Relationships among invasive common carp,native fishes and physicochemical characteristics in upper Midwest (USA) lakes

Abstract – Common carp Cyprinus carpio is a widespread invasive species that, in high abundance, can impose numerous deleterious effects in aquatic ecosystems. Common carp increase turbidity and nutrient availability while reducing invertebrate prey resources and aquatic macrophytes, transforming shallow lakes from the clear‐ to turbid‐water state. However, potential effects of common carp on native fish communities have received limited attention. We evaluated the relationships among relative abundances of nine native fishes and common carp for 81 lakes in eastern South Dakota and their associated physicochemical characteristics. Inverse threshold relationships among relative abundances of native fishes and common carp were identified for black bullhead Ameiurus melas, black crappie Pomoxis nigromaculatus, bluegill Lepomis macrochirus, white bass Morone chrysops and northern pike Esox lucius, while marginally significant relationships were detected for largemouth bass Micropterus salmoides and smallmouth bass M. dolomieu. Lakes where common carp relative abundance exceeded 0.6 fish per net night had low abundance of native fishes, whereas lower abundance of common carp resulted in variable abundance of native fishes. Lakes with abundance of common carp surpassing 0.6 fish per net night were also characterised by larger surface areas and watersheds and impaired water quality (higher dissolved solids and chlorophyll a concentrations and lower secchi depth). Our results are consistent with the biotic‐abiotic constraining hypothesis that proposes biotic factors can regulate fish populations regardless of abiotic conditions. Thus, common carp abundance may need to be reduced and sustained below ecological thresholds to improve water quality and increase abundance of native fishes.     

Relative influences of catchment‐ and reach‐scale abiotic factors on freshwater fish communities in rivers of northeastern Mesoamerica

Esselman PC, Allan JD. Relative influences of catchment‐ and reach‐scale abiotic factors on freshwater fish communities in rivers of northeastern Mesoamerica. Ecology of Freshwater Fish 2010: 19: 439–454. © 2010 John Wiley & Sons A/S Abstract – While the abiotic factors important to freshwater fish assemblages at a reach scale are well understood, studies of larger scale constraints have yielded variable conclusions, spurring a need for further studies in new biogeographic contexts. This study investigated the importance of catchment‐ and reach‐scale abiotic factors to variation in freshwater fish assemblages in rivers of northeastern Mesoamerica. Abiotic variables and fish data from 72 sampling sites on main stem rivers of Belize were used with partial constrained ordination to determine the proportion of spatially structured and unstructured variation in fish presence and absence, relative abundance, and community metrics explained by catchment‐ and reach‐scale environmental factors. Results showed that, combined, catchment and reach variables explained a large portion of the total variation in the fish assemblage data (54–75%), and that catchment environment explained a greater portion of variation (42–63%) than reach environment (34–50%). Variables representing landscape position (local elevation, watershed area) and their reach‐level correlates (channel width, depth variation, and substrate) correlated strongly to the fish assemblage data. Our results suggest that landscape‐scale factors have a stronger relative influence on assemblages than environmental conditions at the reach scale within our study area. These results contrast with past findings that showed greater local scale influence in landscapes with low anthropogenic disturbance levels. Our findings suggest that biodiversity conservation efforts should consider assemblage variation across a longitudinal gradient, and that a multi‐catchment region is a biologically relevant scale for fish conservation planning and coordination in northeastern Mesoamerica.     

Hierarchical faunal filters: an approach to assessing effects of habitat and nonnative species on native fishes

Abstract –  Understanding factors related to the occurrence of species across multiple spatial and temporal scales is critical to the conservation and management of native fishes, especially for those species at the edge of their natural distribution. We used the concept of hierarchical faunal filters to provide a framework for investigating the influence of habitat characteristics and nonnative piscivores on the occurrence of 10 native fishes in streams of the North Platte River watershed in Wyoming. Three faunal filters were developed for each species: (i) large-scale biogeographic, (ii) local abiotic, and (iii) biotic. The large-scale biogeographic filter, composed of elevation and stream-size thresholds, was used to determine the boundaries within which each species might be expected to occur. Then, a local abiotic filter (i.e., habitat associations), developed using binary logistic-regression analysis, estimated the probability of occurrence of each species from features such as maximum depth, substrate composition, submergent aquatic vegetation, woody debris, and channel morphology (e.g., amount of pool habitat). Lastly, a biotic faunal filter was developed using binary logistic regression to estimate the probability of occurrence of each species relative to the abundance of nonnative piscivores in a reach. Conceptualising fish assemblages within a framework of hierarchical faunal filters is simple and logical, helps direct conservation and management activities, and provides important information on the ecology of fishes in the western Great Plains of North America.     

Persistence of native fishes in small streams of the urbanized San Francisco Estuary,California: acknowledging the role of urban streams in native fish conservation

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Environmental factors regulating the recruitment of walleye Sander vitreus and white bass Morone chrysops in irrigation reservoirs

Understanding the environmental factors that regulate fish recruitment is essential for effective management of fisheries. Generally, first‐year survival, and therefore recruitment, is inherently less consistent in systems with high intra‐ and interannual variability. Irrigation reservoirs display sporadic patterns of annual drawdown, which can pose a substantial challenge to recruitment of fishes. We developed species‐specific models using an 18‐year data set compiled from state and federal agencies to investigate variables that regulate the recruitment of walleye Sander vitreus and white bass Morone chrysops in irrigation reservoirs in south‐west Nebraska, USA. The candidate model set for walleye included only abiotic variables (water‐level elevation, minimum daily air temperature during winter prior to hatching, annual precipitation, spring warming rate and May reservoir discharge), and the candidate model set for white bass included primarily biotic variables (catch per unit effort (CPUE) of black crappie Pomoxis nigromaculatus, CPUE of age‐0 walleye, CPUE of bluegill Lepomis macrochirus and CPUE of age‐3 and older white bass), each of which had a greater relative importance than the single abiotic variable (minimum daily air temperature during winter after hatching). Our findings improve the understanding of the recruitment of fishes in irrigation reservoirs and the relative roles of abiotic and biotic factors.     

Biodiversity value of remnant pools in an intermittent stream during the great California drought

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Spatial variation in the somatic growth rates of European barbel Barbus barbus: a UK perspective

The European barbel Barbus barbus is threatened in areas of its range because of its sensitivity to anthropogenic disturbance in riverine habitats and, in the UK, is indigenous to a relatively small number of east‐flowing rivers, with nonindigenous populations present in other rivers following introductions for angling enhancement. Fish stock assessment surveys completed between 2002 and 2010 collated age and growth data from 20 rivers across their indigenous and nonindigenous UK range. Analyses revealed that individuals present in samples are of 21 years old, with growth rates highly variable between rivers. There was no relationship between growth rates and the maximum age of fish per river, and there was no difference in growth rates between their indigenous and nonindigenous ranges. A range of abiotic data were collated and analysed against the growth data; these analyses suggested higher mean growth rates were evident in rivers of higher biological water quality (expressed as British Monitoring Working Party Score) and higher mean air temperatures (used as a surrogate of water temperature). That growth of B. barbus was significantly and positively enhanced by increased biological water quality was in contrast to cyprinid fishes such as roach Rutilus rutilus and suggests that as river water quality continues to improve through reduced nutrient inputs, further ecological changes are likely in riverine fish communities.     

Biogeographical region and environmental conditions drive functional traits of estuarine fish assemblages worldwide

Assessing trait–environment relationships is crucial for predicting effects of natural and human‐induced environmental change on biota. We compiled a global database of fish assemblages in estuaries, functional traits of fishes and ecosystem features of estuaries. And we quantified the relative importance of ecosystem features as drivers of patterns of fish functional traits among estuaries worldwide (i.e. drivers of the proportions of fish traits). In addition to biogeographical context, two main environmental gradients regulate traits patterns: firstly temperature, and secondly estuary size and hydrological connectivity of the estuary with the marine ecosystem. Overall, estuaries in colder regions, with larger areas and with higher hydrological connectivity with the marine ecosystem, have higher proportions of marine fish (versus freshwater), macrocarnivores and planktivores (versus omnivores, herbivores and detritivores) and larger fish, with greater maximum depth of distribution and longer lifespan. The observed trait patterns and trait–environment relationships are likely generated by multiple causal processes linked to physiological constraints due to temperature and salinity, size‐dependent biotic interactions, as well as habitat availability and connectivity. Biogeographical context and environmental conditions drive species richness and composition, and present results show that they also drive assemblage traits. The observed trait patterns and trait–environment relationships suggest that assemblage composition is determined by the functional role of species within ecosystems. Conservation strategies should be coordinated globally and ensure protection of an array of estuaries that differ in ecosystem features, even if some of those estuaries do not support high species richness.     

Diet and trophic niche overlap of native and nonnative fishes in the Gila River,USA: implications for native fish conservation

Pilger TJ, Gido KB, Propst DL. Diet and trophic niche overlap of native and nonnative fishes in the Gila River, USA: implications for native fish conservation. Ecology of Freshwater Fish 2010: 19: 300–321. © 2010 John Wiley & Sons A/S Abstract –  The upper Gila River basin is one of the few unimpounded drainage basins west of the Continental Divide, and as such is a stronghold for endemic fishes in the region. Nevertheless, multiple nonindigenous fishes potentially threaten the persistence of native fishes, and little is known of the trophic ecology of either native or nonnative fishes in this system. Gut contents and stable isotopes (¹³C and ¹⁵N) were used to identify trophic relationships, trophic niche overlap and evaluate potential interactions among native and nonnative fishes. Both native and nonnative fishes fed across multiple trophic levels. In general, adult native suckers had lower ¹⁵N signatures and consumed more algae and detritus than smaller native fish, including juvenile suckers. Adult nonnative smallmouth bass (Micropterus dolomieu), yellow bullhead (Ameiurus natalis) and two species of trout preyed on small‐bodied fishes and predaceous aquatic invertebrates leading to significantly higher trophic positions than small and large‐bodied native fishes. Thus, the presence of these nonnative fishes extended community food‐chain lengths by foraging at higher trophic levels. Although predation on juvenile native fishes might threaten persistence of native fishes, the high degree of omnivory suggests that impacts of nonnative predators may be lessened and dependent on environmental variability.     

The relative influence of spatial context and catchment‐ and site‐scale environmental factors on stream fish assemblages in a human‐modified landscape

Abstract – Environmental factors act in a hierarchical manner at multiple spatial scales to influence the organisation of ecological assemblages; however, the relative influence of the different scale‐related factor groups is poorly known. We evaluated the importance of catchment‐scale and site‐scale environmental variables, as well as the spatial context of the sampling sites, in shaping stream fish assemblages in an agriculture‐dominated landscape in Hungary. Beside the variables describing spatial context (principal coordinates of a truncated distance matrix among sites), altogether 60 environmental variables were used to predict variability using a variance‐partitioning procedure in redundancy analysis. Presence–absence‐ and relative abundance‐based data were examined at two assemblage levels (entire assemblage and native assemblage) at 54 stream sites. Incorporation of spatial variables increased largely the total explained variability in case of relative abundance, but not for presence–absence data. Of the environmentally explained variance, catchment‐scale variables (e.g., land cover types, patch density) were relatively more influential for the native assemblage‐level analyses, than for analyses at the entire assemblage level, where site‐scale variables (e.g., altitude, depth) proved to be more influential. In addition, pure catchment‐ and pure site‐scale variables have the primary role in determining fish assemblage patterns, whereas the influence of shared variance and that of site‐scale riparian variables proved to be less important. Our findings demonstrate the importance of incorporating the spatial context of the sampling sites in predicting fish assemblage patterns and the effects of channelisation (dikes) in shaping assemblage–environment relationships in this human‐influenced landscape.     

Suppression of invasive topmouth gudgeon Pseudorasbora parva by native pike Esox lucius in ponds

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Trophic plasticity of invasive juvenile largemouth bass Micropterus salmoides in Iberian streams

Biological invasions are a major factor for biodiversity loss, particularly in freshwater environments. Largemouth bass Micropterus salmoides is native to North America and is invasive on the Iberian Peninsula, primarily to provide angling opportunities in reservoirs. However, this species is a threat to the endemic Iberian fauna via predation and competition. Currently, there is little information on largemouth bass in European streams. Thus, we assessed the trophic plasticity and body condition of young largemouth bass in both invasive (the regulated Bullaque River) and native (Murray Creek) streams. Abundance of juvenile largemouth bass, percentage of full stomachs and body condition were higher in Bullaque River. Largemouth bass preyed on benthic invertebrates much more heavily in the Bullaque River, whereas fishes were the most important prey in Murray Creek. Prey richness, diet diversity and trophic niche breadth were higher in the Bullaque River population. Largemouth bass preferred water-column fishes as prey and avoided consuming benthic fishes in Murray Creek, whereas water-column fishes were avoided in Bullaque River. These results demonstrate that largemouth bass display substantial trophic plasticity which possibly facilitates its success as invasive species. Regulated Iberian streams may provide both suitable food and habitat resources with minimal predation pressure, and hence may serve as recruitment sources for this invasive fish.     

Longer food chains and crowded niche space: effects of multiple invaders on desert stream food web structure

Tributaries of the Colorado River Basin, historically home to a complex of endemic omnivores collectively referred to as the ‘three species’; flannelmouth sucker (Catostomus latipinnis), bluehead sucker (C. discobolus) and roundtail chub (Gila robusta), have experienced the establishment of numerous non‐native fish species. In this study, we examine the impacts of the trophic ecology of non‐native fishes on the ‘three species’ in the San Rafael River, Utah, USA. We employ a suite of abundance comparisons, stable isotope techniques and size‐at‐age back‐calculation analyses to compare food web structure and growth rates of the ‘three species’ in study areas with and without established populations of non‐native species. We found that the ‘three species’ are more abundant in areas with few non‐native fishes present, regardless of habitat complexity. Stable isotope analyses indicate non‐native fishes lengthen the food chain by 0.5 trophic positions. Further, the trophic niche spaces of the native fishes shift and are narrower in the presence of non‐native fishes, as several non‐native species’ trophic niche spaces overlap almost entirely with each of the ‘three species’ (bluehead sucker and flannelmouth sucker 100%, roundtail chub 98.5%) indicating strong potential for competition. However, the ‘three species’ demonstrated no evidence of reduced growth in the presence of these non‐native fishes. Collectively, these results suggest that while non‐native fishes alter the food web structure presenting novel sources of predation and competition, mechanisms other than competition are controlling the size‐structure of ‘three species’ populations in the San Rafael River.     

Linking temperate demersal fish species to habitat: scales,patterns and future directions

Adoption of the ecosystem approach to fisheries management relies on recognition of the link between fish and other components of the ecosystem, namely their physical and biological habitat. However, identifying the habitat requirements of marine fishes and hence determining their distribution in space and time is scientifically complex. We analysed the methodologies and findings of research on temperate, demersal fish habitat requirements to highlight the main developments in this field and to identify potential shortfalls. Many studies were undertaken over large spatial scales (≥100s km²) and these generally correlated abundances of fish to abiotic variables. Biological variables were accounted for less often. Small spatial scale (≤m²), experimental studies were comparatively sparse and commonly focused on biotic variables. Whilst the number of studies focusing on abiotic variables increased with increasing spatial scale, the proportion of studies finding significant relationships between habitat and fish distribution remained constant. This mismatch indicates there is no justification for the tendency to analyse abiotic habitat variables at large spatial scales. Innovative modelling techniques and habitat mapping technologies are developing rapidly, providing new insights at the larger spatial scales. However, there is a clear need for a reduction in study scale, or increase in resolution additional to the integration of biotic variables. We argue that development of sound predictive science in the field of demersal fish habitat determination is reliant on a change in focus along these lines. This is especially important if spatial management strategies, such as Marine Protected Areas (MPA) or No Take Zones (NTZ), are to be used in future ecosystem‐based approaches to fisheries management.     

The demography of introduction pathways,propagule pressure and occurrences of non‐native freshwater fish in England

• 1. Biological invasion theory predicts that the introduction and establishment of non‐native species is positively correlated with propagule pressure. Releases of pet and aquarium fishes to inland waters has a long history; however, few studies have examined the demographic basis of their importation and incidence in the wild.
• 2. For the 1500 grid squares (10×10 km) that make up England, data on human demographics (population density, numbers of pet shops, garden centres and fish farms), the numbers of non‐native freshwater fishes (from consented licences) imported in those grid squares (i.e. propagule pressure), and the reported incidences (in a national database) of non‐native fishes in the wild were used to examine spatial relationships between the occurrence of non‐native fishes and the demographic factors associated with propagule pressure, as well as to test whether the demographic factors are statistically reliable predictors of the incidence of non‐native fishes, and as such surrogate estimators of propagule pressure.
• 3. Principal coordinates of neighbour matrices analyses, used to generate spatially explicit models, and confirmatory factor analysis revealed that spatial distributions of non‐native species in England were significantly related to human population density, garden centre density and fish farm density. Human population density and the number of fish imports were identified as the best predictors of propagule pressure.
• 4. Human population density is an effective surrogate estimator of non‐native fish propagule pressure and can be used to predict likely areas of non‐native fish introductions. In conjunction with fish movements, where available, human population densities can be used to support biological invasion monitoring programmes across Europe (and perhaps globally) and to inform management decisions as regards the prioritization of areas for the control of non‐native fish introductions.

© Crown copyright 2010. Reproduced with the permission of her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.     

Diet of non‐native northern snakehead (Channa argus) compared to three co‐occurring predators in the lower Potomac River,USA

Abstract – Introductions of large, non‐native, carnivorous fishes continue to occur worldwide and represent a substantial management concern to global biodiversity. One of the most recent non‐native fishes to successfully establish in North America is the northern snakehead (Channa argus), found in the lower Potomac River catchment. Dispersal of the northern snakehead throughout this system has been well documented since its original discovery in May 2004; however, little is known about the foraging habits of this species and its interactions with co‐occurring predators. Here, we quantify northern snakehead diet in comparison with the diets of naturalised largemouth bass (Micropterus salmoides), and native American eel (Anguilla rostrata) and yellow perch (Perca flavescens) collected from tidal freshwaters bordering Virginia and Maryland near Fort Belvoir, Virginia. Over 97% of northern snakehead gut contents were fishes, with fundulid and centrarchid species consumed most frequently. Dietary overlap was biologically significant only between northern snakehead and largemouth bass. Aquatic invertebrates were >10 times more common in native predator diets, reducing dietary overlap with northern snakehead. Ontogenic shifts in adult northern snakehead diet were also detected, which may be explained by optimal foraging rather than true prey specificity. Northern snakehead may be occupying a novel niche based on a piscivorous diet, therefore limiting competition with resident predators in the lower Potomac River. Further research into interactions between largemouth bass and northern snakehead is needed to inform management decisions and understand the ecological impacts of this non‐native species.     

Vulnerability of Cape Fold Ecoregion freshwater fishes to climate change and other human impacts

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Assessing long‐term fish responses and short‐term solutions to flow regulation in a dryland river basin

Water resource development and non‐native species have been cited as primary drivers associated with the decline of native fishes in dryland rivers. To explore this topic, long‐term trends in the fish community composition of the Bill Williams River basin were studied over a 30‐year period (Arizona, USA). We sampled 31 sites throughout the basin that were included in fish surveys by Arizona Game and Fish in 1994–97 and the Bureau of Land Management in 1979–80. We found that non‐native species have proliferated throughout the entire basin, with greater densities in the lower elevations. Native species have persisted throughout most of the major river segments, but have experienced significant declines in frequency of occurrence and abundance in areas also containing high abundances of non‐native species. Next, we assessed the short‐term response of the fish assemblage to an experimental flood event from the system's only dam (i.e. Alamo Dam). In response to the flood, we observed a short‐term reduction in the abundance of non‐native species in sites close to the dam, but the fish assemblage returned to its preflood composition within 8 days of the event, with the exception of small‐bodied fish, which sustained lower postflood densities. Our findings demonstrate the importance of natural flow regime on the balance of native and non‐native species at the basin scale within dryland rivers and highlight minimal effects on non‐native fishes in response to short duration flood releases below dams.     

Nile tilapia (Oreochromis niloticus) invasions disrupt the functional patterns of fish community in a large subtropical river in China

Although non‐native species can modify ecosystem function, their effects in southern China have not been investigated, despite their ecological importance. This study assessed how Nile tilapia Oreochromis niloticus (L.) invasions impact the functional patterns of fish communities in the large subtropical Pearl River by analysing the relationships between invasion and body size over a 9‐year period. The relative abundance of Nile tilapia increased significantly over time. In particular, the established Nile tilapia significantly undermined the relative densities and the body size of the native fishes. Importantly, this study provided empirical evidence that functional indices (such as body size) are more sensitive when evaluating the effects of non‐native species on a community than richness. Understanding processes such as those should be the basis of controlling alien fish species and fisheries management in the Pearl River.     

Effects of simulated light intensity,habitat complexity and forage type on predator–prey interactions in walleye Sander vitreus

Predator‐prey interactions can be influenced by the behaviour of individual species as well as environmental factors. We conducted laboratory experiments to test for the influences of two abiotic factors (light intensity and habitat complexity) on predator–prey interactions between walleye Sander vitreus and two prey species, bluegill Lepomis macrochirus and golden shiner Notemigonus crysoleucas. Three light intensities were simulated (day, twilight and night) in the presence or absence of simulated vegetation. Observations of predator behaviour indicated that walleye increased activity and foraging success with decreasing light levels and had most success capturing dispersed, closer prey. While schooling could not be maintained as light levels diminished, prey decreased predation vulnerability by moving into vegetation or higher in the water column. Throughout all treatments, bluegill were more evasive to capture as the number of strikes was similar on both prey but capture rates were higher for golden shiner. Although light intensity and simulated habitat complexity affected predator and prey behaviour, these factors did not interact to influence foraging success of walleye. To fully understand predator and prey behaviours in fishes, an understanding of species‐specific responses to abiotic and biotic factors is necessary.