Doctor of Philosophy (Ph.D.)
Virginia Institute of Marine Science
Jaap van der Meer
Blue catfish Ictalurus furcatus is an invasive species of great concern in coastal habitats throughout the eastern United States, inclulding the Chesapeake Bay and its tributaries. In this dissertation, I use field surveys, laboratory experiments and quantitative modeling to provide insights into several aspects of blue catfish biology at the individual level. In chapter 1, I characterize and compare patterns in growth and body condition in blue catfish populations in the James and York river subestuaries during two stages of invasion. Both the mean growth rate and mean body condition of blue catfish declined in the recent period in response to increases in population abundance. In chapter 2, I uncover life-history plasticity in the reproductive biology of the species: blue catfish in the James River mature at a smaller mean size but provision a greater amount of energy into reproduction than York River fish, which exhibit lower densities than James River fish. In chapter 3, I assess the food demands of blue catfish in a laboratory experiment. I demonstrate that blue catfish have low metabolic demands, as expected for a relatively sedentary benthic fish. Importantly, blue catfish had high survival and significant growth at food levels as low as one third of the maximum, suggesting that the species has a high tolerance of starvation and that individuals may be able to invade and establish in low food habitats in coastal waters. In chapters 4 and 5, I report the results of two laboratory experiments studying the effects of increased salinity on survival, growth and body condition of blue catfish. Blue catfish, typically considered a freshwater species, was found to have a higher salinity tolerance (72-hour LC50 = 15.7 psu) than many freshwater fishes, suggesting the potential of the species to expand its range into most subestuaries of the Chesapeake Bay particularly during wet seasons. Habitats with salinities around 4 psu seemed particularly suitable for blue catfish as growth and body condition were maximized at this salinity despite the lower mean ingestion rates than fish maintained in freshwater. Finally, in chapter 6, I parameterize a full life-cycle bioenergetics model for female blue catfish using data from the literature and from the other chapters of this dissertation. The model supported the implications from other chapters that blue catfish have low maintenance costs, relatively high resistance to starvation and a plastic ability to fuel reproduction even in environments with low food availability. The model, together with results from other chapters, also opened up avenues for further research on characterization of the energetic basis for the observed phenotypic plasticity, identification of physiological modes of action by which salinity might limit survival, growth and reproduction of blue catfish, and ultimately the identification of coastal habitats that might support self-sustaining populations of this invasive fish. This research highlights the need for management efforts to control blue catfish populations in subestuaries where they are already established and to limit the range expansion into novel habitats. Towards this end, this dissertation provides important information on vital rates of blue catfish needed for population models that can be used for management strategy evaluations.
© The Author
Nepal, Vaskar, "A Mechanistic Understanding of Range Expansion of Invasive Blue Catfish in the Chesapeake Bay Region" (2020). Dissertations, Theses, and Masters Projects. William & Mary. Paper 1681950279.