Expansion of Northern Snakehead in the Chesapeake Bay Watershed

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.