Objective A quantitative PCR (qPCR) screening procedure previously showed potential for rapidly assessing the likelihood that ichthyoplankton samples contain bigheaded carp Hypophthalmichthys spp. eggs and larvae. We sought to expand the capabilities of this procedure, assess its sensitivity under realistic field conditions, investigate potential sources of error, and compare the costs of this method with those of traditional microscopy-based sample processing.Methods We refined the qPCR procedure by screening for two additional species of invasive carp, tested whether the quantity of organic debris within ichthyoplankton samples influenced the procedure's accuracy, assessed whether qPCR results could predict the number of target eggs and larvae in a sample, and compared the costs of the qPCR method to those of conventional sample processing.Results Invasive carp DNA copy number was a significant predictor of the presence of invasive carp specimens and had a sigmoidal relationship with the numbers of invasive carp eggs and larvae within a sample. The number of Silver Carp H. molitrix and Grass Carp Ctenopharyngodon idella DNA copies in a sample was also positively related to the number of specimens of each of these species in the sample. A 20% probability threshold of inferring a positive detection based on DNA copy number provided an optimal balance between sensitivity and specificity. High quantities of organic debris within samples increased the probability of obtaining a false-positive result across a range of detection thresholds. Additionally, high quantities of organic matter were associated with overestimation of the number of specimens predicted to occur within samples. The qPCR procedure required less time but incurred a higher monetary cost per sample than manual processing unless a moderate number of specimens was sequenced following visual identification.Conclusions Application and further modification of this qPCR procedure may allow for early detection or more detailed study of spawning by any or all invasive carp species or other pelagic broadcast spawners. A refined quantitative PCR screening procedure was useful for detecting the presence and assessing the numbers of invasive carp eggs and larvae within ichthyoplankton samples in less time than manual processing. The quantity of organic matter within samples can affect the performance of the quantitative PCR procedure.

We conducted a series of studies to assess the effectiveness of an electric barrier in deterring the movements of freshwater fish. Fish responses (detections center dot individual(-1)center dot hr(-1) within the 3 m exclusion zone) were quantified for a mixed assemblage of native and nonnative fishes within 0.4 ha ponds. Additionally, we mapped the surface voltages generated by the electric barrier in a nearby stream. The electric barrier (operated at 10 kW) was effective at deterring native and invasive fishes, as > 99% of all fish detections within the exclusion zone occurred while the electric barrier was off. However, some fish detections occurred while the system was operated at full power, indicating the electric barrier was not 100% effective. A follow-up study found that fish responses differed between low (3.6 kW), medium (6.6 kW), and high (10 kW) field strengths, with smallmouth buffalo Ictiobus bubalus exhibiting a greater sensitivity to the low setting than bighead carp Hypophthalmichthys nobilis and silver carp H. molitrix. Maps of the surface voltages within a nearby stream indicated that the electric barrier was strong enough to deter silver carp (> 1 V/cm). However, the surface voltages quickly dissipated upstream and downstream of the electrodes. Overall, the electric barrier appears to be an effective tool that can be used to combat the spread of invasive fishes in freshwater environments. However, more evaluations are needed to test how the system performs in different conditions and to identify whether fish of varying sizes or life stages respond similarly.

The relationship between the magnitude of reproduction and adult density of pelagically spawning carp (PSC) species (bigheaded carp Hypophthalmichthys spp., Grass Carp Ctenopharyngodon idella, and Black Carp Mylopharyngodon piceus) and the influence of environmental factors on this relationship are valuable information for management and control of these highly invasive cyprinids. Six years of standardized monitoring for PSC reproduction and adult density in navigation pools of the Illinois Waterway (IWW; the Illinois River and its connection to Lake Michigan through the Des Plaines River and Chicago Area Waterway System), in conjunction with removal efforts in the upper IWW, where there is limited fish movement between pools, provided an opportunity to deepen our understanding of factors affecting the reproductive productivity of this invasive assemblage. Reproductive activity most commonly occurred in May and June, with the magnitude of reproduction in June far exceeding that occurring in other months. The highest egg counts were found within a 72-km zone containing the hydromorphological transition between the upper and lower Illinois River, with the majority of PSC larval drift occurring below this zone in the lower Illinois River. Magnitude of reproduction increased nonlinearly with adult PSC density, declining at high adult densities. Annual egg counts were also higher in years that combined more variable spring discharge with higher accumulated degree-days through June. The density-dependent reproduction exhibited by PSC implies that any stock-recruitment variation observed for these species needs to be interpreted cautiously before being ascribed to environmental factors affecting survival from hatching to juvenile stages. An increased understanding of which life stages of PSC are subject to density dependence can refine projections of how these species respond to harvest and other control measures.

This paper reports the first records of Cercopagis pengoi in the Mississippi River Basin, Illinois, USA.In 2017, a total of 11 C. pengoi were collected from two different locations during zooplankton sampling in the Illinois Waterway.One location was in the Chicago Sanitary and Ship Canal and the second location was in the Calumet-Sag Channel, approximately eight and 35 river kilometers from Lake Michigan, respectively.In 2021, eight additional individuals were encountered in ichthyoplankton samples collected in the Chicago Sanitary and Ship Canal, three river kilometers upstream of the 2017 capture location.The extent and density of C. pengoi within the Illinois Waterway is currently unknown; therefore, additional sampling is warranted to better understand their distribution and abundance to facilitate an assessment of the risks of spread to other connected waterways.

Black carp (Mylopharyngodon piceus), a large molluscivorous cyprinid native to eastern Asia, has become established in the Mississippi River basin in North America. The vulnerability of most North American snails and bivalves to black carp predation remains unknown, especially as it relates to juvenile black carp transitioning to mollusk prey. We conducted feeding experiments to assess the relative vulnerability of different mollusks to predation by age-0 and age-1 black carp. Age-0 black carp were tested with the North American native unionid Hamiota perovalis, a native pleurocerid snail Elimia livescens, and a native physid snail in the genus Physella. Age-1 black carp were tested with Elimia livescens, the North American native unionids Lampsilis cardium and Lampsilis cariosa, a native sphaeriid clam in the genus Musculium, and the non-native cyrenid clam Corbicula fluminea. Juvenile black carp readily attacked and consumed mollusks, but differences in vulnerability were evident among prey taxa exposed to age-0 and age-1 black carp. Age-0 black carp were able to consume Physella approaching the extent of their mouth gape. Age-1 black carp displayed greater feeding capabilities than age-0 black carp and easily consumed Elimia, Lampsilis, and Musculium. The only prey taxon that age-1 black carp struggled to consume was Corbicula, which had the thickest and widest shells relative to predator gape of all prey tested. Our results suggest that a wide range of small or juvenile mollusks are susceptible to predation by juvenile black carp but highlight that prey-specific characteristics, such as shell strength and shell size, may drive differential predation pressure on mollusk populations as the invaded range of black carp expands.

Fish herding (driving fish into nets) is used by commercial fishers to increase harvest of invasive bigheaded carp (Hypophthalmichthys spp.), yet has not been widely adopted for fisheries monitoring purposes. We conducted an experiment to assess whether fish herding using percussive sound or electrical stimuli can enhance catch rates and detection of bigheaded carp and other fishes in surface-to-bottom gill nets. Catch rates (fish net set−1) from traditional gill net sets where no herding method was applied were compared to sets combined with either sound stimuli (physical impacts to the boat hull and water surface to produce percussive sound) or electricity produced from a pulsed-DC electrofisher to manipulate fish movements. For most species, herding increased catch rates and detection probability compared to control sets. Sound stimuli increased catch rates of Silver Carp (Hypophthalmichthys molitrix) by over three times, whereas electrical stimuli increased catch rates by over six times. Catch of Bighead Carp (Hypophthalmichthys nobilis) was highest in nets paired with sound stimuli. Herding methods also reduced the number of samples required to attain target detection probabilities for bigheaded carp. Herding techniques combined with gill netting may be a valuable option for targeted bigheaded carp sampling, especially when electrofishing or netting alone is ineffective for these evasive fishes. Synergistic methods may provide a cost effective means of improving detection probabilities for bigheaded carp at their invasion front or other locations where densities are low and uncertainty of capture is high.

The early foraging ecology of alligator gar (Atractosteus spatula) is poorly documented, with little information available on young-of-year food habits or ontogenetic diet shifts. We conducted laboratory experiments to quantify prey selection and foraging behaviours of larval and early juvenile alligator gar (16-80 mm TL) simultaneously offered zooplankton, chironomid larvae and one of three densities of fish prey. The smallest size groups of alligator gar consumed zooplankton almost exclusively, but with increasing size, selection for zooplankton declined and selection for fish prey increased. At higher densities of fish prey, alligator gar exhibited lower selection for zooplankton and positively selected for fish at smaller sizes. Ingestion efficiencies for chironomids were considerably lower than for zooplankton or fish prey, resulting in low rates of consumption and negative selection for chironomids by all size groups of alligator gar. Fish prey elicited a different foraging response from alligator gar than zooplankton or chironomids, as alligator gar pursued and struck at fish over longer distances than for other prey types. With increasing size, alligator gar used a wider vertical range of the water column for foraging, changed their strike tactics and exhibited decreased handling times for zooplankton and fish. These observations indicate that alligator gar undergo several functional and behavioural changes during early ontogeny that facilitate a rapid transition to piscivory, but fish prey density strongly affects prey consumption patterns and the size at which alligator gar transition to piscivory.

Monitoring ichthyoplankton is useful for identifying reproductive fronts and spawning locations of bigheaded carps (Hypophthalmichthys spp.). Unfortunately, sorting and identifying ichthyoplankton to monitor for bigheaded carp reproduction is time consuming and expensive. Traditional methods require frequent egg-larvae sampling, sorting of all samples to obtain presumptively identified bigheaded carp, and genetic validation of presumptively identified eggs. Quantitative PCR (qPCR) has the potential to streamline this process by identifying samples that likely do or do not contain a target species. Our objective was to develop a genetic screening tool using qPCR with the duplex assays SCTM4/5 and BHTM1/2 to prioritize samples that have a higher likelihood of containing bigheaded carp eggs or larvae. We used tandem ichthyoplankton samples collected for monitoring bigheaded carps in the Upper Mississippi, Illinois, and St. Croix rivers to evaluate the effectiveness of qPCR as a screening tool. Samples with >10,000 copies of DNA had 100% occurrence of bigheaded carp eggs or larvae in the traditionally sorted samples, whereas samples with <10 copies of DNA had 0% occurrence of ichthyoplankton from these invasive species. We used a logistic regression model to calculate the probability of finding bigheaded carp eggs or larvae based upon the number of DNA copies; 406 copies corresponded with a 50% probability of having bigheaded carp ichthyoplankton present in a sample. These data can be used to inform management actions (i.e., control, containment) for these invasive fishes, and this tool could be adapted for monitoring for reproduction of other aquatic invasive species.

Identifying spawning grounds of Asian carp is important for determining the reproductive front of invasive populations. Ichthyoplankton monitoring along the Illinois Waterway (IWW) has provided information on abundances of Asian carp eggs in the IWW's navigation pools. Post-fertilization times derived from egg development stages and water temperatures can be used to estimate spawning times of Asian carp eggs, but estimating how far these eggs have drifted requires information on river hydraulics. A Fluvial Egg Drift Simulator (FluEgg) program was designed to predict the drift of Asian carp eggs in the riverine environment with egg growth considered. This paper presents a reverse-time particle tracking (RTPT) algorithm for back-casting the spawning location of eggs from their collection site. The RTPT algorithm was implemented as a module in FluEgg. The new version of FluEgg was coupled with an unsteady hydrodynamic model of the IWW to predict the spawning locations for 530 eggs that were collected in June 2015. The results indicate that tailwater sections below the Locks and Dams (L&Ds) in each navigation pool appear to be preferred spawning locations for Silver Carp (a species of Asian carp). From the data analyzed, the most upstream spawning location for the June 2015 spawning period was in the upper Marseilles navigation pool, downstream of the Dresden Island L&D. The RTPT algorithm can efficiently estimate spawning locations for multiple egg samples.

Effective management and monitoring programs require confidence regarding basic biological sampling. Gear comparisons are often required to determine the most effective techniques. Such is the case for populations of invasive Asian carps Hypophthalmichthys spp., which have recently occurred in large numbers throughout sections of the Mississippi River basin. We tested five gears (mini-fyke nets, beach seine, purse seine, pulsed-DC electrofishing, and gill net) that targeted juvenile (age 0) Silver Carp H. molitrix at sites along the Illinois River during 2014 and 2015 to determine the most effective ones for age-0 Silver Carp. We considered the most cost-effective gear to be the one that provided the largest catch at a minimal expenditure of labor. Mini-fyke nets were the most effective at collecting large numbers of age-0 Silver Carp, followed in decreasing order by beach seines, pulsed-DC electrofishing, purse seines, and gill nets. The smallest Silver Carp were caught in beach seines and the largest were caught in gill nets, and there was considerable variation in size distributions among gears. However, when we considered cost-effectiveness in terms of labor hours for each gear, both beach seines and mini-fyke nets had similar and overlapping labor expenditures. Gill nets and purse seines were not cost-effective, as they required more labor and had lower overall catch rates.

The River Redhorse (Moxostoma carinatum) is a large riverine catostomid that has experienced substantial declines across much of its historic range. Conservation of this species is hindered by a lack of knowledge about many aspects of its life history. In order to better understand the seasonal movements and habitat associations of this species, adult River Redhorse were captured from the Kankakee River, Illinois, implanted with radiotransmitters, and tracked throughout an annual cycle. Habitat data were recorded at all locations where radio-tagged River Redhorse were located. Eight of ten individuals displayed fidelity to a relatively short length of river (total range <= 8.7 km), whereas two individuals exhibited substantially greater movements (total range >= 23.1 km). Movement patterns of River Redhorse varied across seasons, with the largest ranges and highest displacements occurring during spring, and the smallest ranges and lowest movement rates occurring during summer. River Redhorse predominately occupied deep runs (>1.5 m) with moderate to swift currents (>0.4 m/s) over gravel, cobble, or boulder substrates. Habitat use differed among seasons, with River Redhorse occupying faster current velocities during winter and spring than during summer and fall, and using deeper water over smaller substrates in winter than during summer. Conservation of River Redhorse populations may depend on watershed-scale conservation practices to safeguard the mosaic of habitats the species associates with and maintaining viable pathways for movement among these habitats across seasons.

We compared three entrapment gears to determine which method was the most effective for capturing invasive Bighead Carp Hypophthalmichthys nobilis and Silver Carp H. molitrix in terms of numbers of fish captured and labor invested. Gears were deployed concurrently in two backwater lakes of the Illinois River during the summers of 2012-2014. Overall, the nightly catch rates of all fishes, Bighead Carp, and Silver Carp were one to three orders of magnitude greater in pound nets than in either fyke nets or hoop nets. Pound nets collected larger Bighead Carp than hoop nets and fyke nets. Hoop nets were ineffective at catching Asian carp in backwater lakes. Estimation of the effort required to deploy, maintain, and remove each gear type indicated that pound nets were the most cost-effective gear due to their high catch rates of Asian carp relative to the labor hours invested to collect the catch. Pound nets appear to be an effective means of removing Asian carp in backwater lake habitats of the Illinois River.

Channel catfish Ictalurus punctatus is a highly mobile species and is known to make extensive seasonal movements in lotic systems. Dams have been suggested to detrimentally affect this species, although abundant channel catfish populations are known to occur in many fragmented rivers. To examine factors that allow channel catfish to persist in impounded rivers, we assessed relative abundance of channel catfish in three impounded and three flowing sites of the Fox River, Illinois, USA. Radiotelemetry was used to determine movement and habitat use patterns of channel catfish among flowing and impounded areas. Relative abundance of channel catfish was consistently higher at flowing sites than at impounded sites during summer. Several radio-tagged channel catfish moved downstream into impounded areas in fall, and all tagged individuals were found in impounded areas during winter. The majority of tagged channel catfish moved upstream into flowing areas during spring. Channel catfish used a wide range of depths (0.282.60m), and were always found in current velocities less than 0.50ms-1. They selected most strongly for coarse substrates, but were infrequently found near cover. Although low-head dams restrict the movements of channel catfish, impounded areas appear to provide overwintering habitats that may eliminate the need for seasonal long-distance movements. Small run-of-river impoundments, however, may contain unsuitable conditions for channel catfish during other seasons. Copyright (C) 2010 John Wiley & Sons, Ltd.

The common carp Cyprinus carpio is an introduced species that is abundant in many impounded rivers. We assessed habitat conditions and common carp abundance in three flowing sites and three impounded sites of the Fox River, Illinois, to examine factors that influence the success of common carp in these systems. Radiotelemetry was used to determine long-term movement and habitat use patterns of common carp among flowing and impounded areas. Impounded areas were wider and deeper than flowing areas and had lower current velocities, smaller substrates, and lower abundances of cover. Common carp were found at all sites during summer, with catch rates being similar between flowing and impounded areas. The proportion of the fish assemblage consisting of common carp was similar between flowing and impounded areas during two of the study years but was higher in impounded areas than in flowing areas during the other two years. Radio-tagged common carp displayed a variety of movement patterns but used impounded areas most frequently during all seasons. Many common carp were always located in impounded areas, but some individuals moved upstream into flowing areas in spring and summer and returned to impounded areas by fall. Common carp positively selected for intermediate depths and low current velocities. Few consistent relationships were apparent in the use of substrate categories, but common carp selected most strongly for wood cover. Management activities targeting common carp should account for movements of this species among different habitat types and should focus on specific aspects of common carp life history. Dam removal or modification may also lead to declines in common carp abundance in some rivers.