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​Submitted and Published Studies

  • Newhard, J.J. and J.W. Love. Comparison of fish community within the Blackwater River watershed before and after establishment of Northern Snakehead Channa argus. U.S. Fish and Wildlife Service, Maryland Fish and Wildlife Conservation Office, Annapolis. Download PDF.

    • ​Northern Snakehead is an invasive species initially discovered in the Potomac River in 2004, but has since spread to most major river systems of the Chesapeake Bay. In 2012, Northern Snakehead was first reported from the Blackwater River drainage on the eastern shore of Maryland. Fish community surveys were conducted in Blackwater River and Little Blackwater River in 2006 and 2007, before the establishment of Northern Snakehead there. Because of minimal habitat changes owed to protection by Blackwater National Wildlife Refuge, this dataset enabled us to document changes in the fish community that could be attributed to the establishment of Northern Snakehead. We replicated the 2006 and 2007 surveys (pre-Snakehead) over a year from 2018-2019 (post-Snakehead). Over all sampling periods we caught 35 species (32 fish species and 3 invertebrate species) totaling over 50,000 individuals. Of 21 species that were captured both pre- and post-Snakehead, 17 declined in relative abundance with percent reductions ranging from 30%-97%. We found that five of six sites had significantly different fish communities when comparing pre-Snakehead and post-Snakehead surveys. The main difference in fish communities was a reduction in overall biomass of most fish. Species dominance during the post-Snakehead period was significantly higher for both Blackwater and Little Blackwater River. Pre-Snakehead surveys were more evenly distributed and dominated by White Perch, Black Crappie, and Brown Bullhead, while post-Snakehead surveys were less even and dominated by Common Carp and Gizzard Shad. This study is the first to document major shifts in a fish community following the establishment of Northern Snakehead. Further investigation into ongoing fish community changes and continued vigilance in minimizing spread and population growth of Northern Snakehead is warranted.
  • Choi, J. and S. Kim. 2021. Effect of the human utilization of northern snakehead (Channa argus Cantor, 1842) on the settlement of exotic fish and cladoceran community structure. Sustainability 5:1-18.

    • Empirical studies suggest that changes in the density of top predators, such as carnivorous fish, in freshwater food webs, strongly affect not only fish communities but also various primary and secondary consumers. Based on these findings, we explored how differences in the utilization of carnivorous fish (i.e., Northern Snakehead, Channa argus) by humans affected the fish and cladoceran community structure as well as the settlement of exotic fish species (i.e., Lepomis macrochirus and Micropterus salmoides) in 30 wetlands located in the upper and lower reaches of the Nakdong River. Our results show that in the mid–lower reaches of the Nakdong River, the density of C. argus was low, while high densities of L. macrochirus and M. salmoides were observed. Exotic fish species are frequently consumed by C. argus, leading to a low density of L. macrochirus and M. salmoides in the upper reaches, which supported a high density of C. argus. However, in the mid–lower reaches, the density of L. macrochirus was high because of the frequent collection of C. argus by fishing activities. The dominance of L. macrochirus significantly changed the structure of cladoceran communities. L. macrochirus mainly feeds on pelagic species, increasing the density of epiphytic species in the mid–lower reaches. The continued utilization of C. argus by humans induced a stable settlement of exotic fish species and strongly affected the community structures of primary consumers in the 30 wetlands. The frequency of C. argus collection has to be reduced to secure biodiversity in the mid–lower reaches of the Nakdong River, which will reduce the proportion of exotic fish species and increase the conservation of native fish.
  • ​ Love, J.W. and J.J. Newhard. 2021. Using published information to predict consumption by Northern Snakehead in Maryland. Transactions of the American Fisheries Society. ​

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  • Bressman, N.R., J.W. Love, T. King, C. Horne, and M.A. Ashley-Ross. 2019. Emersion and terrestrial locomotion of the northern snakehead (Channa argus) on multiple substrates.  Integrative Organismal Biology. Integrative Organismal Biology​.

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  • Love, J.W. and P. Genovese. Fishing for an Invasive:  Maryland's Toolbox for Managing northern snakehead Fisheries. First International Snakehead Symposium, American Fisheries Society, Alexandria, Virginia, July 17 – 19, 2018. 

    • ​Northern snakehead (Channa argus) was found in ponds of Maryland in 2002 and now occupies most major rivers of Chesapeake Bay watershed. The relatively rapid expansion is owed to both natural dispersal and illegal introductions by humans.The Maryland Department of Natural Resources worked with other agencies and the general public to develop tools that managed the expanding fishery for northern snakehead. These tools included:  1) regulation; 2) a Department of Natural Resources-to-public information network; 3) an agency-to-agency information network; 4) social media initiatives to promote recreational harvest; 5) fishing award initiatives to incentivize recreational harvest; 6) seafood marketing initiatives to support commercial harvest; and 7) tournament initiatives to promote harvest.  Of these, the most likely ones lowering biomass and preventing spread of the species were regulation, the Department of Natural Resources-to-public information network, initiatives involving fishing awards, seafood marketing, and tournaments. Unregulated harvest and prohibited live possession collectively benefit the general public because they afford wide fisher freedom without rewarding unauthorized introductions with expensive conservation management.
  • Love, J.W. and J.J. Newhard. 2018. Expansion of northern snakehead in the Chesapeake Bay watershed. Transactions of the American Fisheries Society 147:342-349.
    • Northern snakehead Channa argus, a nonnative species to North America, was discovered in 2004 in tidal freshwater of the Potomac River, the second largest drainage of the Chesapeake Bay watershed. Since then northern snakehead has expanded its range throughout much of Maryland’s portion of the Chesapeake Bay watershed. We estimated that the species has spread beyond its introduced range at a rate of about 2.7 subwatersheds per year. If that rate is maintained, the species will have spread its range throughout the entire watershed in 52 years. This rate has been consistent over time except for short periods of heightened expansion that followed an introduction of snakeheads into Delaware waters and in years with greater levels of spring precipitation. The expansion by northern snakehead is more widespread than that of other invasive fishes of Maryland’s portion of the Chesapeake Bay, which include Blue Catfish (Ictalurus furcatus) and Flathead Catfish (Pylodictus olivaris). Attempts to control the spread of the species have included public education, incentives for harvest, agency surveys, and law enforcement. The rapid natural and human-aided expansion of northern snakehead throughout the country’s largest estuary highlights the importance of laws that prevent live possession and importation of this species. 
  • Iwanowicz et al. 2016. Mycobacterial infection in northern snakehead (Channa argus) from the Potomac River catchment. Journal of Fish Diseases 39:771-775.
    • ​The northern snakehead (Channa argus) is a non-native predatory fish that has become established regionally in some temperate freshwater habitats within the United States. Over the past decade, northern snakehead populations have developed within aquatic ecosystems throughout the eastern USA, including the Potomac River system within Virginia, Maryland and Washington, D.C. Since this species was initially observed in this region in 2002, the population has expanded considerably (Odenkirk and Owens 2007). In the Chesapeake Bay watershed, populations of northern snakehead exist in the lower Potomac River and Rappahannock Rivers on the Western shore of the Bay, and these fish have also been found in middle or upper reaches of river systems on the Eastern shore of the Bay, including the Nanticoke and Wicomico Rivers among others. Over the past several years, many aspects of northern snakehead life history in the Potomac River have been described, including range and dispersal patterns, microhabitat selection and diet (Lapointe, Thorson and Angermeier 2010; Saylor, Lapointe and Angermeier 2012; Lapointe, Odenkirk and Angermeier 2013). However, comparatively little is known about their health status including susceptibility to parasitism and disease and their capacity to serve as reservoirs of disease for native wildlife. Although considered hardy by fisheries biologists, snakehead fish have demonstrated susceptibility to a number of described piscine diseases within their native range and habitat in Asia. Reported pathogens of significance in snakehead species in Asia include snakehead rhabdovirus (Lio-Po et al. 2000), aeromonad bacteria (Zheng, Cao and Yang 2012), Nocardia (Wang et al. 2007) and Mycobacterium spp. (Chinabut, Limsuwan and Chantatchakool 1990). Mycobacterial isolates recovered from another snakehead species (Channa striata) in the previous studies have included M.marinum and M. fortuitum, as identified through molecular-based diagnostics (Puttinaowarat et al. 2002). We have conducted health screenings of northern snakehead from the Potomac River system over the past several years and have detected few associated pathogens. Typical observations have largely consisted of incidental identification of parasitism with protozoal, monogenean or trematode organisms (unpublished data). We have also identified largemouth bass virus (LMBV) in clinically normal northern snakehead collected from the Potomac River (Iwanowicz et al. 2013). Continued research concerning these and other pathogens of this introduced species is important to fully understand the potential impacts of these fish on indigenous wildlife and aquatic ecosystems.
  • Odenkirk, J. and M. Isel. 2016. Trends in abundance of northern snakeheads in Virginia tributaries of the Potomac River. Transactions of the American Fisheries Society 145:687-692.
    • ​A population of nonnative northern snakeheads (Channa argus) was documented in the Potomac River system during 2004. We estimated relative abundance (fish/h of boat electrofishing) for up to 12 years in four Virginia creeks within and downstream of the original area of colonization. Population estimates were also calculated for adult Northern snakeheads in Little Hunting Creek (one of the four study creeks). Relative abundance increased dramatically after colonization, but trends suggest that increases in abundance may have slowed. Population estimates for Little Hunting Creek (12–22 fish/ha) declined each year from 2013 to 2015, supporting the assertion that Northern snakehead density increases have slowed or that density has stabilized in some creeks. 
  • Wegleitner, B.J., A. Tucker, W.L. Chadderton, and A.R. Mahon. 2016. Identifying the genetic structure of introduced populations of northern snakehead (Channa argus) in Eastern USA. Aquatic Invasions 11:199-208.
    • ​​With new introductions of invasive species occurring at an alarming rate, resource managers must be able to rapidly determine the source of introduction if there is to be a chance of preventing further spread or future invasions. The first North American populations of reproducing northern snakehead (Channa argus) were detected in Maryland in 2002 and have continued to spread into new watersheds. We used four microsatellite markers to describe genetic characteristics of four established C.argus populations in Eastern U.S.A., a collection of samples of unknown origin from a Chinatown market in Manhattan, New York, and of a C. argus population of uncertain status in the Upper Hudson River. We aimed to determine the probable source of the introduction of C. argus to the Upper Hudson River basin and to clarify the genetic structure of C. argus populations in northeast U.S.A., overall. Results from population structure analysis infer two distinct genetic groups among the specimens sampled. Measures of genetic distance suggest the C. argus population in the Upper Hudson is most similar to the population in the Lower Hudson near Queens, NY. Results conclude that the Potomac River and Chesapeake Bay basins represent one genetic population, which suggests that introductions to the Chesapeake Bay were sourced from the Potomac population and/or that the Bay does not represent a barrier to C. argus dispersal. Overall, our analysis provides evidence of multiple introductions into U.S. waters and human mediated secondary spread from these founding populations.​
  • Love, J.W., B. Greenfield, and J.J. Newhard. 2015. A Geospatial Approach for Estimating Suitable Habitat and Population Size of the Invasive Northern Snakehead. Journal of Fish and Wildlife Management. 6:145-157.
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    • Northern snakehead Channa argus, an invasive predatory fish species from Asia, may continue to establish itself throughout temperate areas of the eastern United States, particularly in shallow vegetated habitats of ponds and streams. The species was first collected in the Potomac River in 2004 and has become successfully established in several major rivers within the Chesapeake Bay watershed. The objectives of this work were to develop habitat suitability criteria using a novel methodology that combines geographic information systems technology and fish surveys to estimate population sizes. A combination of catch data and reported or empirically derived habitat relationships were used to analyze seasonal distributions (March–October) in two tidal freshwater tributaries of the Potomac River: Nanjemoy Creek (2013) and Chopawamsic Creek (2010–2013). Adults were collected in relatively deeper sections of the streams (average depth 0.7–1.0 m) with a low cover of submerged aquatic vegetation (0–21% of site). Using additional distributional data, we identified suitability criteria as: 1) edges of submerged aquatic vegetation that included 5 m of vegetation and 5 m of adjacent open water; 2) less than 30% of mid-channel distance from shore, which may or may not include submerged aquatic vegetation; and 3) the upper 15% of the tidal freshwater stream. An adult population estimate derived from a suitable area in Pomonkey Creek (a tributary of the Potomac River) and estimated densities from Nanjemoy Creek and Chopawamsic Creek (i.e., three adults/ha) was not different from that expected using electrofishing surveys. Assuming approximately 7,093 ha of suitable habitat and three adults/ha, the number of adults was predicted to be 21,279 for 44 major tidal freshwater tributaries of the Potomac River. This is our first estimate of population size of northern snakehead for any river of the Chesapeake Bay watershed and its accuracy will undoubtedly improve as additional studies report variation in density for other tributaries. Because of the species’ ability to establish itself in temperate climates, it is important to engage the public to prevent additional releases of northern snakehead, especially to vulnerable habitats.