Fish Assemblages In Reservoirs Research Articles

Characterization of fish assemblages in eleven multi-use reservoirs from North Carolina, USA

Managing impounded river systems is a recurring challenge for aquatic resource professionals because reservoirs serve multiple functions with different ecological and socioeconomic outcomes. However, research on fishes in reservoirs has disproportionally focused on recreationally and economically important species, with less attention directed toward fish assemblages despite the potential for management at the assemblage level. As such, evaluation of relationships between reservoir fish assemblages and biotic and abiotic factors and testing whether assemblage structure is affected by changing environmental conditions may deepen ecological understanding and provide insights for reservoir fisheries management. Our overall objective was to assess these relationships in 11 reservoirs from North Carolina, USA. We sampled fish assemblages in the reservoirs, which spanned five river basins representing a range of habitat conditions, using experimental gillnets and pulsed DC nighttime electrofishing. Multivariate statistical analyses indicated that taxonomic differences in fish assemblage composition among river basins followed a gradient of productivity. The top contributing species to reservoir dissimilarity were bluegill (Lepomis macrochirus), gizzard shad (Dorosoma cepedianum), black crappie (Pomoxis nigromaculatus), and white perch (Morone americana). These four species were positively associated with factors that reflect increasing eutrophic conditions in the 11 reservoirs and could, therefore, serve as indicators of reservoir productivity, anthropogenic influence, and fish assemblage structure, in addition to their key role in reservoir fisheries management. Whereas ­fisheries research has historically focused on assessing fish ­populations, our results illustrate the ecological and management insights derived from simultaneously collecting assemblage- and population-level data. Research on reservoir fish assemblages in relation to biotic and abiotic conditions may help advance fish ecology and management alike.

Invasive peacock basses (Cichla spp.) and decreased abundance of small native fish in Brazilian reservoirs

Abstract Peacock basses (Cichla spp.) have been introduced in impoundments for decades, and their negative impacts on the native fish fauna have been documented. However, previous studies largely focused on the overall responses of fish assemblages, often neglecting specific predator–prey interactions and the underlying effects of environmental characteristics. Here, the effects of peacock bass introduction on the size structure (<120, 120–180 and >180 mm in total length) of fish assemblages in reservoirs of the Paraíba do Sul river basin were assessed. The abundance and time since the introduction of peacock basses were used as predictors, together with reservoir features, limnological variables and habitat composition as potential influencing factors. Descriptors of the overall community (richness, abundance and species composition) were only marginally associated with the occurrence of peacock basses. However, small and (to a lesser extent) medium‐sized fish were adversely affected by the abundance and introduction time of peacock basses. Two pelagic native characids – namely Astyanax cf. bimaculatus and Oligosarcus hepsetus – were the most affected. Redundancy analysis showed that reservoir age and macrophyte cover were the best predictors of fish assemblage composition. Older reservoirs and reservoirs with a higher cover of macrophytes showed a greater abundance of catfish and characids, respectively. Peacock basses appear to affect fish assemblages through predation on small fish. Therefore, analyses of assemblages by size are recommended, as the use of overall assemblage descriptors may not be sufficient to capture the adverse effects of peacock basses. Moreover, these findings underscore the importance of conserving and restoring habitats in littoral zones, which function as refuges for native fish species in reservoirs. Further educational and management measures are warranted to prevent the spread of peacock basses to other reservoirs in Brazil.

Spatial and Temporal Variations in Fish Assemblage in Feitsui Reservoir, in Northern Taiwan, from 2006–2020

Reservoirs are artificial ecosystems that modify the hydrological and environmental components nearby. The long-term monitoring of fish assemblages in reservoirs may provide key information to understand how these artificial ecosystems allow fish population fluctuations and identify proper conservation strategies. A sentinel-site approach method assessed changes in fish assemblages in the Feitsui Reservoir (1024 ha) over 14 years, including the periods 2006–2008, 2010–2011, 2016, 2018, and 2020. Fish assemblages, sampled using gill nets, were composed of 38 species (12 families and 8 orders) with Cyprinidae as the dominant family; the fish fauna were dominated by species of the family Cyprinidae (71%) and Cichlidae (20.3%). Principal component analysis and nonmetric multidimensional scaling categorized the assemblages into two groups (cold and warm seasons), and we identified three parameters that were significantly correlated with the season (p < 0.05): SD (R = −0.04), Chl-a (R = 0.01), and algal count (R = 0.19); the algal count was higher in the warm season than in the cold season. The fish assemblage in the cold and warm seasons contained no exclusive taxa, contributing to the dissimilarity between the groups. The fish assemblage for the years before and after 2010 indicated partial overlap between the two groups; S. macrops contributed greatly to the separation of the two periods (>10% each; SIMPER) and O. mossambicus was dominant in assemblage structures after 2010. Our findings show the importance of long-term fish monitoring for the investigation of the effects of nonnative fish species on native fish species composition.

Taxonomic and functional distinctness of the fish assemblages differing among different types of reservoirs in south‐eastern Brazil

AbstractThe dynamics of fish assemblages in reservoirs depend on factors such as the morphometry of the catchment, habitat structure, and the uses of the reservoir. In the Paraíba do Sul (PSR) basin in southeastern Brazil, there are several types of reservoirs, some on the main channel, some are cascade reservoirs originated from a diversion of the waters of the PSR, and others are isolated reservoirs from tributaries. This study aimed to evaluate the influences of these three types of reservoirs on the taxonomic and functional distinctness of the fish assemblages. It was hypothesized that reservoirs on the main channel (more inflowing waters and habitat availability) have higher taxonomic and functional distinctness compared to cascade reservoirs, which in turn, have greater distinctness than isolated reservoirs. In addition, we expect assemblage structure to differ among these types of reservoirs because of the close relationship with local environmental conditions and habitat structure. Thirty measurements (26 quantitative and 4 categorical) from 34 fish species representing functional traits associated with locomotion, feeding, life strategy, and habitat use were taken. Fish assemblages differed among the three types of reservoirs, which was probably associated with different environmental and local habitat conditions. Higher taxonomic and functional distinctness were found for the isolated reservoirs, and lower for reservoirs on the main channel. This suggests that the fish fauna in this latter type of reservoir were probably composed of phylogenetically close and morphologically similar species. It is likely that limitation of the available resources induces fish to partition the available niches to coexist, favoring assemblages with species adapted to different functions. Our results demonstrate that assessing fish functional and taxonomic distinctness can be used to advance understanding of fish communities from reservoirs in Neotropical regions.

Do river basins influence the composition of functional traits of fish assemblages in Neotropical reservoirs?

In aquatic environments, dams are considered one of the main threats to fish species, acting as an environmental filter for certain functional traits. Although there is some predictability in the composition of the functional traits in reservoirs, it is hypothesized that the environmental filters imposed by evolutionary processes, linked to the characteristics of the basins, are determinant for the functional composition of the traits in reservoirs. For this we performed a PCoA using the functional traits composition matrix of the reservoirs. We used PERMANOVA to test the difference in functional composition between basins. We performed the same process for the species composition matrix to compare the patterns. In this study, there were taxonomic and functional differences among reservoirs inserted in different basins. It was observed that the basin is a determining factor for the functional structure of fish assemblage in reservoirs. When compared, functional and taxonomic structures follow the same pattern, although functionally the reservoir tends to be more similar. These results reinforce the idea that reservoirs act as filters for functional traits (e.g., related with reproduction, feeding and habitat use), although there is a great influence of evolutionary processes related to the basin's characteristics and origin of the ichthyofaunistic province.

Reservoir fish assemblage structure across an aquatic ecotone: Can river‐reservoir interfaces provide conservation and management opportunities?

AbstractRiver‐reservoir interfaces have been described as aquatic ecotones and contain strong environmental gradients of depth, turbidity and trophic resource abundance. These transitional habitats have traditionally been excluded by riverine and reservoir management schemes despite their prevalence in modern riverscapes. By systematically sampling shoreline habitats along a river‐reservoir interface gradient from riverine to lacustrine zones with trammel nets in 2018–2019, strong patterns were identified in total species captured and individuals captured in the San Juan River‐Lake Powell inflow, USA. Changes in assemblage structure were driven mainly by increases in relative abundance of benthic omnivores towards the riverine zone, including imperiled razorback sucker, Xyrauchen texanus (Abbott), but also by increases in predatory species, such as striped bass, Morone saxatilis (Walbaum). Inter‐annual variation in species distributions along the river‐reservoir interface gradient was likely influenced by variation in reservoir water level that differed by nearly 12 m between years. River‐reservoir interfaces provide high‐quality feeding and potentially spawning areas for both benthic omnivores and piscivores, and these areas should be considered in management and conservation efforts for species using these habitats.

Contrasting continental patterns and drivers of taxonomic and functional turnover among fish assemblages across Brazilian reservoirs

In this paper, we investigated composition and trait turnover among fish assemblages in reservoirs distributed across major Brazilian basins, in order to contrast taxonomic and functional turnover and to investigate their respective drivers. We investigated the hypothesis that reservoir assemblages present, on a continental scale, divergent species compositions but with a similar set of traits. Species lists and functional traits were compiled from 79 reservoirs located in the Amazon, Sao Francisco, Parana and Atlantic basins. We observed considerable variation in species and trait composition among reservoirs, with higher intra-basin similarity. Taxonomic turnover ranged between 0 and 1 (0.44 ± 0.22 SD), and functional turnover between 0 and 0.91 (0.37 ± 0.19); functional turnover correlated positively with taxonomic turnover, but showed lower values. Observed functional turnover values did not differ from null expectations, indicating lack of functional convergence. We detected significant effects of basin, longitude, latitude and elevation on turnover values, and the presence of non-native species was associated with either homogenization or differentiation patterns. Our results indicated that fish composition is heterogeneous among impoundments, providing little support to the hypothesis that reservoir assemblages are homogenized on a continental scale. Species and trait composition probably respond to multiple spatial, environmental and biogeographic factors.

Novel cichlid-dominated fish assemblages in tropical urban reservoirs

Recent biodiversity surveys in the lentic habitats of Singapore revealed that non-native cichlids (at least 14 species from different origins) were the most abundant species in the reservoirs of Singapore. To understand the diversity and distribution patterns in six reservoirs (two inland and four coastal), we investigated the species richness and abundances of these cichlids. We also investigated foodwebs to characterise the trophic relationships of cichlids relative to the aquatic community using stable isotope and gut content analyses in each reservoir. Based on various sampling methods (electrofishing, netting and trapping), a total of 5,675 individual cichlids representing 14 species and two hybrids were caught. The three most abundant species (contributing to 66.8% of all cichlids) included the green chromide, Etroplus suratensis, the eartheater cichlid, Geophagus altifrons, and the Orinoco peacock bass, Cichla orinocensis. Based on a canonical correspondence analysis, we found that the distribution and abundances of cichlids appeared to be related to abiotic parameters such as salinity and dissolved oxygen, and that species richness and abundances of cichlids differed between coastal and inland reservoirs. We also found that the trophic positions of different cichlid species varied within and across the reservoirs surveyed, where sympatry between highly specialised as well as generalist cichlid species was commonly observed. This was reflected in both the gut contents as well as the empirical foodwebs generated. While we are unable to determine source and timing of the introductions of these cichlids, we are at least confident that many of the cichlids have already established in these six reservoirs. We postulate that the establishment success and the co-existence of this non-native group has come about through their ability to adapt to the conditions within each reservoir, and this is related to the life history strategies, feeding and behavioural patterns that these different cichlid species display.

The biotic condition of dams run-of-the-river in sequence: adaptation of a multimetric index based on the Neotropical fish fauna.

The synergistic effects of run-of-the-river (ROR) on fish fauna, though still poorly understood, are amplified when dams form reservoir cascades. In an attempt to assist in this understanding, we used an adaptation of the Reservoir Fish Assemblage Index (RFAI) to evaluate the biotic conditions of the Rio das Antas Energy Complex, in the Neotropical Patos Lagoon ecoregion. We evaluated the attributes of the fish fauna from the point of view of the complex, for each reservoir and between different sections. Fish samplings were performed quarterly at nine sites for 2years (2015-2017). We proposed 26 metrics, related to aspects of composition, reproduction, feeding, habitat, and tolerance, selected based on criteria of variability, responsiveness, and redundancy. The final RFAI score was distributed in four categories of biological status, based on the best-observed condition. Eight metrics composed the final index, among which, only the proportion of nektonic individuals + nektobenthic (PNNbI) correlated with all sections. The final RFAI was classified as poor in all sections of the reservoir cascade, showing no significant differences between the sampling sites. This scenario indicates that dams in sequence intensify and homogenize the amplitude of fragmentation impacts on fish fauna. The final RFAI proved to be representative of the transition sections, emphasizing the importance of these reaches in impounded environments. Although the disturbance scales presented here are applicable mainly to ROR systems with reduced discharge section, the index was developed so as to allow its replicability in any dammed water course.

Fisheries and biotic homogenization of freshwater fish in the Brazilian semiarid region

The construction of dams in Brazilian semiarid regions has been a common governmental practice since the early 1900s, initially with the aim of providing water to meet the needs of humans and animals, and, later, to improve fisheries. Along with dams, several nonnative fish species were introduced with the intention of supplying new fisheries. We used a dataset compiled since the 1950s for the following: (i) evaluate fisheries for native and nonnative species across space–time scales and (ii) quantify the spatial and temporal changes in taxonomic and functional similarity of freshwater fish assemblages in semiarid reservoirs. Overall, fisheries for native species decreased over time, while fisheries for nonnative species increased during the early periods, which then, for the most part, decreased after 2000. At the Inter-region scale, we recorded a transition from homogenization to differentiation over time, both in taxonomic and functional terms. At the Intra-region scale, we also found a transition phase from taxonomic homogenization to differentiation over time, while functional differentiation was recorded for most of the regions. This study highlights the variation in fisheries for native and nonnative species over a period of ~ 70 years, and the homogenization dynamics of Brazil’s semiarid freshwater fish resulting from the construction of dams, stocking programs, and aquaculture using nonnative species.

Development of a fish-based index combining data from different types of fishing gear. A case study of reservoirs in Flanders (Belgium)

Fish assemblages in reservoirs and lakes are mainly assessed by multiple sampling gear. The challenge exists in how to combine all the data from the different types of gear to develop a fish-based index. In this paper, we describe a novel approach to this challenge in reservoirs in Flanders. The developed approach can also be used for natural lakes in the same eco-region and for any combination of fishing methods. In a first step, we defined a reference list of fish species occurring in man-made Flemish reservoirs. To compile this reference list, we adapted the reference for Dutch lakes with recent data from freshwater reservoirs in Flanders. This reference list contains guild-specific information needed to define metrics. To pre-classify the reservoirs, a habitat status for each reservoir was set using abiotic parameters (pressures). Fish gear-dependent metrics were selected according to their response to these pressures. Threshold values for metrics were determined based on the species reference list and occasionally on the calculated metric values. The ecological quality ratios derived from the index calculation were validated with an independent set of data. The developed index proved to successfully assess the ecological status of the reservoirs in Flanders.

Scale-dependent patterns of fish faunal homogenization in Neotropical reservoirs

The conservation challenges facing freshwater ecosystems necessitate broadening our science from understanding individual species loss to anticipating multi-faceted changes to biodiversity. In recent decades, the process of biotic homogenization by which regional biotas become more similar through time has attracted considerable attention. Here, we (1) quantified spatial and temporal changes in taxonomic and functional similarity of fish assemblages among Neotropical reservoirs, (2) determined nonnative species contributions to changes in taxonomic and functional composition, and (3) evaluated relationships between the changes in taxonomic and functional similarity among reservoirs. We did so by considering different spatial scales: inter- and intra-ecoregions. At inter-ecoregion scale, reservoir fish assemblages have become taxonomically homogenized over time, whereas functional trait composition has tended to differentiate. At intra-ecoregion scale, we detected both taxonomic and functional differentiation over time. Despite these overall trends, different ecoregions exhibited considerable variation in patterns of fish faunal homogenization and differentiation. We found a moderate positive relationship between changes in mean taxonomic and functional similarity among reservoirs at inter-ecoregion scale, which was no longer evident within ecoregions. In conclusion, this study demonstrates the strong scale-dependence of perceived patterns in homogenization, and further highlights the magnitude of threats to freshwater biodiversity in the Neotropical ecosystems.

Chronological age and reservoir characteristics as predictors of trait composition in Neotropical reservoir fish assemblages

AbstractOne of the main impacts on aquatic environments is the alteration of flow regime, usually caused by dam construction. This impact changes the dynamics and functioning of the environment. We aimed to evaluate changes in the composition of functional traits of fish assemblages from 29 reservoirs of different chronological ages. We assessed if there were any alterations in trophic state of these reservoirs according to their ages (chronological variable). Then, we evaluated the relationship between functional traits and environmental/chronological variables. Results showed that reservoir age is a predictor of fish assemblage functional traits composition. In older reservoirs, there was a predominance of omnivorous species, with multiple spawning and parental care. However, herbivorous species, with total spawning and medium size, had their abundance reduced. Also, it was possible to identify the influence of depth and water retention time on the composition of functional traits. By showing that although age has an influence on composition, the intrinsic characteristics of each reservoir are very important in evaluating the impacts of these projects. Therefore, the findings presented provide insights into what may happen to functional traits of fish assemblages with ageing of reservoirs.

Spatial and environmental factors predict the composition of non-native fish assemblages in Neotropical reservoirs

Hydropower dams are one of the largest sources of anthropogenic impacts on freshwater systems in the world. In addition to the modifications in environmental dynamics (i.e., fish migration barrier, water flow reduction, depth increase, flood regulation), the novel environments are favorable to the dissemination of non-native species in the basin. The lack of native species adapted to the changed environment creates occupations opportunity (i.e., available resources) for non-native species, which end up finding in these environments ideal areas to complete their life cycle. Thus, the aim of the work was identify which reservoir characteristics provide as well benefits for non-native fish species. Specifically, we tested the hypothesis that the spatial structure, reservoir productivity and morphology, and chronological characteristics are factors related to the composition and abundance of non-native fish species in reservoir. Using novel statistical techniques (Principal coordinates of neighbour matrices and Distance-based linear models), it was possible to identify the spatial patterns and to understand how the characteristics of the reservoirs influence the composition of the abundance of these species. Our results show that some reservoir characteristics provide benefits to non-native fish species, thus being localities within the hydrologic basins that can be considered as sources of non-native fish species propagules. In general, our results showed that larger and older reservoirs have a greater abundance of non-native fish species. Also, it was possible to identify spatial patterns, where in smaller scales neighboring reservoir tend to be more similar as to the composition and abundances of non-native fish species and this similarity can reach basin level.

Stock-recruitment dynamics of a freshwater clupeid

The clupeid gizzard shad Dorosoma cepedianum is often the most abundant fish species in North American reservoirs, and this dominance can have cascading trophic effects on entire fish assemblages. Accordingly, a key aspect of managing reservoir fish assemblages involves controlling gizzard shad densities. We used a 33-year time series to evaluate the relative importance of parental stock density, winter temperature, and water regime on recruitment of age-0 gizzard shad in a large reservoir. Recruitment modeled with a Ricker-type curve increased with the size of the adult stock, peaked, and then decreased at high stock densities. This over-compensatory stock-recruitment relationship was made more dynamic by fluctuations in inflow, with recruitment increasing in years of high inflow, however there was no temperature effect at the latitude of the study site. The influence of stock size on recruitment was roughly twice as high as the influence of inflow. This study is the first to report stock-recruitment relationships for a clupeid species in a reservoir and concurs with analyses of marine fishes that have shown that most clupeids exhibit compensatory or over-compensatory patterns in their stock-recruitment relationships.

Fish‐based multimetric index for evaluating land use effects on large neotropical reservoirs

Because of their importance to human well-being and ecosystem services, it is important to have cost-effective methods for assessing reservoir ecological condition or health. To do so, we constructed a preliminary reservoir fish assemblage index (RFAI) to assess the effect of predominantly agricultural land use on two oligotrophic neotropical reservoirs that differed in disturbance level. We first determined the disturbance levels around each reservoir through use of an integrated disturbance index (IDI). The IDI was calculated from the combination of land use metrics at local (Local Disturbance Index - LDI) and buffer scales (Buffer Disturbance Index - BDI). Afterwards, we employed the IDI to assess the response of candidate metrics to environmental disturbance in the RFAI construction. The final RFAI included three metrics selected by range, responsiveness, and redundancy tests. Metrics were scored continuously, and the final RFAI was divided in four quality classes: very poor, poor, acceptable and good. The results showed a clear disturbance gradient in both reservoirs with the IDI values varying between 0.07 and 1.33. However, the IDI values were greater around Volta Grande reservoir because of the predominance of agriculture land use (at local and buffer scales). The RFAI scores in Nova Ponte reservoir were significantly higher than in Volta Grande. All the sites scored as very poor or poor were in Volta Grande and all the sites scored as good were in Nova Ponte. In addition, RFAI scores in the reservoir river arms did not differ from those in the reservoir main body, indicating that it was applicable to both habitat types. Finally, our RFAI scores indicated no significant seasonal difference in the two reservoirs; however, the rainy season produced a greater range and more low scores, particularly in Volta Grande. We related this result to the harmful effect of agriculture and the surface runoff of fertilizers, herbicides, and pesticides. Thus, the RFAI was effective in detecting agricultural impacts at the site scale, even in oligotrophic reservoirs.

Trophic structure of fish assemblages varies across a Mesoamerican river network with contrasting climate and flow conditions

Assessments of trophic diversity are critical for evaluating ecological integrity of habitats, but interpretations of such assessments require an understanding of variation across natural environmental gradients. This can be problematic when comparing structure of assemblages in under-studied regions or habitats, such as watersheds in dry tropical forests. Here, we compared assemblage-wide trophic metrics and intraspecific variation for a subset of consumer traits across rivers and among different ecosystem types within the Grijalva and Usumacinta River basins of Mexico. The two rivers differ with respect to flow-regime alteration and climate: the Grijalva River has been hydrologically altered by a series of dams and has wet and dry tropical forests in its watershed, whereas the Usumacinta River remains unimpounded with a watershed dominated by tropical wet forest. Use of allochthonous resources was pervasive in Usumacinta basin tributaries, with stable isotope signatures suggesting that many fishes directly consumed riparian plants and detritus. In contrast, fish assemblages in Grijalva basin tributaries were supported by higher proportions of in-stream production. Food-chain length was highest in a Grijalva River reservoir fish assemblage, although trophic diversity was low in the impounded system compared to the mainstem Usumacinta River, where fishes consumed the broadest variety of food resources. We also observed differences in trophic ecology and body nutrient content within taxa across habitat types and basins. The differences we observed suggest that even in relatively intact watersheds, expectations for trophic structure in tropical streams should be adjusted based on factors such as discharge, climate, and riparian forest cover.

Long-term monitoring revealed fish assemblage zonation in the Three Gorges Reservoir

Reservoirs are important artificial ecosystems that modify the hydrological and ecological characteristics of a river. Knowledge of the basic characteristics of fish assemblages in reservoirs is a first step toward the development of effective conservation policies. We used the information collected over a 10-year period (2006-2015) to assess the structure of the fish assemblages in the Three Gorge Reservoir (TGR) in a river-dam gradient. Three fish zones were detected in TGR. Species richness was the highest in the upper zone and lowest in the lower zone. The riverine zones were dominated by rheophilic species Coreius guichenoti and Pelteobagrus vachelli. The transitional zones were dominated by Coreius heterodon and Rhinogobio cylindricus. The lacustrine zones were dominated by eurytopic species Hypophthalmichthys molitrix, Aristichthys nobilis, Hemiculter bleekeri and Cvprinus carpio. For the functional characteristics, fish assemblages in riverine and transitional zones were dominated by insectivorous species, equilibrium strategists and rheophilic species (e.g., Coreius heterodon and Coreius guichenoti). In lacustrine zones, the fish assemblage was dominated by habitat generalists common to lakes and reservoirs (e.g., Hemiculter bleekeri, Hypophthalmichthys molitrix, Aristichthys nobilis). Moreover, 18 exotic species (e.g., Protosalanx hyalocranius, Ictalurus punctatus, Megalobrama amblycephala, Tilapia) were collected in TGR, most of which only existed in the lacustrine zone. The results highlight the importance of freely flowing riverine reaches for conserving native fish in the upper Changjiang River and adaptive management strategies for fisheries in TGR.

Study approach and step by step development of a fish-based multimetric index for reservoirs: a case study presentation from a neotropical cascade system

Abstract Aim The present paper approached some issues related to the construction and adaptation of the Reservoir Fish Assemblage Index (RFAI). Method the case study presents the step by step construction of the multimetric index adopted for the Tietê cascade reservoir system, and it is discussed the comparison between discrete and continuous scoring criteria. Results The main questions related to the adaptation of multimetric indexes to reservoir were synthesized as: i – terminology question; ii - representative fish sampling; iii – reference condition. The construction of the RFAI for the Tietê cascade reservoir system resulted in seven steps, and the continuous scoring criterion showed to increase the accuracy of the final index when compared to the discrete scoring especially for the most degraded environment. Conclusion Biological criteria for the assessment of aquatic ecosystems are widely recognized and accepted by scientific community. The increasing value of water resource makes reservoirs important object of scientific and social interest, justifying the definition of proper tools for their assessment and monitoring. Among the available tools, the multimetric approach is one of the most popular. The observed results showed the validity of the approach also for artificial environments, expecting for its official incorporation in biomonitoring programs in Brazil.

Role of riparian shade on the fish assemblage of a reservoir littoral

Research into the effects of shade on reservoir fish assemblages is lacking, with most investigations focused on streams. Unlike many streams, the canopy in a reservoir shades only a narrow fringe of water adjacent to the shoreline, and may not have the influential effect on the aquatic environment reported in streams. We compared fish assemblages between shaded and unshaded sites in a shallow reservoir. Overall species richness (gamma diversity) was higher in shaded sites, and fish assemblage composition differed between shaded and unshaded sites. Average light intensity was 66 % lower in shaded sites, and differences in average temperature and dissolved oxygen were small. Unlike streams where shade can have large effects on water physicochemistry, in reservoirs shade-related differences in fish assemblages seemed to be linked principally to differences in light intensity. Diversity in light intensity in shaded and unshaded sites in reservoirs can create various mosaics of light-based habitats that enable diversity of species assemblages. Managing to promote the habitat diversity provided by shade may require coping with the artificial nature of reservoir riparian zones and water level fluctuations.