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.     

Food habits and relative abundances of native piscivores: implications for controlling common carp

Common carp (Cyprinus carpio, carp) are a widespread and ecologically destructive invasive fish species. Carp management is critical for maintaining healthy aquatic ecosystems, and many control options are available, but most have proven to be ineffective. Carp abundances have increased at The Nature Conservancy’s Emiquon Preserve, Illinois, since its restoration in 2007 despite management efforts to suppress this species. We conducted a comparative diet study in Illinois, Tennessee, and Wisconsin to test whether bowfin (Amia calva), spotted gar (Lepisosteus oculatus, gar), and largemouth bass (Micropterus salmoides) commonly preyed upon carp. We focused on bowfin and gar because they are hypoxia-tolerant, similar to carp. We also assessed whether specific fish community characteristics were correlated with carp relative abundances. We found no evidence that bowfin, gar, and bass consumed large numbers of carp. However, carp may be limited in some ecosystems (e.g., Reelfoot Lake, Tennessee) through alternative mechanisms associated with bowfin, gar, bass, and bluegill (Lepomis macrochirus) included in a diverse native fish community.     

Population genetics of pike,genus <Emphasis Type="Italic">Esox</Emphasis> (Actinopterygii,Esocidae), in Northern Italy: evidence for mosaic distribution of native,exotic and introgressed populations

Biomanipulation, or management actions aimed to structure biological communities to achieve certain goals, has often been used in the restoration of aquatic ecosystems. In 2000, The Nature Conservancy acquired the Emiquon Preserve, which included two former Illinois River floodplain lakes, to restore these ecosystems. Restoration included stocking to establish a native fish community commensurate with historical records. Largemouth bass (Micropterus salmoides, bass) were also introduced to control poor water clarity and invasive common carp (Cyprinus carpio, carp). We summarized fish community characteristics and tested whether bass contributed to water clarity maintenance and limited carp during 2007–2014. The fish community was dominated by species stocked in greatest abundance, 13 of 32 species initially stocked have not been collected, and species diversity increased. No carp were observed in bass diets, water clarity declined significantly, and carp relative abundance increased. Increasing water levels during 2008–2009 diffused bass predation potential upon zooplanktivorous fishes and carp and weakened potential trophic cascading interactions. Our findings suggest that water level management, greater stocking of piscivores to maintain predator densities, prevention of gizzard shad (Dorosoma cepedianum) introduction, and/or a more diverse fish community including other native piscivores may be required to achieve long-term restoration goals.     

Bigheaded carps (<Emphasis Type="Italic">Hypophthalmichthys</Emphasis> spp.) at the edge of their invaded range: using hydroacoustics to assess population parameters and the efficacy of harvest as a control strategy in a large North American river

The threat posed by bigheaded carps (Hypophthalmichthys spp.) to novel ecosystems has focused efforts on preventing further range expansion; upstream progression in the Illinois River is a major concern due to its connection with the uninvaded Great Lakes. In addition to an electric barrier system, commercial harvest of silver carp (H. molitrix) and bighead carp (H. nobilis) in the upper river is intended to reduce propagule pressure and prevent range expansion. To quantify demographics and evaluate harvest efficacy, the upper river was sampled between 2012 and 2015 using mobile hydroacoustic methods. Reach-specific densities, size structures and species compositions varied interannually but the advancing population was characterized longitudinally as small-bodied, silver carp-dominated at the highest densities downstream, shifting to large-bodied, bighead carp-dominated at the low-density population front. The use of hydroacoustic sampling for harvest evaluation was validated in backwater lakes; there was a significant positive correlation between density estimates and the corresponding harvest catch-per-unit-effort of bigheaded carps. Localized densities of bigheaded carps were reduced by up to 64.4 % immediately post-harvest but generally rebounded within weeks. However, annual sampling of the entire upper river indicated that density of bigheaded carps decreased by over 40 % (between 2012 and 2013) and subsequently remained stable (between 2013 and 2014). The annual harvest of bigheaded carps increased during this period (from 45,192 to 102,453 individuals), in years of contrasting discharge conditions. At this spatiotemporal scale, harvest appears to have contributed to initial reduction, and subsequent maintenance of, bigheaded carps density levels, but discharge likely plays an important role (e.g., through immigration) in determining the extent of its impact. Mobile hydroacoustic sampling enabled robust quantification of the population over varying spatial scales and density gradients, highlighting the potential of this approach as an assessment tool for invasive fishes in riverine environments.     

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.     

Diet overlap among two Asian carp and three native fishes in backwater lakes on the Illinois and Mississippi rivers

Bighead and silver carp are well established in the Mississippi River basin following their accidental introduction in the 1980s. Referred to collectively as Asian carp, these species are filter feeders consuming phytoplankton and zooplankton. We examined diet overlap and electivity of Asian carp and three native filter feeding fishes, bigmouth buffalo, gizzard shad, and paddlefish, in backwater lakes of the Illinois and Mississippi rivers. Rotifers, Keratella spp., Brachionus spp., and Trichocerca spp., were the most common prey items consumed by Asian carp and gizzard shad, whereas crustacean zooplankton were the preferred prey of paddlefish. Bigmouth buffalo diet was broad, including both rotifers and crustacean zooplankton. Dietary overlap with Asian carp was greatest for gizzard shad followed by bigmouth buffalo, but we found little diet overlap for paddlefish. Diet similarity based on taxonomy correlated strongly with diet similarity based on size suggesting filtration efficiency influenced the overlap patterns we observed. Although rotifers were the most common prey item consumed by both bighead and silver carp, we found a negative relation between silver carp CPUE and cladoceran density. The competitive effect of Asian carp on native fishes may be forestalled because of the high productivity of Illinois and Mississippi river habitats, yet the potential for negative consequences of Asian carp in less productive ecosystems, including Lake Michigan, should not be underestimated.     

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.     

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.     

Competition among river planktivores: are native planktivores still fewer and skinnier in response to the Silver Carp invasion?

Planktivorous Silver Carp Hypophthalmichthys molitrix and Bighead Carp H. nobilis have successfully invaded much of the Upper Mississippi River System and its tributaries during the last 30 years. During the initial years of the invasion, concurrent declines in the body condition and the catch per unit effort (CPUE) of planktivorous Gizzard Shad Dorosoma cepedianum and Bigmouth Buffalo Ictiobus cyprinellus were attributed to competition with Asian carp. Using an additional seven years of data (2007–2013), we assessed whether Silver Carp have continued to exert adverse pressure on the condition, CPUE, and biomass of native planktivores or whether there is evidence of a potential rebound in the populations of native planktivores. The extended data set reaffirms the body condition and the CPUE of Bigmouth Buffalo remain significantly reduced. However, unlike previous analyses, we also observed significant reductions in the CPUE of Gizzard Shad. Additionally, new results show that the CPUE and biomass of Bigmouth Buffalo were more inversely related to Silver Carp CPUE and biomass relative to the CPUE and biomass of Gizzard Shad. These results reinforce that Silver Carp likely suppress native planktivores and also suggest that diet and other life-history traits may explain some of the subtle differences in species-specific responses. Our results also emphasize that long-term data can be critical to understanding how non-native species can influence native fish population dynamics and how this influence may change over time.     

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.     

Influence of roundup herbicide on the activities of peptidases in the intestines of various fish species

It has been revealed that, as a rule, Roundup herbicide inhibits activities of peptidases in the intestine mucosa and chyme in various fish species, both benthivorous (common carp Cyprinus carpio, silver bream Blicca bjoerkna, roach Rutilus rutilus, and crucian carp Carassius carassius) and piscivorous (perch Perca fluviatilis, pike Esox lucius, and sander Sander lucioperca). The tolerance of peptidases to the herbicide is species-specific. The magnitude and vector of the effects of Roundup depend on its concentration and localization of an enzyme. In the mucosa, the enzymes of common carp and pike are most tolerant, while the enzymes of common carp, silver bream, and pike are most tolerant in the chyme.     

A mark-recapture population estimate for invasive silver carp (<Emphasis Type="Italic">Hypophthalmichthys molitrix</Emphasis>) in the La Grange Reach,Illinois River

Invasive silver carp (Hypophthalmichthys molitrix) populations have expanded greatly in the Upper Mississippi River System (UMRS) since their introduction in the early 1970s. We conducted a Chapman-modified, continuous Schnabel mark-recapture population and biomass estimate for silver carp (106–901 mm) in the La Grange reach, Illinois River during 2007–2008. We estimated a total of 328,192 (95% CI 231,226–484,474) silver carp (2,544 per river km 1,792–3,756) comprising 705 (95% CI; 496–1,040) metric tons of biomass (5.5 metric tons per river km 3.8–8.1). Long Term Resource Monitoring Program (LTRMP) data from the La Grange reach showed an exponential increase in silver carp catches since 1998, with an intrinsic rate of increase approaching 84%. In 2008, silver carp comprised about 51% of the total LTRMP annual fish collection. To our knowledge, this large river reach may contain the greatest ambient densities of wild silver carp in the world. Our findings provide a target for reduction efforts and also emphasize the importance of the La Grange reach as a source population for potential expansion of the species to the Laurentian Great Lakes.     

Widespread and enduring demographic collapse of invasive common carp (<Emphasis Type="Italic">Cyprinus carpio</Emphasis>) in the Upper Mississippi River System

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.     

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.     

Profiles of digestive enzymes of two competing planktivores,silver carp and gizzard shad,differ

Typically, studies in digestive physiology in fish focus on a few enzymes and provide insight into the specific processes of the enzyme in a targeted species. Comparative studies assessing a wide number of digestive enzymes on fishes that compete for food resources are lacking, especially in the context of an introduced species. It is generally thought that the invasive silver carp (SVC; Hypophthalmichthys molitrix) directly compete for food resources with the native gizzard shad (GZS; Dorosoma cepedianum) in waters where they coexist. We compared 19 digestive enzymes between SVC and GZS throughout a year and in two rivers in the Midwestern United States: Illinois River and Wabash River. All digestive enzymes analyzed were detected in both SVC and GZS in both rivers. However, the profiles of the digestive enzymes varied by species. Alkaline phosphatase, valine arylamidase, acid phosphatase, naphthol-AS-BI-phosphohydrolase and N-acetyl-β-glucosaminidase were all much higher in SVC than in GZS. Differences between digestive enzyme profiles were also observed between rivers and months. This study demonstrates the utility of using an ecological approach to compare physiological features in fishes.     

Genetic diversity,effective population size,and structure among black bear populations in the Lower Mississippi Alluvial Valley,USA

Multiple small populations of American black bears Ursus americanus, including the recently delisted Louisiana black bear subspecies U. a. luteolus, occupy a fragmented landscape in the Lower Mississippi Alluvial Valley, USA (LMAV). Populations include bears native to the LMAV, bears translocated from Minnesota during the 1960s, and recently reintroduced and colonizing populations sourced from within the LMAV. We estimated population structure, gene flow, and genetic parameters important to conservation of small populations using genotypes at 23 microsatellite markers for 265 bears from seven populations. We inferred five genetic clusters corresponding to the following populations: White River and western Mississippi, Tensas River and Three Rivers, Upper Atchafalaya, Lower Atchafalaya, and Minnesota. Upper Atchafalaya was suggested as the product of Minnesota-sourced translocations, but those populations have since diverged, likely because of a founder effect followed by genetic drift and isolation. An admixture zone recently developed in northeastern Louisiana and western Mississippi between migrants from White River and Tensas River, resulting in a Wahlund effect. However, gene flow among most populations has been limited and considerable genetic differentiation accumulated (global F_ST?=?0.22), particularly among the three Louisiana black bear populations that existed when federal listing occurred. Consistent with previous bottlenecks, founder effects, and persisting isolation, all LMAV bear populations had low genetic diversity (A_R?=?2.08–4.81; H_E?=?0.36–0.63) or small effective population size (N_E?=?3–49). Translocating bears among populations as part of a regional genetic restoration program may help improve genetic diversity and increase effective population sizes.     

Comparative physiological and immunological characteristics of carps (cyprinidae) grown in aquaculture with different types of food

On the basis of the hematological, cytochemical, and biochemical blood indices, it has been established that the adaptive capabilities in common carp Cyprinus carpio and grass carp Ctenopharyngodon idella are higher than in silver carp hybrid Hypophthalmichthys molitrix × H. nobilis, while the potential for growth is, by contrast, higher in silver carp hybrid.     

Genome-Scale Association Study of Abnormal Scale Pattern in Yellow River Carp Identified Previously Known Causative Gene in European Mirror Carp

Common carp (Cyprinus carpio) is one of the most widely studied fish species due to its great economic value and strong environmental adaptability. Scattered scale, a typical phenotype of the mirror carp that is derived from Europe, has never been observed in the Yellow River carp previously. We recently identified approximately one fourth of the F1 progenies displaying scattered scale in a full-sib Yellow River carp family in our breeding program, despite both parents that showed wild type with normal scale patterns. This family provides us unique materials to investigate the genetic basis underlying the abnormal scale mutant in Yellow River carp population. Genome-wide association study (GWAS) and association mapping were performed based on genome-wide single nucleotide polymorphisms (SNP) genotyped with common carp 250 K SNP genotyping array in 82 samples of the Yellow River carp family. We identified a 1.4 Mb genome region that was significantly associated with abnormal scattered scale patterns. We further identified a deletion mutation in fibroblast growth factor receptor 1 a1 (fgfr1a1) gene within this genome region. Amplification and sequencing analysis of this gene revealed a 311-bp deletion in intron 10 and exon 11, which proved that fgfr1a1 could be the causal gene responsible for abnormal scattered scale in the Yellow River carp family. Since similar fragment mutation with 306-bp and 310-bp deletions had been previously reported as causal mutation of scattered scale patterns in the mirror carp, we speculate that either the deletion mutation was introduced from Europe-derived mirror carp or the deletion independently occurred in the mutation hotspot in fgfr1a1 gene. The results provided insights into the genetic basis of scale pattern mutant in Yellow River carp population, which would help us to eliminate the recessive allele of the abnormal scale patterns in Yellow River carp population by molecular marker-assisted breeding.