River Fragmentation Research Articles

Just add water: rapid assembly of new communities in previously dry riverbeds, and limited long-distance effects on existing communities.

Barriers preventing species from dispersing to a location can have a major influence on how communities assemble. Dispersal success may also depend on whether dispersers have to colonise an established community or a largely depauperate location. In freshwater systems, dams and weirs have fragmented rivers, potentially limiting dispersal of biota along rivers. Decommissioning aqueducts on two weirs, each within a tributary of different regulated rivers, delivered flow to previously dry riverbeds and additional flows to the main stem, regulated rivers further downstream. This provided an opportunity to test how removal of dispersal constraints affected community assembly in new habitats and whether changed dispersal can alter existing communities. The results were very similar for the two systems. Even with dispersal constrained via reduced drift rates, the new communities in the newly formed habitat in tributaries rapidly resembled unimpacted reference communities that were the source of colonists. For established communities (regulated rivers), greater flow increased the densities of filter feeders but this was due to greater areas of fast-flowing habitat (a change in environmental constraints) rather than higher dispersal rates. Our study illustrates that communities can quickly re-assemble when natural channels that have been dry for decades are re-wetted by flows that deliver dispersers from intact locations upstream. Nevertheless, boosting flows and concomitant densities of dispersers had no strong effects on existing communities. Instead, increased discharges effected a reduction in environmental constraints, which altered trophic structure. Thus, increases in discharge and dispersal produced different outcomes in new versus established communities.

Utilization of satellite altimetry retrieved river roughness properties in hydraulic flow modelling of braided river system

ABSTRACT Sand bed braided rivers, such as the Brahmaputra, are highly dynamic in nature. The braided rivers change their course frequently, which causes huge bank erosion and sand bar migration. During the monsoon season the braided river has higher sediment-carrying capacity and the erosion power. A large amount of energy dissipation takes place in terms of river fragmentation and sand bar migration and bar erosion. These are common morphological characteristics within the sand bed braided rivers. The dynamic river bed and planform offer varying resistance to flow based on the hydrologic regime and reach characteristics of the river. Estimation of channel roughness coefficient is important for hydraulic modelling of the river. In this study, roughness characteristics of the Brahmaputra river were estimated using altimetry derived river stage records at different reaches of the river. The estimated Manning's roughness coefficients were incorporated in one-dimensional hydraulic model to perform simulations over the middle reach of the Brahmaputra River. Comparison of seasonal water level differences at different reaches of the river was performed using altimetry retrieved and model simulated water level for 2014 and 2015, respectively. The simulated water levels from altimetry derived Manning's roughness coefficient were found to be in close range with altimetry retrieved water levels for 2014 and 2015. It was found that the spatio-temporal variation of Manning's roughness coefficient proved to be an important parameter for modelling braided river systems such as the Brahmaputra.

Early settlement and growth of stocked European glass eels in a fragmented watercourse

AbstractOne of the actions that has been implemented to support the recovery of the panmictic population of European eel is stocking of waterbodies where natural recruitment is low or null. However, growth conditions of the stocked eels can vary greatly. This circumstance emphasises the importance to determine ideal habitat conditions to contribute to the success of stocking actions and, consequently, to increase the production of silver eels. This study aims to evaluate the early settlement and growth of stocked glass eels in the upper reaches of a fragmented river. Stocking was carried out, in 2014, at three sites of an inland tributary of the Mondego river basin (Central Portugal), and its monitoring was conducted during the following two years, until 2016, along with the collection of environmental and hydromorphological parameters. The results showed a successful dispersion throughout the study area. Growth varied spatially, although environmental parameters have not clearly explained this variation, but overall with high growth rates and a positive allometric growth in this early stage of stocking, suggesting a good condition of the stocked individuals. This study showed that these upper reaches of fragmented watercourses, a shared feature amongst most European rivers that are currently inaccessible for natural recruitment, may be suitable habitats for eel stocking.

Riverscape genetics in brook lamprey: genetic diversity is less influenced by river fragmentation than by gene flow with the anadromous ecotype.

Understanding the effect of human-induced landscape fragmentation on gene flow and evolutionary potential of wild populations has become a major concern. Here, we investigated the effect of riverscape fragmentation on patterns of genetic diversity in the freshwater resident European brook lamprey (Lampetra planeri) that has a low ability to pass obstacles to migration. We tested the hypotheses of (i) asymmetric gene flow following water current and (ii) an effect of gene flow with the closely related anadromous river lamprey (L. fluviatilis) ecotype on L. planeri genetic diversity. We genotyped 2472 individuals, including 225 L. fluviatilis, sampled from 81 sites upstream and downstream barriers to migration, in 29 western European rivers. Linear modelling revealed a strong positive relationship between genetic diversity and the distance from the river source, consistent with expected patterns of decreased gene flow into upstream populations. However, the presence of anthropogenic barriers had a moderate effect on spatial genetic structure. Accordingly, we found evidence for downstream-directed gene flow, supporting the hypothesis that barriers do not limit dispersal mediated by water flow. Downstream L. planeri populations in sympatry with L. fluviatilis displayed consistently higher genetic diversity. We conclude that genetic drift and slight downstream gene flow drive the genetic make-up of upstream L. planeri populations whereas gene flow between ecotypes maintains higher levels of genetic diversity in L. planeri populations sympatric with L. fluviatilis. We discuss the implications of these results for the design of conservation strategies of lamprey, and other freshwater organisms with several ecotypes, in fragmented dendritic river networks.

Single-Stream Recycling Inspires Selective Fish Passage Solutions for the Connectivity Conundrum in Aquatic Ecosystems.

Barrier removal is a recognized solution for reversing river fragmentation, but restoring connectivity can have consequences for both desirable and undesirable species, resulting in a connectivity conundrum. Selectively passing desirable taxa while restricting the dispersal of undesirable taxa (selective connectivity) would solve many aspects of the connectivity conundrum. Selective connectivity is a technical challenge of sorting an assortment of things. Multiattribute sorting systems exist in other fields, although none have yet been devised for freely moving organisms within a river. We describe an approach to selective fish passage that integrates ecology and biology with engineering designs modeled after material recycling processes that mirror the stages of fish passage: approach, entry, passage, and fate. A key feature of this concept is the integration of multiple sorting processes each targeting a specific attribute. Leveraging concepts from other sectors to improve river ecosystem function may yield fast, reliable solutions to the connectivity conundrum.

Is small hydropower beautiful? Social impacts of river fragmentation in China's Red River Basin.

Small hydropower (SHP) is promoted as a pro-poor renewable energy source that does not have the negative social impacts of large dams. This article challenges these claims, using data from a household survey in China's upper Red River Basin. We find that SHP can fragment river systems in ways that reduce irrigation water availability, provoke changes to agricultural practices, and negatively impact river health. These social impacts of river fragmentation mainly occur in villages situated between a plant's intake and outflow. The frequency of plant water diversions due to continued generation in the dry season significantly predicts all social impacts; installed capacity of the plant and the quality of the village's irrigation infrastructure predict some impacts. Villages with strong local governance can negotiate with the plant to temporarily halt generation when irrigation water is needed, lessening social impacts. Our findings reveal that SHP plants are not as benign as they are made out to be; they must be built and managed according to community needs.

The combined effects of climate change and river fragmentation on the distribution of Andean Amazon fishes.

Upstream range shifts of freshwater fishes have been documented in recent years due to ongoing climate change. River fragmentation by dams, presenting physical barriers, can limit the climatically induced spatial redistribution of fishes. Andean freshwater ecosystems in the Neotropical region are expected to be highly affected by these future disturbances. However, proper evaluations are still missing. Combining species distribution models and functional traits of Andean Amazon fishes, coupled with dam locations and climatic projections (2070s), we (a) evaluated the potential impacts of future climate on species ranges, (b) investigated the combined impact of river fragmentation and climate change and (c) tested the relationships between these impacts and species functional traits. Results show that climate change will induce range contraction for most of the Andean Amazon fish species, particularly those inhabiting highlands. Dams are not predicted to greatly limit future range shifts for most species (i.e., the Barrier effect). However, some of these barriers should prevent upstream shifts for a considerable number of species, reducing future potential diversity in some basins. River fragmentation is predicted to act jointly with climate change in promoting a considerable decrease in the probability of species to persist in the long-term because of splitting species ranges in smaller fragments (i.e., the Isolation effect). Benthic and fast-flowing water adapted species with hydrodynamic bodies are significantly associated with severe range contractions from climate change.

Biomechanics of fish swimming and leaping under waterfalls: a realistic field, image-based biophysical model with bioengineering implications**This manuscript has been professionally edited and proofread.

Worldwide river fragmentation by infrastructures is altering essential ecological processes including fish migrations. Unlike laboratory approaches, field methods and biophysical models have the potential to provide realistic representations of interacting fish-obstacle systems, furthering insights in behavioural and biomechanics science, and allowing better bioinspired engineering. We developed a new field, image-based method that integrates a biophysical mechanistic model to describe the swimming and leaping biomechanics of wild populations of fish in the non-lab ecological context where their reproductive migration takes place. A weir obstacle in natural riverine conditions where fish freely migrate upstream to their breeding grounds was filmed. A biophysical model including the relevant biomechanical and hydraulic forces and their interactions was parametrised and calibrated with the spatial coordinates of fish trajectories. The method was validated with independent empirical data under field conditions. The distribution of fish initial velocities and angle of emergence of the sample of filmed leaps were reliably quantified in field conditions. The distribution of burst swimming velocities underwater was differentiated from that of the initial leaping velocities associated with the thrust of hydraulic forces; fish behaviour while emerging from water was described. Fish approximated the optimum angle to negotiate the waterfall but did not reach the minimum velocity needed to negotiate the obstacle. The method demonstrated the ability to provide realistic, accurate and precise ecological data on field-based fish interactions with challenge zones during upstream reproductive migrations. The method is cost-effective as it is based on general purpose digital cameras, image analysis, and modelling equations in spreadsheets; all inexpensive and readily available. This new approach can be directly applied to solve scientific problems and bioengineering challenges in any freshwater ecosystem that has natural or artificial obstacles and migratory fish with leaping behaviour.

An analysis of river fragmentation by dams and river dewatering in Costa Rica

AbstractHydropower development is accelerating in the tropics, especially construction of small dams. Small dams are often classified as those lower than 15 m in height or with reservoir capacity less than 3 × 106 m3. Small dams frequently operate with water diversions from the main river channel, thereby affecting river connectivity through the creation of a dewatered reach. However, the extent and impact of dewatered reaches have been overlooked in most analyses of river fragmentation and dams to date. In Costa Rica, small dam development increased during the 1990s, ahead of current trends in other tropical regions. This study examined the effects of dams and their dewatered reaches on river connectivity at a national scale in Costa Rica. We adapted the Dendritic Connectivity Index and applied it to the four basins where over 80% of hydropower development has occurred. Our results showed that in two basins, the Sarapiqui and San Carlos, dewatered reaches contributed most to river fragmentation. In the Tarcoles and Reventazon basins, dams and dewatered reaches had similar effects on river fragmetnation. These different patterns can be explained by the spatial arrangement of dams in the individual river networks. We also found that dewatered reaches extended the elevation range of rivers affected by hydropower activity; this expansion was most significant in cases with interbasin water transfers. We discuss the implications of our findings on connectivity losses from dams for fishes whose range overlaps with hydropower activity. Our study may provide insights for other tropical countries with ongoing and future small dam development.

Movement ecology of imperilled fish in a novel ecosystem: River‐reservoir movements by razorback sucker and translocations to aid conservation

Abstract Reservoirs and associated river fragments are novel ecosystems not experienced by fishes in their evolutionary history, yet they are now commonplace across the globe. Understanding how fishes use these novel habitats is vital to conservation efforts in contemporary riverscapes. Movement patterns of the endangered razorback sucker (Xyrauchen texanus) synthesized from tagging efforts in the upper Colorado River basin, USA, illustrate the applications of tagging technology and data sharing by multiple agencies to better understand the spatial ecology of large river fishes. Tagging studies between 2014 and 2018 in Lake Powell and its two main tributary rivers, the Colorado (unfragmented) and San Juan (waterfall‐fragmented), were used to quantify movement of razorback sucker within this river–reservoir habitat complex. In addition, facilitated translocations of fish upstream of a waterfall barrier in the San Juan River were assessed in 2016–2017. Extensive movement of fish occurred within and across river and reservoir habitats. Of 722 fish captured in the Colorado River arm of Lake Powell, 36% of re‐encounters occurred upstream in the Colorado or Green rivers, or fish dispersed through the reservoir and were detected in the San Juan River arm. Fourteen fish moved more than 600 km. In the San Juan arm of the reservoir, 29% and 20% of fish in 2017 and 2018, respectively, had moved ~30–40 km upstream below the waterfall in the San Juan River within a year. In 2016–2017, 303 fish were translocated upstream of the waterfall into the San Juan River, but 80% were re‐encountered downstream of the waterfall within a year. Long‐distance movements by razorback sucker were common within and among rivers and reservoirs illustrating how large river fish, in general, might maintain population connectivity in highly altered ecosystems.

Impact of ponds and reservoirs construction on the environmental safety of small river basins of the steppe zone of Ukraine (the case of Dnipropetrovsk region)

Formulation of the problem. For the last 30 years, water management in the basins of small rivers in the steppe zone of Ukraine has led to a deterioration of the environmental safety in water use. The current ecological state of small rivers is close to critical, and for today some river basins are subject to catastrophic environmental changes. Almost all small rivers from 70 to 100% in the south and central water-short regions of Ukraine are under regulation due to the construction of a large number of ponds and reservoirs. In most cases, this causes a lack of transportation and low self-cleaning ability. Thus, the conservation, restoration and rational use of water, based on the principles of basin management, should get started along with the improvement of the ecosystems of small rivers.Research results. The paper describes the dynamics of changes in water management, which shows a rapid increase in the number of new ponds in the period of 1990 - 2018 almost threefold. At the same time, the overall dynamics of water consumption in the region in the same period decreased fourfold. Unjustified imbalance between the construction of new facilities and water demand was determined, as well as non-compliance with the current statutory provisions. Due to the transformation of natural watercourses into cascades of "evaporator ponds" an ecologically dangerous transformation of small river basins with the change of hydrological, hydrochemical, hydrobiological and sanitary regimes takes place. To evaluate the level of environmental hazards associated with water management, it is proposed to determine the river fragmentation coefficient, which is the ratio of the number of ponds and reservoirs to the length of the river. When evaluating the environmental hazard for rivers in a specific territory (administrative area, district or catchment area), the fragmentation coefficient is determined by the ratio of the number of ponds and reservoirs to the size of the territory. Comparative analysis indicates that Dnipropetrovsk region is one of the most environmentally dangerous in terms of the negative impact of river basins fragmentation by artificial reservoirs. The case of a small river basin (the Nyzhnia Tersa River) presents the application of the approach to evaluate the level of environmental safety associated with water management. It is proposed a mechanism for increasing the level of environmental safety in water use by observing and implementing heterogeneous groups of indicators that determine the overall efficiency of the river ecosystem functioning.Conclusions. In order to stabilize and restore the hydrological and ecological state of small rivers in the steppe zone of Ukraine, it is important to: 1) make a detailed evaluation of the compliance of the available number of ponds and small reservoirs in river basins with the requirements of the Water Code of Ukraine; 2) prove ecologically and economically the feasibility of further operation for each individual reservoir and structure; 3) develop regional programs for the elimination of ponds and reservoirs that do not fulfil their water management functions and cause environmental hazards to the functioning of the river basin ecosystem; 4) improve methodological approaches to evaluation of the environmental safety of water facilities in small river basins.

A new method to include fish biodiversity in river connectivity indices with applications in dam impact assessments

Abstract Different indices have been developed to quantify the extent and severity of river fragmentation. These indices vary depending on the specific goals of the study. Here, we present a new Conservation Connectivity Index (CCIP) for potamodromous fish species that considers the conservation value (richness, rarity and vulnerability) of river segments. The Iberian Peninsula holds > 20 endemic and endangered potamodromous fish species as well as > 1000 large dams (> 1 hm3 of capacity). The CCIP was calculated for the eight most important river basins of the Iberian Peninsula and compared to the Dendritic Connectivity Index (DCIP) developed by Cote et al. in 2009, which uses only river length as a habitat variable. With the use of both DCIP and CCIP, the dams were analysed and ranked according to their impacts on the river basin. The main results show that Iberian river basins are heavily fragmented, with river basin connectivity percentages of less than 20% in most cases using both DCIP and CCIP. CCIP values are slightly higher than DCIP values in almost all cases. When the impact of individual dams is analysed, differences also appear between the DCIP and CCIP. CCIP highlights the impact of dams located in areas of high fish conservation value while DCIP emphasize the impact of dams fragmenting large river segments. The CCIP appears to be adequate to highlight important sites for conservation in river connectivity studies. It could be applied in different studies and river basins around the world to prioritize dam removals or plan new dam locations.

Towards transferability in fish migration models: A generic operational tool for predicting silver eel migration in rivers

In the global context of river fragmentation, predicting fish migration is urgent to implement management actions aimed at protecting and promoting the free movement of diadromous fish. However, large-scale applicability of conservation measures requires transferable models that enable prediction of migration even in data-poor regions. Here, we surveyed 12 contrasted European river sites to predict the activity peaks of silver eels (Anguilla anguilla) during river migration towards spawning areas through an ensemble modelling approach. Site-specific Boosted Regression Tree (BRT) models were adjusted using standardized hydrological variables to predict migration probability, which were aggregated in consensus predictions. Results of independent cross-validations demonstrated that silver eel migration runs were accurately predicted in response to changes in river discharge. Transferability and predictive performance were improved by considering catchment-size dissimilarity between river sites (85 to 109,930 km2) when combining the site-specific predictions. Nevertheless, we provided two examples for which the effects of human actions on flow conditions were so high that they prevented reliable predictions of migration runs. Further contributions should thus take advantage of the flexibility of our approach for updating model collection with new sites to extend the predictive performance under a larger range of ecological conditions. Our transferable hydrological-based modelling framework offers an opportunity to implement large-scale management strategies for eel conservation, even in rivers where eel monitoring data lack. The BRT models and prediction functions were compiled in an R package named ‘silvRpeak’ to facilitate operational implementation by end-user managers, which can determine when mitigation measures should be implemented to improve river continuity (e.g. turbine shutdown and sluice gate opening) and balance their economic activity towards eel conservation. The only input required is discharge records that are widely available across European hydrological stations.

Catchment-scale effects of river fragmentation: A case study on restoring connectivity

More than two thirds of large rivers worldwide are fragmented, threatening freshwater biodiversity, river integrity, and the services that freshwater ecosystems provide for human populations around the globe. In an effort to alleviate the impacts of barriers, engineered solutions have been developed, though with somewhat underwhelming results. River restoration, especially dam removal, is viewed as the optimal option though seldom the go-to approach. In this study, we evaluated the effects of a large restoration project (pseudo dam removal) in River Kolding, Southern Jutland, Denmark, via a before-after-control-impact (BACI) approach. Using a large dataset of electrofishing data from 74 sites (including downstream unaffected sites, reconnected sites and upstream regulated sites), we found that habitat connectivity was restored successfully, with a large increase in young-of-the-year brown trout (Salmo trutta) at reconnected sites, reaching similar densities to downstream (non-affected) sites. We further observed a decrease in length at reconnected sites, suggesting that natural spawning and rearing habitats were successfully restored too.

Impacts of artificial barriers on the connectivity and dispersal of vascular macrophytes in rivers: A critical review

Abstract Macrophytes play important functional roles in river ecosystems, providing habitat and food, as well as influencing flow, water chemistry, and sediment dynamics. They also represent an important component of river biodiversity. Artificial river barriers have the potential to disrupt macrophyte dispersal, and compromise their distribution and persistence, but little information is available compared to barrier impacts on fish and macroinvertebrates. Here, we review the mechanisms supporting dispersal of river macrophytes in rivers and evaluate the nature of barrier impacts on macrophytes. Hydrochory (dispersal of propagules by water) is the principal mechanism of downstream dispersal, while zoochory (dispersal of propagules by animals) is likely to be the most important vector of upstream dispersal and inter‐catchment transport. Most studies have focused on the impact of large structures such as dams, and the findings indicate the impact is highly context dependent. Slow‐flowing habitats upstream of dams can act as traps to drifting propagules and thereby interrupt hydrochory. However, the consequences of interrupted hydrochory for downstream populations are unclear. River regulation can result in lower macrophyte diversity, although the lentic habitats associated with reservoirs can also favour an increase in the abundance and richness of macrophyte communities. Instream barriers are unlikely to affect zoochory by birds directly, but barriers are well known to restrict fish movements, so there is considerable potential for barriers to disrupt zoochory by fish, although no empirical study has specifically examined this possibility. There is a paucity of studies examining the impacts of low‐head barriers on macrophyte dispersal. Given the influence of macrophytes on river processes, we call for further research into barrier impacts on macrophyte population dynamics in order to gain a better understanding of the consequences of river fragmentation for fluvial communities and ecosystem functioning.

Evaluation of River Fragmentation and Implications for the Conservation of Migratory Fish in Southeastern Brazil.

In freshwater systems, the abundance and diversity of long-distance migratory fish are limited by the maintenance of longitudinal connectivity and natural flow regimes of rivers. Using a graph-based view of each riverscape, we analyzed the river fragmentation process and overlapped with the probable number of migratory species in each remaining stretch. Applying this methodology in basins, we assess historical and potential scenarios quantifying segment extensions free from dams determining the fish richness based on the available habitat for each species. The highest number of migratory species was observed in fragments longer than 100 km. In the future scenario, there was an increase in the number of fragments, with an increase in the number of stretches shorter than 50 km, inadequate to maintain most of the migratory species. Segments of the highest classification order and located in the longest lotic fragments were considered the most important for the species habitat conservation. Dam construction in these segments could seriously affect the ecological processes at a regional level. The proposed analyses enable to approach basins with high diversity of species and nonsalmonid species, supporting the lack of base data concerning those areas, and determine priorities for studies and conservation.

Characterization of Pallid Sturgeon ( Scaphirhynchus albus ) Spawning Habitat in the Lower Missouri River

Acipenseriformes (sturgeons and paddlefish) globally have declined throughout their range due to river fragmentation, habitat loss, overfishing, and degradation of water quality. In North America, pallid sturgeon (Scaphirhynchus albus) populations have experienced poor to no recruitment, or substantial levels of hybridization with the closely related shovelnose sturgeon (S. platorynchus). The Lower Missouri River is the only portion of the species’ range where successful reproduction and recruitment of genetically pure pallid sturgeon have been documented. This paper documents spawning habitat and behavior on the Lower Missouri River, which comprises over 1,300 km of unfragmented river habitat. The objective of this study was to determine spawning locations and describe habitat characteristics and environmental conditions (depth, water velocity, substrate, discharge, temperature, and turbidity) on the Lower Missouri River. We measured habitat characteristics for spawning events of ten telemetry-tagged female pallid sturgeon from 2008–2013 that occurred in discrete reaches distributed over hundreds of kilometers. These results show pallid sturgeon select deep and fast areas in or near the navigation channel along outside revetted banks for spawning. These habitats are deeper and faster than nearby river habitats within the surrounding river reach. Spawning patches have a mean depth of 6.6 m and a mean depth-averaged water-column velocity of 1.4 m per second. Substrates in spawning patches consist of coarse bank revetment, gravel, sand, and bedrock. Results indicate habitat used by pallid sturgeon for spawning is more common and widespread in the present-day channelized Lower Missouri River relative to the sparse and disperse coarse substrates available prior to channelization. Understanding the spawning habitats currently utilized on the Lower Missouri River and if they are functioning properly is important for improving habitat remediation measures aimed at increasing reproductive success. Recovery efforts for pallid sturgeon on the Missouri River, if successful, can provide guidance to sturgeon recovery on other river systems; particularly large, regulated, and channelized rivers.

Genetic diversity of marginal populations of Populus euphratica Oliv. from highly fragmented river ecosystems

Abstract Populus euphratica Oliv. (Euphrates poplar) is one of the naturally distributed poplar species and limited to south and southwestern Turkey. The species possesses great importance for both renewable energy resources and persistence of a healthy river ecosystem. Due to increased habitat destructions and fragmentation by human activities, the distribution area of this species has become narrower. Hence, searching for potential genetic diversity present in species’ genetic resources is of great importance in terms of its resilience to changing environment as well as breeding and use. To explore genetic structure and diversity of Euphrates poplar, natural populations in the Göksu and Euphrates river ecosystems were studied with 21 microsatellite DNA loci. Results demonstrated reduced level of genetic diversity (Ho:0.44, uHe:0.45) and low differentiation among two river populations (FST= 0.07), suggesting a common origin. It appears that severe past reductions in population sizes have resulted in loss of genetic variation in the species. Native populations of this species in two rivers seemed to be marginal with continued gene pool shrinkage. Therefore, they are in great danger of collapsing, mainly because of continued habitat loss and fragmentation. Genetic data generated with the current study provide important information which could be useful for future restoration and conservation studies of the species.

Passability of Potamodromous Species through a Fish Lift at a Large Hydropower Plant (Touvedo, Portugal)

River fragmentation by large hydropower plants (LHP) has been recognized as a major threat for potamodromous fish. Fishways have thus been built to partially restore connectivity, with fish lifts representing the most cost-effective type at high head obstacles. This study assessed the effectiveness with which a fish lift in a LHP on the River Lima (Touvedo, Portugal), allows potamodromous fish—Iberian barbel (Luciobarbus bocagei), Northern straight-mouth nase (Pseudochondrostoma duriense) and brown trout (Salmo trutta fario)- to migrate upstream. Most fish (79.5%) used the lift between summer and early-fall. Water temperature was the most significant predictor of both cyprinids’ movements, whereas mean daily flow was more important for trout. Movements differed according to peak-flow magnitude: nase (67.8%) made broader use of the lift in the absence of turbined flow, whereas a relevant proportion of barbel (44.8%) and trout (44.2%) passed when the powerhouse was operating at half (50 m3s−1) and full-load (100 m3s−1), respectively. Size-selectivity found for barbel and trout could reflect electrofishing bias towards smaller sizes. The comparison of daily abundance patterns in the river with fish lift records allowed the assessment of the lift’s efficacy, although biological requirements of target species must be considered. Results are discussed in the context of management strategies, with recommendations for future studies.

Trophic and limnological changes in highly fragmented rivers predict the decreasing abundance of detritivorous fish

Abstract The number of dams has had a significant increase in the last six decades, altering the physiography of rivers and creating systems of reservoirs in series. Therefore, it is expected that in a cascade of reservoirs, detritivorous fish will be especially affected due to the loss of nutritional quality in these regions, resulted from the high sedimentation of nutrients and organic matter. The objective of this study was to evaluate whether changes in the abundance of detritivorous fish, throughout a reservoir cascade in Brazil, resulted from trophic and limnological variations associated with sediment and nutrient retention. We used the Structural Equation Models approach (SEM) to test hypotheses. The six reservoirs studied are located in the Sao Francisco River, in the Northeast Brazil. The variables used to index latent variable oligotrophication were divided into trophic (total phosphate, nitrate and chlorophyll-a) and limnological variables (turbidity and water residence time accumulated), and the abundance of the detritivore guild was indexed by the catch per unit effort (CPUE). Our results indicate a significant negative impact of the both trophic (total phosphate, chlorophyll-a and nitrate) and limnological indicators (turbidity) on the oligotrophication process. The longer residence times of the water accumulated along the reservoir cascade augment the oligotrophication process, consequently affecting negatively all the trophic and limnological indicators analysed. Finally, the latent variable oligotrophication had a significant negative effect on the latent variable detritivorous fish abundance throughout the cascade. The Curimatidae family was the most affected by oligotrophication along the cascade, followed by Prochilodontidae. These different responses to the detritivorous fish families reflect different patterns in the morphology of the oral apparatus and forms of food apprehension. Our findings are of particular importance for the management of fish species in highly fragmented rivers.