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Submitted and Published Studies (2016 – 2018, selected)
Love, J.W. and P. Genovese. In Press. 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.
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
and Flathead Catfish
. 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
from the Potomac River catchment. Journal of Fish Diseases 39:771-775.
The northern snakehead
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
in the previous studies have included
, 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
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
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
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
populations in Eastern U.S.A., a collection of samples of unknown origin from a Chinatown market in Manhattan, New York, and of a
population of uncertain status in the Upper Hudson River. We aimed to determine the probable source of the introduction of
to the Upper Hudson River basin and to clarify the genetic structure of
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
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
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.
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