Date of Award
Master of Science
Natural Resource Ecology and Management
Michael J. Weber
The introduction and spread of invasive species has been considered the most serious and least reversible threat to ecosystem function and native biodiversity. Since their introductions in the 1970s, Bighead Hypophthalmichthys nobilis and Silver Carp H. molitrix (collectively Asian Carp) have spread throughout the Mississippi River basin and become two of the most recognizable invasive species in North America. Their migration and possible establishment into reaches of the Upper Mississippi River (UMR) and its major tributaries is not well understood and knowledge of factors influencing population characteristics and dynamics is needed to facilitate assessment and management. Therefore, the objectives of this study were to evaluate 1) Asian Carp seasonal sampling variation (relative abundance, size structure, and condition) along the Des Moines River in southeastern Iowa and 2) the role of climatic variability in inducing synchronous fluctuations in Silver Carp recruitment in the Missouri, Des Moines, Mississippi, Illinois, and Wabash rivers. In chapter one of my thesis, Silver Carp populations were collected monthly (April – October) during 2014 and 2015 from four locations in the Des Moines River with boat electroshocking and trammel net sets. Trammel nets rarely captured Silver Carp (mean = 4.9 fish/net ÃÂ± 1.6 SE; 60% of fish captured in 6.3% of net sets) and therefore were not included in analyses. Boat electroshocking catch rates (CPUE) exhibited a bimodal distribution with peak CPUEs in late-spring and mid-fall and lower in summer. River discharge was positively related to CPUE at upstream sites but the strength of the correlation decreased at downstream sites. Silver Carp size structure was similar among months and sites except at Cliffland where Silver Carp were smaller during the fall compared to earlier in the year. Finally, Silver Carp condition peaked during late spring and decreased throughout the year with the exception of Carp captured at Keokuk where bimodal peaks occurred during late-spring and early-fall. In chapter two of my thesis, Silver Carp were captured from nine sites across the Mississippi River watershed during June – September 2015. Silver Carp recruitment was asynchronous (mean ρ = -0.08 ÃÂ± 0.13 SE) across the Mississippi River watershed. Populations <300 river km apart were synchronized but populations further apart or in relation to linear distance were asynchronous, suggesting dispersal may be occurring at local scales but local environmental conditions are more important determinants of recruitment at larger scales. Silver Carp recruitment was generally negatively related to variability in river discharge (6 of 9 populations) and positively related to cumulative river discharge during the reproductive season (7 of 9 populations), indicating that extended periods of elevated discharges are important local environmental factors regulating recruitment acting independently among sites. Regionally, Silver Carp recruitment was not significantly related to the North Atlantic Oscillation Index (NAO), El NiÃÂ±o Southern Oscillation Index (ENSO), or Palmer Hydrological Drought Index (PHDI), indicating that local environmental factors have more influence on Silver Carp year-class strength than broad climatic conditions. Collectively, these findings suggest that Silver Carp standardized sampling efforts should be concentrated during May-June or September-October when localized Silver Carp catch rates are highest and vulnerable to boat electroshocking. In addition, Silver Carp exhibit asynchronous fluctuations in recruitment and prevailing local environmental conditions regulate Carp year-class strength. As such, sampling efforts targeting Silver Carp populations during the spring may be beneficial as local abundances are highest and the removal of potential spawning stock biomass could aid in decreasing annual reproductive outputs, especially during years where environmental conditions are conducive to local reproductive success (i.e., sustained above average discharge rates). Collectively, understanding spatiotemporal fluctuations in Asian Carp dynamic rates will aid managers in determining how populations will respond to both local and regional environmental conditions, improving our understanding of a highly invasive and injurious fish species.
Christopher Jerod Sullivan
Sullivan, Christopher Jerod, "Asian Carp population characteristics and dynamics in the Mississippi River watershed" (2016). Graduate Theses and Dissertations. 16024.