Fish catch and fishing practices in the Nam Theun 2 Reservoir and watershed (Lao PDR)

A fish catch and fishing practice monitoring survey were conducted from 2008 to 2014 in villages adjacent to the Nam Theun 2 Reservoir and its upstream tributaries. The reservoir fisheries exhibited – the three expected phases following impoundment (i.e. trophic upsurge, trophic depletion and stabilization, respectively). This study focused on assessing fish catches and fishing practices from communities living next to the reservoir, and those living upstream of the reservoir, over these phases, and to identify factors that could influence total fish catch. The fish catch appeared to be higher among communities located next to the reservoir, compared to communities living in upstream areas. Fish catches in the upstream tributaries remained relatively stable after impoundment, with a slight increase in the average catch. The reservoir exhibited a low fish yield, compared to similar reservoirs, which could be linked to its oligotrophic status. The majority of the total catch biomass of the reservoir was comprised primarily of two species (i.e. Oreochromis niloticus; Hampala macrolepidota) since a stabilization of the catches was observed. Reservoir fisheries appeared to be mainly driven by hydrological factors, specifically the influence of the rainy season peak. The results of this study indicated no over‐exploitation of fisheries occurred overall, although the fishery resource is still fragile. Fishing activities are known to occur in protected zones (productive areas with large inundated habitat areas), with higher annual total catch being observed during periods of poor enforcement of these zones. As fisheries have become an important income source for villagers living along the NT2 Reservoir, regulation and adequate management of the reservoir are recommended to maintain the reservoir fisheries as a sustainable activity.     

Sustainable fisheries management in the Great Lakes: Scientific and operational challenges

Fisheries managers seek to sustain Great Lakes' fish populations in a large, complex lake‐watershed ecosystem responding to often competing issues: non‐indigenous species, resource allocation and environmental quality. Within the past 200 years, human activity has caused dramatic changes in the character of this ecosystem. Before the 1900s, the offshore fish communities in each of the Great Lakes were dominated by the piscivorous lake trout and burbot. The current fish fauna of the Great Lakes' basin includes 179 species representing 29 families in 18 orders and two classes of fish. Twenty‐five non‐indigenous fish species have established populations in the Great Lakes' ecosystem. Sustainable management of Great Lakes' fisheries depends on social, economic and ecological factors. Hundreds of millions of dollars are spent annually to protect and preserve Great Lakes' fisheries and their associated ecosystems. Management of Great Lakes' fisheries on a species‐by‐species basis is pointless. Recreational fishing provides larger economic benefits on the Great Lakes, compared to commercial fisheries. Further, quota management, even when practiced at levels well below maximum sustainable yield, does not lead to stable fish communities. Management will be constrained more by ecological reality than by economic forces, but ultimately a managed system comprised of both indigenous and non‐indigenous fishes is a logical objective.     

Environmental impacts of hydroelectric projects on fish resources in China

China has embarked on a programme to vastly expand its hydroelectric generating capacity and this is certain to alter its freshwater and anadromous fish communities. To provide some insight into the direction and consequences of the likely changes, four (>250 000 kW) existing facilities were selected for review. The Gezhouba Dam, on the Changjiang River, commissioned in 1981, is a low-head run of the river facility. The Xinanjiang Dam (1959) is a high-head dam and the Fuchunjiang Dam (1968) is a low-head, run of the river dam, both sited on the Quiantang River. The Danjiangkou Dam (1968) is a high-head dam in the Han River, a tributary of the Changjiang River. Impacts on fish were classified as those caused directly by the structures, those resulting from changes in physical and chemical factors in their environment and those induced through biotic changes in their habitat. Migrations of anadromous and semi-migratory fish were blocked by the Gezhouba Dam, although some species adapted to the new environment by reproducing downstream. Below the Xinanjiang and Danjiangkou dams spawning was delayed 20–60 days by lower water temperatures. Reduced water velocities and less variable discharges caused spawning grounds below the dams to be abandoned. Marked changes in the hydrological regime caused the extinction of Macrura reevesii, a highly valued fish, in the Qiantang River. The fish communities in the Qiantang estuary were affected by the regulated discharge. Freshwater species fell from 96 to 85, whereas marine species increased from 15 to 80. Loss of habitat eliminated torrential habitat species from the areas inundated by Xinanjiang and Danjiangkou Reservoirs; lentic fish replaced lotic species and now dominate the reservoir fish communities. The expanded aquatic habitat was beneficial for fishery production. Catches from the two reservoirs continue to increase 20 years after impoundment, but are supported by extensive artificial propagation and stocking. There is no doubt that, when the expansion of China's hydroelectric facility network is complete, the fish communities in its rivers will be markedly changed.     

Fish Associations among Un‐notched,Notched and L‐head Dikes in the Middle Mississippi River

Wing dikes and other anthropogenic modifications have heavily altered riverine ecosystems. Recent efforts to reach a compromise between the needs of the river transportation industry and natural resource conservation include dike modification. Dike notching permits water flow through the landward portion of the dike and has been purported to provide suitable habitat for fish and other river biota while maintaining the navigation channel. L‐head dikes are flow‐control structures that create calm backwater‐like habitats downstream. However, few researchers have examined the actual effects of dike notching on water quality or fish communities. We compared standardized catch per unit effort and overall community structure for 50 fish species among un‐notched dikes, notched dikes and L‐head dikes in the Middle Mississippi River, sampled as part of the US Geological Survey's Long‐Term Resource Monitoring Program. There were no differences in standardized catch per unit effort for 64% of the fishes examined. Five species known to be associated with lotic habitats were most abundant near L‐head dikes. Seven species were more abundant at un‐notched dikes than notched dikes, while six species were more abundant at notched dikes than un‐notched dikes. Non‐metric multidimensional scaling suggested differences in overall fish community structure between un‐notched and other dike types. Detailed physical habitat studies should be conducted to better understand the effects of dike modification. Copyright © 2015 John Wiley & Sons, Ltd.     

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.     

Anthropogenic Disturbance and Environmental Associations with Fish Assemblage Structure in Two Nonwadeable Rivers

Nonwadeable rivers are unique ecosystems that support high levels of aquatic biodiversity, yet they have been greatly altered by human activities. Although riverine fish assemblages have been studied in the past, we still have an incomplete understanding of how fish assemblages respond to both natural and anthropogenic influences in large rivers. The purpose of this study was to evaluate associations between fish assemblage structure and reach‐scale habitat, dam, and watershed land use characteristics. In the summers of 2011 and 2012, comprehensive fish and environmental data were collected from 33 reaches in the Iowa and Cedar rivers of eastern‐central Iowa. Canonical correspondence analysis (CCA) was used to evaluate environmental relationships with species relative abundance, functional trait abundance (e.g. catch rate of tolerant species), and functional trait composition (e.g. percentage of tolerant species). On the basis of partial CCAs, reach‐scale habitat, dam characteristics, and watershed land use features explained 25.0–81.1%, 6.2–25.1%, and 5.8–47.2% of fish assemblage variation, respectively. Although reach‐scale, dam, and land use factors contributed to overall assemblage structure, the majority of fish assemblage variation was constrained by reach‐scale habitat factors. Specifically, mean annual discharge was consistently selected in nine of the 11 CCA models and accounted for the majority of explained fish assemblage variance by reach‐scale habitat. This study provides important insight on the influence of anthropogenic disturbances across multiple spatial scales on fish assemblages in large river systems. Copyright © 2014 John Wiley & Sons, Ltd.     

Diel patterns in spatial distribution of fish assemblages in lentic and lotic habitat in a regulated river

Fish assemblages in large rivers are governed by spatio‐temporal changes in habitat conditions, which must be accounted for when designing effective monitoring programmes. Using boat electrofishing surveys, this study contrasts species richness, catch per unit effort (CPUE), total biomass, and spatial distribution of fish species in the Saint John River, New Brunswick, Canada, sampled during different diel periods (day and night) and macrohabitats (hydropower regulated river and its reservoir) in the vicinity of the Mactaquac (hydropower) Generating Station. Taxa richness, total CPUE, and total biomass were significantly higher during night surveys, resulting in marked differences in community composition between the two diel periods. Furthermore, the magnitude of diel differences in catch rate was more pronounced in lentic than in lotic macrohabitats. The required sampling effort (i.e., number of sites) to increase accuracy and precision of CPUE estimates varied widely between fish species, diel periods, and macrohabitats and ranged from 15 to 185 electrofishing sites. Determining a correction factor to contrast accuracy and precision of day‐ with night‐time surveys provide useful insights to improve the design of long‐term monitoring programmes for fish communities in large rivers. The study also shows the importance of multihabitat surveys to detect differences in the magnitude of diel changes in fish community metrics.     

The river Vecht fish community after rehabilitation measures: a comparison to the historical situation by using the river Biebrza as a geographical reference

Setting ecological goals for restoring fish communities in larger rivers is hampered by a lack of knowledge of the natural reference conditions. The lowland river Vecht has become highly regulated since 1850. Since the 1970s, measures have been taken to improve water quality followed by the construction of fishways along weirs in the 1990s to rehabilitate migration. We aim to assess the degree of deviation of the current fish community in the river from its pre‐regulation state. The assessment is based on a comparison with the less impacted river Biebrza in Poland as a geographical reference, involving a semi‐quantitative stepwise reconstruction based on available historic evidence. Electrofishing was used to describe the current quantitative species compositions of the fish communities in the rivers Vecht and Biebrza and historical records of the Vecht region were used to crosscheck the reconstructed fish community around 1850 after correcting for zoogeographical differences. Despite various rehabilitation measures, the deviation from the natural reference is still large. Currently, perch Perca fluviatilis and bream Abramis brama are much more abundant, and bleak Alburnus alburnus, white bream Blicca bjoerkna and most rheophilic species are far less abundant, than before. The main reasons for this deviation appears to be the present quality of the habitats and, for some species, the poor connectivity with the sea as well as with small tributaries. The approach used should be widely applicable to derive natural references, assess rehabilitation success or improve the ecological assessment of integrity as imposed by the European Water Framework Directive. Copyright © 2008 John Wiley & Sons, Ltd.     

Dynamics of river fish populations in response to hydrological conditions: a simulation study

Increasing multi‐sectoral demands on water resources have led to water abstraction and transfer activities, and the construction of dams and embankments that have significantly altered the flood regimes of rivers throughout the world resulting in the loss of fish production and biodiversity. The current emphasis on sustainable development and biodiversity conservation is leading efforts to mitigate these impacts by means of interventions such as the release of artificial floods downstream of dams and the manipulation of water levels within impounded floodplains. Whilst much work has been done to determine the hydrological requirements for the maintenance of salmonid populations, few equivalent studies are available from which to develop criteria for the management of hydrological regimes for fishes and fisheries in large floodplain–river systems such as the Mekong. The population dynamics of fish in such rivers are believed to respond to hydrological conditions in a density‐dependent manner. An age‐structured population dynamics model incorporating sub‐models describing density‐dependent growth, mortality and recruitment was used to explore how hydrological conditions within a theoretical floodplain–river system affect the dynamics of a common floodplain–river fish species. Graphical summaries of the response of exploitable biomass to a range of different drawdown rates, dry and flood season areas and volumes, and flood season durations are presented under five different model assumptions concerning density‐dependent processes. Optimal flooding patterns are also described for the model species and theoretical river system. The patterns of predictions that emerge from the simulations provide guidelines for managing or manipulating hydrological conditions in river systems for both fixed and variable volume hydrological scenarios. As a general rule of thumb, exploitable biomass is maximized by minimizing the rate of drawdown and maximizing the flood duration and flood and dry season areas or volumes. However, experiences from dam and other hydraulic engineering projects suggest that these predictions should be treated with caution until we better understand the influence of hydrology on spawning behaviour, system primary production, and critical habitat availability. Copyright © 2004 John Wiley & Sons, Ltd.     

Assessment of the impacts of a new artificial lake mouth on the hydrobiology and fisheries of Chilika Lake, India

The degraded state of the fragile ecosystem of Chilika Lake, located on the east coast of India, was undergoing restoration through an effective hydrological intervention during the year 2000. Studies on the lake’s hydrobiology and fisheries for the period of 7 years before and 7 years after the hydrological intervention indicated a rapid recovery of the lake fishery immediately after opening of the new lake mouth, with a sixfold increase in the average annual fish landings. During 2000–2001 to 2006–2007, the average fisheries output (11 051.3 t), catch per unit effort (6.2 kg boat^?1 day^?1), the economic valuation of the average annual catch (637 million rupees) and productivity (11.97 t km^?2) exhibited dramatic increases of 498%, 464%, 1177% and 498.5%, respectively, compared with the 7‐year pre‐intervention data. Multivariate statistical analysis inferred that most of the lake’s environmental variables are strongly associated with salinity factor, which seems to have governed the lake ecology. The salinity dynamics of the lake are governed by both freshwater inflows and seawater ingress through the new artificial lake mouth. Correlation analysis indicated that salinity was positively correlated with prawn catch (R² = 0.542; d.f. = 25; P < 0.01), crab catch (R² = 0.628; d.f. = 25; P < 0.001) and fish catch (R² = 0.476; d.f. = 25, P < 0.05). The average increase in the salinity regime (43.8%) for the lake during the post‐hydrological intervention period, compared with the pre‐hydrological intervention period, appears to have positively impacted the fish, prawn and mud crab catches. A gradual decrease in total fisheries output since 2005–2006, however, was attributed mainly to a continuing increase in destructive fishing practices in the absence of any conservation and regulatory measures for fishing, and large‐scale collection of shrimp juveniles from the outer channel for shrimp aquaculture. Thus, carefully planned conservation and regulation measures must be ensured, with active participation of local communities during this early phase of lake restoration. In the absence of such measures, the present scenario of fisheries enhancement might not be sustained over the long term.     

Management issues in the Lake Victoria watershed

Lake Victoria is the largest lake in Africa (68 800 km²) and is the eighth largest lake in the world by volume. The three East African countries of Tanzania, Uganda and Kenya share Lake Victoria and its resources. The total annual catch of fish from the lake ranges between 400 × 10⁶ kg and 500 × 10⁶ kg, bringing these riparian countries a combined annual income of approximately US$250 000–500 000 from exports alone. Approximately 30 million people live in the riparian region and the catchment, with about 2 million of these depending directly or indirectly on fishing activities. Tragically, Lake Victoria’s extremely diverse fauna was decimated in only 30 years following the introduction of non‐native Nile perch in the early 1960s. An estimated 200 endemic cichlid species became extinct. Dramatic increases in overfishing, pollution from various sources, effects of noxious water weeds and other associated problems threaten the sustainability of the lake’s resources and the economies of the riparian governments and peoples. Regulations governing Lake Victoria’s resources are different in each country. The laws concerning treatment of effluents from point sources in the three countries are not harmonized, neither are implementation or enforcement provisions. The governments of Kenya, Uganda and Tanzania have begun to put in place regional mechanisms to address the lake’s many problems including the creation of a permanent regional international institution through the establishment of the Lake Victoria Fisheries Organization (LVFO). A strategic vision document and action plans have been developed. Efforts are being made at local, national and regional levels to control the water hyacinth, including manual pulling, mechanical harvesting and introduction of weevils that weaken hyacinth root systems. To address the problem of overfishing, fishermen committees at landing beaches have been put in place. Each country has committed to take all necessary measures including legislation to implement the decisions of the LVFO governing bodies. All three countries have agreed to adopt and enforce legislation and regulations prohibiting the introduction of non‐indigenous species to the lake and to enforce existing regulations regarding fisheries. A Global Environment Facility project which provides funding to the Lake Victoria Fisheries Organization addresses land use management, catchment forestation, fisheries research and management, water hyacinth control, industrial effluent treatment and municipal waste treatment.     

Impacts of the Victoria Nile Bujagali hydropower dam on fisheries and livelihoods

The Upper Victoria Nile (UVN) flows from Lake Victoria into Lake Kyoga, spanning 117 km and supports a diverse aquatic fauna that sustains livelihoods of riverside communities. The UVN is habitat to critically endangered (Labeo victorianus), near threatened (Oreochromis variabilis and Oreochromis esculentus), and rare species (Neochromis simotes). Four hydropower dams were built on the UVN to provide energy for industrial and socioeconomic development, notwithstanding consequential environmental and socioeconomic impacts. The impacts of Bujagali hydropower (BHP) dam on fisheries and livelihoods were assessed biannually (April and September) from 2006 to 2019, using fishing effort, species abundance, catch composition, and economic beach revenue at upstream, mid-reservoir, and downstream transects. The fishing boats increased from 31 in 2009 to 293 in 2019 and fishers from 83 to 500 over the monitoring period. Maximum annual catch of 461.4 t was recorded in 2014 and lowest of 54.2 t in 2009. In all transects, Protopterus aethiopicus and Labeo victorianus were least in the commercial catches and the use of Mormyrus kannume juveniles as bait for Nile perch fishery corresponded with increased catches from 3.3 t in 2009 to 148.2 t in 2019. Women were mostly engaged in post-harvest activities such as fish drying, smoking, and food vending. These observations suggest coupling effects of the hydropower dam and ineffective fisheries management. The harvest of M. kannume wild stocks for bait should be banned and research in possible domestication of the species undertaken. There is a need to strengthen fisheries enforcement to curb illegal effort and overexploitation and to implement conservation actions to mitigate potential biodiversity impacts from the hydropower dam operations.     

Relationship between river surface level and fish assemblage in the Ocklawaha River,Florida

Understanding the relationship between river flows and levels and fish communities is important to setting minimum flow and level regulations designed to prevent ecological harm. We reviewed a long‐term Florida Fish and Wildlife Conservation Commission data set from the Ocklawaha River, Florida, to evaluate trends in fish abundance and fish communities relative to historical river levels. Fish data were collected using electrofishing at the Ocklawaha River, Florida, during 1983–1994. Electrofishing data were used to estimate catch per minute and biomass per minute of selected species, fish diversity, richness and evenness. Catch rate variables were compared among years and significant differences in abundance and community indices were related to historical water levels using multiple regression models. Results indicated that differences in abundance and community indices among years were more common at the site with increased river level variability. Regression models indicated that fish abundance and species richness were positively related to river levels, and species diversity was negatively related to variability in river level during the two years prior to sampling. Spotted sunfish Lepomis punctatus exhibited the most variability in species‐specific catch per effort and spotted sunfish abundance was positively related to river levels. Low river levels negatively influenced fish abundance and fish communities, and minimum flows in Florida should manage for the periodicity of low flow events to prevent sequential years of adverse effects on fish populations. Copyright © 2005 John Wiley & Sons, Ltd.     

Gillnet selectivity estimates for five commercially important fish species in Tono Reservoir,Northern Ghana

Gillnet selectivity is crucial for the effective and sustainable management of fisheries. However, there is inadequate information on gillnet selectivity for commercially important species in Tono Reservoir. To facilitate the sustainable exploitation of fish species, this study was conducted to estimate the selectivity parameters of commonly used monofilament gillnets for commercially important fish species in Tono Reservoir from January 2015 to June 2016. Two common nylon monofilament gillnets used by fishermen in Tono Reservoir with stretched mesh sizes 5 and 7 cm and equal dimensions were placed in the same fishing area and retrieved within 12 h. The fish catches were assessed, and selectivity parameters for Sarotherodon galilaeus, Oreochromis niloticus, Coptodon zillii, Clarias gariepinus and Auchenoglanis occidentalis were estimated using the Holt model. The catch per unit effort of the two gillnets exhibited no significant difference. The optimum total lengths of capture of four fish species excluding C. zillii ranged from 13.53 to 25.43 cm for the 5 cm gillnet, and 18.95 to 35.60 cm for the 7 cm gillnet. Common selection factors varied from 2.71 to 5.09. The mean total length at first sexual maturity for all five fish species ranged from 8.60 to 28.86 cm. Both the 5 and 7 cm gillnets were found to be inappropriate for use in the reservoir. Accordingly, their use should be discouraged to protect juvenile fish so that the sustainable exploitation and conservation of fish species in this multispecies fishery can be achieved.     

Interactive effects of abiotic,hydrological and anthropogenic factors on fish abundance and distribution in natural run‐of‐the‐river shallow lakes

Ecological processes in lowland rivers are mostly dominated by hydrology and its interactions with other environmental factors. Fish–habitat relationships in rivers are also influenced by human impacts. In this study, we describe patterns of abundance and distribution of fish species in a group of natural lowland river lakes along spatial anthropogenic and abiotic gradients when four hydrologically different summers are compared. We also describe the proportion of the total variances in fish species abundances that can be accounted for by selected abiotic (water conductivity), hydrological (water residence time) and human activity‐derived (total phosphorus (TP) concentration and NO₃:NH₄) variables. Consequently, our main purpose is to explore how abiotic and anthropogenic factors interact to affect fish abundance and distribution together with consistent results across different hydrological conditions. We conclude with a briefly discussion of some management implications. The anthropogenic impacts on water quality, the extreme hydrological variability and the fluctuating abiotic environment affected fish abundance and distribution. Pampa inland silverside Odontesthes bonariensis was benefited from a less human disturbed environment with higher water residence time and total salinity, whereas species as Cyphocharax voga, Parapimelodus valenciennis and Cyprinus carpio found these conditions largely disadvantageous. On the other hand, while most species showed stronger—either negative or positive—response to anthropogenic, hydrological or abiotic factors Oligosarcus jenynsii was only slightly affected. This paper identified the ecological function of a lowland river under its natural flow regime. There are not many opportunities to study unmodified rivers worldwide. Therefore, our findings may help in assessment programmes of fish communities in flow altered and human disturbed aquatic ecosystems. Copyright © 2008 John Wiley & Sons, Ltd.     

A COMPARISON OF TWO ELECTROFISHING PROGRAMMES USED TO MONITOR FISH ON THE ILLINOIS RIVER,ILLINOIS, USA

The Illinois River Biological Station monitors fish communities in the Illinois River using two different electrofishing programmes, one using three‐phase alternating current [AC; The Long Term Illinois Fish Population Monitoring Program or long‐term electrofishing (LTEF)] and the other pulsed direct current [DC; The Long Term Resource Monitoring Program (LTRMP)]. In 2001, we replicated three‐phase AC sampling sites with pulsed‐DC electrofishing gear to test for differences between the two collection methods and programmes. Electrofishing runs at each site were standardized by length and time, with 48 samples collected for each gear. Our objective was to test for differences in fish catch rates using total catch, species richness, fish size ranges, and sample composition and structure. Total catch was significantly greater for LTRMP electrofishing (4368 total fish, mean = 91.0 fish per sample) compared with LTEF electrofishing (1423 total fish, mean = 29.6 fish per sample). Species richness also was significantly greater for LTRMP electrofishing (50 total species, mean = 12.9 species per site) compared with LTEF electrofishing (38 total species, mean = 7.9 species per site). Size ranges of fishes, composed of 100‐mm‐length groups, showed higher total catches for the LTRMP within all length groups. Although our analyses suggest that collections from the LTRMP were significantly greater in most instances, a consistent pattern of species composition between the two programmes was not evident. Our results suggest that caution must be taken when attempting to compare fish community composition and structure information between these programmes. Copyright © 2011 John Wiley & Sons, Ltd.     

Fish zonation and indicator species for the evaluation of the ecological status of rivers: example of the Loire basin (France)

In the context of river alteration, ecologists are asked to develop tools for the assessment of river integrity. Fish are known to be good bioindicators of the ecological condition of rivers. The Loire basin (France) is often considered as relatively little impacted compared to most other large European systems. But curiously, no study clearly addressed the question of fish assemblages patterns in this system in order to assess this status. Thus, we studied fish assemblages along the river network in the Loire basin using self‐organizing maps (SOMs) and we built a fish typology. Four basic assemblages were described and indicator species were identified. These assemblages varied in terms of individual species patterns as well as in terms of flow preference guilds and species richness. A discriminant analysis carried out on environmental variables revealed that they could be mainly determined by the slope, temperature and depth. Finally, fish assemblages were arrayed along a longitudinal gradient and roughly fitted the theoretical zonation expected in European rivers with the succession of brown trout (Salmo trutta fario), grayling (Thymallus thymallus), barbel (Barbus barbus) and bream (Abramis brama) zones in a downstream direction. Such patterns are still rarely observed in large European systems. However, the fish assemblage characteristic of the bream zone occurred more frequently than predicted on the basis of environmental variables. Such deviations between field data and theory suggest lotic‐to‐lentic shifts probably due to anthropogenic disturbances, especially in the grayling and barbel zones. In these river sectors, eurytopic and limnophilic species tend to replace rheophilic ones. Finally, the method used in this study to investigate fish patterns may be helpful to detect disturbances and may serve as a tool for the establishment of management plans. Copyright © 2007 John Wiley & Sons, Ltd.     

River regulation and nature conservation

The basic tenet of nature conservation is the protection and management of the environment so as to maintain its wildlife. Much of the effort is presently expended in securing the continued existence of rare, endangered or threatened species, communities, and habitats. River regulation involves considerable environmental manipulation. This extends beyond the modification of discharge regimes through the need for ancilliary operations, including the construction of dams, channel modification and transfer of water between catchments. The imposition of regulation modifies the natural environment in which the original communities of organisms became established. Where the ecological requirements of these organisms are destroyed or modified beyond the limits of their adaptations or tolerances they are unable to survive. The communities are thus changed and replaced by others, perhaps of lesser conservation value. Since the aims of nature conservation and river regulation are intrinsically incompatible the best that can be hoped for is that regulation schemes are designed, constructed, and operated so as to ameliorate environmental damage.