Spatial and temporal influences on the physiological condition of invasive silver carp

Bighead (Hypophthalmichthys nobilis) and silver carp (H. molitrix) (hereafter, Asian carp) are invasive species that have the potential to negatively influence non-native freshwater systems. Following their introduction to the United States in the early 1970s, Asian carp have become established in the Mississippi River Basin, which includes the Illinois, Ohio, and Wabash rivers, and their range is expanding. The establishment of Asian carp has the potential to negatively influence the community structure of native species. For example, Asian carp are efficient, filter-feeding planktivores that may negatively affect native obligate or facultative planktivorous fishes. Currently, factors motivating or controlling the spread of Asian carp have not been well defined, and little is known about the potential consequences of recently discovered hybrids between bighead and silver carp. Improving our understanding of how Asian carp interact with their environment can help provide drivers determining their movement and spread, and what may happen should Asian carp spread into new habitats. The overall goal of my thesis was to test for abiotic and biotic factors that influence stress and nutrition in wild-caught silver and bighead carp across spatial and temporal scales. To accomplish this goal, I performed three distinct field studies involving wild silver carp, bighead carp, and their hybrids. For each of my studies, I sampled blood from wild-caught silver and bighead carp from large rivers in Illinois (Illinois, Mississippi, Ohio, and Wabash). Blood samples were analyzed for metrics of stress and nutrition that provide insights into the health and condition of free-swimming fish sampled across different habitats. My results suggested that silver carp nutrition varied across rivers and time periods, stress varied across time periods, and there were few effects of abiotic and biotic factors on silver carp nutrition. My results also showed that hybrid Asian carp nutrition was intermediate between parental silver and bighead carp. In concert, my research suggests that silver carp spread may be limited by factors at broad spatial and temporal scales, as opposed to local abiotic and biotic interactions, and decreased hybrid nutritional status may further limit Asian carp spread