Brent Knights
Biography
My work focuses on the ecology, behavior and impacts of invasive carp in the Mississippi River basin to inform control efforts. We employ a variety of techniques for these studies including acoustic and satellite telemetry, otolith and fin ray chemistry, diet and condition metrics, and population dynamics. Current work is investigating dam passage of Asian carp at strategic high-head dams to inform the deployment of deterrents in locks and lock approaches of these dams. We are also investigating the timing and factors that influence, off-channel area use by Asian carp to help direct removal by contracted and commercial fishers.
Science and Products
Database and web application for invasive carp telemetry data (FishTracks)
Four types of invasive carp fish species, are currently found in the United States: black, grass, silver, and bighead carps. These species are fast growing, prolific feeders that out-compete native fish species and drastically alter the natural ecosystems they invade. To prevent the spread of invasive carp into the Great Lakes, the multi-agency Asian Carp...
Timing and hydrological conditions associated with bigheaded carp movement past navigation dams on the upper Mississippi river
As the range of non-native bigheaded carps (Hypophthalmichthys spp.) continues to expand throughout river systems of the United States, managers are tasked with preventing or slowing the spread of these invasive species. Main stem navigation dams on the upper Mississippi River, long considered a deterrent to fish migration, may slow or...
Vallazza, Jon; Mosel, Kayle J.; Reineke, David M.; Runstrom, Ann L.; Larson, James H.; Knights, Brent C. Mercury and water level management in lakes of northern Minnesota
Water level (WL) fluctuations substantially alter the fauna, flora, and microbial community of nearshore aquatic ecosystems. Water level management therefore has the potential to strongly influence a wide variety of ecosystem processes. Many northern temperate lake food webs experience substantial methylmercury contamination, which is partially...
Larson, James H.; Maki, Ryan P.; Christensen, Victoria; Hlavacek, Enrika; Sandheinrich, Mark B.; LeDuc, Jaime F.; Kissane, Claire; Knights, Brent C. Lock operations influence upstream passages of invasive and native fishes at a Mississippi River high-head dam
Asian carps continue to expand their range in North America, necessitating efforts to limit the spread and establishment of reproducing populations. Mississippi River Lock and Dam 19 is a high-head dam that represents a population ‘pinch-point’ as passage through the lock chamber is the only means by which fishes can complete upstream movement. As...
Fritts, Andrea; Knights, Brent C.; Stanton, J.C.; Milde, Amanda S.; Vallazza, Jon; Brey, Marybeth; Tripp, Sara J.; Devine, Thomas E.; Sleeper, Wesley; Lamer, James T.; Mosel, Kyle J. USGS Illinois River monitoring and evaluation
Asian carp monitoring and contract removal will continue throughout the Upper Illinois Waterway system as needed for adaptive management to mitigate, control, and contain Asian carp. Compiling data from monitoring and removal efforts into a centralized database (Illinois River Catch Database application) facilitates data standardization, quality,...
Harrison, Travis J.; Hop, Kevin D.; Hlavacek, Enrika; Knights, Brent C. Influence of a high-head dam as a dispersal barrier to fish community structure of the Upper Mississippi River
In river systems, high‐head dams may increase the distance‐decay of fish community similarity by creating nearly impermeable dispersal barriers to certain species from upstream reaches. Substantial evidence suggests that migratory species are impacted by dams, and most previous studies in stream/river networks have focused on small streams and...
Anderson, Rebekah L.; Anderson, Cory A.; Larson, James H.; Knights, Brent C.; Vallazza, Jon; Jenkins, Sean E.; Lamer, James T. Estimating the degree to which distance and temperature differences drive changes in fish community composition over time in the upper Mississippi River
Similarity in community composition declines as distance between locations increases, a phenomenon that has been observed in a wide variety of freshwater, marine and terrestrial ecosystems. One driver of the distance-similarity relationship is the presence of environmental gradients that alter the suitability of sites for particular species....
Larson, James H.; Vallazza, Jon; Knights, Brent C. Development of a quantitative PCR method for screening ichthyoplankton samples for bigheaded carps
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...
Fritts, Andrea; Knights, Brent C.; Larson, James H.; Amberg, Jon J.; Merkes, Christopher M.; Tajjioui, Tariq; Butler, Steven E.; Diana, Matthew J.; Wahl, David H.; Weber, Michael J.; Waters, John D. Evaluating potential effects of bigheaded carps on fatty acid profiles of multiple trophic levels in large rivers of the Midwest, USA
Recent work indicates that the establishment of bigheaded carps (Hypophthalmichthys spp.) in the United States has led to a reduction in condition of native planktivores and may detrimentally affect other trophic levels by altering the base of aquatic food webs. We used fatty acids to evaluate potential effects of bigheaded carps on taxa from...
Fritts, Andrea; Knights, Brent C.; LaFrancois, Toben; Vallazza, Jon; Bartsch, Lynn A.; Bartsch, Michelle R.; Richardson, William B.; Bailey, Sean; Kreiling, Rebecca; Karns, Byron Stable isotope comparison between mantle and foot tissues of two freshwater unionids: Implications for food web studies
Unionid mussels are a key taxon for stable isotope studies of aquatic food webs, often serving as the primary integrator of the pelagic baseline. Past isotope studies with mussels have commonly used either foot tissue or mantle tissue, but no study has yet to quantify the relation of both carbon and nitrogen isotopes between these two tissue...
LaFrancois, Toben; Fritts, Andrea; Knights, Brent C.; Karns, Byron Spatial and temporal variance in fatty acid and stable isotope signatures across trophic levels in large river systems
Fatty acid and stable isotope signatures allow researchers to better understand food webs, food sources, and trophic relationships. Research in marine and lentic systems has indicated that the variance of these biomarkers can exhibit substantial differences across spatial and temporal scales, but this type of analysis has not been completed for...
Fritts, Andrea; Knights, Brent C.; Lafrancois, Toben D.; Bartsch, Lynn A.; Vallazza, Jon; Bartsch, Michelle R.; Richardson, William B.; Karns, Byron N.; Bailey, Sean; Kreiling, Rebecca Using pharyngeal teeth and chewing pads to estimate juvenile Silver Carp total length in the La Grange Reach, Illinois River
The Silver Carp Hypophthalmichthys molitrix is an invasive species in the Mississippi River basin; an understanding of their vulnerability to predation as juveniles may inform control by native predators and predator enhancement (e.g., stocking). Digestion of Silver Carp prey recovered from diets makes it difficult to determine the size‐...
Lampo, Eli G.; Knights, Brent C.; Vallazza, Jon; Anderson, Cory A.; Rechkemmer, Will T.; Solomon, Levi E.; Casper, Andrew F.; Pendleton, Richard M.; Lamer, James T. Evidence of Asian carp spawning upstream of a key choke point in the Mississippi River
Bighead Carp Hypophthalmichthys nobilis, Silver Carp H. molitrix, and Grass Carp Ctenopharyngodon idella(collectively termed “Asian carp”) were introduced into North America during the 1960s and 1970s and have become established in the lower Mississippi River basin. Previously published evidence for spawning of these species in the...
Larson, James H.; Knights, Brent C.; McCalla, S. Grace; Monroe, Emy; Tuttle-Lau, Maren T.; Chapman, Duane C.; George, Amy E.; Vallazza, Jon; Amberg, Jon J.