1. Love, J., B. Williams, T Groves, R. Williams, and M. Groves. 2025. Movement and habitat use by invasive blue catfish Ictalurus furcatus (Valenciennes 1840) in a tidal freshwater river (Maryland, USA). Estuaries and Coasts 48 (5): 123.
1. Blue catfish Ictalurus furcatus (Valenciennes, 1840) has invaded all major rivers of the Chesapeake Bay watershed making it one of the most widespread invasive fishes in the mid-Atlantic region. The objectives of this study were to disclose key aspects of blue catfish movement and habitat use in a tidally influenced river, Patuxent River (Maryland), and to present management suggestions based on observed ecological data. Thirty-eight blue catfish adults (mean total length = 672 mm, SE = 15; mean mass = 3855 g, SE = 331) tagged with dual acoustic-radio DART tags in November 2020, and for 16 of them, we analyzed actively tracked geolocations between December 2, 2020, and February 26, 2021, to identify hot spots during winter using ArcGIS (Version 10.2, ESRI). Two hot spots occurred in the upstream portion of the survey area, in locations where in situ salinity averaged 0.19 (SE = 0.03) and water depth averaged 3.0 m (0.3 to 7.6 m). We compared these habitat conditions with those for 19 actively tracked geolocations for 11 fish in June 2021. We observed a more widespread distribution in June, but fish generally occurred in freshwater (average = 0.25, SE = 0.14) that was less than 4-m depth, similar to winter observations. Approximately two-thirds of all fish (or 67%) had moved less than 100 m ­day−1. Three blue catfish with the greatest movement rates in the dataset had been tracked in June, when distance traveled per day averaged 797 m ­day−1 (SE = 479; range: 1 m ­day−1 and 2938 m ­day−1). Movement downstream, closer to the river mouth and into the mesohaline habitat (salinity > 5), had occurred by June but was not common. Our observations suggest river-wide actions for indiscriminate harvest of blue catfish in freshwater could overfish or reduce abundance of size class(es) of the core population, though immigration from adjacent riverine populations might cause rescue effects or lessen potential biomass reductions.
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2. Iwanowicz, D. D., Schill, W. B., Sanders, L. R., Groves, T., & Groves, M. C. (2019). Establishing molecular methods to quantitatively profile gastric diet items of fish-application to the invasive blue catfish (Ictalurus furcatus). Open-File Report-US Geological Survey, (2019-1021).
   1. Understanding the diet of invasive species helps researchers to more accurately assess the health, survivorship, growth, and stability of an invasive fish species, as well as their effects on native populations. Techniques capable of identifying multiple prey species from fish stomach contents have been developed. In this study, a multi-locus metabarcoding approach was used to identify fish and invertebrate prey in stomach samples of Ictalurus furcatus (blue catfish), which were collected from two sites on the Mattawomen Creek and Nanjemoy Creek in Maryland. The mitochondrial 12S (mt12S) and mitochondrial 16S (mt16S) gene regions were sequenced and compared. First, a mock sample for each gene region was created with the pooled polymerase chain reaction product of known fish species, and quantities of the sample were used to determine efficacy of the amplicon. Results varied between gene regions analyzed. Then, when using the mt12S primers, next-generation sequencing determined that nine fish species were found at levels greater than 1 percent of the diet of blue catfish. The most common species were Perca flavescens (yellow perch) and Cyprinus carpio (common carp). The mt16S gene region analyses found 10 fish species at greater than 1 percent of the diet, which primarily included Orconectes limosus (spinycheek crayfish), Alosa pseudoharengus (alewife), and yellow perch. Partially digested eggs were identified using next-generation sequencing of yellow perch in two of the stomach samples, and a TaqMan® quantitative polymerase chain reaction (qPCR) assay was developed to more economically identify egg species in the future. The yellow-perch-specific TaqMan® qPCR assay was tested using primers that were developed to detect a 154-base-pair amplicon in the mitochondrial control region. Consumption of yellow perch eggs indicates that blue catfish could potentially negatively affect young-of-year recruitment of this native sportfish. Analyses of two gene regions helped confirm the major prey of the fish sampled and allowed identification of fish species as prey that were not included in a database for the two gene regions. We concluded that the mitochondrial ribosomal-marker-based next-generation sequencing method is useful in determining the prey of fish species.
   
   
3. Aguilar, R., Ogburn, M. B., Driskell, A. C., Weigt, L. A., Groves, M. C., & Hines, A. H. (2017). Gutsy genetics: identification of digested piscine prey items in the stomach contents of sympatric native and introduced warmwater catfishes via DNA barcoding. Environmental Biology of Fishes, 100, 325-336.
1. A major focus of ecology is understanding trophic relationships and energy flows in natural systems, associated food web dynamics and changes in food webs due to introduced species. Predator-prey interactions are often assessed by examining stomach contents. However, partially digested remains may be difficult to accurately identify by traditional visual analysis. Here we evaluate the effectiveness of DNA barcoding to identify digested piscine prey remains in invasive Blue Catfish Ictalurus furcatus, non-native, but established Channel Catfish Ictalurus punctatus and native White Catfish Ameiurus catus from Chesapeake Bay, USA. Stomach contents were examined and piscine prey items were scored as lightly digested, moderately digested or severely digested. A 652 base pair region of the cytochrome c oxidase subunit I (COI-5P) mitochondrial DNA gene was sequenced for each prey item. Edited barcode sequences were compared to locally-caught and validated reference sequences in BOLD (Barcode of Life Database). A large majority of prey items were sufficiently digested to limit morphological identification (9.4 % to species and an additional 12.1 % to family). However, overall barcoding success was high (90.3 %) with little difference among the digestion classifications. Combining morphological and genetic identifications, we classified 91.6 % of fish prey items to species. Twenty-three fish species were identified, including species undergoing active restoration efforts (e.g., Alosa spp.) and commercially important species, e.g., Striped Bass Morone saxatilis, White Perch Morone americana, American Eel Anguilla rostrata and Menhaden Brevoortia tyrannus. We found DNA barcoding highly successful at identifying all but the most heavily degraded prey items and to be an efficient and effective method for obtaining diet information to strengthen the resolution of trophic analyses including diet comparisons among sympatric native and non-native predators.
   
   
4. Fabrizio, M. C., Tuckey, T. D., Latour, R. J., White, G. C., Norris, A. J., & Groves, M. (2016). Population Size and Survival Rates of Blue Catfish in Chesapeake Bay Tributaries.
1. This report comprises two studies conducted from 2012 to 2015 to estimate population size, survival rates, and movements of invasive blue catfish in Chesapeake Bay tributaries. The first study of population-size and survival was conducted in the James River, VA (Population Size and Survival Rates of Invasive Blue Catfish in Tidal Waters of the James River Subestuary). The second study on movement and survival of blue catfish was conducted in the Potomac River, the natural boundary between Maryland and Virginia (Movement Patterns and Survival Rate of Blue Catfish in a Non-Native Habitat Estimated with a Tagging Study). The Executive Summary of this report provides a synopsis of both studies.
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5. Schloesser, R. W., Fabrizio, M. C., Latour, R. J., Garman, G. C., Greenlee, B., Groves, M., & Gartland, J. (2011). Ecological role of blue catfish in Chesapeake Bay communities and implications for management.
1. Rapid increase in abundance and expanded distribution of introduced blue catfish Ictalurus furcatus populations in the Chesapeake Bay watershed have raised regional management concerns. This study uses information from multiple surveys to examine expansion of blue catfish populations and document their role in tidal river communities. Originally stocked in the James, York, and Rappahannock River systems for development of commercial and recreational fisheries, blue catfish have now been documented in adjacent rivers and have expanded their within-river distribution to oligo- and mesohaline environments. Range expansions coincided with periods of peak abundance in 1996 and 2003 and with the concurrent decline in abundance of native white catfish I. catus. Blue catfish in these systems use a diverse prey base; various amphipod species typically dominate the diet of smaller individuals ([FL]), and fishes are common prey for larger blue catfish (>300 mm FL). Recent studies based on stable isotope analyses suggest that adult blue catfish in these systems are apex predators that feed extensively on important fishery resources, including anadromous shads and herrings Alosa spp. and juvenile Atlantic menhaden Brevoortia tyrannus. Minimizing effects on Chesapeake Bay communities by controlling high densities of blue catfish populations is a primary goal of management, but conflicting demands of the commercial and recreational sectors must be resolved. Further, low market demand and human consumption concerns associated with purported accumulation of contaminants in blue catfish pose additional complications for regulating these fisheries.​
   

Individuals are able to commercially harvest and sell blue catfish if they are licensed by the Maryland Department of Natural Resources. Commercial license types include: Unlimited Tidal Fish (TFL), Unlimited Finfish (FIN), Hook and Line Finfish (HLI), and Blue and Flathead Catfish Finfish Trotline License.

Figure 1: Over the past years, commercial harvest of blue catfish has increased.
The estimated dockside value for blue catfish has also increased
from under $2.00 in 2015 to about $14.00 in 2025 .