Structure of endemic fish assemblages in the upper Yangtze River Basin

This study focused on characterizing the endemic fish assemblages in the upper Yangtze River Basin and identifying the relative influences of catchment land‐cover variables on observed fish patterns in order to suggest a conservation strategy. A model based on a self‐organizing map was applied to determine endemic fish assemblages along the river network, based on presence/absence data for 124 endemic species. Five fish assemblages (Ia, Ib, IIa, IIb1, IIb2) were described. These assemblages varied significantly in terms of individual species patterns as well as species richness. Indicator species were identified for each class of community (0, 3, 9, 27, 0 species for cluster Ia, Ib, IIa, IIb1, IIb2, respectively). Structure of the endemic fish assemblages in the upper Yangtze River was highly correlated with local topographic and geomorphic characteristics. Simultaneously, the catchment land cover features also reflected out this endemic fish distribution structure. Among 18 land‐cover types, alpine and sub‐alpine meadow, together with farmland, were revealed to be the most important factors both in discriminating the endemic fish assemblages and in correlating species distributions by using discriminant analysis and co‐inertia analysis. Finally, in order to preserve the rare and endemic fish in the upper Yangtze River, reserve networks, rather than a single national nature reserve, should be established. Copyright © 2009 John Wiley & Sons, Ltd.     

Diet partitioning and trophic guild structure of fish assemblages in Chishui River,the last undammed tributary of the upper Yangtze River,China

Knowledge of trophic ecology of fish species is fundamental to understand the organization mechanism of fish assemblages and crucial for developing effective management and conservation strategies. This study examined the diet partitioning and trophic guild structure of fish assemblages in Chishui River, the last undammed tributary of the upper Yangtze River, China. Specimens were collected in three sections along the upstream–downstream gradient in 2012. Digestive tract contents of 54 fish species, represented by 692 individuals, were analysed and quantified. Analysis showed that fish assemblages in the Chishui River utilized aquatic insects, algae, detritus, molluscs, and fishes as the main food resources, whereas terrestrial insects were consumed only occasionally. The trophic guild structure of fish assemblages changed gradually with the longitudinal gradient. Specially, the number of trophic guilds increased with downstream distance. In addition, the relative number of omnivorous species increased longitudinally, whereas the relative number of insectivorous species declined downstream. This study demonstrated how fish assemblages utilize the food resources under near‐natural conditions. These results provide valuable information for fish conservation and ecological restoration.     

An Assessment of Fish Assemblage Structure in a Large River

The Penobscot River drains the largest watershed in Maine and once provided spawning and rearing habitats to 11 species of diadromous fishes. The construction of dams blocked migrations of these fishes and likely changed the structure and function of fish assemblages throughout the river. The proposed removal of two main‐stem dams, improved upstream fish passage at a third dam, and construction of a fish bypass on a dam obstructing a major tributary is anticipated to increase passage of and improve habitat connectivity for both diadromous and resident fishes. We captured 61 837 fish of 35 species in the Penobscot River and major tributaries, through 114 km of boat electrofishing. Patterns of fish assemblage structure did not change considerably during our sampling; relatively few species contributed to seasonal and annual variability within the main‐stem river, including smallmouth bass Micropterus dolomieu, white sucker Catostomus commersonii, pumpkinseed Lepomis gibbosus, and golden shiner Notemigonus crysoleucas. However, distinct fish assemblages were present among river sections bounded by dams. Many diadromous species were restricted to tidal waters downriver of the Veazie Dam; Fundulus species were also abundant within the tidal river section. Smallmouth bass and pumpkinseed were most prevalent within the Veazie Dam impoundment and the free‐flowing river section immediately upriver, suggesting the importance of both types of habitat that supports multiple life stages of these species. Further upriver, brown bullhead Ameiurus nebulosus, yellow perch Perca flavescens, chain pickerel Esox niger, and cyprinid species were more prevalent than within any other river section. Our findings describe baseline spatial patterns of fish assemblages in the Penobscot River in relation to dams with which to compare assessments after dam removal occurs. Copyright © 2014 John Wiley & Sons, Ltd.     

Low-head dam removal increases functional diversity of stream fish assemblages

Despite the growing number of dam removals, few have been studied to understand their impacts on stream fish communities. An even smaller proportion of dam removal studies focus on the impacts of low-head dam removals, although they are the most common type of dam. Instead, the majority of removal studies focus on the impacts of larger dams. In this study, two previously impounded Illinois Rivers were monitored to assess the impacts of low-head dam removal on the functional assemblage of stream fishes. Study sites were sampled each fall from 2012–2015 (pre-dam removal) and 2018–2020 (post-dam removal) in three locations: the tailrace, impoundment, and river channel. Fishes were aggregated into habitat and reproductive guilds, relating community changes to habitat, environmental metrics, and stream quality. Prior to removal, the slackwater guild was the most prevalent habitat guild throughout both rivers, while nest builders and benthic spawners were the most abundant reproductive guilds. During the two years following removal, fish assemblage throughout both rivers shifted to a more evenly distributed representation of habitat and reproductive guilds, while restoration of lotic habitat conditions increased, as surface water temperatures decreased and QHEI, IBI, and dissolved oxygen increased. This shift in environmental metrics and increase in overall stream quality increased, particularly in the formerly impounded reaches, indicate diminished habitat homogeneity, and a shift towards natural habitat diversity. This habitat diversification likely led to the restoration of a range of potential niches, thereby increasing the array of guild types inhabiting these rivers, while simultaneously preventing single-guild dominance.     

Diversity and Community Structure of Fishes in the Regulated Versus Unregulated Tributaries of the Mekong River

Diversity and community structure of fishes were studied in three neighbouring tributaries of the Mekong River in Thailand, namely the Mun, Songkhram and Gam Rivers. The rivers are located in the same ecoregion but have contrasting levels of both hydrological regulations and mitigation measures; the Mun River has a hydropower dam with a fish ladder and sluice gates that are opened during the wet season each year, the Gam River has several irrigation dams with a fish ladder at each dam site, and the Songkhram River has no dams along its river course. A total of 124 freshwater fish species were sampled in these rivers from August 2009 to June 2010. Overall species richness was highest in the Songkhram River (112), followed by the Mun (97) and Gam (54) Rivers. Average per site species richness was also significantly different among rivers but not among sampling months. Abundance–biomass comparison plots revealed considerably overlapping distributions of these two metrics from the dry to early rainy seasons in the Songkhram River and, to a lesser extent, in the Mun River. Fish assemblage data were classified into six clusters with similar community structure. Fish assemblages in the Gam River constituted a single cluster, while those in the other two rivers formed multiple clusters depending on the sampling season. The results of the cluster analysis are discussed in relation to the dominance of the three migration guilds (white, black, and grey fishes) of the Mekong River fishes. The effectiveness of the mitigation measures was determined to be limited in alleviating adverse impacts of dams in these tributaries of the Mekong River. Copyright © 2014 John Wiley & Sons, Ltd.     

Low‐Head Dam Impacts on Habitat and the Functional Composition of Fish Communities

The natural flow regime of many rivers in the USA has been impacted by anthropogenic structures. This loss of connectivity plays a role in shaping river ecosystems by altering physical habitat characteristics and shaping fish assemblages. Although the impacts of large dams on river systems are well documented, studies on the effects of low‐head dams using a functional guild approach have been fewer. We assessed river habitat quality and fish community structure at 12 sites on two rivers; the study sites included two sites below each dam, two sites in the pool above each dam and two sites upstream of the pool extent. Fish communities were sampled from 2012 to 2015 using a multi‐gear approach in spring and fall seasons. We aggregated fishes into habitat and reproductive guilds in order to ascertain dams' effects on groups of fishes that respond similarly to environmental variation. We found that habitat quality was significantly poorer in the artificial pools created above the dams than all other sampling sites. Fast riffle specialist taxa were most abundant in high‐quality riffle habitats farthest from the dams, while fast generalists and pelagophils were largely restricted to areas below the downstream‐most impoundment. Overall, these dams play a substantial role in shaping habitat, which impacts fish community composition on a functional level. Utilizing this functional approach enables us to mechanistically link the effects of impoundments to the structure of fish communities and form generalizations that can be applied to other systems. Copyright © 2017 John Wiley & Sons, Ltd.     

Using habitat guilds to develop habitat suitability criteria for a warmwater stream fish assemblage

The diversity of fish species found in warmwater stream systems provides a perplexing challenge when selecting species for assessment of instream flow needs from physical habitat analyses. In this paper we examined the feasibility of developing habitat suitability criteria (HSC) for the entire fish community of a warmwater stream using habitat guilds. Each species was placed a priori into a guild structure and habitat data were collected for depth, velocity, Froude number, distance to cover, embeddedness and dominant and subdominant substrate. Correct guild classification was tested with linear discriminant analysis for each species. Correct classification based on habitat‐use data was highest for riffle and pool‐cover guilds, whereas the fast‐generalist and pool‐run classes, the broader niche guilds, were more frequently misclassified. Variables most important for discriminating guilds were Froude number, velocity and depth in that order. Nonparametric tolerance limits were used to develop guild suitability criteria for continuous variables and the Strauss linear index was used for categorical variables. We recommend the use of a wide array of variables to establish more accurate habitat analysis. Additionally, guild HSC can be developed with similar effort to that needed to develop HSC for a small number of individual species. Results indicate that a habitat guild structure can be successfully transferred to another river basin and that habitats for a diverse fish assemblage can be adequately described by a small number of habitat guilds. This approach represents an alternative for incorporating entire fish assemblages into habitat analyses of warmwater stream systems. Copyright © 2010 John Wiley & Sons, Ltd.     

Peaking hydropower and fish assemblages: an example from the Tallapoosa River,AL

Dams alter many aspects of riverine environments and can have broad effects on aquatic organisms and habitats both upstream and downstream. While dams and associated reservoirs can provide many services to people (hydropower, recreation, flood control, and navigation), they can also negatively affect riverine ecosystems. In particular, hydropeaking dams affect downstream fish habitats by increasing variability in discharge and temperature. To assess the effects of Harris Dam on the Tallapoosa River, AL, operating under an adaptive management plan implemented in 2005, we sampled fish for community analyses from four sites on the river: three in the regulated reach downstream of the dam, and one unregulated site upstream. Fish were collected every other month using boat/barge electrofishing. We used Shannon's H, nonmetric multidimensional scaling (NMDS), a multiresponse permutation procedure (MRPP), and indicator species analysis to quantify patterns in fish assemblage structure and determine how assemblages varied among sites. NMDS and MRPP indicated significant fish assemblage differences among sites, with the tailrace fish assemblage being distinct from the other downstream sites and sites becoming more similar to the upstream, unregulated site (relative to fish assemblages) with distance downstream of the tailrace. The tailrace fish assemblage included higher proportions of rheophilic species that may be better suited to variable and/or high flows. Altered fish assemblages demonstrated continued effects of Harris Dam on the downstream aquatic systems, particularly close to the dam. These effects may indicate that further mitigation should be considered depending on conservation and management goals.     

Long‐term fish assemblages of inner bends in a large river

We sampled fishes at 17 inner bend sites on the Wabash River in 2008 to compare with collections from 1977 to 1997. We used the same seine collection methods as previous years and collected a total of 37 species. Mean site Shannon‐Wiener diversity, species richness, evenness and abundance for all years were similar. We used multivariate analyses to test for patterns in fish assemblage structure among all sites and all years. The multivariate analyses resulted in distinct assemblages for each collection‐year, suggesting shifts in assemblage composition among years. We used separate multivariate analyses to examine fish assemblage variation within individual years. Variation that corresponded to an upstream–downstream pattern was present in 1977 and 2008, but not in 1997. A hydrologic analysis based on daily discharge revealed that eight large flood events occurred from 1928 to 2007, with four of these events during the recent 20 years. We quantified substrate variation at the 17 sites in 2008 and identified a longitudinal gradient in dominant substrate categories with gravel upstream and sand downstream that was correlated with the first axis of the 2008 fish assemblage ordination. We suggest that observed changes in fish assemblages in decadal periods were from hydrologic impacts of large floods on local habitats. Copyright © 2010 John Wiley & Sons, Ltd.     

Implications of an invasive fish barrier for the long‐term recovery of native fish assemblages in a previously degraded northeastern Illinois River system

Barriers to fish movement have been used to prevent the spread of invasive fishes but may also limit the movements of native fishes. We evaluated the potential consequences of a proposed barrier on the Illinois River Waterway, meant to inhibit the spread of silver and bighead carps, to the continued recovery of native fishes in the Des Plaines River following water quality improvements. We compared changes in upstream cumulative species richness and community structure from 1983 to 2013 in the DuPage River, an adjacent tributary with an impassable dam, to the area upstream of a newly proposed barrier on the Des Plaines River where fish can currently pass through a navigational lock. Fewer species displayed truncated distributions upstream of the passable lock and dam (n = 18) compared with the impassable dam (n = 23). Due to water quality improvements in the Illinois River as a whole, cumulative species richness downstream of both dams steadily increased over time. Richness also increased upstream of the passable dam but plateaued upstream of the impassable dam. Fifteen to 18 species accounted for differences in community structure between areas downstream and upstream of either dam. Most species (78–100%) were found in greater relative abundance downstream of the impassable dam, and only 53% were found in greater relative abundance downstream of the passable dam. The truncation in species richness and abundance at the impassable dam foreshadows the potential consequences of an indiscriminate barrier on native fishes and the continued recovery of native assemblages.     

Effects of dams in river networks on fish assemblages in non‐impoundment sections of rivers in Michigan and Wisconsin,USA

Regional assessment of cumulative impacts of dams on riverine fish assemblages provides resource managers essential information for dam operation, potential dam removal, river health assessment and overall ecosystem management. Such an assessment is challenging because characteristics of fish assemblages are not only affected by dams, but also influenced by natural variation and human‐induced modification (in addition to dams) in thermal and flow regimes, physicochemical habitats and biological assemblages. This study evaluated the impacts of dams on river fish assemblages in the non‐impoundment sections of rivers in the states of Michigan and Wisconsin using multiple fish assemblage indicators and multiple approaches to distinguish the influences of dams from those of other natural and human‐induced factors. We found that environmental factors that influence fish assemblages in addition to dams should be incorporated when evaluating regional effects of dams on fish assemblages. Without considering such co‐influential factors, the evaluation is inadequate and potentially misleading. The role of dams alone in determining fish assemblages at a regional spatial scale is relatively small (explained less than 20% of variance) compared with the other environmental factors, such as river size, flow and thermal regimes and land uses jointly. However, our results do demonstrate that downstream and upstream dams can substantially modify fish assemblages in the non‐impoundment sections of rivers. After excluding river size and land‐use influences, our results clearly demonstrate that dams have significant impacts on fish biotic‐integrity and habitat‐and‐social‐preference indicators. The influences of the upstream dams, downstream dams, distance to dams, and dam density differ among the fish indicators, which have different implications for maintaining river biotic integrity, protecting biodiversity and managing fisheries. Copyright © 2010 John Wiley & Sons, Ltd.     

DISTRIBUTION AND ABUNDANCE OF STREAM FISHES IN RELATION TO BARRIERS: IMPLICATIONS FOR MONITORING STREAM RECOVERY AFTER BARRIER REMOVAL

Dams are ubiquitous in coastal regions and have altered stream habitats and the distribution and abundance of stream fishes in those habitats by disrupting hydrology, temperature regime and habitat connectivity. Dam removal is a common restoration tool, but often the response of the fish assemblage is not monitored rigorously. Sedgeunkedunk Stream, a small tributary to the Penobscot River (Maine, USA), has been the focus of a restoration effort that includes the removal of two low‐head dams. In this study, we quantified fish assemblage metrics along a longitudinal gradient in Sedgeunkedunk Stream and also in a nearby reference stream. By establishing pre‐removal baseline conditions and associated variability and the conditions and variability immediately following removal, we can characterize future changes in the system associated with dam removal. Over 2 years prior to dam removal, species richness and abundance in Sedgeunkedunk Stream were highest downstream of the lowest dam, lowest immediately upstream of that dam and intermediate farther upstream; patterns were similar in the reference stream. Although seasonal and annual variation in metrics within each site was substantial, the overall upstream‐to‐downstream pattern along the stream gradient was remarkably consistent prior to dam removal. Immediately after dam removal, we saw significant decreases in richness and abundance downstream of the former dam site and a corresponding increase in fish abundance upstream of the former dam site. No such changes occurred in reference sites. Our results show that by quantifying baseline conditions in a small stream before restoration, the effects of stream restoration efforts on fish assemblages can be monitored successfully. These data set the stage for the long‐term assessment of Sedgeunkedunk Stream and provide a simple methodology for assessment in other restoration projects. Copyright © 2011 John Wiley & Sons, Ltd.     

Ecological consequences of hydropower development in Central America: impacts of small dams and water diversion on neotropical stream fish assemblages

Small dams for hydropower have caused widespread alteration of Central American rivers, yet much of recent development has gone undocumented by scientists and conservationists. We examined the ecological effects of a small hydropower plant (Doña Julia Hydroelectric Center) on two low‐order streams (the Puerto Viejo River and Quebradon stream) draining a mountainous area of Costa Rica. Operation of the Doña Julia plant has dewatered these streams, reducing discharge to ～10% of average annual flow. This study compared fish assemblage composition and aquatic habitat upstream and downstream of diversion dams on two streams and along a ～4 km dewatered reach of the Puerto Viejo River in an attempt to evaluate current instream flow recommendations for regulated Costa Rican streams. Our results indicated that fish assemblages directly upstream and downstream of the dam on the third order Puerto Viejo River were dissimilar, suggesting that the small dam (< 15 m high) hindered movement of fishes. Along the ～4 km dewatered reach of the Puerto Viejo River, species count increased with downstream distance from the dam. However, estimated species richness and overall fish abundance were not significantly correlated with downstream distance from the dam. Our results suggested that effects of stream dewatering may be most pronounced for a subset of species with more complex reproductive requirements, classified as equilibrium‐type species based on their life‐history. In the absence of changes to current operations, we expect that fish assemblages in the Puerto Viejo River will be increasingly dominated by opportunistic‐type, colonizing fish species. Operations of many other small hydropower plants in Costa Rica and other parts of Central America mirror those of Doña Julia; the methods and results of this study may be applicable to some of those projects. Copyright © 2006 John Wiley & Sons, Ltd.     

Downstream Passage of Fish Larvae at the Salto Grande Dam on the Uruguay River

We evaluated the passage of early‐stage fishes through the Salto Grande Dam using high‐frequency downstream ichthyoplankton monitoring and five surveys involving samples taken upstream and downstream of the dam. Eggs and larvae of migratory fishes were captured downstream of the dam, usually during high discharges. Upstream and downstream larvae were frequently unyolked, which corresponds to individuals aged 4+ days, and represents a time significantly longer than that required for the displacement of the water mass from the dam to the sampling location. In low flow rate surveys, fish larvae of the same species and degree of development were captured immediately upstream and at 1, 10, 24 and 40 km downstream of the dam. The densities and percentage of Pimelodinae larvae captured alive by short time and low speed tows were similar upstream and downstream of the dam, indicating that larval mortality was a result of sampling and not to the passage through the turbines. The results show that the larvae of fish that spawn in the middle section are partly transported to the lower section, and suggest that both spillway and turbine discharge should be considered part of the passage. We also found evidence that the passage of small and fragile Pimelodinae larvae through the Salto Grande Kaplan turbines does not significantly affect survival rates. Copyright © 2016 John Wiley & Sons, Ltd.     

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.     

Fish and Benthic Macroinvertebrate Assemblage Response to Removal of a Partially Breached Lowhead Dam

Dam removal is an increasingly common restoration technique in lotic ecosystems. Potential dam removal benefits include improved aquatic organism passage, restoration of natural flow dynamics and a general improvement in habitat for native species. However, understanding potential dam removal outcomes requires data on ecosystem response in a wide variety of settings. We evaluated fish and benthic macroinvertebrate response to removal of the Spruce Pine dam in western North Carolina, USA. This dam was partially breached prior to removal, and impounded a coolwater river, both scenarios under which dam removal has been under‐studied. Post‐removal shifts in fish and benthic macroinvertebrate assemblages did not occur, suggesting that previously documented patterns of assemblage change in response to dam removal, particularly in the area upstream from the dam, are not universal, and may depend upon factors such as river gradient and water temperature, and the available species pool. Such information can aid managers in identifying conditions under which an expectation of significant instream habitat improvement in response to dam removal may not be warranted. Copyright © 2016 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.     

Fish assemblages and stream hydraulics: consistent relations across spatial scales and regions

General relationships between organisms and their habitat, consistent across spatial scales and regions, suggest the existence of repeatable ecological processes and are useful for the management of stream networks. From published data, we defined four guilds of European fish species with contrasting preferences for microhabitat hydraulics within stream reaches. At the scale of stream reaches and across 139 French sites (590 460 fishes sampled), we analysed how fish guild proportions were related to reach hydraulics (proportion of pools vs. riffles %POOL; median discharge by unit width Q50/W). The strongest correlations were observed between two fish guilds and %POOL (p < 0.001, r² ≥ 0.41) and between one fish guild proportion and Q50/W (p < 0.001, r² = 0.10). These reach–scale relationships were consistent across six large French basins, and consistent with the analyses made at the microhabitat scale. Therefore, microhabitat preferences for hydraulics are strong enough to generate consistent reach‐scale community responses to hydraulics across regions, despite the influence of other filters such as temperature, nutrient levels or history. The distribution of basic geomorphic features (pools, riffles) in streams and their modification (by dams, weirs and dikes) can modify the proportion of fish guilds by up to 80%, probably contributing to the long‐term decline of riffle‐dwelling species in Europe. Copyright © 2006 John Wiley & Sons, Ltd.     

Impacts of a reservoir on fish assemblages of small tributaries of the Corumbá river,Brazil

Fish community surveys were conducted in five tributaries of the Corumbá River before and after damming. Electrofishing samples were collected monthly in the pre‐impoundment period (March 1996 to August 1996) and 15 in the post‐impoundment period (September 1996 to February 1999). A self‐organizing map (SOM, an Artificial Neural Network algorithm) was used to represent the patterns of fish assemblages. Samples collected in both the pre‐ and post‐impoundment periods were randomly dispersed on the SOM, and, therefore, a clear and significant pattern of separation between samples collected during these two time periods was not found. Mean and maximum water depth, which is correlated with ground water level, did not significantly separate the pre‐ and post‐impoundment samples. However, we found significant differences between the two periods for water temperature, pH, conductivity, DO and current velocity, but abundances of fish species (summarized in the clusters identified by the SOM) did not differ significantly. Instead, the validity of the clusters distinguished by the SOM was confirmed by significant differences in some biotic variables: species richness, equitability and log transformed total abundance. Indicator species values identified the most preferred cluster (and respective complex of environmental factors) for a given species. Only one cluster did not contain any significant species indicator values, but it was dominated by samples from the Furnas Stream, which was the only effluent that could be entered by fish from the main river channel after the damming owing to its location below the dam, which has no fish ladder. Copyright © 2008 John Wiley & Sons, Ltd.     

Spatial effects of reservoirs on fish assemblages in Great Plains streams in Kansas,USA

Reservoirs are important components of modern aquatic ecosystems that have negative impacts on native aquatic biota both up‐ and downstream. We used a landscape‐scale geographic information system (GIS) approach to quantify the spatial effects of 19 large reservoirs on upstream prairie fish assemblages at 219 sites in Kansas, USA. We hypothesized that fish assemblage structure would vary with increasing distance from a reservoir and that the abundance of reservoir fishes in upstream reaches would decline with distance from a reservoir. Ordination of sample sites showed variation in fish assemblage structure occurred primarily across river basins and with stream size. Variance partitioning of a canonical ordination revealed that the pure effect of reservoir distance explained a small but significant (6%; F = 4.90, P = 0.002) amount of variability in fish assemblage structure in upstream reaches. Moreover, reservoir species catch per unit of effort (CPUE) significantly declined with distance from a reservoir, but only in fourth‐ and fifth‐ order streams (r² = 0.32, P < 0.001 and r² = 0.49, P < 0.001, respectively). Finally, a multivariate regression model including measures of stream size, catchment area, river basin, and reservoir distance successfully predicted CPUE of reservoir species at sites upstream of Kansas reservoirs (R² = 0.45, P < 0.001). Overall, we found significant upstream effects of reservoirs on Kansas stream fish assemblages, which over time has led to a general homogenization of fish assemblages because of species introductions and extirpations. However, characteristic reservoir species are present throughout these systems and the importance of spatial proximity to reservoirs is probably dependent on the availability of suitable habitat (e.g. deep pools) in these tributary streams. Copyright © 2005 John Wiley & Sons, Ltd.