Expansion of a northern snakehead population in the Potomac River system

A population of northern snakeheads Channa argus was documented in the Potomac River system in 2004. The expansion of this population was monitored from 2004 to 2006. Boat electrofishing mean catch per unit effort increased significantly each year from 0.2 fish/h in 2004 to 6.1 fish/h in 2006 (analysis of variance [ANOVA]: P = 0.01). Reported angler catches (N = 24) during 2006 equaled the combined total of the two previous years. Mean total length (TL) and weight (W) in 2006 were 475 turn (SD = 146) and 1,381 g (SD = 1,009), respectively, and maximum size increased each year. The weight-length relationship for all years combined was log(e)W = -5.21 + 3.07 . log(e)TL (r(2) = 0.996, n = 348). Natural reproduction was confirmed by the location of a nest, and eight year-classes were estimated based on otolith interpretations. Total annual mortality was estimated to be 38%. Trends in female gonadosomatic index and otolith daily ring counts of age-0 fish suggested protracted or repeat spawning from May to September. Females were fecund, carrying an average of 40,786 eggs. Collection patterns suggested that this population of northern snakeheads originated from Dogue Creek. Seventeen food items, including 15 fish species, were identified from stomach contents. The banded killifish Fundulus diaphanus was the dominant food item. Bluegills Lepomis macrochirus, pumpkinseeds L. gibbosus, and white perch Morone americana were also commonly consumed. Although population size increased, known range did not appear to increase or increased at a slower rate. Increases in angler catch during 2006 at the northern and southern termini of the existing distribution suggest that northern snakehead range expansion is imminent.