15 Apr 2026

Field Evaluation of the Automated Barge Clearing Deterrent (ABCD): Hydrodynamic, Navigation, and Fish Response Effects

Abstract: The escape and subsequent spread of invasive carp (notably, bighead carp [Hypophthalmichthys nobilis] and silver carp [H. molitrix]) from aquaculture ponds and sewage lagoons into the Mississippi and Illinois Rivers poses a significant risk to further spread of these fish into the Great Lakes. Prior research demonstrated that commercial tows can transport juvenile invasive carp through locks and other barriers to fish migration. A recent physical model study recommended a linear array of bubble diffusers, the Automated Barge Clearing Deterrent (ABCD), for further evaluation in mitigating the transport of small fish in commercial tows. The present field study evaluated the ABCD for navigation safety and barge junction flushing capacity. An instrumented commercial tow executed 119 lock approaches with the ABCD both operating and idle. Pilot interviews and tow trajectory analysis indicated no significant navigation safety issues. The measured velocity data, fish recapture data, and a simple fish displacement model indicated that the ABCD produced sufficient flow to expel all passive objects and many small juvenile invasive carp. However, the ABCD is less likely to expel large juvenile invasive carp due to their stronger swimming ability. The ABCD and two alternative configurations prove strong contenders for further development and application.

9 Apr 2026

Identifying Overwintering Habitat of Silver and Bighead Carp in the Lower Mississippi River: Implications for Harvesting and Population Reduction

Purpose: A total of 41 sites along a 58 mi reach of the Lower Mississippi River (LMR) were surveyed during winter 2022 for invasive carp aggregation. Sites consisting of scallops closest to the dike-vegetated bank interface with deeper, slow-moving water and consistent access back to the main channel were preferred. Carp avoided strong currents, and there was no trend in depth selection other than avoiding shallow (less than 20 ft) water. In January 2023, recreation-grade sonar (e.g., side-scan and down-imaging) surveys were conducted in the same reach of the LMR to demonstrate the technology and evaluate carp population size at sites with high abundances based on previous surveys. Fish density was estimated to be 32 fish/10,000 yd3 (95% confidence interval [CI; 31–34]) using down-imaging software, which is the first estimate of assumed bigheaded carp density in the LMR. Additional fish collections are needed to confirm species composition and size abundance provided by sonar technology. Resurveying sites with high carp abundance over a range of river stages would be necessary to fully characterize habitat conditions, evaluate influence of river stage on occupancy duration, and continue to evaluate species composition and mass removal techniques as a management option in the Lower Mississippi River.

26 Sep 2022

Occurrence of Silver, Bighead, and Black Carp in Waters Managed by the US Army Corps of Engineers

Abstract: This technical report (TR) documents the distribution of Invasive Carp - Silver Carp (Hypophthalmichthys molitrix), Bighead Carp (Hypophthalmichthys nobilis), and Black Carp (Mylopharyngodon piceus) in US Army Corps of Engineers (USACE) managed waters. Invasive carp were introduced into the US nearly half a century ago. As they spread across the US, they compete with and consume native species and Silver Carp jumping behavior reduces recreational use. The USACE is responsible for management of waterbodies at more than 440 projects. Information on these projects including the presence of Invasive Carp is reported in the USACE Operations and Maintenance Business Information Link (OMBIL) database. To supplement the Invasive Carp information from OMBIL, 47 online ichthyology collection and observation databases were searched; 18 had information on Invasive Carp locations. Combining the collection, observation and OMBIL reporting information, 82 USACE projects in 19 districts in 6 of 8 divisions have Silver/Bighead Carp and 19 projects in 9 districts and 3 divisions have Black Carp. Understanding the distribution of Invasive Carp is important to enable managers to be pro-active: planning control efforts, posting informational signs, instituting live bait restrictions, and thus reducing the chances of species introduction or limiting species impact.

30 Aug 2021

Variation in Inhibitor Effects on qPCR Assays and implications for eDNA Surveys

Abstract: Aquatic environmental DNA (eDNA) surveys are sometimes impacted by polymerase chain reaction (PCR) inhibitors. We tested varying concentrations of different inhibitors (humic, phytic, and tannic acids; crude leaf extracts) for impacts on quantitative PCR (qPCR) assays designed for eDNA surveys of bighead and silver carp (Hypophthalmichthys nobilis and Hypophthalmichthys molitrix). We also tested for inhibition by high concentrations of exogenous DNA, hypothesizing that DNA from increasingly closely related species would be increasingly inhibitory. All tested inhibitors impacted qPCR, though only at very high concentrations — likely a function, in part, of having used an inhibitor-resistant qPCR solution. Closer phylogenetic relatedness resulted in inhibition at lower exogenous DNA concentrations, but not at relatively close phylogenetic scales. Inhibition was also influenced by the qPCR reporter dye used. Importantly, different qPCR assays responded differently to the same inhibitor concentrations. Implications of these results are that the inclusion of more than one assay for the same target taxa in an eDNA survey may be an important countermeasure against false negatives and that internal positive controls may not, in the absence of efforts to maximize inhibition compatibility, provide useful information about the inhibition of an eDNA assay.