Spatial organization of fish diversity in a species‐rich basin

Many abiotic and biotic environmental characteristics in river basins show spatial gradients from river source to main stem. We examined the spatial organization of fish within the Duck River Basin to document patterns in diversity that could help guide conservation strategies relevant to controlling the detrimental effects of basin development. In all, over 0.33 million fishes representing 145 species and 18 families, including 9 non‐native species, were collected in 207 samples distributed throughout the basin. Main stem sites with large catchment areas supported more fish diversity than smaller sites in tributaries. Moreover, rare species were most common in the main stem and ubiquitous species in tributaries. The spatial organization of species assemblages was mostly nested, as assemblages appeared to disassemble in an upstream direction from main stem sites and confluences. These findings suggest that fish conservation efforts might emphasize main stem segments and confluences that support higher biodiversity including the rare species often most in need of protection. The main stem can support the populations needed to recolonize tributaries and rescue populations that might periodically go extinct after droughts or other major disturbances. In tributaries, conservation of species assemblages may focus on managing between‐patch connectivity via corridor maintenance or creation.     

INTRA‐ANNUAL VARIATION IN RIVER–RESERVOIR INTERFACE FISH ASSEMBLAGES: IMPLICATIONS FOR FISH CONSERVATION AND MANAGEMENT IN REGULATED RIVERS

While much is known about the fish assemblages, habitats, and ecology of rivers and reservoirs, there has been limited study of the fish assemblages in transitional habitats between these lotic and lentic habitats. Data about these river–reservoir interface (RRI) fish assemblages are needed to guide integrated management efforts of river–reservoir ecosystems. The aim of these efforts is to recommend flows for natural river function, conserve native riverine fish assemblages, and maintain reservoir sport fisheries. We used a multigear approach to assess the fish assemblages of four RRIs in the Colorado River Basin, Texas. In addition to characterizing RRI fish assemblages using species richness and evenness metrics, and habitat‐use guilds, we used a multivariate approach to evaluate intra‐annual shifts in species composition and abundance. All RRIs had high species richness and evenness values and included both macrohabitat generalist and fluvial species. RRIs also contained high proportions of the fish species available within each river–reservoir ecosystem, ranging from 55% to 80%. Observed intra‐annual shifts in RRI fish assemblages resulted from changes in abundance of dominant species rather than changes in species composition, with abundance of most species increasing from early spring to summer. Fish species responsible for intra‐annual shifts included mostly floodplain and migratory species, suggesting that species both used littoral habitats within RRIs and migrated through RRIs to river and reservoir habitats. The diversity of fishes found within RRIs highlights the importance of including these areas in future conservation and management efforts of river–reservoir ecosystems. Copyright © 2013 John Wiley & Sons, Ltd.     

PATTERNS OF ICHTHYOFAUNAL DISTRIBUTION AND CONNECTIVITY IN NAVIGABLE AND FREE‐FLOWING REACHES OF A MAJOR RIVER SYSTEM: THE ALLEGHENY RIVER IN PENNSYLVANIA

Connectivity throughout large riverine networks is often compromised by lock and dam (L/D) structures designed to facilitate year‐round navigation. The resultant interruption of flow inhibits free passage of aquatic biota potentially isolating mainstem and tributary communities. Our objectives were (i) to evaluate the impact of a series of navigational L/D structures on two targeted fish assemblages (TFAs): large‐bodied (>250 mm total length) pelagic and benthic (darter) communities and (ii) to examine patterns of tributary and mainstem connectivity. We systematically captured fishes utilizing gillnets, benthic trawls and backpack electrofishers from an impounded and a free‐flowing reach extending over 203 km of the Allegheny River in Pennsylvania. Species richness among the large‐bodied targeted fish assemblage was distributed somewhat evenly throughout each pool, peaking near dams and in an undredged pool. Depauperate darter assemblages of low species richness characterized most of the navigable reach with diversity and abundance concentrated in L/D tailrace areas. By contrast, darter communities inhabiting the free‐flowing reach were more diverse, abundant and evenly distributed, indicating the influence of uninterrupted connectivity. Community similarity at mainstem/tributary junctions increased with increasing tributary size with 50% of the mainstem species complement also inhabiting the largest tributary. This study underscores the importance of dams as barriers to ichthyofaunal connectivity, particularly to those benthic fishes which are relatively immobile and habitat specific, and the importance of mainstem/tributary junctions as avenues of riverine connectivity. Copyright © 2013 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.     

Towards improving an Area of Concern: Main-channel habitat rehabilitation priorities for the Maumee River

The Maumee River watershed in the Laurentian Great Lakes Basin has been impacted by decades of pollution and habitat modification due to human settlement and development. As such, the lower 35 km of the Maumee River and several smaller adjacent watersheds comprising over 2000 km² were designated the Maumee Area of Concern (AOC) under the revised Great Lakes Water Quality Agreement in 1987. As part of pre-rehabilitation assessments in the Maumee AOC, we assessed fish and invertebrate communities in river km 24–11 of the Maumee River to identify: 1) areas that exhibit the highest biodiversity, 2) habitat characteristics associated with high biodiversity areas, 3) areas in need of protection from further degradation, and 4) areas that could feasibly be rehabilitated to increase biodiversity. Based on benthic trawl data, shallow water habitats surrounding large island complexes had the highest fish diversity and catch per unit effort (CPUE). Electrofishing displayed similar fish diversity and CPUE patterns across habitat types early in the study but yielded no discernable fish diversity or CPUE patterns towards the end of our study. Although highly variable among study sites, macroinvertebrate density was greatest in shallow water habitats <2.5 m and around large island complexes. Our results provide valuable baseline data that could act as a foundation for developing rehabilitation strategies in the lower Maumee River and for assessing the effectiveness of future aquatic habitat rehabilitation projects. In addition to increasing in-channel habitat, watershed-scale improvements of water quality might be necessary to ensure rehabilitation strategies are successful.     

Large‐bodied fish assemblage characteristics in large rivers across Ontario

Large‐bodied fish assemblages were assessed in large rivers across Ontario. The objectives of this study were to (i) determine if there were relationships in large‐bodied fish species within rivers; (ii) determine what factors explain the variability in the abundance of large‐bodied fish within rivers across Ontario; and (iii) assessed variation in large‐bodied fish biodiversity among these river. Standardized index netting was conducted at 22 sites across 12 major rivers and sampled 3889 fish representing 26 species. Species associations were evident based on correspondence analysis. Walleye, Common White Sucker, Northern Pike and Lake Whitefish formed one group; Silver Redhorse, Shorthead Redhorse and Lake Sturgeon (adult and juvenile) formed another; Burbot, Longnose Sucker and Sauger were closely associated; and Cisco, Yellow Perch, Rock Bass, Smallmouth Bass and Brown Bullhead grouped. Canonical correspondence analysis was conducted to link species abundance patterns to environmental conditions. Walleye, Common White Sucker, Lake Whitefish and Smallmouth Bass were ubiquitous. Northern Pike abundance was negatively correlated with river discharge and longitude. Burbot, Sauger and Longnose Sucker abundance were positively correlated with deep rivers and discharge. Whereas Cisco, Yellow Perch and Rock Bass abundance were greater in wider rivers with lower discharge. Lake Sturgeon (adult and juvenile), Silver Redhorse and Shorthead Redhorse abundance were greater in narrow, longer rivers. Juvenile Lake Sturgeon abundance was positively correlated with longitude and river discharge. Mean species diversity and richness of large‐bodied fish among all sites was 1.58 (0.36 SD) and 7.7 (2.6 SD). Species diversity was not significantly related to any of the variables used in the Generalized Linear Model; however, species richness was significantly related to maximum depth. This study demonstrated subtle differences in environmental variables affecting large‐bodied fish at the landscape scale rather than those observed at the river scale.     

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.     

The influence of hydro‐climatic and anthropogenic effects on the long‐term variation of commercial fisheries in a large floodplain river

This study deals with the effects of climate fluctuations and anthropogenic impacts on fisheries of Paraná River over the last 100 years. It is the first attempt to appraise the influence of hydro‐climatic and anthropogenic variables on the population changes of the most important inland fisheries of Argentina. Datasets covering more than eight decades (1935–2016) of a number of frequent and abundant commercial species inhabiting the main channel as well as the large floodplain of Paraná River were used. Our results suggest that fish catches and structure changed over time. Long and short‐term changes and reductions were closely related to fluctuations of 18 hydro‐climatic variables. Positive effects on the ichthyofauna were recorded during humid periods (1930–1940 and 1970–2000), when the frequency of large spring–summer floods increased. An increase in anthropic impacts (accounted for with nine variables) were recorded during the last two decades. We highlight the usefulness of the approach to support the management of the resources, ensuring sustainability of commercial fish assemblages and the long‐term conservation of biodiversity in big rivers.     

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.     

Patterns of species richness and introduced species in native freshwater fish faunas of a Mediterranean‐type basin: the Guadiana River (southwest Iberian Peninsula)

In this study, we analysed the factors affecting species richness and introduced species component patterns in native fish faunas of 30 streams of the Middle Basin of the Guadiana River. From a principal component analysis and a stepwise multiple regression analysis performed on a data matrix composed of ten hydrological and biotic variables, we showed that: (1) fish species richness increased with stream length and watershed area, (2) the number of native species in a stream declined as channelizations and river regulation (constructions of dams) are higher, whereas introduced species increased in the same way, (3) the two main negative factors affecting native ichthyofaunas affected dissimilar ecological areas: channelizations, which depend on land‐use intensity of floodplain, mainly occurred in lower reaches of streams, but construction of dams mainly took place in upper sections of rivers, (4) the length of the remaining well‐preserved reaches in a stream appeared to be the only factor accurately predicting native fish species richness, and (5) native fish faunas of small isolated streams are more vulnerable to habitat alteration than those of large streams. Both isolation and fragmentation of populations were recorded, so the conservation status of native and highly endemic fish fauna of the study area is extreme. Protection of the few still extant, well‐preserved small streams and upper reaches, habitat restoration of channeled areas, and inclusion of the need for native fish fauna conservation in long‐term public planning of water use become a priority. Fish communities appear to be a sensitive indicator of biological monitoring to assess environmental degradation. Copyright © 2001 John Wiley & Sons, Ltd.     

Effects of low‐head dams on fish assemblages in subtropical streams: Context dependence on species category and data type

Anthropogenic disturbances may cause cosmopolitan species to replace endemic species, which will alter both the within‐community diversities and between‐community similarities of stream fish assemblages. In this study, we used data collected from headwater streams within the Xin'an basin, China, to evaluate the effects of low‐head dams on the alpha diversity and community similarity of fish assemblages. Our aims were to determine whether the changes in fish diversities and similarities related to dam‐associated disturbance are dependent on the species category (i.e., indigenous vs. native‐invasive species) or data type (i.e., occurrence‐based vs. abundance‐based indices). We found that low‐head dams significantly decreased the alpha diversity of the indigenous species in the impoundments but increased that of the native‐invasive species. However, the magnitude of this change was weakened if the two categories of fishes were not distinguished. Additionally, low‐head dams significantly decreased the occurrence‐based similarities of the indigenous fishes but increased those of the native‐invasive fishes. Despite the positive correlation between the occurrence‐based and abundance‐based indices, the former significantly overestimated the community similarities. Although most pairs of communities showed the same direction of changes for the two indices, some cases presented contrasting outcomes, including “perceived homogenization” (i.e., occurrence‐based differentiation but abundance‐based homogenization) and “perceived differentiation.” Our results suggest the importance of distinguishing indigenous and native‐invasive species and considering both occurrence‐based and abundance‐based indices in future research on how anthropogenic activities affect fish diversities and similarities in streams.     

Habitat fragmentation has interactive effects on the population genetic diversity and individual behaviour of a freshwater salmonid fish

Sufficient genetic diversity can aid populations to persist in dynamic and fragmented environments. Understanding which mechanisms regulate genetic diversity of riverine fish can therefore advance current conservation strategies. The aim of this study was to investigate how habitat fragmentation interacted with population genetic diversity and individual behaviour of freshwater fish in large river systems. We studied a population of the long‐distance migratory, iteroparous freshwater salmonid European grayling (Thymallus thymallus) in south‐eastern Norway. Genotyping (n = 527) and radio‐tracking (n = 54) of adult fish throughout a 169‐km river section revealed three major migration barriers limiting gene flow and depleting genetic diversity upstream. Individuals from upstream areas that had dispersed downstream of barriers showed different movement behaviour than local genotypes. No natal philopatry was found in a large unfragmented river section, in contrast to strong fidelity to spawning tributaries known for individuals overwintering in lakes. We conclude that (a) upstream sub‐populations in fragmented rivers show less genetic variation, making it less likely for them to adapt to environmental changes; (b) fish with distinct genotypes in the same habitat can differ in their behaviour; (c) spawning site selection (natal philopatry) can differ between fish of the same species living in different habitats. Together this implies that habitat loss and fragmentation may differently affect individual fish of the same species if they live in different types or sections of habitat. Studying behaviour and genetic diversity of fish can unravel their complex ecology and help minimize human impact.     

Restoration of fish passage: development and results of a master plan established for the Ruhr River Basin.

According to the central aim of the European Water Framework Directive, the protection and sustained management of the aquatic ecological system, the ecological condition of a specific type of water, will be the primary parameter in future. Aiming at good ecological status in surface water bodies, population diversity and abundance of fish and macroinvertebrates is decisive. Free passage in river systems, to allow the natural migration of fish and all other aquatic organisms, is a prerequisite. To achieve this for the Ruhr River Basin a study has been commissioned in order to develop a master plan for river continuum restoration. Sustainable development aimed at promoting biodiversity in the surface water body system is a key objective. This project is complemented by investigations of the sediment--which is the nursery of the fish--in the rivers to identify river sections or tributaries which obviously provide a suitable habitat for the successful reproduction of big Salmonidae. The master plan illustrates the inherent problems of projects aimed at the restoration of fish passage in water bodies which are strongly affected by anthropogenic modifications. The results obtained may as well be transferred to other catchments with similar use patterns.     

Response by fish assemblages to an environmental flow release in a temperate coastal Australian river: A paired catchment analysis

Defining appropriate environmental flow regimes and criteria for the use of environmental water allocations requires experimental data on the ecological impacts of flow regime change and responses to environmental water allocation. Fish assemblages in one regulated and one unregulated tributary paired in each of two sub‐catchments of the Hunter River, coastal New South Wales, Australia, were sampled monthly between August 2006 and June 2007. It was predicted that altered flow regime due to flow regulation would reduce species richness and abundance of native fish, and assemblage composition would differ between paired regulated and unregulated tributaries. Despite significant changes in richness, abundance and assemblage composition through time, differences between regulated and unregulated tributaries were not consistent. In February 2007, an environmental flow release (‘artificial flood’) of 1400 ML was experimentally released down the regulated tributary of one of the two catchments over 6 days. The flow release resulted in no significant changes in fish species abundances or assemblage composition when compared to nearby unregulated and regulated tributaries. Flow regulation in this region has reduced flow variability and eliminated natural low‐flow periods, although large floods occurred at similar frequencies between regulated–unregulated tributaries prior to and during 2006–2007, resulting in only moderate changes to regulated flow regimes. Barriers to dispersal within catchments also compound the effects of flow regulation, and findings from this study indicate that the location of migratory barriers potentially confounded detection of the effects of flow regime change. Further experimental comparisons of fish assemblages in regulated rivers will refine river‐specific response thresholds to flow regime change and facilitate the sustainable use of water in coastal rivers. Copyright © 2010 John Wiley & Sons, Ltd.     

A spatial assessment of riverine ecosystems and water supply in a semi‐arid environment

A spatial assessment was conducted in the semi‐arid area of South Africa, to: (1) identify priority areas for the conservation of river and groundwater ecosystems; (2) examine surface and groundwater quality for human consumption and (3) investigate the rehabilitation of degraded areas to highlight ‘win‐win’ situations for both environmental and human use. A systematic conservation plan was produced, highlighting river conservation areas (river types, fish species and connectivity areas), moderate‐impact management areas (groundwater‐surface water interaction and recharge areas) and river rehabilitation areas. The proposed river selections would achieve the biodiversity targets of 33 (66%) of the 50 river types; feasible rehabilitation would increase this to 92%. The greatest groundwater‐surface water interaction and recharge (30 to > 50 mm^?1) values are concentrated around the mountainous regions of the Little Karoo. This is because the main aquifers in the mountains, table mountain group (TMG) quartzites, yield naturally good quality water for human consumption. River reaches of unacceptable surface water quality were classified as degraded water resource delivery areas where the poor water quality was primarily due to saline return flows from irrigation and the impacts of other anthropogenic activities including abstraction of freshwater which otherwise would have diluted the return flows. Only the middle reaches of the Gouritz and Groot Rivers represent a possible win–win situation for both the environment and human use. Copyright © 2010 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.     

STABLE ISOTOPE ANALYSIS REVEALS ANTHROPOGENIC EFFECTS ON FISH ASSEMBLAGES IN A TEMPERATE RESERVOIR

Effluent from anthropogenic inputs can affect fish assemblages in aquatic ecosystems by altering species richness, diversity and trophic structure. To investigate the effects of a bleached kraft pulp mill effluent (PME) and municipal sewage treatment plant (STP) discharge on fish assemblages in a temperate reservoir, we combined standard ecological methodologies with stable isotope analysis of δ¹³C and δ¹⁵N. Total catch, species richness, diversity and coefficient of community loss indicated lower species richness and diversity at sites exposed to PME, whereas sewage‐exposed assemblages had intermediate richness and diversity relative to reference sites. Stable isotope analysis of δ¹³C and δ¹⁵N revealed that many species fed at higher relative trophic positions in the presence of both effluents and showed shifts towards increased reliance on littoral‐derived and benthic‐derived carbon at sites downstream of the PME discharge. Fishes at PME‐influenced sites had also generally higher condition factor whereas fishes at STP‐influenced sites were more variable in condition factor. These differences may, in part, be due to decreased species diversity at these sites and to nutrient enrichment manifest from the effluent discharge. While standard fisheries and ecological methodologies and stable isotope analysis have been separately used in other studies of anthropogenic effects on fishes, their integration in this study provides greater resolution than either could alone. Copyright © 2011 John Wiley & Sons, Ltd.     

A MULTITAXONOMIC APPROACH TO UNDERSTANDING LOCAL‐ VERSUS WATERSHED‐SCALE INFLUENCES ON STREAM BIOTA IN THE LAKE CHAMPLAIN BASIN,VERMONT, USA

Twenty‐one stream reaches in northwestern Vermont were surveyed to assess the relative influence of local‐ and watershed‐scale variables on stream biotic assemblages including fish, aquatic macroinvertebrates and birds. Data were collected during the summers of 2003 and 2004 and included quantitative and qualitative geomorphic and habitat assessments (local‐scale) and land‐use characterization and modelled annual flow and sediment loading (watershed‐scale). Biotic assemblages were surveyed to capture characteristics related to abundance, diversity and composition. Principal components analysis (PCA) was used to generate sets of factors representing unique scenarios of geophysical data derived from various spatial extents within the watershed. These factors were then used as the independent variables in multiple regression models using the biotic data as the dependent variables. Forty significant models were built from the combination of the eight scenarios and 11 dependent variables. Fish assemblage diversity and composition were influenced by a combination of local‐scale and watershed‐scale variables; however, the qualitative local data were more predictive than the quantitative data. Local‐scale data and sediment (model‐derived) were important factors in building significant macroinvertebrate models. Bird abundance and species richness were best predicted using local geomorphic characteristics and the qualitative local data. Our results reinforce the concept that whereas both local‐ and watershed‐scale variables affect stream biota, their relative influence depends upon the individual ecology of each taxon. In order to address these issues, comprehensive watershed management, restoration and conservation plans would benefit from assessments at multiple scales and from geomorphological, watershed and multitaxonomic perspectives. Copyright © 2010 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.     

Impoverishment of YOY‐fish assemblages by intense commercial navigation in a large Lowland river

Navigation‐induced physical forces have been suggested to modify the structure of riverine fish assemblages by impeding especially the recruitment of littoral bound species. To investigate the effect of vessel frequency on fish, we compared the composition and seasonal succession of young‐of‐the‐year (YOY) fish assemblages in three similarly degraded river reaches differing in average vessel passages (2, 6 and 41 per day). Fish were caught by electrofishing biweekly between May and September. Multivariate tests were used to analyse differences between YOY‐fish assemblages and hurdle regression models applied to determine abiotic factors predicting fish occurrence and abundance. Roach (Rutilus rutilus) and perch (Perca fluviatilis) densities were compared. Roach larvae remain in the littoral zone while perch larvae shift to the pelagic zone immediately after hatch. YOY‐fish assemblage structure substantially changed along the traffic intensity gradient. In the high traffic intensity reach, species number and total fish density were markedly reduced compared to the other reaches. Roach densities were lowest in the high traffic intensity reach whereas perch densities did not decline along the gradient. Hurdle regressions confirmed a stronger effect of commercial navigation traffic intensity on roach than on perch. The total zooplankton biomass was highest in the high traffic intensity reach. Our results provide empirical evidence that intensive commercial navigation impoverishes fish assemblages in width‐restricted waterways. They underlined that in particular those species that have their first nursery habitats in shoreline areas were more affected by intensive commercial navigation than species whose larvae live predominantly pelagic. The results indicate that the negative effect of intensive navigation on riverine fish results primarily from the navigation‐induced hydraulic disturbances along the banks. Therefore, mitigation of navigation‐induced hydraulic forces is required to prevent degradation of fish communities in waterways. Copyright © 2010 John Wiley & Sons, Ltd.