Trophic reorganization of native planktivorous fishes at different density extremes of bigheaded carps in the Illinois and Mississippi rivers,USA

The widespread introduction of non-native fishes has contributed to freshwater ecosystems being considered among the most altered ecosystems globally. Of particular concern are invasive planktivorous fishes (e.g., silver carp Hypophthalmichthys molitrix and bighead carp H. nobilis, collectively known as bigheaded carps) that have the potential to modify basal food web structure and compete for planktonic resources with native planktivores and young-of-year fishes. Bigheaded carps have proliferated throughout the Mississippi River basin, creating an outsized potential for resource competition with native fishes. Studies have showed niche overlap between bigheaded carps and native planktivores is generally high but that overlap varies among rivers. Importantly, niche overlap has not been assessed for density extremes of bigheaded carps within a river to determine whether trophic niches changed as a result of the invasion. The objectives of this study were to determine whether (1) silver and/or bighead carps share a similar isotopic niche with four native planktivores, and (2) that association varies ecologically (i.e., low- and high-densities of bigheaded carps) and spatially (i.e., between rivers). Our results generally show high trophic overlap among species, suggesting potential direct resource competition. Niche overlap was higher in study reaches with low densities of bigheaded carps compared to reaches with high densities, presumably due to intense resource competition and limiting of resources under high densities of bigheaded carps. Across density extremes, trophic reorganization by bigmouth buffalo (Ictiobus cyprinellus) was divergent from other native planktivores. Species-specific responses may be due to subtle differences in feeding strategies, degree of planktivory, food selectivity, and correlated food size distributions.

     

Multistate models of bigheaded carps in the Illinois River reveal spatial dynamics of invasive species

Knowledge of the spatial distributions and dispersal characteristics of invasive species is necessary for managing the spread of highly mobile species, such as invasive bigheaded carps (Bighead Carp [Hypophthalmichthys nobilis] and Silver Carp [H. molitrix]). Management of invasive bigheaded carps in the Illinois River has focused on using human-made barriers and harvest to limit dispersal towards the Laurentian Great Lakes. Acoustic telemetry data were used to parameterize multistate models to examine the spatial dynamics of bigheaded carps in the Illinois River to (1) evaluate the effects of existing dams on movement, (2) identify how individuals distribute among pools, and (3) gauge the effects of reductions in movement towards the invasion front. Multistate models estimated that movement was generally less likely among upper river pools (Starved Rock, Marseilles, and Dresden Island) than the lower river (La Grange and Peoria) which matched the pattern of gated versus wicket style dams. Simulations using estimated movement probabilities indicated that Bighead Carp accumulate in La Grange Pool while Silver Carp accumulate in Alton Pool. Fewer Bighead Carp reached the upper river compared to Silver Carp during simulations. Reducing upstream movement probabilities (e.g., reduced propagule pressure) by?≥?75% into any of the upper river pools could reduce upper river abundance with similar results regardless of location. Given bigheaded carp reproduction in the upper Illinois River is presently limited, reduced movement towards the invasion front coupled with removal of individuals reaching these areas could limit potential future dispersal towards the Great Lakes.     

Long-term changes in fish community structure in relation to the establishment of Asian carps in a large floodplain river

The Upper Mississippi River System, including the Illinois River, has been invaded by a number of nonnative species including silver carp Hypophthalmichthys molitirx and bighead carp H. nobilis, collectively referred to here as Asian carps. Silver carp densities in the Illinois River have increased dramatically and now represent some of the highest densities of wild silver carp anywhere in the world. Asian carps have the potential to alter existing ecosystems by consuming planktonic resources and therefore, could have the ability to alter existing fish communities as most fishes are dependent on planktonic resources during early development. However, identifying the relationship of fish community structure to the establishment of Asian carps has yet to be thoroughly investigated. Using long-term fish community data collected by the Upper Mississippi River Restoration’s Long Term Resource Monitoring element, we investigate changes in fish community structure pre- and post-establishment of Asian carps. Significant differences in the pre- and post-establishment communities were observed for the majority of gears and habitats. Species contributing to changes between establishment periods included most sportfish species and catostomids, which were less abundant post-establishment of Asian carps, while shortnose gar, grass carp, and emerald shiner were more abundant. While our analyses show Asian carps are likely contributing to major differences in fish community structure, future research and long-term monitoring should investigate the mechanisms and interactions responsible for community changes as well as identifying any potential concurrent or confounding factors such as changes in river hydrology or sedimentation.     

Anticipating the spread and ecological effects of invasive bigheaded carps (<Emphasis Type="Italic">Hypophthalmichthys</Emphasis> spp.) in North America: a review of modeling and other predictive studies

Bighead carp (Hypophthalmichthys nobilis Valenciennes 1844) and silver carp (H. molitrix Richardson 1845), collectively called bigheaded carps, have invaded the Mississippi River Basin and may have already entered the Laurentian Great Lakes where they could affect fishing and other industries. Developing models to predict potential spread and effects is difficult because local adaptation may have occurred among populations, parameter values for biological characteristics vary widely for these opportunistic generalists, and methodological differences complicate comparison and synthesis of studies. I review bigheaded carp biological parameters across a wide range of literature, including studies of native and introduced populations. I then evaluate how predictive models are parameterized, noting inconsistencies and highlighting data gaps. My analysis finds that although parameter values tend to vary substantially among and within systems, models are generally parameterized using the best information available, although bioenergetics and trophic models particularly need improvement. Some predictive tools can be updated using existing data (e.g., velocity requirements for spawning), but in other cases further research is needed. Research priorities include (1) better understanding bigheaded carp phenotypic plasticity among and within systems, (2) determining key biological traits of bigheaded carp populations at risk of seeding further invasions (e.g., Illinois River populations that may spread to Lake Michigan), and (3) monitoring bigheaded carp ecological effects on native fishes and plankton communities. A more complete awareness of strengths and limitations of predictive tools will lead to their improvement, thereby aiding managers in anticipating and counteracting bigheaded carp spread and effects.     

Temperature dependent effects of carbon dioxide on avoidance behaviors in bigheaded carps

Effective behavioral deterrents are needed to prevent aquatic invasive species from entering novel ecosystems. One deterrent strategy that shows promise is elevated carbon dioxide (CO₂) concentrations in water which can alter the behavior of freshwater fishes, including invasive bigheaded carps (Hypophthalmichthys spp.). However, few studies have evaluated behavioral responses to elevated CO₂ concentrations at different water temperatures. The objective of this study was to quantify CO₂ concentrations needed to achieve avoidance (voluntary response) and narcosis (involuntary response observed by loss of equilibrium) behaviors in silver carp (H. molitrix) and bighead carp (H. nobilis) at 5, 15, and 25 °C. Overall, silver carp and bighead carp displayed avoidance and narcosis behaviors to CO₂ at each water temperature, however bighead carp responded at higher CO₂ concentrations than silver carp. Behavioral avoidance and narcosis were observed at approximately 40% lower CO₂ concentrations in 5 °C water relative to 25 °C suggesting considerable influence of water temperature on a CO₂ stimulus for both species. Results indicate that fluctuating water temperature (e.g., spatial and temporal variation across management sites) can influence how fish respond to elevated CO₂, and may usefully be considered when applying CO₂ as a behavioral deterrent.     

Aspects of Embryonic and Larval Development in Bighead Carp Hypophthalmichthys nobilis and Silver Carp Hypophthalmichthys molitrix

As bighead carp Hypophthalmichthys nobilis and silver carp H . molitrix (the bigheaded carps) are poised to enter the Laurentian Great Lakes and potentially damage the region’s economically important fishery, information on developmental rates and behaviors of carps is critical to assessing their ability to establish sustainable populations within the Great Lakes basin. In laboratory experiments, the embryonic and larval developmental rates, size, and behaviors of bigheaded carp were tracked at two temperature treatments, one “cold” and one “warm”. Developmental rates were computed using previously described stages of development and the cumulative thermal unit method. Both species have similar thermal requirements, with a minimum developmental temperature for embryonic stages of 12.1° C for silver carp and 12.9° C for bighead carp, and 13.3° C for silver carp larval stages and 13.4° C for bighead carp larval stages. Egg size differed among species and temperature treatments, as egg size was larger in bighead carp, and “warm" temperature treatments. The larvae started robust upwards vertical swimming immediately after hatching, interspersed with intervals of sinking. Vertical swimming tubes were used to measure water column distribution, and ascent and descent rates of vertically swimming fish. Water column distribution and ascent and descent rates changed with ontogeny. Water column distribution also showed some diel periodicity. Developmental rates, size, and behaviors contribute to the drift distance needed to fulfill the early life history requirements of bigheaded carps and can be used in conjunction with transport information to assess invasibility of a river.     

Persistence of DNA in Carcasses,Slime and Avian Feces May Affect Interpretation of Environmental DNA Data

The prevention of non-indigenous aquatic invasive species spreading into new areas is a goal of many resource managers. New techniques have been developed to survey for species that are difficult to capture with conventional gears that involve the detection of their DNA in water samples (eDNA). This technique is currently used to track the invasion of bigheaded carps (silver carp and bighead carp; Hypophthalmichthys molitrix and H. nobilis) in the Chicago Area Waterway System and Upper Mississippi River. In both systems DNA has been detected from silver carp without the capture of a live fish, which has led to some uncertainty about the source of the DNA. The potential contribution to eDNA by vectors and fomites has not been explored. Because barges move from areas with a high abundance of bigheaded carps to areas monitored for the potential presence of silver carp, we used juvenile silver carp to simulate the barge transport of dead bigheaded carp carcasses, slime residue, and predator feces to determine the potential of these sources to supply DNA to uninhabited waters where it could be detected and misinterpreted as indicative of the presence of live bigheaded carp. Our results indicate that all three vectors are feasible sources of detectable eDNA for at least one month after their deposition. This suggests that current monitoring programs must consider alternative vectors of DNA in the environment and consider alternative strategies to minimize the detection of DNA not directly released from live bigheaded carps.     

Tag retention and survival of juvenile bighead carp implanted with a dummy acoustic tag at three temperatures

Bighead carp Hypophthalmichthys nobilis and silver carp Hypophthalmichthys molitrix (together, the bigheaded carps) are invasive fishes in North America that have resulted in substantial negative effects on native fish communities and aquatic ecosystems. Movement and behavior of adult bigheaded carps has been studied previously using telemetry, while similar studies with juvenile bigheaded carps have yet to be attempted. Recent technological advances in telemetry transmitters has increased the availability of tags sufficiently small enough to implant in juvenile carps. However, the effects of surgical implantation of telemetry tags on juvenile bigheaded carps have not been evaluated. We determined tag retention and survival associated with surgical implantation of acoustic telemetry tags into juvenile bighead carp (range 128–152 mm total length) at three temperatures (13, 18, and 23°C). In addition, we assessed the effect of surgically implanted transmitters on the fitness, defined as changes in weight or critical swimming speed, of carp implanted with transmitters. Survival was high among tagged fish (85%) with 47% of tags retained at the conclusion of the 45‐day study. No substantial decline in fitness of the fish was observed in tagged fish compared to untagged fish.     

Swimming performance of adult bighead carp Hypophthalmichthys nobilis (Richardson, 1845) and silver carp H. molitrix (Valenciennes, 1844)

Although the movement of invasive bighead carp (Hypophthalmichthys nobilis) and silver carp (H. molitrix) in the Upper Mississippi River system is dependent on their ability to swim through its numerous lock‐and‐dams, the swimming performance of adults of these species is at present unknown. Using a large (2,935‐L) mobile swim tunnel, the swimming performance of adult bighead and adult silver carp was quantified at water velocities that challenged them to exhibit either prolonged and/or burst swimming (76–244 cm/s) with fatigue times of less than 10 min. Simple log‐linear models best described the relative swim speed to fatigue relationships for both species. Under these conditions, the swimming performances of adult bighead and silver carp were similar to several species of adult fishes native to the Mississippi River system, but relatively low (<3 total body lengths per second, TL/s) compared to previously studied juveniles and sub‐adult bigheaded carps (3–15 TL/s). The decline in endurance with water velocity was three times greater in bighead carp (slope = ?2.98) than in silver carp (slope = ?1.01) and the predictive ability of the bighead model was appreciably better than the silver carp model. The differences in adult swimming performance between the two species were coincident with behavioral differences (e.g. breaching in silver carp but not in bighead carp). The swimming performance data of adult bighead and silver carp can now be used to evaluate whether their passage through manmade river structures including the gates of lock‐and‐dams in the Upper Mississippi River might be reduced.     

Using marketing to fish‐down bigheaded carp (Hypophthalmichthys spp.) in the United States: Eliminating the negative brand name, “carp”

Invasive bigheaded carp species (Hypophthalmichthys spp.) from Asia have experienced rapid range expansion and population explosions in rivers of the United States resulting in ecosystem damage currently being witnessed and documented by fishery biologists. In addition, silver carp (H. molitrix) present a danger of injury and death to unsuspecting boaters, water skiers or recreational fishers due to their propensity to jump in response to boat motor noise. Fishing‐down bigheaded carp populations for human consumption will reduce environmental damage and potential human injury and mortality until other control measures become available. The name “carp” conveys an extremely negative brand name for purposes of product marketing. We suggest that the silver carp be renamed by the professional scientific community to silverfin (a trademarked name currently used in culinary circles) and the bighead carp (H. nobilis) to bighead. The suggested common names changes represent a simple, albeit small step to reducing bigheaded carp population numbers based on sound product naming strategies developed and used in marketing science.     

Influence of environmental factors and individual traits on the diet of non-native hybrid bigheaded carp (Hypophthalmichthys molitrix × H. nobilis) in Lake Balaton,Hungary

Planktivorous silver carp and bighead carp (collectively, the bigheaded carps) have been stocked worldwide and their invasion has caused severe impacts on many freshwater ecosystems. Exploiting the chance provided by the specific hybrid bigheaded carp stock in Lake Balaton (Hungary) covering the entire morphological range between the two species (including gill raker morphology), we implemented a comprehensive study (1) to reveal the feeding habits of hybrid bigheaded carps living in a mesotrophic, lacustrine habitat and (2) to assess how biotic and abiotic environmental factors and gill raker morphology affect diet composition. We found that all bigheaded carps utilized primarily zooplankton and neglected the scarce and inefficiently digestible phytoplankton, irrespective of gill raker morphology. Moreover, we observed strikingly high levels of inorganic debris consumption, but the proportion of inorganic matter in the guts was not associated directly with the concentration of suspended inorganic particles. Variance in the diet composition of bigheaded carps was related mostly to environmental factors, including the wind-induced resuspension of inorganic particles and seasonally variable availability of food resources. In conclusion, the effects of abiotic environmental factors and available food resources could overwhelm the effect of gill raker morphology in shaping the feeding habits of bigheaded carps.

     

Water guns affect abundance and behavior of bigheaded carp and native fish differently

Water guns have shown the potential to repel nuisance aquatic organisms. This study examines the effects of exposure to a 1966.4 cm³ seismic water gun array (two guns) on the abundance and behavior of Bighead Carp Hypophthalmichthys nobilis, Silver Carp H. molitrix (collectively referred to as bigheaded carp) and native fishes (e.g., Smallmouth Buffalo Ictiobus bubalus). Water guns were deployed in a channel that connects the Illinois River to backwater quarry pits that contained a large transient population of bigheaded carp. To evaluate the effect of water guns, mobile side-looking split-beam hydroacoustic surveys were conducted before, during and between replicated water gun firing periods. Water guns did not affect abundance of bigheaded carp, but abundance of native fish detected during the firing treatment was 43 and 34% lower than the control and water guns off treatments, respectively. The proximity of bigheaded carp to the water gun array was similar between the water guns on and water guns off treatments. In contrast, the closest detected native fish were detected farther from the water guns during the water guns on treatment (mean ± SE, 32.38 ± 3.32 m) than during the water guns off treatment (15.04 ± 1.59 m). The water gun array had a greater impact on native fish species than on bigheaded carp. Caution should be taken to the extrapolation of these results to other fish species and to fish exposed to water guns in different environments (e.g., reduced shoreline interaction) or exposure to a larger array of water guns, or for use of water guns for purposes other than a barrier.     

In situ study on effect of food competition on diet shifts and growth of silver and bighead carps in large biomanipulation fish pens in Meiliang Bay, Lake Taihu

Silver and bighead carps were cultured in large fish pens to reduce the risks of cyanobacterial bloom outbreaks in Meiliang Bay, Lake Tauhu in 2004 and 2005. Diet compositions and growth rates of the carps were studied from April to November each year. Both carp species fed mainly on zooplankton (>50% in diet) in 2004 when competition was low, but selected more phytoplankton in 2005 when competition was high. Silver carp had a broader diet breadth than did bighead carp. Higher densities and fewer food resources increased diet breadths but decreased the diet overlap in both types of carps. It can be predicted that silver and bighead carps would be released from diet competition and shift to feed mainly on zooplankton at low densities, decreasing the efficiency of controlling cyanobacterial blooms. Conclusively, when silver and bighead carps are used to control cyanobacterial blooms, a sufficiently high stocking density is very important for a successful practice.     

Phenotypic plasticity in the spawning traits of bigheaded carp (Hypophthalmichthys spp.) in novel ecosystems

1. Bigheaded carp, including both silver (Hypophthalmichthys molitrix) and bighead (H. nobilis) carp, are successful invasive fishes that threaten global freshwater biodiversity. High phenotypic plasticity probably contributes to their success in novel ecosystems, although evidence of plasticity in several spawning traits has hitherto been largely anecdotal or speculative. 2. We collected drifting eggs from a Midwestern U.S.A. river from June to September 2011 and from April to June 2012 to investigate the spawning traits of bigheaded carp in novel ecosystems. 3. Unlike reports from the native range, the presence of drifting bigheaded carp eggs was not related to changes in hydrological regime or mean daily water temperature. Bigheaded carp also exhibited protracted spawning, since we found drifting eggs throughout the summer and as late as 1 September 2011. Finally, we detected bigheaded carp eggs in a river reach where the channel is c. 30 m wide with a catchment area of 4579 km², the smallest stream in which spawning has yet been documented. 4. Taken with previous observations of spawning traits that depart from those observed within the native ranges of both bighead and silver carp, our findings provide direct evidence that bigheaded carp exhibit plastic spawning traits in novel ecosystems that may facilitate invasion and establishment in a wider range of river conditions than previously envisaged.     

Modelling bioenergetic and population-level impacts of invasive bigheaded carps (Hypophthalmichthys spp.) on native paddlefish (Polyodon spathula) in backwaters of the lower Mississippi River

1. While invasions of large rivers by exotic fish species are well documented, assessing actual or potential impacts on native species is a challenge. Rapid assessments may be possible through the application of a combination of bioenergetic and population dynamic models.
2. Paddlefish (Polyodon spathula) is a native species in the central USA with a history of population decline due to waterway development and overharvesting for roe. It is not known whether paddlefish are impacted by resource competition from invasive bigheaded carp populations, including silver (Hypophthalmichthys molitrix) and bighead carp (Hypophthalmichthys nobilis), which have expanded dramatically in the Mississippi River.
3. We used bioenergetic models to project the potential impact of invasive silver and bighead carp on zooplankton density and paddlefish somatic growth in backwater habitat. Bioenergetic outputs were translated to impacts on fecundity, becoming inputs for 50-year metapopulation simulations of backwater habitat connected to the main-stem Mississippi River by episodic flood events.
4. Competition with carp reduced growth and increased the risk of population decline for paddlefish. Impacts increased disproportionately with increased carp abundance and were further exacerbated in scenarios with increased diet overlap or decreased zooplankton abundance.
5. We also analysed paddlefish condition data collected at sites near the lower Mississippi River with varying histories of carp invasion. These data give credence to the bioenergetic model output; paddlefish had reduced body condition at sites with long-established, high-density carp populations.
6. We conclude that invasive bigheaded carps have great potential to reduce paddlefish growth, fecundity, and abundance. The pairing of bioenergetics and population models is likely to be broadly useful in assessing the risks posed by other invasive species.

     

Introduction and cage culture of exotic carps and their impact on fish harvested in Lake Begnas,Nepal

The suitability of exotic carps namely Aristichthys nobilis (Bighead carp), Hypophthalmichthys molitrix (Silver carp), Ctenopharyngodon idellus (Grass carp), Cyprinus carpio (Common carp) and Labeo rohita (Rohu) in a sub-tropical lake was evaluated. The impact of their introduction on native fishes was also studied. After the introduction and cage culture of exotic carps the total harvest reached 92 kg·ha^–1; an increase of 266% within eight years. The planktivorous bighead and silver carps were most successful. The harvest of the other three species was poor. Since the introduction of exotic carp the harvest of indigenous fishes declined by 42%. Considering the food habits of these fish, further stocking should be limited to bighead and silver carps to limit the adverse effects on the indigenous species.     

Trophic niche differences between coexisting omnivores silver carp and bighead carp in a pelagic food web

Understanding how omnivorous consumers are affected by their resources and how this is expressed through the food chain is a fundamental issue in ecology. We used stable isotope analysis of archived scales of two pelagic single-chain omnivorous fish species, bighead carp (Hypophthalmichthys nobilis) and silver carp (H. molitrix), to reconstruct historical trophic interactions patterns along a gradient of resources. We found that, although bighead carp and silver carp utilize the similar resources from the pelagic food chain, they can coexist and persist not only by regulating their trophic position and trophic dissimilarity, but also by regulating trophic niche width. Omnivorous fish often exhibit flexible foraging strategies, which is closely related to the availability of ecologic context. We found a positive relationship between trophic dissimilarity and zooplankton density, which may indicate that the competitive interactions induce strong top-down effects on zooplankton, and/or that high zooplankton availability release the between-population trophic interaction through bottom-up effect. The trophic niche width of bighead carp was positively related with zooplankton availability, probably reflecting that the niche of an omnivore at a higher trophic position is more sensitive to high quality resources. Our results indicate how different aspects of the trophic partitioning of coexisting omnivores may be regulated by different ecological contexts. These alternatives are not mutually exclusive and further theoretical work should include both these mechanisms to re-evaluate the effects of omnivory on food web properties.     

Reproductive condition and occurrence of intersex in bighead carp and silver carp in the Missouri River

Little is known about the reproductive biology of the exotic bighead carp Hypophthalmichthys nobilis and silver carp Hypophthalmichthys molitrix in the Missouri River. In order to fill this gap in understanding, herein is described the reproductive condition of these Asian carps. Evidence is presented which indicates that bighead and silver carp in the Missouri River have a protracted spawning period that extends from early spring through fall and some individual bighead and silver carp are spawning multiple times during a reproductive season. Although bighead and silver carps are successfully maturing and spawning in the Missouri River some reproductive abnormalities such as intersex, atresia, and sterility were observed. Knowledge of the reproductive activity of these invasive carps may be useful to resource managers tasked with their control. Furthermore, the reproductive abnormalities observed should be considered when evaluating the environmental condition of the Missouri River relative to supporting a healthy fish fauna.     

Development of microsatellite DNA markers of silver carp (Hypophthalmichthys molitrix) and their cross‐species application in bighead carp (Aristichthys nobilis)

Forty‐four microsatellite DNA markers were developed for silver carp, and used to investigate polymorphisms of 41 wild silver carps and seven wild bighead carps collected from Jingzhou fragment of Yangtze River. In silver carp, 40 markers were polymorphic. A total of 297 alleles were detected at 40 polymorphic loci. The number of alleles per locus varied from two to 16 with an average of 7.4 and the expected heterozygosities of each locus ranged from 0.07 to 0.91 with an average of 0.69. All markers amplified both silver carp and bighead carp DNAs.