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 Asian carp telemetry data (FishTracks)
Four types of Asian carp, an invasive 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 Asian carp into the Great Lakes, the multi-agency Asian...
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. USGS Integration of New Science and Technology, Appendix A
This product summarizes the USGS plans for integration of new science and technology into Asian Carp control efforts for 2017. This includes the 1) implementation and evaluation of new tactics and behavioral information for monitoring, surveillance, control and containment; 2) understanding behavior and reproduction of Asian carp in established...
Brey, Marybeth; Knights, Brent C.; Cupp, Aaron R.; Amberg, Jon J.; Chapman, Duane C.; Calfee, Robin D.; Duncker, James J. Mercury and water level fluctuations in lakes of northern Minnesota
Large lake ecosystems support a variety of ecosystem services in surrounding communities, including recreational and commercial fishing. However, many northern temperate fisheries are contaminated by mercury. Annual variation in mercury accumulation in fish has previously been linked to water level (WL) fluctuations, opening the possibility of...
Larson, James H.; Maki, Ryan P.; Christensen, Victoria G.; Sandheinrich, Mark B.; LeDuc, Jaime F.; Kissane, Claire; Knights, Brent C. Spatial and temporal dynamics of suspended particle characteristics and composition in Navigation Pool 19 of the Upper Mississippi River
Suspended particles are an essential component of large rivers influencing channel geomorphology, biogeochemical cycling of nutrients, and food web resources. The Upper Mississippi River is a large floodplain river that exhibits pronounced spatiotemporal variation in environmental conditions and biota, providing an ideal environment for...
Milde, Amanda S.; Richardson, William B.; Strauss, Eric A.; Larson, James H.; Vallazza, Jon; Knights, Brent C. Do water level fluctuations influence production of walleye and yellow perch young-of-the-year in large northern lakes?
Many ecological processes depend on the regular rise and fall of water levels (WLs), and artificial manipulations to WL regimes can impair important ecosystem services. Previous research has suggested that differences in WL between late summer and early spring may alter the suitability of shoals used by Walleyes Sander vitreus for spawning. Other...
Larson, James H.; Staples, David F.; Maki, Ryan P.; Vallazza, Jon M.; Knights, Brent C.; Peterson, Kevin E.