The long-term frequency of submersion by the water of the main river channel is the first factor that controls the erosion and sedimentation within the different backwaters. Three types of site can be distinguished: the lotic sites are the main channel and one dike field, five dike fields comprise the semi-lotic sites and the cluster lentic sites include the three remaining dike fields and the four dead arms sites. These three groups also differ in their riparian habitats and in their juvenile fish assemblages. As juvenile fish were most abundant in the semi-lotic dike fields, the use of such structures can be envisaged in order to restore high fish diversity in rivers where the former floodplain has disappeared or is no longer accessible to fish because of human modifications. © 1997 John Wiley & Sons, Ltd.     

Linking flow alteration with fish assemblage structure in a river regulated by a small hydropower project in the Western Ghats of Karnataka,India

Small hydropower projects (SHPs) are promoted as low-impact alternatives for large hydropower. SHPs are generally commissioned on small- to medium-sized mountainous rivers, often in biodiverse regions, with backing in the form of subsidies, facultative policies and exemption from impact assessments as they are considered ‘green’. However, the ecological impacts of SHPs are understudied especially in highly seasonal tropical streams of Western Ghats of India, a global biodiversity hotspot and a distinct freshwater fish eco-region. We compared SHP-affected segments of a dammed and an undammed river in the Western Ghats of Karnataka, to assess how altered flow regime affects seasonal variability in habitat and water quality, and influences fish assemblage structure. We found that flow alteration by the SHP varied between different segments of the dammed river and with season. Furthermore, the nature of flow alteration influenced habitat variability, water quality and fish assemblage response in the dammed river. We observed that the dewatered segment of the dammed river experienced a lotic to lentic shift in habitat and water quality, which favoured fish species with eurytopic affinities. Fluctuating flows in the downstream segment subdued natural variability in flow regime and created novel habitats and water-quality conditions, affecting fish assemblages. The upstream segment of the dammed river retained natural variability in habitat and water quality, but did not mimic the undammed river in terms of fish composition. We also observed potential constraints on recruitment for migratory species of fish in the dammed river. Based on our results, we suggest how the placement of dewatered segment, and timing the closure of SHP operation in dry season based on ecological thresholds are potential solutions to mitigate the impacts of the SHPs. Furthermore, we recommend effective impact assessments, and adaptive management with active interventions to maintain genetic and ecological connectivity, as key to enhance the sustainability of the SHPs.     

Riparian vegetation and channel change in response to river regulation: a comparative study of regulated and unregulated streams in the Green River Basin,USA

The effects of river damming on geomorphic processes and riparian vegetation were evaluated through field studies along the regulated Green River and the free‐flowing Yampa River in northwestern Colorado, USA. GIS analysis of historical photographs, hydrologic and sediment records, and measurement of channel planform indicate that fluvial processes and riparian vegetation of the two meandering stream reaches examined were similar prior to regulation which began in 1962. Riparian plant species composition and canopy coverage were measured during 1994 in 36, 0.01 ha plots along each the Green River in Browns Park and the Yampa River in Deerlodge Park. Detrended correspondence analysis (DCA) of the vegetation data indicates distinctive vegetation differences between Browns Park and Deerlodge Park. Canonical correspondence analysis (CCA) indicates that plant community composition is controlled largely by fluvial processes at Deerlodge Park, but that soil chemical rather than flow related factors play a more important role in structuring plant communities in Browns Park. Vegetation patterns reflect a dichotomy in moisture conditions across the floodplain on the Green River in Browns Park: marshes with anaerobic soils supporting wetland species (Salix exigua, Eleocharis palustris, Schoenoplectus pungens, and Juncus nodosus) and terraces having xeric soil conditions and supporting communities dominated by desert species (Seriphidium tridentatum, Sarcobatus vermiculatus, and Sporobolus airoides). In contrast, vegetation along the Yampa River is characterized by a continuum of species distributed along a gradual environmental gradient from the active channel (ruderal species such as Xanthium struminarium and early successional species such as S. exigua, Populus deltoides subsp. wislizenii, and Tamarix ramossissima) to high floodplain surfaces characterized by Populus forests and meadow communities. GIS analyses indicate that the channel form at Browns Park has undergone a complex series of morphologic changes since regulation began, while the channel at Deerlodge Park has remained in a state of relative quasi‐equilibrium with discharge and sediment regimes. The Green River has undergone three stages of channel change which have involved the transformation of the historically deep, meandering Green River to a shallow, braided channel over the 37 years since construction of Flaming Gorge Dam. The probable long‐term effects of channel and hydrologic changes at Browns Park include the eventual replacement of Populus‐dominated riparian forest by drought tolerant desert shrublands, and the enlargement of in‐channel fluvial marshes. Copyright © 2000 John Wiley & Sons, Ltd.     

Channel response to sediment replenishment in a large gravel‐bed river: The case of the Saint‐Sauveur dam in the Buëch River (Southern Alps,France)

The Saint‐Sauveur dam was built in 1992 in the middle section of the Buëch River. Downstream of the dam, a channel incision by several meters was observed. A gravel replenishment operation was planned in order to restore the active channel. An equivalent of two times the mean annual bedload‐transport capacity (43,500 m³) was replenished downstream of the dam in September 2016. The aim of this paper is to quantify morphological change associated with sediment remobilization in order to evaluate the efficiency of the restoration works. The monitoring was based on a combination of (a) change detection using sequential high‐resolution digital elevation models (from airborne LiDAR data), (b) bedload tracing using active ultrahigh‐frequency radio‐frequency identification technology, and (c) complementary field surveys of channel grain‐size distribution and morphology for bedload‐transport computation. Field monitoring allows us to capture a net aggradation along a 2‐km reach after the first post‐replenishment flood. A sediment balance analysis was performed to back‐calculate bedload supply coming from the sluicing operation during the flood. Although the sediment replenishment operation clearly had a positive impact on the morphological conditions of the starved river reach, the effective bedload supply from artificial berms (22,650 m³) was insufficient to initiate substantial channel shifting along the restored reach and a subsequent amplification of the sediment recharge. The combination of high‐resolution topographic resurveys and sediment tracing was successful to evaluate the downstream propagation of sediment replenishment effects.     

Effects of transferring glacier-fed water to a clear-water mountain river on the production and food organisms of brown trout (Salmo trutta L.) in Southern Norway

The effects of transferring glacier-fed water to a clear-water river on production and food organisms of brown trout (Salmo trutta L.) were investigated in a mountain river, in southern Norway. Production in unregulated fluvial habitat was 271.5 g 100 m^?2 yr^?1 compared with 103.1 g 100 m^?2 yr^?1 in a glacier-fed reach of the river. This difference was due to low fish density and recruitment rate. The growth rate, at least for younger fish (2+ to 4+ age groups), was significantly higher in the regulated reach of the river. The main difference in food composition was the low abundance of crustaceans Eurycercus lamellatus and Gammarus lacustris in the regulated reach. Trichopterans were the main diet component in both sites.     

The response of phytoplankton and zooplankton to river damming in three cascading reservoirs of the Tana River,Kenya

River damming reduces the ecological heterogeneity of ecosystems, with a resultant shift of communities adapted to lotic conditions to those better adapted to the newly created lentic environment. Whereas the response of phytoplankton and zooplankton community composition and structure to river damming has been extensively studied in individual reservoirs, this study assessed three cascading reservoirs on the Tana River, Kenya. A total of five sampling campaigns were carried out in 2011, 2012 and 2013 for different sampling sites within each of the reservoirs, as well as upstream and downstream of the reservoirs. Plankton communities within each of the three reservoirs, and upstream of the reservoirs, were compared, indicating (i) the disappearance of 13 phytoplankton and 2 zooplankton taxa; (ii) the appearance (invasion) by 26 phytoplankton and 33 zooplankton taxa; and (iii) an opportunistic presence of 7 phytoplankton and 6 zooplankton taxa. Thirty‐two genera of potentially harmful algae were also encountered, suggesting a potential future threat of harmful algal blooms. A significant reduction in phytoplankton diversity and taxa evenness was also observed, as well as increases in overall abundance in the reservoirs, compared to the river upstream of the study reservoirs. However, these ecological indices were restored to the original levels observed upstream of the study reservoirs at sites hundreds of kilometres downstream of the reservoirs.     

Growth,Condition and Survival of Three Forage Fish Species Exposed to Two Different Experimental Hydropeaking Regimes in a Regulated River

Hydroelectric dam operation can alter discharge and temperature patterns, impacting fish populations downstream. Previous investigations into the effects of river regulation on fish have focused on a single species within a river, yet different results among studies suggest the potential for species‐specific impacts. Here, we compare the impacts of two different hydropeaking regimes relative to a naturally flowing river on three ecologically important members of the forage fish community: longnose dace (Rhinichthys cataractae), slimy sculpin (Cottus cognatus) and trout‐perch (Percopsis omiscomaycus). Annual growth, estimated from otolith back‐calculations, was higher for each of the species in the regulated river relative to the naturally flowing river but did not differ between hydropeaking regimes. Condition was assessed using weight–length relationships and differed between rivers for each species, and between hydropeaking regimes for longnose dace and slimy sculpin. Survival of longnose dace and slimy sculpin was lower in the regulated river relative to the naturally flowing river, but comparable between rivers for trout‐perch. Annual growth was significantly related to mean summer discharge in the regulated river and to mean summer water temperature in the naturally flowing river for each species, and significantly different slopes among species indicate species‐specific responses to discharge and temperature alterations. This study demonstrates different biological responses among fish species within rivers to regulation in general, as well as to specific hydropeaking regimes. Future studies should focus on multiple species and multiple indicators of fish health to more fully characterize the impacts of river regulation on downstream fish communities. Copyright © 2016 John Wiley & Sons, Ltd.     

Spawning behaviour and early development of the Clanwilliam yellowfish (Barbus capensis; Cyprinidae), linked to experimental dam releases in the Olifants River,South Africa

This paper describes an investigation of how experimental releases of pulses of high flow from Clanwilliam Dam (Olifants River, South Africa) affect spawning of the Clanwilliam yellowfish, Barbus capensis. This species is endemic to the Olifants River system and is listed as rare in the Red Data Book of fishes for South Africa. Spawning sites are described, as is the spawning behaviour of B. capensis after specific experimental pulses released during the suspected spawning season of the species. Spawning and the developmental stages of embryos, free embryos, and larval B. capensis were studied using direct observations, video recordings, and microscopic examination of live embryos. B. capensis was found to be a repeat-spawner over several days as well as a multiple-spawner throughout the 4 month reproductive season. At present, spawning of B. capensis occurs down-stream of the dam sporadically (and possibly with limited recruitment), concurrent with releases of water for irrigation purposes. Experimental pulses appeared to trigger an increase in spawning activity, as an abundance of larvae was found down-stream 2 months later. It is suggested that a water-release strategy from Clanwilliam Dam could be designed to increase the number of B. capensis in the Olifants River. © 1997 John Wiley & Sons, Ltd.     

Examining the ecological consequences of restoring flow intermittency to artificially perennial lowland streams: Patterns and predictions from the Broken—Boosey creek system in northern Victoria,Australia

The reinstatement of natural flow regimes is a rapidly emerging issue in river restoration worldwide. In northern Victoria, Australia, efforts are presently underway to restore a natural, intermittent flow regime to several streams which have received perennial diversions for both irrigation and stock and domestic water‐supplies for over 100 years. A pipeline to deliver water to landholders will significantly reduce transmission losses throughout the system allowing irrigation canals and diversion weirs to be decommissioned. The motivation for flow alteration in this system lies primarily in reducing inefficiencies in water delivery which, in turn, will be used to meet escalating demands on water resources. The ecological impact of the flow regime shift on these streams is likely to be substantial. This study utilized an existing artificial hydrological gradient (from perennial to intermittent) in two creek systems, to explore relationships between flow regime and a range of ecological variables. These data provide a benchmark against which to assess ecological changes once flow has been altered and form the basis for predicting changes that can assist future management decisions. Data collected from 10 sites across a strong hydrological gradient detected clear differences in geomorphology, water quality and biotic assemblages (macrophytes, macroinvertebrates and fish). By examining the relationship between flow regime and the distribution of biota we identify both the positive and negative outcomes of restoring naturally intermittent flow regimes within artificially perennial lowland streams. The reinstatement of intermittent flow regimes in artificially perennial streams will continue in many parts of the world as water delivery via these systems becomes increasingly uneconomical. While flow restoration may in principle be regarded as a positive step, these findings emphasize the need to consider fully the ecological consequences of restoring historical hydrological regimes to streams within the context of other human induced catchment disturbances. Copyright © 2009 John Wiley & Sons, Ltd.     

Effect of flow variability modification and hydraulics on invertebrate communities in the great fish river (Eastern Cape province,South Africa), with particular reference to critical hydraulic thresholds limiting larval densities of Simulium chutteri lewis (Diptera,Simuliidae)

Flow patterns in the Great Fish River in the Eastern Cape province of South Africa have changed from being seasonal, with predictable no‐flow periods during winter, to perennial following the completion of an inter‐basin transfer scheme in 1977 to provide a regular supply of irrigation water. Simulium chutteri (Diptera: Simuliidae) consequently became a problem species of pestilential proportions, due to increased flow volumes and current velocities favouring this species. In this study, aquatic invertebrates were sampled from the stones‐in‐current biotope with a range of current velocities at three sites on the Great Fish River, with a particular focus on pool/rapid areas favouring S. chutteri. The main aim of this paper was to determine whether critical hydraulic thresholds, including current velocity, could be derived for this species. Knowledge of the hydraulic preferences of S. chutteri is a prerequisite for any integrated control programme which combines larvicidal control with flow manipulation. S. chutteri was found to favour the rapids biotope with current velocities in excess of 90 cms⁻¹, with preferences for higher current velocities increasing with life cycle stage. Additional hydraulic variables, at the scale measured in this study, did not correlate with larval densities. There is potential for more effective long‐term control of problem populations of larval blackfly in the Great Fish River through further research on the potential for using constructed in‐stream vanes to reduce current velocities in rapids of the river at critical periods of the year (July–October), based on flow duration/current velocity relationships. Copyright © 2007 John Wiley & Sons, Ltd.