Common carp distribution, movements, and habitat use in a river impounded by multiple low-head dams

The common carp Cyprinus carpio is an introduced species that is abundant in many impounded rivers. We assessed habitat conditions and common carp abundance in three flowing sites and three impounded sites of the Fox River, Illinois, to examine factors that influence the success of common carp in these systems. Radiotelemetry was used to determine long-term movement and habitat use patterns of common carp among flowing and impounded areas. Impounded areas were wider and deeper than flowing areas and had lower current velocities, smaller substrates, and lower abundances of cover. Common carp were found at all sites during summer, with catch rates being similar between flowing and impounded areas. The proportion of the fish assemblage consisting of common carp was similar between flowing and impounded areas during two of the study years but was higher in impounded areas than in flowing areas during the other two years. Radio-tagged common carp displayed a variety of movement patterns but used impounded areas most frequently during all seasons. Many common carp were always located in impounded areas, but some individuals moved upstream into flowing areas in spring and summer and returned to impounded areas by fall. Common carp positively selected for intermediate depths and low current velocities. Few consistent relationships were apparent in the use of substrate categories, but common carp selected most strongly for wood cover. Management activities targeting common carp should account for movements of this species among different habitat types and should focus on specific aspects of common carp life history. Dam removal or modification may also lead to declines in common carp abundance in some rivers.