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Catostomids are among the most widespread and ecologically important groups of fishes in North America, particularly in large river systems. Despite their importance, little information is available on their population demographics and even less is known about factors influencing their population dynamics. The objectives of this study were to describe annual mortality, recruitment variation, and growth of eight catostomid species, and to evaluate the effects of discharge and temperature on year‐class strength and growth in Iowa rivers. Catostomids were sampled from 3‐km reaches in four nonwadable rivers during June–August 2009. Northern hogsucker, Hypentelium nigricans, golden redhorse, Moxostoma erythrurum, and shorthead redhorse, M. macrolepidotum, typically lived 6–8 years, had very stable recruitment, and had high total annual mortality (i.e., 40–60%). Golden redhorse exhibited the fastest growth of all species. Growth of northern hogsucker and shorthead redhorse was intermediate to the other catostomids. Highfin carpsucker, Carpiodes velifer, quillback, Carpiodes cyprinus, and white sucker, Catostomus commersonii, had high growth rates, low mortality (i.e., 25–30%), and relatively stable recruitment. River carpsucker, Carpiodes carpio, and silver redhorse, M. anisurum, had higher maximum ages (up to age 11), slower growth, lower total annual mortality (20–25%), and higher recruitment variability than the other species. Neither discharge nor temperature was strongly related to recruitment of catostomids. In contrast, several interesting patterns were observed with regard to growth. Species (e.g., carpsuckers, Carpiodes spp.) that typically consume prey items most common in fine substrates (e.g., chironomids) had higher growth rates in reaches dominated by sand and silt substrate. Species (e.g., northern hogsucker) that consume prey associated with large substrates (e.g., plecopterans) had much faster growth in reaches with a high proportion of rocky substrates. Temperature was weakly related to growth of catostomids; however, discharge explained a substantial amount of the variation in growth of nearly all species. Results of this study provide important information on the autecology of catostomids that can be used for comparison among species and systems. These data also suggest that connection of rivers with their floodplain is an important feature for catostomids in temperate river systems. Published in 2011 by John Wiley & Sons, Ltd.

Understanding the trophic ecology of closely-related species is important for providing insight on inter-specific competition and resource partitioning. Although catostomids often dominate fish assemblages in lotic systems, little research has been conducted on their ecology. This study was developed to provide information on the trophic ecology of catostomids in several Iowa rivers. Food habits, diet overlap, and gill raker morphology were examined for highfin carpsucker Carpiodes velifer, quillback C. cyprinus, river carpsucker C. carpio, golden redhorse Moxostoma erythrurum, shorthead redhorse M. macrolepidotum, silver redhorse M. anisurum, and northern hogsucker Hypentelium nigricans sampled from four Iowa rivers (2009). Diet overlap among all species was calculated with MoristaÕs index (C). Food habit niche width was quantified with LevinÕs index (B) and similarity in gill raker morphology was compared with analysis of covariance. Values from MoristaÕs index suggested significant overlap in the diets of highfin carpsucker and river carpsucker (C = 0.81), quillback and river carpsucker (C = 0.66), and shorthead redhorse and silver redhorse (C = 0.67). LevinÕs index indicated that golden redhorse (B = 0.32), quillback (B = 0.53), and river carpsucker (B = 0.41) had the most generalized feeding strategies as their food niche widths were substantially wider than the other species. Gill raker length and spacing were positively correlated with the standard length of the fish for all species (gill raker length: r 2 = 0.67-0.88, P £ 0.01; gill raker spacing: r 2 = 0.63-0.73, P £ 0.01). Slopes of regression of gill raker length and spacing to standard lengths were significantly (P £ 0.05) different among species, indicating that rates of change in gill raker morphology with body length varied among species. Differences in gill raker morphology likely allow catostomids to partition resources and reduce competitive interactions.

Introduction Methods Results Discussion References Tables v LIST OF FIGURES CHAPTER 2. vi ACKNOWLEDGEMENTS Without the help of many people at Iowa State University my completion of this thesis would not have been possible. My major professor, Dr. Joseph Morris, and committee member, Dr. Michael Quist, both provided me with advice, equipment and always had time to visit about my research. I greatly appreciate all of the effort they put forth to help me successfully finish my project. I also thank Dr. Richard Schultz for serving on my committee. Fellow graduate student Travis Neebling generously helped me with site selection. I also thank the technicians who helped me throughout the project. Lucas Brown, Matthew Mork, Adam Hemer and Nick Hogberg all made the process possible and much more enjoyable. Additionally, I also thank the faculty and staff of the Department of Natural Resources Ecology and Management for their support and contributions to my graduate education. I thank my father, Gary Spiegel, who has always encouraged me to continue my education and pursue my dreams and Andrea DeRubeis for her steadfast love, support and understanding as I completed this project. I dedicate this thesis to them for without them my completion of this thesis could not have happened.