Patterns Of Fish Assemblage Structure Research Articles

Can spatial and temporal differences in fish assemblage structure inform conservation of an endangered sucker in a large western reservoir?

AbstractObjectiveConversion of lotic to lentic habitat after river impoundment can lead to habitat loss and threats from introduced species to native aquatic organisms. Some native species can persist in reservoirs despite these alterations. Some of the largest reservoirs in North America were constructed in the Colorado River basin and are used by endangered Razorback Sucker Xyrauchen texanus. This species successfully spawns in several reservoirs and recruits to adulthood in Lake Mead, whereas recruitment in other reservoirs and altered river habitats is limited or nonexistent. Hypothesized mechanisms for the general lack of recruitment include flow and habitat alteration as well as competition and predation from nonnative fishes.MethodsWe analyzed 16 years of netting data from Lake Mead to assess spatial and temporal patterns in fish assemblage structure and the size structure of Razorback Sucker across four sites.ResultThere was a substantial shift in assemblage structure across all sites after the establishment of Gizzard Shad Dorosoma cepedianum in 2010–2011 and an apparent decline in Threadfin Shad D. petenense. Captures of juvenile Razorback Sucker (<450 mm total length in Lake Mead) were higher at sites where overall fish abundance was also higher, suggesting that all fishes might be responding to similar spatial and temporal environmental variation. We identified differences in Razorback Sucker size structure that varied over time and among sites, largely driven by the presence of juvenile Razorback Sucker at some sites in some years.ConclusionRazorback Sucker was among the top‐10 most abundant species at all sites sampled, but assemblages were dominated by abundant nonnative fishes. Razorback Sucker continue to recruit in Lake Mead in the face of abundant and diverse nonnative fishes, but the adult population size remains relatively small (<1000). Further investigation of limiting factors will be necessary to understand which actions might be successful at improving recruitment conditions.

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

AbstractDams 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.

Regional patterns in demersal fish assemblages among subsea pipelines and natural habitats across north-west Australia

Regional patterns of fish diversity, abundance, distribution, and assemblage composition are driven by a combination of biotic and abiotic conditions in the marine environment, but these conditions can be altered through anthropogenic activities, such as those associated with oil and gas extraction. The present study utilises data on fish relative abundance and diversity obtained from 1546 baited remote underwater video deployments conducted between 2004 – 2019 in depths of 9 – 170 m across 2000 km of coastline in north-west Australia on natural habitats and subsea pipelines to understand the influence of oil and gas infrastructure on fish assemblages. A total of 450 fish taxa from 56 families was observed, with populations dominated by generalist and invertebrate carnivore taxa. At the regional scale, subsea pipelines had lower diversity (lower taxonomic richness) than natural environments, but possessed a higher abundance of piscivorous and herbivorous fish taxa. Clear patterns in fish assemblage composition were observed in multivariate analyses, reflecting the proximity of oceanic shoals and banks, depth, and to a lesser extent, oil and gas infrastructure. Shallow-water and close to shoals assemblages were characterised by a diversity of site-attached (e.g., wrasses, tuskfish), reef-associated taxa (e.g., emperors). Mesophotic fish assemblages were characterised by commercially important (e.g., goldband snapper), wide-ranging (e.g., sharks) and sand-affiliated (e.g., toadfish, threadfin bream) taxa. Proximity to pipelines and platforms ranked low as predictors in the multivariate analyses suggesting a negligible regional influence of these structures on fish communities in comparison to depth and shoal habitats. Local-scale influences of subsea infrastructure, however, may be important for some fish species (infrastructure vs. immediate surrounds). Our study highlights the influence of abiotic factors on regional-scale patterns in fish assemblage structure across north-west Australia.

Fish Community Structure and Environmental Correlates in Nepal’s Andhi Khola, Province No. 4, Syangja

The study of correlations between fish diversity, environmental variables and fish habitat aspects at different space and time scales of Nepal’s rivers and streams is scanty. This study investigated spatial and temporal patterns of fish assemblage structure in Nepal’s Andhi Khola. The field survey was conducted from September 2018 to May 2019 and the fishes were sampled from three sites using a medium size cast net of mesh size ranging from 1.5 to 2.5 cm and gill net having 2-3 cm mesh size, 30-35 feet length and 3-4 feet width, with the help of local fisher man. A total of 907 individuals representing 15 species belonged to four orders, six families and 11 genera were recorded during the study time. To detect the feasible relationships between fish community structure and environmental variables, we executed a Canonical Correspondence Analysis (CCA). Based on similarity percentage (SIMPER) analysis, the major contributing species are Barilius barila (26.15%), Barilius vagra (20.48%), Mastacembelus armatus (8.04%), Puntius terio (6.64%), and Barilius bendelisis (5.94%). One-way analysis similarity (ANOSIM) tried out for both time and space variations in fish community structure suggested that there was a significant difference in temporal variation (R = 0.794, P = 0.0037) but no significant difference in spatial variation (R = -0.18, P = 0.923). Results from the Canonical Correspondence Analysis (CCA) vindicated that dissolved oxygen, free carbon-dioxide and total hardness were the principle physio-chemical correlates of fish assemblage structure. One-way analysis of similarity (ANOSIM) on the Non-metric Multidimensional Scaling (NMDS) showed significant difference between spring, autumn and winter season but no significant difference was found in spatial variation. The extraction and transportation of boulders, cobbles, pebbles, sand mining, haphazard ongoing road development and dam construction for the irrigation without fish ladders were found to be existing threats to the fish diversity of Andhi Khola.
 
 Keywords: Fish assemblage, multivariate analysis, rivers, spatio-temporal, streams

Response of Fish Assemblages to Habitat Changes and Fishing Activity in a Tributary of the Jinsha River in Southwest China

AbstractReservoir impoundment affects fish habitat condition, in turn likely influencing the spatial and temporal distribution patterns of fish assemblage structure in the impounded area. Fishing activity and instream gravel and sand mining are important anthropogenic factors, and flow discharge, water temperature, and precipitation are important natural environmental variables; both anthropogenic and natural factors likely have impacted fish assemblage structure in impounded and unimpounded waterbodies. We used multivariate analysis to evaluate the combined effects of two adjacent reservoir impoundments in the main stem of a large river (Jinsha River; the upper segments of the Yangtze River), overfishing, instream gravel and sand mining, the natural flow regime, and other environmental variables (water temperature and precipitation) on fish assemblage structure in the Heishui River, a small, free‐flowing tributary upstream of the mainstream reservoirs. Fish assemblage data and abiotic data collected over 10 years (2008, 2010, and 2011–2017) were analyzed. The results showed that fish assemblages of the Heishui River temporally clustered into two groups that were strongly associated with the two downstream cascade reservoirs (Xiangjiaba and Xiluodu reservoirs) in the main‐stem Jinsha River. The relationships between fish assemblage structure and abiotic factors were tested using a distance‐based linear model and were visualized using distance‐based redundancy analysis, showing that the main factors explaining the interannual and seasonal variation in fish assemblage structure were instream gravel and sand mining, mainstream reservoir impoundment, and seasonal flow regime. Among these, instream gravel and sand mining in this tributary played the most significant role in affecting the temporal variation of fish assemblage structure and explained 34.12% of the total variability. Mainstream reservoir impoundment and seasonal flow regime exerted secondary effects on the temporal variation of fish assemblage structure and together explained 13.39% (7.00% and 6.39%, respectively) of the total variability. This study suggests that the relevant administrative agencies should focus more on free‐flowing habitat maintenance in this tributary and the control of instream gravel and sand mining.

Longitudinal and seasonal patterns of fish assemblage structure in the Zhougong River, Sichuan Province, southwest China

Abstract The Zhougong River is one of the most important tributaries of the Qingyi River in upper Yangtze River drainage, Sichuan Province, southwest China. The river has been dammed in several places by hydroelectric stations and thus, we aimed to characterize the longitudinal and seasonal patterns of fish assemblage structure in it and whether anthropogenic perturbations have impacted fish assemblages. An extensive survey of fish was conducted in spring (April), summer (August) and autumn (November) of 2015, and winter (February) of 2016 at a total of 18 sampling locations across the river’s watershed. It was found that fish abundance, richness and Shannon-Wiener diversity all increased from upstream to downstream. Fish assemblage showed significant spatial differences between the upstream, midstream and downstream, while there were no differences between seasons as was expected. The spatial variation in the abundance of Rhodeus sinensis, Schizothorax prenanti, Pseudorasbora parva, Zacco platypus and Abbottina obtusirostris were considered to contribute most to the spatial pattern in fish assemblage. The canonical correspondence analysis (CCA) results revealed that spatial variations of fish community in the Zhougonng River were significantly correlated with water velocity, total phosphorus and water depth. Our findings indicate that spatial differences and no seasonal change in fish assemblage were partially attributed to the physicochemical changes caused by cascade hydroelectric dams (e.g., channel blocking, hydrological alterations) and water pollution (e.g., phosphorus) and it is also likely that overfishing has exacerbated impacts. We recommend that pollution prevention, dam removal, modifying dam ecological operations and fishery control may effectively lessen the impacts on fish biodiversity in the Zhougong River.

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.

Geography and island geomorphology shape fish assemblage structure on isolated coral reef systems.

We quantify the relative importance of multi‐scale drivers of reef fish assemblage structure on isolated coral reefs at the intersection of the Indian and Indo‐Pacific biogeographical provinces. Large (>30 cm), functionally‐important and commonly targeted species of fish, were surveyed on the outer reef crest/front at 38 coral reef sites spread across three oceanic coral reef systems (i.e. Christmas Island, Cocos (Keeling) Islands and the Rowley Shoals), in the tropical Indian Ocean (c. 1.126 x 106 km2). The effects of coral cover, exposure, fishing pressure, lagoon size and geographical context, on observed patterns of fish assemblage structure were modelled using Multivariate Regression Trees. Reef fish assemblages were clearly separated in space with geographical location explaining ~53 % of the observed variation. Lagoon size, within each isolated reef system was an equally effective proxy for explaining fish assemblage structure. Among local‐scale variables, ‘distance from port’, a proxy for the influence of fishing, explained 5.2% of total variation and separated the four most isolated reefs from Cocos (Keeling) Island, from reefs with closer boating access. Other factors were not significant. Major divisions in assemblage structure were driven by sister taxa that displayed little geographical overlap between reef systems and low abundances of several species on Christmas Island corresponding to small lagoon habitats. Exclusion of geographical context from the analysis resulted in local processes explaining 47.3% of the variation, highlighting the importance of controlling for spatial correlation to understand the drivers of fish assemblage structure. Our results suggest reef fish assemblage structure on remote coral reef systems in the tropical eastern Indian Ocean reflects a biogeographical legacy of isolation between Indian and Pacific fish faunas and geomorphological variation within the region, more than local fishing pressure or reef condition. Our findings re‐emphasise the importance that historical processes play in structuring contemporary biotic communities.

Patterns of Fish Assemblage Structure and Habitat Use among Main‐ and Side‐Channel Environments in the Lower Kootenai River, Idaho

AbstractThe lower Kootenai River, Idaho, was sampled during the summers of 2012 and 2013 to evaluate its fish assemblage structure at seven sites within main‐ and side‐channel habitats where large‐scale habitat rehabilitation was undertaken. Understanding the current patterns of fish assemblage structure and their relationships with habitat is important for evaluating the effects of past and future rehabilitation projects on the river. Species‐specific habitat associations were modeled, and the variables that best explained the occurrence and relative abundance of fish were identified in order to guide future habitat rehabilitation so that it benefits native species. The results indicated that the side‐channel habitats supported higher species richness than the main‐channel habitats and that nonnative fishes were closely associated with newly rehabilitated habitats. This research provides valuable insight on the current fish assemblages in the Kootenai River and the assemblage‐level responses that may occur as a result of future rehabilitation activities.

An Assessment of Fish Assemblage Structure in a Large River

AbstractThe 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.

Nursery Function Drives Temporal Patterns in Fish Assemblage Structure in Four Tropical Estuaries

Despite estuary-to-estuary differences in assemblage composition, fish faunas of tropical Indo-Pacific estuaries show parallel patterns of temporal change, suggesting a common set of ecological drivers. One potentially important driver is the interaction of different patterns of occupancy by functional groups that display different life-history patterns. However, most studies that have considered temporal change lack the detail needed to understand life-history utilisation. Most have focussed on changes in catch per unit effort (CPUE) or probability of encounter, with only one study going further and investigating changes in size structure and then only for a single estuary. One of the reasons for this lack of detail is the large volume of work needed to collect comprehensive data on size structures of species rich assemblages across multiple estuary systems over time. To overcome the logistical limitations on data collection, we used joint patterns of change in CPUE and mean biomass per fish (BPF) as proxies for changes in size structure. We investigated how different life-history strategies contributed to overall temporal patterns of assemblage change across four tropical Indo-Pacific estuaries. The three life-history strategies displayed characteristically different patterns in CPUE and BPF and the relationships between CPUE and BPF that reflect differences in the way that the three groups use estuaries. These different patterns interacted to produce complex assemblage patterns that are likely to be sensitive to location-specific differences in the mix of species from each group, providing at least part of the explanation for the site-specific fish assemblage structures that are characteristic of tropical estuarine fish fauna.

Fish assemblages of an African river floodplain: a test of alternative models of community structure

AbstractIn the Oueme River, a lowland river in Benin, Africa, artificial ponds constructed in the floodplain (whedos) are colonised during the high‐water period by a presumably random sample of fishes from the river channel. As water slowly recedes from the floodplain, fishes are isolated in whedos until they are harvested near the end of the dry season. We surveyed fishes in whedos and adjacent main‐channel and floodplain habitats during two low‐water periods (2008 and 2009) and one falling‐water period (2010–2011) to evaluate the relevance of four alternative metacommunity models to these systems. In 2010–2011, we also measured a suite of physicochemical variables including dissolved oxygen, temperature, specific conductivity and per cent cover of aquatic vegetation. Whedos were covered with dense growth of aquatic vegetation, and dissolved oxygen concentrations were lower in whedos and a natural floodplain depression compared with the main channel. Multivariate analyses revealed that habitat types were distinct with regard to assemblage structure and abiotic conditions. Assemblages in whedos and natural floodplain depressions were differentiated from those of the river channel, with the floodplain habitats being dominated by piscivorous fishes that tolerate aquatic hypoxia. Dispersal, aquatic hypoxia and predation act in concert to shape local community structure. Patch dynamics, species sorting and mass effect models all were consistent with patterns in fish assemblage structure in this system. We conclude that the underlying mechanisms of drift, speciation, selection and dispersal ultimately may be more useful for explaining patterns in ecological communities than alternative metacommunity models.

Spatio‐temporal patterns of fish assemblage structure in a coastal plain stream: appropriate scales reveal historic tales

AbstractQuantifying assemblage structure across spatio‐temporal scales is ecologically important and further aids in the understanding of community organisation processes. Currently, few studies have assessed assemblage structure across generous magnitudes of scale, and influences of processes (biotic and abiotic) responsible for structuring assemblages are still questioned. Using community and hydrologic data collected over a 22‐year period from a stretch of river nearing 150 km, we examined spatio‐temporal fish assemblage structural patterns in a temperate coastal plain stream. Results indicated that significant changes in assemblage structure across time were influenced by environmental disturbances, including drought and hurricane events. Assemblages were restructured in a punctuated manner directly following these events, and complete recovery of initial assemblage structure did not occur across the study period. Additionally, we found spatial differentiations between upstream and downstream assemblages, which were driven by greater abundances of several species in downstream sites. Our results suggest that assemblage structure is influenced by environmental variation, specifically, extreme disturbance events and spatial habitat heterogeneity.

Variabilidad espacial en la estructura de la ictiofauna asociada a praderas de Cymodocea nodosa en las Islas Canarias, Atlántico nororiental subtropical

A description of the patterns in spatial variability of fish assemblages is particularly relevant to guarantee an adequate management of these marine resources. Thirty six trawls were considered on six seagrass meadows (10 km apart) in three islands (100 km apart) of the Canary Islands to (i) analyze the spatial variability in the structure (richness, abundance and diversity) of fish assemblages associated with Cymodocea nodosa seagrass meadows, and to (ii) assess how the structural complexity of this habitat affects fish assemblage structure. A total of 3,616 fishes were captured, belonging to 30 species and 15 families. The total length of ca. 95% of individuals was < 10 cm, and ca. 90% of individuals were juveniles. Spatial variability in fish assemblage structure was larger when considering the scale of meadows than the scale of islands (27.28% vs. 6.64% respectively, in the amount of explained total variability); the smallest spatial scale (i.e., the variability among replicated trawls within each seagrass meadow) accumulated the largest amount of variability (66.07%). Differences in fish assemblage structure were largely driven by changes in the abundance of a few species, including Diplodus annularis, Spondyliosoma cantharus, Mullus surmuletus and Symphodus trutta. These species recruited into seagrass meadows, and confirmed the nursery role of this habitat in the canarian coastal waters. Mean shoot density and variation of the seagrass canopy height were the descriptors that accounted for the most variability when explaining patterns in fish assemblage structure.

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

AbstractWe 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 &amp; Sons, Ltd.

Assemblage and Population‐Level Responses of Stream Fish to Riparian Buffers at Multiple Spatial Scales

AbstractRiparian buffers can improve stream water and habitat quality by reducing non‐point‐source pollution (e.g., nutrients and sediment), increasing canopy cover and thereby reducing water temperature, and contributing allochthonous organic matter (e.g., leaf litter and woody debris). However, the influence of riparian buffers on biotic assemblages in streams is poorly understood, particularly in the Midwestern United States. In this study, we evaluated the effects of riparian buffers on instream habitat, fish assemblage structure, and population characteristics (i.e., the growth of two small‐bodied species) in three streams in central Iowa. The streams were surveyed at two spatial scales; specifically, 41 reaches were sampled and 247 macrohabitat types (i.e., pool, riffle, and run) were subsampled in the summer of 2007. Fish assemblage structure data were summarized into separate data sets by the relative abundance of individual species (i.e., fish per minute of electrofishing) and guilds (e.g., trophic and spawning). Multivariate analysis of variance was used to evaluate the differences in instream habitat and fish assemblage structure between areas with and without riparian buffers. The results indicated little to no relationship between the presence of buffers and fish assemblage structure and instream habitat characteristics. Nonmetric multidimensional scaling (NMS) was used to evaluate the patterns of fish assemblage structure for the reaches and macrohabitat types. The NMS further illustrated the similarity in fish assemblages between buffered and unbuffered reaches. However, the growth of central stonerollers Campostoma anomalum was greatest in unbuffered reaches, while that of creek chub Semotilus atromaculatus was greatest in buffered reaches. Differences in food availability associated with riparian buffers (e.g., increased algal production and decreased terrestrial invertebrate contributions in unbuffered reaches) probably resulted in growth disparities. The results of this study suggest that while riparian buffers have minimal local effects on instream habitat and fish assemblage structure in Iowa streams, they influence instream features (e.g., food availability) that affect fish population dynamics.

An Evaluation of the Relative Influence of Habitat Complexity and Habitat Stability on Fish Assemblage Structure in Unregulated and Regulated Reaches of a Large Southeastern Warmwater Stream

AbstractRiver regulation and development are the foremost problems threatening lotic fishes and other aquatic biota in the United States. The operation of hydroelectric facilities can influence both habitat availability and environmental stability in downstream reaches. We evaluated the relative influence of habitat complexity and environmental stability on fish assemblage structure at unregulated and hydropower‐regulated reaches of the Flint River in southwestern Georgia. The availability of different habitat types was highly variable at the regulated reach owing to large, daily fluctuations in discharge. Habitat‐specific fish assemblages also differed between reaches, as a greater number of species occupied identical habitat types at the unregulated reach, most notably in shallow, slow‐flowing habitats. Differences in fish assemblage structure between study reaches in comparable habitat types were explained equally well by patterns of habitat structure and variability. Within‐reach patterns of fish assemblage structure were best explained by patterns of habitat structure at both study reaches. However, the relative influence of habitat complexity and habitat stability differed within each study reach, habitat variability influencing fish assemblage structure to a greater extent at the regulated reach than at the unregulated reach. These differences suggest that both habitat structure and variability influence Flint River fish assemblages and that flow regulation associated with hydropower operation primarily affects riverine fish communities by increasing environmental variability. Thus, flow management plans for regulated rivers based on minimum flows may be most effective when implemented in conjunction with plans that reduce the spatial and temporal variability of habitat availability, particularly in shallow, slow‐flowing habitats.

Spatial Patterns of Fish Assemblage Structure in a Tributary System of the Upper Colorado River Basin

ABSTRACT This study was conducted to describe the distributions of both native and nonnative fishes and to identify spatial patterns in fish assemblage structure of Muddy Creek in the upper Colorado River basin of Wyoming using data collected from 77 reaches during 1999–2004. Fish assemblages in high-elevation reaches were characterized by brook trout (Salvelinus fontinalis) and represented a coldwater faunal zone. Reaches at lower elevations were characterized by warmwater fish species. The upper segment of the warmwater faunal zone contained four native (i.e., bluehead sucker [Catostornus discobolus], flannelmouth sucker [C. latipinnis], speckled dace [Rhinichthys osculus], roundtail chub [Gila robusta]) and two nonnative (i.e., white sucker [C. commersoni] and creek chub [Semotilus atromaculatus]) species. The lower segment of the warmwater faunal zone included species present in upstream segments and three additional nonnative species (i.e., common carp [Cyprinus carpio], redside shiner [Richardsonius baleatus], and fathead minnow [Pimephales promelas]). Differences in fish assemblage structure between coldwater and warmwater faunal zones were likely due to physiological constraints of species adapted for either coldwater or warmwater habitats. Changes in fish assemblages over the warmwater faunal zone are due to introduction and naturalization of nonnative fishes and anthropogenic barriers preventing upstream movements and colonization by some of these species.

Spatiotemporal Patterns of Fish Assemblage Structure in a River Impounded by Low-Head Dams

Abstract We studied spatiotemporal patterns of fish assemblage structure in the Neosho River, Kansas, a system impounded by low-head dams. Spatial variation in the fish assemblage was related to the location of dams that created alternating lotic and lentic stream reaches with differing fish assemblages. At upstream sites close to dams, assemblages were characterized by species associated with deeper, slower-flowing habitat. Assemblages at sites immediately downstream from dams had higher abundance of species common to shallow, swift-flowing habitat. Temporal variation in assemblage structure was stronger than spatial variation, and was associated with fish life history events such as spawning and recruitment, as well as seasonal changes in environmental conditions. Our results suggest that low-head dams can influence spatial patterns of fish assemblage structure in systems such as the Neosho River and that such assemblages also vary seasonally.

Fish assemblage structure and relations with environmental conditions in a Rocky Mountain watershed

Fish and habitat were sampled from 110 reaches in the Salt River basin (Idaho and Wyoming) during 1996 and 1997 to assess patterns in fish assemblage structure across a Rocky Mountain watershed. We identified four distinct fish assemblages using cluster analysis: (1) allopatric cutthroat trout (Oncorhynchus clarki (Richardson, 1836)); (2) cutthroat trout – brook trout (Salvelinus fontinalis (Mitchell, 1814)) – Paiute sculpin (Cottus beldingi Eigenmann and Eigenmann, 1891); (3) cutthroat trout – brown trout (Salmo trutta L., 1758) – mottled sculpin (Cottus bairdi Girard, 1850); and (4) Cyprinidae–Catostomidae. The distribution of fish assemblages was explained by thermal characteristics, stream geomorphology, and local habitat features. Reaches with allopatric cutthroat trout and the cutthroat trout – brook trout – Paiute sculpin assemblage were located in high-elevation, high-gradient streams. The other two fish assemblages were generally located in low-elevation streams. Associations between habitat gradients, locations of reaches in the watershed, and occurrence of species were further examined using canonical correspondence analysis. The results suggest that stream geomorphology, thermal conditions, and local habitat characteristics influence fish assemblage structure across a Rocky Mountain watershed, and they provide information on the ecology of individual species that can guide conservation activities.