Mesohabitat associations in the Mississippi River Basin: A long-term study on the catch rates and physical habitat associations of juvenile silver carp and two native planktivores

Fish community structure is a complex and integrated part of an aquatic ecosystem; a balanced system is often rich in species diversity and abundance. Invasive species can alter this balance, and the expansion of invasive silver carp may have similar deleterious effects. Recently, catches of silver carp in the Midwestern United States have increased and there is evidence of successful spawning and recruitment. However, early life history attributes of silver carp have not been fully evaluated within the Mississippi River Basin. A thorough understanding of early-life history is imperative to facilitate control efforts for silver carp populations. Furthermore, age-0 silver carp survival and subsequent recruitment may be regulated by habitat availability during this critical life stage. Thus, the objective of this study was to evaluate age-0 silver carp mesohabitat (i.e., depth, velocity, and substrate) use in three reaches of the Mississippi River Basin and potential habitat overlap with two native planktivorous fish species, gizzard shad Dorosoma cepedianum and emerald shiner Notropis atherinoides. Using data collected from the three lower most reaches of the Long Term Resource Monitoring Program (Pool 26 at Alton, Illinois, USA; Open River at Cape Girardeau, Missouri, USA of the Mississippi River; and the LaGrange reach at Havana, Illinois, USA of the Illinois River), we investigated age-0 silver carp, age-0 gizzard shad and age-0 emerald shiner habitat associations from 2007 to 2012. Overall, 79,358 age-0 silver carp, 89,990 gizzard shad and 41,119 emerald shiner were captured with mini fyke nets during this long-term study. Generally, all three species were collected most frequently in shallow (\u3c 1.5 meters), low velocity (\u3c0.6 meters/second) habitat with greater variability in substrate use ranging from silt to rock. Given the scarcity of these habitat types in the channelized Mississippi River Basin, our results suggest that invasive silver carp exhibit habitat overlap with gizzard shad and emerald shiner. This overlap may result in reduced growth and body condition of these fishes. To this end, this extensive data set has provided new information about silver carp early life history mesohabitat use and overlap occurring between two age-0 native planktivores in the Mississippi River Basin and potential consequences of this association