Patterns Of Fish Assemblages Research Articles

A functional group approach reveals important fish recruitments driven by flood pulses in floodplain ecosystem

The periodical flood pulses, assisting by the connectivity between rivers and lakes in floodplain ecosystems, are of paramount importance in underpins fish meta-communities. Regardless of the unprecedented anthropogenic disturbances on natural flood regimes, there is limited understanding for the response of fish assemblages to flood pulses. Most studies documented the issue sorely on floodplain rivers or floodplain lakes, but the dynamics of fish communities in the transitional floodplains accounting for both lentic and lotic environments are rarely reported. Here we measure temporal (high and low water seasons) and spatial (lotic and lentic environments) patterns of fish assemblages in the transitional floodplain between the Yangtze River and Lake Caizi using taxonomic and functional group metrics. Our results demonstrated significantly variations in fish community composition among different environments between high and low water seasons. During flooding season in high water phase, we observed significantly patchy population recruitments of riverine fish species. Then in low water season, widespread lake residents dominated the lentic environments due to their higher environment tolerance. Benefitting from the functional group measurement, we identified three flooding related functional groups i.e., G2, G9 and G10 (consisting of riverine catfishes, gudgeons, and loaches), that may bear the brunt of natural flood pulses alterations. Despite the significant variations of richness in taxonomic diversity, we detected higher sensitivity of functional diversity, since three functional diversity indices were significantly higher in high water season. This findings demonstrated important functional recruitments triggered by flood pulses, highlighting a pressing need to sustain natural flood regime with hydrological connectivity for better conservation of fish assemblages in floodplain ecosystem.

Patterns in Fish Assemblage Structure in a Small Western Stream

Knowledge of how patterns in fish assemblages are spatially structured is important for guiding management and conservation actions. However, most studies have taken place in the eastern and midwestern U.S., resulting in a poor understanding of factors influencing western stream fishes. The objectives of this study were to evaluate habitat and species associations of fishes in Deep Creek, a small tributary of the Kootenai River in Idaho. Fishes and habitat were sampled from 58 reaches in Deep Creek. In total, 7,129 individual fishes representing 18 species were sampled. Patterns in species richness were largely a function of channel gradient and associated habitat characteristics. Species richness decreased with increased channel gradient. Species-specific habitat relationships for native and nonnative fishes in Deep Creek provided specific insights into the ecology of each species. Predicted probability of occurrence and relative abundance varied by species and were related to a broad suite of environmental characteristics. This study provides insight on patterns of fish assemblage structure, as well as important information on the ecology of native and nonnative fishes in a western stream system.

Larval fish assemblages in the eastern and western Gulf of Alaska: Patterns, drivers, and implications for connectivity

As stewardship goals in marine environments expand to encompass ecosystem dynamics, our comprehension of ecological structure must incorporate complex interactions among ecosystem components to define linkages and spatial boundaries for management. For example, the Gulf of Alaska (GOA) is currently considered a single Large Marine Ecosystem (LME), yet the GOA spans a large geographic domain, suggesting that ecosystem linkages may vary depending upon population, community, or process-based assessments. We used six years of larval fish assemblage data (2010–2015), co-collected oceanographic data, satellite-tracked drifters, adult fish trawl surveys, and an individual-based biophysical model to determine the processes that structure larval fish assemblages in the GOA focusing on 1) the local physical environment, 2) seasonality, 3) oceanographically-driven connectivity, and 4) adult fish distributions. Larval assemblages occurred along an eastern to western longitudinal gradient with regionally distinct assemblages in the spring and to a lesser degree in the summer. Assemblage patterns were largely driven by regional spring spawning events and only minimally influenced by temperature, salinity, and bottom depth over the continental shelf. Assemblage analyses and modeled particle trajectories suggest that longitudinal gradients in larval assemblages across the LME are influenced by the prevailing currents that promote connectivity despite variability in species-specific life-history characteristics such as spawning location and pelagic larval duration. Divergences in eastern and western GOA assemblages during the spring, and similarities in the summer, were consistent across most study years, but there were shifts in larval assemblages in the western GOA and not the eastern GOA during 2013 and 2015. Such geographic decoupling of assemblages in recent years highlights the potential for differential regional responses to environmental change across the GOA. Patterns in larval fish assemblages underscore the complex processes that structure pelagic ecosystems and suggest that assemblages diverged along a longitudinal gradient resulting in distinct communities in the eastern and western GOA. We propose that the influence of environmental or climatic variability on regional larval assemblages and life-history traits such as pelagic larval duration and phenology may alter future ecosystem linkages in rapidly changing environments.

Drought Facilitates Species Invasions in an Urban Stream: Results From a Long-Term Study of Tropical Island Fish Assemblage Structure

The natural flow regime is a key regulator of the dynamics of stream communities and ecosystem processes. Native fish assemblages are evolutionarily adapted to their local flow regime. In the Caribbean, streams are vulnerable to changes in climate that will alter their flow regimes. We assessed long-term patterns in fish assemblages (2008-2016) in an urban stream in San Juan, Puerto Rico. We hypothesized that drought periods would result in negative effects on native fish species and positive effects on introduced species. Fish assemblages were sampled annually from 2008 to 2016 by backpack electrofishing, with additional sampling during 2015, which was a drought year. Cumulative dry season discharge was consistently over 300 m3/s from 2008 to 2013, except from 2014 to 2016 when it dropped below 170 m3/s. Thirteen species were found, including most native species reported for Puerto Rico and introduced species (e.g., Cichlids, Poeciliids, and Loracariids). Native species were dominant in abundance during most years, except during drought and post-drought sampling events when introduced species became dominant. Introduced species increased in richness with time from less than two species between 2008 and 2013 to seven in 2015. The increase in introduced species was mostly attributed to the appearance of several species of cichlids towards the end of the study. Cluster analysis divided the data set in two groups: drought and non-drought sampling events. Introduced cichlids and the native A. monticola accounted for more than 60% of assemblage dissimilarity. Fish assemblage abundance and richness were negatively related to several components of stream hydrology (e.g., cumulative daily stream discharge, the number of major floods). A significant change in size over time was found for the native A. monticola, which decreased in size during the drought period. Overall, our study documents drought-facilitated invasions by several aggressive and highly ecologically competitive species, highlights the importance of the natural flow regime as a source of environmental resilience to invasions in tropical island streams, and provides an example of how climate change has and will likely continue to alter Caribbean stream fish assemblages.

Environmental DNA reveals quantitative patterns of fish biodiversity in large rivers despite its downstream transportation

Despite the ecological and societal importance of large rivers, fish sampling remains costly and limited to specific habitats (e.g., river banks). Using an eDNA metabarcoding approach, we regularly sampled 500 km of a large river (Rhône River). Comparisons with long-term electrofishing surveys demonstrated the ability of eDNA metabarcoding to qualitatively and quantitatively reveal fish assemblage structures (relative species abundance) but eDNA integrated a larger space than the classical sampling location. Combination of a literature review and field data showed that eDNA behaves in the water column like fine particulate organic matter. Its detection distance varied from a few km in a small stream to more than 100 km in a large river. To our knowledge, our results are the first demonstration of the capacity of eDNA metabarcoding to describe longitudinal fish assemblage patterns in a large river, and metabarcoding appears to be a reliable, cost-effective method for future monitoring.

Larval fish assemblage patterns in three tributaries of Mekong River in Thailand

The assemblage patterns of larval fishes from three neighboring tributaries <em>viz.,</em> Songkram, Gam and Mun of the Mekong River in Thailand were investigated between August 2009 and June 2010. These rivers interact with their floodplains, which are important spawning and nursery grounds for the Mekong fishes. There is no dam along the Songkram River; meanwhile the Gam River has several irrigation dams with a fish ladder at each dam site and the Mun River has a hydropower dam with a fish ladder and sluice gates that are opened during the wet season each year. A total of 97 fish species were collected from the study sites. Assemblage of Gam River was dominated by larvae of resident, black fish species. Assemblage of Mun River during sluice gate opening scheme was similar to that of Songkram River during wet season. Assemblage during flood period of Songkhram River showed the most diversity and abundance of migratory, white fish larvae. Conservation of integrity of the floodplain-river system of Songkhram River is among the crucial strategies for sustaining fish diversity and fisheries in the Lower Mekong River Basin.

Fish assemblages along the coasts of Tunisia: a baseline study to assess the effectiveness of future Marine Protected Areas

The present study investigated coastal fish assemblages, using Underwater Visual Census (UVC) transects, in Tunisia (south Mediterranean basin). The rationale behind this work is to get i) a suggestive evidence about the status of fish assemblages, and ii) baseline data at 3 locations in Tunisia where 3 MPAs will be established, before the implementation of protection measures. At each location, we used a sampling design where fish censuses were performed in two types of zone: zones that will be inside MPAs, and zones that will remain outside. On the whole, 49 taxa belonging to 19 families were censused. Data reveal clear symptoms of overfishing, especially in terms of dominance of small- and medium-sized individuals of commercially relevant species. Our analyses, moreover, did not show any significant difference in whole fish assemblage structures (considering both density and biomass), patterns of average species richness, total fish density and biomass, density and biomass of different trophic categories of fishes, size distribution of commercially relevant species, between future-protected and unprotected zones. Overall, results suggest that 1) current fish assemblages at the three studied locations are likely to be seriously impacted by fishing activities, and 2) these data could be used as reliable baselines to assess the effectiveness of protection measures within the MPAs that will be established in the future. Our study is the first in Tunisia, and in North African coasts, that assessed distribution patterns of coastal fish assemblages by means of UVC, using a formal spatially replicated sampling design for resource management.

Fish assemblage changes over half a century in the Yellow River, China.

Riverine environments have been threatened by anthropogenic perturbations worldwide, whereby their fish assemblages have been modified by habitat changes and nonendemic species invasions. We assessed changes in fish assemblages by comparing the species presence in historical and contemporary fish data in the Yellow River from 1965 to 2015. The temporal change in species assemblages was found with increased nonendemic species and fewer natives. Fish species richness of the river declined 35.4% over the past fifty years. Moreover, the decreased mean Bray–Curtis dissimilarity among reaches suggested that the fish assemblages of different reaches in the Yellow River were becoming more similar over time. However, temporal patterns of fish assemblages varied among reaches. In the upper Yellow River, higher species richness and more invasive species were found than those in the historical record, while the lower reaches experienced significant species loss. Dam constructions, exotic fish invasions, and flow reductions played the vital role in structuring the temporal fish assemblages in the Yellow River. It is suggested that river basins which experienced different types and levels of stressors by anthropogenic perturbations can produce varied effects on their temporal trends of species assemblages.

Spatial and temporal pattern of sympatric fish assemblage in the Al-Sweib River South of Iraq

Spatial and temporal pattern of fish assemblages in the Al-Sweib River Southern Iraq was investigated from January to December 2017 to determine the nature of the fish community structure in the river. Two stations were chosen for the implementation of the work. Monthly variations in rates of water temperature were measured; it has been ranged from 11°C in December to 36°C in July and August. Salinity rates differ from 0.81ppt in February to 1.66 ppt in August. The value rates of dissolved oxygen in the studying area varied from 6.7 mg/l in August to 9.9 mg/l in January. The total alkalinity values rates in the work area differ from 115 mg/l in February to 156 mg/l in August. Several fishing methods were used to collect the samples of fishes: drift and fixed gill net, seine net and cast net. 
 A total of 6902 fish individuals collected from the Al-Sweib River included 27 species, represented 27 genera and 12 families, all of them belonging to Osteichthyes. The species were 11 native, ten alien and six marine. Four species topped the total numerical relative abundance in present the investigated area, formed 81.72% of the total number, Planiliza abu 35.34%, Oreochromis aureus 18.68%, Carassius gibelio 17.51% and Coptodon zillii 10.19%. The diversity index values classified as poor in the studying area, the values ranged from 1.48 in December to 2.07 in March at station 1, whereas station 2 from 1.33 in December to 2.17 in May. Values of richness index were between turbulent to half integrate, they ranged from 1.33 in December to 2.31 March in station1, while from 1.50 in November to 2.78 in June station 2. Evenness index between half balanced to balance varied from 0.65 in October and 0.89 in August station 1, but at station 2 it was between 0.56 in December and 0.87 in July. The total similarities between the stations formed 36.84% in June and 72.73% in November. The study showed that the composition of fish community in Al-Sweib River was similar to that of the northern part of Shatt Al-Arab River.

Patterns in larval reef fish distributions and assemblages, with implications for local retention in mesoscale eddies

Benthic marine populations are often replenished by a combination of larvae from local and distant sources. To promote retention of locally spawned larvae in strong, unidirectional boundary current systems, benthic marine organisms must utilize biophysical mechanisms to minimize advective loss. We examined patterns in larval fish abundance, age distribution, and assemblage in relation to environmental variables in the Straits of Florida to better understand the factors underlying larval transport and retention in a boundary current system. Depth was the primary structuring element; larval assemblages were more distinct across vertical distances of tens of metres than they were over horizontal distances of tens to hundreds of kilometres. However, depth distributions were species-specific, and larval assemblages inside and outside of mesoscale eddies were distinct. Age distributions were consistent with the hypothesis that mesoscale eddies provide opportunities for retention. Our data indicate that the effect of eddies on larval retention is likely taxon-specific and temporally variable, as synchronization of reproductive output, larval distribution, and timing of eddy passage are prerequisite to entrainment and subsequent retention of locally spawned larvae.

Patterns in reef fish assemblages: Insights from the Chagos Archipelago.

Understanding the drivers of variability in the composition of fish assemblages across the Indo-Pacific region is crucial to support coral reef ecosystem resilience. Whilst numerous relationships and feedback mechanisms between the functional roles of coral reef fishes and reef benthic composition have been investigated, certain key groups, such as the herbivores, are widely suggested to maintain reefs in a coral-dominated state. Examining links between fishes and reef benthos is complicated by the interactions between natural processes, disturbance events and anthropogenic impacts, particularly fishing pressure. This study examined fish assemblages and associated benthic variables across five atolls within the Chagos Archipelago, where fishing pressure is largely absent, to better understand these relationships. We found high variability in fish assemblages among atolls and sites across the archipelago, especially for key groups such as a suite of grazer-detritivore surgeonfish, and the parrotfishes which varied in density over 40-fold between sites. Differences in fish assemblages were significantly associated with variable levels of both live and recently dead coral cover and rugosity. We suggest these results reflect differing coral recovery trajectories following coral bleaching events and a strong influence of ‘bottom-up’ control mechanisms on fish assemblages. Species level analyses revealed that Scarus niger, Acanthurus nigrofuscus and Chlorurus strongylocephalos were key species driving differences in fish assemblage structure. Clarifying the trophic roles of herbivorous and detritivorous reef fishes will require species-level studies, which also examine feeding behaviour, to fully understand their contribution in maintaining reef resilience to climate change and fishing impacts.

Fish Diversity and Limnological Parameters Influencing Fish Assemblage Pattern in Chambal River Basin of Madhya Pradesh, India

An attempt was made to systematically study the fish diversity and assemblage patterns in response to limnological dynamics of Chambal river basin in central India. A total of 56 fish species belonging to 09 orders, 18 families and 39 genera were recorded in the present study. Group-wise distribution of fishes showed that catfishes were the most dominant (23.21%). The most dominant species as per total relative abundance of the river was Glossogobius giuris (6.84%). The abundance of fishes was found to be highest in winter. Six fish diversity indices—Shannon-Wiener, Dominance, Simpson, Margalef, Evenness and Equitability indices were calculated and ranged 3.05–3.61, 0.03–0.08, 0.94–0.96, 5.21–6.35, 0.49–0.85 and 0.81–0.96, respectively. Threat status of fishes suggests that 3 species were near threatened and 01 species (Tor khudree) as endangered. Water temperature plays the key role in influencing fish assemblage pattern. A 1 °C rise in water temperature alone may result in an increase in Shannon (+ 0.1 units), Simpson (+ 0.02 units), Margalef (+ 0.16 units) biodiversity indices while 1 °C rise and 10 ppm increase of total dissolved solids may increase Evenness by + 0.05 units. There are two distinct fish assemblage events prevalent in the river basin viz. winter assemblage (near 20 °C) and non-winter assemblage (above 25 °C). The winter assemblage is most likely to be threatened under climate change. Ranching and creation of a winter-time freshwater protected area is recommended at Ghatbilod (Indore, Madhya Pradesh) dedicated for conservation of T. khudree.

Patterns of larval fish assemblages along the direction of freshwater input within the southern branch of the Yangtze Estuary, China: implications for conservation

ABSTRACTThe Yangtze Estuary is the largest estuary in the western Pacific Ocean, and harbors a high diversity of fish fauna. In this study, larval fish were surveyed monthly across three sections within the southern branch of the Yangtze Estuary (SBYE). A total of 49 taxa were collected, with 51.4% of the identified species being freshwater fishes. The collected numbers of larval taxa in the upper, middle, and lower sections were 22, 28, and 43, respectively. Species with differing salinity adaptations displayed different patterns along the direction of freshwater input. The collected numbers of larval taxa were 47 and 29 in the near-shore and mid-stream areas, respectively; and the abundances of larval fish in the near-shore areas tended to be higher than in the mid-stream areas in all the three sections. Larval fish occurred year-round with two peaks of abundance. Our results suggest that the freshwater input was the dominant factor shaping larval fish assemblage structure and dynamics within the SBYE. Influences of the Three Gorges Dam and South-to-North Water Transfer Project on larval fish assemblages within the SBYE should be considered with regard to conservation practices.

Intra‐annual patterns of coastal larval fish assemblages along environmental gradients in the northeastern Mediterranean

AbstractTo date, little is known about the larval‐fish assemblages (LFAs) in the eastern Mediterranean. The purpose of this study is to investigate the intra‐annual variations of LFAs with an emphasis on the effects of physical, chemical, biological and meteorological conditions in the gulf of Iskenderun, which is a shallow (100 m maximum depth), semi‐enclosed bay located in the northeastern corner of the Mediterranean. The gulf is under the influence of offshore waters throughout the year. The study was based on an ichthyoplankton survey program performed at 28 stations over 12 months, between November 2009 and October 2010. During the study, a total of 11,411 larval individuals belonging to 177 taxa were sampled. The jackknife estimate of maximum species richness was 225 ± 19 for the study area. The maximum larval richness (84 species) and abundance (827 larvae/10 m2) values coincided with spring bloom in April. Gobiids dominated the ichthyoplankton of Iskenderun Bay by constituting 9% of species richness and 42% of total individuals. Four LFAs were identified which were in early winter (November to January), late winter (February and March), spring (April to June) and summer (July to October). The intra‐annual variations of richness, abundance and composition of ichthyoplankton were significantly correlated with the temperature and mesozooplankton biomass. The wind conditions and thermal stratification were also significantly correlated with the composition of LFAs. In conclusion, phenology of LFAs were formed under the influence of physical and tropho‐dynamic conditions in Iskenderun Bay, Northeastern Mediterranean.

Evaluating the relationship between spatial heterogeneity and temporal variability of larval fish assemblages in a coastal marine ecosystem (Haizhou Bay, China)

AbstractIn coastal marine ecosystems, spatial patterns of larval fish assemblages (LFAs) tend to exhibit geographic stability because of relatively stable spawning site selection and predictable oceanographic phenomena such as eddies. To evaluate the relationship between spatial heterogeneity and temporal variability of LFAs, we conducted a high spatiotemporal resolution ichthyoplankton survey from April to July in 2013 in the shallow waters (<20 m) of Haizhou Bay, China. Our analysis indicated three distinct assemblages, which were stable geographically but exhibited a gradual and directional change of species composition and abundance over our study period. Sea surface temperature was the most important environmental co‐variate for determining temporal variability of LFAs, likely owing to temperature effects of species composition and spawning period selection of adult fish, along with known temperature‐dependent survival rates of larval fish. Study of LFA spatiotemporal dynamics is essential for improved understanding of adult fish spawning behavior, and has potential to inform design and implementation of conservation and management measures (e.g. marine protected areas) in coastal systems.

Seasonal fluctuations in taxonomic and functional diversity in assemblages of catfishes in the Venezuelan Arauca River Floodplain

ABSTRACTThe Arauca River harbors a considerable fish biodiversity, yet it remains poorly sampled and the knowledge about its fish communities is incomplete. We studied the taxonomic and functional composition and diversity of catfish assemblages in one lotic and one lentic habitat of a segment of this floodplain during one hydrological cycle, from August 2014 to August 2015, comprising six samplings using gillnets, and identified the relationships between catfish traits and the environment based on five limnological variables. The functional structure was studied through 11 morphological measures and the species diets. We identified 31 catfish species and nine trophic groups. There were significant differences in species composition and diversity between habitats and months, but the functional structure of the catfishes was only determined by the temporal variability. The functional structure of the catfish assemblages was ordered by morphological traits related to locomotion, habitat use, and trophic ecology and these traits were correlated with the limnological variables, supporting the existence of environmental filters. Integrating the taxonomic and functional perspectives can provide a more complete picture of the ecological patterns of freshwater fish assemblages in the Neotropics and can help us predict how these assemblages might change in response to anthropogenic alterations of the environment.

Regional‐scale environmental drivers of highly endemic temperate fish communities located within a climate change hotspot

AbstractAimWe used modelled environmental data to identify important drivers of bioregional patterns of demersal fish assemblages characterized by a high proportion of endemic species.LocationOf 1,600 km of coastal marine environment in south‐western Australia.MethodsWe compiled data from 1090 stereo‐BRUVs samples; a total of ~55,000 individuals belonging to 219 demersal fish species. Multivariate Regression Trees and Distance‐based Linear Models distinguished which biological and/or environmental variables, amongst an initial set of 49, were most correlated to observed patterns of demersal fish assemblage structure. Indicator species analysis identified fish species most representative of the assemblage types.ResultsThe most parsimonious model (constrained by five benthic variables and one spatial variable) explained 42% of the variation in spatial patterns of fish community structure. Canopy‐forming seaweeds were the major benthic drivers, and, when found on structurally complex hard habitat, supported the highest diversity of species after sites dominated by hard coral cover. Indicator species analysis revealed that 28 of 35 significant species for this habitat type were endemics with fish assemblages associated with these habitats often spatially restricted to tens of kilometres.Main conclusionsDemersal fish assemblage composition and biogeographical ranges in south‐western Australia are strongly influenced by the presence of canopy‐forming macroalgae. Canopy‐dominated habitats have already been subject to catastrophic temperature‐related die‐offs in the northern part of this study, indicating its vulnerability to temperature‐driven climate change. These results highlight not only the crucial role of this habitat in supporting endemic fish communities in the region, and the tenuous nature of their existence, but also the challenges facing marine managers who, unable to manipulate the influence of climate change variables, can only focus on alleviating stresses operating on local scales.

Inter-estuarine and temporal patterns of the fish assemblage of subtropical subestuaries along the Río de la Plata coast (Uruguay)

ABSTRACT Fish assemblages in subestuaries have been poorly studied worldwide. In order to evaluate the inter-estuarine and temporal variability of the ichthyofauna of subestuaries along the Uruguayan coast of the Río de la Plata (RdlP), the Pando, Solís Chico and Solís Grande systems were sampled between 2011 and 2013. Fish biomass, abundance, species richness and diversity indices were analysed, defining fish assemblages characterised by a few species and great abundance. Estuarine resident and freshwater species represented 55.5% of the fish assemblage according to estuarine use guilds. Species occurrence was similar in the three subestuaries, but the relative abundances differed among them. The analysed community parameters showed a decreasing trend from west to east along the Uruguayan coast. Highest diversity and fish abundance were recorded in the Pando system located in the proximities of an important spawning area in the inner RdlP estuary. In the Solís Grande subestuary occurred the lowest species richness and fish abundance. The Solís Chico was characterised as a transitional subsystem. All three subestuaries showed an increase in species richness and abundance during high temperature periods, probably related to the life cycle of the species sharing habitats between the RdlP and the coastal subestuaries. This study constitutes the first step in assessing the fish assemblage patterns in coastal ecosystems of the RdlP and an approach about the ecological role of the subestuaries in the southwest Atlantic Ocean.

Environmental drivers of α-diversity patterns in monsoonal tropical stream fish assemblages: a case study from tributaries of Narmada basin, India

Environmental factors, such as local physico-chemical water parameters, habitat-structural conditions, geography and human disturbances can have a profound impact on the structure and composition of biotic communities. This study investigates the relationship of these factors with fish diversity in medium to small streams in Central India and identifies the key determinants of species richness and diversity in habitats increasingly facing impacts of urban development. Data on fish diversity on eighteen sites, representative of undisturbed and disturbed aquatic habitats, located in the Narmada river basin were collected across different seasons over two years. Seasonal patterns of alpha diversity for this region were analysed and the effect of environmental drivers on seasonal patterns of alpha diversity were assessed. Analyses of species data revealed significant differences in diversity patterns across seasons for both species richness and Shannon diversity. Results of generalized linear mixed models showed that along with disturbance, altitude and substrate heterogeneity, dissolved oxygen, pH and stream width proved to be important environmental variables that predict species richness. Further, variations in pH, dissolved oxygen, temperature, stream width, stream depth and stream width heterogeneity were found to also predict Shannon diversity index. Our study revealed that seasonal changes across the year play a crucial role in shaping diversity patterns. This study is relevant as an important step in identifying roles of various ecological factors driving fish diversity in the region and towards developing long term management plans for critical catchment areas of major rivers in tropical systems.

Patterns of fish diversity, community structure and ecological integrity of River Yamuna, India

The Yamuna River, one of the most important and sacred rivers of the northern plains of India, is highly polluted. The river originates at the Yamunotri glacier, traverses 120 km to emerge onto the Indo-Gangetic plains at Dakpathar in Uttarakhand, and finally joins the Ganges River at Allahabad after traversing 1376 km. During 2007–2010 this study assessed the fish diversity, community structure, and ecological status in a 1200 km stretch of the river from Dakpathar to Allahabad. The waters were alkaline (pH 7.6–8.0). Dissolved oxygen was high at most sites (7.3–9.8 mg l−1), except at Wazirabad and Agra (3.4–3.7 mg l−1). A total of 143 fish species were recorded in the river. Cyprinidae was the most abundant family followed by Schilbeidae, Bagridae, and Sisoridae, respectively. The abundance was dominated by 48 species with = > 250 individuals caught. The highest intersite species similarities were recorded between Yamunanagar and Panipat, followed by Wazirabad and Hamirpur, and Yamunanagar and Allahabad. The middle stretch of the river was dominated by small-bodied erytopic, indigenous, and exotic fish species with periodic and opportunistic life history strategies, and had reduced abundances of the large–bodied, prized Indian Major Carps. A trophic shift towards dominance of carnivore catfish species was evident. Multivariate analysis indicated 83.50% of the total variability in species composition in the river could be attributed to gradients of the environmental variables: dissolved oxygen, turbidity, conductivity, total dissolved solids, stream velocity, and water temperature. Insufficient flows in the middle stretch of the river have altered fish habitat availability, resulting in changes in fish composition and assemblage patterns. The study will aid efforts to conserve the aquatic communities and their habitats in the river.