Degree Name

Master of Science (MS)

Semester of Degree Completion


Thesis Director

Robert E. Colombo


Large floodplain rivers are among the most complex natural systems characterized by exchange between the river and its floodplain. Information regarding fishes in main channel habitats is abundant, however much less understanding extends into their tributaries. Tributaries of large rivers provide critical habitats for main channel fishes, important for foraging, spawning, and refuge. In addition to native diversity, large rivers are host to multiple exotic species invasions, threatening biodiversity, ecosystem function, and habitat quality. Two notorious invaders are Silver Carp (Hypophthalmichthys molitrix) and Bighead Carp (H. nobilis), collectively Asian Carp, presenting an imminent threat of invasion to the Great Lakes. Reproduction in lentic systems such as the Great Lakes is unlikely, however, a knowledge gap remains regarding their use of small rivers and tributaries, a large network of which is associated with the Great Lakes. This study sought to quantify invasive Asian Carp population characteristics and reproductive abilities in tributaries of the Illinois River, a highly invaded system artificially connected to Lake Michigan. To accomplish this, I sampled five Illinois River tributaries: Salt Creek, the Mackinaw, Kankakee, Sangamon, and Spoon Rivers during 2013-2014 for larval fish and adult Asian Carp, as well as the Illinois River main channel. I compared relative density, size structure, relative weight, reproductive condition, age structure, mortality, and growth of Asian Carp among the Illinois River and its tributaries. Relatively high abundances of Silver Carp were encountered in the main channel and all tributaries sampled except for the Kankakee River. Silver carp were found to temporally increase in size and age, but no differences were observed in condition. Reproductive condition of Silver Carp followed temporal hydrography, with peaks in gonad fullness and stage following peaks in discharge. In addition to adult population dynamics, I also examined spatial and temporal distributions, community assemblages, and size structure of eggs and larval fish. Peak abundances of eggs and larval fish followed peaks in discharge during May-June in each tributary, indicating that the fish in these systems are behaving like fluvial specialists in terms of spawning activity. Ten different families were sampled; clupeids and cyprinids were the most abundant taxa. Significant temporal and spatial effects (p < 0.05) of community assemblages were driven by secchi depth and water temperature, respectively. Post gas bladder emergent larvae of Asian Carp species were sampled in high abundance in the Spoon and Mackinaw Rivers, representing over 80% of our sample. Asian Carp were first sampled in late May with peak densities in July. My study suggests Illinois River tributaries are important habitats for early life stages of multiple fish species and contribute to the diversity of fishes in the main channel habitats. Understanding population characteristics of Asian Carps and larval fish community dynamics in small North American rivers helps bridge the knowledge gap and advance future efforts for the control of these species.