Stream Fish Research Articles

Effects of stream intermittency on minnow (Leuciscidae) and darter (Percidae) trophic dynamics in an agricultural watershed

AbstractStream intermittency is predicted to increase where water withdrawals and climate warming are increasing. In regions coupled with high fish diversity, understanding how intermittency influences fish trophic ecology is critical for informing ecosystem function. This study compared fish diets across seasons in perennial and intermittent streams to estimate the immediate and cumulative effects of stream drying on fish foraging patterns. We used gut content analysis to compare the diets of small‐bodied, secondary consumer fishes, including two minnow and three darter species found in the lower Flint River Basin of southwestern Georgia, during both the summer (before stream dry‐down) and fall (post flow resumption) seasons. Fish communities in perennial streams had greater diet richness compared to fishes in intermittent streams for both seasons. Darter diets were characterised by rheophilic aquatic insects in perennial streams and by benthic crustaceans (copepods, cladocerans and isopods) and predatory aquatic insects in intermittent streams. Minnow diets were typified by freshwater sponges, eggs and organic detritus in intermittent streams and by terrestrial insects and diatoms in perennial streams. Fishes in intermittent streams consumed significantly more benthic crustaceans in the fall (37% increase in proportional volume) compared to preflow cessation conditions in the summer, suggesting these organisms play an important, yet relatively unrecognised role in supporting fish communities in southeastern streams. Our findings enhance our understanding of how stream intermittency influences the trophic dynamics of secondary consumer fishes in an agricultural watershed increasingly affected by water scarcity.

Environmental filters of freshwater fish community assembly along elevation and latitudinal gradients

AbstractAimThe aim was to identify drivers of historical freshwater fish community assembly by testing for interactions between functional traits and two climatic gradients, namely elevation and latitude. Many studies conclude that environmental filtering is the dominant process of community‐wide trait convergence at high elevations and high latitudes, but a full understanding of which specific filters cause trait convergence is lacking.LocationGreat Plains–Rocky Mountains, USA.Time period1960–2018.Major taxa studiedFreshwater fish.MethodsUsing 2,539 stream fish community surveys documenting the native distributions of 51 species, we evaluated trait–environment relationships (trade‐offs) and trait–dispersion relationships (standardized effect sizes from null models) along elevation and latitudinal gradients in four functional trait categories. We tested whether elevation and latitude exhibited similar trait–environment and trait–dispersion relationships using four functional trait categories (life history, habitat, trophic and locomotion). We predicted that elevation and latitude would have similar relationships owing to shared environmental filters of cold stress and dispersal constraints.ResultsLife history was the only trait category to display evidence of increased environmental filtering along both gradients, with trait dispersion more constrained at high elevations and high latitudes. Trade‐offs revealed that periodic strategies (high fecundity, low juvenile survivorship) decreased with elevation and increased with latitude, whereas equilibrium strategies (low fecundity, high juvenile survivorship) declined along both gradients. Despite the observation of predictable trade‐offs for habitat, trophic and locomotion trait strategies, there was little evidence for environmental filtering of these traits at high elevations and high latitudes.Main conclusionsElevation and latitude appear to be environmental filters of freshwater fish community assembly when mediated through life‐history strategies, which is likely to be attributable to thermal constraints on growth and reproduction. Our results support the role of environmental filtering in trait convergence patterns along climatic gradients, and we identify cold stress as one specific filter of community assembly.

Morphological diversity within the Ozark minnow (Notropis nubilus: Leuciscidae).

The Ozark minnow, Notropis nubilus, is a small stream fish that has a disjunct distribution in the Ozark Plateau and upper Mississippi River basin. Three reciprocally monophyletic and deeply divergent lineages have been hypothesized within the species based on molecular data. These lineages are allopatric and isolated from each other. The objective of this study was to test the hypothesis that these lineages and the disjunct population in the upper Mississippi River basin are morphologically distinct. Meristic and geometric morphometric data were used to identify and quantify morphological diversity within the Ozark minnow. Analyses of the meristic data and a principal component analysis of the morphometric data were unable to find any noticeable differences in morphology among groups. However, canonical variates analyses of the morphometric data and linear models were able to define statistically significant differences in shape. Analyses of all-individuals were able to identify shape differences between all groups. Males-only analyses were less conclusive, but there was some indication that males may be diverging more quickly than all-individuals. The detection of subtle variation in shape implies selection is not a strong factor in morphological divergence and observed differences are most likely due to morphological drift. This indicates that the lineages within the Ozark minnow are likely on the trajectory for speciation. The allopatric nature of these clades makes the Ozark minnow an interesting model for the study of morphological drift and speciation.

Geomorphology variables predict fish assemblages for forested and endorheic rivers of two continents.

Stream fishes are restricted to specific environments with appropriate habitats for feeding and reproduction. Interactions between streams and surrounding landscapes influence the availability and type of fish habitat, nutrient concentrations, suspended solids, and substrate composition. Valley width and gradient are geomorphological variables that influence the frequency and intensity that a stream interacts with the surrounding landscape. For example, in constrained valleys, canyon walls are steeply sloped and valleys are narrow, limiting the movement of water into riparian zones. Wide valleys have long, flat floodplains that are inundated with high discharge. We tested for differences in fish assemblages with geomorphology variation among stream sites. We selected rivers in similar forested and endorheic ecoregion types of the United States and Mongolia. Sites where we collected were defined as geomorphologically unique river segments (i.e., functional process zones; FPZs) using an automated ArcGIS‐based tool. This tool extracts geomorphic variables at the valley and catchment scales and uses them to cluster stream segments based on their similarity. We collected a representative fish sample from replicates of FPZs. Then, we used constrained ordinations to determine whether river geomorphology could predict fish assemblage variation. Our constrained ordination approach using geomorphology to predict fish assemblages resulted in significance using fish taxonomy and traits in several watersheds. The watersheds where constrained ordinations were not successful were next analyzed with unconstrained ordinations to examine patterns among fish taxonomy and traits with geomorphology variables. Common geomorphology variables as predictors for taxonomic fish assemblages were river gradient, valley width, and valley slope. Significant geomorphology predictors of functional traits were valley width‐to‐floor width ratio, elevation, gradient, and channel sinuosity. These results provide evidence that fish assemblages respond similarly and strongly to geomorphic variables on two continents.

American mink (Neovison vison) preying on hatchery and wild brown trout (Salmo trutta) juveniles in semi‐natural streams

AbstractPredator–prey interactions are one of the main ecological factors influencing the structure of fish communities. The impact of wading and diving semi‐aquatic predators on riverine fish populations is poorly known. We studied the effect of feral American mink predation on brown trout juveniles during winter in two experiments conducted in semi‐natural streams (length 26 m, width 1.5 m).In the first experiment, we compared the vulnerability of age‐1+ hatchery (length 142 ± 16 mm, average ±SD) and wild (112 ± 8 mm) brown trout of similar genetic origin in sympatry and allopatry. In the second experiment we used age‐0+ brown trout (79 ± 5 mm), increased habitat heterogeneity by addition of fine wood, and compared those to treatments without fine wood addition.Hatchery fish were more vulnerable to mink predation than their wild counterpart, and the predation rate increased with increasing body size among the hatchery trout. Predation by mink on wild trout was higher in sympatric than in allopatric treatments suggesting that stocking of hatchery fish may increase predation on wild conspecifics. Increased habitat heterogeneity resulted in reduced predation rate.The results show that a large size of hatchery fish in small streams was a negative trait, which was opposite to the mainstream observations of salmonid stockings made directly of feeding areas in lakes and oceans. Adding habitat heterogeneity was found important for habitat enhancements in streams with mammalian predators.We highlight the importance of taking all the habitats during the life cycle of migratory fish into account in management decisions and carefully considering whether using hatchery fish to support wild populations in streams.

Heterogeneous movement by a small non-migratory stream fish

Heterogeneous movement by a small non-migratory stream fish

Air temperatures over-predict changes to stream fish assemblages with climate warming compared with water temperatures.

Studies predicting how the distribution of aquatic organisms will shift with climate change often use projected increases in air temperature or water temperature. However, the assumed correlations between water temperature change and air temperature change can be problematic, especially for mountainous, high elevation streams. Using stream fish assemblage data from 1,442 surveys across a mountain-plains gradient (Wyoming, USA; 1990-2018), we compared the responsiveness of thermal guilds, native status groups, and assemblage structure to projected climate warming from generalized air temperature models and stream-specific water temperature models. Air temperature models consistently predicted greater range shift differences between warm-water and cold-water species, with air temperatures predicting greater increases in occurrence and greater range expansions for warm-water species. The "over-prediction" of warm-water species expansions resulted in air temperature models predicting higher rates of novel species combinations, greater increases in local species richness, and higher magnitudes of biotic homogenization compared with water temperature models. Despite differences in model predictions for warm-water species, both air and water temperature models predicted that three cold-water species would exhibit similar decreases in occurrence (decline of 1.0% and 1.8% of sites per 1°C warming, respectively) and similar range contractions (16.6 and 21.5 m elevation loss per 1°C warming, respectively). The "over-prediction" for warm-water species is partially attributable to water temperatures warming at slower rates than air temperatures because local, stream-scale factors (e.g., riparian cover, groundwater inputs) buffer high elevation streams from rising air temperatures. Our study provides the first comparison of how inferences about climate-induced biotic change at the species- and assemblage-levels differ when modeling with generalized air temperatures versus stream-specific water temperatures. We recommend that future studies use stream-specific water temperature models, especially for mountainous, high elevation streams, to avoid the "over-prediction" of biotic changes observed from air temperature variables.

Variation in processes structuring fish assemblages as inferred from metacommunity analyses: Differences between headwater and adventitious streams within a river network

Community assembly is generally affected by the spatial position of local patches. Examining metacommunity processes and structures in small streams with different river network positions (e.g., headwater streams in the periphery of river networks vs adventitious streams in relatively central positions) may help us better understand how spatial position influences metacommunity structuring. In this study, based on data collected from sampling 24 headwater and 15 adventitious stream sites in the Xin’an Basin, China, we examined whether and how fish metacommunity processes and structures differed between the 2 stream types. We used distanced-based redundancy analysis coupled with forward selection to assess the relative roles of environmental and spatial factors in metacommunity processes, and we applied the elements of metacommunity structure analysis, extended by using different ordinations, to identify metacommunity structures. We found that the 2 types of streams were similar in environmental heterogeneity, but fish assemblages in adventitious streams were more dissimilar to one another than were assemblages in headwater streams and had more riverine immigrants. The amount of among-stream variation in species composition was low in both stream types. In headwater streams, assemblage–environment relationships were stronger than assemblage–space relationships, but we found the opposite pattern in adventitious streams. Species turnover was strong in both headwater and adventitious streams. However, assemblages in headwater streams showed both nested and quasi-nested structures, whereas the assemblages in adventitious streams were more consistent with Clementsian structure. Our results suggest that different metacommunity processes may occur in small streams with distinct river network positions and that extended elements of metacommunity structure analysis can help identify the underlying mechanisms that produce metacommunity structure. The effect of spatial position within river networks on stream fish metacommunity structuring appears to be weak, but our analyses do imply that river immigrants can influence species composition in adventitious streams to some extent.

Riparian vegetation structure and seasonality influence functional diversity more than taxonomic diversity of stream fish assemblages in the Colombian Amazon

Riparian vegetation structure and seasonality influence functional diversity more than taxonomic diversity of stream fish assemblages in the Colombian Amazon

Effects of a natural precipitation gradient on fish and macroinvertebrate assemblages in coastal streams.

Anthropogenic climate change is expected to increase the aridity of many regions of the world. Surface water ecosystems are particularly vulnerable to changes in the water-cycle and may suffer adverse impacts in affected regions. To enhance our understanding of how freshwater communities will respond to predicted shifts in water-cycle dynamics, we employed a space for time approach along a natural precipitation gradient on the Texas Coastal Prairie. In the spring of 2017, we conducted surveys of 10 USGS-gauged, wadeable streams spanning a semi-arid to sub-humid rainfall gradient; we measured nutrients, water chemistry, habitat characteristics, benthic macroinvertebrates, and fish communities. Fish diversity correlated positively with precipitation and was negatively correlated with conductivity. Macroinvertebrate diversity peaked within the middle of the gradient. Semi-arid fish and invertebrate communities were dominated by euryhaline and live-bearing taxa. Sub-humid communities contained environmentally sensitive trichopterans and ephemeropterans as well as a variety of predatory fish which may impose top-down controls on primary consumers. These results warn that aridification coincides with the loss of competitive and environmentally sensitive taxa which could yield less desirable community states.

Habitat selection and foraging success by an endangered Mediterranean cyprinid: implications for habitat restoration

Habitat loss and degradation are causing collapses in freshwater fish in the Mediterranean region, where habitat restoration actions are still hampered by poor understanding of fish habitat selection and fitness. Here, we combined field surveys and laboratorial experiments to investigate how water velocity, body size and intra-specific interactions influence habitat selection and foraging success by the highly endangered Mira chub Squalius torgalensis. Velocity negatively affected habitat selection and fitness of chub via its negative effects on prey capture rate. Small chub occupied lower velocity ranges than large chub, and both captured the most prey at the range of velocities selected in the stream. Size-based intra-specific interactions also affected capture success, with small chub capturing proportionally less prey in the presence of large chub. Our results suggest that, during base-flow conditions, restoring low and moderate velocities up to 26 cm/s will help ensure suitable habitat and improve the fitness of small and large chub occurring in interacting groups. Integrated approaches uncovering factors directly related to habitat selection and individual fitness should guide habitat restoration for fish in Mediterranean streams and may help identify critical habitat features for other endangered species.

Influence of environmental parameters on habitat use by sympatric freshwater eels Anguilla marmorata and Anguilla japonica on Yakushima Island, Japan

It is known that environmental parameters, such as water depth, size of substrate material, and current velocity, influence the organization of stream fish communities. However, few studies have investigated the effects of these parameters on the sympatric freshwater eels. Here, the habitat use of two anguillid eels, the Indo-Pacific eel (Anguilla marmorata Quoy and Gaimard, 1824) and the Japanese eel (Anguilla japonica Temminck and Schlegel, 1846), coexisting in the same river systems in Japan, was investigated. It was found that the tropical species A. marmorata exclusively used habitats with larger substrate materials, fewer fallen leaves and less leaf detritus, higher current velocity, and lower turbidity than the temperate species A. japonica, and the distributions of the two anguillid eels were clearly segregated. Thus, when both species co-occur in the same river systems, clear flowing mainstems and tributaries are preferred habitats for A. marmorata, whereas stagnant muddy estuaries, backwater areas, irrigation channels, and reservoirs are preferred habitats for A. japonica. These habitat segregations were consistent as body size increased and life-stage developments from elver to yellow eel and did not show ontogenetic shifts. The findings indicated that both species had strong habitat preferences, and these environmental parameters must be considered in the conservation of anguillid eels in sympatric zones.

Size Matters, but Species Do Not: No Evidence for Species-Specific Swimming Performance in Co-Occurring Great Basin Stream Fishes

For fishes, swimming performance is an important predictor of habitat use and a critical measure for the design of effective fish passage systems. Few studies have examined burst and prolonged types of swimming performance among several co-occurring species, and swimming performance in many fish communities is undocumented. In this study, we characterize both burst (c-start velocity) and prolonged speed (critical swim speed) across a poorly documented, co-occurring group of stream fishes within the Great Basin of the western USA. We documented the variation in swim speed associated with species, habitat, and body size. Body size had an overwhelming effect on both burst speed and prolonged speed, whereas habitat use and species identity were not significant predictors. Among species, there is no evidence of a trade-off between burst swim speed and prolonged swim speed. Lack of a trade-off in performance between burst swim speed and prolonged swim speed among species may be due to unexpectedly high prolonged swim speeds exhibited by species that used substrate-bracing behaviors. Incorporating body size and variation in behavior, such as substrate-bracing behaviors, into fish passage models will likely be sufficient to ensure the passage of all species without the need to account for species-specific swimming abilities. However, these results characterize the swimming performance for threatened and common fish species such that other comparisons can be made and species-specific studies can access accurate data.

Attitudes to forest conditions and fishing activities in the mountain area in Japan

Stream fishing plays a key role in provisioning services for obtaining fish, and also provides cultural services in terms of enjoyable walking along streams while listening to the sounds of flowing water. However, in Japan, the economic value of stream fishing has been emphasised mainly from the viewpoint of the fishing industry. Few attempts have been made to estimate the socioeconomic importance of stream fishing as an ecosystem service. In this study, a questionnaire survey was conducted to elucidate the current status of stream-fishing activities and people’s awareness of forest conditions. The contributions of stream fishing to the local economy were evaluated in terms of fry release and angler numbers. Respondents to the questionnaire reported changes in the forest and reduced numbers of fish. However, there were considerable differences in recognising the importance of both the forest and fishing, based on the respondents’ residential area and whether they interacted with the forest. Distance from the mountains, potential for industrial activity, depopulation, and interest in mountains and nature closely influenced the respondents’ behaviour. In an area where many people regard fishing as a source of food, specific fish were collected, the respondents fished all year round and ate the fish they caught. In this area, and considerable amounts of fish were harvested. Because people want to catch and eat many stream fish, the quantities of fry released has also increased, which might attract anglers from other regions, increasing the numbers of anglers. This would contribute to greater quantities of fish being harvested from this area in the future. In providing incentives for anglers, some people may be destroying their local natural environment. The goal of appreciating the scenic beauty of the landscape while having a low environmental impact is needed to ensure the preservation of local natural areas.

Estimating the effects of fish quality and size on the economic value of fishing in Oklahoma streams and rivers: A revealed preference and contingent behavior approach

Fishing in Oklahoma’s rivers and streams provides a unique experience for anglers in the state. Despite its popularity, information on total demand and economic benefits associated with stream fishing is limited in the state. Research on the role of site quality indicators, such as fish size and quantity, on recreational fishing has shown mixed results. Whether fish size or quantity plays an important role in determining fishing demand and economic value may have important management implications. We estimated the demand and economic value of fishing under varying scenarios by using anglers’ responses to hypothetical behavioral questions related to fishing in Ozark Highland streams and rivers in Oklahoma. We asked how intended number of trips might change in the future given hypothetical increases in catch rates of fish, catch rates of trophy-sized fish, and catch rates of preferred fish species, in combination with anglers’ trip-related data. Under current conditions, we estimated consumer surplus per person per trip to be $55 and aggregate value across all stream anglers in Oklahoma to be $68.51 million. Changes in marginal benefits varied among hypothetical scenarios of fish size and abundance but was maximized with a 25% increase in catch rates of trophy-sized fish. The study findings contribute to the understanding of the economic benefit of fishing in streams and suggest that fish size, rather than fish quantity, is more important to stream anglers in the area.

Complex effects of body length and condition on within‐tributary movement and emigration in stream salmonids

AbstractMovement patterns of stream fish vary individually, but little is known about how a set of individual characteristics affect movement at multiple spatial scales. We investigated the effect of body length and condition (i.e. weight relative to length) on emigration from a tributary and movement within the tributary during summer in Japanese salmonids (white‐spotted charr Salvelinus leucomaenis and masu salmon Oncorhynchus masou) using mark‐recapture and PIT antenna technology. Emigration from the tributary was influenced more strongly by body length than by body condition, whereas movement within the tributary (> 20 m) was influenced by body condition and their interaction with body length. Specifically, larger individuals in better body condition were more likely to stay locally (≤20 m), but smaller individuals in better condition were more likely to move in the tributary. We discuss benefits and costs of movement that vary with individual characteristics (i.e. body length and condition) and spatial scales. In one instance (charr between June and July), survival rates were lower in smaller individuals, which also were more likely to emigrate from the tributary, suggesting that emigration might have been facilitated by the mortality cost of staying in the tributary. This study indicates that stream fish movement is shaped by complex mechanisms that differ by spatial scale. Although complex, two study species often responded similarly, indicative of emerging regularities across species in determinants of multi‐scale stream fish movement.

Characteristics of the natural flow regime paradigm explain occurrence of imperiled Great Plains fishes

AbstractThe natural flow regime (NFR) paradigm posits that naturally occurring temporal fluctuations in streamflow are necessary for maintaining natural ecological communities. Conservation actions guided by the paradigm have contributed to stream organism conservation on a global scale, yet NFR applications in highly altered Great Plains streams are lacking. We analyzed historical (1980–2017) fish occurrence and flow data from sixteen gage locations across three Great Plains river basins with the goal of relating flow indices calculated for one year prior to each fish collection with the occurrence of fishes belonging to the highly imperiled pelagic‐broadcast spawning (PBS) reproductive guild. We fit random forest models using flow indices, gage identification, and watershed area as predictor variables and PBS fish occurrence as the response variable for all suspected or confirmed PBS fishes in each basin. Results revealed that flow indices from all NFR characteristics were useful for predicting PBS fish occurrence, but the identity of the most important flow indices varied by species and river basin. We also found that gage location was an important predictor variable, indicating flow–ecology relationships are spatially contingent and suggesting the influence of other factors that vary spatially (e.g., river fragmentation and water quality). Partial dependence plots identified thresholds in flow indices such as the timing of maximum flows and fall rate that may be associated with the presence or absence of PBS fishes, and these plots can be used to identify flow index target values to benefit conservation efforts. Time series predictions for likelihood of occurrence at a single gage in the Brazos River basin revealed a positive correlation between likelihood of occurrence and non‐drought years for three of four species present, supporting recent findings that drought suppresses PBS fish populations. This study provides insight into the flow requirements of some of the most imperiled stream fishes in North America and contributes to environmental flow science on a global scale by establishing a robust methodology for delineating flow–ecology relationships.

Non‐random dispersal in sympatric stream fishes: Influences of natural disturbance and body size

AbstractAlthough the prevailing paradigms in spatial ecology have treated dispersal as a stochastic process, there is an increasing awareness that spatial processes are non‐random such that individual characteristics and ecological contexts influence dispersal. Natural disturbance, such as river flooding, is known to stimulate dispersal behaviour, but its interactive effects with individual‐level characteristics (e.g. body size) of potential dispersers remain elusive. It is critical to fill this knowledge gap because anthropogenic impacts (including climate change) alter both disturbance regimes and population structures.Here, we examined how extreme high flows and individual body size combined to influence dispersal of three fishes (creek chubSemotilus atromaculatus, bluehead chubNocomis leptocephalus, and striped jumprockMoxostoma rupicartes) in two streams (740 and 520 m long) in South Carolina, U.S.A. We focused on extreme high flows as a natural disturbance, whereas body size was used as an individual‐level characteristic of dispersers. A total of 5,604 individuals were uniquely marked in the two streams over a >2‐year study period, during which sampling occurred every 2 months.The intensive capture–recapture study revealed differential effects of disturbance and body size among sympatric stream fishes. Extreme high flows increased dispersal of striped jumprock and creek chub, whereas body size influenced dispersal of striped jumprock with larger individuals traveling longer distances. Bluehead chub showed a complex dispersal response. That is, size‐dependence in dispersal emerged only during high‐flow periods.The results of this study build upon previous efforts by providing field‐based evidence of how disturbance and individual characteristics (body size) combine to drive non‐random dispersal and how it varies among sympatric species. This finding is important because metapopulations that are maintained by different non‐random dispersal (i.e. externally or internally driven) may show varied sensitivities to human‐induced environmental changes.

A test of a generalized, optimal habitat selection model for drift‐feeding fishes: brook charr

AbstractOptimality theory is useful for modeling habitat use in animals, although many models have not been rigorously tested. We evaluated the ability of the Grossman et al. net‐energy‐intake (NEI) optimal foraging model for drift‐feeding stream fishes, to predict the holding velocity (microhabitat) of native brook charr (BC; Salvelinus fontinalis) inhabiting a southern Appalachian stream. This model postulates that fish choose holding velocities that maximize their NEI, and is broadly applicable to stream fishes, many of which are drift‐feeders. We used laboratory prey capture success versus water velocity data to quantify the relationship between prey capture success, water velocity, and holding velocity of BC (N = 21, mean standard length = 147 mm ± 14 sd). Parameterization of the Grossman et al. model yielded an optimal holding velocity prediction of 18.5 cm·s−1. Based on fitting criteria from previous work, the model prediction was successful because it fell within the 95% confidence interval (13.5–20.5 cm·s−1) of mean holding velocities (17.0 cm·s−1, N = 26) of BC in Lynn Camp Prong, Tennessee. Consequently, NEI maximization likely is a causal factor affecting BC habitat choice. Our result argues strongly for the general usefulness of this model.

A new composite abundance metric detects stream fish declines and community homogenization during six decades of invasions

AbstractAimWe developed a new technique, utilizing species‐specific counts of individuals from historical fish community samples, to examine landscape‐level, spatio‐temporal trends in relative abundance distributions. Abundance‐based historical distribution analyses are often plagued by data comparability issues, but provide critical information about community composition trends inaccessible to those using analyses based only on species presence–absence. We established trends in native and non‐native fish abundance and community homogenization, uniqueness and diversity to help local conservation managers prioritize targets and motivate similar studies globally to support fish conservation.LocationUpper and middle New River (UMNR) basin, Appalachian Mountains, USA.MethodsWe compiled catch data from 61 years of fish community surveys (1958–2019) and tested for community homogenization by comparing data from repeatedly sampled sites (1900s versus 2000s samples) using dispersion analyses. We measured community uniqueness (site contributions to beta diversity) and species diversity (Shannon index) at sampled streams to identify potential conservation hotspots. We then used regression analyses and Wilcoxon signed‐rank tests to examine species‐specific basin‐wide and local abundance trends and identify species of potential conservation concern.ResultsDispersion of sites in species abundance space was significantly greater in the 1900s compared with the 2000s, indicating homogenization had occurred. Of 36 native species analysed, 44.4% (16) showed basin‐wide declines. Non‐native species exhibited mixed patterns; site‐level abundance increased in 2 of 15 species analysed (13%).Main conclusionsOur results indicate basin‐wide community homogenization has occurred within the UMNR, but many unique and diverse communities persist. If conserved, these could help maintain regional fish diversity. We found basin‐wide declines in four endemic species, as well as spread patterns of non‐native and native species that were not detected by a presence–absence analysis applied within the same study area. This finding illustrates the importance of considering both species’ abundance and occurrence patterns as separate dimensions of biodiversity to inform conservation planning.