Geographic expansion and small stream use by three species of invasive Asian carp in Illinois

Grass carp (Ctenopharyngodon idella), bighead carp (Hypophthalmichthys nobilis), and silver carp (H. molitrix), are three species of Asian carp that were intentionally introduced into the United States in the 1960s and 70s for use in aquaculture and fisheries management. These three species have established populations throughout the lower Mississippi River and its tributaries, and have spread into the Upper Mississippi and its tributaries. Asian carp are very fecund and feed at lower trophic levels, potentially posing serious negative impacts for native species by the removal of essential forage and habitat. In the United States, research on Asian carp has focused nearly exclusively on large rivers (e.g., the Mississippi, Missouri, and Illinois rivers) and little is known about the use of smaller rivers and streams by Asian carp. Because small streams are usually less productive than larger rivers, they may be more vulnerable to potential depletion of zooplankton, phytoplankton, aquatic vegetation, and other negative effects from invasive Asian carp. To assess the use of stream habitats by Asian carp, I compared rates of geographic expansion of Asian carp in the Mississippi and Illinois rivers with their tributaries, and conducted a field survey of first through fourth order streams along a 128 km reach of the Illinois River. Data for my analysis of geographic expansion came from four independent survey programs: routine monitoring by the Illinois Department of Natural Resources, the Long Term Resource Monitoring Program, the Long Term Illinois, Mississippi, Ohio, and Wabash River Fish Population Monitoring Program, and the Illinois Natural History Survey Collections Database. Geographic expansion by Asian carp in Illinois began in the southwest quadrant of the state and moved upstream along the Mississippi and Illinois rivers. Cumulative frequency distributions indicate that, similar to other invasive species, Asian carp in Illinois experienced a substantial period of lag followed by a period of rapid geographic expansion. Grass carp began to expand rapidly, in the mainstem rivers and tributaries, after 25 years of lag. Silver carp entered rapid expansion after 16 years. Bighead carp experienced 10 years of lag in the mainstem rivers, but just 8 years in tributaries. Though lag times differed, all three species began rapid expansion within a seven year period. Cumulative frequency distributions of occurrence in the mainstem rivers were very similar for bighead and grass carp. For silver carp, cumulative frequency distributions in the mainstem rivers and tributaries were very similar. Sampling efforts in 35 sites in first- through fourth-order streams along the La Grange Reach of the Illinois River during the summer of 2009 produced five grass carp and no bighead or silver carp. Cumulative frequency distribution analysis of survey records suggests that geographic expansion of Asian carp in tributaries of the Illinois and Mississippi rivers is in an early stage and likely still increasing. The small number of stream occurrences of Asian carp in my field work are consistent with this notion. Continued monitoring of tributaries throughout the state is recommended