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Abstract

AimEven successful invaders are abundant only in a fraction of locales they inhabit. One of the main challenges in invasion ecology is explaining processes that drive these patterns. We investigated recruitment of a globally invasive fish, common carp (Cyprinus carpio), across three ecoregions to determine the role of environmental characteristics, predatory communities and propagule pressure on the invasion process at coarse and fine spatial scales.LocationLakes across Northern Forest, Temperate Forest and Great Plains ecoregions of North America.Methods We used data from 567 lakes to model presence or absence of carp recruitment using environmental conditions (lake clarity, area, maximum depth), native predatory fishes (micropredators, mesopredators, large predators) and propagule pressure (abundance of adult carp). We formed a set of alternative models and evaluated their support using an information theoretic approach. Once most supported models were identified, we used classification tree to determine how variables included in these models interacted to affect carp recruitment. Finally, we conducted a field experiment to test the predictions of the classification tree analysis.ResultsCarp recruitment was strongly regulated by processes associated with water clarity, which appeared to function as a broad-scale ecological filter. Carp were unlikely to recruit in clear, oligotrophic lakes (Secchi depth > 2 m) despite the presence of adults in many such systems. Recruitment was more likely to occur in regions with turbid lakes, but abundant micropredators could inhibit it there.Main conclusionsCarp recruitment and invasions across large geographic areas are attributable to a two-layer ecological filter with lake clarity/productivity acting as a coarse-scale filter and micropredators acting as a fine-scale filter. This two-layer filter might explain the complex patterns of carp invasions among and within different ecoregions. Ecological filters may also explain the success of other aquatic invaders that show similarly patchy spatial distribution patterns.

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... Given the presence of vegetated spawning habitat, recruitment of carp is regulated primarily by processes associated with water productivity (most likely through increased abundance of larval food), abundance of small predators that forage on carp eggs and larvae (micropredators), such as the bluegill (Lepomis macrochirus), and abundance of adult carp (Bajer et al. , 2015aWeber and Brown 2013). Regional differences among these processes lead to distinct recruitment patterns that have important implications for managing carp via physical removal, or winter seining in particular. ...
... This can be illustrated by two different ecoregions of temperate North America. In lakes of the Great Plains ecoregion, which are very productive and typically have low abundance of micropredators (prairie lakes), carp recruitment is frequent (Bajer et al. 2015a) and is primarily regulated by the density of adults (recruitment tends to be especially high at low densities of adult carp) (Weber and Brown 2013;Bajer et al. 2015b). Such populations may be difficult to manage with removal because percapita reproductive success increases as adult density is being reduced (Weber et al. 2011;Colvin et al. 2012). ...
... Such populations may be difficult to manage with removal because percapita reproductive success increases as adult density is being reduced (Weber et al. 2011;Colvin et al. 2012). However, in lakes of the Temperate Forests ecoregion, which are less productive and typically have more abundant populations of bluegill, in-lake recruitment is very low and carp populations are sustained by spawning migrations of adults into winterkill-prone marshes in which communities of micropredators are unstable and in which carp can periodically overcome recruitment bottlenecks (Bajer et al. 2015a(Bajer et al. , 2015b. Carp populations driven by such external recruitment dynamics may be more suitable for management via removal because recruitment is sporadic (it occurs only after winterkills when native micropredators perish) and also because out-migration rates of juveniles from marshes into lakes are often low (Bajer et al. 2015b). ...
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Common carp (Cyprinus carpio) is one of world’s most invasive fish and managers have long searched for practical control strategies for this species. In temperate systems, common carp forms large winter aggregations that can be located with telemetry and removed with seine nets. This has been viewed as an excellent management possibility, but its success has been mixed. Using a modeling approach, we demonstrate that the usefulness of winter seining in controlling common carp in temperate North American lakes depends on whether carp populations are driven by one of two distinct recruitment dynamics. In lakes where carp can easily recruit within systems from which they are being removed, such as within productive lakes with poor communities of micropredators, winter seining is unlikely to be effective. Even very high removal rates (90 % adults annually) were not sufficient to reach management goal (biomass <100 kg/ha) in such systems. However, in regions with strong predatory communities where carp can recruit only in outlying, seasonally unstable marshes, removal rates as low as 30 % annually or 50 % every other year were able to reduce carp biomass below the management threshold. Such removal rates are achievable as they fall within the range of empirically measured values. Because many carp populations are driven by external recruitment dynamics, strategically conducted winter removal could be used to control this species in a large number of systems across temperate North America and elsewhere.
... Mississippi River Basin of North America, especially where it overlaps with the Great Plains Ecoregion (Bajer et al., 2015a). This region is characterised by interconnected lakes, wetlands and rivers. ...
... Indeed, for a generalist, these areas are likely to coincide with dissolved nutrient levels and vary by lake and shifting carp densities. A numeric model of carp abundance in the Great Plains Ecoregion shows that a combination of water productivity (as measured by clarity), the presence of piscine micropredators (bluegill sunfish, Lepomis macrochirus) and adult propagule pressure can explain their numbers (Bajer et al., 2015a). Adult carp have no known predators of significance, so such movements would have little risk and might also reduce chances of their being stranded in low or hypoxic waters. ...
... Moreover, our results suggest the common carp might be restored in areas of Europe (where native) by opening migratory pathways that have been blocked by dams and restoring the connected ephemeral wetlands on which they presumably depend as nurseries. We expect future research will show the carp's life-history strategy involving homing and partial migration to vary among different temperate freshwater ecosystems across the globe, including large shallow lakes with extensive wetlands (Bajer et al., 2015a;Hennen & Brown, 2014;Yick et al., 2021). The spatial ecology of other riverine fishes, especially cyprinids, might also be studied to see whether they too employ a similar combination of adaptive life-history traits in productive, unstable temperate ecosystems that experience extreme spatial and temporal variability. ...
Article
The common carp, Cyprinus carpio, is a large, long‐lived, fecund and mobile cyprinid, which evolved in complex inter‐braided Ponto‐Caspian rivers that experience both springtime flooding and freezing winters. Studies suggest adults often move to productive, shallow lakes and floodplains to spawn because they often lack egg predators and then return to deeper normoxic waters to overwinter. Whether these movements involve individuals consistently selecting, or homing to, the same spawning and refuge lakes as part of a strategy benefiting their reproductive success is unknown. To address this question, we examined the movements of 67 radio‐tagged adult carp for 3 years in a watershed with 11 interconnected lakes. Carp were tagged and released into a centrally located, normoxic deep lake in spring and fall. Each spring over 95% of its adults left via a single stream and swam into one of 5 shallow lakes, with most individuals (84%) selecting the same lake(s) in which to spawn each year (median Bhattacharyya affinity coefficient of similarity of 0.82). Young were later found in those lakes without egg predators, which cannot survive winter anoxia. After spawning, carp spent summers moving between productive lakes in an individualistic fashion, presumably foraging, with most (89%) eventually returning to the same deep lake to overwinter (median Bhattacharyya affinity of 1.0). These movements appear to reveal a life‐history tactic involving seasonal homing migration, first to a spawning location and later to winter refuges, that is well adapted to productive but highly heterogeneous and interconnected freshwater environments.
... Across the globe, the common carp (or "carp") is a highly invasive fish whose success has been hypothesized to be linked with ecosystem productivity and zooplankton resources for its larvae. Carp tend to be most abundant in eutrophic waters (Kulhanek et al. 2011a, b) and Bajer et al. (2015a) showed that carp recruitment is generally found in productive lakes despite the fact that adults are also commonly found (although in low abundance) in meso-and oligotrophic lakes. This pattern in carp recruitment might be caused by reduced larval survival in oligotrophic lakes due to starvation or nutritional deficiencies, or increased larval predation rates as a result of reduced growth. ...
... We collected zooplankton from three lakes located in the Upper Mississippi River Basin near Minneapolis, Minnesota, USA, a region where carp populations show pronounced differences in abundance and recruitment among lakes (Bajer et al. 2015a). Each year (2014 and 2015), our goal was to sample the same set of three lakes comprised of one eutrophic, one mesotrophic, and one oligotrophic lake. ...
... We conducted controlled laboratory experiments to shed light on processes that might explain the mechanism by which common carp recruitment occurs in eutrophic lakes but not in oligotrophic lakes (Bajer et al. 2015a). Our results suggest that common carp larvae are likely to grow much faster in productive lakes where densities of macrozooplankton that larval carp select as food are highest (Pace 1986). ...
Article
Across-ecoregion analyses showed that the recruitment of common carp, Cyprinus carpio (Linnaeus 1758), a globally invasive fish, is strongly influenced by lake productivity: while recruitment was frequent in hypereutrophic lakes, it was invariably absent in oligotrophic lakes. This led to a hypothesis that common carp larvae might have faster growth rates in productive lakes that allow them to outgrow native predators, whereas larvae might encounter nutritional bottlenecks in oligotrophic lakes. We shed some light on this hypothesis by documenting how zooplankton communities found in oligo-, meso-, and eutrophic lakes in Minnesota, USA affected larval carp survival, growth and diet composition. We cultured larval carp in tanks fed zooplankton at naturally occurring densities from three lakes of varying trophic states for 20 days during two consecutive springs. The growth rates were significantly higher (up to 5 times) among larvae fed zooplankton from the eutrophic lake and lowest in larvae fed zooplankton from the oligotrophic lake. Despite their small size (~6 mm), carp larvae selected large zooplankton (0.3–0.6 mm), primarily Bosmina spp., even on the first day of exogenous feeding. This pattern was consistent across all treatments. Rotifers were generally not found in the stomachs of larval carp, despite their high abundance, even if other food items were scarce. The densities of cladocera were highest in the productive lake, especially during one of the two years when larval carp showed very rapid growth rates. Our study shows that larval carp have well defined dietary preferences and that common carp recruitment might be especially likely to occur in productive systems with abundant cladocera populations in which carp larvae are expected to be more likely to escape gape-limited, native predators.
... Although the common carp is generally considered to be a large river fish [13], it also does very well in many temperate lakes, especially systems of shallow eutrophic lakes with extensive littoral zones or lakes associated with such areas [6,14]. Adult carp are seasonal spawners and migrate, sometimes great distances, into shallow waters (floodplains, wetlands, ponds or shallow lakes) where females release up 3 million eggs each onto submersed vegetation [15,16]. ...
... This scenario results in watersheds in which peripheral shallow waterbodies including floodplains, wetlands, ponds and shallow lakes can serve as population "sources", while deeper lakes function as "sinks"-a scenario known as a "source-sink" (Figure 1) [21,[23][24][25]. Although not well studied, source-sink dynamics appear to be common in many watersheds in the North American Midwest, especially in its temperate forested zones where shallow lakes that frequently winterkill are commonly connected, sometimes in chains which flow to rivers or deep lakes [14,16,23]. Importantly, source-sink dynamics create special opportunities for controlling invasive species [25] because their recruitment is spatially restricted to a few locations so they can be easier to manage, as can removal of adults from population sinks. ...
... Importantly, source-sink dynamics create special opportunities for controlling invasive species [25] because their recruitment is spatially restricted to a few locations so they can be easier to manage, as can removal of adults from population sinks. zones or lakes associated with such areas [6,14]. Adult carp are seasonal spawners and migrate, sometimes great distances, into shallow waters (floodplains, wetlands, ponds or shallow lakes) where females release up 3 million eggs each onto submersed vegetation [15,16]. ...
Article
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The common carp has been highly problematic in North American ecosystems since its introduction over a century ago. In many watersheds, its abundance appears to be driven by source-sink dynamics in which carp reproduce successfully in peripheral ponds that lack egg/larva micro-predators which then serve as sources of recruits for deeper lakes. This manuscript describes how carp were sustainably reduced in two chains of lakes by disrupting source-sink dynamics in three steps. First, we ascertained whether lakes had problematic densities of carp that could be explained by source-sink dynamics. Second, ways to control recruitment were developed and implemented including: (i) aerating source ponds to reduce hypoxia and increase micro-predator abundance, (ii) blocking carp migration, and (iii) locating and removing adults from sinks using targeted netting guided by Judas fish. Third, we monitored and adapted. Using this strategy, the density of carp in 3 lakes in one chain was reduced from 177 kg/ha to ~100 kg/ha in 3 years and held constant for a decade. Similarly, adult density was reduced from 300 kg carp/ha in 2 lakes in the other chain to 25 kg/ha. Once carp densities were low, aluminum sulfate treatments became reasonable and once conducted, water quality improved.
... Predation, lake productivity, adult density, and movement of adults and juveniles between interconnected systems of seasonally unstable habitats have all been suggested to have an effect on carp recruitment and population abundance in North America (Bajer and Sorensen 2010;Bajer et al. 2012;Silbernagel and Sorensen 2013;Weber and Brown 2013;Bajer et al. 2015a, b). Bluegill sunfish (Lepomis macrochirus), which have been shown to consume carp eggs and larvae (Bajer et al. 2012;Silbernagel and Sorensen 2013;Bajer et al. 2015a), have been hypothesized to function as an important biocontrol agent in many lakes in the Upper Mississippi region. However, this hypothesis has not been tested experimentally. ...
... However, this hypothesis has not been tested experimentally. Lake productivity has also been suggested to be an important driver of carp recruitment, possibly due to increased prey abundance for larval carp in productive lakes (Bajer et al. 2015a), but diets, growth and survival of larval carp have not been documented in lakes of varying productivity level. Finally, carp recruitment has a strong spatial component related to predator instability across the landscape. ...
... The possibility that a native predator can control an invasive fish is perhaps best developed for the common carp (Cyprinus carpio, hereafter "carp") (Bajer et al. 2012;2015a). Carp's life cycle suggests that this species could be controlled by predators that target eggs, larvae and juveniles. ...
Thesis
Processes that regulate common carp (Cyprinus carpio) recruitment (i.e. survival of eggs, larvae and juveniles) are largely unknown. In interconnected lake-marsh systems of Minnesota, young of year (YOY) carp are generally found in marshes that winterkill and lack bluegill sunfish (Lepomis macrochirus), an abundant native predator. This suggests that bluegills might function as a biocontrol agent for carp. Further, whereas YOY carp are commonly found in winterkill marshes of south-central Minnesota, they are not found in similar systems in northern Minnesota where lake productivity is much lower, suggesting an aquatic productivity bottleneck on carp recruitment. Finally, in marshes where carp recruit (productive and bluegill-free), YOY must disperse into adjacent lakes to drive high population abundance. In this study, I conducted three experiments to test 1) the effect of bluegills on carp recruitment; 2) the effect of aquatic productivity on larval carp survival, growth and diet; 3) natural dispersal tendencies of YOY carp from a marsh into an adjacent lake. The first experiment employed four (20 m diameter) impermeable enclosures from 2011-2014. Each year, enclosures were stocked with carp eggs and every other one was stocked with bluegills. Backpack electrofishing surveys conducted five weeks later showed that carp catch per unit of effort (CPUE) was over 10-fold lower in the enclosures stocked with bluegills than in the controls. The second experiment, conducted in 2014 and 2015 used aquaria stocked with carp larvae and supplied with zooplankton densities and community structures from lakes of three different trophic states (oligo-, meso-, and eutrophic). It showed that carp larvae selectively consumed macrozooplankton (> 200 μm) and their growth rates were highest in the eutrophic lake and lowest in the oligotrophic lake. Survival, however, was high in all treatments. The third study was conducted in a natural lake-marsh system and utilized passive integrated transponder (PIT) tags to quantify the outmigration of YOY carp from the marsh to the lake. It showed that < 6% YOY carp outmigrated to the lake, supporting previous indirect estimates. The results of these three studies are important to understanding recruitment dynamics of carp in lake-marsh systems in Minnesota.
... The extent to which native fish communities, especially native predators, might control the establishment and success of invasive fish has been of interest to marine and freshwater ecologists [1,2,3,4]. Shedding light on this relationship might explain fish invasions at local and regional scales [5], examine the need to conserve native fish communities-many of which are severely eroded [6], and suggest management strategies to hinder invasions [2]. The hypothesis that predation might play an important role in hindering fish invasions is supported by several lines of evidence. ...
... Thus, we hypothesize that predation might have similar effects on fishes that are introduced to new habitat. Further, non-native fish become invasive in only a fraction of locales to which they are introduced, despite seemingly favorable abiotic conditions, suggesting that biotic processes such as predation might often be limiting their success [10,5] Finally, smallscale (laboratory, mesocosm, pond) experiments suggested a strong effect of native predators on at least some invasive fish [2,11,12]. Despite significant interest among aquatic ecologists and potential management applications, the hypothesis that native predatory fish might be instrumental in controlling invasive fish has never been tested using large-scale, natural experiments. ...
... Nevertheless, experimental studies might help addressing key tenants of the predationinvasibility relationship in fish and might identify certain types of species or habitats where predation is likely to be important. Arguably, the case of the invasive common carp (Cyprinus Carpio) in the Upper Mississippi Region (UMR) is one of the best documented scenarios where native predatory fish might control the success of the invader to a significant degree [13,2,16,5,17,18]. The common carp (or 'carp') is a large and highly fecund fish [19]. ...
Article
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The extent to which native fish communities might control the success of invasive fish has been of interest to ecologists, but it has been rarely addressed using experiments. We conducted an experiment in six small lakes in the Upper Mississippi Region to test the effects of a small native predator, bluegill sunfish (Lepomis macrochirus) on the recruitment of a large, invasive fish, the common carp (Cyprinus carpio). Bluegills are predominant throughout the region and were previously shown to consume carp eggs and larvae. We stocked both lakes at each of our 3 sites with adult carp (spawners) and one lake at each site with bluegills. We repeated the experiment at two of the three sites for two consecutive years. In each lake we assessed the abundance of post-larval carp one month after spawning (backpack electrofishing surveys) and at the end of the season (mark-recapture). For each site/year combination, catch rate of post-larval carp was typically an order of magnitude higher in control than bluegill lakes, but it often declined quickly over time. The abundance of end-of-seasonal juveniles was significantly higher (no 95% CI overlap) in control lakes than in bluegill lakes, except for one pair of lakes during one year when both the control and bluegill lake had similar, low abundance of end-of-season carp. Overall, our results support the hypothesis that common carp recruitment is substantially reduced in habitats dominated by bluegills. We also suggest our results may be applicable to other species, and that managers should explore how predation on early life stages may control other invasive species.
... Bluegill and similar native predators, combined with abiotic constraints, may be capable of regulating common carp populations (Bajer et al. 2015). For instance, in field experiments, bluegill have demonstrated a capacity to reduce carp recruitment by feeding on small common carp (Bajer et al. 2012). ...
... The Moran effect, or widespread synchronization of population abundance, occurs in common carp in the upper Midwest (Phelps et al. 2008). Widespread abiotic factors, such as changes in hydrology or temperature, could act to simultaneously decrease carp abundance across 1300 km of river habitat (sensu Bajer et al. 2015). We cannot dismiss this possibility, although we are unable to provide an example of an abiotic factor(s) that are both influential enough to lead to such strong trends in abundance and that have changed simultaneously over the entire basin during the period in question. ...
Article
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Populations of invasive species that undergo rapid expansions after establishment in a new system can also be subject to collapse. Although the dynamics of the establishment and expansion phases and their ecological effects are well documented, substantially fewer studies document collapses despite their importance for understanding invasion dynamics. Two long-term fish monitoring programs sample the fish assemblage of the Upper Mississippi River System. These data provide an opportunity to document the collapse of common carp (Cyprinus carpio), a globally invasive freshwater fish species. Here we describe their population trajectory over several decades and examine several hypotheses to explain the decline, including: boom-bust population dynamics; suppression by native predators; resource exhaustion; improvements in environmental conditions; and disease. The observed trends appear to be most consistent with the hypothesis that disease was the most important factor contributing to the collapse. In particular, cyprinid herpesviruses have been shown to affect common carp in a manner consistent with the observed decreases in catch rates and increases in size distributions. The apparent role of a viral agent in causing the decline of common carp across one of the largest river basins in North America suggests similar collapses may occur elsewhere.
... Bullfrog tadpoles are also mostly unpalatable to predatory fishes (Kruse & Francis, 1977), but they are, however, vulnerable to predation by salamanders and dragonfly larvae (Werner & McPeek, 1994), and adult and juvenile bullfrogs are also frequently preyed by large vertebrates (Lannoo, 2005). Recent evidence suggests that environmental controls and predation pressure can interact and influence invasive fish at hierarchical spatial scales (Bajer et al., 2015). Although this possibility could not be addressed in our case due to the nature of our data, increasing availability of large-scale, spatially explicit databases should open opportunities to test, in the near future, if similar hierarchical filters exist in amphibian communities. ...
... As discussed above, this hinders the identification of hierarchical structures in the controls of invasion (e.g. biotic interactions filtering out non-natives at the local community scale, and environmental filters preventing or allowing them at the regional scale; Bajer et al., 2015). Nevertheless, because spatial aggregation decreases variance, patterns that can be observed using our approach should be at least as clear using finer-scale data. ...
Article
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AimInvasive species present negative impacts on native biodiversity at a global scale. A key goal of community ecology is to identify what drives invasiveness, but hypotheses relying on biotic mechanisms remain largely untested for many groups. Here we asked whether source and recipient communities of two highly successful invasive anurans (the bullfrog Lithobates catesbeianus and the cane toad Rhinellla marina) differ consistently from a taxonomic and/or functional standpoint. If affirmative, this pattern could suggest that taxonomic and/or functional distances between an invasive species and a potentially recipient community might influence the alien's invasive potential. LocationWorld-wide. Methods Based on co-occurrence data of 1061 amphibian species, we compared 30 source to 30 recipient communities of bullfrogs and cane toads by means of biotic metrics that summarize taxonomic and functional diversity and the relative position of the invasive species within the community. We also included environmental drivers that reportedly influence invasibility (climate, resource availability, spatial heterogeneity, and propagule pressure). ResultsBoth invasive species were functionally distant to their respective recipient communities; in contrast, community diversity did not explain much variation between source and recipient communities. Climate matching possibly influenced cane toad's but not bullfrog's invasiveness, and landscape factors had little relevance overall. Main conclusionThis study advances the notion that the relative position of a recently introduced species within the native functional space may help predicting its invasive potential.
... Previous studies show that the invasiveness of carp can often be attributed to recruitment hotspots that serve as productive nurseries across large spatial scales (e.g., Bajer and Sorensen 2010;Stuart and Jones 2006;Crook et al. 2013). Related work provides evidence that carp recruitment can be controlled by egg and larval predators in portions of their invasive range, but that optimal spawning habitats that lack predators often exist as part of the landscape mosaic (Bajer et al. 2012(Bajer et al. , 2015aSilbernagel and Sorensen 2013). These studies also speculate that such localized predator-free habitats are the primary source of carp to connected waters, but did not provide any direct evidence of dispersal as we have. ...
... Although source-sink dynamics may explain the invasiveness of common carp in many complex heterogeneous systems, this concept is not universally applicable. For instance, the source-sink framework would not apply to carp populations that lack metapopulation structure or occur in homogenous habitats such as lakes in the western plains of the Midwest where carp recruitment dynamics seem to be driven by other factors including high YOY survival and lake productivity (Weber and Brown 2013;Bajer et al. 2015a). Winter hypoxia and patchily distributed predators is only one of many possible mechanisms that may result in source-sink dynamics. ...
Article
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Source–sink theory is an ecological framework that describes how site and habitat-specific demographic rates and patch connectivity can explain population structure and persistence across heterogeneous landscapes. Although commonly used in conservation planning, source–sink theory has rarely been applied to the management of invasive species. This study tested whether the common carp, one of the world’s most invasive species, exhibits source–sink dynamics in a representative watershed in the Upper Mississippi River Basin comprised of a dozen interconnected ponds and lakes. To test for source–sink population structure, we used standard fish sampling techniques, tagging, and genetic assignment methods to describe habitat-specific recruitment rates and dispersal. Five years of sampling revealed that while adult carp were found across the entire watershed, reproductive success (the presence of young carp) was restricted to shallow ponds. Additionally, nearly a third of the carp tagged in a representative pond dispersed into the connected deeper lakes, suggesting that ponds in this system serve as sources and lakes as sinks. This possibility was confirmed by microsatellite analysis of carp tissue samples (n = 1041) which revealed the presence of two distinct strains of carp cohabitating in the lakes, whose natal origins could be traced back to one of two pond systems, with many adult carp attempting to migrate back into these natal ponds to spawn. We conclude that the distribution and persistence of invasive carp in complex interconnected systems may often be driven by source–sink dynamics and that their populations could be controlled by suppressing reproduction in source habitats or by disrupting dispersal pathways, instead of culling individuals from sink habitats. © 2018 Springer International Publishing AG, part of Springer Nature
... Further, both native and nonnative benthic fishes that occur in sympatry can be driven by the same processes related to habitat modifications by humans. For example, the increasing lake productivity increases reproductive success and abundance of the non-native common carp (Cyprinus carpio Linnaeus, 1758) in temperate lakes of North America (Bajer et al., 2015a). At the same time, anthropogenic eutrophication also promotes the native black bullhead (Ameiurus melas Rafinesque, 1820) with the increasing frequency of hypoxia that gives the bullheads a competitive advantage over other native fishes (Hanson & Butler, 1994). ...
... Because of species-specific gear differences, we used gillnets to represent common carp CPUEs (kg/net) and trapnets to represent black bullhead CPUEs (kg/net). We also used trapnet catches to estimate values for bluegill CPUs, which represented the dominant planktivorous fish in our study lakes, and which can influence both the abundance of carp and water clarity (Bajer et al., 2015a). The lakes were sampled during July-September. ...
Article
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While it is accepted that invasive species are non-native organisms that become abundant and cause ecological damage in areas where they are introduced, the problem of ‘native invaders,’ native species that become excessively abundant due to anthropogenic impacts, is frequently encountered by ecologists. Often, native and non-native invaders occur in sympatry. Understanding relative severity of their impacts and niches they occupy is needed to inform management actions. Here, we quantify relative impact of native (black bullhead) and non-native (common carp) benthic fish on macrophytes species richness in over 200 lakes in North America. The impact of each species was addressed while accounting for the effects of water clarity, depth, lake area, watershed size, shoreline irregularity, land use by humans, abundance of planktivorous fishes, and ecoregion. Using model selection, we show that both species had negative impact on macrophytes richness, but the impact of carp was approximately two times as
... The acknowledged epicentre and only formally defined containment area for invasive koi carp (an ornamental strain of Cyprinus carpio) in New Zealand is located in the North Island in the Lower Waikato River Basin (LWRB; Grainger, 2015). Eutrophic conditions combined with a temperate climate and connected shallow riverine lakes and wetlands provide ideal conditions for the proliferation of this (Bajer et al., 2015;Vilizzi, Tarkan, & Copp, 2015) and other invasive fish such as the brown bullhead catfish Ameiurus nebulosus and goldfish Carassius auratus. ...
... Reducing common carp biomass in natural waters could reduce the incidence of the disease. Research in Minnesota has shown that clear (unproductive) lakes and high bluegill (egg predator) abundance are major influences in controlling carp abundance (Bajer et al. 2012(Bajer et al. , 2015. Regulations to control svcv can have unintended consequences. ...
... Specific comparisons of biotic resistance to high-versus low/moderate-impact invaders have not been pursued and may represent an interesting avenue for future research. Current evidence suggests that certain mechanisms of biotic resistance, namely herbivory and predation, may have an effect on the rate of spread or abundance of high-impact invaders (e.g., Bajer et al. 2015;Dorn and Hafsadi 2016). On the other hand, the ability of established resident exotic species to contribute to a community's resistance may be positively related to their potential impact (Henriksson et al. 2016), providing an additional layer of complexity. ...
Article
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Biotic resistance, the ability of communities to resist exotic invasions, has long attracted interest in the research and management communities. However, inconsistencies exist in various biotic resistance studies and less is known about the current status and knowledge gaps of biotic resistance in forest ecosystems. In this paper, we provide a brief review of the history and mechanisms of the biotic resistance hypothesis, and summarize the central topics and knowledge gaps related to biotic resistance with a special emphasis on forest ecosystems. Overall, although the amount of research efforts on biotic resistance in forest ecosystems has increased since the mid-2000s, aspects such as resistance to exotic pests and pathogens remain understudied. In addition, we synthesize ecological and statistical explanations of observed inconsistencies and provide suggestions for future research directions. Some of the observed inconsistencies on biotic resistance can be attributed to (1) the interactive or additive effects of other ecological processes and (2) the statistical artifacts of modifiable areal unit problem. With the advancement of new statistical knowledge and tools, along with availability of big data, biotic resistance research can be greatly improved with the simultaneous consideration of key ecological processes, the attention to various scales involved, and the addition of understudied systems.
... Recruitment patterns of common carp populations may act independently of one another and may be driven by lake-specific biotic conditions. For instance, predator abundance appears to be an important variable affecting common carp recruitment in Minnesota (Bajer et al. (Weber and Brown 2012;Bajer et al. 2015). In some instances, broad-scale environmental conditions may synchronize reproductive output, but local processes may regulate survival to later life stages (Grenouillet et al. 2001). ...
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Understanding spatial and temporal fluctuations in animal populations remains a central theme in ecology. Here, we investigated the extent of common carp Cyprinus carpio recruitment synchrony across North America in relation to a suite of climatic conditions. Common carp were collected from 21 populations up to a linear distance of 2,300 km. Age-frequency histograms were used to estimate year-class strength and correlation coefficients were used to evaluate synchrony among populations and environmental variables. We then evaluated relationships between common carp recruitment and winter growing degree days (GDD), summer GDD, precipitation, wind events, and the El Niño-Southern Oscillation Index (ENSO). Common carp recruitment was synchronous up to 756 km but asynchronous at larger scales. Winter and summer GDD, precipitation, and wind were also synchronous among locations up to 1,640 km apart. Summer GDD appeared most influential to common carp recruitment but varied across latitudes, with negative effects identified at low latitudes and positive effects identified at higher latitudes. Our results provide new insights into the spatial scale of recruitment synchrony of a non-native freshwater fish and indicate that climatic conditions at local to regional scales likely influence recruitment patterns.
... Reservoirs provide new habitats with initially few colonizer species and with changes in environmental conditions, such as an increase in water temperature and transparency (Henry 2014). The large variation in productivity and water transparency serve as ecological filters promoting invasions across large geographic areas, through either predator abundance or propagule pressure (Bajer et al. 2015). Despite the fact that propagule pressure favors alien species establishment, it is still ignored as a hypothesis in studies on the importance of ecological filters (Cassey et al. 2018). ...
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The South American silver croaker is a popular fish that has recently received substantial attention from scientists, mainly due to its importance as source of animal protein and as a key fisheriesspecies. However, little is known about the conditions that explain its historical and current spatial distribution, both in its native habitat and where it is a successful invasive species. The aim of the present study was to explore the ecological information available for this species, to then critically examine ecological theories related to the conditions underpinning its success. To this end, an exhaustive literature search was conducted with the immediate aim of investigating whether the success of South American silver croaker was driven by species-climate orspecies–human interactions. The non-native populations were found to occupy climate niche spaces different from those observed in their native ranges. In addition, it was clear that humans played a role in facilitating the large-scale dispersion of silver croaker, and assisted as agents of impact driving the observed current and, probably, the future spatial distribution, which we can predict from our data and from the pattern of propagule pressure. Overall, the current biogeography of this species illustrates how the construction of dams, along with the introduction and stocking of non-native species, overfishing and other human activities can alter fish populations and assemblages. Such processes can reduce native species, increase the abundance and distribution of invasive species, as well as cause changes in life-history traits and genetic variability, all with long-term socioeconomic consequences.
... Unintentionally introduced species can be detrimental to intentionally introduced fishes through predation or competitive interactions for shared prey resources (Gardunio et al. 2011;Guy et al. 2011). However, even intentionally introduced species may not be successfully established Williamson and Fitter 1996;Bajer et al. 2015). Successful introductions, whether intentional or not, may initiate novel predator-prey interactions Romare and Hansson 2003;Schoen et al. 2012), alter trophic structure (Reissig et al. 2006;Skov et al. 2010;Ellis et al. 2011), or increase the potential for competition (Tyus and Saunders 2000;Tronstad 2008;Winters and Budy 2015). ...
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Maintaining a balance between predator and prey populations can be an ongoing challenge for fisheries managers, especially in managing artificial ecosystems such as reservoirs. In a high-elevation Utah reservoir, the unintentional introduction of the Utah Chub Gila atraria and its subsequent population expansion prompted managers to experimentally shift from exclusively stocking Rainbow Trout Oncorhynchus mykiss to also stocking tiger trout (female Brown Trout Salmo trutta × male Brook Trout Salvelinus fontinalis) and Bonneville Cutthroat Trout O. clarkii utah (hereafter, Cutthroat Trout) as potential biological control agents. We measured a combination of diet, growth, temperature, and abundance and used bioenergetic simulations to quantify predator demand versus prey supply. Utah Chub were the predominant prey type for tiger trout, contributing up to 80% of the diet depending on the season. Utah Chub represented up to 70% of the total diet consumed by Cutthroat Trout. Although Utah Chub dominated the fish biomass in the reservoir, we still estimated abundances of 238,000 tiger trout, 214,000 Cutthroat Trout, and 55,000 Rainbow Trout. Consequently, when expanded to the population level of each predator, tiger trout and Cutthroat Trout consumed large quantities of Utah Chub on an annual basis: tiger trout consumed 508,000 kg (2,660 g/predator) of the standing prey population, and Cutthroat Trout consumed an estimated 322,000 kg (1,820 g/predator). The estimated combined consumption by Cutthroat Trout and tiger trout exceeded the estimate of Utah Chub annual production. As such, our results suggest that the high rates of piscivory exhibited by Cutthroat Trout and tiger trout in artificial lentic ecosystems are likely sufficient to effectively reduce the overall abundance of forage fishes and to prevent forage fishes from dominating fish assemblages. Collectively, this research provides the first documented findings on tiger trout ecology and performance, which will aid managers in designing and implementing the best stocking strategy to optimize sport fish performance, control undesirable forage fish, and enhance and maintain angler satisfaction. Received April 1, 2016; accepted November 8, 2016
... (4) Invasion history of common carp in lakes of similar morphometry and physico-chemical conditions to Lake Malawi: Across-ecoregion analysis has shown that the invasivity of common carp is regulated by a number of ecological filters such as depth and trophic status of a water body (Bajer et al., 2015). However, no studies have been conducted to establish invasion history of common carp farmed in catchment areas of lakes with depth and trophic status similar to Lake Malawi. ...
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The lack of better performing native fish species for aquaculture led the government of Malawi to import the exotic common carp (Cyprinus carpio L.) from Israel in 1976. Growth trials at Domasi and Kasinthula Experimental Stations had shown that common carp grew faster and to a larger size than the indigenous fish species. The government decided to distribute the fish to farmers for grow-out. Barely five years into common carp distribution to farmers, the government reversed its policy and banned the use of the species in aquaculture. The government not only became unpopular but also lost the confidence of the farmers who had begun to see positive impacts of common carp to their livelihoods. The farmers are as unconvinced today as they were before with the reasons behind the banning of common carp. This paper explores the background to common carp farming in Malawi, why the fish was later banned, and the impacts of the fish’s ban on the status of Malawi’s aquaculture. The paper further highlights the farmers’ call for a return of common carp to Malawi’s aquaculture and the research needed to be undertaken to inform government’s policy for the development of a sustainable aquaculture industry in Malawi.
... This significant positive influence of chlorophyll-a in the abundance of C. kelberi appears to be a result of a bottom-up process, in which the increase in phytoplanktonic productivity reflects in the increase in abundance of C. kelberi population. Some studies have already shown the relationship between the trophic state of the environment with the abundance of invasive species of fish (Vatland & Budy 2007, Bajer et al. 2015, Lechelt & Bajer 2016. In general, environments that are more productive seem to favor the recruitment of juveniles and support greater biomass and abundance of invasive species (Lechelt & Bajer 2016). ...
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... Interestingly, like Northern Pike and other species (Brodersen et al. 2014), adult Common Carp appear to be highly selective in their choices of stream inlets and outlets, selecting those that lead to the marsh and ignoring others irrespective of whether they were inflowing or outflowing. We speculate that this may reflect homing to nursery habitats as winterkill-prone marshes have been shown to be important Common Carp nurseries in the region (Bajer et al. 2015a). ...
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Inundated floodplains, backwaters, and wetlands are important spawning habitats for many freshwater fish. In Midwestern North America and areas of northern Europe, the Common Carp Cyprinus carpio and Northern Pike Esox lucius inhabit many of the same watersheds and perform migrations to interconnected wetlands during the spring to spawn. In this study, the movement patterns of adult Northern Pike and Common Carp from lakes into adjoining wetlands were assessed in Minnesota to determine how and when these species moved, and if Common Carp might be blocked or trapped without disrupting the Northern Pike. Adult Northern Pike migrated over an extended several-week period starting early each March, when temperatures were greater than 4ºC and when the fish were fully sexually mature (i.e., females were ovulated and running with eggs, and males were spermiating). In contrast, adult Common Carp migrated over relatively short time periods that lasted just a few days between April and June, and whose specific timing varied but always occurred after water temperatures rose to 10ºC and usually coincided with rain. Migrating Common Carp were in prespawning condition (i.e., females were not yet ovulated) and appeared to be homing as stream selection was very specific. Less than half of the Common Carp population migrated each year, reinforcing earlier observations that Common Carp likely conduct partial migrations. Overlap between Northern Pike and Common Carp was minimal, suggesting that management strategies using removable barriers, for example, could be used to control invasive Common Carp without affecting native Northern Pike populations. Received August 12, 2015; accepted March 11, 2016 Published online July 8, 2016
... Indeed, studies of common carp recruitment showed that in some lakes in Minnesota, common carp are unable to produce young because native predatory fishes, such as the bluegill sunfish (Lepomis macrochirus) that consumes common carp eggs and larvae. As common carp evolved spawning migrations that access predator-free habitats, such as shallow marshes prone to winter hypoxia, predator escape was achieved (Bajer and Sorensen, 2010;Bajer et al., 2012Bajer et al., , 2015. This allows for several possible control strategies. ...
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Aquatic invasive species (AIS) are of concern in North America due to their devastating impacts on ecosystems and economies. The Great Lakes region is particularly vulnerable to AIS introduction and establishment with at least 184 nonindigenous species reported in this region from a large number of taxa including viruses, bacteria, diatoms, protozoa, arthropods, mollusks, fish, and plants. Representative species from these groups were explored, describing the features of their natural history and current efforts in prevention and control. Specifically, five AIS that are expected to spread to novel areas in the region are discussed: viral hemorrhagic septicemia virus and heterosporis (pathogens affecting fish), starry stonewort (an alga), zebra mussels (a bivalve), and carps (fishes). Novel strategies for AIS control include next-generation sequencing technologies, gene editing, mathematical modeling, risk assessment, microbiome studies for biological control, and human-dimension studies to address tensions related to AIS management. Currently, AIS research is evolving to adapt to known technologies and develop novel technologies to understand and prevent AIS spread. It was found that AIS control in this region requires a multidisciplinary approach focusing on the life history of the species (e.g., pheromones), adaptive management of anthropogenic structures (e.g., bubble curtains), and the integration of human dimensions to develop efficient management plans that integrate local citizens and management agencies.
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Biological invasions are projected to be the main driver of biodiversity and ecosystem function loss in lakes in the 21(st) century. However, the extent of these future losses is difficult to quantify because most invasions are recent and confounded by other stressors. In this study we quantified the outcome of a century-old invasion, the introduction of common carp to North America, to illustrate potential consequences of introducing non-native ecosystem engineers to lakes worldwide. We used the decline in aquatic plant richness and cover as an index of ecological impact across three ecoregions: Great Plains, Eastern Temperate Forests, Northern Forests. Using whole lake manipulations, we demonstrated that both submersed plant cover and richness declined exponentially as carp biomass increased such that plant cover was reduced to less than 10% and species richness was halved in lakes in which carp biomass exceeded 190 kg/ha. Using catch rates amassed from 2,000+ lakes we showed that carp exceeded this biomass level in 70.6% of Great Plains lakes, 23.3% of EasternTemperate Forests lakes, but 0% of Northern Forests lakes. Using model selection analysis we showed that carp was a key driver of plant species richness along with Secchi depth, lake area and human development of lake watersheds. Model parameters showed that carp reduced species richness to a similar degree across lakes of various Secchi depths and areas. In regions dominated by carp (e.g. Great Plains), carp had a stronger impact on plant richness than human watershed development. Overall, our analysis shows that the introduction of common carp played a key role in driving a severe reduction in plant cover and richness in majority of Great Plains lakes and a large portion of Eastern Temperate Forests lakes in North America. This article is protected by copyright. All rights reserved.
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This chapter reports the patterns and drivers of improved water clarity in the Upper Mississippi River from 1993-2019, https://pubs.usgs.gov/of/2022/1039/ofr20221039.pdf
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This report assesses the status and trends of selected ecological health indicators of the Upper Mississippi River System (UMRS) based on the data collected and analyzed by the Long Term Resource Monitoring element of the Upper Mississippi River Restoration program, supplemented with data from other sources. This report has four objectives: providing a brief introduction of the UMRS, including its significance, history, modern-day stressors, and recent research; using ecological indicators to describe the status of the river system and where and how it has changed from circa 1993 to 2019; discussing management and restoration implications of these changes; and highlighting the fundamental role of long-term monitoring in the understanding, management, and restoration of large-floodplain rivers. The data were collected in the six Long Term Resource Monitoring element study reaches that spanned much of the UMRS and the various gradients contained therein. These study reaches included Navigation Pools 4, 8, 13, and 26; the part of the Unimpounded Reach of the Upper Mississippi River between Grand Tower and Cairo, Illinois; and the La Grange Pool on the Illinois River. The indicators included in this report describe the status and trends for the hydrology, geomorphology, floodplain vegetation, water quality, vegetation, and fishes of the UMRS. Many of the indicators of river ecosystem health changed significantly over the nearly 30 years of our evaluation. However, there was substantial spatial variability in the magnitude and timing of those changes among study reaches. Few indicators changed everywhere or nowhere; most indicators changed in some reaches but not others. The quantitative assessments of these indicators describe how the conditions of the river differ across hydrogeomorphic and climate gradients and through time and are intended to support the restoration and management of the UMRS.
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Concern about electrofishing inadvertently harming the embryos of species of conservation concern has motivated much of the research that describes what electrical conditions can kill fish embryos. As a result, targeted electrofishing might be underutilized as a potential control method to reduce the recruitment of nuisance fishes like common carp (Cyprinus carpio), one of the most widely distributed invasive fish in North America. We evaluate the efficacy of using electricity to reduce common carp recruitment by examining embryonic survival while manipulating the transfer of electric power to developing carp embryos. Embryos were shocked in water from a carp-occupied area (ambient conductivity 127 μS/cm) using a variety of voltage gradient and waveform treatments common to commercial electrofishing units and generators. Survival of electroshocked common carp embryos was ≤ 50% at power densities (12,700 μW/cm3) and voltage gradients (10 V/cm) that failed to cause significant mortality in other cyprinid species; however, embryonic resistance to electroshock was first noted at almost 3 d after fertilization (survival ≤ 50% at 79,375 μW/cm3). Power transfer theory was used to explore optimal water conductivities for the deployment of electrical control of fish embryos at shallow endorheic lakes by using conditions at Malheur Lake as an example. Power transfer theory suggests that at relatively high water conductivities it becomes more difficult to achieve power transfer thresholds sufficient to kill small fish embryos without exceeding the power capabilities of commercially-available electrofishing equipment, and that power transfer to the embryo drops below 50% of the total power applied when water conductivities exceed 325 μS/cm. Thus, water chemistry conditions most amenable to killing carp embryos with electricity in an arid, endorheic lake like Malheur Lake would most likely occur at lake inflows or more generally when the lake level is elevated. However, when spawning is dispersed or more spawning habitat is available during higher lake levels, the resulting increase in areas that require treatment may present logistical challenges. Managers considering the use of electrofishing to control recruitment of an invasive fish like common carp should consider the spatiotemporal arrangement of spawning sites, the spatial scale of the necessary control treatment, how compensatory effects may influence the overall population response, and the need for concurrent control methods targeting other life stages.
Chapter
Eutrophication and species invasion are formidable problems triggered by the effects of anthropogenic activities in the aquatic environment. Several researchers have highlighted the synergistic impact of climate change on specific aspects of the two problems separately. There is a need of scientific literature that depicts all the existing inter linkages simultaneously so that a complete understanding could be developed. This would enable the development of appropriate mitigation measures; especially in the present times when ecosystems are exposed to multiple environmental issues. The present review addresses this lacuna in the aquatic ecosystem and is the first hand approach to simultaneously link climate change with eutrophication and species invasion. Statistical analysis revealed that such linkages play an important role in magnifying the issues and should always be considered while devising mitigation measures. Aquatic ecosystems can then be effectively conserved and protected against the harmful effects of global change.
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Biotic resistance is often posited, but rarely known, to be the cause of invasion failure. Competition and predation are the most frequently identified processes that may prevent or limit the establishment of non‐native species. Interactions between non‐native and native species that involve intraguild predation (IGP) are very common in nature, although theory predicts most IGP systems should be unstable and lead to extinction. If this prediction is true, the frequency of invasion failures due to IGP may be underappreciated because of their fleeting nature and thus, studies of unstable IGP systems are lacking, despite the opportunities they offer for understanding the factors affecting their unstable dynamics. We investigated a failed invasion involving an IGP relationship. In Florida, the guppy (Poecilia reticulata), a worldwide invader, fails to establish in the presence of eastern mosquitofish (Gambusia holbrooki). We tested whether and how resident mosquitofish cause guppy invasion failure using replicated mesocosm and aquarium trials. Both the predator and competitor components of the IGP relationship were strongly asymmetrical, with large impacts on guppies. We identified two effects, direct consumption of neonates and aggressive interference competition, that limited survival and recruitment. The highly unstable nature of this IGP relationship is the primary cause of the failure of the guppy to establish in Florida. Our study shows that the transient nature of an ephemeral IGP relationship can yield important insights into the underlying causes of invasion failure, including the role of strong biotic resistance.
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Understanding habitat use and reproductive biology of invasive species is essential to predicting invasions, designing early detection programs, and developing management plans. The rudd (Scardinius erythrophthalmus; Linnaeus, 1758) is an omnivorous fish native to Europe and western Asia that has been translocated to several countries in western Europe, New Zealand, North America, and Africa. However, little is known about early life history of rudd, particularly in invaded ecosystems, limiting our ability to predict invasions and create early detection and control programs. The upper Niagara River has the most abundant population of rudd in North America and has been the focus of several ecological investigations. Our study identified critical nursery habitats by determining which nearshore habitat factors were most strongly associated with presence of age-0 rudd. We found that emergent vegetation was the most important habitat characteristic associated with the presence of age-0 rudd. When emergent vegetation was not present, rudd were more likely to be present at sites with abundant submerged aquatic vegetation. Additionally, the odds of rudd presence decreased as distance to the nearest wetland increased. These findings can be used to create habitat-driven predictive models of rudd invasion and guide early detection programs for rudd outside their native range.
Technical Report
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This report assesses the status and trends of selected ecological health indicators of the Upper Mississippi River System (UMRS) based on the data collected and analyzed by the Long Term Resource Monitoring element of the Upper Mississippi River Restoration program, supplemented with data from other sources. This report has four objectives: providing a brief introduction of the UMRS, including its significance, history, modern-day stressors, and recent research; using ecological indicators to describe the status of the river system and where and how it has changed from circa 1993 to 2019; discussing management and restoration implications of these changes; and highlighting the fundamental role of long-term monitoring in the understanding, management, and restoration of large-floodplain rivers.
Chapter
Full-text available
This report assesses the status and trends of selected ecological health indicators of the Upper Mississippi River System (UMRS) based on the data collected and analyzed by the Long Term Resource Monitoring element of the Upper Mississippi River Restoration program, supplemented with data from other sources. This report has four objectives: providing a brief introduction of the UMRS, including its significance, history, modern-day stressors, and recent research; using ecological indicators to describe the status of the river system and where and how it has changed from circa 1993 to 2019; discussing management and restoration implications of these changes; and highlighting the fundamental role of long-term monitoring in the understanding, management, and restoration of large-floodplain rivers. The data were collected in the six Long Term Resource Monitoring element study reaches that spanned much of the UMRS and the various gradients contained therein. These study reaches included Navigation Pools 4, 8, 13, and 26; the part of the Unimpounded Reach of the Upper Mississippi River between Grand Tower and Cairo, Illinois; and the La Grange Pool on the Illinois River. The indicators included in this report describe the status and trends for the hydrology, geomorphology, floodplain vegetation, water quality, vegetation, and fishes of the UMRS. Many of the indicators of river ecosystem health changed significantly over the nearly 30 years of our evaluation. However, there was substantial spatial variability in the magnitude and timing of those changes among study reaches. Few indicators changed everywhere or nowhere; most indicators changed in some reaches but not others. The quantitative assessments of these indicators describe how the conditions of the river differ across hydrogeomorphic and climate gradients and through time and are intended to support the restoration and management of the UMRS.
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Fish recruitment is complex, regulated by environmental factors that induce high mortality early in life. Additionally, age-0 fish can be difficult to sample, making recruitment difficult to detect. We used a robust design occupancy model to evaluate the effects of biotic (age-0 and adult common carp (Cyprinus carpio), bluegill (Lepomis macrochirus), walleye (Sander vitreus), and northern pike (Esox lucius) relative abundance, prey availability, age-0 carp length) and abiotic (water level, temperature) factors on age-0 carp occupancy, detection, and extinction in 13 lakes in South Dakota, USA, for July–April 2008–2010. Age-0 carp occupancy decreased with increasing adult carp abundance and increased with increasing water levels. Age-0 carp detection probability was high during summer (>0.75) but decreased in fall and spring (0.34). Most lakes were occupied in July but overwinter extinction probability was high (59%), resulting in 51% occupancy probability by April. Other environmental factors were not supported, suggesting they had little effect on reproduction and survival. Our results indicate reproduction was universally successful but difficult to detect and that overwinter mortality often resulted in recruitment failure.
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The characterization of physiological phenotypes that may play a part in the establishment of non-native species can broaden our understanding about the ecology of species invasion. Here, an assessment was carried out by comparing the responses of invasive and native species to thermal stress. The goal was to identify physiological patterns that facilitate invasion success and to investigate whether these traits are widespread among invasive ectotherms. Four hypotheses were generated and tested using a review of the literature to determine whether they could be supported across taxonomically diverse invasive organisms. The four hypotheses are as follows: (i) broad geographical temperature tolerances (thermal width) confer a higher upper thermal tolerance threshold for invasive rather than native species; (ii) the upper thermal extreme experienced in nature is more highly correlated with upper thermal tolerance threshold for invasive vs. native animals; (iii) protein chaperone expression—a cellular mechanism that underlies an organism's thermal tolerance threshold—is greater in invasive organisms than in native ones; and (iv) acclimation to higher temperatures can promote a greater range of thermal tolerance for invasive compared with native species. Each hypothesis was supported by a meta-analysis of the invasive/thermal physiology literature, providing further evidence that physiology plays a substantial role in the establishment of invasive ectotherms.
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Invasive species distributions tend to be biased towards some habitats compared to others due to the combined effects of habitat-specific resistance to invasion and non-uniform propagule pressure. These two factors may also interact, with habitat resistance varying as a function of propagule supply rate. Recruitment experiments, in which the number of individuals recruiting into a population is measured under different propagule supply rates, can help us understand these interactions and quantify habitat resistance to invasion while controlling for variation in propagule supply rate. Here, we constructed recruitment functions for the invasive herb Hieracium lepidulum by sowing seeds at five different densities into six different habitat types in New Zealand's Southern Alps repeated over two successive years, and monitored seedling recruitment and survival over a four year period. We fitted recruitment functions that allowed us to estimate the total number of safe sites available for plants to occupy, which we used as a measure of invasion resistance, and tested several hypotheses concerning how invasion resistance differed among habitats and over time. We found significant differences in levels of H. lepidulum recruitment among habitats, which did not match the species' current distribution in the landscape. Local biotic and abiotic characteristics helped explain some of the between-habitat variation, with vascular plant species richness, vascular plant cover, and light availability, all positively correlated with the number of safe sites for recruitment. Resistance also varied over time however, with cohorts sown in successive years showing different levels of recruitment in some habitats but not others. These results show that recruitment functions can be used to quantify habitat resistance to invasion and to identify potential mechanisms of invasion resistance.
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Invasive species are leading drivers of environmental change. Their impacts are often linked to their population size, but surprisingly little is known about how frequently they achieve high abundances. A nearly universal pattern in ecology is that species are rare in most locations and abundant in a few, generating right-skewed abundance distributions. Here, we use abundance data from over 24,000 populations of 17 invasive and 104 native aquatic species to test whether invasive species differ from native counterparts in statistical patterns of abundance across multiple sites. Invasive species on average reached significantly higher densities than native species and exhibited significantly higher variance. However, invasive and native species did not differ in terms of coefficient of variation, skewness, or kurtosis. Abundance distributions of all species were highly right skewed (skewness>0), meaning both invasive and native species occurred at low densities in most locations where they were present. The average abundance of invasive and native species was 6% and 2%, respectively, of the maximum abundance observed within a taxonomic group. The biological significance of the differences between invasive and native species depends on species-specific relationships between abundance and impact. Recognition of cross-site heterogeneity in population densities brings a new dimension to invasive species management, and may help to refine optimal prevention, containment, control, and eradication strategies.
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Florida is a hotspot for nonindigenous fishes with over 30 species established, although few of these are small-bodied species. One hypothesis for this pattern is that biotic resistance of native species is reducing the success of small-bodied, introduced fishes. The eastern mosquitofish Gambusia holbrooki is common in many freshwater habitats in Florida and although small-bodied (<50 mm), it is a predator and aggressive competitor. We conducted four mesocosm experiments to examine the potential for biotic resistance by eastern mosquitofish to two small-bodied nonindigenous fishes, variable platyfish (Xiphophorus variatus) and swordtail (X. hellerii). Experiments tested: (1) effect of eastern mosquitofish density on adult survival, (2) effect of eastern mosquitofish on a stage-structured population, (3) role of habitat structural complexity on nonindigenous adult survival, and (4) behavioral effects of eastern mosquitofish presence and habitat complexity. Eastern mosquitofish attacked and killed non-native poeciliids with especially strong effects on juveniles of both species. Higher eastern mosquitofish density resulted in greater effects. Predation on swordtails increased with increasing habitat complexity. Eastern mosquitofish also actively drove swordtails from cover, which could expose non-native fish to other predators under field conditions. Our results suggest that eastern mosquitofish may limit invasion success.
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Floodplain inundation in rivers is thought to enhance fish recruitment by providing a suitable spawning environment and abundant food and habitat for larvae. Although this model has not previously been tested in Australian rivers, it is often extrapolated to fishes of the Murray-Darling Basin. Fortnightly sampling of larvae and juveniles was conducted in the unregulated Ovens River floodplain during spring-summer of 1999 (non-flood year) and 2000 (flood year). The only species that increased in larval abundance during or shortly after flooding was an introduced species, common carp (Cyprinus carpio). Additionally, the peak abundance of larvae on the floodplain occurred during a rapidly declining hydrograph under low flow conditions in isolated billabongs and anabranches. The low use of the inundated floodplain for recruitment contradicts previous models. We propose a model of the optimum environmental conditions required for use of the inundated floodplain for fish recruitment. The model suggests that the notion of the flood pulse alone controlling fish recruitment is too simplistic to describe all strategies within a system. Rather, the life history adaptations in the fauna of the system and aspects of the hydrological regime such as duration and timing of inundation will control the response of a river's fish fauna to flooding.
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Estimates of the biological production of entire lake fish communities were collected from the published literature on lakes covering a wide range of geographic areas and tropic status. Fish production is uncorrelated with the morphoedaphic index but closely correlated with annual phytoplankton production (r2 = 0.79), mean total P concentration (r2 = 0.67), and annual average fish standing stock (r2 = 0.67). Conversion of phytoplankton into fish production is 100 times more efficient in oligotrophic lakes than hyper-eutrophic ones, but a much lower fraction of fish production can be channeled to sustainable yield in oligotrophic lakes. Sustained yields were frequently as little as 10% of the annual community fish production. -from Authors
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A model for the prediction of total phosphorus was developed and tested using data on 704 natural and artificial lakes including 626 lakes in the U.S. Environmental Protection Agency (EPA) National Eutrophication Survey. A statistical analysis showed that the best estimate for the sedimentation coefficient (σ) in the Vollenweider equation was: σ = 0.162(L/z)0.458 for natural lakes, and σ = 0.114(L/z)0.589 for artificial lakes, where L is the areal phosphorus loading rate (mg.m-2.yr-1) and z is the mean depth (m). The model yields unbiased estimates of phosphorus concentrations over a wide range of lake types and has a 95% confidence interval of 31-288% of the calculated total phosphorus concentration. Other models are less precise. Though total phosphorus concentrations can be predicted equally well in natural and artificial lakes, predictions of algal densities and water transparency are less reliable in artificial lakes, as the phosphorus-chlorophyll and chlorophyll-Secchi depth relationships are less precise. This seems to be due to the influence of nonalgal particulate materials.
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The floodplains of many large rivers worldwide are important spawning and nursery habitats for multiple fish species. We investigated the potential importance of different floodplain habitats for fish larvae. Samples were collected from 14 sites along the Waikato River, northern New Zealand, from September to October 2010. Larval fishes were identified using traditional morphological identification and DNA analyses. Our results revealed high densities of invasive koi carp and goldfish larvae in flooded terrestrial habitats compared to other habitat types. Species richness was highest in the wetland habitat. Redundancy analysis revealed that koi carp and goldfish abundances were strongly positively correlated with chlorophyll a concentrations and zooplankton densities. Floodplain habitats seem to be important habitat for larvae of both native and introduced fish species in the lower Waikato River. Because introduced larval fish out-numbered native fishes in floodplain habitats managers should consider implementing measures that at key times provide controlled access to floodplain habitats for native species and also limit access of introduced fishes.
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Climatic variation and dispersal are two primary factors thought to induce recruitment synchrony in fish populations. We hypothesized that climate factors correlated across a broad geographical scale (i.e., the Moran effect) would induce synchrony in recruitment for common carp Cyprinus carpio among 18 glacial lakes across a 175-km area in eastern South Dakota. Cross-correlation analysis indicated that common carp population fluctuations were highly synchronous among lakes. To evaluate the influence of the Moran effect on recruitment, we examined several candidate models using an information-theoretic approach. The model with the most support included the interaction of temperature, precipitation, and wind during the open-water period. This model indicated that the effects of any one of these climate variables on recruitment strength depended on the level of each of the other variables in any given year. Our results suggest that common carp populations in the Midwestern United States exhibit synchronous recruitment across regionwide geographic areas as a result of climatic variability.
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Ecoregion-based phosphorus “criteria” that reflect the diversity of lake condition, varying from deep pristine lakes in the north to shallow hypereutrophic lakes in the south, were developed by the Minnesota Pollution Control Agency (MPCA) in the late 1980s. Since then the criteria, including several refinements, have been widely used for local, state, and federal lake watershed management efforts in Minnesota. More recently, the criteria have been used to define thresholds for Clean Water Act Section 303(d) listing of nutrient-impaired lakes and are being advanced as lake standards to protect a wide diversity of beneficial uses. This paper summarizes the evolution of these criteria and describes data and research used in their development. A weight-of-evidence approach describes how this information was used to refine the criteria values.
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Why certain species of fish become inva-sive is poorly understood and a key obstacle to restoring many of the world's ecosystems. In this study we tested whether variation in biotic resistance exerted by native predators might explain the repro-ductive success of the common carp, a large and fecund invasive species that typically spawns in outlying and unstable shallow habitat. An initial three-year study of the relative abundance of young-of-year (YOY) carp in interconnected lakes in the Upper Mississippi River Basin discovered that YOY carp are only found in shallow waters that experience winter hypoxia (winterkill) and have low densities of the native egg-predators that otherwise dominate these locales. A follow-up experiment tested if native fish predation on carp eggs could explain this distribution. It found that while carp eggs survived in winterkill lakes, they only survived in non-winterkill lakes when protected by a mesh that excluded fish. Large numbers of carp eggs were found in the stomachs of native fish inhabiting lakes that did not winterkill. We conclude that common carp, and likely many other highly mobile and fecund invasive fish, have evolved life histories to avoid egg predators and can become invasive when they are absent.
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The location, size, and geography of California, combined with extensive knowledge of successful and failed fish invasions, provide an unusual opportunity to test predictors of invasion success. Our analyses show that different characteristics of alien fishes are important at different stages of the invasion process. We found no set of characters that predicted success for all fish invasions, although some characters increase the probability of success. The factors that best predict invasion success are (a) a history of successful establishment outside the species' native range; (b) characters that promote success at multiple stages of the invasion process (e.g., high physiological tolerance); (c) invaded habitat that more or less matches the alien's native habitat; (d) high fish species richness, including other alien fishes; and (e) propagule size exceeding 100 individuals. The difficulty of predicting the invasion success of alien species points to the need to allow only introductions that have proved to be nonharmful and to take quick action to prevent the spread of new invaders.
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Although the common carp (Cyprinus carpio), an invasive benthic fish from Eurasia, has long been strongly implicated in the disappearance of vegetative cover and reduced waterfowl abundance in North American shallow lakes, the details of this relationship are obscure. This study documented ecological changes in a recently restored shallow lake (Hennepin and Hopper Lakes, IL, USA) at a time that it was experiencing a large increase in its carp population. We estimated the abundance and biomass of carp 7years after this lake had been restored and then back-calculated carp population size across time while examining changes in the lake’s plant and waterfowl communities. We found that the biomass of carp remained below ~30kg/ha for 5years following restoration, but then increased to ~100kg/ha in the sixth year following a strong recruitment event. Although a carp biomass of <30kg/ha had no discernible effects on vegetative cover (which exceeded 90%) or waterfowl (which exceeded 150,000 individuals during fall censuses), the increase to 100kg/ha was associated with a ~50% decrease in both vegetative cover and waterfowl. A further increase in carp biomass to over 250kg/ha during the seventh year coincided with a decrease in the vegetative cover to 17% of the lake’s surface and a decline in waterfowl use to ~10% of its original value. These data suggest that the common carp is extremely damaging to the ecological integrity of shallow lakes when its density exceeds ~100kg/ha. Since the biomass of carp in Midwestern shallow lakes commonly exceeds this value by 3–4times, it seems likely that carp are responsible for the large-scale habitat deterioration described in many of these ecosystems.
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Although the common carp is globally distributed, it only reaches extreme densities in certain regions. We hypothesized that this phenomenon might be linked to recruitment bottlenecks which carp overcome where environmental conditions create unstable peripheral areas that it can access for spawning and nursery habitat. To test this hypothesis, the abundance, movement and reproductive success of carp was determined in two systems of inter-connected lakes in the North American Midwest whose shallow basins frequently experience winter-hypoxia (‘winterkill’). Radio-tracking demonstrated that while adult carp overwinter in deep lakes that do not winterkill, they aggressively move into winterkill-prone shallow regions in the spring to spawn. The significance of this behavior was demonstrated by ageing analyses which found that carp recruit only in interconnected shallow lakes and then only in years following severe winter hypoxia. Presumably this strategy allows carp to exploit nursery habitat that is relatively free of predators. It likely evolved in response to seasonally variable conditions in the carp’s native habitat in the Ponto-Caspian region. This life history may also explain the carp’s abundance in other unstable regions such as southern Australia and could potentially be exploited to control this damaging invasive. KeywordsInvasiveness-Life history-Movement-Instability-Winterkill-Propagule pressure-Predatory release
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Common carp (Cyprinus carpio) larvae at different ages up to 30 days were offered prey of three different size classes (rotifers and cladocerans) at different densities in the range 25–400/l. The proportion of larger prey in the diet increased with age. At any age, prey size selection was related to prey density; at low densities all three sizes were taken as encountered, but with increasing prey density the larvae selectively captured larger (more prcfitable) prey.
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In order to efficiently manage nonindigenous species (NIS), predictive tools are needed to prioritize locations where they are likely to become established and where their impacts will be most severe. While predicting the impact of a NIS has generally proved challenging, forecasting its abundance patterns across potential recipient locations should serve as a useful surrogate method of estimating the relative severity of the impacts to be expected. Yet such approaches have rarely been applied in invasion biology. We used long-term monitoring data for lakes within the state of Minnesota and artificial neural networks to model both the occurrence as well as the abundance of a widespread aquatic NIS, common carp (Cyprinus carpio). We then tested the ability of the resulting models to (1) interpolate to new sites within our main study region, (2) extrapolate to lakes in the neighboring state of South Dakota, and (3) assessed the relative contribution of each variable to model predictions. Our models correctly identified over 83% of sites where carp are either present or absent and explained 73% of the variation in carp abundance for validation lakes in Minnesota (i.e., lakes not used to build the model). When extrapolated to South Dakota, our models correctly classified carp occurrence in 79% of lakes and explained 32% of the variation in carp abundance. Variables related to climate and water quality were found to be the most important predictors of carp distribution. These results demonstrate that ecological niche-based modeling techniques can be used to forecast both the occurrence and abundance patterns of invasive species at a regional scale. Models also yielded sensible predictions when extrapolated to neighboring regions. Such predictions, when combined, should provide more useful estimates of the overall risk posed by NIS on potential recipient systems.
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The ecological impact stemming from a biological invasion is the most poorly understood aspect of the invasion process. While forecasting methods are generally lacking, a potential means of predicting future impacts is to examine the effects caused by a nonindigenous species (NIS) at previously invaded locations, i.e., its invasion history. However, given the context dependence of impact and the scarcity of data, it is uncertain whether invasion history can in fact be used to forecast the effects of most introduced species. Using a sample of 19 aquatic NIS listed with the IUCN's 100 World's Worst Alien Invasive Species, we reviewed the literature to determine (1) the amount of information currently available concerning their ecological impacts, (2) if the effects reported to be caused by each NIS are consistent across multiple studies, and (3) whether their invasion histories provide sufficient quantitative information to assess and forecast the severity of their impacts on recipient environments. As a case study, we conducted a meta-analysis and developed models that relate the severity of the impacts of a well-documented invader, common carp (Cyprinus carpio), to two potential predictor variables: biomass and time since introduction. We then tested whether models developed from one set of observations can predict the severity of impacts reported at other sites. Models incorporating biomass and pre-impact conditions explained 91% of the variation in carp impact severity at new locations (i.e., those not used to build the models). For most other NIS, limited availability of comparable quantitative data currently prevents the development of similar empirical models for predicting the severity of future impact. Nonetheless, invasion history can often be used to develop informative predictions concerning the type and direction of impacts to be expected at novel recipient sites.
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Back in print! This magnificent, encyclopedic reference to 157 fish species which are found not only in Wisconsin but also in much of the Great Lakes region and Mississippi River watershed has been a model for all other such works. In addition to comprehensive species accounts, Becker discusses water resources and fisheries management from both historical and practical policy perspectives."
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Abstract Predation is an important force structuring aquatic communities, but predator–prey interactions are complex and regulated by multiple factors. Invasive fishes may interact with native fishes to alter predator–prey preferences and community dynamics. For example, common carp, Cyprinus carpio L., is an invasive species that can become abundant and negatively affect aquatic ecosystems. Juvenile common carp are occasionally found in predator diets, but predator preferences for common carp compared with alternative prey remains unknown. Prey selection and feeding behaviour of five piscivores (flathead catfish, Pylodictis olivaris (Rafinesque); largemouth bass, Micropterus salmoides (Lacepède); smallmouth bass, M. dolomieu Lacepède; walleye, Sander vitreus (Mitchill); and northern pike, Esox lucius L.) foraging on juvenile common carp and two alternative prey (fathead minnow, Pimephales promelas Rafinesque, and yellow perch, Perca flavescens Mitchill) at variable densities and habitats were evaluated. Common carp and fathead minnow were generally selected for or neutrally selected across predator species, habitat types and prey assemblages. By contrast, yellow perch was generally selected against. Common carp were easily captured but difficult to manipulate and ingest compared with other prey. These results reveal that common carp are vulnerable to a variety of predators, suggesting control of this detrimental invader may be possible through biomanipulation.
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Field and laboratory experiments tested the hypothesis that recruitment of the invasive Common Carp Cyprinus carpio is often controlled by the feeding activity of egg and larval predators in interconnected lakes of the upper Mississippi River basin. The survival of naturally spawned carp eggs was monitored in a seemingly typical lake by sampling the abundance of such eggs in spawning areas and in the diets of fish caught at these locations. Over 95% of the carp eggs found attached to spawning substrate disappeared within 4 d of spawning, at the same time that large numbers of eggs were found in the stomachs of Bluegills Lepomis macrochirus. Egg predation closely paralleled but lagged egg disappearance. Concurrent laboratory studies showed that carp eggs hatched after 4.75 d at lake temperatures, demonstrating that most (but perhaps not all) of the eggs had been eaten by egg predators prior to hatching. A second laboratory experiment found that Bluegills readily find and consume carp larvae while Black Bullheads Ameiurus melas do not, suggesting that predation on larvae contributes to carp recruitment. These data, together with previous studies of the survival of carp eggs placed into lakes and the distribution of young carp relative to various species of native fish, add strong support to the hypothesis that the recruitment of carp in interconnected lakes of the upper Mississippi River basin is often controlled by native fish predators.Received August 8, 2012; accepted March 13, 2013
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1. Invasive species frequently have adverse impacts on native communities and ecosystems. Management options are often limited. Our goal is to evaluate the effect of intensive trapping and fish predation on the population dynamics of an invasive crayfish. 2. From 2001 to 2005, we removed invasive rusty crayfish (Orconectes rusticus) by trapping in Sparkling Lake in northern WI. In addition, the Wisconsin Department of Natural Resources restricted harvest of fish species known to consume crayfish, thereby increasing predation on crayfish that are too small to trap. 3. After an initial increase, catch rates of rusty crayfish declined by approximately 95%, from 11 crayfish per trap per day in 2002 to 0.65 in 2004. The catch rate in 2005 remained low at 0.5 crayfish per trap. Females comprised nearly 50% of the catch from 2002 to 2004. Unlike rusty crayfish in Sparkling Lake, catch rates of O. rusticus and Orconectes propinquus in three nearby lakes increased or remained relatively constant over the 5-year removal period. 4. We also examined the influence of habitat and temperature on crayfish catch rates. Catch rates were highest at water temperatures between 20 and 25 °C and on cobble, log or macrophyte habitats that may serve as refuge from fish predation. 5. Five summers of intensive trapping and fisheries management practices reduced abundances, but did not extirpate rusty crayfish in Sparkling Lake. To determine the potential of trapping as a management option for invasive crayfishes, these methods must be tested in other systems.
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Ontogenetic diet shifts from zooplankton to macroinvertebrates represent an important transition for many fishes during early life stages. However, some fishes have plastic feeding habits that allow them to take advantage of abundant prey resources or display diet specialization instead of undergoing distinct diet shifts. In this study, we evaluated ontogenetic changes in energy sources (based on the carbon isotope signature, δ13C) and trophic position (based on the nitrogen isotope signature, δ15N) for age-0 Common Carp Cyprinus carpio from eight natural lakes in eastern South Dakota. In general, Common Carp trophic position decreased and energy sources shifted from pelagic to littoral prey resources from July to August. As anticipated, substantial inter- and intrapopulation variation existed in Common Carp isotope signatures. Common Carp trophic position increased with increasing fish TL in three lakes but decreased with fish TL in two systems. Intrapopulation variation in trophic position was related to Common Carp relative abundance during July, indicating that individuals may have specialized on different energy resources as a result of intraspecific interactions. The δ13C values decreased with increasing fish size in two populations during July, suggesting a shift toward pelagic resources; δ13C increased with fish size in six populations during August, suggesting a shift toward littoral resources. Our results indicate a high degree of trophic variation in juvenile Common Carp populations, indicative of a foraging generalist. Year-class strength may increase trophic specialization of individuals but without negative effects on fish growth, suggesting that diet plasticity is an important factor contributing to the success of this invasive species.Received September 24, 2012; accepted April 29, 2013
Article
Recruitment dynamics of fishes can determine their abundance and subsequent effects of adult populations on ecosystem properties. Common Carp Cyprinus carpio is a widespread invasive species that can exert negative density-dependent effects on aquatic food webs. However, little is known concerning processes that regulate their recruitment. We used summer-through-fall electrofishing catch rates of age-0 Common Carp to investigate the importance of biotic (stock size, prey availability, egg and juvenile predation, intraspecific competition) and abiotic (water level fluctuation, temperature, wind events) factors on recruitment and growth in 13 lakes across eastern South Dakota from 2008 to 2010. Mean relative abundance of age-0 Common Carp was highly variable spatially and temporally, ranging from 0 to 152.2 fish per hour of electrofishing. Ricker stock–recruitment models indicated that peak production of age-0 Common Carp occurred when adult Common Carp relative abundance was low. Recruitment also increased with spring–summer temperatures, decreased with wind events, and was affected by annual water level fluctuations. Age-0 Common Carp growth, estimated by mean size in August, was highly variable (mean TL = 42–165 mm) and influenced by the abundance of conspecifics and wind events, indicating that density-dependent interactions may have occurred during early life stages. Combined, our results suggest that the early life history of Common Carp is regulated by density-dependent processes and abiotic environmental conditions, which provide new insights into mechanisms regulating recruitment of this widespread invasive species. Received October 29, 2012; accepted November 21, 2012
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Many autecological effects of temperature on fish are known, and fishery biologists have begun to incorporate this knowledge into population-level relations that can be used to assess possible effects of climatic warming on fishes and their habitats. However, the problem of extrapolating these or other relations to multispecies assemblages is not straightforward, given the complexity of community-level phenomena. I present a conceptual framework that views fish assemblages as products of a series of filters, operating at different spatial and temporal scales, through which an assemblage's component species must pass. This framework can facilitate an understanding of the processes that organize fish assemblages and suggest ways in which the complex problem can be divided into manageable pieces. I apply this framework in an examination of small-lake fish assemblages in three regions on two continents. The procedure reveals local and regional relations of richness and composition and highlights the importance of isolation, extinction, and colonization, as well as temperature, that must be considered in climate change assessments. This community-level framework can organize accumulated knowledge of fish assemblages, identify causal processes behind community-level patterns, and focus research needed for the management of fish assemblages in the face of major anticipated changes in climate.
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Over the last decade, the porcelain crab Petrolisthes armatus invaded oyster reefs of Georgia, USA, at mean densities of up to 11000 adults m–2. Interactions affecting the invasion are undocumented. We tested the effects of native species richness and composition on invasibility by constructing isolated reef communities with 0, 2, or 4 of the most common native species, by seeding adult P. armatus into a subset of the 4 native species communities and by constructing communities with and without native, predatory mud crabs. At 4 wk, recruitment of P. armatus juveniles to oyster shells lacking native species was 2.75 times greater than to the 2 native species treatment and 3.75 times greater than to the 4 native species treatment. The biotic resistance produced by 2 species of native filter feeders may have occurred due to competition with, or predation on, the settling juveniles of the filter feeding invasive crab. Adding adult porcelain crabs to communities with 4 native species enhanced recruitment by a significant 3-fold, and countered the effects of native biotic resistance. Differences in recruitment at Week 4 were lost by Weeks 8 and 12, when densities of recent recruits reached ~17000 to 34000 crabs m–2 across all treatments. Thus, native species richness slows initial invasion, but early colonists stimulate settlement by later ones and produce tremendous propagule pressure that overwhelms the effects of biotic resistance.
Article
Total fish biomass per unit area was positively correlated with total phosphorus, total nitrogen, chlorophyll a, and inversely correlated with Secchi disk transparency in 65 Florida (U.S.A.) lakes selected to range from oligotrophic to hypereutrophic. Species numbers were positively related to lake surface area but not trophic state. There were some shifts in species composition with changes in trophic state, though only a few species showed significant changes in their standing crops. In particular the recreationally important centrarchids did not show important changes with trophic state, and there were no critical points on the trophic spectrum where there were dramatic changes in fish abundance or standing crops. The facts that Florida lakes do not have deep, cold hypolimnia, do not have salmonid species, and have no ice in the winter are among the possible reasons that the more eutrophic Florida lakes do nor show the same changes in fish populations often described for northern lakes.
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The introduction of fishes into habitats outside their native range may result in dramatic ecosystem alterations. Circumpolar introductions of common carp Cyprinus carpio commonly induce perturbations to shallow lakes, inducing a phase shift from clear to turbid water. Cahn (1929) Cahn, A. R. 1929. The effect of carp on a small lake: The carp as a dominant. Ecology, 10: 271–274. [CrossRef] [Google Scholar] first reported a phase shift following common carp introduction. Since then, ecologists have sought to understand ecosystem responses to common carp perturbation. We present a synthesis on how common carp can affect aquatic ecosystems through a middle-out framework due to their capability to alter bottom-up and top-down processes. Common carp affect bottom-up processes by modifying nutrient and turbidity concentrations and phytoplankton abundance and diversity through benthic foraging, whereas zooplankton and benthic invertebrates can be affected by top-down processes through predation and reduced foraging efficiency. Common carp also reduce aquatic macrophytes that may switch lakes from the clear to turbid water equilibrium. Restoration efforts seeking to return ecosystems to the clear water state have attempted to remove common carp populations through numerous methods with varying success. Restoration efforts should focus on entire ecosystems (humans, habitats, and biota) in conjunction with common carp reductions to achieve the greatest success at minimizing the effects of common carp and to return lakes to the clear water state.
Article
Three alternate and distinct fish assemblages were identified in 43 N Wisconsin lakes encompassing a gradient from bog ponds to small, oligotrophic lakes having little bog character. Multivariate analysis of physical/chemical variables identified 3 general environmental factors that influence community type and species richness: 1) habitat size and heterogeneity; 2) lake productivity-pH; and 3) winter oxygen concentrations. Ordination of lake fish assemblages along these environmental gradients revealed that lake pH and winter anoxia were especially crucial in determining assemblage type. Maintenance of these discrete assemblages is also the result of biotic interactions (exclusion of cyprinids due to predation or competition from centrarchids). -from Author
Article
The hypothesis was tested that zooplankton community size structure shifts toward an increased relative biomass of microzooplankton with increased lake trophy at 12 sites in Quebec, The seasonal mean abundance and biomass of ciliates, rotifers, nauplii, cladocerans, and cyclopoid copepods were significantly (P < 0.1) related to lake trophy, but Calanoid copepod abundance and biomass varied independently of lake trophy. Regressions of microzooplankton and macrozooplankton biomass with total phosphorus (TP) were highly significant (P < 0.000 l), and TP explained a large proportion of the total variation (microzooplankton: Y* = 0.72; macrozooplankton: r2 = 0.86). The regression models for microzooplankton and macrozooplankton were not significantly different, refuting the hypothesis that relative biomass changes with lake trophy. Further analysis with a community structure index (the slope of the log weight-log abundance relationship) and mean lengths of various taxa indicated that zooplankton community size structure was not correlated with either TP or chlorophyll. On average, about 40% of the total zooplankton biomass is accounted for by microzooplankton in the Quebec lakes. The inverse relationship between body size and specific flux rates suggests that microzooplankton account for the major portion of zooplankton community rates.
Article
This paper reviews state-of-the-art techniques for culture of larval common carp, Cyprinus carpio, silver carp, Hypophthalmichthys molitrix, bighead carp, H. nobilis, and grass carp, Crenopharyngodon idella. Water temperature, food, and predation are important factors influencing larval survival and growth. Lower and upper lethal temperatures range from 3 to 44°C. Optimum growth temperatures range from 38 to 40°C. Lethal and optimum temperatures vary with acclimation temperature, fish age, and development stage of fish. Water temperatures are close to optimum for larval culture in tropical regions but are often too low in temperate climates. Intensive culture in temperature-controlled systems is important in temperate climates. The first food eaten by larvae in ponds consists mainly of protozoa, rotifers, and copepod nauplii. As fhe larvae grow, they quickly shift to larger food items, including cladocera and insect larvae. Management practices to enhance natural food development in earthen ponds include bottom drying, soil preparation, liming, fertilization, and agricultural crop cultivation. The development of food organisms in freshly filled ponds follows a pattern of succession. For best results, a pond should be stocked at the stage of succession when the size relationship between fish larvae (predators) and zooplankton (prey) is proper. A common practice is to stock larvae 3-7 days after filling. If ponds are filled too long before larvae are stocked, food relationships between fish and invertebrates can be reversed. Predator control includes biological, chemical, physical, and mechanical methods. Although great progress has been made in the development of dry starter diets, prepared feeds are not yet available for successful large-scale production. This problem is usually overcome by starting larvae with live food or with a mixture of live food and dry feed and by shifting larvae to dry diets as they grow. Live food either is collected from zooplankton ponds or is produced in intensive culture conditions. Systems for larval culture can range from ponds to intensive culture with water recirculation systems. Choice of the best system depends on the local climate, technical, and socio-economic conditions.
Article
Empirical models based on regression analysis were derived using published values of phytoplankton and crustacean zooplankton biomass from lakes. Equations presented predict crustacean zooplankton biomass from measures of phytoplankton biomass. Zooplankton biomass was shown to be positively related to phytoplankton biomass based on an inter-lake comparison. Analyses of functional regression equations suggest that the ratio of zooplankton to phytoplankton biomass decreases as phytoplankton biomass increases among lakes. It is hypothesized that variation in the biomass of nannoplankton, representing the principal food source for crustaceans present in the phytoplankton community, can account for the variation in the biomass of the crustacean zooplankton community.Key words: phytoplankton, zooplankton, biomass, nannoplankton
Article
Although most studies of factors contributing to successful establishment and spread of non-native species have focused on species traits and characteristics (both biotic and abiotic), increasing empirical and statistical evidence implicates propagule pressure—propagule sizes, propagule numbers, and temporal and spatial patterns of propagule arrival—as important in both facets of invasion. Increasing propagule size enhances establishment probability primarily by lessening effects of demographic stochasticity, whereas propagule number acts primarily by diminishing impacts of environmental stochasticity. A continuing rain of propagules, particularly from a variety of sources, may erase or vitiate the expected genetic bottleneck for invasions initiated by few individuals (as most are), thereby enhancing likelihood of survival. For a few species, recent molecular evidence suggests ongoing propagule pressure aids an invasion to spread by introducing genetic variation adaptive for new areas and habitats. This phenomenon may also explain some time lags between establishment of a non-native species and its spread to become an invasive pest.
Article
Untersuchungen zur Trockenfutterzusammensetzung für Karpfenlarven (Cyprinus carpio L.) In einem 28-tägigen Versuch wurden einige Trockenfutter hinsichtlich ihrer Anwendung für Karpfenlarven getestet. Die Futtermittel bestanden aus verschiedenen Hefearten und aus getrockneten bzw. gefriergetrockneten tierischen Geweben. Es wurde festgestellt, daß insbesondere Candida tropicalis in der Mischung eingesetzt werden kann und zwar mit besserem Erfolg als die auf Kohlenwasserstoff gewachsene Candida lypolitica. Verglichen wurden die Trockenfutter mit lebendem Zooplankton. Die mit Zooplankton gefütterten Tiere wiesen eine höhere überlebensrate und ein höheres Einzelgewicht der Larven auf. Während die mit Zooplankton gefütterten Tiere ein Gewicht von 144,5 ± 26,6 mg und eine überlebensrate von 96% aufwiesen betrugen die entsprechenden Werte für die mit Trockenfutter gefütterten Larven 102,0 ± 54,9 mg und 56%. Der Index aus Länge/Gewicht ist zwischen den Gruppen unterschiedlich. Außerdem wurden die Aminosäurezusammensetzung im Futter und in Fischen untersucht. Der Ca-Gehalt in den mit Zooplankton gefütterten Fischen erreichte 3,55% und in den mit Trockenfutter ernährten Larven nur 1,48-2,22%. Die P-Konzentration lag ebenfalls in den mit Zooplankton versorgten mit 1,355% höher als bei den mit Trockenfutter gefütterten Tieren mit 0,87-1,001%. Diese Unterschiede im Ca- und P-Gehalt der Fische wurden nicht durch das Futter widergespiegelt.
Article
The Laurentian Great Lakes basin has been invaded by at least 182 non-indigenous species. A new invader is discovered every 28 weeks, which is the highest rate recorded for a freshwater ecosystem. Over the past century, invasions have occurred in phases linked to changes in the dominant vectors. The number of ship-vectored invaders recorded per decade is correlated with the intensity of vessel traffic within the basin. Ballast water release from ocean vessels is the putative vector for 65% of all invasions recorded since the opening of the St. Lawrence Seaway in 1959. As a preventive measure, ocean vessels have been required since 1993 to exchange their freshwater or estuarine ballast with highly saline ocean water prior to entering the Great Lakes. However, this procedure has not prevented ship-vectored species introductions. Most ships visiting the Great Lakes declare ‘no ballast on board’ (NOBOB) and are exempt from the regulation, even though they carry residual water that is discharged into the Great Lakes during their activities of off-loading inbound cargo and loading outbound cargo. Recently introduced species consist predominantly of benthic invertebrates with broad salinity tolerance. Such species are most likely to survive in a ballast tank following ballast water exchange, as well as transport in the residual water and tank sediments of NOBOB ships. Thus, the Great Lakes remain at risk of being invaded by dozens of euryhaline invertebrates that have spread into Eurasian ports from whence originates the bulk of foreign ships visiting the basin.
Article
Invasive species are increasingly recognized as one of the main threats to biodiversity and both an urgent need and a unique tool for ecological research. Although attempts to identify future invasive species are not new to ecology, rigorous quantitative analyses emanate mostly from the last decade. In 2001, quantitative studies dealing with the distinguishing ecological features of invasive species were reviewed but no papers on fish species were identified. Subsequently, several quantitative studies have addressed this issue for freshwater fishes, including those that have focused on California, Colorado, the Great Lakes of North America and the Iberian Peninsula. In the present paper, 12 such studies are reviewed and compared with regard to their conclusions and methodology. The issues of different invasion stages and comparison strategies, propagule pressure, information-theoretic analyses v. sequential techniques, use of phylogenetic comparative methods and spatial scale are discussed. Non-native fish transport and release are the least investigated although taxonomy and human interests seem key in these first initial stages. Establishment success, which has received more study, seems more multi-factorial, context-dependent and more mediated by species-specific life-history traits. The dispersal and impact phases are less understood, although the comparison of traits (and taxonomy) between native and invasive species and particularly its variability holds promise. The lack of data on propagule pressure and the use of sequential techniques for observational data sets with many intercorrelated variables could affect the conclusions of previous studies. Research on the dispersal, impact and particularly transport and introduction phases should be prioritized rather than establishment. All the studies identified were at temperate latitudes in the northern hemisphere; studies in other regions and comparison of different regions and multiple scales are lacking.
Article
Domestication of mammals such as cattle, dogs, pigs and horses preceded that of fishes by at least 10 000 years. The first domesticated fish was the common carp Cyprinus carpio. Initially it was held as an exploited captive and did not undergo major changes in body shape or colour variations. About 2000 years ago, wild common carp were most abundant in the inland delta of the Danube River. These fish were torpedo shaped, golden-yellow in colour and had two pairs of barbels and a mesh-like scale pattern. Large schools of them thrived and reproduced on the flood plains of the Danube. The Romans kept fishes in specially built ponds at that time. The common carp was an ideal candidate and its rearing became more popular in medieval times. Common carp culture gradually became the most profitable branch of agriculture in central Europe and many special ponds were built. Soon common carp were being produced in pond systems including spawning and growing ponds. Unintentional artificial selection had taken place between the 12th and mid-14th century, and deep bodied and variously scaled or scaleless domesticated forms appeared in nearly every pond system. Some colour aberrations appeared in the 1950s in Japan, which, as koi, became the most expensive of fish. Common carp were not originally domesticated in China but wild ‘chi’Carassius auratus occasionally appeared as a xanthic form that, as the goldfish, has been known since 960 A.D. By the 1200s the fish were used as ornamental animals in the garden pools of rich landowners. Circa 1276 to 1546, the Chinese began keeping golden chi in aquarium-like vessels and soon rich and poor alike became breeders of the fancy domesticated goldfish. The variously shaped monstrosities and colour aberrants were freaks but they became very fashionable at that time and still are. Domesticated goldfish monstrosities were first exported from China to Japan and much later to Europe and around the world. More recently other species have been domesticated by aquarists, such as the guppy Poecilia reticulata or the neon tetra Paracheirodon innesi. Other fishes kept as ornamentals, like swordtails Xiphophorus hellerii and platies Xiphophorus maculatus, the discus and angelfishes (Cichlidae), as well as those cultured for food like the rainbow trout Oncorhynchus mykiss, channel catfish Ictalurus punctatus or sturgeons (Acipenseridae) are merely exploited captives.
Article
Most studies analyzing patterns in biotic homogenization of fish communities have used large-scale approaches, while the community-level effects of species introductions and local extinctions within river basins have been sparsely analyzed. In this article, we examine patterns in freshwater fish α- and β-diversity in relation to the presence of reservoirs in a Mediterranean river (Guadiana river; Iberian Peninsula). We used fish samples from 182 river localities and 59 reservoir ones to address two main questions: (i) do reservoirs favor the establishment of invasive fish species?; and (ii) do reservoirs bear taxonomically homogenized fish communities? Although total species richness was not different between rivers and reservoirs, the latter had more invasive species and less native ones. Fish species found in reservoirs tended to be larger ones, but invasive species of any size showed higher preferences for reservoirs. Native species that were rare or absent in reservoirs were those that showed higher sensitivity to invasive species in rivers. Reservoir fish communities were taxonomically homogenized in relation to river ones, both when considering all fish species and using only natives or only invasive ones. Our results suggest that invasive species occupying reservoirs constitute an ecological filter excluding most native species from such systems. Invasive species in the study area are often widely introduced elsewhere, while native species found in reservoirs are congeneric and ecologically similar to those found in other Iberian studies. Thus, we conclude that reservoirs promote taxonomic homogenization at multiple spatial scales, while could also be promoting the functional homogenization of Iberian fish communities. KeywordsBiotic homogenization–β-diversity–Freshwater fish–Fish conservation–Mediterranean rivers–Invasive species–Regulated rivers
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