Management Implications from a Stock-Recruit Model for Northern Snakehead in Virginia Waters of the Tidal Potomac River
Michael H. Hoff and John S. Odenkirk
Abstract.—The U.S. Congress directed the U.S. Fish and Wildlife Service (USFWS) to identify, contain, and eradicate Northern Snakehead Channa argus in the United States. Later, the Mississippi River Basin Panel on Aquatic Nuisance Species requested that the Aquatic Nuisance Species Task Force develop a management plan to include additional snakehead species (Channidae) that are, or have the potential to become, invasive in United States waters. Objectives of the snakehead management and control plan, which was developed by USFWS and collaborators, include developing long-term adaptive management and control methods. We developed a Ricker stock-recruit model using Northern Snakehead population data collected in four northern Virginia tidal tributaries during 2009–2015 to inform management and control efforts. The resulting model functional relationship explained 93% of recruitment variability using adult stock size (mean electrofishing catch/h [CPUE] of adults) and mean river flow during May. Recruitment was quantified using boat electrofishing CPUE of age-2 fish lagged for two years, because age-0 and even age-1 fish did not appear to be fully recruited to the gear. Seventy-six percent of recruitment variation was explained by adult abundance, while an additional 17% was explained by mean river flow during May (inverse relationship). Model predictions indicated management efforts to reduce adult stock size, from the optimum of 2–4 fish/h to <0.5 fish/h, should be the most effective tool to reduce recruitment and resulting adult abundance over the long term. That level of adult abundance (approximately 12% of the mean during 2009–2015) should be the target maximum for Northern Snakehead control efforts in the study areas.